SUMMARY 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 MWth (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.

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This paper proposes an ammonia–water Kalina cycle driven by low-grade waste energy released from the combustion reactions of mill's rejection which is coupled with 500 MWe coal-fired thermal power plant to quantify the additional electrical power. Energy of combustion for mill rejection is computed by combustion modeling equations. A thermodynamic property calculator for the binary mixture and a computer simulation program have been developed by MS-Excel and Visual Basic for Application (VBA) to calculate and optimize the Kalina cycle operating parameters based on thermodynamic modeling equations. Variation of key operating parameters, namely, turbine inlet pressure, mass flow rate of binary mixture, and ammonia mass fraction in mixture is studied and filters the optimum value accordingly to maximize the cycle efficiency. Techno-commercial feasibility is also done through economic analysis. The results show that about 562.745 kWe power generation can be added with total plant generation for organization profit. This will enhance the combined plant efficiency from 38.559% to 38.604%. Maximum net Kalina cycle efficiency of 24.74% can be achieved with ammonia mass fraction of 0.4 at condenser back pressure of 1.957 bar and turbine inlet pressure and temperature of 20 bar and 442.40 K, respectively. Ammonia mass fraction of 0.4 is the optimum choice for 20 bar turbine inlet pressure to get maximum output after maintaining minimum 50 K degree of superheat compared to ammonia mass fraction of 0.3. The cycle performance at ammonia mass fraction of 0.4 is better than 0.5 due to less condenser back pressure. Kalina cycle operating with less mass flow rate performs higher cycle efficiency when dryness fraction at turbine exhaust is less than 1 and performance deteriorates at above 1. This deterioration is due to higher condenser energy loss carried away by cooling water (CW) flow. The simple payback period of this system is around 5.5 years if the system is running with 80% plant availability factor and 100% plant load factor.

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