Modeling of the chemical-looping combustion of methane using a Cu-based oxygen-carrier

Abstract

A mathematical model for a bubbling fluidized bed has been developed to simulate the performance of the fuel-reactor in chemical looping combustion (CLC) systems. This model considers both the fluid dynamic of the fluidized bed and freeboard and the kinetics of reduction of the oxygen-carrier, here CuO impregnated on alumina. The main outputs of the model are the conversion of the carrier and the gas composition at the reactor exit, the axial profiles of gas concentrations and the fluid dynamical structure of the reactor. The model was validated using measurements when burning CH 4 in a 10 kW th prototype using a Cu-based oxygen-carrier. The influence of the circulation rate of solids, the load of fuel gas, the reactor temperature and size of the oxygen-carrier particles were analyzed. Combustion efficiencies predicted by the model showed a good agreement with measurements. Having validated the model, the implications for designing and optimizing a fuel-reactor were as flows. The inventory of solids for a high conversion of the fuel was sensitive to the reactor's temperature, the solids' circulation rate and the extent to which the solids entering to the reactor had been regenerated. The optimal ratio of * Corresponding author. oxygen-carrier to fuel was found to be 1.7 to 4 for the Cu-based oxygen-carrier used here. In this range, the inventory of solids to obtain a combustion efficiency of 99.9% at 1073 K was less than 130 kg/MW th . In addition, the model's results were very sensitive to the resistance to gas diffusing between the emulsion and bubble phases in the bed, to the decay of solids' concentration in the freeboard and to the efficiency contact between gas and solids in the freeboard. Thus, a simplified model, ignoring any restriction to gas and solids contacting each other, will under-predict the inventory of solids by a factor of 2 to 10.Keywords: Chemical-looping combustion; methane; natural gas; copper oxide; fluidization;

Numerical Analyses of Heterogeneous CLC Reaction and Transport Processes in Large Oxygen Carrier Particles

“…In the past two decades, plenty of investigations on CLC, implemented with either fluidized bed or fixed bed reactors at laboratory and pilot scales, have been conducted [1][2][3][4][5][6]. Fluidized bed-based CLC, typically with a riser as an air reactor and a bubbling bed as a fuel reactor, is characterized by advantages such as higher heat transfer efficiency, continuous operation and stable production of hot gas.…”

Modeling and Simulation of Chemical Looping Combustion Using a Copper-Based Oxygen Carrier in a Double-Loop Circulating Fluidized Bed Reactor System

“…The outlet concentrations of different components show reasonable agreement with the measurements despite a over-prediction with the CH 4 and O 2 conversion. This can be explained as the CuO used in the current study is slight different from the literature, 32,34 which would lead to a certain amount of uncertainties of the kinetic parameters. The reactor performance can be characterised by CH 4 conversion, which expressed as:…”

“…The detailed kinetic parameters are listed in table 2. 32,34 The source term in the species mass balance equation for the j th species can be modelled by:…”

Numerical Investigation of Solid-Fueled Chemical Looping Combustion Process Utilizing Char for Carbon Capture

“…Initially, the particles of oxygen carrier accumulate in the fuel reactor under N 2 atmosphere. The initial volume fraction of solid phase is set to be 0.55 with the bed height of 1.1 m. The selected oxygen carrier is the so-called Cu14Al-I which contains 14 wt% of CuO as the active component and 86 wt% of inert Al 2 O 3 [61,62,72]. The detailed model parameters and initial conditions used in the simulations are summarized in Table 2.…”