Thermo-economic multi-objective optimization of an innovative cascaded organic Rankine cycle heat recovery and power generation system integrated with gas engine and ice thermal energy storage

Abstract

Abstract For providing cooling, heating and electricity loads of buildings with high thermal efficiency and low energy consumption, an innovative cascaded organic Rankine cycle (CORC), an electrical chiller (with Vapor compression refrigeration cycle, VCR) and an ice thermal energy storage system (ITES) are integrated with a gas engine (GE). CORC heat recovery and power generation system with two high and low temperature loops uses the gas engine exhaust as heat source and generate electricity in an innovative heat recovery cogeneration plant. VCR-ITES provides the cooling demand. It shifts the electricity consumption from on-peak hours to off-peak low load hours (23–8). The electricity consumption of VCR-ITES is estimated based on variable cooling load during a year and not based on the cooling load at the hottest day in the year. Thermo-economic modeling and multi-objective optimizing the new proposed integrated system (GE-CORC-VCR+ITES) are performed to find the required capacity of equipment. After optimizing procedure, three 393 kW gas engines are selected. Results for CORC show that HT loop with R11 working fluid generated 75.6 kW and LT loop with R152a working fluid generated 72.9 kW (148.5 kW in sum) power output. Moreover, the thermal efficiency of CORC as well as overall thermal and exergy efficiency of integrated system were 23%, 68% and 63% respectively. The innovative CORC with dual loop configuration had higher net power output, higher thermal efficiency and lower investment cost per unit of power output ($/W) in comparison with a single loop ORC and other dual loop ORCs. VCR-ITES also had 44.2% lower energy consumption, 43.9% lower emission and 64% lower electricity cost in comparison with that for simple VCR system. Results for the proposed integrated system are also compared with that for the traditional system (buying electricity from the grid, generating heat by a hot water boiler and providing cooling load by an electrical chiller), the reduction in annual cost of buying electricity from the grid was 1.35 × 105 $/year (61.5%), also the annual income from selling electricity was estimated to be 9.8 × 105 $/year, the annual fuel cost consumption reduced due to heat recovery for 9.8 × 104 $/year (31%), and the annual CO2 and NOx emission production decreased for 3.02 × 104 $/year. The payback period of the optimized integrated system is 3.63 years.