UBC Theses and Dissertations
Chemical looping combustion : cold model hydrodynamics and modeling of methane combustion Xu, Min
A novel interconnected fluidized bed (IFB) reactor with a bypass line for chemical looping combustion (CLC) has been developed to overcome the problem of short residence time of oxygen carrier in the air reactor. A comprehensive hydrodynamic study was carried out on the cold-flow model of the proposed reactor. Detailed mapping of the operating conditions for the reactor system was studied. Pressure transducers were applied to investigate the pressure loops and the cross-sectional average solids hold-up along the air reactor. Solids circulation flux between the two reactors was measured using butterfly valves by estimating the time interval for collecting a given volume of solids. Helium was used as gas tracer for gas leakage measurement. The experiments examined the gas leakage from air reactor to fuel reactor, from fuel reactor to air reactor, from loop-seals to fuel reactor and from fuel reactor to the cyclone. For scaling consideration, the cold-flow reactor was operated with fluidizing gas mixture of helium and air to simulate the hydrodynamics of the hot unit. The effect of density ratio of solids to gas on the solids circulation flux, pressure loops and voidage distribution along the air reactor was investigated. The connection between cold unit and hot unit is achieved by applying a scaling law. It can be stated that the cold-flow model operated with fluidizing gas mixture of 96 vol% helium and 4 vol% air can be used to simulate the hydrodynamics of an atmospheric CLC hot unit. A comprehensive model for the investigation of the reactor is introduced by combining fluidization properties and a particle population balance for calculation of the bed particle conversion, considering the chemical reaction of a single particle. The dimensionless parameters, Mrfuel and Mrair, which represent the mass ratio of input oxidized-particles to the input fuel in unit time for the fuel reactor and the mass ratio of reduced-particles to the input oxygen in unit time for the air reactor, respectively, are introduced. The model shows that Mrfuel should be more than 50 for achieving fuel conversion of 90% in the fuel reactor and Mrair should be more than 60 for achieving oxygen conversion of 85% in the air reactor. A procedure for optimizing the performance of the atmospheric CLC reactor is developed. The modeling analysis indicated that the optimum operating condition of an atmospheric CLC reactor hot unit should be chosen as follows: fuel capacity is 80 kW, Ua0=6.6 m/s, Uf0= 0.076 m/s, UA1=4Umf, UA2=1Umf, and the temperature in air reactor is 1223 K and in fuel reactor is 1173 K.
Item Citations and Data
Attribution-NonCommercial-NoDerivatives 4.0 International