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Thermal efficiency of coal-fired power plants: From theoretical to practical assessments
... While defining efficiency as the fraction of incident irradiance power converted into electricity is an established metric to compare research results, this metric should not be compared to the efficiency that conventional fossil fuel power plants report. Announcing a new record of 26.7% power conversion efficiency for silicon solar cells [18] sounds impressive to an expert, but for non-experts, these values are deficient in comparison to reported efficiencies of coal power plants, which range between 35% to 42% [19,20], and the efficiencies of combined cycle gas power plants, which now exceed 60% [21]. ...
... The thermal efficiency of a coal power plant can reach 45.5% [19]. Practical ητ values reported range between 35% and 42% [19,20] when the energy required to construct the power plant and mine the coal is included. ...
... The thermal efficiency of a coal power plant can reach 45.5% [19]. Practical ητ values reported range between 35% and 42% [19,20] when the energy required to construct the power plant and mine the coal is included. The CO2 equivalent for producing electricity from brown coal/lignite amounts to 1075 g of CO2 per kWh of electricity [27]. ...
1500% is the efficiency of a standard solar power plant-when the same metrics are applied as for conventional fossil fuel power plants. In this paper, a proper comparison is drawn between efficiencies reported by coal, combined cycle gas and solar power plants with the goal to clarify understanding of PV potential amongst a non-technical population. Feedback and critical input from PV experts on this potentially controversial methodology are highly welcome and will enable us to derive best practices for broader communication and outreach.
... Though this method compares the real process with an advanced process, their efficiency improvement is limited to technological constraints. Moreover, efficiency limited by technology is not predictable and may change over time for a given process [26] as a result of subjective decisions [22]. Hence, a modified exergy-base improvement evaluation method is introduced. ...
... The theoretical process, in contrast to the real case, is not limited by technological conditions such as physical and economical constraints. It gives the highest efficiency of the process; even though its efficiency cannot be achieved in practice it does, however, provide a benchmark or target for the design of the process [26]. Here, the greatest improvement in the plant is achieved by optimizing the entire system, using the parameters of the component that give the greatest efficiency. ...
... The Tsatsaronis and Park [22] method showed a lower improvement potential than the current method as a result of the technological constraints their method employs. Technological limitations are subjected to change over time for a given process, whereas the method developed here is based on theoretical limits that are fixed for a given process [26]. ...
Evaluation of different alternatives for enhancement in a waste combustion process enables adequate decisions to be made for improving its efficiency. Exergy analysis has been shown be an effective tool in assessing the overall efficiency of a system. However, the conventional exergy method does not provide information of the improvements possible in a real process. The purpose of this paper is to evaluate state-of-the art techniques applied in a municipal solid-waste fired heat and power plant. The base case plant is evaluated first; the results are then used to decide upon which technical modifications should be introduced and they are thereafter evaluated. A modified exergy-based method is used to discover the improvement potential of both the individual components and the overall base case plant. The results indicate that 64% of exergy destruction in the overall process can theoretically be improved. The various modifications selected involve changing the bed material, using a gasifier followed by a gas boiler and incorporating a more durable material into the boiler walls. In addition, changing the heating medium of the incoming air (from steam to flue gas) along with a reduction in the stack temperature and the integration of flue gas condensation were considered for utilizing the exergy in the flue gases. The modification involving gasifier, gas boiler and flue gas condensation proved to be the best option, with the highest exergy efficiency increment of 21%. Keywords: Theoretical process, Exergy efficiency, Flue gas condensation, Municipal solid-waste fired plant, Improvement potential, Gasification-combustion process
... This high water demand in thermoelectric power generation is due to low efficiencies of conventional cycles. In the past, typical power plants were operated at 28-30% energetic efficiency that is recently increased to 50% due to rapid development in combustion processes and cascading operations as shown in Figure 2 [15][16][17][18][19][20]. Recently, General Electric (GE) in partnership with EDF made history and set a Guinness The energy utilized in desalination processes is in the majority (80%) produced by thermoelectric processes that consume huge amount of water for heat rejection to complete the thermodynamic cycle. ...
... This high water demand in thermoelectric power generation is due to low efficiencies of conventional cycles. In the past, typical power plants were operated at 28-30% energetic efficiency that is recently increased to 50% due to rapid development in combustion processes and cascading operations as shown in Figure 2 [15][16][17][18][19][20]. Recently, General Electric (GE) in partnership with EDF made history and set a Guinness World Records title for operating the world's most efficient combined-cycle power plant at 62.22%. ...
... Combined cycle efficiency and environment impact trend from 1870-2018[15][16][17][18][19][20][21][22]. ...
For future sustainable seawater desalination, the importance of achieving better energy efficiency of the existing 19,500 commercial-scale desalination plants cannot be over emphasized. The major concern of the desalination industry is the inadequate approach to energy efficiency evaluation of diverse seawater desalination processes by omitting the grade of energy supplied. These conventional approaches would suffice if the efficacy comparison were to be conducted for the same energy input processes. The misconception of considering all derived energies as equivalent in the desalination industry has severe economic and environmental consequences. In the realms of the energy and desalination system planners, serious judgmental errors in the process selection of green installations are made unconsciously as the efficacy data are either flawed or inaccurate. Inferior efficacy technologies’ implementation decisions were observed in many water-stressed countries that can burden a country’s economy immediately with higher unit energy cost as well as cause more undesirable environmental effects on the surroundings. In this article, a standard primary energy-based thermodynamic framework is presented that addresses energy efficacy fairly and accurately. It shows clearly that a thermally driven process consumes 2.5–3% of standard primary energy (SPE) when combined with power plants. A standard universal performance ratio-based evaluation method has been proposed that showed all desalination processes performance varies from 10–14% of the thermodynamic limit. To achieve 2030 sustainability goals, innovative processes are required to meet 25–30% of the thermodynamic limit.
... The efficiency of conventional fossil-fueled power plants that are based on the Rankine Cycle mostly depends on the steam temperature and pressure [4], with the majority of previous work on efficiency optimization of these plants focusing on steady-state analyses. The work by Fu et al. [13] showed an average efficiency increase of 0.1% points for every increment of 8 • C in boiler feedwater temperature, every decrement of 4.5 • C in flue gas temperature and every increment of 10 bar in main steam pressure, compared to a reference case with an efficiency of 45.5%. Sanpasertparnich and Aroonwilas [14] presented potential efficiency improvements of up to 8.88% points for subcritical coal-fired power plants. ...
... Table 2 summarizes the optimization variables, range of variability and efficiency improvements achieved in relevant previous work. In the majority of previous analyses [13][14][15][36][37][38][39][40][41][42][43][44], plant efficiency optimization was performed by manipulating the temperature of superheated steam (T SH ). For example, Xiong et al. [41] showed that the higher superheated steam temperature increases the power generated by the HP turbine, improving cycle efficiency. ...
... In Case Study II, plant optimization was performed by manipulating the set points ofṁ ST , i.e., the set points of the mass flow rates of steam streams extracted from the first IP turbine (IP1), the second IP turbine (IP2), the first LP turbine (LP1), and the second LP turbine (LP2) (ṁ IP1 ,ṁ IP2 ,ṁ LP1 , andṁ LP2 , respectively). The ranges of the admissible inputs, shown in Table 3, were based on common practice and previous work [13][14][15]27,36,38,[41][42][43]45]. The optimization horizon, τ, was set to 24 h in Case Study I and 4 h in Case Study II, and the control action interval, τ n , was set to 1 h. ...
The increasing variability in power plant load in response to a wildly uncertain electricity market and the need to to mitigate CO2 emissions, lead power plant operators to explore advanced options for efficiency optimization. Model-based, system-scale dynamic simulation and optimization are useful tools in this effort and are the subjects of the work presented here. In prior work, a dynamic model validated against steady-state data from a 605 MW subcritical power plant was presented. This power plant model was used as a test-bed for dynamic simulations, in which the coal load was regulated to satisfy a varying power demand. Plant-level control regulated the plant load to match an anticipated trajectory of the power demand. The efficiency of the power plant’s operation at varying loads was optimized through a supervisory control architecture that performs set point optimization on the regulatory controllers. Dynamic optimization problems were formulated to search for optimal time-varying input trajectories that satisfy operability and safety constraints during the transition between plant states. An improvement in time-averaged efficiency of up to 1.8% points was shown to be feasible with corresponding savings in coal consumption of 184.8 tons/day and a carbon footprint decrease of 0.035 kg/kWh.
... Wind and water power plants have much higher energy efficiency, and the production of electricity is accompanied by a low heat emission. Much more information about the energy conversion efficiency in thermal power stations is presented in the papers [5][6][7]. ...
... Moreover, sooner or later, almost 100% of that useful energy-electrical energy or chemical energy in fuels-is finally converted to heat energy. Because average efficiency of a thermal electric plant is about 40% [5][6][7], most of the primary energy (chemical energy in coal or natural gas, nuclear energy in nuclear fuel, etc.) is converted directly to heat. Engines in cars, where chemical energy in petrol is converted to mechanical energy, have similar efficiency. ...
The global warming phenomenon is commonly associated with the emission of greenhouse gases. However, there may be other factors related to industry and global energy production which cause climate change—for example, heat emission caused by the production of any useful form of energy. This paper discussed the importance of heat emission—the final result of various forms of energy produced by our civilization. Does the emission also influence the climate warming process, i.e., the well-known greenhouse effect? To answer this question, the global heat production was compared to total solar energy, which reaches the Earth. The paper also analyzed the current global energy market. It shows how much energy is produced and consumed, as well as the directions for further development of the energy market. These analyses made it possible to verify the assumed hypothesis.
... According to Eqs. (4), (7) and (8), the total energy input of the boiler in coal pre-drying power plant is M Á LHV Á b, and thus the gross electric power output can be calculated by energy equilibrium according to the following equation [20,23]: ...
... In the coal pre-drying power plant, dryers, coal crushers and bag houses are required, which will lead to an increase in ICC, i.e., D P ICC ¼ ICC dryers þ ICC crushers þ ICC bag houses . For a given equipment, ICC is calculated using the scaling up method according to Ref. [23]: ...
... Correlation coefficient (dimensionless) O daf O content of air-dried basis (%) S daf S content of air-dried basis (%) T Thermokinetic temperature (K) T 1 First characteristic temperature, critical temperature (°C) T 2 Second characteristic temperature, active temperature (°C) T 3 Third characteristic temperature, pyrolysis temperature (°C) T 4 Fourth characteristic temperature, ignition temperature (°C) T 5 Fifth characteristic temperature, burned-out temperature (°C) ...
... Coal is an indispensable resource not only in China but also worldwide [1,2]. China is the largest coal-producing country [3,4], and the problem of coal spontaneous combustion [5][6][7] is gaining increasing attention. To govern the wastage of coal resources, numerous coal mines in China have begun to re-mine old coal mines and mined-out areas, which have a risk of second or multiple oxidations. ...
Among coal-producing countries, China has witnessed the highest frequency and severity of coal fires. During mining in the re-mining face and the lower part of the thick coal seam (or coal seam group), second or multiple oxidations of the residual coal can readily occur in mined-out areas, severely increasing the risk of coal fires. The study of multiple oxidations of coal aids in the early detection of spontaneous combustion of remaining coal in the mined-out areas. The characteristics of coal fires are demonstrated using fresh coal samples (first-oxidized coal) and oxidized coal samples (second-oxidized coal) from four different ranks of coals. Proximate and elemental analysis, Fourier transform spectroscopy, and thermogravimetry–differential scanning calorimetry were adopted to investigate the quality, microcharacteristics, characteristic temperatures, and apparent activation energy of second-oxidized coal. In addition, the effect of spontaneous combustion at heating rates of 5.0, 10.0, and 15.0 °C min−1 was studied. Compared with the four samples of first-oxidized coal, those of second-oxidized coals cause fire easily under the same conditions.
