Thermodynamic analysis of high‐ash coal‐fired power plant with carbon dioxide capture

A thermodynamic analysis of a 500‐MWe subcritical power plant using high‐ash Indian coal (base plant) is carried out to determine the effects of carbon dioxide (CO₂) capture on plant energy and exergy efficiencies. An imported (South African) low‐ash coal is also considered to compare the performance of the integrated plant (base plant with CO₂ capture plant). Chemical absorption technique using monoethanolamine as an absorbent is adopted in the CO₂ capture plant. The flow sheet computer program “Aspen Plus” is used for the parametric study of the CO₂ capture plant to determine the minimum energy requirement for absorbent regeneration at optimum absorber–stripper configuration. Energy and exergy analysis for the integrated plant is carried out using the power plant simulation software “Cycle‐Tempo”. The study also involves determining the effects of various steam extraction techniques from the turbine cycle (intermediate‐pressure–low‐pressure crossover pipe) for monoethanolamine regeneration. It is found that the minimum reboiler heat duty is 373 MW_th (equivalent to 3.77 MJ of heat energy per kg of CO₂ captured), resulting in a drop of plant energy efficiency by approximately 8.3% to 11.2% points. The study reveals that the maximum energy and exergy losses occur in the reboiler and the combustor, respectively, accounting for 29% and 33% of the fuel energy and exergy. Among the various options for preprocessing steam that is extracted from turbine cycle for reboiler use, “addition of new auxiliary turbine” is found to be the best option. Copyright © 2011 John Wiley & Sons, Ltd.     

3‐E analysis of advanced power plants based on high ash coal

The objective of the study is to identify the ‘best’ possible power plant configuration based on 3‐E (namely energy, exergy, and environmental) analysis of coal‐based thermal power plants involving conventional (subcritical (SubC)) and advanced steam parameters (supercritical (SupC) and ultrasupercritical (USC)) in Indian climatic conditions using high ash (HA) coal. The analysis is made for unit configurations of three power plants, specifically, an operating SubC steam power plant, a SupC steam power plant, and the AD700 (advanced 700°C) power plant involving USC steam conditions. In particular, the effect of HA Indian coal and low ash (LA) reference coal on the performance of these power plants is studied. The environmental impact of the power plants is estimated in terms of specific emissions of CO₂, SO_x, NO_x, and particulates. From the study, it is concluded that the maximum possible plant energy efficiency under the Indian climatic conditions using HA Indian coal is about 42.3% with USC steam conditions. The results disclose that the major energy loss is associated with the heat rejection in the cooling water, whereas the maximum exergy destruction takes place in the combustor. Further, the sliding pressure control technique of load following results in higher plant energy and exergy efficiencies compared to throttle control in part‐load operation. Copyright © 2009 John Wiley & Sons, Ltd.     

Conceptual design and analysis of a novel system based on ash agglomerating fluidized bed gasification for co-production of hydrogen and electricity

In this paper, a novel system with ash agglomerating fluidized bed gasification and CO₂ capture to produce hydrogen and electricity is firstly designed in Aspen Plus. The newly-proposed system is composed of eight subsystems, namely air separation unit, gasification unit, water gas shift unit, Rectisol unit, CO₂ compression unit, Claus unit, pressure swing adsorption unit, gas and steam turbine unit. The thermodynamic performance and hydrogen to coal ratio of the new proposed system are investigated. The results demonstrate that the hydrogen to coal ratio, energy efficiency, net electricity power and exergy efficiency of the overall system for Yangcheng anthracite are 0.096 kg/kg, 46.52%, 1.71 MW and 43.92%, respectively. Additionally, the exergy destruction ratio and exergy efficiency of each subsystem are researched. More importantly, the influences of the oxygen to coal ratio, steam to coal ratio and coal types on the hydrogen to coal ratio, energy efficiency and exergy efficiency are also studied.     

