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Title: Coal combustion: Effects of process conditions on char reactivity

Abstract

During the past quarter, we carried out a study of the kinetics of char combustion, assessed the reproducibility error of our experiments, and continued our systematic study of the effects of particle size and oxygen concentration on the reactivity of chars. The results from the kinetic study indicated that the rate expression for combustion of Illinois No. 6 chars is first order with respect to the oxygen concentration. The activation energy and the preexponential factor for this reaction were also calculated. The reproducibility error assessment shows that the average relative error increases with increasing particle size. Thus, the number of combustion runs needed for accurate measurements of the reaction rate increases with increasing particle size. For combustion in the regime of diffusional limitations, our results show the ignition temperature decreases with increasing pyrolysis heating rates, increasing coal particle size, decreasing heat treatment temperatures and increasing oxygen concentrations. The kinetic parameters (activation energy, preexponential rate factor, and order of reaction) for the combustion of Illinois No. 6 coal were determined using our thermogravimetric reactor with video microscopy imaging (TGA/VMI). In order to obtain a constant slope from the Arrhenius plot, the experiments were performed in the kinetic control regime. Our previousmore » results demonstrated that in this regime char reactivity is independent of pyrolysis heating rate, heat treatment temperature (HTT), soak time and particle size. For this study therefore, we chose to pyrolyze and combust particles from the 28--32 mesh (500--600 [mu]m) fraction of Illinois No. 6 coal.« less

Authors:
Publication Date:
Research Org.:
Rice Univ., Houston, TX (United States). Dept. of Chemical Engineering
Sponsoring Org.:
DOE; USDOE, Washington, DC (United States)
OSTI Identifier:
6746157
Alternate Identifier(s):
OSTI ID: 6746157; Legacy ID: DE93009689
Report Number(s):
DOE/PC/91307-T6
ON: DE93009689
DOE Contract Number:
FG22-91PC91307
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; CHARS; CHEMICAL REACTION KINETICS; COMBUSTION; POROSITY; COAL; ACTIVATION ENERGY; ARRHENIUS EQUATION; HEATING RATE; OXYGEN; PARTIAL PRESSURE; PARTICLE SIZE; PROGRESS REPORT; PYROLYSIS; THERMAL GRAVIMETRIC ANALYSIS; CARBONACEOUS MATERIALS; CHEMICAL ANALYSIS; CHEMICAL REACTIONS; DECOMPOSITION; DOCUMENT TYPES; ELEMENTS; ENERGY; ENERGY SOURCES; EQUATIONS; FOSSIL FUELS; FUELS; GRAVIMETRIC ANALYSIS; KINETICS; MATERIALS; NONMETALS; OXIDATION; PYROLYSIS PRODUCTS; QUANTITATIVE CHEMICAL ANALYSIS; REACTION KINETICS; SIZE; THERMAL ANALYSIS; THERMOCHEMICAL PROCESSES 014000* -- Coal, Lignite, & Peat-- Combustion

Citation Formats

Zygourakis, K. Coal combustion: Effects of process conditions on char reactivity. United States: N. p., 1992. Web. doi:10.2172/6746157.
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Zygourakis, K. Coal combustion: Effects of process conditions on char reactivity. United States. doi:10.2172/6746157.
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Zygourakis, K. Wed . "Coal combustion: Effects of process conditions on char reactivity". United States. doi:10.2172/6746157. https://www.osti.gov/servlets/purl/6746157.
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@article{osti_6746157,
title = {Coal combustion: Effects of process conditions on char reactivity},
author = {Zygourakis, K.},
abstractNote = {During the past quarter, we carried out a study of the kinetics of char combustion, assessed the reproducibility error of our experiments, and continued our systematic study of the effects of particle size and oxygen concentration on the reactivity of chars. The results from the kinetic study indicated that the rate expression for combustion of Illinois No. 6 chars is first order with respect to the oxygen concentration. The activation energy and the preexponential factor for this reaction were also calculated. The reproducibility error assessment shows that the average relative error increases with increasing particle size. Thus, the number of combustion runs needed for accurate measurements of the reaction rate increases with increasing particle size. For combustion in the regime of diffusional limitations, our results show the ignition temperature decreases with increasing pyrolysis heating rates, increasing coal particle size, decreasing heat treatment temperatures and increasing oxygen concentrations. The kinetic parameters (activation energy, preexponential rate factor, and order of reaction) for the combustion of Illinois No. 6 coal were determined using our thermogravimetric reactor with video microscopy imaging (TGA/VMI). In order to obtain a constant slope from the Arrhenius plot, the experiments were performed in the kinetic control regime. Our previous results demonstrated that in this regime char reactivity is independent of pyrolysis heating rate, heat treatment temperature (HTT), soak time and particle size. For this study therefore, we chose to pyrolyze and combust particles from the 28--32 mesh (500--600 [mu]m) fraction of Illinois No. 6 coal.},
doi = {10.2172/6746157},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Jan 01 00:00:00 EST 1992},
month = {Wed Jan 01 00:00:00 EST 1992}
}
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Technical Report:
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DOI:  10.2172/6746157
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  • During the past quarter, we carried out a study of the kinetics of char combustion, assessed the reproducibility error of our experiments, and continued our systematic study of the effects of particle size and oxygen concentration on the reactivity of chars. The results from the kinetic study indicated that the rate expression for combustion of Illinois No. 6 chars is first order with respect to the oxygen concentration. The activation energy and the preexponential factor for this reaction were also calculated. The reproducibility error assessment shows that the average relative error increases with increasing particle size. Thus, the number ofmore » combustion runs needed for accurate measurements of the reaction rate increases with increasing particle size. For combustion in the regime of diffusional limitations, our results show the ignition temperature decreases with increasing pyrolysis heating rates, increasing coal particle size, decreasing heat treatment temperatures and increasing oxygen concentrations. The kinetic parameters (activation energy, preexponential rate factor, and order of reaction) for the combustion of Illinois No. 6 coal were determined using our thermogravimetric reactor with video microscopy imaging (TGA/VMI). In order to obtain a constant slope from the Arrhenius plot, the experiments were performed in the kinetic control regime. Our previous results demonstrated that in this regime char reactivity is independent of pyrolysis heating rate, heat treatment temperature (HTT), soak time and particle size. For this study therefore, we chose to pyrolyze and combust particles from the 28--32 mesh (500--600 {mu}m) fraction of Illinois No. 6 coal.« less

