No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
New correlation predicts flue gas sulfuric acid dewpoints
Abstract
A new correlation accurately predicts the flue-gas sulfuric-acid dewpoints to lessen corrosion problems in process equipments and heat-recovery systems in oil and gas industry. This accurate and reliable correlation predicts sulfuric-acid dewpoints over wide ranges of sulfur trioxide and water vapor concentrations. Verhoff and Banchero provided the correlation for predicting flue-gas sulfuric-acid dewpoint. Okkes proposed a correlation in which the partial pressures are expressed in atmosphere and the dew-point is in °C. In the new correlation setup, an equation is used to predict flue-gas sulfuric-acid dewpoints and to compare them with experimental data provided by Verhoff and Banchero and Okkes at different SO3 and H2O concentrations. The results reveal that the effect of moisture concentration on acid dewpoint is moderate, however, especially at high SO3 concentrations. It is also observed that at moisture concentrations higher than 30 vol %, the H2O content does not have a major influence on the sulfuric-acid dewpoint.
... This represents a significant issue in coal fired power plants, with the flue gas exhausted at temperatures above the ADP in order to prevent its condensation in the lines. ADP is dependent on the amounts of SO3 and H2O present, and in oxy-fuel is expected to be around 10 -30°C higher than those for air-firing of the same coal [6,16,50]. Stanger and Wall [6] gave a comprehensive review on the impacts of sulfur in an oxy-fuel process which will be discussed further in Section 2.6. ...
... Besides, in the case of mist condensation, high gas velocities or local high flow disturbances will push the droplets onto the metal walls and a thin liquid film is formed as well by this mechanism [73]. Although correlations such as the ones by Verhoff and Banchero (VB) and the ones by Okkes exist and have previously been used in estimating acid dew points, the more recent correlation between SO3 and H2O by ZareNezhad [50] were employed in this study. In ZareNezhad's study, the VB correlation has shown over prediction of ADP which could lead to higher operating temperatures in the air preheaters (APH) and cause boiler efficiency losses whilst the Okkes correlation has shown under prediction of the ADP that the APH could potentially be at risk for cold end corrosion. ...
... In ZareNezhad's study, the VB correlation has shown over prediction of ADP which could lead to higher operating temperatures in the air preheaters (APH) and cause boiler efficiency losses whilst the Okkes correlation has shown under prediction of the ADP that the APH could potentially be at risk for cold end corrosion. The ZareNezhad correlation [50] estimates the ADP as presented in ...
Oxy-fuel combustion is one of the three main CO₂ capture and storage (CCS) technologies for coal-fired power generation; the other two being post-combustion and pre-combustion. Oxy-fuel combustion uses oxygen diluted with recycled flue gas as the oxidant rather than air to regulate temperature within the boiler. As a result, flue gas compositions are more concentrated in CO₂ and up to 4 times higher in impurities such as SOₓ and mercury. Emissions of SOₓ as well as condensation and deposition of corrosive sulfates are detrimental to processes utilised in oxy-fuel flow sheets and also to the plant efficiency. An understanding of the role and impacts of sulfur during coal combustion will benefit control of sulfur emissions and potential corrosion throughout the plant. It is vital for the Callide Oxy-fuel Project (COP) as no SOₓ and Hg removal is used at this plant due to the low sulfur coal used, as expected in all Australian plants. This study aims to establish an understanding of the reactions, transformations and impacts of SOₓ in oxy-fuel combustion by an experimental and theoretical study comparing oxy-fuel sulfur species with those in air firing for which plant impacts are known, including: (1) pilot scale coal combustion experiments to evaluate the overall impacts of coal quality on sulfur release and capture; (2) ash decomposition experiments to test the capture and retention of sulfur in the fly ash and the different sulfur species in fly ash; (3) conversion experiments to establish effects of different flue gas cleaning configurations on the pathways of SO₃ formation and the catalytic effect of fly ash on the conversion of SO₂ to SO₃; and (4) mercury and SOₓ interaction experiments to investigate the speciation and competition between mercury and SOₓ species in the bag filter. Ash produced during oxy-fuel combustion is expected to differ to ash produced during air combustion due to the higher CO₂ and SO₂ atmosphere in which it is generated. For a quantitative understanding of the sulfation behaviour of fly ash in oxy-fuel combustion, fly ash from three commercial Australian sub-bituminous coals were tested and decomposed under an inert atmosphere. Thermal evolved gas analysis was completed for ash produced in both air and oxy-fuel environments. Pure salts were also tested under the same conditions to allow identification of the species in the ash which potentially capture sulfur, along with thermodynamic modelling using FactSage 6.0. Sulfur evolved during the decomposition of air and oxy-fuel fly ash was compared with the total sulfur in the ash to close the sulfur balance. Both total sulfur captured by the ash and sulfur evolved during decomposition were higher for oxy-fuel fly ash than their air counterparts. The extent of sulfation resulting from thermal decomposition