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Energy and exergy analyses of a Zero emission coal system
... Hence, considering the potentialities introduced above, SOFCs are a powerful solution for the exploitation of low-carbon gases [9,10] that can support the transition towards the hydrogen society [11e13]. Specifically, SOFCs could be able to penetrate the market apart from the existence of a hydrogen grid, still using fuels obtained from both fossil [14,15] and renewable sources [16] (like methane, syngas, biogas, reformate gases). ...
... A linear trend is assumed sufficient to get a good correlation coefficient (R 2 ). Hence, the linear regression provides an OCV model such as illustrated in Eq. (15). x and y in Eq. (14) are constant coefficients and they are determined iteratively, in order to maximize R 2 . ...
... Then, voltage forecasts for the given current points (0 A and 0.5 A) are reported. Predictions about OCV are done evaluating the expression at Eq. (15). Similarly, predictions about 0.5 A voltage are done applying Eq. (24) and setting j * to 250 mA/cm 2 (it is recalled that tested SOFC BC have a 2 cm 2 actove area). ...
... An improved Zero Emission Coal (ZEC) system was also studied by Yan et al. [211]. The layout diagram of the ZEC system is depicted in Fig. 38. ...
... Schematic diagram of the ZEC system[211]. ...
... Energy characteristics of hybrid systems with SOFC employing coal gasification products[211]. ...
This paper presents a comprehensive review of the possible layout configurations of hybrid power plants based on the integration of solid oxide fuel cells (SOFC) and gas turbine (GT) technologies. SOFC/GT power plants have been investigated by using a plurality of approaches, such as: numerical simulations, experimental analyses, and thermo-economic optimizations. The majority of SOFC/GT hybrid systems are fed by methane, which is much cheaper and easier to manage than hydrogen. In fact, SOFC/GT systems use the capability of the fuel cell to internally perform the reforming process required to convert methane into hydrogen. The steam required to drive the reforming reaction can be supplied by the anode recirculated stream. Alternatively, such steam can be produced externally, by using the heat of the exhaust gases. In this case, steam can be used also for thermal purposes and/or for further system hybridization (e.g. Cheng cycle). The majority of the SOFC/GT power plants analyzed in literature are based on the pressurized arrangement, potentially able to ensure lower capital costs and higher efficiencies. Conversely, atmospheric plants are easier to manage, due to the possibility of operate the SOFC and the GT independently one of each other. The paper also investigates more complex SOFC/GT configurations, including: HAT turbines, IGCC SOFC/GT power plants, ORC cycles, etc. A detailed analysis of the SOFC/GT control strategies and part-load performance analyses is also presented, showing that such systems reach their best performance at nominal capacity, and are affected by significant reduction of the electrical efficiency in case of large variations of the load. Finally, the paper also presents a review of hybrid SOFC/GT power plants fed by alternative fuels, such as coal and biomass.
... Exergy is defined as the maximum work available from an overall system consisting of a specific system and the environment as the system comes into equilibrium with the environment [40]. Exergy E xr is usually divided into kinetic energy exergy E xr,Kn , potential energy exergy E xr,Pt , chemical exergy E xr,Ch , and physical exergy E xr,Ph . ...
... Using the above three methods, the energy efficiencies of corresponding IGCC systems were between 34.6% and 37.2% and the exergy efficiencies were among 31-34% when the CO 2 capture efficiencies were higher than 90%. For Case 6 [40], an IGCC system based on syngas calcium looping reforming (Fig. 1b) and hightemperature solid oxide fuel cell (SOFC) was developed, which adopted CaO to absorb the produced CO 2 in a water gas shift reactor. Compared with the cases using conventional CO 2 capture methods (Cases 2-5), Case 6 took advantages of calcium looping as well as advanced SOFC, which significantly improved the overall energy efficiency (about 41%) and exergy efficiency (slightly less than 40%) of the Fig. 15 Effects of GT compression ratio on the exergy loss rates of CL-BIGCC system (gasification temperature: 650 °C; steam to carbon molar ratio: 1.5; calcium to carbon molar ration: 1:1) Fig. 16 Effects of the GT compression ratio on the system efficiencies of CL-BIGCC system (gasification temperature: 650 °C; steam to carbon molar ratio: 1.5; calcium to carbon molar ration: 1:1) Content courtesy of Springer Nature, terms of use apply. ...
In order to achieve the targets of Paris Agreement and carbon neutrality, developing CO2 negative emission technologies such as biomass energy with carbon capture and storage (BECCS) is of great significance. Biomass integrated calcium looping gasification combined cycle (CL-BIGCC) with in situ carbon capture during gasification is an attractive option among various options. In this work, Aspen Plus software was used to establish the thermodynamic model of CL-BIGCC system based on “gasification-combustion” dual reactors and traditional biomass integrated gasification combined cycle (BIGCC) system with carbon capture. The reliability of both models was first verified, and then, energy analysis and exergy analysis were used to examine the loss of key units and overall performance for the two systems. The results showed that comparing with the BIGCC system, the CL-BIGCC system significantly promoted the overall exergy efficiency. The largest two sources of exergy loss for the CL-BIGCC system were the “gasification-combustion” dual reactors and the gas turbine. Under a typical case with CO2 capture efficiency larger than 90%, the energy efficiency, exergy efficiency, and CO2 specific emission of the CL-BIGCC system were 42.42%, 38.77%, and 58.45 g kWh⁻¹, respectively. Moreover, the effects of key parameters such as gasification temperature, steam to carbon molar ratio, and gas turbine compression ratio on the exergy loss and overall performance of the CL-BIGCC system were discussed. Finally, the calculated results of a typical case of CL-BIGCC system were compared with those of other reported BIGCC systems with carbon capture in literature, which verified the advantages of CL-BIGCC system over other BIGCC systems with negative carbon emission.
... The indirect hybrid system is another compound in that the fuel cell and the GT cycle are in two separate cycles, and heat exchange was done by a heat exchanger. An improved Zero Emission Coal (ZEC) system was also studied by Yan et al. [243]. The layout diagram of the ZEC system is depicted in Fig. 51. ...
... Flowchart of the ZEC system[243]. ...
Recently, to reach zero emission levels, some new energy systems based on fuel cells have been developed. This paper presents a review of investigations of these systems by thermodynamics performance, mainly, energy and exergy analysis. With energy analysis, the performance of an energy conversion system cannot be effectively and accurately evaluated. But exergy analysis complements and reinforces energy analysis. Using exergy analysis in relation to the degree of irreversibility in each section is a quality method and can be useful in fuel cell analysis. Analysis based on the first and second laws of thermodynamics seems useful in most cases and here reviews for low-temperature and high-temperature fuel cells are given. As a result, regardless of the type of the FC-system and its application, there is always a need of thermo-economic analysis to investigate the effect of various parameters on the system performance, such as different fuel sources, different operating conditions, different subsystems and energy sources to combine with the fuel cell.
... The chemical exergy of a solid fuel can be estimated from its proximate and ultimate analysis (see Eq. 32) [36,45]. ...
