Thermodynamic modeling and analysis of the heat integration and power generation in pig manure supercritical water gasification system

Highlights: • Supercritical water gasification of pig manure for power generation was simulated. • The Exergy Sankey diagram shows the largest destruction occurs in exchangers. • Modified system exergy efficiency favors an efficient heat exchanger network. • The effect of operating parameters on exergy efficiency was investigated. • An efficient zero-carbon emission system was achieved by involving a steam turbine. A tremendous amount of livestock manure is produced every day, and its harmless and efficient utilization is of profound significance for environmental protection and alternative energy supply. Supercritical water gasification (SCWG) is an efficient and clean technology for high-moisture waste utilization. However, very few researchers have studied the SCWG of manure from system-level modeling. Here, an original or reference pig manure SCWG plant is established for power generation based on previous studies. Detailed exergy analysis shows that the most significant part of exergy destruction occurs in the recuperation process, accounting for 38.05% of total exergy loss. Then, several optimizations were made in a modified system, focusing on a better layout of heat exchangers and critical streams. The modified system had a substantial gain of 23% in overall exergy efficiency and produced 14.12 MW power at an electric efficiency of 27.7%, much higher than 2.08 MW and 5.07% in the original system. Sensitivity analysis further proves that increasing feedstock concentration, preheating temperature, and turbine parameters while decreasing the water-slurry ratio can increase total system efficiency. The efficient multi-stage heat exchanger network and steam turbine in this paper are preferred for SCWG of pig manure, considering system capacity, complexity, and zero-carbon emission.