Power by waste heat recovery from low temperature industrial flue gas by Organic Flash Cycle (OFC) and transcritical-CO2 power cycle: A comparative study through combined thermodynamic and economic analysis

Both Organic flash cycle and transcritical CO2 power cycle (T-CO2 power cycle) allow cooling of hot flue gas stream to an appreciably lower temperature due to the absence of pinch limitation. In the present study, a combined thermodynamic and economic comparison is conducted between a T-CO2 power cycle and Organic flash cycles using R-245fa and R600 as the working fluids. It is observed that work output per kg of flue gas flow rate is slightly higher for the T-CO2 power cycle if the flue gas is allowed to cool to the corresponding lowest possible temperature in the Heat Recovery Unit (HRU). It is also observed that with maximum possible cooling of flue gas, minimum bare module costs (BMCs) for each kW power output of OFCs are somewhat higher compared to that of T-CO2 power cycle. Minimum BMCs for each kW output of OFCs can be reduced substantially by increasing terminal temperature difference at the low temperature end of the HRU. However, the increasing terminal temperature difference at the low temperature end of the HRU is having negligible effect on BMC ($/kW) of T-CO2 power cycle.