Use of Pyrite Cinder as an Iron-Based Oxygen Carrier in Coal-Fueled Chemical Looping Combustion

Abstract

Selection of low cost oxygen carriers with abundant reserves while being environmentally benign is preferred in the chemical looping combustion (CLC) process. Pyrite cinder is characterized as a waste material and poses potential environmental risk while having issues associated with disposal. In this study, pyrite cinder was utilized as a potential iron-based oxygen carrier. The reactivity, recyclability, and attrition behavior of pyrite cinder were evaluated in a laboratory scale fluidized bed reactor. The oxygen carrier to fuel ratio, steam concentration in the fluidization gas, fuel particle size, and temperature on the reactivity of pyrite cinder were investigated. The attrition behavior of pyrite cinder under both inert and reacting conditions was evaluated. The chemical and physical analyses of pyrite cinder confirmed it as a ready source of oxygen carrier. It displayed sufficient reactivity to convert char gasification products to CO2 and H2O. The performance of the system was found to be improved with respect to the carbon conversion rate and gasification rate under the following conditions: higher oxygen carrier to fuel ratio, higher steam concentration in the fluidization gas, smaller fuel particle size, and higher temperature. Cyclic redox tests of pyrite cinder over 20 cycles revealed that it behaved steadily with a stable CO2 yield being achieved. Additionally, pyrite cinder exhibited good resistance to sintering and agglomeration. The attrition behavior of pyrite cinder under inert conditions showed that the collisions of pyrite cinder particles with each other and with reactor wall at high superficial fluidization velocity was the predominant factor influencing its attrition behavior. The cyclic attrition tests showed that the attrition rate was higher in the initial cycle, but this reduced as the redox cycles progressed. It can be inferred from this study that pyrite cinder is a suitable iron-based oxygen carrier for CLC of coal while alleviating the environmental problems associated with its disposal.