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Title: A model of coal particle drying in fluidized bed combustion reactor

Abstract

Experimental and theoretical investigation on drying of a single coal particle in fluidized bed combustor is presented. Coal particle drying was considered via the moist shrinking core mechanism. The results of the drying test runs of low-rank Serbian coals were used for experimental verification of the model. The temperature of the coal particle center was measured, assuming that drying was completed when the temperature equalled 100{sup o}C. The influence of different parameters (thermal conductivity and specific heat capacity of coal, fluidized bed temperature, moisture content and superheating of steam) on drying time and temperature profile within the coal particle was analyzed by a parametric analysis. The experimentally obtained results confirmed that the moist shrinking core mechanism can be applied for the mathematical description of a coal particle drying, while dependence between drying time and coal particle radius, a square law relationship, implicates heat transfer control of the process and confirms the validity of assumptions used in modeling.

Authors:
; ;  [1]
  1. Natural Resources Canada, Ottawa, ON (Canada). CANMET, Energy Technology Centre
Publication Date:
OSTI Identifier:
20885779
Resource Type:
Journal Article
Resource Relation:
Journal Name: Energy Sources, Part A: Recovery, Utilization, and Environmental Effects; Journal Volume: 29; Journal Issue: 3
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; FLUIDIZED-BED COMBUSTORS; PARTICLES; COAL; DRYING; PARAMETRIC ANALYSIS; MATHEMATICAL MODELS; FLUIDIZED BEDS; BROWN COAL; LIGNITE

Citation Formats

Komatina, M., Manovic, V., and Saljnikov, A. A model of coal particle drying in fluidized bed combustion reactor. United States: N. p., 2007. Web. doi:10.1080/00908310600688796.
Komatina, M., Manovic, V., & Saljnikov, A. A model of coal particle drying in fluidized bed combustion reactor. United States. doi:10.1080/00908310600688796.
Komatina, M., Manovic, V., and Saljnikov, A. Thu . "A model of coal particle drying in fluidized bed combustion reactor". United States. doi:10.1080/00908310600688796.
@article{osti_20885779,
title = {A model of coal particle drying in fluidized bed combustion reactor},
author = {Komatina, M. and Manovic, V. and Saljnikov, A.},
abstractNote = {Experimental and theoretical investigation on drying of a single coal particle in fluidized bed combustor is presented. Coal particle drying was considered via the moist shrinking core mechanism. The results of the drying test runs of low-rank Serbian coals were used for experimental verification of the model. The temperature of the coal particle center was measured, assuming that drying was completed when the temperature equalled 100{sup o}C. The influence of different parameters (thermal conductivity and specific heat capacity of coal, fluidized bed temperature, moisture content and superheating of steam) on drying time and temperature profile within the coal particle was analyzed by a parametric analysis. The experimentally obtained results confirmed that the moist shrinking core mechanism can be applied for the mathematical description of a coal particle drying, while dependence between drying time and coal particle radius, a square law relationship, implicates heat transfer control of the process and confirms the validity of assumptions used in modeling.},
doi = {10.1080/00908310600688796},
journal = {Energy Sources, Part A: Recovery, Utilization, and Environmental Effects},
number = 3,
volume = 29,
place = {United States},
year = {Thu Feb 15 00:00:00 EST 2007},
month = {Thu Feb 15 00:00:00 EST 2007}
}
  • In the second part, the model is applied to the study of an atmospheric fluidized-bed coal combustor. Case studies are investigated to show the effects of a number of parameters. Proper representation of the grid region and use of actual feed distributions are shown to be essential to the prediction of combustor performance. Better particle elutriation and single-particle combustion sub-models are found to be key requirements for improved combustor modelling.
  • The purpose of this study was to investigate the thermal behavior of coal during devolatilization in fluidized bed. Temperatures in the center of single coal particle were measured by thermocouple. Two coals were tested (brown coal Bogovina and lignite Kosovo), using dry coal particle, shaped into spherical form of diameters 7 and 10 mm, in temperature range from 300 to 850{sup o}C. Unsteady behavior of coal particle during heating and devolatilization in fluidized bed was described by a model that takes into account heat transfer between bed and particle surface, heat transfer through particle and an endothermic chemical reaction ofmore » first-order. Based on the mathematical model analysis and compared with experimental results, values of heat conductivity {lambda}{sub C} and heat capacity (C-p) of coal were determined. The best agreement was obtained for constant thermal properties, for brown coal {lambda}{sub C} = 0.20 W/mK and C{sub p} = 1200 J/kgK and for lignite {lambda}{sub C} = 0.17 W/mK and C-p = 1100 J/kgK.« less
  • Intra-particle temperatures and the emissions of carbon dioxide, carbon monoxide, and total hydrocarbons have been measured during devolatilization and char combustion of large spheres (3--20 mm diameter) of selected fuels. The fuels range from a carbon-rich, bituminous coal to two different, sub-bituminous coals of very different moisture and ash contents, to a highly volatile and ash-rich sewage sludge and to beech wood with the highest volatile content. To obtain results under various fluidized bed combustor conditions and to independently change the governing parameters, the experiments were performed in three different laboratory-scale fluidized bed combustors (FBCs). The beds` temperatures varied betweenmore » 700 and 950 C, the oxygen partial pressure in the fluidizing gas varied from 0 to 21 kPa, the superficial gas velocity from 0.3 to 9 m/s, the voidage of the fluidized particles in the beds was usually 0.5 or 0.997, and the mean diameter of the fluidized particles was 200 or 900 {micro}m. A dynamic simulation model has been developed to describe the behavior of a single fuel particle during its lifetime in a combustor. The model considers drying, devolatilization, volatile and char combustion, external and internal heat and mass transfer, and changing fuel properties. Calculated temperature profiles and emission data are in good agreement with observations.« less
  • Beds of silica sand were fluidized by mixtures of C{sub 3}H{sub 8}, CH{sub 4}, or CO with air. Staring from cold the way such a bed behaved before it reached a steady state was observed visually. In addition, high-speed cine films were taken, as well as measurements of the loudness of the noise emitted. These beds behave in a way indicating that such hot gas mixtures at up to 1000{degrees}C do not burn in the interstices between the sand particles. Instead, combustion occurs either above the bed or in the ascending bubbles. Measurements of the diameter (d{sub ig}) of amore » bubble made immediately prior to ignition confirmed that the ignition temperature (T{sub ig}) of the bubble varies with d{sub ig} {proportional to} exp (E{sub ig}/RT{sub ig}), so that larger bubbles ignite at lower temperatures. It proved possible to generate combustion of these gas mixtures in the particulate phase by adding Pt-coated catalyst pellets. This leads to a new model for the burning of char particles in a fluidized bed. In the model, char is first oxidized to CO with the reaction C{sub s} + 1/20{sup b} {yields} CO occurring mainly inside the pores of each particle. The resulting CO burns either above the bed or in bubbles rising up the bed, but not in the particulate phase. Considerable uncertainties exist as to the correct values of Nusselt and Sherwood numbers, as well as of, e.g., the intrinsic rate constant for the initial production of CO. However, the model is capable of predicting the temperatures observed for char particles burning in fluidized beds. This paper addresses some of the problems of O{sub 2} diffusing inside the pores of a char particle and then reacting to give CO.« less