A novel combined cooling-heating and power (CCHP) system integrated organic Rankine cycle for waste heat recovery of bottom slag in coal-fired plants

Abstract

The extensive use of organic Rankine cycle (ORC) in waste heat recovery motivates the employment of ORC technique to recover the waste heat in coal-fired plants. A novel combined cooling-heating and power (CCHP) system integrated Organic Rankine Cycle (CCHP-ORC) for recovering the waste heat of bottom slag in coal-fired plant is first proposed in this paper. A MATLAB procedure with REFPROP database is developed for the proposed system based on the mass, energy and exergy balances of each component. With the application of Analytic Hierarchy Process (AHP) method, R1234ze(E) and heptane/R601a are adopted as the optimal working fluids for the Sing Fluid CCHP-ORC and Dual Fluid CCHP-ORC systems, respectively. Parametric studies are conducted to investigate the effect of superheat degree of turbine inlet temperature, chilled water mass flow rate and condenser temperature on the coefficient of performance, thermal efficiency, heat exergy, cooling exergy, total exergy production and exergy production rate. The results show that the superheat degree of turbine inlet temperature benefits the enhancement of the exergy production rate. The enhancement of chilled water mass flow rate leads to an increase in coefficient of performance and refrigerating capacity while the cooling exergy, total exergy production and exergy production rate decrease. Except for exergy production rate in Dual Fluid CCHP-ORC system, the rise of condenser temperature leads to a decrease of performance parameters. As the condenser temperature rises from 25 °C to 40 °C, the thermal efficiency of Cycle2 declines 19.4% and 18.3% respectively in the Sing Fluid CCHP-ORC system and Dual Fluid CCHP-ORC system.