Use of a Waste Heat Boiler to Capture Energy From Flammable Noncondensable Gas at Geothermal Power Plants

摘要

A study was performed to determine if a waste heat boiler could economically capture energy from a flammable noncondensable gas stream at a geothermal power plant. Vendors of combustion and waste heat boiler equipment were contacted to gain purchased equipment costs. Operating costs related to the waste heat boiler were estimated. The economics of H_2S abatement were then evaluated both with and without waste heat recovery to determine the cost effectiveness of the waste heat recovery boiler. Additional information was learned from the vendors regarding the various types of waste heat boilers that could be used in this application, as well as how the boilers are integrated with the upstream combustion device. Different options for the materials of construction of the combustion unit and waste heat boiler were also investigated to help mitigate the potential for corrosion from sulfuric acid condensation. The economic and design details for the waste heat boiler as an integral part of a burn/scrub H_2S abatement process are discussed in this paper. For the application being considered, the waste heat boiler was estimated to have a payback of 25 to 34 months when used as an integral part of the burn/scrub H_2S abatement system. The waste heat boiler economics were also evaluated for the case where a different H_2S abatement technology was used (i.e., Stretford) such that the combustion unit and boiler could be located after the H_2S had already been removed; in this scenario, the payback on the waste heat boiler was about 12 to 17 months due to the slightly higher steam recovery and a less expensive waste heat boiler. For the cases considered, the waste heat boiler would generate steam equivalent to about 2%-3% of the inlet flow of geothermal steam.