The role of outlet temperature of flue gas in organic Rankine cycle considering low temperature corrosion

Abstract

This paper gives a special focus on the role of outlet temperature of flue gas (Tgo) in organic Rankine cycle (ORC) system for low tem- perature flue gas waste heat recovery. The variations of performance indicators: net work (Wnet), exergy efficiency (ηex) and levelized energy cost (LEC) versus Tgo are discussed. Considering the corrosion of low temperature flue gas, the necessity and reasonability of limiting Tgo at its minimum allowed discharge temperature (355.15 K) are analyzed. Results show that there exist optimal Tgo (Tgo,opt) for Wnet and LEC, while Tgo,opt for ηex does not appear under the investigated range of Tgo. Moreover, the Tgo,opt for Wnet is always lower than 355.15 K, the Tgo,opt for LEC, despite being greater than the one for Wnet, is just slightly higher than 355.15 K when the inlet temperature of flue gas varies from 408.15 K to 463.15 K. For the waste heat recovery of low temperature flue gas, it is reasonable to fix Tgo at 355.15 K if Wnet or LEC is selected as primary performance indicator under the pinch point temperature difference of evaporator (ΔTe) below 20 K.