ABSTRACT

The study investigated the thermodynamic and thermo-environmental analysis of a solar and biomass based trigeneration energy system for power, cooling, and domestic hot water production. The system is powered by municipal waste burnt in an incinerator, and a solar tower for an embedded gas turbine with natural gas as a supplementary fuel. It comprises a simple organic Rankine cycle (ORC) unit for power production, a vapour absorption system (VAS) for refrigeration, and a gas turbine unit energised by a solar tower and minimal supply of natural gas. The objectives were to model and analyse the system from a thermodynamic, exergoeconomic and thermo-environmental perspective. Accordingly, several thermo-environmental indicators were considered including the exergetic utility index (EUI), exergo thermal index (ETI), waste exergy ratio (WER), and sustainability index (SI). The system was simulated using a developed code written in Engineering Equation Solver (EES). The results show that the systems net output, cooling capacity, and the quantity of cooling water is 6.128 MW, 131.1 kW, and, 65.14 kg/s (at 75 oC) respectively. Also, the energy and exergy efficiencies were observed as 66.68 % and 53 %, respectively. Furthermore, the solar tower contributes to reduction of natural gas for firing the system at 633.6 kg/h thereby aiding reduction of carbon emissions to the environment.  In terms of exergy destruction, the incinerator and combustion chamber had the highest share of the total in the system. The exergoeconomic analysis suggests little reduction in the investment costs of the gas turbine air compressor, and the incinerator which has nearly hundred per cent exergoeconomic factors. Lastly, the thermo-environmental parameters: EUI, ETI, WER, and SI were recorded as 0.6992, 0.9161, 1.092, and 0.6109, respectively for the entire system. This demonstrates the environmental friendless of the system due to very high ETI stemming from almost complete utilization of the energy stream with minimal discharge temperature to the atmosphere