[01] Ifeanyi Henry Njoku, Department of Mechanical Engineering, Faculty of Engineering, University of Port Harcourt, Choba, Port Harcourt, Nigeria. [02] Chika Oko, Department of Mechanical Engineering, Faculty of Engineering, University of Port Harcourt, Choba, Port Harcourt, Nigeria. [03] Joseph Ofodu, Department of Mechanical Engineering, Faculty of Engineering, University of Port Harcourt, Choba, Port Harcourt, Nigeria.

This paper presents the thermodynamic, economic and environmental impact assessment of an existing combined cycle power plant to be retrofitted with a waste heat driven aqua lithium bromide absorption refrigerator for cooling the inlet air streams to the compressor and air cooled steam condenser. The power plant is located in the hot and humid tropical region of Nigeria, latitude 4°45′N and longitude 7°00′E. Using the operating data of the plant, the results of the analysis showed that by cooling the inlet air to the compressors to 15°C, the net power output of the gas turbine cycles increased by 48.3MW, and by cooling the inlet air streams to the air cooled steam condenser to 29°C, the net power output of the steam turbine cycle increased by 1.4MW. The overall thermal efficiency of the plant increased by 8.1% while the specific fuel consumption decreased by 7.0%. The stack flue gas exit temperature reduced from 126°C to 84°C in the absorption refrigerator, thus reducing the exhaust heat discharge rate to the atmosphere. The total capital cost, life cycle cost, annual sales revenue and net present value increased by 3.3%, 2.3%, 7.7% and 17%, respectively while the levelized cost of energy production in the plant and the break-even point of the investment reduced by 4.8% and 5.6%, respectively. Environmental impact analysis revealed that the emission rates of NOx and CO₂ emissions per MWh decreased by 65% and 7.3% respectively while the rate of CO emission increased with inlet air cooling by 12.1%. Thus inlet air cooling offers improved thermodynamic output, increased return on investment and greater environmental sustainability.

Absorption Refrigeration, Combined Cycle Power Plant, Techno-economic Analysis, Environmental Impact Analysis, Psychrometric Processes, Waste Heat Utilization

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