Parametric techno‐economic studies of coal/biomass co‐gasification for IGCC plants with carbon capture using various coal ranks,fuel‐feeding schemes,and syngas cooling methods

Because of biomass's limited supply (as well as other issues involving its feeding and transportation), pure biomass plants tend to be small, which results in high production and capital costs (per unit power output) compared with much larger coal plants. Thus, it is more economically attractive to co‐gasify biomass with coal. Biomass can also make an existing plant carbon‐neutral or even carbon‐negative if enough carbon dioxide is captured and sequestered (CCS). As a part of a series of studies examining the thermal and economic impact of different design implementations for an integrated gasification combined cycle (IGCC) plant fed with blended coal and biomass, this paper focuses on investigating various parameters, including radiant cooling versus syngas quenching, dry‐fed versus slurry‐fed gasification (particularly in relation to sour‐shift and sweet‐shift carbon capture systems), oxygen‐blown versus air‐blown gasifiers, low‐rank coals versus high‐rank coals, and options for using syngas or alternative fuels in the duct burner for the heat recovery steam generator (HRSG) to achieve the desired steam turbine inlet temperature. Using the commercial software, Thermoflow^®, the case studies were performed on a simulated 250‐MW coal IGCC plant located near New Orleans, Louisiana, and the coal was co‐fed with biomass using ratios ranging from 10% to 30% by weight. Using 2011 dollars as a basis for economic analysis, the results show that syngas coolers are more efficient than quench systems (by 5.5 percentage points), but are also more expensive (by $500/kW and 0.6 cents/kW h). For the feeding system, dry‐fed is more efficient than slurry‐fed (by 2.2–2.5 points) and less expensive (by $200/kW and 0.5 cents/kW h). Sour‐shift CCS is both more efficient (by 3 percentage points) and cheaper (by $600/kW or 1.5 cents/kW h) than sweet‐shift CCS. Higher‐ranked coals are more efficient than lower‐ranked coals (2.8 points without biomass, or 1.5 points with biomass) and have lower capital cost (by $600/kW without using biomass, or $400/kW with biomass). Finally, plants with biomass and low‐rank coal feedstock are both more efficient and have lower costs than those with pure coal: just 10% biomass seems to increase the efficiency by 0.7 points and reduce costs by $400/kW and 0.3 cents/kW h. However, for high‐rank coals, this trend is different: the efficiency decreases by 0.7 points, and the cost of electricity increases by 0.1 cents/kW h, but capital costs still decrease by about $160/kW. Copyright © 2016 John Wiley & Sons, Ltd.     

Mathematical modeling of gasification of high‐ash Indian coals in moving bed gasification system

Simulation of gasification of high‐ash Indian coal in an updraft moving bed gasification system is presented in this paper. A steady one‐dimensional numerical model, which takes into account of drying, devolatilization, combustion and gasification processes, is used to solve the mass and energy balances in the gasification system. The results from the model have been validated against the experimental data available in literature for various types of coals. The predicted product gas composition, its calorific value and the exit temperature are in agreement with the reported results. The validated model is used to study the effect of input parameters such as oxygen content in air stream, steam flow rates and the pressure of the gasification system. Results indicate that the value of oxygen mole fraction around 0.42 in the oxidizer stream can provide optimum performance in oxygen‐based gasification systems. There is a range of steam‐to‐coal ratio that is dependent on the oxygen content in oxidizer stream. For air‐based systems, this value is around 0.4 and for oxygen‐based systems it is 1.5. The gasification performance improves with operating pressure significantly. An operating pressure of around 8 bar and higher, based on the application, can be used for achieving the required performance with high‐ash coals. The model is useful for predicting the performance of high‐ash Indian coals in a moving bed gasification system under different operating parameters. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of ash fouling on heat transfer during combustion of cattle biomass in a small‐scale boiler burner facility under unsteady transition conditions