... Overall, gasification-based plants show their clear advantage over combustion-based plants, especially for the production of CO 2 . Equipment such as SOFC can double the exergy losses as compared to those of power cycles based on steam and gas [45]. However, it is possible to achieve low exergy costs with such technology despite the net electrical power (pure exergy) generation capacity of the fuel cells being lower than that of the IGCC. ...
Four coal-based power plants were evaluated with respect to their capacity to produce CO2 for Enhanced Oil Recovery (EOR). The plant characteristics were evaluated using energy and exergoeconomic criteria and a robust coal gasification/combustion mathematical model that can predict temperature, converted fraction and particle size distribution for solids have been used for a high pressure fluidized bed. Other models based on Python, Aspen Hysys and Microsoft Excel have been used too. Integrating carbon sequestration reduces the global energy and exergy efficiencies of all power plants (up to 10%). However, the Integrated Gasification Combined Cycle (IGCC) is a promising technology utilizing coal for generating electrical energy and direct compression of CO2 (11–20 MPa). Similarly, integrating gasification with Solid Oxide Fuel Cells (SOFC), allows for the pre-combustion capture of CO2, with the advantage of lower initial investment costs. The oxy-fuel combustion (OXY) plant offers high energy and exergy efficiencies, but the exergoeconomic cost of CO2 is increased by 31 USD/t as compared to IGCC. The conventional thermoelectric (CT) plant exhibit disadvantages due to their simple power cycle and the elevated initial investment costs. This suggests that coal-gasification based plants are the best alternatives for CO2 production for EOR and co-generated electrical power.
... By optimizing the key parameters, the total efficiency and CO 2 sequestration ratio reaches to 69.1% and 87%, respectively. In other work, energy and exergy analyses are applied to a zero emission coal (ZEC) [37]. The maximum energy and exergy losses occurred in the steam turbine (35.2%) and solid oxide fuel cell (37%), respectively. ...
... The water flow of the steam turbine can be calculated as follows [37]: ...
A novel integrated multi-fuel multi-product electrical power plant with a net electrical power output of 5.97 × 10⁵ kW is developed and investigated by energy and exergy analyses. The electrical power plant including coal gasification, natural gas solid oxide fuel cell, cryogenic air separation unit, carbon dioxide transcritical and steam cycles, and liquefied natural gas regasification sub-systems. The potential of operating performance improvement by conducted energy and exergy analyses is assessed. Also, the thermal design and heat integration analyses are performed for studying the system sustainability and emphasizing on no requirement for external hot and cold utilities. Effects of the main design parameters such as fuel cell operating parameters, ambient temperature and liquefied natural gas thermodynamic specifications on the system operating performance are examined. The obtained results indicate that the overall energy and exergy efficiencies reach to a maximum value of about 56.4% and 57.9%, respectively; in the case of fuel utilization of solid oxide fuel cell is about 80.0%. Furthermore, increasing the ambient temperature and current density decrease the system operating performance. In contrast, the system performance increases with the liquefied natural gas vapor pressure.
... Membrane technologies require further development for improving the stability and increasing the capacity, while the cryogenic processes exhibit high energy costs (6-10 MJ kg À1 CO 2 ). Calcium looping uses the carbonation-calcination cycle to separate CO 2 : the CO 2 produced in methane reformers in presence of CaO is converted into CaCO 3 that is then sent into a calciner where CO 2 is recovered for sequestration [36]. This process is presently proposed in ZEC (zeroemission coal) systems: a high carbon sequestration ratio (87.4%) can be achieved by maintaining high total energy efficiency (46.8%) of the ZEC process. ...
... Its production in 2012 has been of about 197 Mt y À1 [35]. In our analysis, we consider two kinds of coals, DE1 and DE2, as representative of German hard coals: DE1 with high carbon content while DE2 with low carbon and high moisture content [36]. ...
... Exergy analysis, which combines thermodynamic first law and second law, pays more attention to quality of energy conversion than energy analysis. Exergy analysis has recently been proposed by many scientists and engineers as a technique for thermodynamic assessment in many fields, e.g., latent heat thermal energy storage for solar power generation [18], power and fresh water cogeneration systems that combine a GT (gas turbine) power plant [19], the zero emission coal (ZEC) system [20], etc. The main purpose of exergy analysis is to identify the causes, locations, and magnitudes of process inefficiencies, to better understand the limit of efficiency, and to provide a strong basis for the efficient design and management of complex processes [21]. ...
... Furthermore, the overall exergy efficiency expressions of the charging, discharging processes and thermodynamic cycle of the gas-hydrate cool storage system, i.e., Eqs. (20)e (22) are obtained. The effects of number of transfer units, the inlet temperature of the cooling medium and the inlet temperature of the heating medium on exergy efficiencies of the gas-hydrate cool storage system are emphatically analyzed. ...
Based on exergy analysis of charging and discharging processes in a gas-hydrate cool storage system, the formulas for exergy efficiency at the sensible heat transfer stage and the phase change stage corresponding to gas-hydrate charging and discharging processes are obtained. Furthermore, the overall exergy efficiency expressions of charging, discharging processes and the thermodynamic cycle of the gas-hydrate cool storage system are obtained. By using the above expressions, the effects of number of transfer units, the inlet temperatures of the cooling medium and the heating medium on exergy efficiencies of the gas-hydrate cool storage system are emphatically analyzed. The research results can be directly used to evaluate the performance of gas-hydrate cool storage systems and design more efficient energy systems by reducing the sources of inefficiency in gas-hydrate cool storage systems.
... Even with the development of renewable energy resources like solar power, wind turbines, biomass and waste utilization, coal use is expected to continue for power generation for a few decades more. With the development of carbon capture and sequestration (CCS), coal-fueled power generation will be acceptable (Fan, 2010;Yan et al., 2013). ...
Carbon capture and sequestration (CCS) technology is needed for fossil fuels (FFs) based power generation, in order to make it sustainable in future. Calcium looping gasification (CLG) is a novel energy technology that fulfils CCS, unlike IGCC post combustion, CO2 capture is not required, making it less energy demanding and saving capital cost, moreover CaO-CaCO3 is an exothermic reaction, hence the generated heat is adequate to perform CLG. In this study, both experiments and simulations of CLGCC, with CaO as a CO2 sorbent, were performed at varying gasifier temperatures and pressures using Aspen Plus, while results were compared to maximize the overall efficiency. Here, we propose calcium looping gasification with combined cycle (CLGCC) simulation using Aspen Plus with CaO as CO2 sorbent, and results are validated against experimental data in terms of gasifier temperature and pressure. The IGCC without CCS system along with CLGCC are simulated simultaneously for comparison. The CLGCC system achieved an efficiency as high as 54.93%, while IGCC's system without CCS efficiency was calculated as 53.22% and corresponding exergetic efficiencies are 51.67% and 50.03%, respectively. The carbon capture efficiency of CLGCC is 83.5 % with 94.4 vol% of CO2 achieved after steam condensation for carbon capture system. On the basis of results, we demonstrate the applicability of CLGCC against the conventional power plants and it has a great window for adaptation in the future in advanced power plants.
