Sustainability assessment of power production by chemical looping combustion

Abstract

This study investigated the chemical looping combustion (CLC) process improvement for power production from energy management, system hydrodynamics, and sustainability perspectives. In the first part, the 3k factorial design was used for systematically investigating the operating variables that affect the thermal efficiency of the CLC combined with the humid air gas turbine (HAT) cycle. A set of operating variables, A) pressure of the air reactor, B) air compressor stages number, C) air compression methods, and D) air flow rate, were explored. The result showed that the highest thermal efficiency was at 55.87 % when operated at (A) 15 atm, (B) 7 stages, (C) method 3, and (D) 61,000 kmol/hr. Moreover, the efficiency could be improved further to 57.67% by increasing the Ni loading to 28% (by weight). The second part, the dual circulating fluidized bed reactor (DCFBR), was selected for the CLC system and investigated its operation by 2-D computational fluid dynamics (CFD) simulation. For the solid fuel, the result showed that the low value of temperature and ratio of coal velocity to the weight of an oxygen carrier provided the best performance. For the gaseous fuel, the high pre-exponential factor, the low initial solid volume fraction, velocity, and CH4 mass fraction in feed increased temperature and conversion. The result also indicated that the operating conditions are crucial for suitable hydrodynamics achievement and the CO2 capture efficiency. In the last part, three analyses, which were energy performance, economics, and sustainability, were evaluated to identify the best case by enhancing the process sustainability. Six case studies have been investigated the effects of the combustion types (conventional combustion (CC) and CLC) and system configuration (CO2 capture stages and operating conditions). According to emergy analysis, which is the tool that gives a more holistic view of the solution than the others, Case 4 was the best case due to its emergy sustainability index (ESI), when local content was taken into consideration. However, Case 5 would be the best case from a global perspective.