Thermo-economic and environmental multi-objective optimization of a novel arranged biomass-fueled gas engine and backpressure steam turbine combined system for pulp and paper mills

Abstract

For gaining both the maximum profit and the minimum exergy loss, a novel arranged gas engine combined heating and power system is proposed. This system was modeled in four aspects of energy, exergy, economic and environmental. By defining two objective functions including percentage of exergy destruction to the total inlet exergy and relative annual benefit, Genetic Algorithm was used for system multi-objective optimization. Modeling two strategies including selling mode and no-selling mode during system lifetime was another novel part of the present research. Modeling and optimization results in selling mode for Mazandaran pulp and paper plant in Iran showed that combined heating and power cycle included five gas engines each one with 6737 kW nominal power output and one steam turbine which had 667.4 kW power output. The overall efficiency of the above CHP system was 80.5% with about 1.07 years as the payback period. Comparison of results with that for traditional system showed 3.1 × 107 m3/year fuel saving, 2.63 × 106 US $/year fuel cost saving, and 1.84 × 108 kgCO2/year reduction in emission production. With no-selling mode condition, relative annual benefit decreased for about 19% and payback period increased for about 11.6%.