... However, the most efficient traditional solar panels obtainable in the market have peak efficiencies of 22.8% (Most Efficient Home Solar Panels Available and Sun-Power 2021). Meanwhile, the maximum efficiencies obtained from subcritical coal-fired vapour power plant cycles are 45.5% (Fu et al. 2015). Furthermore, ultra-supercritical and supercritical cycles can even reach efficiencies of 54-55% and 51%, respectively (Braimakis et al. 2020). ...
The performance improvement of a concentrated photovoltaic-thermoelectric system by exploiting thermoelements with altered cross-sections is presented. The regular rectangular cross-sectional area adopted in thermoelectric devices is replaced with circular cross-sectional area and the accuracy of the numerical results are established by comparisons with experimental data. The numerical model is setup in ANSYS software and thermoelectric material temperature dependency is considered. The optimized parameters
of the system include the solar concentration ratio, convective cooling, ambient temperature, and the wind speed while the performance parameters are the solar cell temperature, system power, energy efficiency, and thermoelectric generator temperature difference. It was found that the proposed system with circular legs improved the power and energy efficiency of the conventional system with rectangular legs by 226% and 68% at a concentration ratio of 45, respectively. The optimum design conditions necessary for fabricating the proposed device using additive manufacturing technology are also provided.
... By using coal for energy purposes, problems like particulate emission, smog, acid rains and emissions of ash particles arise. The efficiency offered by thermal plants is low, but modifications have been increased by 5-45% over the last decades [10]. Thus, the cost of using coal at the expense of the environment seems unfair. ...
Energy is a basic necessity. In this modern world, energy is produced using different resources and technology , which helps sustain our energy demands. All the present economies have relied on fossil fuel-based energy generation for past decades. The continuous exploitation of resources for energy purposes has left areas uninhabitable. While renewable energy technologies are emerging and in trend, the same story goes for them. Almost all present-day energy methods have some effect on the environment. The nexus of energy and the environment is a fragile balance. This balance should remain. The study includes a comparison of renewable and nonrenewable sources; the problem associated with fossil fuel extraction, and analyzes the impact of various energy-producing infrastructures on the environment. In mining rare earth elements, toxic chemicals are released into the atmosphere. The extraction of such materials leads to environmental concerns. Energy production should remain as neutral as possible.
... Esta tecnología convierte alrededor del 82 % de la energía de los residuos en electricidad y calor, mostrando aproximadamente una eficiencia de conversión de energía eléctrica de 18 % a 27 % (Pour et al. 2018). Las eficiencias son relativamente bajas en comparación con las plantas de combustión de carbón (e.j, 40 ̶ 45 % VCIcarbón) (Fu et al. 2015, Yang et al. 2015, Xu et al. 2016) debido al menor valor calorífico del combustible. Además, los parámetros termodinámicos del vapor de la caldera presentan limitaciones, ya que no pueden excederse de 420 °C de temperatura y 400 kPa de presión para evitar la corrosión excesiva causada por los gases ácidos y otros compuestos producidos por la combustión de los RSU (Eboh et al. 2019). ...
Las estrategias de manejo de residuos sólidos urbanos (RSU) en La Habana son
anticuadas. El objetivo de este trabajo es proponer la alternativa más adecuada de una
instalación de recuperación de materiales (MRF) integrada a tecnologías de recuperación
energética para el tratamiento de los RSU de La Habana. Se consideraron siete
alternativas de recuperación energética: combustión, gasificación y carbonización
hidrotermal (HTC) con y sin captura de CO2 y digestión anaerobia (AD). La selección se
basó en criterios ambientales, tecno-económicos y sociales utilizando un proceso de
jerarquía analítica (AHP) como una herramienta de toma de decisiones multicriterio
(TDMC). La TDMC-AHP consideró criterios cualitativos (basados en juicios de
expertos) y cuantitativos (basados en modelos de simulación de Aspen Plus). Los
resultados del AHP mostraron que los criterios ambientales tenían la máxima prioridad
(61 %), mientras que los criterios sociales y tecno-económicos, tuvieron una prioridad de
22,5 % y 16,5 % respectivamente. Asimismo, los subcriterios contaminación, seguridad
laboral y riesgo de inversión tuvieron la mayor prioridad. La instalación de recuperación
de materiales integrada a la digestión anaerobia como alternativa de recuperación
energética (MRF+AD) fue la más adecuada (21 % de preferencia) para el tratamiento de
los RSU de La Habana, seguido de la combustión y la gasificación con captura de CO2,
respectivamente. Este estudio confirma que la digestión anaerobia es una opción de
preferencia para economías emergentes como Cuba, principalmente por la baja
contaminación ambiental, alta aceptación social y estabilidad financiera a largo plazo.
Palabras claves: Instalación de recuperación de materiales, Recuperación energética,
Aspen Plus, Toma de decisiones multicriterio (TDMC), Proceso de jerarquía analítica
(AHP).
... The optimum pressure value is obtained as 46bar and flow rate of 240kg/s to the inlet pressure turbine is found as the value for maximum plant performance. Chao Fu et al. [7] in a paper presented a systematic study on coal to power processes with respect to thermodynamic, technological and economic factors. Unlike the traditional exergy analysis which focuses on irreversibility in existing processes, a new methodology is adopted to investigate the thermal efficiency from its theoretical maximum to practical values by adding irreversibility one by one. ...
In this paper, the effects of variation in ambient temperature, flue gas temperature and condenser pressure over performance of boiler and turbine cycle is presented. The study is carried out with EES software. The change in ambient temperature is seriously deteriorating the boiler exergetic performance as its exergy efficiency reduces by 2.5% with increase in environmental temperature from 27C to 45C while the boiler total energy loss reduces almost 1% for same increase in ambient temperature. The turbine second law efficiency is affected slightly by ambient temperature. Increase in temperature of exhaust flue gas has adverse effect over boiler energy efficiency, which reduces by almost 1% with flue gas temperature variation from 110C to 130C. The increase in condenser pressure is reducing the turbine energy efficiency to more than 3% with variation from 0.05bar to 0.3bar. Condenser exergy efficiency is decreasing sharply with increase in its pressure. The effect of variation in condenser pressure over net output of the boiler-turbine cycle has also been studied and it is found to be decreasing with increase in condenser pressure. Keyword: Ambient temperature, Boiler-turbine cycle, Condenser pressure, Flue gas, Plant performance.
... Using data from all non-carbon energy sources (geothermal, nuclear, photovoltaic, water, wind) for indicator thirty-two, the total overall generation is valued at 33,673,002.62 toe (Fu et al. 2015;IEA 2018b;Patel 2017). Divided by TPES, this represents 7.1%. ...
Current energy consumption and how to mitigate the negative environmental effects alongside rising demand have become prominent issues in everyday discourse. Following this trend, the topic of energy security too has stepped back into the spotlight. This article aims to analyse the energy security situation of three East Asian countries, Japan, South Korea, and Taiwan. All three countries feature similar predicaments, being overly reliant on imports, having minuscule natural reserves, and also being high-tech and service-based economies. In this article the author attempts to determine similarities and differences from an energy security perspective. In order to assess these countries, a framework is created with thirty-five distinct indicators relating to energy security. Each indicator is then systematically compared with each of the three countries. The results are then presented in a table and with graphs to illustrate a comparison of each country’s values. Through these results, the largest differences can be observed in energy efficiency and diversification of energy supply. The concluding remarks offer possible avenues for further studies and deliberate on lessons to be learned from these results.
... As over one-third of the world's electricity is generated from coal [47], improving the efficiency of coal plants presents a substantial opportunity to reduce emissions. However, even at the state-of-the-art efficiency (∼40%) coal plants emit 70% more carbon than an average gas plant today [48], hence the priority is rapid coal phase out. Nuclear generation declined substantially following the Fukushima-Daiichi disaster, not just in Japan but in nations across the world, with a growing number of nations committing to nuclear phase-out [49]. ...
Fifteen years ago, Pacala and Socolow argued that global carbon emissions could be stabilised by mid-century using a portfolio of existing mitigation strategies. We assess historic progress for each of their proposed mitigation strategies and convert this into the unit of ‘wedges’. We show that the world is on track to achieve 1.5 ± 0.9 wedges relative to seven required to stabilise emissions, or 14 required to achieve net-zero emissions by mid-century. Substantial progress has been made in some domains that are not widely recognised (improving vehicle efficiency and declining vehicle use); yet this is tempered by negligible or even negative progress in many others (particularly tropical tree cover loss in Asia and Africa). By representing global decarbonisation efforts using the conceptually simple unit of wedges, this study helps a broader audience to understand progress to date and engage with the need for much greater effort over the coming decades.
... In the past period of time the power plant efficiency saw a surge from around 5-45%. The growing cognizance about the greenhouse gases further encourages the efficiency enhancement in the thermal power plants [2]. The efficiency of the power plant gradually deteriorates over a period of time. ...
Usage of conventional energy resources has high limitations and constrains now a days. The thermal efficiency of the equipments in the modern thermal based power plant is mandatory for effective power generation with low production cost and pollution. The systems and equipments in the thermal power plant should be operated with optimum efficiency. An assessment of these system performance and comparing it with the design value is necessary for its improvement. This paper presents the findings of the observations and trials carried out on thermal power plant energy equipments. The main objective of this work is to assess the performance of various thermal power plant systems in respect of efficiency and determining the main factors which contribute to the efficacy of the power plant by indirect method. Further, suitable measures are recommended to enhance the energy performance with cost benefits. While making the measurements, care is taken to maintain the accuracy and wherever any discrepancy is found, the readings were again taken to ensure the best possible results.
... Ekserji analizi uygulanma amacı açısından karar verme mekanizması olarak da kullanılmaktadır. Bu çerçevede, birçok çalışmada sistem performansının olumlu etkilendiği rapor edilmiştir [16][17][18][19][20]. Xiong vd. ...
In this study, conventional exergy analysis of circulating fluidized bed boiler with 75 t/h steam capacity in an industrial facility located in Seyitgazi district of Eskişehir, Turkey was carried out. In this analysis, it was aimed to see the effect of the change in ambient temperature on the exergy performance of the boiler and air heater. For this purpose, exergy values for the standard dead state 25℃ 101.325 kPa and the average measurement values of 17.27℃ 89.4 kPa as well as 30℃, 28℃, 20℃, 15℃ and 12℃ were calculated. The circulating fluidized bed boiler is considered to be a whole rather than being examined in sections. The air heater was evaluated separately from the boiler. As a result of the calculations, exergy losses realized in boiler and air heater were determined. In addition, exergy performances of boiler and air heater was determined by calculating exergy efficiency. This study showed that exergy performance criteria of circulating fluidized bed boiler and air heater were significantly affected by the change in ambient temperature.
... Temperatures close to those observed in air-fired conditions are achieved by recycling 70% of the flue gas back to the furnace (IEAGHG, 2017(IEAGHG, , 2013Wall et al., 2013;Spero et al., 2014;Jurado et al., 2014;Stanger et al., 2015;Fu et al., 2015), avoiding the need for O 2 -specific materials (Dillon et al., 2005). A flue gas with 60-70 mol% of CO 2 is generated depending upon fuel used, which must be further purified to transport specification in a gas processing unit (GPU) (Boot-Handford et al., 2014;Wall et al., 2013;Kolster et al., 2017;Cabral and Mac Dowell, 2017). ...