... Chemical exergy is defined as the maximum obtainable work from an out of equilibrium state system. Exergy analysis has been applied in many evaluation studies regarding energy and thermodynamic performances of different chemical processes (Ahmadi, Rosen, & Dincer, 2012;Atılgan, Turan, Altuntaş, Aydın, & Synylo, 2013;Bao & Zhao, 2012;Dimopoulos, Stefanatos, & Kakalis, 2013;Hackl & Harvey, 2013;Quijera, Garc ıa, Alriols, & Labidi, 2013;Simpson & Edwards, 2013;Singh & Kaushik, 2013;Takla, Kamfjord, Tveit, & Kjelstrup, 2013;Utlu & Kincay, 2013;Voldsund, Ertesvåg, He, & Kjelstrup, 2013;Yan, He, Pei, Li, & Wang, 2013;Zhu, Deng, & Qu, 2013). Standard molar chemical exergy of a compound can be evaluated using equation (1), considering appropriate Gibbs formation energy function and exergy values of the constituent chemical elements of the compound: ...
Prediction of standard molar chemical exergy value for organic compounds is investigated using a quantitative structure-property relationship (QSPR) model combined with adaptive neuro-fuzzy inference system (ANFIS) strategy. Particle swarm optimization (PSO) method is also implemented to determine the optimal ANFIS structure. The proposed model uses three constitutional descriptors in model development’s procedure. The QSPR-ANFIS model represents a great performance in prediction of the standard molar chemical exergy values with 0.9999, 44548, and 1.49 values for R², RMSE, and %AARD, respectively.
... The specific chemical exergy of a solid fuel can be calculated with Eq. (12) [41,42]. ...
Two power generation systems composed of the chemical looping air separation (CLAS) technology and the integrated gasification combined cycle (IGCC) with CO2 capture are conceptually presented, thermodynamically analyzed and compared. Different CO2 capture approaches including the pre-combustion with polyethylene glycol dimethyl ether (PGDE) and the post-combustion with monoethanolamine (MEA) are respectively adopted in the two systems. Blocked energy losses and exergy destructions are calculated to investigate the overall efficiencies of the systems. Sensitivity analyses are carried out to investigate the effects of different operating parameters including the oxygen to coal mass ratio (ROC), the steam to coal mass ratio (RSC) and the temperature of the reduction reactor (TRR) on the energy efficiencies (ηen) and exergy efficiencies (ηex) of the two systems. The maximum energy losses and exergy destructions are found in the CO2 capture units. ROC of 0.75, RSC of 0.06 and TRR of 850 °C are recommended as the optimum operation parameters based on the sensitivity analyses. With the optimized parameters, the energy and exergy efficiencies are predicted to be 37.36% and 34.50% for the system with post-combustion CO2 capture, while 38.67% and 36.19% for the system with pre-combustion CO2 capture.
... In order to accomplish objectives above, the Sankey diagram from 2001 to June 2017 searched in Web of Science, this work obtained 124 articles, of which over a half were energy and environment-related documents and mainly were published after 2010 (Cullen and Allwood 2010a, b;Paszota 2011;Caliskan et al. 2011;Nakamura et al. 2011;Bode et al. 2011;Giuffrida et al. 2011;Qiu and Davies 2011;Perez-Lombard et al. 2011;Skelton et al. 2011a, b;Kong and Liu 2012;Paszota 2012a, b;Ma et al. 2012a, b;Bode et al. 2012;Cullen et al. 2012;Paszota 2013;Hu et al. 2013;Nakajima et al. 2013;Curmi et al. 2013a, b;Yan et al. 2013;Kalt 2015;Huang et al. 2015;Guyonnet et al. 2015;Cullen and Allwood 2010a, b). Technical factors were taken into consideration when accelerating efficiency reflected by the 2005 Sankey map of energy flow in the world following the four processing steps, i.e., primary energy, conversion devices, passive systems and services (Ma et al. 2012a, b). ...
China has promised to optimize its energy structure and reduce its CO2 emission in the 13th Five-Year Plan. To track the energy structure, the conversions, efficiencies, end consumptions of total energy and coal and the whole CO2 emission status, the energy flow, coal flow and CO2 flow in 2015 were, respectively, drawn at the national level based on Sankey diagrams. Besides, each provincial fossil fuel structure, CO2 structure and CO2 intensity were calculated and plotted. It is mainly found that China’s energy structure consisted of 69.2% of coal, 19.9% of oil, 6.3% of natural gas and 4.7% of non-fossil energy, where 45.5% of energy was consumed by industry and 23.9% by losses and statistical difference; coal was distributed to industry (55.6%), etc., with a utilization rate of 70.1%; and CO2 were derived from coal (84.7%), oil (11.1%) and natural gas (4.2%), of which 39.0% was released through the process of thermal power generation and 19.4% by industry. The structures of fossil fuels and their CO2 emissions together with the evolution of CO2 intensity at the provincial level and the regional level were also given. Besides, two pieces of policy implications were proposed to provide the government with reference.
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... The ZE concept has led to zero energy buildings (ZEB), zero emission vehicles (ZEV), zero emission coal (ZEC), and zero emission power (ZEP) plants. The ZEV [140,141], ZEB [142,143], ZEC [144], ZEP [145] and AZEP [146] strategies can reduce 30%, 40%, 50%, 80% and 95% GHG emissions. ...
Abstract Fossil fuel consumption, luxurious lifestyles, population and economic growths are drivers of climate change. Rampant rise in Greenhouse Gases (GHG) emissions drives the big wheel of climate change which affects human societies, animal habitats and woodlands by flash floods, glacial melts, acidic rains, droughts, famines, wildfires, epidemics, heat and cold waves. South Asia is one of the most severely affected regions on the planet due to its demographics. The per capita impact of climate change on the millions of Pakistanis is very high compared to their diminutive per capita share of global GHG emissions. Environmental issues of South Asian Association for Regional Cooperation (SAARC) countries include deforestation, air pollution, desertification, glacial melts, sea level rise, water contamination and loss of biodiversity. Pakistan is among the top ten countries worst hit by climate change, where native populations of lions, leopards, dolphins, tortoise and vultures face extinction threat. Acacia and rosewood tree forests in Sindh, Punjab and Pak-Afghan precincts have already dried by dieback disease during 1998–2005. Hundreds of people succumb to death annually by heat waves in South during summer and cold waves in North during winter. Climate change is a global phenomenon; nevertheless, higher GHG emissions first affect local and regional territories and later impact worldwide. Pakistan's CO2 emissions are greater than least developed SAARC countries but much lower than the nearby Himalayan slope countries. This paper reports impact of CO2 emissions on society, forests, crops and wildlife in Pakistan recounting adaptation and mitigation strategies in SAARC countries. We present simulation results for a future super smart grid connecting Central Asian States (CAS) to SAARC countries for bilateral electricity trade, progress in carbon capture and storage technologies in SAARC countries, and original research on utilizing CO2 (R744) for water heating in extremely cold regions.
