Parametric study on the effects of a recuperator on the design and off-design performances for a CO2 transcritical power cycle for low temperature geothermal plants

Abstract

A CO2 transcritical power cycle (CDTPC) is a promising power system to utilize low temperature geothermal heat source. Many researchers mainly focus on the thermodynamic and thermo-economic performance analysis or optimization for a CDTPC, or compare the design performance of a CDTPC with that of organic Rankine cycle. The objective of this paper is to study the effects of a recuperator on the design and off-design performances of a CDTPC for low temperature geothermal plants. Detailed off-design mathematical models of the basic and regenerative CDTPCs are built to complete this study under the variable mass flow rates and temperatures of the geothermal water and the cooling water temperatures conditions by a sliding pressure operation control strategy. The results reveal that no matter how the geothermal water mass flow rate and temperature or the cooling water temperature vary, both the overall net power and overall thermal efficiency of the regenerative CDTPC system are higher than those of the basic CDTPC system. Meanwhile, a recuperator can improve the overall system performance of a CDTPC system under the both design and off-design conditions, although the recuperator might weaken the off-design behavior of some key components. In addition, a recuperator can improve off-design behaviors of the CO2 pump performance under the off-design conditions. The guidelines for the rotational speed listed in the tables for CO2 pumps might provide some reference for practical operation.