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Keywords
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absorption refrigeration cycle, biogas upgrading cycle, combined power plant, exergy analysis, molten carbonate fuel cell
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Abstract
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The main purpose of this study is to develop an integrated structure of si-
multaneous generation of electricity and refrigeration as the main product and
hot water as a by‐product. This proposed structure consists of a water scrub-
bing 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 elec-
trical and overall efficiencies are 78.68% and 79.86%, respectively. The in-
vestigation 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 effi-
ciency 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.
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