... To avoid this issue, only H 2 was used as the reducer in this work [18]. Actually, for many solid carbonaceous fuel based clean power generation systems [19,20], the hydrogen mole fraction in the syngas entering the chemical looping section is usually very high. For example, the hydrogen mole fraction in the syngas generated from the coal/biomass steam gasification with calcium looping [21] or from the hydrogasification with or without further reformation [22] is usually very high. ...
Iron-based oxygen carrier (IBOC) is widely used in chemical looping processes (CLP) due to many advantages, and the low-cost ones are prospective for industry application. However, research on the redox properties of the low-cost IBOCs during CLP is still rarely seen, compared to those on the well prepared ones. In this work, an experiment is implemented with a thermo-gravimetric analyzer (TGA) to investigate the reactivity of a low-cost IBOC through several periods of the “three-reactor” loop including hydrogen reduction, steam oxidation, and air combustion. The isothermal approach is used to analyze the TGA data obtained at different temperatures. An X-ray diffractometer (XRD) is used to detect the final forms of iron. It is found that the main forms of IBOC presenting in the “three-reactor” redox cycles are Fe2O3, Fe3O4 and Fe. The Avrami-Erofeev equations are found to be the most probable reaction mechanisms for the hydrogen reduction and steam oxidation processes. The corresponding reaction kinetic constants for each cycle are calculated. The IBOC reactivity increases with temperature but decreases with the increasing circulation number, and becomes relatively stable within 7 cycles. The final form of iron in IBOC is mainly Fe2O3, along with a little Fe3O4.
... The above revived the interest for alternative routes for synthetic natural gas production. Due to its obvious advantages [3][4][5], there is a renewed interest on coal hydrogasification (CHG) [6,7]. At the United States, the existence of huge domestic coal reserves, estimated to last for more than two centuries [7,8], boosted considerable interest in the coal to SNG process. ...
Potassium catalyzed isothermal coal hydrogasification was investigated, as an alternative route for synthetic natural gas production. Potassium chemisorption occurred on oxygen sites in the coal structure and was strongly affected by the solution pH and followed the Cation Exchange Capability (CEC) which is also pH-dependent. A quadratic function described the relation between the solution pH and the fraction of the chemisorbed potassium, while; the cumulative distribution function of two Weibull probability density functions correlated the solution pH with the CEC that was linearly correlated with the fraction of the chemisorbed potassium. Coal hydrogasification is strongly affected by the increased alkalinity of the impregnating solution and increased methane yields were obtained while carbon conversion was slightly affected. This was attributed to the formation of profuse K
... To better understand the exergy destruction in the MC processes presented, exergetic analysis of each device within the three processes is conducted, and the results are presented in Table 5. Also, the exergy balance of the CLC-MC process and its corresponding Grassmann diagram [47,48] is shown in Fig. 5. The inlet exergy, outlet exergy and destroyed exergy of each device in the process can be seen in this figure. ...
This paper proposes a novel hydrogen production process by Methane Cracking thermally coupled with Chemical Looping Combustion (MC–CLC) which provides an advantage of inherent capture of CO2. The energy utilisation performance of the MC–CLC process is compared with that of conventional Methane Cracking with combusting CH4 (MC-CH4) and Methane Cracking with combusting H2 (MC-H2) using exergy analysis, with focus on exergy flows, destruction and efficiency. The three MC processes are simulated using Aspen Plus software with detailed heat integration. In these processes, the majority of the exergy destruction occurs in the combustors or CLC mostly due to the high irreversibility of combustion. The CO2 capture unit has the lowest exergy efficiency in the MC-CH4 process, leading to a lower overall exergy efficiency of the process. The combustor in the MC-H2 process has a much higher energy efficiency than that in the MC-CH4 process or the CLC in the MC–CLC process. Although the use of H2 as fuel decreases the H2 production rate, the MC-H2 process provides the advantage of an absence of CO2 generation, and stores more chemical exergy in the solid carbon which can be utilised appropriately. The MC–CLC process obtains the highest exergy efficiency among the three models and this is primarily due to the absence of a CO2 capture penalty and the CLC’s higher fuel utilization efficiency than the conventional combustion process.
... One of the SLT-based analysis techniques that has attracted the attention of many researchers in various fields is the method of exergy analysis. Exergy is a very useful method for the evaluation of the thermodynamic and energy performance of various chemical processes such as study of auto-cascade Rankine cycles [1], evaluation of polygeneration energy systems [2], environmental impact assessment of turboprop engines [3], investigation of steam methane pre-reforming systems [4], analysis of refrigeration shaft power in industrial clusters [5], analysis of thermosolar and heat pumps [6], utilizing of the criteria for decision making in energy systems [7], improving the performance of natural gas fired combined cycle power plants by coupling Kalina cycles [8], assessment of silicon production processes [9], modifying pulp and paper mills [10], analysis of oil and gas processing platforms [11], analysis of coal systems [12], and bottoming rankine cycle for engine exhaust heat recovery [13]. In chemical processes, the components of process streams are changed as a result of different unit operations which occur in different unit operations such as distillation towers, reactors, etc. ...
Exergy analysis can be used to achieve the optimal conditions at which a system or a process can precede; as close as possible to the environmental conditions (with minimum loss of energy). In order to do such an analysis, the chemical exergy of each compound should be available. Since there are a limited number of organic compounds for which the chemical exergy values have been reported in the literature, it would be of great interest to have a reliable method for the estimation of this parameter. In this communication, a group contribution method is proposed for the prediction of the chemical exergy of pure organic compounds at the standard condition of 1 atm and 298.15 K for pressure and temperature respectively. In order to develop and validate the model, and also to evaluate its predictive capability, a dataset of 133 pure organic compounds composed of carbon, hydrogen, nitrogen, oxygen, and sulfur was used. The model proposed has a low average absolute relative deviation of 1.6% from literature data and indicates the reliability of the method. It can be used as a predictive tool for the estimation of the standard chemical exergy of pure organic compounds.
Sorption-enhanced reaction process (SEPR) can produce high yield of hydrogen with in-situ CO2 removal using CaO. A key requirement for the process is the integration of effective Ca-based sorbents into catalytic schemes. In this work, the research progress of Ca-based CO2 sorbents in SEPR is summarized. The positive effects by Ca-based sorbents are analyzed. The methods to improve the reactivity of Ca-based sorbents are discussed. A good prospect of compound materials of catalysts/sorbents in SERP is pointed out, for which the relationship between the performance and structure or reaction condition should be further studied. The optimization of process parameters is critically reviewed to provide recommendations for industrial operation. The comprehensiveness of this work extends to the discussion about the applications of Density Functional Theory study in SERP. Process economics requires the integrated H2 production with by-product conversion, renewable resources utilization, waste recycling and heat coupling optimization for the future research.
