Optimum operations and performance comparison of CO2-propane and CO2-R152a mixture-based transcritical power cycles recovering diesel power plant waste heat

Though CO2 power cycles are preferred for diesel engine waste heat recovery, a very high operating pressure of the CO2 power cycle is an issue of concern. To address this issue, in the present study, CO2-propane and CO2-R152a mixtures with various CO2 mass fractions are proposed as the working fluid of a regenerative transcritical power cycle recovering waste heat of a diesel power plant. To reduce the possibility of accidental fire hazard; the minimum permissible CO2 mass fraction is restricted to 0.3. It is observed that reducing CO2 mass fraction ensures higher output power and lesser levelized electricity cost (LEC), specifically at a lower turbine inlet pressure. Between two considered CO2-based mixture pairs, the transcritical cycle exhibits a superior performance with CO2-R152a-based mixtures. The LEC of the presented CO2-propane-based optimized cycle is about 6.36% lower compared to that of the optimized supercritical CO2 power cycle. For the CO2-R152a mixture-based cycle, the corresponding achievable reduction in LEC is about 15.20%. Turbine inlet pressures corresponding to the minimum LECs of the optimized CO2-propane and CO2-R152a mixture-based cycles are, respectively, close to 33% and 39% lower than that of the optimized supercritical CO2 power cycle. As R152a is less flammable than propane, an R152a-based mixture working fluid also ensures a safer operation compared to a propane-based mixture. [GRAPHICS] .

Automated summary

Using CO2-propane and CO2-R152a mixtures as working fluids can reduce the operating pressure of the CO2 cycle, resulting in higher output power and lower electricity costs.