of oxy-fuel fly ash was 2 to 3 times greater than air fly ash. Correlations of capture with ash chemistry were attempted to show extent of sulfur capture and to identify active species in the fly ash responsible for the capture. The reaction of SO₂ with fly ash in the presence of O₂ and H₂O may lead to the formation of SO₃ and eventually H₂SO₄. Homogeneous experiments were conducted to evaluate the effects of the procedural variables: temperature, gas concentrations and residence time on the post-combustion conversion of SO₂ to SO₃. Results were compared to those predicted by existing global kinetics and found to be dependent on SO₂, O₂, residence time and temperature and independent of H₂O content. For a residence time of 1 s, at least 900°C is needed to have an observable conversion of SO₂ to SO₃. Literature suggests that the conversion of SO₂ to SO₃ is dependent on the iron oxide content of the fly ash. Experiments using the same fly ash were used to investigate the catalytic effects of fly ash on SO₂ conversion to SO₃ at a temperature range of 400°C to 1000°C. It was observed that fly ash acts as a catalyst in the formation of SO₃, with the largest conversion occurring at 700°C. Homogeneous reaction at 700°C, without fly ash present, converted 0.10% of the available SO₂ to SO₃. When fly ash was present the conversion increased to 1.78%. The catalytic effect accounts for roughly 95% of the total conversion at 700°C. Average SO₃/SO₂ conversion values between fly ash derived from air and oxy-fuel firing and under different flue gas environments were found to be similar. Increased mercury concentration is of concern because mercury is known to attack aluminium heat exchangers required in the compression of CO₂ during oxy-fuel combustion. A recent study has indicated that interaction of Hg and SOₓ may occur at oxy-fuel concentrations and so the competition between SOₓ and Hg was investigated in this study. The effect of Hg, SOx, H₂O and temperature on the native capture of Hg by fly ash was assessed using a quartz flow reactor packed with fly ash to simulate a bag filter. Doubling Hg in the system from 5 to 10 μg/Nm³ doubled the amount of Hg captured in the fly ash from 1.6 to 2.8% and increases the amount of Hg unaccounted from 5.8 to 18.1%. Increased SO₂ decreased the proportion of Hg⁰ in the flue gas. Temperature in the bag filter was found to have a huge impact on the mercury capture by fly ash. As temperature was increased from 90 to 200°C, Hg⁰ in the flue gas was found to increase from 77.9 to 98.3%, indicating better capture of Hg at lower temperatures. The COP is the largest existing plant utilising oxy-fuel technology that combines retrofit options for existing power plants; electricity generation and CO₂ processing. As there is no dedicated SOₓ, NOₓ and Hg removal in place, removal is expected to occur at the fabric filter or during compression. With higher SO₂, SO₃ and H₂SO₄ during oxy-fuel combustion, sulfur capture by the ash is higher compared to oxy-fuel firing. Higher SO₂ forms sulfates responsible for fireside corrosion, SO₃ captured in the fabric filter causes corrosion in the metal components while H₂SO₄ causes fouling of the air pre-heater (APH) and low temperature corrosion due to condensation of H₂SO₄ on surfaces. Shifting from air to oxy-fuel with full flue gas recycling can easily increase the H₂SO₄ dew point by as much as 60°C. Apart from corrosion and fouling, maintaining the APH at high temperature results in efficiency losses. Native mercury capture by the bag filter is also decreased with increasing ADP since the BF must be operated at much higher temperatures. With these reductions in capture at the bag filters due to an increase in operating BF temperature, downstream impacts in the CO₂ processing requiring a need for secondary Hg removals could be created.
... In addition to a suitable catalyst, formation of SO 3 in the heat recovery boiler requires oxygen, which is available due to its addition to the process to ensure effective sulfation of the flue dust. It should also be noted that, in addition to SO 3 formation in the heat recovery boiler, SO 3 can also form in the smelting or converting furnace and when entering the heat recovery boiler, increasing the overall concentration of SO 3 41 The partial pressures in Eq. 9 are expressed in mmHg, and the sulfuric acid dew point in K. To overcome the shortcomings of these two equations, a more recent equation (Eq. 10), based on 188 validated data points, has been developed. ...
... 10), based on 188 validated data points, has been developed. 41 The partial pressures in Eq. 9 are expressed in mmHg, and the sulfuric acid dew point in°C. In addition to the equations presented above, new computational approaches based on an artificial neural network model 42 or Vandermonde matrix 43 have been developed to estimate and predict the effect of the SO 3 concentration on the sulfuric acid dew point temperature. ...
The aim of this work is to examine the catalytic role of copper smelter, copper converter, and nickel smelter process dusts in SO2-to-SO3 conversion at 750°C. To clarify the role of specific oxides in greater detail, synthetic dusts containing varying concentrations of either CuO or Fe3O4 were also studied. All studied dusts catalyzed SO3 conversion. Among the industrial flue dusts, the highest concentration of SO3 formed in the presence of copper smelter dust. Comparing individual oxides, CuO had a greater impact on the SO3 formation. Such catalytic effects of smelter dusts may lead to SO3 concentrations in the process gas so high that sulfuric acid dew point corrosion may occur.