There is a need for a rapid and large scale decarbonisation to reduce CO2 emissions by 45% within 12 years. Thus, we propose a method that accelerates decarbonisation across multiple sectors via a synergistic approach with bioenergy with CCS (BECCS), which is able to remove 740 kg CO2 from air per MWh electricity generated. Industry is a hard-to-decarbonise sector which presents a unique set of challenges where, unlike the power sector, there are no obvious alternatives to CCS. One of these challenges is the significant variation of CO2 concentration, which directly influences CO2 capture costs, ranging from $10/t CO2 to over $170/t CO2 for high (95-99% CO2) and low CO2 concentration (4% CO 2) applications, respectively. Re-purposing the existing coal-fired power plant fleet into BECCS displaces CO2 emissions from coal-use and enables a just transition, i.e., avoiding job loss, providing a supportive economic framework that does not rely on government subsidies. Negative emissions generated from capturing and storing atmospheric CO2 can be converted into negative emission credits (NECs) and auctioned to hard-to-decarbonise sectors, thus providing another revenue stream to the power plant. A levelised cost of electricity (LCOE) between $70 and $100 per MWh can be achieved through auctioning NECs at $90-$135 per t CO2. Offsetting the global industrial CO 2 emissions of 9 Gt CO2 would require 3000 BECCS plants under this framework. This approach could jumpstart industrial decarbonisation whilst giving this sector more time to develop new CCS technologies.
... Today, almost 40% of worldwide electricity production is based on conventional coal-fired power plants [1], as shown in Figure 1. Coal-fired power plants have been in continuous development for a long time with considerable efforts to improve their capacity and thermal efficiency, since an increase in their efficiency can significantly reduce the overall cost of electricity production, as well as reduce the environmental impact generated by the burning of coal [2,3]. The main objective of any electric power generation system is to provide the energy demanded by the market, as well as to comply with the regulatory requirements [4]. ...
Determining the ideal size of maintenance staff is a daunting task, especially in the operation of large and complex mechanical systems such as thermal power plants. On the one hand, a significant investment in maintenance is necessary to maintain the availability of the system. On the other hand, it can significantly affect the profit of the plant. Several mathematical modeling techniques have been used in many different ways to predict and improve the availability and reliability of such systems. This work uses a modeling tool called generalized stochastic Petri net (GSPN) in a new way, aiming to determine the effect that the number of maintenance teams has on the availability and performance of a coal-fired power plant cooling tower. The results obtained through the model are confronted with a thermodynamic analysis of the cooling tower that shows the influence of this system's performance on the efficiency of the power plant. Thus, it is possible to determine the optimal size of the repair team in order to maximize the plant's performance with the least possible investment in maintenance personnel.
... The use of heat of condensation of water vapor from the flue gas leads to a general increase in thermodynamic efficiency of the entire power plant. The studies [13] show that with a decrease in the temperature of flue gases for every 4.5 °C, there is an increase in the plant thermal efficiency by approximately 0.1%. The values presented correspond to combustion of coal dust with humidity about 10-15%. ...
The study regards the issues of increasing the thermodynamic efficiency of a typical condensing thermal power plant using coal-water and organic coal-water fuels as the main source. The attention is paid to the use of the phase transition heat of the water vapor of the flue gas. We have shown that it is possible to increase the power plant efficiency by about 3.7% (gross) relative to the base value (in the case of using pulverized coal). We propose to use the flue-gas desulfurization technology for creating fuel slurries in which a liquid incombustible base will be replaced, for example, with aqueous solutions of Ca(OH)2. This will create a closed water cycle, improve the efficiency of Sox flue gas purification and improve the performance of scrubbers.
... The traditional power plant efficiencies varies from 38 to 50% in terms of primary energy transformation to the secondary or derived energy. The chronological trend of power plants efficiency improvement since 1880s can be observed in Fig. 2. [8][9][10][11][12][13][14][15] It can be noticed that from 1880 to 1970, only a marginal efficiency improvement from 26% to 33% was observed that spanned over a century due to the "bottle necks" arising from conventional heat and mass transfer processes. A significant increase from 33% to 50% was observed during 1970 to 2000 and it was attributed to the implementation of efficient combined cycle gas turbines (CCGT) cycle and concomitantly, a quantum reduction in environmental pollution was also noted. ...
Desalination: assessing efficiency A thermodynamic framework enables comparison of different desalination plants and processes. Desalination of seawater is a key process for meeting the worlds growing need for potable water, enabled by substantial increases in efficiency of the process of over the last few decades. Now, Kim Choon Ng and colleagues from King Abdullah University of Science & Technology argue that the grade of input energy used during desalination, defined by how the energy is generated, must be considered when determining the efficiency of desalination plants. They define a metric to assess process efficiency, suggesting that the majority of desalination processes are operating below the ideal thermodynamic limit.
... Evidently, a higher thermal efficiency of power plant leads to a lower emission. Therefore, the ultra-supercritical (USC) coal-fired power units have been widely applied to mitigate emissions by coal consumption reduction [2]. The 700°C level and double reheat technology, as two prospective USC technical routes, have been proposed successively. ...
This paper presented a coupled heat transfer model combining the combustion in the furnace and the ultra-supercritical (USC) heat transfer in the water wall tubes. The thermal analysis of the spiral water wall in a 1000 MW double reheat USC boiler was conducted by the coupled heat transfer simulations. The simulation results show that there are two peak heat flux regions on each wall of spiral water wall, where the primary combustion zone and burnt-out zone locate respectively. In the full load condition, the maximal heat flux of the primary combustion zone is close to 500 kW/m2, which is higher than that in the conventional single reheat USC boilers. The heat flux along the furnace width presents a parabolic shape that the values in the furnace center are much higher than that in the corner regions. The distribution of water wall temperature has a perfect accordance with the heat flux distribution of the parabolic shape curves, which can illustrate the distribution of water wall temperature is mainly determined by heat flux on the water wall. The maximal water wall temperature occurs at the middle width of furnace wall and approaches 530°C, which can be allowed by the metal material of water wall tube 12Cr1MoVG. In the primary combustion zone, the wall temperatures in half load are almost close to the values in 75% load condition, caused by the heat transfer deterioration of the subcritical pressure fluid under the high heat flux condition. The simulation results in this study are beneficial to the better design and operational optimization for the double reheat USC boilers.
... A study of energy and mass balances of thermal power plants is therefore required. Modeling is often combined with field tests on industrial boilers [10][11][12][13][14][15][16][17][18][19][20][21][22][23] and prediction algorithms and statistical tools are developed [24][25][26][27][28][29]. These studies are applicable as, for instance, thermal power unit control systems can be modified based on these algorithms [30][31][32][33], and start-up processes are optimized taking into account thermal stresses in the boiler [34]. ...
A major challenge in the modern power system is the load cycling (ramping down and up) of thermal power plants due to the increase in electricity production from renewable power plants and other sources. The motivation for this paper is to quantify the effect of this on fuel consumption and as a result, variable costs. In this study, an experimental method for determining the fuel flow rate and corresponding power unit characteristics in a load-ramping operating regime was introduced and experimentally tested. The method is based on the static pressure drop of flue gas flowing through some convective heating surfaces of a boiler being proportional to the gas velocity, that is, in turn, proportional to the mass fuel rate. Therefore, after measuring the pressure drop during a steady-state regime, for example, in a tubular air preheater as the heat surface that is less susceptible to contamination from particle laden gas flow, and at the same time calculating the fuel mass flow rate through an indirect heat balance, the two parameters can be interrelated. The semi-empirical relationship obtained in this way can then be used for determining the actual fuel mass flow rate during transient boiler loads. The proposed method was used to determine the technical and economical characteristics of a pulverized combustion power unit utilizing oil-shale. Large-scale experiments were conducted in a high-pressure pulverized combustion steam generator TP-101, with a rated capacity of 300 MWth. The dual-boiler unit load ramping was constrained to 2.5 MWel/min. The results show that during ramping down the load to 50% maximum continuous rating, the mean fuel consumption decreased by 10%, and during ramp-up back to 100% maximum continuous rating, the mean fuel consumption increased by 14%. The total increase in fuel consumption during ramping cycle at given conditions, was approximately 4%.
... It is hard to define the theoretical condition for the system with chemical reactors and heat exchangers. The setting of theoretical status of coal combustion refers to Ref. [33]. As for heat exchangers, both pressure drops and minimum temperature differences at the pinch point (DT) should equal zero. ...
Advanced exergy and exergoenvironmental analyses based on life cycle assessment (LCA) are conducted to an SCPP with and without dust, SO2 and NOX mitigation controls. The analyses show that environmental impacts of components are mainly caused by exergy destruction while combustion chamber (COM) still has great potential to reduce pollutant environmental impact reduced by 99.5% by near-zero air pollutant emission standards. Avoidable environmental impact within each component is endogenous other than most regenerative feedwater heaters. COM has the largest environmental impact of exergy destruction but lower avoidable part compared with superheat transfer (SH) including boiling process. Reheat transfer (RH) shows similar avoidable environmental impact but less exergy destruction in contrast with COM. Turbines play well in exergy efficiency and over 50% of environmental impact within intermediate-pressure turbine (IP) can be avoided. Air preheater (APH) displays a higher avoidable environmental impact than condenser (CND) albeit lower exergy destruction. Pumps and fans have small environmental impacts with over 45% can be avoided. Most environmental impact related to pollutant formation is avoidable and endogenous except for wet flue gas desulfurization (WFGD) which imposes a negative environmental impact on other components. The specific environmental impact of electricity generation is higher than European.
... Oxy-combustion is a promising technology where fuel is burnt in a high-oxygen (O 2 ) environment, using O 2 obtained from an air separation unit (ASU), instead of with air, improving combustion efficiency [12]. Safe operation conditions are maintained by recycling a fraction of the flue gas back to the furnace, thus keeping the temperatures inside the boiler close to air-firing mode [9,[13][14][15]. Burning coal under these conditions generates an flue gas rich in CO 2 (60-70 mol%) with appreciable quantities of H O Oxy-combustion can also be applied to natural gas combined cycle (NGCC), however the gas turbines need to be redesigned because the increased CO 2 concentrations in the flue gas alter its physical properties [9,12]. ...
Carbon capture and storage is widely recognised as essential for the cost effective decarbonisation of the power and industrial sectors. However its capital and operating costs remain a barrier to deployment, with significant reduction in the cost per unit of decarbonised product considered vital. In the context of power generation, this is best expressed in terms of cost per MWh of electricity generated. To achieve a meaningful reduction in the cost of low carbon electricity, capital costs must also be reduced. Thus, this work presents a novel approach for identifying system improvements via a combination of process integration and intensification based on minimisation of thermodynamic losses. Application of this methodology to an oxy-combustion CCS process led to a 3% increase of net efficiency and a 13% reduction of £/MWh of electricity.
... Ameri et al. [24] concluded that the greatest exergy loss occurs during combustion because of its high irreversibility. Fu et al. [25] presented a systematic study on direct combustion coal to power processes and investigated various measures for increasing the thermal efficiency and the cor- responding improvement potential according to the exergy analy- sis method. The exergy analysis method has been used widely in recent years because of its ability to capture the variation of the energy grade. ...
This study evaluates the performance of a 1000 MW double reheat ultra-supercritical power plant. An exergy analysis was performed to direct the energy loss distribution of this system. Based on the exergy balance equation, together with exergy efficiency, exergy loss coefficient, and exergy loss rate, the exergy distribution and efficiency of the unit were determined. Results show that the highest exergy loss in furnace is as high as 85%, which caused by the combustion of fuel and heat exchange of water wall. The VHP and the two LPs suffer the highest exergy losses, namely 1.86%, 2.04% and 2.13% respectively. The regenerative heating system has an exergy loss rate of 2.3%. The condenser suffers a heat loss of 999 MW, but its exergy is as low as 20.49 MW. The sensitivity variations of the unit’s exergy efficiency with load, feedwater temperature, main steam temperature and pressure, the twice reheat steam temperatures, and steam exhaust pressure were also analyzed, indicating that load, feedwater temperature, and steam exhaust pressure influence the exergy efficiency of this unit than other elements. The overall exergy efficiency decreases along with the gradual increase of steam exhaust pressure at any constant outlet boiler temperature, but it increases as the load, feedwater temperature, main steam temperature and pressure, and twice reheat steam temperatures increase at fixed steam exhaust pressure.
