Fuel reactor modelling in chemical-looping combustion of coal: 1. model formulation

A fundamental part of the reliability of the chemical-looping combution system when a solid fuel, such as coal, is fed to the reactor is based on the behaviour of the fuel reactor, which determines the conversion of the solid fuel. The objective of this work is to develop a model describing the fuel reactor in the chemical-looping combustion with coal (CLCC) process. The model is used to simulate the performance of the 1 MWth CLCC rig built in the Technology University of Darmstadt. The fuel reactor is a fluidized bed working at high velocity regime, using ilmenite as oxygen carrier. The developed model is based on semi-empirical correlations, and considers the reactor fluid dynamics, the coal conversion and the reaction of the oxygen carrier with evolved gases from coal. The efficiency of a carbon separation system is also considered in order to analyze this parameter on the fuel reactor performance. The main outputs of the model are presented in this work, i.e., (1) the fluid dynamics structure of the reactor; (2) the axial profiles of gas composition and flows (volatiles, CO, H-2, CO2 and H2O); (3) the conversion of the oxygen carrier and char in the reactor; (4) the char concentration in the reactor; (5) the gas composition and solids flow in the upper reactor exit; and (6) the char flow to the air reactor. From these outputs the oxygen demand of the flue gases and the CO2 capture efficiency are calculated. Simulations on the effect of the efficiency of the carbon separation system are presented. A highly efficient carbon separation system should be used to reach a high carbon capture value. Also incomplete combustion of gases is predicted in the fuel reactor, mainly from unconverted volatile matter. The model can be later used to obtain basic design parameters of the fuel reactor and optimize its operation. (C) 2012 Elsevier Ltd. All rights reserved.