... Gaseous H 2 SO 4 starts to form from SO 3 and water vapor when the flue gas temperature drops below some 500 °C, and at 200 °C all the SO 3 has reacted to H 2 SO 4 (g) [47] . The sulfuric acid dew point temperature can be estimated when the water vapor and H 2 SO 4 concentrations are known using correlations, such as by: Verhoff and Banchero [81] , Okkes [82] , and more recently by ZareNezhad [83] . A comparison of these correlations for the concentrations of 1, 10, and 50 ppm v of H 2 SO 4 (g) is shown in Fig. 15 . ...
... Comparison of the sulfuric acid dew point at three concentrations as a function of the concentration of water vapor in the gas, calculated with the correlations by Verhoff and Banchero[81] , Okkes[82] , and ZareNezhad[83] . ...
Biomass fuels differ in many ways from the conventional fossil fuels used in combustion processes, such as coal. They often have high moisture contents, lower heating values, and a variety of minor constituents, such as chlorine, sulfur, phosphorus, nitrogen, and a variety of ash-forming metals. These special properties of biomass fuels cause several challenges, but in many cases also provide advantages, to their use in combustion processes. Design of the combustion devices and choice of their operating parameters are very dependent on the detailed properties of the biomass fuel or fuels to be used. Often these challenges are connected to the fate and chemistry of the many minor constituents or impurities of the fuels. This paper reviews some of such chemical details related to biomass combustion that are important to take into consideration in the use of biomass combustion processes. The focus of the paper is in large, industrial scale combustion technologies for biomass and biomass derived waste fuels, either in district heating or also power production. Areas discussed are biomass particle conversion and biomass char oxidation reactivity, nitrogen and sulfur reactions in furnaces, superheater fouling and corrosion due to biomass ashes, low-temperature corrosion, and bed sintering in fluidized bed furnaces. The advances in understanding chemical details of biomass combustion have strongly contributed to the development of more reliable and efficient boiler technologies. Unresolved challenges are still connected to simultaneous combustion of several different biomasses and interaction of fuel ashes in such applications.
... The acid dew point of the formed H 2 SO 4 depends on the concentrations of H 2 O and SO 3 /H 2 SO 4 in the flue gas. It can be calculated based on those species' partial pressures according to empirical equations proposed by Verhoff and Banchero [48], Okkes [49] or more recently by ZareNehzhad [50]. In power plants, ADPs typically range between 95 and 160°C. ...
... When temperature falls below the ADP, gaseous H 2 SO 4 starts to condense. In power plants, relevant temperatures are found in the region of filters/precipitators and air pre-heaters, where substantial problems due to low temperature corrosion can occur [50]. In oxy-fuel plants, also the recycle lines are critical in respect to low temperature H 2 SO 4 corrosion. ...
This paper presents results on experiments carried out at a 20 kW combustion rig simulating different extents of oxy-fuel recycle gas cleaning by impurities injection to the oxidant gas of the once-through combustion reactor. A comprehensive set of total (Hgtot), elemental (Hg0) and oxidized (Hg2+) mercury as well as SO3 concentrations was obtained before and after the combustion rig's baghouse filter for in total 14 air and oxy-fuel experiments with 3 Australian coals. Based on this data, an assessment in respect to Hg oxidation, SO2/SO3 conversion and Hg and SO3 capture on the test rig's filter was performed. The air and the oxy-fuel experiments with different extents of recycle gas cleaning, revealed differences in the Hg and SO3 formation and capture behavior: The Hg2+/Hgtot ratios in the flue gas are higher during oxy-fuel combustion compared to air-firing. This effect is even more pronounced at the filter outlet, after flue gas has passed through the filter ash. In some experiments, even a net oxidation of Hg0 entering the filter to Hg2+ was observed. The Hg capture by ash in the baghouse filter has been found to reduce the Hg emissions considerably. However, the Hg capture was altered by the different oxy-fuel recycle configurations, leading to decreased Hg capture efficiencies on the filter for one of the coals. A coal-specific trend of increased SO2/SO3 conversion ratios with increased flue gas SO2 levels was observed that could be related to the ash composition of the three different coals. This and the higher SO2 concentrations in the flue gas lead to considerably higher SO3 levels in oxy-fuel combustion with SO2 recycling. During the experiments, also a considerable capture of SO3 in the baghouse filter was observed (up to 80% under air- and up to 66% under oxy-fired conditions). A reduction of the SO3 capture on the filter under oxy-fuel conditions may be related to the higher SO3 levels in this process.
... At temperatures below about 400 • C gaseous sulfuric acid (H 2 SO 4 ) starts to form from the equilibrium between SO 3 and water vapour and reaches complete conversion of SO 3 at approximately 200 • C. The dew point of the H 2 SO 4 in the flue gas depends on the concentrations of H 2 O and SO 3 /H 2 SO 4 and may be calculated according to available correlations (ZareNezhad, 2009). In power plants, H 2 SO 4 dew points typically range between 95 and 160 • C. With increased H 2 O and SO 3 /H 2 SO 4 concentrations in oxy-fuel, considerably higher dew points can be found. ...
