A revision of transcritical power cycle with reheat enhancement is proposed in this paper. Energy analysis is carried out to investigate parametric effects on cycle performance, and further detailed cost and economic analysis is conducted to evaluate the feasibility of the reheat cycle in practical applications. CO2 is chosen as the working fluid and heat source is from the geothermal energy in the present study. Results show that reheat pressure is a very important parameter affecting the cycle performance, and its optimal value corresponding to the maximum cycle performance is that makes the same expansion ratio across each stage turbine. There is more potential for regeneration enhancement in the reheat cycle, since the exhaust out of the turbine has a higher temperature than without reheat.
From the economic analysis and optimization, it is found that in both cycles the cost minimization is obtained at a corresponding optimal value of the high pressure which is significantly lower than that maximizing the cycle performance based on the first law of thermodynamics. This is due to the fact that the turbine and pump costs are dominant over other major components considered and their costs increase significant with the high operating pressure. The comparison of their unit costs reveal the existence of a critical high pressure for a given turbine inlet temperature Th above which reheat cycle is more cost effective than the baseline. And this value of the critical pressure increases with Th.
Overall, reheat enhancement method has great potential to improve thermal efficiency and especially net work output of transcritical power cycle using a low-grade geothermal heat source.