Small pore closure and the deactivation of the limestone sulfation reaction

Simons, Girard A.; Garman, A.R.

doi:10.1002/aic.690320910

“…In accordance with the above remarks, the experimental evidence in most of the studies of the literature indicates strong effects of the pore size distribution on the overall reactivity of the calcined solids (Borgwardt and Harvey, 1972;Wen and Ishida, 1973;Coughlin, 1974,1976;Ulerich et al, 1977;Vogel et al, 1977;Hasler et al, 1984;Simons and Garman, 1986;Yu, 1987;Gullett and Bruce, 1987;Zarkanitis and Sotirchos, 1989;Zarkanitis, 1991). Unfortunately, the immense volume of information that has been accumulated over the years on the reaction of calcined limestones and dolomites with SO2 is not applicable to SO2 emissions control by limestones and dolomites under PFBC conditions.…”

Section: Background Informationsupporting

confidence: 55%

Removal of H{sub 2}S and SO{sub 2} by CaCO{sub 3}-based sorbents at high pressures. Semiannual report, August 1995--January 1996

Sotirchos¹

1996

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“…The reaction of calcined limestones (primarily) and dolomites with SO 2 has been the subject of extensive investigation. In accordance with the above remarks, the experimental evidence in most of the studies of the literature indicates strong effects of the pore size distribution on the overall reactivity of the calcined solids (Borgwardt and Harvey, 1972;Wen and Ishida, 1973; Coughlin, 1974, 1976;Ulerich et al, 1977;Vogel et al, 1977;Hasler et al, 1984;Simons and Garman, 1986;Yu, 1987;Gullett and Bruce, 1987; Zarkanitis and 2 Sotirchos, 1989;Zarkanitis, 1991). Unfortunately, the immense volume of information that has been accumulated over the years on the reaction of calcined limestones and dolomites with SO 2 is not applicable to SO 2 emissions control by limestones and dolomites under PFBC conditions.…”

supporting

confidence: 56%

REMOVAL OF H{sub 2}S AND SO{sub 2} BY CaCO{sub 3}-BASED SORBENTS AT HIGH PRESSURES

Sotirchos¹

1998

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ii EXECUTIVE SUMMARYThe theoretical and experimental investigation of the mechanism of SO 2 and H 2 S removal by CaCO 3 -based sorbents (limestones and dolomites) in pressurized fluidized-bed coal combustors (PFBC) and high pressure gasifiers, respectively, is the main objective of this study.It is planned to carry out reactivity evolution experiments under simulated high pressure conditions or in high pressure thermogravimetric and, if needed, fluidized-bed reactor (high pressure) arrangements. The pore structure of fresh, heat-treated, and half-calcined solids (dolomites) will be analyzed using a variety of methods. Our work will focus on limestones and dolomites whose reaction with SO 2 or H 2 S under atmospheric conditions has been studied by us or other research groups in past studies. Several theoretical tools will be employed to analyze the obtained experimental data including a variable diffusivity shrinking-core model and models for diffusion, reaction, and structure evolution in chemically reacting porous solids.During the six months of this reporting period, more work was done on the study of the behavior of the sulfidation of calcined limestones in the presence of small amounts of oxygen. As it was mentioned in the previous report, the incentive for carrying out sulfidation experiments in the presence of oxygen was provided by the observation that some sulfidation experiments that were conducted as oxygen was accidentally leaking into the feed mixture of the reactor showed completely different behavior from that obtained in the absence of oxygen. Experiments were carried out in the thermogravimetric analysis system that we developed for studying gas-solid reactions at atmospheric or subambient pressures using the two CaCO 3 solids (Greer limestone and Iceland spar) that we employed in our previous experiments. It was decided to conduct more experiments on the sulfidation of calcined limestones in the presence of small amounts of oxygen because the experimental curves that were obtained in our past experiments not only exhibited unsatisfactory quantitative reproducibility, but also in a few cases, the solid material that was placed on the pan (initially CaCO 3 ) was completely converted to gaseous products during exposure to a N 2 -H 2 S atmosphere containing small amounts of oxygen (below 0.2-0.3%). The new results led to conclusions that were in agreements with those reached in our iii previous studies. For small oxygen concentrations, the weight gained by small particles of the calcined sample during sulfidation went through a maximum, whereas for oxygen concentrations above 0.5-0.8%, it increased continuously and could reach values corresponding to complete conversion of CaO to CaSO 4 .The above behavior was more pronounced for the Greer Limestone sample, which past studies had shown that it exhibited much lower resistance to intraparticle mass transport than the other sample (Iceland Spar). The large particles (297-350 µm) of Greer Limestone and Iceland Spar we used in the experiments did not sho...