... The acid dew point of flue gas is a function of the H2SO4 concentration inside the flue gas and of the water content. Assuming a H2SO4 concentration of around 6 mg Nm -3 and a water content of around 8 vol%, the acid dew point is estimated to be around 110 °C [27]. The PSD measurements made using the ELPI + confirm low particle numbers of around 6.5 E5 cm -3 , which most likely relate to the small fly ash particles present in the flue gas. ...
This study presents the results of two field tests that aimed at evaluating two countermeasures (WESP and GGH) to avoid acid mist formation. A WESP is shown to be very efficient for the removal of nuclei from the flue gas (100 % efficient) and thus can prevent aerosol formation inside an amine based absorber. This is however only valid in the absence of SO2 in the flue gas entering the WESP. A decreasing WESP efficiency is noted in the presence of SO2 with increasing voltages as a result of newly formed aerosols inside the WESP. This implies that no or very low levels of SO2 should be present in the flue gas entering the WESP. Since most of the amine carbon capture installations have a pre-scrubber (usually using NaOH to remove residual SO2 in the flue gas leaving the power plant's Flue Gas Desulphurisation) in front of their amine absorber, the WESP must be installed behind this pre-scrubber and not in front of it. Having a Gas-Gas Heater (or any type of flue gas cooling such as a Low Temperature Heat Exchanger) installed upstream of the wet scrubbing may prevent homogenous nucleation and thus prevent the conversion of H2SO4 into sulfuric acid aerosols and consequently mist formation issues in the amine based carbon capture installation. Which option to choose amongst the two countermeasures presented in this study will depend on whether a new built installation is being considered or whether a carbon capture is planned as a retrofit into an existing installation.
... At temperatures below about 400 • C gaseous sulfuric acid (H 2 SO 4 ) starts to form from the equilibrium between SO 3 and water vapour and reaches complete conversion of SO 3 at approximately 200 • C. The dew point of the H 2 SO 4 in the flue gas depends on the concentrations of H 2 O and SO 3 /H 2 SO 4 and may be calculated according to available correlations (ZareNezhad, 2009). In power plants, H 2 SO 4 dew points typically range between 95 and 160 • C. With increased H 2 O and SO 3 /H 2 SO 4 concentrations in oxy-fuel, considerably higher dew points can be found. ...
The Callide Oxy-fuel Project is the world's largest operating oxy-fuel plant. This work details an experimental test campaign at the Callide Oxy-fuel Project monitoring mercury and SO3 levels exiting the fabric filter during transitions between air and oxy firing conditions. The measurements were taken using two custom built probes; the first allowing combined collection of SO3 and mercury over short time intervals; the second allowing on-line measurements of Hgtotal and Hg0 with SOx removal. Total mercury emissions in oxy-firing measured a maximum of 6–7 μg/m3 of which 89% was in oxidised form (Hg2+). The use of low NOx burners had an overriding influence on the mercury measurements reducing the total mercury levels to 0.13 and 0.15 μg/m3 (air, oxy respectively) with no Hg2+ being measured. The SO3 concentrations were also lower than expected, estimated at ∼0.5–0.8 ppm (based on a practical estimate of 1% conversion of SO2). Overall mercury capture in either operating mode was estimated at 92–93% for the existing burners and 98–99% with the low NOx burners used (being 2 of the 4 burners operating). Total SOx captured from the flue gas was 16% in oxy-mode and 19% in air firing. These findings suggest that operational conditions have a primary impact on capture of Hg and SOx during transitions with a secondary impact of firing mode (i.e. air or oxy).
... Among these, sulfuric acid turns out to be the most critical in regard to the dew point and the corrosivity of the exhaust gas [4,5,6]. There are several empirical correlations in the literature to determine the dew point of exhaust gases as a function of humidity and sulfuric acid content [7,8,9]. These formulas were parameterized with measured vapor liquid equilibrium (VLE) data of the system water -sulfuric acid. ...
EGR cooling is a worthwhile technology capable of reducing NOx-emissions and increasing the efficiency of CI engines. Challenges arise when low-temperature cooling is applied with high fuel sulfur contents. The resulting sulfuric acid condenses in conjunction with the water of the exhaust gas and gives rise to corrosion of coolers and engine components. Additionally, fouling of the EGR cooler is exacerbated by the condensation of acidic components compromising EGR performance. In order to gain a better understanding of the underlying processes a combined experimental and model-based approach is presented. Tests of two different EGR-cooler concepts under various conditions showed a strong influence of the fuel sulfur content on fouling and condensation. The one-dimensional cooler model developed alongside these experiments consists of an activity coefficient model (NRTL) of the binary system water - sulfuric acid and a condensation model that allows for simulating the coupled condensation of both vapor components. Comparison of experimental fouling and simulated condensation results show good agreement in interpreting critical fouling phenomena that occur at temperatures in between the acid-water dew point and the dew point of pure water.
