Fate of NO and Ammonia in Chemical Looping Combustion─Investigation in a 300 W Chemical Looping Combustion Reactor System

Chemical looping combustion (CLC) is a novel combustion concept that transfers oxygen from air to fuel using an oxygen carrier that circulates between an air reactor and a fuel reactor. Thus, the combustion products, H2O and CO2, are obtained in a separate flow, and ideally, a pure CO2 gas stream is obtained after condensation of H2O. Consequently, CLC has a unique potential for avoiding the high costs and energy penalties of CO2 capture. Further, NO emissions can potentially be avoided. CLC is flameless, and the temperature is too low for the formation of thermal NOx. Moreover, fuel NOx and prompt NOx do not form in the air reactor in the absence of fuel. In the fuel reactor, the absence of oxygen prevents normal NOx formation. However, when using fuels containing nitrogen, NO may form in the fuel reactor because the oxygen carrier can oxidize fuel nitrogen compounds. To achieve a CO2 stream suited for storage, NO must be removed. Dependent upon how NO is removed, the process could be free from any NO emissions. NO formation and NO reduction were investigated in a 300 W CLC reactor by adding either NH3 or NO. The work involved two different oxygen carriers, Linz–Donawitz (LD) slag and ilmenite, two temperatures, 850 and 900°C, two circulation rates, and different flows of syngas fuel. Further, operation without fuel with a fully and partially oxidized oxygen carrier was studied. For LD slag, lower fuel flow promoted the formation of NO and decreased the reduction of NO. Likewise, higher temperatures raised NO formation and lowered NO reduction. Ilmenite, however, was by far more superior with respect to NO. Thus, NO formation only occurred in the absence of fuel and with a fully oxidized oxygen carrier. Likewise, NO was fully reduced to N2 for all conditions, except in the absence of fuel and with fully oxidized ilmenite.