Technical and Economical Evaluation Of Landfill-Biogas Fired Combined Cycle Plants

ABSTRACT

Many cities are taking advantage of gas extracted from urban solid waste or USW landfills. The landfill gas is used as fuel in internal combustion engines (ICE). This is possible when the gas has been previously scrubbed and conditioned. Natural-gas-fired combined cycle plants (gas turbine, heat recovery boiler and steam turbine) can achieve overall system electrical efficiencies of 60%. On the other hand, an Organic Rankine Cycle (ORC) yields efficiencies of 10-20% by using low temperature heat sources, such as solar heat, turbine or ICE exhaust gas. In this context, by adding a power generator to an ORC and an ICE plant, it's possible to increase the overall power production by recovering 5-10% of the fuel energy content. This is in addition to the 35-40% power generated by the ICE. Thus, overall primary fuel-to-electricity efficiencies between 40% to 50% (based on the fuel's lower heating value or LHV) are possible, while using a “free” waste-derived fuel. In this article, we present a methodology based on heat integration for the conceptual design of landfill-gas fired combined cycle plants which integrate ICE and ORC technologies. The methodology has been applied to evaluate the repowering of landfill gas plant by retrofitting an ORC-based combined cycle into an existing biogas fired ICE plant, with a nominal output of 6 MWe, located in Monterrey, Mexico.

Keywords:

• Combined Cycle
• Energy Planning
• Landfill Biogas
• Internal Combustion Engine
• Organic Rankine Cycle
• Pinch Method
• Urban Solid Waste