... When temperature falls below the H 2 SO 4 dew point, gaseous H 2 SO 4 starts to condense. In power plants, relevant temperatures are found in the region of filters/precipitators and air pre-heaters, where substantial problems due to low temperature corrosion can occur (ZareNezhad, 2009). In oxyfuel plants also the recycle lines are critical in respect to low temperature H 2 SO 4 corrosion. ...
Oxyfuel combustion is one of the leading technologies considered for capturing CO2 from power plants with CCS. This involves the process of burning the fuel with nearly pure oxygen instead of air. In order to control the flame temperature, some part of the flue gas are recycled back into the furnace/boiler.Since the publication of the Special Report on CO2 Capture and Storage by the International Panel for Climate Change (IPCC, 2005), the development of oxyfuel combustion technology has progressed significantly and could be considered at par in terms of technology maturity as compared to other leading CO2 capture technologies.This paper presents an overview to the current state-of-the-art technology on the development of oxyfuel combustion applied to (a) PC and CFB coal fired power plants and (b) gas turbine based power plant. It should be noted that it is not the intention of this paper to provide a comprehensive review but to present what have been achieved in the past 10 years of RD&D efforts.For coal fired power plant using oxyfuel combustion, this paper primarily presents the different development aspects of the burners and boilers (combustion and heat transfer), emissions, operation of the plant (i.e. start-up and turndown) and its integration to the ASU and CPU.For gas turbine based power plant using oxyfuel combustion, the different GT cycles are described, looking at the different aspects in combustion, emissions, cycle efficiency and development of the turbomachineries.Also presented in this paper is a snapshot to what we have learned from the operation of the different large-scale pilot plants and development of large scale demonstration projects worldwide.The paper concludes by presenting the potential of this technology and highlighting the importance of realizing large scale demonstration plant as a necessary step to achieve its ultimate goal of technology commercialization.
... The acid dew point of flue gas is a function of the H 2 SO 4 concentration inside the flue gas and of the water content. Assuming a H 2 SO 4 concentration of around 6 mg Nm −3 and a water content of around 8 vol%, the acid dew point is estimated to be around 110 @BULLET C (ZareNezhad, 2009). The PSD measurements made using the ELPI + confirm low particle numbers of around 6.5 E5 cm −3 , which most likely relate to the small fly ash particles present in the flue gas. ...
... − Formation starts at about 400°C.• Condensation of H 2 SO 4 when temperature falls below acid dew point temperature: T Dew = f(p SO3 , p H2O )• T Dew calculation at IFK according to Zarenezhad[5] • T Dew formerly calculated according to Verhoff/Banchero[6] or Okkes[7]:− Verhoff/Banchero equation overpredicts T Dew − Okkes equation underpredicts T Dew • Acid dew points calculated according to Zarenezhad equation: • Typical dew points in air fired power plants: 95-150°C • Sampling with glass wool for dust removal (all samples taken behind catalyst) − Variation of the sampling volume: acid mist not or late (after 30 min of sampling) visible in H 2 SO 4 collector − Addition of SO 2 with secondary air (sampling volume 190l (STP)): acid mist visible after 10-15 minutes of sampling ...
In the present work, a supercritical CO2 cycle, designed for recovering waste heat originating specifically from heavy-duty turbocharged diesel engines, constitutes the basis of an integrated energy system. The purpose of this system is to cover the time-varying power loads required during the operation of ships, appearing in diverse forms of energy (propulsive/mechanical, electrical, thermal). Optimization procedures are applied for the determination of the optimal design and of the optimal operational characteristics of the CO2 cycle during partial loading conditions. Appropriate techno-economic criteria are used for evaluating the optimality of the proposed engineering solutions. The effects of the added capital costs of the CO2 cycle on its useful power output are investigated, while the temporal variations of the energy loads are appropriately taken into account in the determination of the optimum CO2 cycle design characteristics. The inclusion of the CO2 cycle is economically justified, while a reduction of operational fuel costs from 5.8% to 6.3 % is achieved for a typical yearly energy profile, according to the optimal allocation of the useful power produced by the CO2 waste heat recovery cycle towards the propulsive or electric loads.