... It is likely to continue as a key component of the fuel mix in the generation of power even though these plants account for over 28% of the total global emissions of carbon dioxide [45]. In order to maximize the utility of coal used in the production of energy, considerable efforts need to be made to enhance the capacity and efficiency of plants whilst simultaneously reducing their environmental impact and costs of power generation [46]. Improving both the efficiency and cost effectiveness of power plants can be achieved by reducing the thermodynamic inefficiencies associated with the system that result in a reduction of the CO 2 emission per MW of electricity generated [47]. ...
The growing demand for energy is particularly important to engineers with respect to how the energy produced by heat and power plants can be used efficiently. Formerly, performance evaluation of thermal power plants was done through energy analysis. However, the energy method does not account for irreversibilities within the system. An effective method to measure and improve efficiency of thermal power plant is exergy analysis. Exergy analysis is used to evaluate the performance of a system and its main advantage is enhancement of the energy conversion process. It helps identify the main points of exergy destruction, the quantity and causes of this destruction, as well as show which areas in the system and components have potential for improvements. The current study is a comprehensive review of exergy analyses applied in the solid fuels heat and power sector, which includes coal, biomass and a combination of these feedstocks as fuels. The methods for the evaluation of the exergy efficiency and the exergy destruction are surveyed in each part of the plant. The current review is expected to advance understanding of exergy analysis and its usefulness in the energy and power sectors: it will assist in the performance assessment, analysis, optimization and cost effectiveness of the design of heat and power plant systems in these sectors.
... The new units designed for high steam parameters must meet strict limits for emissions of gaseous pollutants. Meeting the requirements of CO 2 emissions while maintaining highly efficient production process is still the subject of many research [1][2][3][4][5][6]. Regulations for reducing NO x and SO x emissions become more strict and meeting them must be achieved by both new and old production units. ...
The paper presents experimental and numerical investigation of pulverized coal combustion process analysis and optimization. The research was conducted on the frontfired pulverized coal boiler with dedicated low-NOx furnace installation. In order to find optimal boiler operating conditions the acoustic gas temperature measurement system and mass flow rate of pulverized coal measurement system was applied. The uniform
temperature distribution as a result of uniform coal and air flow provides the optimal combustion process with low level of NOx emission and total organic carbon content in ash. Experimental results confirm that the monitoring and control of fuel and air flow distribution allows to optimize combustion process by increasing thermal efficiency of the boiler. In the numerical part of investigation, the complex CFD model of pulverized
coal boiler was made. The calculations of turbulent, reactive, and thermal flow processes were performed at different boiler operating conditions retrieved from power plant online monitoring system. The results of numerical simulations enable to identify the optimal boiler operating conditions.
The energy transition needs secure and sustainable solutions to supply the growing demand for energy with minimal environmental pollution and ecological damage. However, energy supply involves numerous interconnected sectors with a high resource intensity, requiring a holistic solution for minimizing the environmental impact. Energy system modelling offers such a comprehensive way to include a wide range of energy production, transmission, and storage technologies in the model. The objective of the project is to integrate environmental life cycle considerations into an existing optimization model for minimizing the cost of future energy systems economically and environmentally. Three methods are developed in this project. Firstly, life cycle final embodied energy demands of various technologies are estimated by establishing a database of life cycle material and direct energy demand for constructing various technologies based on literature data. Secondly, a database of life cycle impact cost is identified by evaluating the impacts of raw materials and fuels conducted by Simapro with the Ecoinvent database, connected by monetary valuation coefficients of impact categories derived from literature data. Finally, these two data sets are integrated into a system-scale model developed in GAMS with profiles of energy load demand and wind/solar availability in Germany. Preliminary results show blue hydrogen production is cheaper than green hydrogen due to its relatively lower embodied energy consumption and higher energy efficiency. Life cycle impact costs vary widely in the literature and the method of averaging over the available data has a large impact on the full economic-environmental cost of the energy system. Economic efficiency (used to determine indirect embodied energy and environmental impacts) and renewable energy mandates have relatively light effects on the total system cost.
Today,
there is an oversupply of 23.5 GW (47.7%) in the electricity system of
Indonesia. PT.PLN, the state-owned electricity company, needs decision criteria
to decide whether the power plant should be continue operated, rehabilitated or
demolished. Base on the literature review, none of the frameworks in the world
could be used to solve this problem. Therefore, this research proposed a new
method or framework called HOME (Holistic Operation & Maintenance
Excellence). The method has proposed and analysed in this research combines
engineering analysis (efficiency and reliability) and economic analysis, which
are total cost (acquisition cost, fuel cost, operation cost, and maintenance
cost) and revenue. The objective is to define decision criteria to maximize the
profit and minimize the cost has spent by a power plant. The final results are
the decision criteria for a power plant, wheater to continue operated,
rehabilitated, relocated, or demolished. A sub-critical coal power plant, 400
MW, has been selected as a case study. Two scenarios of coals (LRC and HRC) and
CF (79.46% and 60.96%) have been analyzed. Coal variation is used to evaluate
its impact on efficiency and reliability, while CF change would represent the
external and uncontrollable factor that impacts its revenue. The results showed that the thermal
efficiency when using LRC (4,220 kcal/kg) reduced from 36.99% to 35.18%
compared to HRC (4,917 kcal/kg), while the plant availability decreased from 97.93%
to 97.45%. Nonetheless, the annualized profit when using LRC at the CF of
79.46% was 18.31 million USD/year, and it was a preferable option compared to
7.80 million USD/year when using HRC. Furthermore, the CF has
predicted a reduction to 60.96%. In this situation, the power plant was better
rehabilitated or relocated when it used HRC because it needs a minimum CF of
63.83% to get a break-even point (CFBEP). Conversely, the plant
could continue to operate when LRC is used because CFBEP was 50.82%.
Based on the analysis results, HOME is a good approach to determine and aid
decision-making on the strategies required to operate and maintain a power
plant comprehensively through its whole life cycle.
The increase of man-made greenhouse gas (GHG) emissions is a serious global problem. Hence the 2015 Paris Agreement and the COP meetings, which show the willingness of governments to reduce emissions and fight climate change. Their main goals are keeping average temperatures to max 2°C above pre-industrial times, and reaching net-zero emissions by 2050. But how realistic are these goals? GHG emissions may be everyone's long-term problem, but they are nobody's short-term problem. The huge benefits we all reap from the free energy provided by fossil fuels, and the way that governments, companies and people handle risk, create enormous barriers. I will show here, using simple back-of-the-envelope calculations, that we will not reach the Paris Agreement goals. Moreover, I will explain the reasons why much excellent research in sustainable chemistry will not make a sizable dent in CO2 emissions. This doesn't mean we should give up. We must keep on developing and implementing sustainable technologies. But we should also prepare to adapt to living in a world with average temperatures 3–4°C higher than pre-industrial times. Optimistic scenarios make people complacent. Wake up. It is later than you think.
Advanced ultra-supercritical (A-USC) steam power generation technology is characterized by main steam conditions of >700 °C and >35 MPa, enhanced cycle efficiency, and reduced environmental footprint, and is one of the important development goals of the thermal power plants today. However, scarce studies were conducted on the heat transfer characteristics of supercritical water (SCW) under A-USC operating conditions. An experimental platform to safely measure the heat transfer of SCW flowing in a vertical tube at temperature up to 760 °C and pressure up to 42 MPa was designed and built in this study. Experimental measurements of the heat transfer characteristics of SCW were performed on this platform in a wide range of temperature and pressure, up to a maximum bulk fluid temperature of 750 °C and a maximum pressure of 38 MPa. The effects of pressure, mass flux, and heat flux on the heat transfer characteristics of SCW in the ultrahigh enthalpy region (over 3200 kJ·kg⁻¹) were then analyzed based on the experimental data. Results show that in the ultrahigh enthalpy region, the bulk fluid temperature and wall temperature increase approximately linearly with increasing bulk fluid enthalpy. The heat transfer coefficient decreases gently and then gradually stabilizes in the same range, with values in the range of 4 − 10 kW·m⁻²·K⁻¹. In the ultrahigh enthalpy region, increasing the mass flux or decreasing the heat flux will improve the heat transfer performance. And at a pressure of >35 MPa, increasing the pressure will improve the heat transfer performance moderately. By comparing with experimental data, the Gupta’s correlation has acceptable accuracy in predicting the heat transfer coefficient and inner wall temperature.
Flexibility enhancement is crucial for thermal power plants to assist the power grid in accommodating the high penetration of intermittent renewable power. In this study, a new scheme for controlling the steam temperatures of a double-reheat coal-fired power unit is proposed. The scheme uses the leading signal correction of the low-temperature reheater for the control loop regulating the dampers fixed in the fuel gas ducts of the boiler. The scheme was tested using a dynamic model and applied to an in-service double-reheat coal-fired power plant. The results show that both flexibility and efficiency were enhanced when the new control scheme was adopted. The quantity of spray water for the secondary reheat steam could be reduced by 10%–50% during the peak-shaving transients with a load cycling rate in the range of 1%–4% rated power per minute. The average coal consumption rate decreased by 0.8–1.9 g kW⁻¹ h⁻¹, which accounted for 0.29%–0.69% of the thermal efficiency of the power plant. The variation trends of the reheat steam temperatures became smooth, and the maximal measured metal temperature decreased by 12 ℃. The results can guide the control optimization of modern peak-shaving power plants.
The design of adsorption systems for separation of CO2/N2 in carbon capture applications is notoriously challenging because it requires constrained multiobjective optimization to determine appropriate combinations of a moderately large number of system operating parameters. The status quo in the literature is to use the nondominated sorting genetic algorithm II (NSGA-II) to solve the design problem. This approach requires 1000s of time-consuming process simulations to find the Pareto front of the problem, meaning it can take days of computational time to obtain a solution. As an alternative approach, we have employed a Bayesian optimization algorithm, the Thompson sampling efficient multiobjective optimization (TSEMO). For constrained productivity/energy usage optimization, we find that the TSEMO algorithm is able to find an essentially identical solution to the design problem as that found using NSGA-II, while requiring 14 times less computational time. We have used the TSEMO algorithm to design a postcombustion carbon capture system for a 1000 MW coal fired power plant using two adsorbent materials, zeolite 13X and ZIF-36-FRL. Although ZIF-36-FRL showed promising process-scale performance in previous studies, we find that the industrial-scale performance is inferior to the benchmark zeolite 13X, requiring a 21% greater cost per tonne of CO2 captured. Finally, we have also tested the performance of the Bayesian design framework when coupled with a data-driven machine learning process modeling framework. In this instance, we find that the incumbent NSGA-II offers better computational performance than the Bayesian approach by a factor of 3.
The thermo-economic and environmental analysis of an integrated power system with carbon capture and storage was investigated. The plant comprises solid oxide fuel cell (SOFC), gas turbine (GTC), steam turbine (STC), organic Rankine (ORC), absorption refrigeration (ARC), and carbon capture and storage (CCS) technologies. The system was modelled in terms of energy, exergy and economics, and implemented in the Engineering Equation Solver and MS Excel spreadsheet. Key results show that net power is 147.2 MW, with energy and exergy efficiencies of 40.2 and 39.9%, respectively. A total exergy destruction rate of 217.4 MW is obtained, and distributed as 38, 18, 14, 13, 10, and 7%, respectively, for gas turbine, SOFC, ARC, CCS, ORC and STC. The study further propose that 96.7% of carbon dioxide (CO2) can be captured from the flue gases, and 807.3 kton of CO2 can be transported to depleted oil reservoirs annually for enhanced oil recovery. Cost analysis suggests that the plant's total cost, including the cost of transporting and storing CO2, is $ 186 million and cost of CO2 avoidance is $ 110 per tonne, while the levelized cost of energy and payback on investment are put at $ 0.123 per kWh and 5.2 years, respectively. Parametric simulation of pressure ratio, SOFC temperature, fuel utilization factor, excess combustion air, length of pipeline and interest rate were also investigated. The study has the potentials of pushing the energy policy landscape of an energy disadvantaged economy into a broader energy access and climate action terrains.