As calcium carbide (CaC2) production is an energy-intensive industry, a novel low rank coal to CaC2 (LRCtCC) process has been developed. This study is aimed to evaluate the techno-economic performance of the LRCtCC process. A model integrating particle swarm optimization and nonlinear programming (PSO-NLP) is developed to predict the behavior of coal pyrolysis. The techno-economic assessment of the LRCtCC process is analyzed. Results show that the power consumption of electric arc furnace is expected to drop to 2845 from 3169 KW·h/t with the hot material (HM) temperature increasing from 25 to 850 °C. The effect of increasing HM temperature is greater than that of adjusting the composition of fuel on system efficiency, cost of CaC2, and internal rate of return. In addition, the effects of typical economic factors on net present value (NPV) of the LRCtCC process are compared. Results show that variations of CaC2 price and power consumption pose a remarkable impact on NPV. The findings of this study suggest that the LRCtCC process would be an attractive method for the improvement of CaC2 production.
In order to improve the thermal efficiency of coke-oven gas power generation, this work establishes electrochemical and thermodynamic models for a novel process of coke-oven gas fueled solid oxide fuel cell integrated with its anode off-gas recirculation and chemical looping combustion. It begins with a traditional process with all anode off-gas combusted with air in an after burner for heat recovery, which suffers from higher steam consumption, lower power generation, and higher CO 2 emissions. Key operating parameters of the steam/COG ratio of steam methane reforming, fuel utilization factor and recycle ratio of solid oxide fuel cell, as well as oxygen carrier and air inputs of chemical looping combustion are thoroughly analyzed and optimized for power generation of the proposed process. The net electricity generation for the novel and traditional processes are 315.8 and 290.7 MW per 500.3 MW of coke-oven gas consumption, respectively. Moreover, the exergy efficiency is improved from 56.4% to 63.1% and about zero direct CO 2 emissions is achieved in the novel process.
The augmenting necessity of energy saving and environmental protection has led to the increasing technical requirements about on-line monitoring of key parameters and elements in coal. In this study, terahertz spectroscopy combined with PCA (principal components analysis) was employed to analyze nine kinds of coal materials. Due to the strong absorption of the organics with the relatively high C/H ratio, such as aromatic compounds, coals with lower hydrogen content show higher absorption effects in terahertz range. Based on PC1 score calculated by PCA, the anthracite and bituminous coal can be clearly classified, and the clean as well as meagre coals were also distinguished by opposite trends. All the critical points in PCA system are in agreement with those (volatile matter and ash, respectively) classified in international standard of coal classification. In addition, significant elements, including carbon, hydrogen, nitrogen and sulfur, can be directly characterized using PC1 score with linear and non-linear models. This research indicates that the terahertz spectral analysis of key parameters and elements of coal is a promising tool for improving the detection method and advancing the technical innovation in coal processing industry.
The share of the fossil-fuel power systems in the European Union energy portfolio has recently increased, even with new environmental incentives aimed at the reduction of CO2 emissions from the power sector. Implementation of carbon capture technologies has been identified as a critical step towards reduction of CO2 emissions. As the power plants usually operate with changing loads to meet the electricity demand, it is important to evaluate the process performance under different operating loads. Therefore, this study provides a methodology for modelling of part-load operation of coal-fired power plants in a process simulator, such as Aspen Plus. The part-load power plant model is validated using data from the literature, and it was demonstrated that a maximum discrepancy of 5% was obtained for the live steam pressure prediction at 40% load, while the discrepancy for all other compared parameters at other loads did not exceed 3%. Furthermore, the part-load model is used to evaluate the performance of the retrofitted power plant with the CO2 capture plant at different loads, with monoethanolamine as a solvent, revealing that the net efficiency varied between 28.2%HHV and 21.1%HHV. Moreover, the analysis showed that neglecting the off-design conditions due to steam extraction would result in overestimating the net thermal efficiency by up to 1.3%HHV points at 100% load operation and steam extracted at 11.9 bar.
Since solid oxide fuel cells (SOFC) produce electricity with high energy conversion efficiency, and chemical looping combustion (CLC) is a process for fuel conversion with inherent CO2 separation, a novel combined cycle integrating coal gasification, solid oxide fuel cell, and chemical looping combustion was configured and analyzed. A thermodynamic analysis based on energy and exergy was performed to investigate the performance of the integrated system and its sensitivity to major operating parameters. The major findings include that (1) the plant net power efficiency reaches 49.8% with ∼100% CO2 capture for SOFC at 900 °C, 15 bar, fuel utilization factor = 0.85, fuel reactor temperature = 900 °C and air reactor temperature = 950 °C, using NiO as the oxygen carrier in the CLC unit. (2) In this parameter neighborhood the fuel utilization factor, the SOFC temperature and SOFC pressure have small effects on the plant net power efficiency because changes in pressure and temperature that increase the power generation by the SOFC tend to decrease the power generation by the gas turbine and steam cycle, and v.v.; an advantage of this system characteristic is that it maintains a nearly constant power output even when the temperature and pressure vary. (3) The largest exergy loss is in the gasification process, followed by those in the CO2 compression and the SOFC. (4) Compared with the CLC Fe2O3 and CuO oxygen carriers, NiO results in higher plant net power efficiency. To the authors’ knowledge, this is the first analysis synergistically combining in a hybrid system: (1) coal gasification, (2) SOFC, and (3) CLC, which results in a system of high energy efficiency with full CO2 capture, and advances the progress towards the world’s critically needed approach to “clean coal”.
Energy and exergy analyses were studied for IGCC power plant with CO2 capture using hot potassium carbonate solvent. The study focused on the combined impact of the CO conversion ratio in the Water Gas Shift (WGS) unit and CO2 recovery rate on component exergy destruction, plant efficiency and energy penalty for CO2 capture. A theoretical limit for the minimal efficiency penalty for CO2 capture was also provided. It was found that total plant exergy destruction increased almost linearly with CO2 recovery rate and CO conversion ratio at low CO conversion ratios. But the exergy destruction from the WGS unit and the whole plant increased sharply when the CO conversion ratio was higher than 98.5% at design WGS conditions, leading to a significant decrease in plant efficiency and increase in efficiency penalty for CO2 capture. When carbon capture rate was over around 70%, via a combination of around 100% CO2 recovery rate and lower CO conversion ratios, the efficiency penalty for CO2 capture was reduced. The minimal efficiency penalty for CO2 capture was estimated to be around 5.0% at design conditions in an IGCC plant with 90% carbon capture. Unlike the traditional aim of 100% CO conversion, it was recommended that extremely high CO conversion ratios should not be considered in order to decrease the energy penalty for CO2 capture and increase plant efficiency.
In this paper a novel integrated plant, designed for the co-production of electricity and synthetic natural gas (SNG), has been proposed as suitable strategy for renewable energy storage and CO2 emission control.
The hydrogen generation by electrolysis and its use for SNG production is the approach chosen for the energy storage (chemical storage), while the CO2 control is performed by using (or recycling) the CO2, concentrated in the anode exhausts of a molten carbonate fuel cell, in the chemical processes of the plant (coal hydrogasification and SNG production processes).
The proposed HyCRESt plant, acronym of Hydrogasification of Coal for Renewable Energy Storage, consists of three main sections: i) the hydrogasification island, in which the coal is gasified in hydrogen environment to a methane rich fuel gas stream (syngas); ii) the power island, in which the syngas is used as fuel for the electric power generation by using a molten carbonate fuel cell (MCFC) power unit; iii) the SNG island, in which the syngas is converted into a synthetic natural gas stream.
