Thermo-economic Assessment of an Organic Rankine Cycle System for Repowering Application in a Landfill Biogas Power Plant

Abstract

Marca Ambiental is a Brazilian company that collects and treats solid waste from Grande Vitória, state of Espírito Santo, since 1997. In order to recovery this waste energy, mainly the landfill biogas, the company installed a steam power plant, in 2008, generating 1 MW of electricity. A study showed that greater efficiency and electric power, by recovering the landfill biogas energy, would be possible using internal combustion engines (ICE). This first repowering has already occurred using three internal combustion engine gensets, generating more than 3 MW of electricity. This work carried out a thermo-economic analyse for this plant new repowering, using organic Rankine cycle (ORC) systems. The energy and exergy balances showed that, although more than 40% of the biogas energy is converted into electricity, more than 54% is lost through exhaust gases (27.2%) and cooling water (27.4%), which represent, respectively, 14.13% and 4.12% of the biogas total exergy. The simulation and economic evaluation of this repowering, using ORC systems, shows technical and economic feasibility, respectively, for 400 kW and 300 kW of additional electricity generation.