Wall temperature of heat transfer tubes is one of the most important parameters indicating the operation safety of various heat transfer facilities, and as a result, estimation of the wall temperature becomes one of the main tasks in the design of heat transfer facilities. The wall temperature look-up table (Tw-LUT) can be established directly from experimental data and can be then used to estimate the wall temperature of the heat transfer tubes, avoiding the approximation or extrapolation of fluid properties that inevitably exists in the heat transfer correlations. In view of the problems existing in applications with wall temperature estimations of the heat transfer tube, such as limited data points and the limited application scopes of parameters, a look-up table is built in this paper for wall temperatures of vertically-upward round tubes of 10 mm tube diameter with heat transfer to supercritical water (SCW), under conditions with pressure in the range from 22.5 to 31 MPa, the mass velocity in the range from 200 to 3000 kg·m⁻²·s⁻¹, the heat flux in the range from 200 to 1800 kW·m⁻², and the bulk fluid enthalpy in the range from 1000 to 3000 kJ·kg⁻¹. In order to cover the gaps between the experimental data points, and to improve the prediction accuracy of the Tw-LUT, the best heat transfer correlation is selected for each local area of interest in the LUT based on its prediction accuracy in the corresponding local area, and then the best heat transfer correlation is adopted to supplement wall temperature results to fill up the Tw-LUT. The comparison between the wall temperatures by the Tw-LUT and the experimental wall temperatures is carried out to verify the accuracy of the Tw-LUT, and it is shown that the mean absolute deviation of the results is 0.87%, and 87.81% of the results fall into the ±3% error band, indicating that the Tw-LUT has a good accuracy for wall temperature prediction and the establishment method is reliable and can be used to build other look-up tables. The Tw-LUT can be applied not only to normal heat transfer conditions but also to deteriorated heat transfer conditions and enhanced heat transfer conditions with a satisfactory accuracy.
The thermokinetics and gaseous products of Jurassic coals collected from northern Shaanxi, China at four different heating rates were determined via thermogravimetry-Fourier transform infrared spectroscopy experiments. The results showed that the trends of thermogravimetric pyrolysis and oxidation curves were divided into three stages and five stages, respectively, and presented the same variations. As the heating rate increased, their curves moved the high temperature. In addition, the characteristic temperatures indicated that the coal samples had a relatively significant spontaneous combustion tendency. In the stage of water evaporation and gas desorption, the rates of formation of CO and CO2 went up promptly, and gaseous water produced during the oxidation reaction began to increase, but its generation rate was lower than that in the stage of oxygen absorption and mass increase. The apparent activation energy (Ea) showed a characteristic jump with increasing temperature, and the optimal mechanism function was chosen by integration and differentiation. Moreover, the relationship between Ea and lnA was linear, which indicated that there was a kinetic compensation effect.
Coal-direct CLHG is a novel hydrogen production technology with inherent CO2 capture. Potassium-decorated Fe2O3/Al2O3 oxygen carrier (OC) has been proved to be a potential OC for the technology. However, the ash in the coal could influence the OC performance. In this work, the effect of ash addition on the reactivity, the morphology structure and phase composition of OC, and the potassium migration in the reduction stage were investigated. Furthermore, the effect of OC on the ash fusion temperature was discussed. Results indicated that the OC reactivity had no significant change when SM (Shenmu) ash addition was less than 1% in the reduction stage and decreased when the addition was more than 2%. In the steam oxidation stage, the H2 yield varied between 5.80–5.57 mmol/g when the SM ash addition was less than 10% and decreased to 4.31 mmol/g when the addition was 40%. FeO could react with SiO2 deriving from coal ash to form Fe2SiO4, which could cause the loss of Fe and the OC sintering; K2CO3 could react with silicon-aluminum minerals which could cause the potassium loss. The ash with high CaO content had a less negative effect on the OC reactivity. With the increase of SM ash addition, the potassium in OC decreased, the potassium in char increased and the volatile potassium decreased after the reduction stage. After the OC addition, the deformation temperature decreased from 1242 °C to 1114 °C in the weak reduction atmosphere while increased from 1162 °C to 1300 °C in the air atmosphere.
This chapter discusses oxy-fuel combustion for the capture and subsequent sequestration of carbon dioxide. Technologies for oxygen production based on air separation will be presented and the need to reduce energy consumption of these units will be discussed along with some potential strategies. A pulverized coal-fired power plant and a natural gas combined cycle will be analysed as case studies for oxy-combustion and the benefits of using pure oxygen will be discussed as well as how the changes in the thermodynamic properties affect boiler operation. Purification of carbon dioxide in the resulting flue gas to pipeline transport specifications will end the discussion of this chapter with two examples of gas processing units. The parasitic power consumption of this gas processing unit combined with the air separation unit reduces the net efficiency of the plant even though the thermal efficiency is increased, which emphasises the importance of developing new technologies, such as ion transport membranes for oxygen production. The possibility to reduce the energy consumption of both air separation unit and gas processing unit combined with the increased combustion efficiency by using pure oxygen make this a promising technology for carbon capture and storage.
A novel supercritical CO2 power cycle with oxygen fired fuel of supercritical water gasification of coal is schemed and studied in this paper. The coal gasification syngas is combusted with pure O2 and the combustion products mix with the circulation CO2 forming CO2 dominant CO2/H2O mixture for power generation. By setting the backpressure of turbine at the saturated value of ambient temperature, the circulation CO2 can be pressurized only by pump without compressors. The turbine inlet temperature is set at 950–1000 °C for suitable turbine exhaust temperature for gasification heating. The turbine exhaust vapor is first led to heat the gasification process before releases heat in regenerators and condenser. The effect of key parameters on the cycle performance was investigated and the results show that the turbine inlet temperature, the condensation temperature and the ASU specific power consumption have significant effects on net efficiency of the cycle. Under the parameters of turbine inlet parameters of 25 MPa/1000 °C, condensation temperature of 25 °C and ASU specific power consumption of 0.245 kWh·kg⁻¹(O2), the net efficiency of the cycle achieves 47.3% with full CO2 capture.
There is considerable potential to decarbonise household energy consumption through the electrification of heating systems which can absorb excess renewable power and mitigate power network constraints through intelligent control. However, current standards discourage low carbon electricity sources through outdated assumptions; predicated upon a traditional electricity network which had higher emissions. Consequently, the implementation of product Energy labelling across Europe is biased against electric space and water heating systems in favour of gas. This paper examines the impact of this bias through a case study of the European Union's product labelling directive for domestic hot water systems. Laboratory testing of a market leading electric water tank and an A rated instantaneous gas boiler has demonstrated efficiencies of 87.4% and 72.9% respectively. In spite of this, the labelling directive assigns a C rating to the tank. This is due to a conversion coefficient (CC) within the directive's calculation based on an average electricity generation efficiency of 40% without a similar coefficient for gas. This paper advocates the removal of the CC factor from the directive to normalise the comparison, thus promoting a technology uniquely suited towards absorbing intermittent renewable energy sources with negligible costs.
Thermophysical properties govern the heat transfer during coal spontaneous combustion. Under different oxygen concentrations, the mass and heat intensity of three metamorphic levels of bituminous coal were investigated through synchronous thermal analysis, and their thermophysical parameters were tested using a laser-flash apparatus. The results indicated that as the oxygen concentration increased, the T 3 (the temperature at maximum mass)and exothermic initial temperature slowly decreased. The changes in T 1 (maximum adsorption temperature)and T 2 (initial temperature at the oxygen-absorption and mass-gain stage)were nonsignificant. The effect of oxygen concentration on mass, heat intensity, and thermophysical parameters was primarily concentrated in high-temperature regions. As the temperature increased, the thermal diffusivity first decreased and then increased. The specific heat capacity gradually increased, then plateaued until it began to decrease; meanwhile, the thermal conductivity increased, first slowly and then quickly. A calculation model for different temperatures and oxygen concentrations was established through curve fitting.
The aim of this study is to analyze the suitability of one heater removal as a strategy for maintaining full load operation of steam power cycles when superheated and/or reheated temperatures (TSS, TRS) decrease and the effect on the net heat rate (HRNet). For this purpose, three regenerative cycles with different numbers of closed feedwater heaters were chosen. The cycles were analyzed at different steady states with Thermoflex software. Removing a heater has an important influence on the cycle operation and performance, leading to the redistribution of extraction mass flows, with the heater immediately downstream being the most affected. This may make it necessary to reduce the load of the cycle. However, when the highest pressure heater (highest PH) is removed from service, the changes are not so significant. When TSS and/or TRS decrease, the plant may not achieve full load operation. Nevertheless, if the highest PH is removed from service, it can help to recover full load. This is due to the decrease in the water/steam mass flow through the steam generator, which produces an increase in TSS and/or TRS. On the one hand, this measure leads to higher HRNet in comparison to that of the nominal conditions. On the other hand, there are certain conditions at which HRNet is lower than when all the heaters are in service and the values of TSS and/or TRS are low. Thus, for maintaining full load, the highest PH removal can be applied and cycle parameters optimized in order to reach a HRNet closer to its nominal value. The higher the number of closed feedwater heaters, the more adequate is the application of this strategy.
This study examined the combustion characteristics and kinetics of coal samples treated with imidazole-based ionic liquids (ILs), namely, [Emim][BF4], [Bmim][BF4], [Bmim][NO3], and [Bmim][I], under oxidation. The oxidation of the coal samples was investigated using thermogravimetry (TG) at heating rates of 4.0, 6.0, 8.0, and 10.0 °C·min⁻¹. The results for the IL-treated samples revealed that the composite index S (representing the ignition, combustion, and burnout properties) decreased and Hf (representing the rate and intensity of the combustion process) increased with high correlation coefficients. The characteristic temperatures of the maximum oxidization mass gain (T2), ignition point (T3), maximum mass loss rate (T4), and burnout point (T5) increased by 13.1 ± 0.5, 9.2 ± 0.5, 21.5 ± 0.5, and 35.9 ± 0.5 °C, respectively. At T3 and the maximum mass loss rate, the release of CO and CO2 was further altered, suggesting that the C[dbnd]O functional groups were damaged or oxidized. The results of the Ozawa-Flynn-Wall kinetic equation used to determine the apparent activation energy (Ea) of coal samples revealed that the Ea of the treated samples increased. The reaction rate constant characterizes the effect of Ea and pre-exponential factors (A), and the results showed that ILs can weaken the reaction process at low temperatures (<130 °C).
Thermal analysis was used to investigate the oxidation and heat-release characteristics of four coal samples from the Huainan mining area in China. Temperature and the evolution of heat and gaseous products were studied to identify each sample’s ignition temperature and inform fire-prevention advice to avoid the spontaneous combustion of the coals studied. Thermogravimetry–differential scanning calorimetry (TG–DSC) tests demonstrated lower heating rates resulted in lower characteristic temperatures, corresponding to a greater propensity for spontaneous combustion. Using the Flynn–Wall–Ozawa method, spontaneous combustion was predicted from approximately 300°C, which agreed well with the TG–DSC analysis. The apparent activation energies for combustion were also obtained and gas products that were released throughout the entire oxidation process were monitored. Simultaneous thermal analysis–Fourier transform infrared spectroscopy was used to explain the changes in the evolution of CO and CO2, the results of which agreed well with those of TG.