Combustion of cattle biomass (CB) as a supplementary fuel has been proposed for reducing emissions of NO_x, Hg, SO₂, and nonrenewable CO₂ in large coal‐fired power plants; however, its high ash content resulted in fouling and slagging problems when the CB was co‐fired with coals during small‐ and pilot‐scale tests. Ash depositions during combustion of the CB as a reburn fuel were investigated using a 30 kW_t (100 000 Btu h^?1) boiler burner facility with water‐cooled heat exchangers (HEXs) under unsteady transition conditions and short‐term operations. Two parameters were used to characterize the effects of the ash deposition: (1) Overall heat transfer coefficient (U) and (2) Burnt fraction (BF). A methodology was presented and empirically demonstrated for the effects of ash deposition on heat transfer under unsteady transition conditions. Experiments involving ash deposition during reburning the CB with coals were compared with experiments involving only ash‐less natural gas. It was found that the growth of the ash layer during reburning the CB and coals lowered the heat transfer rate to water in the HEXs. In low‐temperature regions, the thin layer of the ash deposition promoted radiation effects, while the thick layer of the ash deposition promoted the thermal resistance of the ash layer. A chemical analysis of the heavy ash indicated that the BF increased when a larger fraction of the CB was used in the reburn fuels, indicating better performance compared with coal combustion alone. However, the results of ash fusion temperature indicated the ash deposited during combustion of the CB and coals was more difficult to remove than the ash deposited during coal combustion alone. Copyright © 2010 John Wiley & Sons, Ltd.     

Evaluation of feasibility of pelletized wood co-firing with high ash Indian coals

To reduce anthropogenic CO₂ emissions from power plants, biomass is an immediate alternative fuel which has similar properties as coal. In this regard, the present study discusses about pelletized wood (PW) co-firing with high ash Indian coal by conducting co-milling and co-firing trials in a 1000 kg/hr of pilot scale test facility. Indian coals are typically high ash content and low calorific value fuels, therefore, its interaction with coal during combustion and ash deposition have studied in detail. Based on co-milling trails of PW and coal, it was observed that as PW proportion in coal increases, the quantity of particles of size below 50 μm and as well above 500 μm were increased. From co-firing studies, it was observed that higher volatile content in PW helping in stabilizing flames while co-firing. At lower proportions, up to 10% weight PW co-firing with coal, the flame temperature and heat flux values are very close to base test of 100% coal firing. However, beyond 10% by weight of PW co-firing with coal, the flame temperature and heat flux values were increased significantly from 100% coal tests. This is because of higher calorific value of PW than coal. The CO emission was decreased with increase in PW proportion in coal but at 30% of PW in coal, CO emission was increased suddenly. However, NO and SO₂ concentrations were decreased up to 8% and 16% respectively with increase in PW proportion in coal due to lower fuel nitrogen and sulphur content in PW than coal. Analytical analysis of slagging indices suggest that the slagging potential for PW co-firing with coal is increasing as the PW proportion in coal increases.     

Energy,exergy and economic analyses and multiobjective optimization of a novel solar multi-generation system for production of green hydrogen and other utilities

Renewable energy based multi-generation systems can help solving energy-related environmental problems. For this purpose, a novel solar tower-based multi-generation system is proposed for the green hydrogen production as the main product. A solar-driven open Brayton cycle with intercooling, regeneration and reheat is coupled with a regenerative Rankine cycle and a Kalina cycle-11 as a unique series of power cycles. Significant portion of the produced electricity is utilized to produce green hydrogen in an electrolyzer. A thermal energy storage, a single-effect absorption refrigeration cycle and two domestic hot water heaters are also integrated. Energy, exergy and economic analyses are performed to examine the performance of the proposed system, and a detailed parametric analysis is conducted. Multiobjective optimization is carried out to determine the optimum performance. Optimum energy and exergy efficiencies, unit exergy product cost and total cost rate are calculated as 39.81%, 34.44%, 0.0798 $/kWh and 182.16 $/h, respectively. Products are 22.48 kg/h hydrogen, 1478 kW power, 225.5 kW cooling and 7.63 kg/s domestic hot water. Electrolyzer power size is found as one of the most critical decision variables. Solar subsystem has the largest exergy destruction. Regenerative Rankine cycle operates at the highest energy and exergy efficiencies among power cycles.     

