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Title: The kinetics of sulfation of calcium oxide. [Quarterly] project status report, February 27, 1989--May 31, 1989

Abstract

Studies of the sulfation rate behavior show an initial fast rate followed by a rate decrease. It is generally agreed that product layer diffusion limitations are the explanation for this behavior. Many investigators tried to model this observed rate change, more or less successfully. No agreement has been reached, however, as to the value of the produce layer diffusivity. Hence, in this work we want to investigate the mechanism of this process. In addition to understanding the initial kinetics, two questions will be focused on. First, we should understand what is diffusing. It appears that the driving force for this diffusion phenomenon is not first order with the SO{sub 2} concentration in the gas. This would indicate that some other, intermediary step is occurring. The second question concerns the composition of the product layer. Different conditions at the start of the reaction were observed to produce different diffusion rates at a later stage. The microscopic appearance of the product layer also appeared to be different.

Authors:
;
Publication Date:
Research Org.:
Massachusetts Inst. of Tech., Cambridge, MA (United States)
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
10167950
Report Number(s):
DOE/PC/89754-T6
ON: DE92018751
DOE Contract Number:
FG22-89PC89754
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: [1989]
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 20 FOSSIL-FUELED POWER PLANTS; 54 ENVIRONMENTAL SCIENCES; CALCIUM OXIDES; SORPTIVE PROPERTIES; SULFATION; CHEMICAL REACTION KINETICS; SULFUR DIOXIDE; AIR POLLUTION CONTROL; PROGRESS REPORT; DIFFUSION; POROSITY; LAYERS; 010800; 400201; 200202; 540120; WASTE MANAGEMENT; CHEMICAL AND PHYSICOCHEMICAL PROPERTIES; NOXIOUS GAS AND PARTICULATE EMISSIONS; CHEMICALS MONITORING AND TRANSPORT

Citation Formats

Sarofim, A.F., and Longwell, J.P. The kinetics of sulfation of calcium oxide. [Quarterly] project status report, February 27, 1989--May 31, 1989. United States: N. p., 1989. Web. doi:10.2172/10167950.
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Sarofim, A.F., & Longwell, J.P. The kinetics of sulfation of calcium oxide. [Quarterly] project status report, February 27, 1989--May 31, 1989. United States. doi:10.2172/10167950.
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Sarofim, A.F., and Longwell, J.P. Sun . "The kinetics of sulfation of calcium oxide. [Quarterly] project status report, February 27, 1989--May 31, 1989". United States. doi:10.2172/10167950. https://www.osti.gov/servlets/purl/10167950.
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@article{osti_10167950,
title = {The kinetics of sulfation of calcium oxide. [Quarterly] project status report, February 27, 1989--May 31, 1989},
author = {Sarofim, A.F. and Longwell, J.P.},
abstractNote = {Studies of the sulfation rate behavior show an initial fast rate followed by a rate decrease. It is generally agreed that product layer diffusion limitations are the explanation for this behavior. Many investigators tried to model this observed rate change, more or less successfully. No agreement has been reached, however, as to the value of the produce layer diffusivity. Hence, in this work we want to investigate the mechanism of this process. In addition to understanding the initial kinetics, two questions will be focused on. First, we should understand what is diffusing. It appears that the driving force for this diffusion phenomenon is not first order with the SO{sub 2} concentration in the gas. This would indicate that some other, intermediary step is occurring. The second question concerns the composition of the product layer. Different conditions at the start of the reaction were observed to produce different diffusion rates at a later stage. The microscopic appearance of the product layer also appeared to be different.},
doi = {10.2172/10167950},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Dec 31 00:00:00 EST 1989},
month = {Sun Dec 31 00:00:00 EST 1989}
}
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Technical Report:
View Technical Report (1.55 MB)
DOI:  10.2172/10167950
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  • ;
    Studies of the sulfation rate behavior show an initial fast rate followed by a rate decrease. This behavior has generally been interpreted as product layer diffusion limitations taking over after an initial kinetic rate regime. Many investigators tried to model this observed rate change, more or less successfully. No agreement has been reached, however, as to the value of the product layer diffusivity. In this work we want to investigate the mechanism of this process. During the last quarter, most attention has been paid to analyzing the results obtained earlier. In the light of some unexpected results, we returned tomore » the most fundamental question: what is the rate-limiting mechanism? It appeared that whatever the mechanism is, no rate ``constant`` could be used, since the rate is a function of the product layer composition, which changes during the reaction. When comparing the results obtained with different samples, however, it appeared that the best correlation was found if one assumes the limiting rate to occur at the CaSO{sub 4} interphase. This point of view has never been presented before and requires therefore a more attentive analysis.« less

  • ;
    The rate of sulfation of a CaO surface is rapid at first, limited by the intrinsic kinetics, but slows down with increasing conversion as a consequence of the increased resistance to diffusion through the product layer. The objectives of this study are to determine the intrinsic kinetics and the product layer diffusion pate by minimizing the resistances to gas-phase pore diffusion, and eliminating complications due to pore filling. This is achieved by the use of nonporous CaO. A wide range of particle sizes are used to change the relative importance of the regimes in which the intrinsic kinetics and productmore » layer diffusion control. The assumption of constant product layer diffusivity can then be tested and the variables that determine this diffusivity independently studied. Information on product layer diffusion can also be obtained from studies of porous particles after the pore mouths are all plugged and a uniform surface coating is obtained. This information on diffusion rate and intrinsic reactivity can then be combined with a geometrical model to describe the rate of reaction over the entire range of conversions and is particularly useful in treating the effect of particle size on conversion history.« less

  • ;
    The objectives of this study are to determine the intrinsic kinetics and the product layer diffusion rate by minimizing the resistances to gas-phase pore diffusion, and eliminating complications due to pore filling. In the report, a grain model was used to introduce the various potentially rate-limiting processes. It was compared with results obtained with a distributed pore model by Bhatia & Perlmutter (1981). Comparing the predicted behavior of the surface areas with conversion, it was even possible to compare experimental results with other models. The conclusion of this study was that, even thought the kinetic parameters obtained with different samplesmore » differed much more if product layer diffusion assumed rate-limiting rather than the surface reaction, the shape of the predicted curve approached the experimental findings so much better, that product layer diffusion is indeed most likely to be rate-limiting. (VC)« less

  • ;
    Studies of the sulfation rate behavior show an initial fast rate followed by a rate decrease. This behavior has generally been interpreted as product layer diffusion limitations taking over after an initial kinetic rate regime. Many investigators tried to model this observed rate change. As pore diffusion was a limiting phenomenon in most of the experiments, authors have used several pore models to described this complication, more or less successfully. Product layer diffusivity has been assumed to be constant as conversion increased; however, there is no general agreement as to its value. In this work we are investigating the mechanismmore » of this process with emphasis on measurement of product layer diffusivity and the surface reaction rate. Some additional experimental work was done to investigate the order and activation energy of the sulfation under different conditions. The effect of additives was studied again, by sprinkling some KCl or NaCl salt on top of partially reacted synthetic lime, in an effort to change the surface reaction rate rather than the diffusion rate.« less

  • The general objective of the project is to investigate the combustion behavior of single Coal-Water Slurry particles burning at high temperature environments. Both uncatalyzed as well catalyzed CWS drops with Calcium Magnesium Acetate (CMA) catalyst will be investigated. Emphasis will also be given in the effects of CMA on the sulfur capture during combustion.