Performance investigation of a power generation system with CO₂ transcritical rankine cycle

As a natural working fluid, CO₂ has been widely used in refrigeration and heat pump systems due to its good thermophycical properties such as higher values of density, latent heat, specific heat and thermal conductivity etc. It can also be employed for power generation from low temperature heat resources including renewables and industry waste heat. However, the low temperature CO₂ power generation system and its associated thermodynamic power cycles need to be well designed, evaluated and optimised. A research project has been carried out on low temperature power generation and heat recovery with CO₂ transcritical (T-CO₂) Rankine cycles. A small scale test rig was developed for the experimental investigations consisting of: A CO₂ turbine, CO₂ plate recuperator, air cooled condenser, liquid receiver, CO₂ liquid pump and CO₂ gas generator. The CO₂ power generation system was heated by a thermal oil rig with the oil heated by the exhaust gas of an 80 kW_e CHP unit. Preliminary experimental results show that the T-CO₂ Rankine Cycle is applicable for the low temperature heat to power generation although more efficiency improvements are needed. To further evaluate the system performance, a detailed model of the tested CO₂ power generation system was developed and used to simulate the system performance at different operating conditions such as heat source and sink temperatures to establish optimisation parameters.