Thermodynamic and exergoeconomic evaluation of biothermogen h₂ cogeneration plant integrating orc and kalina cycles

¹ Department of Mechanical Engineering, Topfaith University, Mkpatak, Akwa Ibom State, Nigeria.
² Mechanical Engineering, University of Calabar, Calabar, Cross River State Nigeria
³ Department of Mechanical Engineering, Michael Okpara University of Agriculture, Umudike, Abia State Nigeria

^* Corresponding Author Email: uk.akpan@topfaith.edu.ng 08030789651

Abstract

This study presents a thermodynamic and exergoeconomic evaluation of the Biothermogen H2 Cogeneration Plant, which integrates the Organic Rankine Cycle (ORC) and Kalina cycle for combined power generation, cooling, and hydrogen production using cassava peel biomass as the primaray fuel. With the hot water temperature fixed at 70 °C, the plant achieved an energy efficiency of 44.24% and an exergy efficiency of 21.32%, producing 3.58 kg of hydrogen per day. Under these operating conditions, the Kalina turbine generated 179.7 kW of power and delivered 1757 kW of cooling, while the ORC turbine ensured stable power output. Exergoeconomic analysis showed that the biomass combustor, driven by cassava peel, experienced the largest exergy destruction (31,090 kW) but was dominated by capital investment costs ($361.1/hr). Significant exergy destruction was also observed in the Kalina vapour generator (627.9 kW), ORC vapour generator (161.1 kW), and dryer (2390 kW), making them the most cost-intensive units. The ORC subsystem maintained a steady exergy input profile with gradually declining demand, whereas the Kalina subsystem absorbed more energy, peaking at approximately 18,000 kW before declining due to inefficiencies. Overall, the plant demonstrates stable operation with moderate efficiency and manageable economic performance, though improvements are required in high-destruction subsystems to enhance both thermodynamic and cost effectiveness.