Testing of a Novel Post Combustion Acid Removal Process for the Direct-Fired, Oxy-Combustion Allam Cycle Power Generation System

The Allam Cycle is a high-performance oxy-fuel, supercritical CO₂ power cycle that offers significant benefits over traditional fossil and hydrocarbon fuel-based power generation systems. A major benefit arises in the elimination of costly precombustion acid gas removal (AGR) for sulfur- (SO_x) and nitrogen-based (NO_x) impurities by utilizing a novel downstream cleanup process that utilizes NO_x first as a gas phase catalyst to effect SO_x oxidation, followed by NO_x removal. The basic reactions required for this process, which have been well demonstrated in several facilities for the cleanup of exhaust gasses, ultimately convert SO_x and NO_x species to sulfuric, nitric, and nitrous acids for removal from the supercritical CO₂ stream. The process results in simplified and significantly lower cost removal of these species and utilizes conditions inherent to the Allam Cycle that are ideally suited to facilitate this process. 8 Rivers Capital and the Energy & Environmental Research Center (EERC), supported by the state of North Dakota, the U.S. Department of Energy and an Industrial consortium from the State of North Dakota, are currently working together to test and optimize this novel impurity removal process for pressurized, semi-closed supercritical CO₂ cycles, such as the Allam Cycle. Both reaction kinetic modeling and on-site testing have been completed. Initial results show that both SO_x and NO_x can be substantially removed from CO₂-rich exhaust gas containing excess oxygen under 20 bar operating pressure utilizing a simple packed spray column. Sensitivity of the removal rate to the concentration of oxygen and NO_x was investigated. Follow-on work will focus on system optimization to improve removal efficiency and removal control, to minimize metallurgy and corrosion risks from handling concentrated acids, and to reduce overall capital cost and operating cost of the system.