Thermodynamic analysis of representative power generation cycles for low‐to‐medium temperature applications

This study is focused on the analysis of representative thermodynamic cycles for power generation at low‐to‐medium temperatures (with the highest cycle temperature from 450 to 700 K). The natural working fluid of carbon dioxide is selected for the current tests and comparisons with suitable operation ranges. Energy balance and exergy loss models are established and applied to 10 selected representative thermodynamic cycles. One modified efficiency parameter is also defined for better comparison of performances, which has considered the effects of both specific thermodynamic process and cycle complexity. Based on the modified efficiency parameter, it is found that Rankine cycle yields the highest performance at 450–500 K among the 10 representative cycles, while regenerative Brayton cycle shows better behavior for 550–700 K. Detailed behaviors and optimal principals of regenerative Brayton cycles are also identified and compared in this study. Also, a new cycle is also proposed in this study, which combines the advantages of Rankine cycle and Brayton cycle. The new cycle is proved to have better work output potential but higher system complexity factor. In addition, based on the thermodynamic analysis, possible future directions of low‐to‐medium temperature power cycles are summarized. It is hoped that the results can be of help for related power generation system designs. Copyright © 2014 John Wiley & Sons, Ltd.     

Cofiring coal and dairy biomass in a 29 kWt furnace

Cofiring biomass with fossil fuels is emerging as a viable option for promoting the use of low quality renewable biomass fuels including energy crops. In the current work, dairy biomass (DB) is evaluated as a cofiring fuel with coal in a small scale 29 kW_t boiler burner facility. Two types of coal (Texas lignite, TXL and Wyoming Powder River Basin coal, WYO) and two forms of partially composted DB fuels were investigated (low ash separated solids LA-PC-SepSol-DB and high ash soil surface HA-PC-SoilSurf-DB). Proximate and ultimate analyses performed on both coals and both DBs reveal the following: higher heating value (HHV) of 28,460–29,590 kJ/kg for dry ash free (DAF) coals and 21,450 kJ/kg for DB; nitrogen loading of 0.36 and 0.48 kg/GJ for WYO and TXL, respectively and 1.50 and 2.67 kg/GJ for the LA-PC-SepSol-DB and the HA-PC-SoilSurf-DB respectively; sulfur loading of 0.15 and 0.42 kg/GJ WYO and TXL, respectively and 0.33 and 0.43 kg/GJ for the LA-PC-SepSol-DB and the HA-PC-SoilSurf-DB respectively; ash loading from 3.10 to 8.02 kg/GJ for the coals and from 11.57 to 139 kg/GJ for the DB fuels.     

Development of a new solar,gasification and fuel cell based integrated plant

Despite its shortcomings, fossil-based fuels are still utilized as the main energy source, accounting for about 80% of the world's total energy supply with about one-third of which comes from coal. However, conventional coal-fired power plants emit relatively higher amounts of greenhouse gases, and the derivatives of air pollutants, which necessitates the integration of environmentally benign technologies into the conventional power plants. In the current study, a H₂–CO synthesis gas fueled solid oxide fuel cell (SOFC) is integrated to the coal-fired combined cycle along with a concentrated solar energy system for the purpose of promoting the cleaner energy applications in the fossil fuel-based power plants. The underlying motivation of the present study is to propose a novel design for a conventional coal-fired combined cycle without altering its main infrastructure to make its environmentally hazardous nature more ecofriendly. The proposed SOFC integrated coal-fired combined cycle is modeled thermodynamically for different types of coals, namely pet coke, Powder River Basin (PRB) coal, lignite and anthracite using the Engineering Equation Solver (EES) and the Ebsilon software packages. The current results show that the designed hybrid energy system provide higher performance with higher energy and exergy efficiencies ranging from 70.6% to 72.7% energetically and from 35.5% to 43.8% exergetically. In addition, carbon dioxide emissions are reduced varying between 18.31 kg/s and 30.09 kg/s depending on the selected coal type, under the assumption of 10 kg per second fuel inlet.     