The plant performance, in terms of co-production efficiency, CO2 avoided and fuel saving, has been evaluated by means of thermochemical and electrochemical models able to predict energy and mass balances.
Results have pointed out that the co-production of electric and chemical powers allows to achieve system efficiencies greater than 55% with fuel saving values higher than 6% and CO2 avoided ranging from 20% (only electric power generation) to 120% (only SNG generation).
Hydropyrolysis of coal is considered to be a third coal conversion technology between the coal liquification and gasification technologies. It is also the primary process for coal hydrogasification (CHG). However, the detailed kinetic characteristics of coal hydropyrolysis (CHP) are still rarely studied, which is adverse to the further development of the CHP and CHG technologies. In this work, the hydropyrolysis kinetics of a lignite coal is studied in a pressurized thermogravimetric analyzer (P-TGA). The non-isothermal thermogravimetric method is used and the effect of pressure on the pyrolysis kinetics of the lignite coal is detected. Finally, some useful results are found from the analyses for the lignite hydropyrolysis under P-TGA. With the increment of the pyrolysis pressure, the initial pyrolysis temperature increases when the pressure is higher than 1 MPa; the temperature span of the pyrolysis process shrinks; the weight loss peak value position of the derivative thermogravimetric (DTG) curve shifts rightwards when the pressure is lower than 1 MPa, while it shifts leftwards when the pyrolysis pressure is higher than 1 MPa; the reaction process will be restrained when the pressure is lower than 2 MPa. In addition, the kinetic triplets including the pre-exponential factor, the activation energy and the kinetic mechanism function are defined for the hydropyrolysis process under different pressures. Copyright
Solid oxide fuel cell (SOFC) is adopted in the zero emission (ZEC) coal system to generate environment-friendly electrical energy at high efficiency. A model of solid oxide fuel cell (SOFC) using ASPEN™ PLUS with the assistance of FORTRAN based on the Siemens Power Generation Inc. (SPGI) 100 kW combined heat and power (CHP) SOFC was set up. The model was validated against data available in the literatures. Then, the model was used to do some sensitivity analyses about the influences of different parameters including the fuel utilization factor Kf, the current density J and the steam to carbon ratio Rsc on SOFC operation characteristics. Keeping the cell power constant, the cell efficiency was found reaching its peak value when Kf is about 0.8. When the other parameters were kept invariable, the amount of fuel exhausted increases with J increasing while the cell voltage and efficiency decrease; the cell power reaches its peak value when J is about 3500 mA. The exhaust fuel recirculation flow rate, the pre-reformer inlet gas temperature and the methane reforming ratio all increase with Rsc increasing.
Coal offers an abundant widely spread fossil energy resource. It is available at a stable price from many international suppliers and it will continue to play a significant role in new generating capacity, if security and diversity of supply remain fundamental. In this paper we point out the state of the art in the field of " Clean Coal Technologies " evidencing the perspectives of improvement and the critical elements. Both the emission control of NO x , SO x and Particle Matter and the advanced coal conversion pathways like USC, PFBC and IGCC are reviewed and analysed. At the end some elements concerning the perspectives of CO 2 emission control strategies are outlined.
The operation and performance of a SOFC (solid oxide fuel cell) stack on biomass syn-gas from a biomass gasification CHP (combined heat and power) plant is investigated. The objective of this work is to develop a model of a biomass-SOFC system capable of predicting performance under diverse operating conditions. The tubular SOFC technology is selected. The SOFC stack model, equilibrium type based on Gibbs free energy minimisation, is developed using Aspen Plus. The model performs heat and mass balances and considers ohmic, activation and concentration losses for the voltage calculation. The model is validated against data available in the literature for operation on natural gas. Operating parameters are varied; parameters such as fuel utilisation factor (Uf), current density (j) and STCR (steam to carbon ratio) have significant influence. The results indicate that there must be a trade-off between voltage, efficiency and power with respect to j and the stack should be operated at low STCR and high Uf. Operation on biomass syn-gas is compared to natural gas operation and as expected performance degrades. The realistic design operating conditions with regard to performance are identified. High efficiencies are predicted making these systems very attractive.
Coal offers an abundant widely spread fossil energy resource. It is available at a quite-stable price from many international suppliers and it will continue to play a significant role in new generating capacity, if security and diversity of supply remain fundamental. In this paper we point out the state of the art in the field of “clean coal technologies” evidencing the perspectives of improvement and the critical elements. Both the emission control of NOx, SOx, and particle matter and the advanced coal conversion pathways like ultra-supercritical (USC), pressurized fluidized bed combustion (PFBC), and integrated gasification combined cycle (IGCC) are reviewed and analyzed. At the end some elements concerning the perspectives of CO2 emission control strategies are outlined.
This book provides a thorough development of the second law of thermodynamics (featuring the entropy-production concept), an up-to-date discussion of availability analysis (including an introduction to chemical availability), and a sound description of the application areas. Topics covered include control volume energy analysis, vapor power systems, gas power systems, thermodynamic relations for simple compressible substances, nonreacting ideal gas mixtures and psycrometrics, reacting mixtures and combustion, and chemical and phase equilibrium.
This book is a unique, multidisciplinary effort to apply rigorous thermodynamics fundamentals, a disciplined scholarly approach, to problems of sustainability, energy, and resource uses. Applying thermodynamic thinking to problems of sustainable behavior is a significant advantage in bringing order to ill-defined questions with a great variety of proposed solutions, some of which are more destructive than the original problem. The articles are pitched at a level accessible to advanced undergraduates and graduate students in courses on sustainability, sustainable engineering, industrial ecology, sustainable manufacturing, and green engineering. The timeliness of the topic, and the urgent need for solutions make this book attractive to general readers and specialist researchers as well. Top international figures from many disciplines, including engineers, ecologists, economists, physicists, chemists, policy experts and industrial ecologists among others make up the impressive list of contributors.
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.
An exergy analysis of methanol autothermal generating hydrogen system for PEMFC is presented. The process combines a catalytic combustion heat exchanger (CCHE), using partial off-gases containing hydrogen as feedstock, with an auto-thermal reformer (ATR), two water gas shift (WGS) reactors and four preferential oxidation (PROX) reactors. Energy and exergy of system were calculated and analyzed. The results demonstrated that inner exergy losses resulted from the irreversible heat transfer and reaction were the dominant factors. The most important destruction of exergy within the system was found to occur in the reformer and the catalytic combustion heat exchanger. Their ratios of exergy loss accounted for 25.03% and 24.95%, respectively, of the whole system. Based on results of thermodynamic and exergetic analysis, the reformer was optimized. The optimal W/M (molar water to methanol) is around 1.5–2.0 and A/M (molar air to methanol) is around 1.5. Certain recommendations were posed. The conclusions could help to optimize methanol autothermal generating hydrogen system for PEMFC.
