(361b) CFD Simulations of the Fuel Reactor of a Coal-Fired Chemical Looping Combustor

Due to its impact on global climate change the future utilization of coal for power generation will require responsible carbon management (CM). CO₂ separation is the more costly part of CM, not sequestration, because of the energy penalty associated with gas separation to obtain a CO₂-rich stream.  Chemical Looping Combustion (CLC), in which an oxygen carrier is used to provide the oxygen for combustion, inherently separates CO₂ but requires two reaction vessels, an Air Reactor (AR) and a Fuel Reactor (FR).  The carrier is oxidized in the AR, separated from the hot, vitiated air stream and transported to the FR where it oxidizes the hydrocarbon fuel, yielding an exhaust gas stream of mainly H₂O and CO₂. The reduced carrier then returns to the air reactor for regeneration, hence the term ?looping.?  The net chemical reaction and energy release is identical to that of conventional combustion of the fuel.  In the FR, the solid coal fuel must be heated by the recycled metal oxide, driving off moisture and volatile material.  The remaining char must be gasified by H₂O (or CO₂), which is recycled from the product stream.  The gaseous product of these reactions must then contact the carrier before leaving the bed to obtain complete conversion to H₂O and CO₂.  Further, the reduced carrier particles must be removed from the bed and returned to the air reactor without any accompanying unburned fuel.  This paper presents a simulation of the gas-particle granular flow, with heat transfer and chemical reactions, in the FR.  Accurate simulation of the segregation processes, depending on particle density and size differences between the carrier and the fuel, allows the design of a reactor with the desired behaviour.