Thermoeconomic analysis of conventional and recuperative ORC for heat recovery of exothermic reactions

Abstract

The possibility of using medium temperature (478–506 K) saturated steam from a reactor cooling system as heat source for generating electricity is evaluated in this work. Both usual Organic Rankine Cycle (ORC) and recuperative (RORC) configurations were modeled for 3 different boiler heat loads (Cases 1, 2 and 3) so that the electricity generation capacity effect on the economic performance could be evaluated. From the power cycle simulations, methanol and ethanol had shown the best performance in the ORC configuration with average First and Second Laws’ efficiencies of 16% and 44%, respectively. By adding a recuperator, most of the dry fluids have also shown similar performances. In the economic analysis, net power generation plays a major role. For Case 2 ( ≈ 250 kW net) and Case 3 ( ≈ 850 kW net), the power generation revenue was insufficient to cover the operational expenses, yielding unfeasible scenarios. However, for Case 1 ( ≈ 2.5 MW net), economic feasibility was achieved even for low operating pressures. The best power cycle thermoeconomic performance was found for methanol as working fluid. In the best scenario, an attractive internal rate of return of 14.5% was achieved for an specified electricity cost of US$ 0.0671 per kW h. • Heat from medium temperature latent heat source is recovered to power an ORC. • Optimal evaporation temperature for dry fluids in RORC configuration is defined. • Minimum temperature difference automatic adjustment during power cycle simulation. • Heat exchanger detailed design based on literature correlations. • Power cycle NPV and pay-back calculation.