  • During the past quarter, we systematically investigated the effects of particle size, pyrolysis heating rate, and heat treatment temperature on the reactivity of chars. The results show that pyrolysis heating rates or particle size do not affect the reactivity of chars in the kinetic control regime (420[degree]C). High heat treatment temperatures (HTT) slightly lowered the char intrinsic reactivities. When the char particles were reacted in the regime of diffusional limitations (625[degree]C), a significant effect of particle size was detected. We observed that decreasing final heat treatment temperatures resulted in small increases of the intrinsic reactivity for the smallest particles. Formore » the largest particles, however, the effect of decreasing HTT was dramatic. By lowering the HTT from 775 to 625[degree]C, the reactivity of chars at 625[degree]C increased by a factor of 6 for chars produced from 20--25 mesh coal particles. Finally, the shape of the reactivity patterns changed significantly as we moved from the regime of kinetic control to the regime of intraparticle diffusional limitations.« less

  • The project will quantify the effect of the following pyrolysis conditions on the macropore structure and on the subsequent reactivity of chars: (a) pyrolysis heating rate; (b) final heat treatment temperature (HTT); (c) duration of heat treatment at HTT (or soak time); (d) pyrolysis atmosphere (N{sub 2} or O{sub 2}/N{sub 2} mixtures); (e) coal particle size (100--1000 {mu}m in diameter); (f) sulfur-capturing additives (limestone); and (g) coal rank. Pyrolysis experiments will be carried out for three coals from the Argonne collection: (1) a high-volatile bituminous coal with high ash content (Illinois {number_sign}6), (2) a bituminous coal with low ash contentmore » (Utah Blind Canyon) and (3) a lower rank subbituminous coal (Wyodak-Anderson seam). A systematic study was carried out in the past quarter to validate the mathematical model for ignition phenomena presented in the previous quarterly report. Model predictions of the effect of pyrolysis heating rate, particle size, and oxygen concentration on ignition behavior are in excellent agreement with experimental results. Moreover, our results show that the model can be used to estimate the particle temperature during ignition and the minimum ignition temperature for various process conditions.« less

  • The project will quantify the effect of the following pyrolysis conditions on the macropore structure and on the subsequent reactivity of chars: (a) pyrolysis heating rate; (b) final heat treatment temperature (HTT); (c) duration of heat treatment at HTT (or soak time); (d) pyrolysis atmosphere (N{sub 2} or O{sub 2}/N{sub 2} mixtures); (e) coal particle size (100--1000 {mu}m in diameter); (f) sulfur-capturing additives (limestone); and (g) coal rank. Pyrolysis experiments will be carried out for three coals from the Argonne collection: (1) a high-volatile bituminous coal with high ash content (Illinois No. 6), (2) a bituminous coal with low ashmore » content (Utah Blind Canyon) and (3) a lower rank subbituminous coal (Wyodak-Anderson seam). A systematic parametric study was carried out in the past quarter to quantify the effect of different process parameters on the ignition phenomena. Using the mathematical model presented in the previous quarterly report, we investigated how char properties (porosity, particle size, macropore surface area, and micropore radius) and operating conditions (oxygen concentration, flow rate) affect ignition phenomena. In every case, we clearly identified the temperature range in which thermal ignitions may be expected. Model predictions will next be compared to experimental results to validate our theoretical model.« less

  • The project will quantify the effect of the following pyrolysis conditions on the macropore structure and on the subsequent reactivity of chars: (a) pyrolysis heating rate; (b) final heat treatment temperature; (c) duration of heat treatment at HTT (or soak time); (d) pyrolysis atmosphere (N{sub 2} or O{sub 2}/N{sub 2} mixtures); (e) coal particle size (100--1,000 {mu}m in diameter); (f) sulfur-capturing additives (limestone); and (g) coal rank. Pyrolysis experiments will be carried out for three coals from the Argonne collection: (1) a high-volatile bituminous coal with high ash content (Illinois No. 6), (2) a bituminous coal with low ash contentmore » (Utah Blind Canyon) and (3) a lower rank subbituminous coal (Wyodak-Anderson seam). A systematic study was carried out in the past quarter to validate the mathematical model for ignition phenomena presented in the previous quarterly report. Model predictions of the effect of pyrolysis heating rate, particle size, and oxygen concentration on ignition behavior are in excellent agreement with experimental results. Moreover, our results show that the model can be used to estimate the particle temperature during ignition and the minimum ignition temperature for various process conditions.« less