A Comparative Study of Superheat Utilization Measures of Extraction Steam in Double Reheat Power Plants

Abstract

The extremely high superheat degree of regenerative extraction steam in double reheat systems lead to a large temperature difference in the heat transfer process and worse thermal performance. This paper presents two typical systems that can contribute to the reasonable use of the extraction steam superheat. These systems are double reheat system with outer steam coolers and double reheat system with a regenerative steam turbine. Thermodynamic and techno-economic analyses are conducted to reveal the energy-saving effects of different systems. The results show that: the power generation efficiency of the system with outer steam coolers increases by 0.16%-points compared with the conventional double reheat system. The power generation efficiency of the system with a regenerative steam turbine can further increase by 0.51% points. Moreover, the cost of electricity of the system with a regenerative steam turbine is relatively lower than the system with outer steam coolers. This indicates that the two measures are both effective to use the superheat of the extraction steam. In addition, the system with a regenerative steam turbine is better than the system with outer steam coolers in both thermal and economic performances.