Movable injection point–based syngas production in the context of underground coal gasification

Underground coal gasification (UCG) has been proven as a viable technology for the generation of high calorific value syngas using deep mine coal seams. The use of multiple injection points/movable injection point method could be an alternate technique for efficient gasification of high ash Indian coals. In this context, the present study is focused on evaluating the heating value of syngas using a variety of gasifying agents such as pure O₂, air, humidified O₂, and CO₂-O₂ dual-stage gasification under movable injection method for high ash coals. It is found that the use of movable injection point method had significantly increased the heating value of the product gas, compared with the fixed point injection method. For high and low ash coal under pure O₂ gasification, the calorific value of syngas obtained using movable injection point is 123.2 and 153.9 kJ/mol, which are 33.5% and 24.3% higher than the syngas calorific value obtained using fixed injection point, respectively. Further, the air as a gasification agent for high ash coals had increased the gross calorific value of the syngas by 24%, using this technology. The results of high ash coal gasification using humidified oxygen at optimum conditions (0.027-kg moisture/kg dry O₂) and CO₂-O₂ gas had enhanced the syngas calorific value by 12.6% and 5%, respectively. Humidified O₂ and CO₂-O₂ gasifying agents produced a high-quality syngas with the calorific value of 190 kJ/mol, among the gasifying agents used. The experimental results had shown that the movable injection point method is found to be a better alternative for the generation of calorific value-enriched syngas using high ash-based Indian coals.     

Exergy‐based performance analysis of packed‐bed solar air heaters

This paper presents an experimental investigation of the thermal performance of a solar air heater having its flow channel packed with Raschig rings. The packing improves the heat transfer from the plate to the air flow underneath. The dimensions of the heater are 0.9 m wide and 1.9 m long. The aluminium‐based absorber plate was coated with ordinary black paint. The characteristic diameter of the Raschig rings, made of black polyvinyl chloride (PVC) tube, is 50 mm and the depth of the packed‐bed in flow channel is 60 mm. Energy and exergy analyses were applied for evaluating the efficiency of the packed‐bed solar air heater. The rate of heat recovered from the packed‐bed solar air heater varied between 9.3 and 151.5 W m^?2, while the rate of thermal exergy recovered from the packed‐bed solar air heater varied between 0.04 and 8.77 W m^?2 during the charging period. The net energy efficiency varied from 2.05 to 33.78%, whereas the net exergy efficiency ranged from 0.01 to 2.16%. It was found that the average daily net energy and exergy efficiencies were 17.51 and 0.91%, respectively. The energy and exergy efficiencies of the packed‐bed solar air heater increased as the outlet temperature of heat transfer fluid increased. Copyright © 2004 John Wiley & Sons, Ltd.     

Lignite‐fired air‐blown IGCC systems with pre‐combustion CO2 capture

Detailed analyses based on mass and energy balances of lignite‐fired air‐blown gasification‐based combined cycles with CO₂ pre‐combustion capture are presented and discussed in this work. The thermodynamic assessment is carried out with a proprietary code integrated with Aspen Plus^® to carefully simulate the selective removal of both H₂S and CO₂ in the acid gas removal station. The work focuses on power plants with two combustion turbines, with lower and higher turbine inlet temperatures, respectively, as topping cycle. A high‐moisture lignite, partially dried before feeding the air‐blown gasification system, is used as fuel input. Because the raw lignite presents a very low amount of sulfur, a particular technique consisting of an acid gas recycle to the absorber, is adopted to fulfill the requirements related to the presence of H₂S in the stream to the Claus plant and in the CO₂‐rich stream to storage. Despite the operation of the H₂S removal section representing a significant issue, the impact on the performance of the power plant is limited. The calculations show that a significant lignite pre‐drying is necessary to achieve higher efficiency in case of CO₂ capture. In particular, considering a wide range (10–30 wt.%) of residual moisture in the dried lignite, higher heating value (HHV) efficiency presents a decreasing trend, with maximum values of 35.15% and 37.12% depending on the type of the combustion turbine, even though the higher the residual moisture in the dried coal, the lower the extraction of steam from the heat recovery steam cycle. On the other hand, introducing the specific primary energy consumption for CO₂ avoided (SPECCA) as a measure of the energy cost related to CO₂ capture, lower values were predicted when gasifying dried lignite with higher residual moisture content. In particular, a SPECCA value as low as 2.69 MJ/kg_CO2 was calculated when gasifying lignite with the highest (30 wt.%) residual moisture content in a power plant with the advanced combustion turbine. Ultimately, focusing on the power plants with the advanced combustion turbine, air‐blown gasification of lignite brings about a reduction in HHV efficiency equal to almost 1.5 to 2.8 percentage points, depending on the residual moisture in the dried lignite, if compared with similar cases where bituminous coal is used as fuel input. Copyright © 2016 John Wiley & Sons, Ltd.     