Before the commercialization of zero emission coal (ZEC), some technical hurdles must be settled and the performance of the whole system needs to be studied. The main technical hurdles of ZEC system are analyzed and some solutions are presented in this paper. A detailed ZEC system is setup and its characteristics are studied. High temperature solid oxide fuel cell (SOFC) is used to produce electricity and served as the heat source for the decarbonater. ZnO and NaHCO3 are proposed to deeply eliminate H2S and HCl. H2 recycle ratio should be kept at 0.75 for the high conversion ratio of carbon in the gasifier and the high system efficiency. Calcium to carbon mole ratio (CTCR) should be kept around 0.6 to reach high CO2 sequestration rate and acceptable economic penalty. Fuel utilization factor (Uf) of SOFC should be kept around 0.55 so as to supply enough heat to the decarbonater, and steam to carbon ratio (STCR) for the reformers in the system should be kept around 2.0. With these optimized parameters, the total efficiency of the system of 69.1% and the CO2 sequestration ratio of 87% can be reached.
This paper examines an integrated gasification and solid oxide fuel cell (SOFC) system with a gas turbine and steam cycle that uses heat recovery of the gas turbine exhaust. Energy and exergy analyses are performed with two different types of coal. For the two different cases, the energy efficiency of the overall system is 38.1% and 36.7%, while the exergy efficiency is 27% and 23.2%, respectively. The effects of changing the reference temperature on the exergy destruction and exergy efficiency of different components are also reported. A parametric study on the effects of changing the pressure ratio on the component performance is presented.
In spite of the rapid development and introduction of renewable and alternative resources, coal still continues to be the most significant fuel to meet the global electricity demand. Emission from existing coal based power plants is, besides others, identified as one of the major sources of anthropogenic carbon dioxide, responsible for climate change. Advanced coal based power plants with acceptable efficiency and low carbon dioxide emission are therefore in sharp focus for current development. The integrated gasification combined cycle (IGCC) power plant with pre-combustion carbon capture is a prospective technology option for this purpose. However, such plants currently have limitations regarding fuel flexibility, performance, etc. In an EU initiative (H2-IGCC project), possible improvements of such plants are being explored. These involve using premix combustion of undiluted hydrogen-rich syngas and improved fuel flexibility without adversely affecting the availability and reliability of the plant and also making minor modifications to existing gas turbines for this purpose. In this paper, detailed thermodynamic models and assumptions of the preliminary configuration of such a plant are reported, with performance analysis based on available practical data and information. The overall efficiency of the IGCC power plant with carbon capture is estimated to 36.3% (LHV). The results confirm the fact that a significant penalty on efficiency is associated with the capture of CO2. This penalty is 21.6% relative to the IGCC without CO2 capture, i.e. 10.0% points. Estimated significant performance indicators as well as comparisons with alternative schemes have been presented. Some possible future developments based on these results and the overall objective of the project are also discussed.
The design of a fuel cell system involves both optimization of the fuel cell stack and the balance of plant with respect to efficiency and economics. Many commercially available process simulators, such as AspenPlusTM, can facilitate the analysis of a solid oxide fuel cell (SOFC) system. A SOFC system may include fuel pre-processors, heat exchangers, turbines, bottoming cycles, etc., all of which can be very effectively modelled in process simulation software. The current challenge is that AspenPlusTM or any other commercial process simulators do not have a model of a basic SOFC stack. Therefore, to enable performing SOFC system simulation using one of these simulators, one must construct an SOFC stack model that can be implemented in them. The most common approach is to develop a complete SOFC model in a programming language, such as Fortran, Visual Basic or C++, first and then link it to a commercial process simulator as a user defined model or subroutine. This paper introduces a different approach to the development of a SOFC model by utilizing existing AspenPlusTM functions and existing unit operation modules. The developed “AspenPlusTM SOFC” model is able to provide detailed thermodynamic and parametric analyses of the SOFC operation and can easily be extended to study the entire power plant consisting of the SOFC and the balance of plant without the requirement for linking with other software. Validation of this model is performed by comparison to a Siemens-Westinghouse 100 kW class tubular SOFC stack. Sensitivity analyses of major operating parameters, such as utilization factor (Uf), current density (Ic) and steam–carbon ratio (S/C), were performed using the developed model, and the results are discussed in this paper.
A concept of zero-emission coal technology, proposed by ZECA Corporation, is presented and discussed. The process can produce electricity at 60–70% efficiency with zero emission to the atmosphere. The carbon dioxide is produced as concentrated, clean stream, which is easy to sequestrate. The process uses CaO/CaCO3 reaction to enhance hydrogen production and to separate carbon dioxide. Hydrogen feeds a stack of solid oxide fuel cells (SOFCs), which produce electricity. High-temperature byproduct heat from the SOFC drives the calcination reaction, which restores CaO. Unfortunately, the possible realization of the process may encounter various technical difficulties mainly connected with requirements for the SOFC (very high operating temperature, high sulfur tolerance, integrated heat exchanger) and CaO/CaCO3 process (the decrease of the performance with increasing number of cycles and problematic heat transport into calcination vessel).
Zero Emission Coal (ZEC) power generation, via Hydrogen Gasification and Solid Oxide Fuel Cell (SOFC), is a newly developed technology that could meet the future energy demand through the continuous utilization of abundant fossil fuel resources while overcoming potential environmental hurdles, especially greenhouse gas CO2 emission. In this paper, chemical kinetics-based analysis for future ZEC system was conducted using the conceptual design operation conditions. The major finding from this research indicated that under a preferred condition, the major reactions occurred in ZEC system can perform with maintaining the high equilibrium rate of conversion. In the light of higher fractions converted by the hydro-gasification process, the reaction temperature in the gasification vessel should be controlled lower than 1100K and the pressure a little higher than 60atm in the practical operation. The temperatures for Reformers A and B should be kept under 1100K and the pressure in Reformer B should be lower than that in Reformer A, which is almost the same as the SOFC in order to drive the CO2 absorption reaction. The reaction temperature should be kept lower than 1500K and the pressure higher than 3atm, preferably higher than 10atm for higher power generation by the electrochemical process in the fuel cell. These findings will provide necessary reference data for the future designs, guide practical operations, and build a solid foundation for further research on Zero Emission Coal power generation systems.
Coal use for electricity generation will continue growing in importance. In the present work the optimization of a high efficiency and zero emissions coal-fired plant, which produces both hydrogen and electricity, has been developed. The majority of this paper concerns an integration of gasification unit, which is characterized by coal hydrogasification and carbon dioxide (CO2) separation, with a power island, where a high-hydrogen content syngas is burnt with pure oxygen stream. Another issue is the high temperature CO2 desorption. Because of the elevated temperature heat supply, the regeneration process affects the overall performance of ZECOMIX plant. An advanced steam cycle characterized by a medium pressure steam compressor and expander has been considered for power generation. A preliminary study of different components leads to analyze possible routes for optimization of the whole plant. The plant equipped with a CO2 capture unit could reach efficiency close to 50%. The simulations of a thermodynamic model were carried out using the software ChemCAD.This study is a part of a larger research project, named ZECOMIX, led by ENEA (Italian Research Agency for New technologies, Energy and Environment), other partners being ANSALDO and different Italian Universities. It is aimed at analyzing an integrated hydrogen and power production plant.
