Thermodynamic analysis and economic assessment of biomass-fired organic Rankine cycle combined heat and power system integrated with CO₂ capture

Biomass-fired combined heat and power system with electric scale below 500 kW down to 100 kW (or even lower) constitutes an emerging distributed market. Organic Rankine cycle coupled with biomass combustion boiler is an appealing and promising technology for small-scale combined heat and power systems. In this paper, a biomass-fired ORC-CHP system integrated with monoethanolamine-based CO₂ capture is designed, in which the pressurized hot water is used as heat source for ORC system and the condensation heat can be fully utilized to supply domestic hot water. The pinch point temperature difference analytic method is adopted to investigate thermodynamic performance. Thermodynamic analysis, parametric optimization and economic assessment with a special focus on CO₂ capture have been conducted for eleven candidate working fluids. Results show that an optimal evaporation temperature exists with a given pressure ratio in the ORC system. The optimal heat source temperature for ORC system in the bioenergy system can be obtained by optimizing the total investment, dynamic payback period and profit ratio of investment, and the condensation temperature is also optimized using a thermo-economic evaluation. The biomass-fired ORC-CHP system with cyclopentane presents excellent thermodynamic performance with the highest primary energy saving ratio, the lowest net power indicator and levelized energy cost, followed by R141b, R113, R123 and Pentane; while HFE7000 achieving the largest profit ratio of investment and net present value is the best preferable working fluid in terms of economic assessment, followed by R1233zd, isobutane, isopentane and R113. The bioenergy system with optimized parameters is thermodynamically feasible and economically attractive, eco-friendly with negative carbon dioxide emissions thanks to the CO₂ capture.