ANN-GA based optimization of a high ash coal-fired supercritical power plant

The efficiency of coal-fired power plant depends on various operating parameters such as main steam/reheat steam pressures and temperatures, turbine extraction pressures, and excess air ratio for a given fuel. However, simultaneous optimization of all these operating parameters to achieve the maximum plant efficiency is a challenging task. This study deals with the coupled ANN and GA based (neuro-genetic) optimization of a high ash coal-fired supercritical power plant in Indian climatic condition to determine the maximum possible plant efficiency. The power plant simulation data obtained from a flow-sheet program, “Cycle-Tempo” is used to train the artificial neural network (ANN) to predict the energy input through fuel (coal). The optimum set of various operating parameters that result in the minimum energy input to the power plant is then determined by coupling the trained ANN model as a fitness function with the genetic algorithm (GA). A unit size of 800 MWe currently under development in India is considered to carry out the thermodynamic analysis based on energy and exergy. Apart from optimizing the design parameters, the developed model can also be used for on-line optimization when quick response is required. Furthermore, the effect of various coals on the thermodynamic performance of the optimized power plant is also determined.     

Optimization study of large‐scale low‐grade energy recovery from conventional Rankine cycle power plants

This study evaluates large‐scale low‐grade energy recovery (LS‐LGER) from a conventional coal‐fired Rankine cycle (RC) as a ‘green’ option to offsetting the cost of treating pollution. An energy and exergy analysis of a reference generating station isolates the key areas for investigation into LS‐LGER. This is followed by a second law analysis and a detailed optimization study for a revised RC configuration, which provides a conservative estimate of the possible energy recovery. Cycle optimization based on specific power output, and including compact heat exchanger designs, indicates plant efficiency improvements (with high‐capacity equipment) of approximately 2 percentage points with reduced environmental impact. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of ambient conditions on the thermodynamic performance of hybrid nuclear‐combined cycle power plant

This paper provides a theoretical study of the effects of ambient conditions on the thermodynamic performance of a hybrid combined‐nuclear cycle power plant. The operational parameters investigated are based on the first and second laws of thermodynamics, which include the ambient air temperature and ambient relative humidity (Φ). The results obtained for the gas turbine model are shown to agree very well with operational data from the Al‐Zour Emergency power plant in Kuwait. The ambient temperature was studied within the range of 0–55 °C. The analysis shows that the ambient air temperature has strong effects on plant performance and that operating the system at a high temperature will degrade the performance. Power output is reduced when the temperature is above the standard ambient temperature of 15 °C, and this loss rate is about 17% at 55 °C. The effect of ambient relative humidity (Φ) becomes significant only at higher temperatures. The ambient temperature has a large effect on the exergy destruction of the heat recovery steam generator exhaust, but it has little effect on other components of the plant. The analysis also indicates that reducing the temperature from 55 to 15 °C could help decrease the total exergy destruction of the plant by only 2%. Copyright © 2011 John Wiley & Sons, Ltd.     

