(653b) Attrition Prediction and Reactive Jet Cup Testing of Oxygen Carriers for Chemical Looping Combustion

Novel technologies for chemical productions and carbon capture utilizing circulating fluidized bed (CFB) reactor configurations have garnered much attention in recent years. An example of these technologies is the chemical looping combustion (CLC) scheme. CLC provides an increase in power efficiencies for lower cost, while providing low energy penalty carbon capture, than traditional combustion or gasification processes that additionally utilize CO₂ capture. Chemical looping combustion uses metal oxide particles often termed “oxygen carriers” in a cyclic redox mode using two separate reactors termed the fuel and air reactors, respectively. Uncertainty lies in the chemical looping’s economic feasibility, which is partially due to the required solids makeup rate. Attrition due to impact and wear affect the solids makeup rate needed in CLC systems. Additionally, an oxygen carriers structure can be severely affected by the extreme conditions it experiences during operation. This includes high temperatures (800-1000°C) and shrinking/expanding of the particles due to the reduction/oxidation of the oxygen carrier. This can lead to additional change in the oxygen carriers structure such as crack formation and pore structural changes which can affect the overall oxygen carrier resistance to attrit.

This work investigates attrition of oxygen carriers for CLC on two fronts: (1) development of a simple spreadsheet model to help predict attrition expected in different CFB systems and (2) design and operation of a high-temperature, reactive jet-cup to help validate a portion of the model. The spreadsheet model uses developed models for predicting attrition rates in various portions of CFB units including: fluidized beds, cyclones, standpipes, impactors, risers, and corners such as L-valves. The model uses inputs based off the material properties (hardness, wear constant, impact constant, and fracture toughness), gas properties, flows, temperature, and the dimensions and number of each configuration encountered in the CFB system. An example modelling case using hematite as an oxygen carrier is performed using the design aspects for the 50kW_th chemical looping reactor at the National Energy Technology Laboratory (NETL). Additionally, the model can be used to perform a sensitivity analysis on key configurations and variables that could affect attrition the most. Additionally, the design of a reactive jet cup will be discussed as a novel determination of how thermal and chemical stresses undergone by oxygen carriers affect the overall attrition rates of the oxygen carrier. Investigation of a hematite oxygen carrier will be presented at a room temperature attrition test to show best case scenario for attrition of the oxygen carrier as well as under hot temperatures under both inert and reactive cases. For the reactive cases, the oxygen carrier is tested under fluidized bed conditions in methane/air redox schemes with nitrogen as a diluent. After specific reduction and oxidization cycles, attrition studies using the jet portion of the reactor is conducted to test the attrition rate observed.