Simulation of a Circulating Fluidized Bed Combustor with Shrinking Core and Emission Models

Abstract

A Circulating Fluidized Bed Combustor (CFBC) is a highly efficient combustor. It can handle various types of solid fuels such as coal, biomass or agricultural wastes. Coal and biomass have been used as fuel to generate heat for a boiler in many industries. To predict the proper amount of mixed fuel and to reduce the emission from coal burning, a rigorous mathematical model for the CFBC is needed. This paper describes the CFBC model developed as additional subroutines working with ASPEN PLUS version 11.1. The model was divided into three parts: reaction, hydrodynamic, and gas emission. In the first part, the reactions in the combustor were represented by a Continuous Stirred Tank Reactor (CSTR) module. The module was modified by adding the shrinking core model for calculating the size and the weight fraction of particles in each region. In the second part, the hydrodynamics in CFBC were divided into two regions: a lower region with one interval, and an upper region with three intervals. In each region the characteristics, such as the height of the bed, void, and volume, were calculated and sent to CSTR module for adjusting reaction rates in the regions. In the third part, gas emission models were used to calculate the kinetic rates of NO, N2O and the conversion of SO2 to predict the emission to the environment.