Advanced exergy analysis of organic Rankine Cycles for Fischer-Tropsch syngas production with parallel dry and steam methane reforming

Abstract

The process for producing Fischer-Tropsch syngas (FTS) with the combination of steam and dry methane reforming (operating in parallel) is demonstrated with the most favorable economics. Conventional exergy analysis (CEA) is firstly used to diagnose the part and degree of inefficiency in the process. The energy-saving potential of each equipment and thermodynamic interactions are further evaluated and classified by advanced exergy analysis (AEA). The Organic Rankine Cycle (ORC) with (or without) recuperators is introduced to recover the waste heat according to the obtained exergy analysis results. The thermodynamic efficiency and total exergy destruction of the ORC are defined as the objective function to determine best working fluids and optimal operation conditions. The performance assessment of proposed three different ORC schemes indicates the dual-pressure ORC system has the best performance with highest thermal efficiency accounting to 15.39%, annual net profit (ANP) accounting to 1.55 E+07dollar/year and 4.6 years payback period. The exergy loss of the novel system integrating with the dual-pressure ORC scheme is reduced to 13.21 MW compare to that of existing process accounts to 34.92 MW, and 88.21% of avoidable endogenous exergy destructions are recovered from waste heat sources. The proposed energy conservation approach in this study can be extended to some other similar chemical processes to achieve the maximum energy and exergy savings.