The distribution of water wall temperature in the ultra-supercritical (USC) boilers was obtained by establishing a coupled heat transfer model. The reliability of this model has been validated through the comparisons of simulated and measured water wall temperatures along different dimensions in the furnace of reference USC boiler. Then, the effect of flame offset on water wall tube temperature in 600°C and 700°C USC boilers was investigated by importing the flame offset variables into the coupled model. The water wall temperature distribution is significantly influenced by flame offset, and both the fluctuation and growth rate of temperature are increased with the ascent of flame offset distance, especially on the furnace walls that flame deviates toward. The radiative and convective heat flux to water walls is strengthened simultaneously during the flame offset process, resulting in the local overheating of water wall. In the 600°C USC boilers, when the distance of flame offset exceeds 5 m, multiple peak distribution of wall temperatures appears, which can increase the burst risk of water wall tubes because of shear stress inside the tube material. The maximal distance of flame offset should be limited to 3 m to avoid the tube burst accidents. In the 700°C USC unit, the variation tendency of water wall temperature is resemble with that in 600°C USC unit, but the fluctuation of wall temperature is larger. As the flame offset distance approaches 3 m, the maximal water wall temperature reaches 595°C, which greatly exceeds the material allowable temperature in the 600°C USC unit. The material of water wall tubes with allowable temperature of 605°C is recommended for the 700°C USC unit. Based on the thermal security of metal material, the maximal distance of flame offset should be yielded to 2 m.
Globally coal-fired power plants are still predominantly utilised for production of electrical energy. The efficiency of a coal-fired power plant is greatly influenced by the performance of the boiler. In turn, the boiler performance is affected by the coal type, combustion characteristics, and the heat transfer from the flue gas side to water-steam side. In the boiler the heat transfer is impeded by the accumulation of ash deposits, known as slagging and fouling, on the heat transfer surfaces. In this paper the effects of slagging and fouling on the boiler performance are investigated by means of energy and exergy analyses. A boiler simulation model, representative of the combustion and heat transfer characteristics, is used to perform the analyses. From the results it is seen that slagging has the most significant effect, while fouling has a less significant influence, on the boiler energy and exergy efficiency.
p>A indústria siderúrgica produz quatro subprodutos com significativa capacidade de geração de energia. Esses subprodutos podem ser utilizados como combustível na caldeira siderúrgica, equipamento da central termoelétrica. O objetivo deste estudo é propor uma modelagem para estimar a temperatura adiabática da chama da fornalha de uma caldeira siderúrgica com a variação de ar e combustível disponível. A técnica empregada consiste no princípio da Primeira Lei da Termodinâmica. O balanço de energia do sistema foi proposto definindo assim o modelo. A solução do modelo possibilita estimar a temperatura adiabática do sistema. Na indústria, a temperatura adiabática é determinada pelo poder calorífico inferior dos combustíveis. A metodologia proposta neste estudo faz com que não sejam necessários levantamentos experimentais do poder calorífico inferior. Os valores da temperatura adiabática simulados indicam que utilizar condições operacionais distintas na alimentação do combustível e do ar podem afetar significativamente o valor deste parâmetro. Nas simulação com a variação de ar, nota-se que a temperatura adiabática decresce com o acréscimo do excesso de ar. Tal resultado é esperado, uma vez que o aumento da massa, contida no sistema, diminui a eficiência energética do processo. Conclui-se que a metodologia proposta provou ser eficaz de descrever o sistema quando diferentes condições de alimentação são adotadas.
ABSTRACT
Steel industry produces four by-products with significant capacity of energy generation. These products can be used as fuel at steel boiler, equipment thermoelectric plant. The objective of this study is to propose a modeling to estimate the adiabatic flame temperature furnace’s of an industrial boiler steelmaking with the variation of available air and fuel. The technique employed consists in principle of the First Law of Thermodynamics. The system's energy balance was proposed thus defining the model. The solution’s model enables to estimate the system’s temperature of the adiabatic. In industry, the adiabatic temperature is determined by the fuel’s lower heating value. The methodology proposed in this study makes is not necessary experimental surveys of the lower heating value. The values at the adiabatic temperature simulated to indicate that use different operating conditions in the feed of fuel and air can significantly affect the value of this parameter. In the simulation with the variation in air, it is noted that the adiabatic temperature decreases with the increase of excess air. This result is expected since the increase of the mass contained in the system decreases the energy efficiency of the process. It is concluded that the methodology proved to be effective to describe the system when different air and fuel feed are adopted.
Toluene, a typical volatile organic compounds (VOCs), is raising growing concern due to its harm to human health and atmospheric environment. However, it also can become a fuel for that C-C and C-H bonds contain considerable chemical energy. In here, we utilize a solid oxide fuel cell (SOFC) reactor to degrade toluene as an environment pollutant and to take full advantages of its chemical energy simultaneously to generate electricity. The scanning electron microscopy (SEM) results show a uniform three-layer structure of the cell and the porous morphology of the anode. Energy dispersive spectroscopy (EDS) illustrates the atomic ratio of the fuel cell and reveals a diffusion layer of the cell between the cathode and the electrolyte with an atomic ratio of Ce: Gd: O=5:26:69. In the reactor, the toluene can be removed from a low temperature of 600 °C. It can be totally removed under 650 °C and obtain a power density of 14 mW/cm2. The removal efficiency can reach 94.19% under high toluene concentration of 1.874×105 ppmv and a temperature of 650 °C and obtain a power density of 14 mW/cm2. However, it decreases as the flow rate increases to 200 mL/min. With the initial concentrations varying from 1.243×105 ppmv to 5.472×105 ppmv, the cell efficiency declines from 29.93%, 20.89%, 19.13% and19.61% to 16.06%, 5.030%, 8.297% and 7.874% as the flow rate increases from 50 mL/min to 200 mL/min. The impedance spectra are analyzed for the mechanism of cell performance. The economic analysis shows that it can save energy not only in that it generates electricity while removing toluene but also in that the heat it releases can well help preheat the cathode air.
A consistent and transparent benchmarking methodology is required for comparison and ranking of different technologies for CO2 capture, and also for evaluation of different means of integrating novel capture process units into power cycles. A novel benchmarking methodology is presented in this work where the difference between the thermodynamic maximum and the technology limited efficiencies quantifies the theoretical improvement potential and is a benchmark for the process. Additionally, the source(s) of this difference in efficiency can point to possible future directions for technology development. . The benchmarking methodology is applied to the three CO2 capture routes – post-combustion, pre-combustion and oxy-combustion – using simplifying assumptions and with fuels of varying HC ratios. The first step of the benchmarking methodology is defining ideal reversible processes for CO2 capture with no detailed process information. This enables determination of a consistent thermodynamic maximum efficiency of processes. Results show that apart from methane as fuel, where post-combustion has the lowest thermodynamics limited efficiency penalty, pre-combustion process routes have the lowest thermodynamics limited efficiency penalty, followed by post-combustion and then oxy-combustion. These results should not be seen as an attempt to rank the different capture routes, but rather as the thermodynamic limit for technological improvements.
Approximately 1/3 of the useful energy of the fuel is destroyed during the combustion process used in electrical power generation. This study is an attempt to clarify and categorize the reasons for the exergy destruction taking place in combustion processes. The entropy production is separated into three subprocesses: (1) combined diffusion/fuel oxidation, (2) “internal thermal energy exchange” (heat transfer), and (3) the product constituent mixing process. Four plausible process paths are proposed and analyzed. The analyses are performed for two fuels: hydrogen and methane. The results disclose that the majority (about 3/4) of the exergy destruction occurs during the internal thermal energy exchange. The fuel oxidation, by itself, is relatively efficient, having an exergetic efficiency of typically 94% to 97%.
In this study, the energy and exergy analysis of Al-Hussein power plant in Jordan is presented. The primary objectives of this paper are to analyze the system components separately and to identify and quantify the sites having largest energy and exergy losses. In addition, the effect of varying the reference environment state on this analysis will also be presented. The performance of the plant was estimated by a component-wise modeling and a detailed break-up of energy and exergy losses for the considered plant has been presented. Energy losses mainly occurred in the condenser where 134 MW is lost to the environment while only 13 MW was lost from the boiler system. The percentage ratio of the exergy destruction to the total exergy destruction was found to be maximum in the boiler system (77%) followed by the turbine (13%), and then the forced draft fan condenser (9%). In addition, the calculated thermal efficiency based on the lower heating value of fuel was 26% while the exergy efficiency of the power cycle was 25%. For a moderate change in the reference environment state temperature, no drastic change was noticed in the performance of major components and the main conclusion remained the same; the boiler is the major source of irreversibilities in the power plant. Chemical reaction is the most significant source of exergy destruction in a boiler system which can be reduced by preheating the combustion air and reducing the air–fuel ratio.
While capture of carbon dioxide from coal-fired power plants has important potential for abating climate change, capturing nearly all of the emissions, or full capture, currently has a significant impact on plant technology, performance, and economics. Capturing only part of the emissions, or partial capture, can take advantage of technological differences that result in a reduction of capital investment and improved plant performance. By reducing technical and economic disincentives for first movers, partial capture can serve as an important near-term strategy to meet electrical demand while expediting widespread deployment of full capture.
An advanced, practical approach to the first and second laws of thermodynamics. Advanced Engineering Thermodynamics bridges the gap between engineering applications and the first and second laws of thermodynamics. Going beyond the basic coverage offered by most textbooks, this authoritative treatment delves into the advanced topics of energy and work as they relate to various engineering fields. This practical approach describes real-world applications of thermodynamics concepts, including solar energy, refrigeration, air conditioning, thermofluid design, chemical design, constructal design, and more. This new fourth edition has been updated and expanded to include current developments in energy storage, distributed energy systems, entropy minimization, and industrial applications, linking new technologies in sustainability to fundamental thermodynamics concepts. Worked problems have been added to help students follow the thought processes behind various applications, and additional homework problems give them the opportunity to gauge their knowledge. The growing demand for sustainability and energy efficiency has shined a spotlight on the real-world applications of thermodynamics. This book helps future engineers make the fundamental connections, and develop a clear understanding of this complex subject. Delve deeper into the engineering applications of thermodynamics. Work problems directly applicable to engineering fields. Integrate thermodynamics concepts into sustainability design and policy. Understand the thermodynamics of emerging energy technologies. Condensed introductory chapters allow students to quickly review the fundamentals before diving right into practical applications. Designed expressly for engineering students, this book offers a clear, targeted treatment of thermodynamics topics with detailed discussion and authoritative guidance toward even the most complex concepts. Advanced Engineering Thermodynamics is the definitive modern treatment of energy and work for today's newest engineers.
This review reports recent advances on chemical-looping combustion (CLC). CLC is a promising technology for fossil fuel combustion preventing CO2 dilution with flue gases, mainly nitrogen. In CLC, the solid oxygen carrier supplies the stoichiometric oxygen needed for CO2 and water formation, and this leads to a free nitrogen mixture. As a result, the requirement of CO2 separation from flue gases, a major cost for CO2 capture, is circumvented. Furthermore, formation of NOx is also reduced. A good oxygen carrier for CLC shall readily react with the fuel gas and shall be reoxidized upon being contacted with oxygen. An oxygen carrier is typically formed by a metal oxide and an inert binder, which provide, respectively, oxygen storage, fluidizability and mechanical strength. Over the last 10 years, several research groups have been researching oxygen carriers which are both active and stable under fluidized bed conditions. While Fe, Ni, Cu, Mn and Co oxides are potential oxygen carrier materials, recent studies show that Ni is best suited for CLC. Few studies have been devoted to the solid-state kinetics of both reduction and oxidation with either a nucleation–nuclei growth or unreacted shrinking core models being considered. In order to implement CLC, two interconnected fluidized bed reactors (the fuel and air reactor) with the oxygen carrier circulated between units have been proposed. While reactor design, modeling and hydrodynamics are matters that have been analyzed by several research groups; these topics still require more attention and investigation. Preliminary economic assessments, have suggested that CLC holds great promise for combustion processes, having the potential for achieving very efficient and low cost CO2 capture. Even with these favorable prospects, commercial scale-up of CLC still depends nowadays on the availability of highly performing and stable oxygen carriers.