In the present work, an investigation is carried out for the assessment of the energy efficiency improvement, which can be achieved with the employment of a supercritical CO2 power cycle operating in conjunction with a marine Diesel engine. The focus is directed towards the appropriate design of the CO2 cycle, which recovers heat from three distinct waste heat sources exhibiting different temperature levels (exhaust gas, compressed scavenge air and jacket cooling water), and contributes to the propulsion load in order for the total fuel consumption to be minimized. Engineering optimization problems, based on the superstructure optimization concept, are formulated and solved, in order for the optimal configuration of the CO2 cycle and the thermodynamic states of the working fluid to be specified. For this purpose, several possible alternatives regarding the CO2 cycle are examined, and a CO2 cycle configuration resulting to improved performance of the overall system is proposed as an outcome of the optimization algorithms application. The implications of size limitations of several of the heat exchangers included in the CO2 cycle and their effects on the performance of the overall system are also assessed. The results indicate that, in comparison with a standalone operating marine Diesel engine, an efficiency enhancement in a range approximately between 6.6% and 7.25% is attainable with the best performing CO2 cycle configuration, according to the heat exchangers size limitations that may be imposed in a practical implementation of the proposed solution. Although applied for the case of a marine Diesel engine, the findings and results of the present study can also be relevant to other applications as well, in which a heavy duty turbocharged Diesel engine is used.
The study of an integrated energy system is presented in this article that will cover all types of energy loads (mechanical, electrical, thermal) on a Very Large Crude Carrier (VLCC) with the maximum technically possible and economically feasible exploitation of fuel energy, thus reducing the operating cost and environmental footprint of the ship. There may be a large variety of configurations, design specifications and operating states that can cover the loads, making it necessary to apply synthesis, design and operation optimization of the system. The net present value of the system is selected as the objective function. For this purpose, a superconfiguration of the system is considered, which includes a number of Diesel engines adapted for possible operation in a combined Diesel and Rankine cycle, heat recovery steam generators producing high and low pressure steam, steam turbines that can contribute to propulsion and/or to the electricity production, an exhaust gas boiler and auxiliary boilers, as well as Diesel-generator sets. The synthesis of the system, that is, the components that will finally exist in the system, and their interconnections, the design specification of the components and the operating properties at characteristic operating states of the ship are not predetermined, but they are the result of formal, mathematical optimization. In addition, the speed of the vessel in each state, an important operational variable that has a crucial effect on the propulsion power and thus on the fuel consumption, is also determined by the optimization. The hull characteristics, the loading condition and the weather state are taken into account for the calculation of the propulsion power. For the optimization, proper models of the various components have been developed and the optimization problem is solved by addressing the three levels (synthesis, design, and operation) at a single computational step. The benefits of optimization, as well as the conditions that make the combined cycle economically justified, are demonstrated through an application example. The numerical solution is obtained for various values of fuel price and freight rate, so that the effects of these two crucial parameters on the optimal solution are assessed.
In oxy‐fuel combustion, fuel is burned using oxygen together with recycled flue gas, which is needed to control the combustion temperature. This leads to higher concentrations of sulfur dioxide and sulfur trioxide in the recycled gas, which can result in the formation of sulfuric acid and enhanced corrosion. Current experimental data on SO3 formation, reaction mechanisms, and mathematical modelling have indicated significant differences in SO3 formation between air‐ and oxy‐fuel combustion for both the wet and dry flue gas recycle options. This paper provides an extensive review of sulfur trioxide formation in air‐ and oxy‐fuel combustion environments, with an emphasis on coal‐fired systems. The first part summarizes recent findings on oxy‐fuel combustion experiments, as they affect sulfur trioxide formation. In the second part, the review focuses on sulfur trioxide formation mechanisms, and the influence of catalysis on sulfur trioxide formation. Finally, the current methods for measuring sulfur trioxide concentration are also reviewed along with the major difficulties associated with those measurements using data available from both bench‐ and pilot‐scale units. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.
Wet type electrostatic precipitators (ESPs), or Cold ESPs can effectively remove particulate matters, particularly fine particles (PM2.5), from flue gases. The present paper describes a numerical model for assessing ESPs' performance, considering a series of factors including dust layer resistivity, dewpoint, acid condensation, electric field distribution, particle charging and gas-particle flow. The roles of sulfur trioxide (SO3) in the flue gas and temperature are analysed together with case studies. Without SO3 in flue gas, the collection efficiency of the dry ESP is controlled by the dust layer resistivity. With SO3 present, different physics are involved, which are considered according to the following steps: Firstly, the acid dewpoint and acid condensation are calculated based on mass balance and phasic equilibrium. Then the electric field around a dielectric sphere and the field charging mechanism in relation to wet particles are discussed. An effective electric permittivity for a composite sphere is verified by a sub-particle scale electric field simulation and implemented in a wet particle charging model. The collection efficiencies for ash particles with dielectric constant of 3.9–80 are predicted over a wide range of particle sizes from 0.02 to 25 μm under various conditions. Some questions of industry interest have been clarified by both qualitative and quantitative manners.
The term Off-Highway includes a great variety of diesel engine applications like propulsion of ships, mining trucks, harvesters, trains, power generation and pump drives, e.g. for hydraulic fracturing.
To solve the low-temperature corrosion problems existing in oxy-fuel combustion boilers, a study was carried out to the effects of recirculation mode, coal category and boiler load on the low-temperature corrosion of the mill by taking a 600 MW oxy-fuel combustion boiler as an example. Results show that the acid dew point of flue gas at mill outlet is sensitive to the desulfurization and dehydration process under re¬circulation mode; when high sulphur coal is burned, serious low-temperature corrosion will occur in the mill; the acid dew point of flue gas decreases with the reduction of boiler load, which is determined by both the SO2 and H2O concentration, however, the effect of SO2 is slightly greater than that of H20.
