INVESTIGATION OF PULVERIZED COAL COMBUSTORS AND GASIFIERS: MULTIPLE SUB-REACTOR MODEL AND EXPERIMENTAL RESULTS
Abstract
A continuous stirred tank reactor model is developed for combustion and gasification of pulverized coal or hydrocarbon fuels. Elementary gas phase reactions are used for wet carbon monoxide and methane combustion. Global reaction mechanisms are used for hydrocarbons other than methane. Coal mass loss due to pyrolysis is modeled using a competing reaction method. Realistic combustion characteristics are ascribed to the pyrolysis products by approximating their composition. A shrinking core model is used for char reactions with oxygen, water vapor and carbon dioxide. A unique method is developed for determining the particle size distribution in the reactor. Char particles are assumed to enter at constant size, but variations in residence time produce a distribution of particle sizes in the reactor. Using a power law approximation for variation of the effective carbon rate coefficient with particle radius, the particle size distribution may be determined by integrating over the allowed residence times in the reactor. This method compensates for the change of effective carbon radius with increased residence time and provides accurate prediction for a very wide range of throughput. Conditions from equilibrium to blowout may be predicted over a range of equivalence ratios from 0.5 to 10.0. The CSTR coal model is used as a building block for multiple sub-reactor modeling of pulverized coal combustors and gasifiers. Model predictions are compared to exhaust data from small scale cyclone and jet reactors investigated in this work and to internal data from a large experimental furnace at IJmuiden, Holland. Model accuracy ranges from fair to excellent for both exhaust and internal predictions. In addition to providing data for model comparison, the experimental results show that both the cyclone and swirled jet reactors may be used for low calorific value coal gasification. Problems with the small scale of the experiments, particularly slag deposition and coal feed fluctuations, were encountered but do not invalidate the results.
Degree
Ph.D.
Subject Area
Mechanical engineering
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