We present an update on the development of technologies required for the Zero Emission Carbon (ZEC) concept being pursued by ZECA Corporation. The concept has a highly integrated design involving hydrogasification, a calcium oxide driven reforming step that includes simultaneous C02 separation, coal compatible fuel cells for electricity production and heat recovery, and a closed loop gas system in which coal contaminants are removed either as liquids or solids. The process does not involve any combustion and as such has neither smokestack nor air emissions. An independent assessment of the concept by Nexant, a Bcchtel affiliated company, suggests a net efficiency of approximately 70% for conversion of the higher heat value fuel energy into electrical output. This is even after the penalties of carbon dioxide separation and pressurization to 1000 psi are taken into account. For carbon dioxide sequestration a variety of options are being considered, which include enhanced oil recovery in the near-term and mineral carbonation as a long-term approach. We report on our early results in the development of sulfur tolerant anode materials for solid oxide fuel cells; a critical analysis of the calcium oxide - calcium carbonate cycle; trace element removal; and the recent results of hydrogasification tests.
In this paper, the integration of a solid oxide fuel cell operating at a very high temperature (900–1000 °C, 55–60% efficiency) in a near-zero emission power cycle is presented. A more efficient and powerful hybrid near-zero emission CO2/O2 cycle is obtained with a CO2 release as small as 6 g CO2/kW he. Based on a trade-off analysis, the net efficiency is around 47–48%, similar to a current one-pressure level natural gas fired combined cycle, and the power output (940 kWe) is increased by 66% compared to the so-called E-MATIANT cycle but currently at a much higher cost than those of other known zero-emission power cycles.
The Zero Emission Coal Alliance (ZECA) is developing an integrated zero emission process that will generate clean energy carriers (electricity or hydrogen) from coal. The process exothermically gasifies coal using hydrogen to produce a methane rich intermediate state. The methane is subsequently reformed using water and a CaO based sorbent. The sorbent supplies the energy needed to drive the reforming reaction and simultaneously removes the generated CO 2 by producing CaCO 3 The resulting hydrogen product stream is split, approximately 1/2 going to gasify the next unit of coal, and the other half being the product. This product stream could then be split a second time, part being cleaned up with a high temperature hydrogen separation membrane to produce pure hydrogen, and the remainder used to generate electricity via a solid oxide fuel cell (SOFC). The inevitable high temperature waste heat produced by the SOFC would in turn be used regenerate the CaO by calcining the CaCO 3 product of the reforming stage thereby generating a pure stream of CO 2 . The CO 2 will be dealt with a mineral sequestration process discussed in other papers presented at this conference. The SOFC has the added advantage of doubling as an oxygen separation membrane, thereby keeping its exhaust stream, which is predominantly steam, free of any air. This exhaust stream is largely recycled back to the reforming stage to generate more hydrogen, with a slipstream being extracted and condensed. The slipstream carries with it the other initial contaminants present in the starting coal. Overall the process is effectively closed loop with zero gaseous emissions to the atmosphere. The process also achieves very high conversion efficiency from coal energy to electrical energy (~ 70 %) and naturally generates a pure stream of CO 2 ready for disposal via the mineral sequestration process.
A new approach to zero emission coal-based power generation originated at Los Alamos National Laboratory is being pursued by the Zero Emission Coal Alliance (ZECA), an international coalition whose goal is no atmospheric emissions from coal-fueled power and hydrogen production plants. The avoidance of atmospheric emissions addresses carbon dioxide, in addition to the more commonly considered coal by-products such as NO X , SO X , particulates, and heavy metals. The new approach combines and updates a number of concepts previously tested separately at the pilot plant scale, but in a new, highly integrated design. The integrated approach will provide fuel to electric energy conversion efficiencies of approximately 70%, double that of today's conventional power plants, while simultaneously yielding a pure, high-pressure CO 2 stream that is ready for sequestration. For sequestration, ZECA is examining the conversion of the CO 2 into mineral carbonates, thereby achieving safe and permanent disposal of the CO 2 in an inert solid form. The high efficiency power generation step provides for a substantial reduction (~ a factor of 2) in the amount of fuel consumed per unit of power reduced, thereby reducing the amount and cost of by-product disposal by a similar factor. Unlike most other emission reduction processes being investigated, which typically offer only marginal and short-term improvements, the ZECA concept is a long-term solution capable of supplying many centuries of abundant, secure, clean, low cost, coal-based fossil energy. As the underlying chemistry of the process works on carbon, the zero emission coal (ZEC) technology is also adaptable to a wide range of other fuels including biomass, heavy oils, tars, natural gas, etc.
The zero emissions coal alliance (ZECA) have proposed a highly efficient integrated coal hydrogasification power producing scheme, where carbon is removed from product gas through a cyclic CaO–CaCO3 process and electricity is produced with solid oxide fuel cells. In recent years a lot of research effort has been put towards the realisation of the ZECA cycle. This paper has two purposes: (a) to present optimal solutions to the technical challenges of the envisaged cycle, i.e. achieving the required product gas recycling to the gasifier with steam ejector, heat transfer to the calcination process via heat pipes, and required gas cleaning with appropriate sorbents and (b) to re-evaluate the cycle’s performance and operating regime adopting these solutions.The complete power plant was designed in detail using ASPENPLUS™ simulation software and results include all critical operation parameters in order to achieve optimal integration. The maximum realistically achievable net power production efficiency was estimated at ∼40%, with ∼90% decarbonisation.
Biomass is usually gasified above the optimal temperature at the carbon-boundary point, due to the use of different types of gasifiers, gasifying media, clinkering/slagging of bed material, tar cracking, etc. This paper is focused on air gasification of biomass with different moisture at different gasification temperatures. A chemical equilibrium model is developed and analyses are carried out at pressures of 1 and 10 bar with the typical biomass feed represented by CH1.4O0.59N0.0017. At the temperature range 900–1373 K, the increase of moisture in biomass leads to the decrease of efficiencies for the examined processes. The moisture content of biomass may be designated as “optimal” only if the gasification temperature is equal to the carbon-boundary temperature for biomass with that specific moisture content. Compared with the efficiencies based on chemical energy and exergy, biomass feedstock drying with the product gas sensible heat is less beneficial for the efficiency based on total exergy. The gasification process at a given gasification temperature can be improved by the use of dry biomass and by the carbon-boundary temperature approaching the required temperature with the change of gasification pressure or with the addition of heat in the process.
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.
In this paper, a novel biomass-based hydrogen production plant is investigated. The system uses oil palm shell as a feedstock. The main plant processes are biomass gasification, steam methane reforming and shift reaction. The modeling of the gasifier uses the Gibbs free energy minimization approach and chemical equilibrium considerations. The plant, with modifications, is simulated and analyzed thermodynamically using the Aspen Plus process simulation code (version 11.1). Exergy analysis, a useful tool for understanding and improving efficiency, is used throughout the investigation, in addition to energy analysis. The overall performance of the system is evaluated, and its efficiencies become 19% for exergy efficiency and 22% energy efficiency while the gasifier cold gas efficiency is 18%.
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