The paper discusses a "hot-wet" SO2 analyzer at a sulfuric acid plant for inter-stage measurement of SO2. Upon start-up, SO3 and H2SO4 carryover often foul the sample system. An unforeseen process condition was adding moisture causing formation of acid mist. While conditions were being assessed it was incumbent the analyzer be in service and a number enhancements were implemented, will be discussed. The mechanism and mitigation of acid mist formation will also be presented. This experience can be applied to any process with high concentrations of SO2. The emphasis is on lessons learned and collaboration between end user and vendor to arrive at a solution to suit process conditions.
This article summarizes scientific knowledge and practical experiences on the release and capture of SO2 and SO3 with a special focus on the implications of oxy-fuel combustion conditions on sulphur emission behaviour. Results, obtained at the experimental, 500 kWth atmospheric, pulverized fuel combustion rig (KSVA) of the IFK regarding sulphur oxide (SO2/SO3) emissions and capture behaviour are presented. The experimental plant was operated with pre-dried sulphur rich lignite in air and oxy-fuel combustion mode. The following issues are highlighted in particular:
Homogeneous experiments and Catalytic conversion experiments were conducted in a laboratory to evaluate the post-combustion conversion of SO2 to SO3. Homogeneous conversion results were compared to existing global kinetics and was found to be dependent on SO2, O2, residence time and temperature and independent of H2O content. Experiments using three different fly ash samples from Australian sub-bituminous coals were used to investigate the catalytic effects of fly ash on SO2 conversion to SO3 at a temperature range of 400oC to 1000oC. It was observed that fly ash acts as a catalyst in the formation of SO3, with the largest conversion occurring at 700oC. Homogeneous reaction at 700°C, without fly ash present, converted 0.098% of the available SO2 to SO3. When fly ash was present the conversion increased to 1.784%. The catalytic effect accounts for roughly 95% of the total conversion. Average SO3/SO2 conversion values between fly ash derived from air and oxy-fuel firing and under different flue gas environments were found to be similar.
The sulfur oxide (SOx) concentrations during oxy-fuel combustion are generally higher compared to conventional air firing. The higher SOx concentrations, particularly SO3 in combination with high concentration of water in the recycled flue gas, increase the sulphuric acid dew point temperature in oxy-fuel fired systems, thereby increasing allowable flue gas temperatures and reducing the thermal efficiency of a power plant. This paper presents results of experiments carried out at a 20 kW once-through combustion rig of Institute of Combustion and Power Plant Technology (IFK) of the University of Stuttgart simulating different extents of oxy-fuel recycle gas cleaning by impurities injection to the oxidant gas of a once-through combustion reactor. Three Australian coals that have previously been tested under air and oxy-fuel conditions at the Aioi furnace of IHI in Japan, were used in the experiments. The SOx emissions were measured, conversion ratios of SO2 to SO3 were calculated and results were compared with existing literature, finding good agreement. The experiments with different extents of recycle gas cleaning and therefore different SO2 levels in the system, revealed differences in the SO3 generation behaviour: A coal specific trend of increasing conversion ratios of SO2 to SO3 with increased flue gas SO2 levels was observed that could be related to the ash composition of the three different coals. The capture of SOx in a baghouse filter was also evaluated. Acid dew point temperatures (ADPs) for the flue gas were calculated for the various firing conditions. Acid dew point (ADP) temperatures increased by up to 50 K when changing from air to oxy-firing with recycling of H2O and SO2. Considerable differences in the ADPs were found for different extents of oxy-fuel recycle gas treatment and were evaluated in respect to power plant efficiency implications.
The availability of acid dew-point correlations (for flue gases containing the precursors of sulfuric-, nitric-, hydrochloric acids, etc.) that directly relate Tw,dpTw,dp to the participating species partial pressures (e.g., 1 and 19) without the explicit need for liquid phase thermodynamic properties has led to their popularity for preliminary design estimates of onset surface temperatures for corrosive deposits. Despite the fact that these correlations cannot be used when either or both precursor partial pressures become too small, when they are invoked within their intended domains of validity, we show here that they can be conveniently used to not only quickly estimate acid dew-point temperatures in the presence of unavoidable gas phase precursor species Soret separation effects, but also to provide preliminary estimates of the surface temperatures, Tw,AMOTw,AMO, associated with the local onset of acid mists in the vicinity of cooled surfaces. Our present simple theoretical/numerical methods are illustrated for the most familiar case of sulfuric acid deposits. While we indicate that increased accuracy and generality will require a more fundamental approach in which condensate thermodynamic non-ideality is explicitly introduced, we show here that prudent use of these earlier engineering correlations can lead to immediately useful preliminary estimates of both transport-shifted Tw,dp-Tw,dp- and Tw,AMO-valuesTw,AMO-values.