There is an intimate connection between energy, the environment and sustainable development. A society seeking sustainable development ideally must utilize only energy resources which cause no environmental impact (e.g. which release no emissions to the environment). However, since all energy resources lead to some environmental impact, it is reasonable to suggest that some (not all) of the concerns regarding the limitations imposed on sustainable development by environmental emissions and their negative impacts can be in part overcome through increased energy efficiency. Clearly, a strong relation exists between energy efficiency and environmental impact since, for the same services or products, less resource utilization and pollution is normally associated with increased energy efficiency. Presented in this paper are (i) a comprehensive discussion of the future of energy use and the consequent environmental impacts in terms of acid precipitation, stratospheric ozone depletion and the greenhouse effect, (ii) some solutions to current environmental issues in terms of energy conservation and renewable energy technologies, (iii) some theoretical and practical limitations on increased energy efficiency, (iv) discussions of the relations between energy and sustainable development, and between the environment and sustainable development, and an (v) illustrative example. In this regard, a number of issues relating to energy, environment and sustainable development are examined from both current and future perspectives. In addition, some recommendations are drawn from the results we present for the use of energy scientists and engineers and policy makers, along with the anticipated effects.
In this paper, both conventional and advanced exergy analyses were conducted to a large-scale ultra-supercritical coal-fired power plant. The objectives of the conventional one are to compare the exergetic performances of different components, to identify and quantify the sites with the largest exergy destruction and losses, and to find the fuel-savings potential by improving each component in isolation. The advanced exergetic analysis focuses on the thermodynamic interactions among components and the sources for energy-saving potential of each component. Moreover, comparisons with several subcritical units are conducted and a sensitivity analysis shows the dependencies of the overall exergetic efficiency on a number of key design parameters. The results display the spatial distribution of exergy destruction and losses in detail and three performance ranges for different types of heat exchangers involved in the system. The energy-saving potentials at both the system and the component levels by improving an individual component are not in accordance with the amount of its exergy destruction. Improvement strategies for different components differ significantly due to the varied contributions of endogenous/exogenous parts to their avoidable exergy destructions. With an increase in the steam conditions, the exergy destruction ratio of the boiler is significantly reduced, contributing mainly to the system improvement. The most effective and achievable measure for reducing the fuel consumption is still the reasonable utilization of available low-grade heat. This framework provides a basis for the quantifying proposals of exergy-driven strategies for improving the system.
Integrating a power plant with CO2 capture incurs serious efficiency and energy penalty due to use of energy for solvent regeneration in the capture process. Reducing the exergy destruction and losses associated with the power plant systems can improve the rational efficiency of the system and thereby reducing energy penalties. This paper presents steady state simulation and exergy analysis of supercritical coal-fired power plant (SCPP) integrated with post-combustion CO2 capture (PCC). The simulation was validated by comparing the results with a greenfield design case study based on a 550 MWe SCPP unit. The analyses show that the once-through boiler exhibits the highest exergy destruction but also has a limited influence on fuel-saving potentials of the system. The turbine subsystems show lower exergy destruction compared to the boiler subsystem but more significance in fuel-saving potentials of the system. Four cases of the integrated SCPP-CO2 capture configuration was considered for reducing thermodynamic irreversibilities in the system by reducing the driving forces responsible for the CO2 capture process: conventional process, absorber intercooling (AIC), split-flow (SF), and a combination of absorber intercooling and split-flow (AIC + SF). The AIC + SF configuration shows the most significant reduction in exergy destruction when compared to the SCPP system with conventional CO2 capture. This study shows that improvement in turbine performance design and the driving forces responsible for CO2 capture (without compromising cost) can help improve the rational efficiency of the integrated system.
Oxy-combustion is a competitive technology to enable the capture of CO2 from coal-based power plants. The main challenge to implement this technology is the large energy penalty and investment cost related to CO2 capture. A comprehensive exergy analysis has been performed for an entire coal-based oxy-combustion power plant. The exergy flows and irreversibilities are presented. The thermal efficiency penalty related to CO2 capture is about 9.4 percentage points (on the basis of the higher heating value) and is mainly caused by the air separation unit and the CO2 compression and purification unit. The theoretical minimum is 3.4 percentage points when the two units are assumed to be reversible, where the air separation unit contributes 1.4 percentage points and the CO2 compression and purification unit is responsible for 2.0 percentage points. The compression processes are causing the largest exergy losses related to CO2 capture. The case studies show that the integration of the compression heat with the steam cycle can increase the thermal efficiency by up to 0.72 percentage points.
The paper establishes a theoretical basis for approximate relationships which have been found to apply to feed heating calculations for a wide range of operating conditions. The designer, looking for short-cut methods in the calculation of multistage feed heating problems, will not find sufficient accuracy in the approximations to satisfy his more precise requirements. Other papers† have already catered for such requirements, but it is hoped that the present paper will give the designer and student a more complete understanding of the problem.
Since in the use of coal the direct recourse to combined cycles is impractical, binary alkali metal steam cycles are recognized as an interesting and feasible option. Past attempts to employ metal vapour conversion cycles for power generation are surveyed. After selecting potassium and cesium as possible candidate fluids, the binary cycle is optimized taking as variables the top temperature, the number of condensation levels of the metal vapour cycle, and the characteristics of the bottoming steam cycle. At vaporization temperatures in the range of 750—850 °C, metal vapour cycle efficiencies of about 20—24 per cent and binary cycle efficiencies of 57—61 per cent seem achievable.
A survey of available building materials in the steel and in the super-alloy class showed that top temperatures of 800–850 °C could be reached with state-of-the-art alloys. Metal vapour turbines are recognized as a key issue of binary plant design in that exhaust volume flows are very large even for a moderate turbine capacity. For a double flow solution, limiting turbine dimensions to those of existing 1500 r/min steam low pressure stages leads to metal vapour turbine capacity of 120 MW for potassium and 170 MW for cesium.
Assuming that in the future, better materials will be available allowing alkali metal vaporization temperatures in the range of 1400–1500 °C, a ternary solution is proposed which employs lithium, potassium, and steam as working fluids. At 1450 °C top temperature, a cycle efficiency in excess of 70 per cent is attained.
The modern pulverized-coal power plant is the product of continuous design experience and component improvement in the 20th century. In recent years, studies of the effect of high temperatures on turbine materials have led to major worldwide research and development programs on improving the thermal cycle by raising turbine-inlet pressure and temperature. This paper reviews the importance of various parameters in trying to optimize a turbine cycle designed for advanced steam conditions. Combinations of throttle pressure (between 3500 psi [24.1 MPa] and 10,000 psi [70 MPa]), throttle and reheat temperature (1000-degrees-F[538-degrees-C] to 1400-degrees-F [760-degrees-C]), and number of reheats are explored to establish a realistic turbine cycle design. Assessments and trade-offs are discussed, as applicable. Critical cycle components, feedwater cycle arrangements, and reheat pressure selections are analyzed in establishing an optimized steam turbine-boiler cycle for a 1000 MW turbine-generator. Applicability of results to smaller advanced steam turbines is given. A brief update on the high-temperature Wakamatsu turbine project in Japan is also given.
A new thermodynamic energy cycle has been developed using a multicomponent working agent. This cycle is designed to replace the currently used Rankine Cycle as a bottoming cycle for a combined-cycle energy system as well as for generating electricity using low-temperature heat sources. Several combined power systems based on this cycle have been designed and cost-estimated. The efficiency of this cycle is from 1. 6 to 1. 9 times higher than that of the Rankine Cycle system, at the same border conditions. The investment cost per unit of power output for this cycle is lower than that for the Rankine Cycle system in approximately direct proportion to the energy advantage.
The performance of different working fluids to recover low-temperature heat source is studied. A simple Rankine cycle with subcritical configuration is considered. This work is to screen working fluids based on power production capability and component (heat exchanger and turbine) size requirements. Working fluids considered are R134a, R123, R227ea, R245fa, R290, and n-pentane. Energy balance is carried out to predict operating conditions of the process. Outputs of energy balance are used as input for exergy analysis and components (heat exchanger and turbine) design. The heat exchanger is divided into small intervals so that logarithmic mean temperature difference (LMTD) method is applicable. R227ea gives highest power for heat source temperature range of 80–160°C and R245fa produces the highest in the range of 160–200°C. There is optimal pressure where the heat exchanger surface area is minimum. This optimal pressure changes with heat source temperature and working fluid used. The least heat exchanger area required at constant power rating is found when the working fluid is n-pentane. At lower heat source temperature (80°C), the maximum power output and minimum heat exchanger surface area for different working fluids is comparable.
In this paper, a cost analysis method based on thermoeconomics is applied to a 300MW pulverized coal fired power plant located in Yiyang (Hunan Province, China). This method, as derived from the second law of thermodynamics, can provide detailed analysis for cost formation of the power plant as well as the effects of different operating conditions and parameters on the performance of each individual component.To perform the thermoeconomic analysis of the plant, a simulator is developed from thermodynamic modeling of the plant. With the thermodynamic properties of the most significant mass and energy flow streams being obtained from the plant, this simulator can reproduce the cycle behavior for different operating conditions with relative errors less than 2%. The models of the simulator are refined using data from designed performance tests in this plant.After simulation, an exergy analysis is performed to calculate the exergy and negentropy of the flows. Then, a thermoeconomic model of the plant is defined based on the functionality of each component using the fuel–product definition. The distribution of the resources throughout the plant and the costs of all flows in the production structure can be calculated by solving a set of equations including the thermoeconomic model of the plant. Three thermoeconomic variables are defined for improving the exergy cost equations in the structural theory of thermoeconomics. Several simulation cases have been analyzed in detail using the improved exergy cost method. The results show that the specific irreversibility cost is more suitable than the unit exergy cost of product in quantifying and representing the production performance of a component. The results provide insights useful to designers and managers of the plant into the relations between the thermodynamic losses and exergetic costs. This work demonstrates the merits of this advanced thermoeconomic analysis over those conventional analysis techniques based on the first and second laws of thermodynamics.
Exergy losses in gasification and combustion of solid carbon are compared by conceptually dividing the processes into several subprocesses: instantaneous chemical reaction, heat transfer from reaction products to reactants (internal thermal energy exchange) and product mixing. Gasification is more efficient than combustion because exergy losses due to internal thermal energy exchange are reduced from 14–16 to 5–7% of expended exergy, while the chemical reactions are relatively efficient for both processes. The losses due to internal thermal energy exchange may be reduced by replacing air with oxygen, although this introduces additional process losses for separation of oxygen from air, or alternatively, preheating of air by heat exchange with product gas. For oxygen-blown gasification of fuels with high calorific value, such as solid carbon, it is advisable to moderate the temperature by introduction of steam. At optimum gasification temperatures in the ranges of 1100–1200K (for atmospheric pressure) and 1200–1300K (for 10bar pressure), up to 75% of the chemical exergy contained in solid carbon can be preserved in the chemical exergy of carbon monoxide and hydrogen.
This paper compares the theoretical maximum efficiency of a fuel cell to the efficiency of a Carnot cycle driven by the same net reaction. The comparison dispels the misconception that an ideal fuel cell is potentially more efficient than an ideal heat engine. The paper presents expressions for the thermal efficiencies of an ideal fuel cell and a Carnot heat engine. To show that the maximum efficiency is the same, the analysis of the Carnot cycle is modified to consider an engine driven by a combustion reaction. The derivation invokes the approximations that the enthalpy and entropy changes for the reaction are independent of temperature; these approximations are justified by the hydrogen-oxidation reaction.The analysis extends that presented by Appleby and Foulkes (Fuel Cell Handbook, Van Nostrand Reinhold, New York 1989) by showing that with proper accounting for heat addition, the maximum efficiency of a fuel cell is 100%—not larger—for reactions with a positive entropy change. In addition, this paper explains the difference between the combustion temperature, at which an idealized Carnot cycle would operate, and the adiabatic flame temperature.
