Superstructure optimization of absorption chillers integrated with a large internal combustion engine for waste heat recovery and repowering applications: Thermodynamic and economic assessments

Internal combustion engines can suffer derating due the knocking phenomenon, which is caused by harsh climate conditions. In addition, large internal combustion engines release considerable heat to the environment through the cooling water and exhaust gas systems. This work is part of an R&D project, sponsored by a Brazilian thermal power plant, in which waste heat recovery and intake air conditioning are explored. The major contribution is the development of a superstructure modelling based on absorption systems integrated with one engine, permitting to determine the best chiller that should be installed at the power plant. Genetic algorithm is used to optimize the complex system, presenting as an optimal result a single-effect chiller powered by the engine's cooling water, which is preheated at an exhaust gas heat exchanger. The benefits are demonstrated in terms of additional electric power output (1.47 MW approximate to 17.2%) and reduction of brake specific fuel consumption (2.4 g kWh(-1) approximate to 1.44%) over the engine's performance on site (8.54 MW and 167.06 g kWh(-1)). Moreover, 37.35% of electrical energy savings are achieved at the radiator after the optimization. The optimal profit is 30.7 US$ h(-1) with a Levelized Cost of Energy of 19.2 US$ MWh-1. The investment risk requires a payback under three years. The exergy analysis revealed that the absorption chiller is recovering 391.55 kW of wasted exergy, which is 1.67% of the total amount of chemical exergy from the fuel and 11.33% of the total amount of available exergy in the waste streams (cooling water and exhaust gases).