Exergy analysis of a polygeneration-enabled district heating and cooling system based on gasification of refuse derived fuel

- A DHC system was modified to incorporate a gasifier and gas upgrading equipment.
- The gasifier uses refuse derived fuel as feedstock.
- New system can produce various products in addition to heat, cold, and electricity.
- System performance was evaluated from exergetic and exergoeconomic perspectives.
- Production of char and syngas is the most favorable for the system capability.

District heating and cooling (DHC) systems, modified or retrofitted with integration of gasifiers and gas upgrading equipment, represent promising alternatives to traditional approaches since various scenarios of products complementary to heat, cold, and electricity can be realized, namely: char only; char and syngas; char, synthetic natural gas (SNG) and hydrogen (H2); and char, syngas, SNG and H2. This manuscript evaluates a polygeneration-enabled DHC system in detail (operation during a typical year) from exergetic and exergoeconomic perspectives. The base DHC system utilizes natural gas as fuel with a nominal capacity of 29 MW heat, 35 MW of cold, and 5 MW of electricity. The retrofit employs refuse derived fuel (RDF) as feedstock to an atmospheric gasifier with downstream gas clean-up, a gas turbine, and a heat recovery steam generator along with heat exchangers for integration with the base DHC system. The exergy analysis revealed that the polygeneration system presents adequate performance at all scenarios established. Among the sets of value-added products the combination of char and syngas is the most beneficial as the system efficiency reaches a value of ∼72%. The outcomes of the exergoeconomic analysis support the exergy results. The lower production costs for value-added products are achieved for the maximum simultaneous char and syngas production, with each of these costs estimated to be 6.1 USD/GJ.