Performance analysis of a waste‐heat‐powered thermodynamic cycle for multieffect refrigeration

A multieffect refrigeration system that is based on a waste‐heat‐driven organic Rankine cycle that could produce refrigeration output of different magnitudes at different levels of temperature is presented. The proposed system is integration of combined ejector–absorption refrigeration cycle and ejector expansion Joule–Thomson (EJT) cooling cycle that can meet the requirements of air‐conditioning, refrigeration, and cryogenic cooling simultaneously at the expense of industrial waste heat. The variation of the parameters that affect the system performance such as industrial waste heat temperature, refrigerant turbine inlet pressure, and the evaporator temperature of ejector refrigeration cycle (ERC) and EJT cycles was examined, respectively. It was found that refrigeration output and thermal efficiency of the multieffect cycle decrease considerably with the increase in industrial waste heat temperature, while its exergy efficiency varies marginally. A thermal efficiency value of 22.5% and exergy efficiency value of 8.6% were obtained at an industrial waste heat temperature of 210°C, a turbine inlet pressure of 1.3 MPa, and ejector evaporator temperature of 268 K. Both refrigeration output and thermal efficiency increase with the increase in turbine inlet pressure and ERC evaporator temperature. Change in EJT cycle evaporator temperature shows a little impact on both thermal and exergy efficiency values of the multieffect cycle. Analysis of the results clearly shows that the proposed cycle has an effective potential for cooling production through exploitation of lost energy from the industry. Copyright © 2014 John Wiley & Sons, Ltd.     

Design and analysis of a novel structure for green syngas and power cogeneration based on PEM electrolyzer and Allam cycle

In this study, a new process with the aim of producing green synthesis gas (syngas) with high thermodynamic energy and exergy efficiency is presented. This process consists of four units including a water electrolysis unit (WEU), an Allam power cycle (APC), a Water/Ammonia power cycle (WAPC), and an organic Rankine cycle (ORC). The process was simulated, and the results showed that the overall efficiency of energy and exergy is 60.44% and 63.22%, respectively. It was also found that for this novel process, total exergy destruction is 10.97 MJ/kg_syngas, whereas APC, ORC, WAPC, and WEU units have 66%, 4%, 2%, and 28% share in exergy destruction, respectively. Additionally, the energy analysis results showed that APC, ORC, WAPC, and WEU units have an energy efficiency of 19.07%, 17.76%, 14.48%, and 83.22% respectively. According to the environmental assessment, the direct and indirect emission of carbon dioxide in the proposed process is zero. In this respect, the proposed process has a significant advantage compared to other syngas production methods.     

Hybrid clean energy technologies for power generation from sub-bituminous coals: a case of 250 MW unit

Major re-thinking is required on the conventional pulverized fuel conversion route of power generation wherein the ash and mineral burden in coals is transported through the entire flow passage of the boiler. For high-ash fuels, this has to be contained and the boiler must be clear of all mineral matter. The two independent clean coal candidate technologies for efficiency enhancement and emission controls – ultra-supercritical cycle (USC) and integrated gasification with combined cycle (IGCC) – both have limitations in adaptation to high-ash coals. While the USC is limited by the steam temperature up to 600°C (commercial scale) (700°C pilot scale) and boiler tube failure risks, IGCC is limited to high-quality fuels like diesel, naphtha, etc. (commercial scale) and high-grade coals (pre-commercial scale). The hybridization of the two technologies in their current form (ultra-supercritical cycle with gasification conversion) and carbon capture and storage (CCS) together with solar energy (solar thermal and solar photovoltaic) integration presents possibilities for immediate application to low-grade sub-bituminous coals to achieve the clean technology goals. The energy efficiency of the hybrid system is around 44.45%, which is of the order of the USC with pulverized coal combustion. But the predominant benefits of a clean operation override. The benefits are reduction in CO₂ generation from 0.86 to 0.70 kg/kWh and reduction in ash expelled from 0.20–0.24 to 0.12–0.18 kg/kWh besides elimination of dispersion of ash around the power station and facilitating CCS.