Evaluation of dust and gas explosion potential in chemical looping processes

The explosibility of metals typically used as oxygen carriers in chemical looping processes are reviewed. Chemical looping processes use intensified process conditions such as elevated temperatures and pressures to accelerate reduction and oxidation reactions of metals. A review of literature on metals indicates they are generally non-explosible under standard test conditions, however, at conditions used in chemical looping processes the opportunity to remove kinetic limitations exists resulting in reclassification of these dusts as marginally explosible under these circumstances. Potential locations and scenarios for explosions involving oxygen carriers in chemical looping processes are described. Operating conditions (temperature, pressure) and oxygen carrier qualities (base metal, support/loading) are reviewed for their effect on explosion severity parameters. These studies show explosions are unlikely to be severe in chemical looping reactors, but severity can increase while likelihood decreases in windboxes and in downstream process units following cooling. The potential for explosions where a metal oxide dust acts as the oxidizing agent for gaseous fuels through heterogeneous (chemical looping combustion – CLC) and homogenous (chemical looping oxygen uncoupling – CLOU) pathways as may be found in chemical looping processes is introduced, which we term a metal oxide reducing environment (MORE) explosion. Methane was shown to have the potential for the most serious consequences when reacting with copper- and manganese-oxides due to their reduction both being exothermic and increasing the quantity of gas present. Hematite and nickel oxide do not demonstrate this behaviour with common gaseous fuels. Potential prevention and mitigation strategies for explosions in chemical looping processes are briefly introduced. Particulate management strategies, venting, and downstream concerns are discussed.