The Exergy Method, also known as ''availability analysis,'' is a technique of thermodynamic analysis which uses the Second Law of Thermodynamics as its basis of assessment. Recent developments in the technique, combined with the increasing need to conserve fuel, has attracted much attention. Its advantages over traditional techniques using the First Law are now generally recognized. The book introduces the subject in a manner that can be understood by anyone familiar with the fundamentals of applies thermodynamics. Numerous examples will help the reader to understand the basic concepts and master the techniques. There are also many tables and charts for calculations in thermoeconomics, refrigeration, cryogenic processes, combustion power generation and various aspects of chemical and process engineering.
The most mature CO2 carbon capture process comes with a 12–10% pts efficiency loss when coupled with a coal-fired power plant and for both post and oxy-combustion. Pre-combustion induces less efficiency loss but at the cost of a more complicated overall process. Since the last decade numerous improvements have been made and this work tries to evaluate the thermodynamic minimum impact of CO2 capture processes on such coal power plants. After detailing the calculation hypothesis, the purely thermodynamic impact has been assessed: they are 3.2% pt for post-combustion divided into 40% for separation and 60% for compression, 4.2% for pre-combustion especially due to CO-shift (60%), the rest evenly divided between separation and compression and 2.9% for oxy-combustion divided into one third for O2 production and two thirds for compression and with a small efficiency gain compared to aero-combustion due to the reduction in flue gas volume. In the second part of this work, the realistic minimum energy consumption is assessed with some assumptions about compressor and pump efficiency, temperature pinch and overall process conditions. This study shows a 6.8% pt loss of efficiency for MEA absorption post-combustion process combined with classical compression train, 5.8% pt for a cryogenic post-combustion process, 6.6% pt for a MDEA absorption pre-combustion process with classical compression train, 5.4% pt for the cryogenic ASU oxy-combustion with standard cryogenic CPU.
The poor performance of internal combustion (IC) engines can be attributed to the departure from equilibrium in the combustion process. This departure is expressed numerically, as the difference between the working fluid's temperature and an ideal ‘combustion temperature’, calculated using a simple expression. It is shown that for combustion of hydrocarbons to be performed reversibly in a single reaction, impractically high working fluid temperatures are required — typically at least 3500 K.
Chemical-looping combustion (CLC) is an alternative to traditional, single-stage combustion that performs the oxidation of fuels using two reactions, in separate vessels: the oxidizer and reducer. An additional species circulates between the oxidizer and reducer carrying oxygen atoms. Careful selection of this oxygen carrier can reduce the equilibrium temperature of the two redox reactions to below current metallurgical limits. Consequently, using CLC it is theoretically possible to approach a reversible IC engine without resorting to impractical temperatures. CLC also lends itself to carbon capture, as at no point is N 2 from the air allowed to mix with the CO 2 produced in the reduction process and therefore a post-combustion scrubbing plant is not required.
Two thermodynamic criteria for selecting the oxygen carrier are established: the equilibrium temperature of both redox reactions should lie below present metallurgical limits. Equally, both reactions must be sufficiently hot to ensure that their reaction velocity is high. The key parameter determining the two reaction temperatures is the change in standard state entropy for each reaction.
An analysis is conducted for an irreversible CLC system using two Rankine cycles to produce shaft work, giving an overall efficiency of 86.5 per cent. The analysis allows for irreversibilites in turbine, boiler, and condensers, but assumes reactions take place at equilibrium. However, using Rankine cycles in a CLC system is considered impractical because of the need for high-temperature, indirect heat exchange. An alternative arrangement, avoiding indirect heat exchange, is discussed briefly.
This paper assesses the three leading technologies for capture of CO2 in power generation plants, i.e., post-combustion capture, pre-combustion capture and oxy-fuel combustion. Performance, cost and emissions data for coal and natural gas-fired power plants are presented, based on information from studies carried out recently for the IEA Greenhouse Gas R&D Programme by major engineering contractors and process licensors. Sensitivities to various potentially significant parameters are assessed.
This paper presents a summary of technical-economic studies. It allows evaluating, in the French context, the production cost of electricity derived from coal and gas power plants with the capture of CO2, and the cost per tonne of CO2 avoided. Three systems were studied: an Integrated Gasification Combined Cycle (IGCC), a conventional combustion of Pulverized Coal (PC) and a Natural Gas Combined Cycle (NGCC). Three main methods were envisaged for the capture of CO2: pre-combustion, post-combustion and oxy-combustion.For the IGCC, two gasification types have been studied: a current technology based on gasification of dry coal at 27 bars (Shell or GE/Texaco radiant type) integrated into a classical combined cycle providing 320 MWe, and a future technology (planned for about 2015–2020) based on gasification of a coal–water mixture (slurry) that can be compressed to 64 bars (GE/Texaco slurry type) integrated into an advanced combined cycle (type H with steam cooling of the combustion turbine blades) producing a gross power output of 1200 MWe.
The exergy of an energy form or a substance is a measure of its usefulness or quality or potential to cause change. A thorough understanding of exergy and the insights it can provide into the efficiency, environmental impact and sustainability of energy systems, are required for the engineer or scientist working in the area of energy systems and the environment. Further, as energy policies play an increasingly important role in addressing sustainability issues and a broad range of local, regional and global environmental concerns, policy makers also need to appreciate the exergy concept and its ties to these concerns. During the past decade, the need to understand the connections between exergy and energy, sustainable development and environmental impact has become increasingly significant. In this paper, a study of these connections is presented in order to provide to those involved in energy and environment studies, useful insights and direction for analyzing and solving environmental problems of varying complexity using the exergy concept. The results suggest that exergy provides the basis for an effective measure of the potential of a substance or energy form to impact the environment and appears to be a critical consideration in achieving sustainable development.
Nine different concepts for natural gas fired power plants with CO2 capture have been investigated, and a comparison is made based on net plant efficiency and emission of CO2. The cycles are one post-combustion, six oxy-fuel and two pre-combustion capture concepts. A 400 MW combined cycle plant is applied as a reference case. A common basis for the comparison of all concepts is defined and employed in heat- and mass-balance simulations of the various concepts. As gas turbine cooling impacts the net plant efficiency at high turbine inlet temperatures, a simplified turbine cooling model has been applied in the simulations. It is found that the concepts, in which novel technology (the hydrogen membrane separation reformer—-MSR-H2, the advanzed zero emission power plant—AZEP, the solid oxide fuel cell combined with a gas turbine—SOFC+GT and the chemical looping combustion—CLC concepts) is employed, exhibit the best performance with respect to both efficiency and in most cases also CO2 capture (capture rates close to 100%). Post-combustion capture and pre-combustion capture with auto-thermal reforming, which are based on more mature technology, show a lower efficiency and a capture rate of typically 90%. The SOFC+GT concept exhibits the best cycle performance and even better than a standard CC plant, however, any realization of a SOFC-GT 400 MW plant has a very distant future perspective. In order to conduct a complete assessment of these diverse concepts, other criteria for comparison such as e.g. technology level and costs should also be considered. This is not, however, included in the present work.
Analysis and abatement of air pollution involve a variety of technical disciplines. Formation of the most prevalent pollutants occurs during the combustion process, a tightly coupled system involving fluid flow, mass and energy transport, and chemical kinetics. Its complexity is exemplified by the fact that, in many respects, the simplest hydrocarbon combustion, the methane-oxygen flame, has been quantitatively modeled only within the last several years. Nonetheless, the development of combustion modifications aimed at minimizing the formation of the unwanted by-products of burning fuels requires an understanding of the combustion process. Fuel may be available in solid, liquid, or gaseous form; it may be mixed with the air ahead of time or only within the combustion chamber; the chamber itself may vary from the piston and cylinder arrangement in an automobile engine to a 10-story-high boiler in the largest power plant; the unwanted byproducts may remain as gases, or they may, upon cooling, form small particles.
The only effective way to control air pollution is to prevent the release of pollutants at the source. Where pollutants are generated in combustion, modifications to the combustion process itself, for example in the manner in which the fuel and air are mixed, can be quite effective in reducing their formation. Most situations, whether a combustion or an industrial process, however, require some degree of treatment of the exhaust gases before they are released to the atmosphere. Such treatment can involve intimately contacting the effluent gases with liquids or solids capable of selectively removing gaseous pollutants or, in the case of particulate pollutants, directing the effluent flow through a device in which the particles are captured on surfaces.
The study of the generation and control of air pollutants can be termed air pollution engineering and is the subject of this book. Our goal here is to present a rigorous and fundamental analysis of the production of air pollutants and their control. The book is intended for use at the senior or first-year graduate level in chemical, civil, environmental, and mechanical engineering curricula. We assume that the student has had basic first courses in thermodynamics, fluid mechanics, and heat transfer. The material treated in the book can serve as the subject of either a full-year or a one-term course, depending on the choice of topics covered.
In the first chapter we introduce the concept of air pollution engineering and summarize those species classified as air pollutants. Chapter 1 also contains four appendices that present certain basic material that will be called upon later in the book. This material includes chemical kinetics, the basic equations of heat and mass transfer, and some elementary ideas from probability and turbulence.
Chapter 2 is a basic treatment of combustion, including its chemistry and the role of mixing processes and flame structure. Building on the foundation laid in Chapter 2, we present in Chapter 3 a comprehensive analysis of the formation of gaseous pollutants in combustion. Continuing in this vein, Chapter 4 contains a thorough treatment of the internal combustion engine, including its principles of operation and the mechanisms of formation of pollutants therein. Control methods based on combustion modification are discussed in both Chapters 3 and 4.
Particulate matter (aerosols) constitutes the second major category of air pollutants when classified on the basis of physical state. Chapter 5 is devoted to an introduction to aerosols and principles of aerosol behavior, including the mechanics of particles in flowing fluids, the migration of particles in external force fields, Brownian motion of small particles, size distributions, coagulation, and formation of new particles from the vapor by homogeneous nucleation. Chapter 6 then treats the formation of particles in combustion processes.
Chapters 7 and 8 present the basic theories of the removal of particulate and gaseous pollutants, respectively, from effluent streams. We cover all the major air pollution control operations, such as gravitational and centrifugal deposition, electrostatic precipitation, filtration, wet scrubbing, gas absorption and adsorption, and chemical reaction methods. Our goal in these two chapters, above all, is to carefully derive the basic equations governing the design of the control methods. Limited attention is given to actual equipment specification, although with the material in Chapters 7 and 8 serving as a basis, one will be able to proceed to design handbooks for such specifications.
Chapters 2 through 8 treat air pollution engineering from a process-by-process point of view. Chapter 9 views the air pollution control problem for an entire region or airshed. To comply with national ambient air quality standards that prescribe, on the basis of health effects, the maximum atmospheric concentration level to be attained in a region, it is necessary for the relevant governmental authority to specify the degree to which the emissions from each of the sources in the region must be controlled. Thus it is generally necessary to choose among many alternatives that may lead to the same total quantity of emission over the region. Chapter 9 establishes a framework by which an optimal air pollution control plan for an airshed may be determined. In short, we seek the least-cost combination of abatement measures that meets the necessary constraint that the total emissions not exceed those required to meet an ambient air quality standard.
Once pollutants are released into the atmosphere, they are acted on by a variety of chemical and physical phenomena. The atmospheric chemistry and physics of air pollution is indeed a rich arena, encompassing the disciplines of chemistry, meteorology, fluid mechanics, and aerosol science. As noted above, the subject matter of the present book ends at the stack (or the tailpipe); those readers desiring a treatment of the atmospheric behavior of air pollutants are referred to J. H. Seinfeld, Atmospheric Chemistry and Physics of Air Pollution (Wiley-Interscience, New York, 1986).
We wish to gratefully acknowledge David Huang, Carol Jones, Sonya Kreidenweis, Ranajit Sahu, and Ken Wolfenbarger for their assistance with calculations in the book.
Finally, to Christina Conti, our secretary and copy editor, who, more than anyone else, kept safe the beauty and precision of language as an effective means of communication, we owe an enormous debt of gratitude. She nurtured this book as her own; through those times when the task seemed unending, she was always there to make the road a little smoother.
R. C. Flagan
J. H. Seinfeld
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