An innovative integrated CCHP system with water scrubbing‐based biogas upgrading unit and molten carbonate fuel cell

Abstract

AbstractThe main purpose of this study is to develop an integrated structure of simultaneous generation of electricity and refrigeration as the main product and hot water as a by‐product. This proposed structure consists of a water scrubbing biogas upgrading process, molten carbonate fuel cell (MCFC) unit, gas/steam power (GSP) cycle, and absorption refrigeration (AR) system. In this regard, 10.71 kg/s untreated biogas enters the integrated system and 158,351 kW net power is produced. Wasted heat of the structure is utilized to generate cooling of 253.9 kW at a temperature of 243.6 K by applying the AR system and the rest of the heat is used to generate 8.391 kg/s hot water as the system byproducts. The process integration between the different parts has led to an increase in the thermal efficiency of the whole system so that the electrical and overall efficiencies are 78.68% and 79.86%, respectively. The investigation of the exergy study demonstrates that the exergy destruction of the entire structure is 71,859 kW, of which the turbine/compressor/pump section with 24,700 kW (with a share of 34.37% of the total) and MCFC/reformer section with 22,285 kW (with a share of 31.01% of the total) have the most irreversibility. The exergy efficiency of the hybrid structure is 71.06%. Through a parametric study, the present integrated system in various conditions is assessed. One of the results of main outcomes is the increase of overall efficiency up to 83.39% due to the reduction of inlet biogas methane mole content up to 50%. Rising the methane in inlet biogas, although leading to more production of system products, reduces the efficiencies of various parts of the system, including the MCFC unit and GSP cycle, as well as integrated system total efficiency.