POTENTIAL OF TRIGENERATIVE WASTE HEAT RECOVERY CO2- MIXTURE TRANSCRITICAL POWER PLANTS FOR INCREASING THE SUSTAINABILITY OF DISTRICT HEATING AND COOLING NETWORKS

The waste heat released by high-temperature processes can be exploited by power cycle designed for full electric or combined heat and power applications, with the potential to cover even the cooling demand in a trigenerative perspective. The use of CO2-based mixtures as working fluids for power cycles can be a promising solution for power production. These systems present a rejected heat in a temperature range (50–180 °C) that allows, depending on the needs, an effective coupling with a district heating and cooling network. This work investigates the potential of trigenerative system adopting CO2based power cycles which exploit the residual thermal power of the exhaust gases of a small-scale gas turbine. First, the performances of lithium bromide absorption chiller are investigated for various heat source levels, adopting different configuration. Then, various designs of CO2-based power cycles are simulated focusing on the coupling with both the district heating and the chiller. A sensitivity analysis on the cycle minimum temperature is presented, evidencing that CO2 mixtures can achieve remarkable net electric efficiency values even at high cycle minimum temperatures, marking a significant difference with respect to CO2 cycles. Considering the yearly demand of district heating and cooling, keeping the electric output at design value, the economic profitability of the investment is characterized presenting the LCOE of the retrofitted solution, considered comparable with actual selling prices.