When cooling combustion flue gas for heat recovery and efficiency gain, the temperature must not be allowed to drop below the sulfur trioxide dew point. Below the SO3 dew point, very corrosive sulfuric acid forms and leads to operational hazards on metal surfaces. In the present work, simple-to-use predictive tool, which is easier than existing approaches, less complicated with fewer computations is formulated to arrive at an appropriate estimation of acid dew point during combustion flue gas cooling which depends on fuel type, sulfur content in fuel, and excess air levels. The resulting information can then be applied to estimate the acid dew point, for sulfur in various fuels up to 0.10 volume fraction in gas (0.10 mass fraction in liquid), excess air fractions up to 0.25, and elemental concentrations of carbon up to 3. The proposed predictive tool shows a very good agreement with the reported data wherein the average absolute deviation percent was found to be around 3.18%. This approach can be of immense practical value for engineers and scientists for a quick estimation of acid dew point during combustion flue gas cooling for heat recovery and efficiency gain for wide range of operating conditions without the necessity of any pilot plant setup and tedious experimental trials. In particular, process and combustion engineers would find the tool to be user friendly involving transparent calculations with no complex expressions for their applications.
The oxy-fuel process is one of three carbon capture technologies which supply CO2 ready for sequestration – the others being post-combustion capture and IGCC with carbon capture. As yet no technology has emerged as a clear winner in the race to commercial deployment. The oxy-fuel process relies on recycled flue gas as the main heat carrier through the boiler and results in significantly different flue gas compositions. Sulphur has been shown in the study to have impacts in the furnace, during ash collection, CO2 compression and transport as well as storage, with many options for its removal or impact control. In particular, the effect of sulphur containing species can pose a risk for corrosion throughout the plant and transport pipelines. This paper presents a technical review of all laboratory and pilot work to identify impacts of sulphur impurities from throughout the oxy-fuel process, from combustion, gas cleaning, compression to sequestration with removal and remedial options. An economic assessment of the optimum removal is not considered. Recent oxy-fuel pilot trials performed in support of the Callide Oxy-fuel Project and other pilot scale data are interpreted and combined with thermodynamic simulations to develop a greater fundamental understanding of the changes incurred by recycling the flue gas. The simulations include a sensitivity analysis of process variables and comparisons between air fired and oxy-fuel fired conditions - such as combustion products, SO3 conversion and limestone addition.
The aim of this work is to investigate the level of damage to the heat exchanger in a Sulfur Recovery Unit (SRU) of a petroleum refinery. The by-products of oil refining are submitted to special treatment in order to meet technical specifications of corrosivity, sulfur content, acidity, formation of pollutant compounds, and color alteration. Sulfur is removed from the by-products in the form of H2S, which is an acid gas that is sent to the SRU for sulfur production. The gases in the SRU are H2S, CO2, SO2, and SO3, which are corrosive to the mild steel equipment. The Unit is frequently forced to paralyze its activities due to the corrosion of its heat exchangers and pressure vessels, and the acid gas load is burnt causing the release of SOx into the atmosphere. The above occurs when generalized corrosion damages SRU equipment. The importance of this work is to emphasize that the leakage of acid gas and sulfur into the atmosphere is a direct result of corrosion, which causes economical and environmental damage. This study may be used to improve the control of The Claus Process and to minimize corrosion damage. The SRU does not, at present, carry out any corrosion prevention methods. The corrosion of mild steel is controlled by correct air admission to oxide H2S, and to produce SO2, which is the reagent in the reaction of sulfur production.
In a new build waste incinerator, the waste (refuse derived fuel) was burned on a discontinuous moving grate. Frequent furnace overpressure peaks occurred because of this firing method and as a result, flue gas and fly-ash were pushed out of the boiler and into the building. During the plant start up period, a seal in a water-feed pipeline broke, and a large amount of condensed steam was discharged into the boiler house. Shortly thereafter, very severe corrosion was noticed on the galvanised gangways, steel building components, the boiler aluminium sheeting and on processing lines. A theoretical study of the condensation of the flue gas indicated that sulphuric acid would condense before it reached the external aluminium sheeting and that under normal conditions, dry hydrochloric acid fumes would be removed by the boiler house ventilators. However, the steam leakage had caused the hydrochloric acid to be dissolved in the condensed water and that had resulted in the severe corrosion damage, which had become evident subsequently.
The aim of air pre-heaters is to raise the temperature of the combustion air in boilers, using heat recovered from the power plant combustion gases. On the one hand, this paper compares the effects of the acid dew point temperature (ADT) on pre-heaters in a reference thermal power plant for two types of fuel, “fuel No. 2” and “low sulphur fuel” respectively and on the other hand, it shows how a changeover to this latter fuel would increase the useful lifetime of this equipment, reducing this way cost of maintenance due to the considerable decrease in the area exposed to ADT with the subsequent increase in the boiler’s performance.