3E investigation of ORC and absorption chiller for repowering a Brazilian landfill biogas power plant

Abstract

The expansion of biomass, biogas, and waste-to-energy (WtE) technologies is one of the strategies established by the Government of the State of Espírito Santo (Brazil) to increase renewable electricity generation and support decarbonization. In this context, landfill biogas power plants represent an important opportunity for repowering through waste heat recovery (WHR). However, under tropical operating conditions, internal combustion engines commonly operate under derating due to high ambient temperature and humidity while simultaneously rejecting significant amounts of thermal energy through exhaust gases and cooling water. This scenario motivated an R&D Project to investigate integrated WHR alternatives using Organic Rankine Cycle (ORC) and absorption chiller technologies based on a combined energy, exergy, and economic (3E) assessment. Mass, energy, and exergy balances were performed to determine the thermodynamic limits of WHR, using EES software. Two ORC configurations and an absorption cooling system for intake-air and biogas conditioning were simulated using IPSEpro 8.0 software. Using EES software, economic feasibility was evaluated through equipment sizing, parametric cost estimation, and investment indicators, including net present value (NPV), internal rate of return (IRR), and payback period. The results demonstrated that the exhaust-gas-driven ORC is economically feasible, generating an additional 423 kW of electricity, corresponding to approximately 14% of plant repowering. In contrast, the cooling-water-driven ORC was not economically attractive. However, utilizing the same low-grade heat in an absorption chiller for intake-air and biogas conditioning provided an equivalent gain of 452 kW of electricity, which represents approximately 15% of additional repowering. The integrated viable solution requires a total investment of US$ 2.48 million, achieves a discounted payback period of 3.57 years, and increases the overall plant repowering capacity by approximately 29%. These findings demonstrate that matching waste heat sources with recovery technologies according to their thermodynamic quality provides an effective strategy for improving the efficiency and more sustainability of landfill biogas power plants.