Optimization of Hybrid Noncondensable Gas Removal System for a Flash Steam Geothermal Power Plant

Abstract

The energy required to operate the Noncondensable Gas (NCG) Removal System for the condenser of a flash steam geothermal power plant constitutes a significant parasitic load affecting the overall power production potential and efficiency of the generating unit. Hybrid vacuum systems, incorporating steam jet air ejectors and liquid ring vacuum pumps, have proven to be a more efficient alternative for traditional multi-stage steam jet air ejector systems in geothermal applications. The higher capital cost and installation cost of the hybrid vacuum system is more than offset by the reduced operating cost, but, for maximum benefit, the designer of the hybrid vacuum system must consider key process information to optimize the NCG Removal System design for each specific application. Both environmental and commercial factors must be considered along with the properties of the geothermal resource in the optimization of NCG Removal System design. Environmental factors such as ambient temperature and absolute barometric pressure physically limit the operating range of the liquid ring vacuum pump. The relative values of geothermal steam, cooling water and electrical power for the NCG Removal System must be considered in the division of the gas compression work between the steam jet air ejector stage and the vacuum pump stage. This paper defines the required operating parameters and illustrates how these parameters are used to optimize the NCG Removal System design for a typical flash steam geothermal power plant.