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“…In accordance with the above remarks, the experimental evidence in most of the studies of the literature indicates strong effects of the pore size distribution on the overall reactivity of the calcined solids (Borgwardt and Harvey, 1972;Wen and Ishida, 1973;Coughlin, 1974, 1976;Ulerich et al, 1977;Vogel et al, 1977;Hasler et al, 1984;Simons and Garman, 1986;Yu, 1987;Gullett and Bruce, 1987;Zarkanitis and Sotirchos, 1989;Zarkanitis, 1991 Smith et al (1982).…”

Section: Background Informationmentioning

confidence: 60%

“…The reaction of calcined limestones (primarily) and dolomites with SO 2 has been the subject of extensive investigation. In accordance with the above remarks, the experimental evidence in most of the studies of the literature indicates strong effects of the pore size distribution on the overall reactivity of the calcined solids (Borgwardt and Harvey, 1972;Wen and Ishida, 1973; Coughlin, 1974, 1976;Ulerich et al, 1977;Vogel et al, 1977;Hasler et al, 1984;Simons and Garman, 1986;Yu, 1987;Gullett and Bruce, 1987; Zarkanitis and 2 Sotirchos, 1989;Zarkanitis, 1991). Unfortunately, the immense volume of information that has been accumulated over the years on the reaction of calcined limestones and dolomites with SO 2 is not applicable to SO 2 emissions control by limestones and dolomites under PFBC conditions.…”

Section: Executive Summarymentioning

confidence: 60%

REMOVAL OF H2S AND SO2 BY CaCO3-BASED SORBENTS AT HIGH PRESSURES

Sotirchos¹

2000

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iii EXECUTIVE SUMMARYThe mechanism of the removal of SO 2 and H 2 S by CaCO 3 -based sorbents in pressurized fluidized-bed coal combustors (PFBC) and high pressure gasifiers was investigated in this project. Reactivity evolution experiments were carried out in thermogravimetric apparatuses both under simulated high pressure conditions and at high pressures. Experiments at high pressure were conducted in a high pressure thermogravimetric arrangement that was set up and developed under this project. Two calcitic solids of high calcium carbonate content (over 97%) were employed in the experiments: a fine-grained distributed by Greer Limestone Co. (Greer Limestone) and a solid supplied in the form of large calcitic crystals (Iceland Spar). The decision to work with these solids was mainly based on the fact that they have been employed in several past studies of sulfation, sulfidation, and calcination in our laboratory, and therefore, a large volume of data on their performance under different conditions was available for comparison purposes. In addition to the experimental studies, work was also done on the development of rigorous mathematical models for the description of the occurrence of simultaneous processes (e.g., calcination and sulfation and carbonation and sulfation) in the interior of porous solids and for the simulation of the evolution of the pore structure of porous solids that undergo chemical transformation in their interior.A number of processes were investigated in our experiments in addition to the reaction of CaCO 3 solids with SO 2 or H 2 S under high pressure (noncalcining) conditions. Specifically, we investigated: i) the simultaneous occurrence of the calcination and sulfation (reaction with SO 2 ) of limestones, ii) the simultaneous occurrence of the calcination and sulfidation (reaction with H 2 S) of limestones, iii) the simultaneous occurrence of the carbonation and sulfation of calcined limestones, and iv) the sulfidation of limestones in the presence of small amounts of oxygen.Our high pressure experiments on the sulfation and sulfidation of limestones under noncalcining conditions revealed that the effects of pressure on the behavior of these processes are mainly manifested through its effects on the concentration of the sulfuration species (SO 2 or H 2 S). iv Experiments at different pressures but corresponding to the same concentration of SO 2 or H 2 S gave weight vs. time curves that showed very small differences from each other. This was construed as an indication that the pressure of reaction did not affect the structure of the product layer formed around the shrinking core of the unreacted material and that transport in that layer took place in a mode that was not influenced by the total pressure. Some experiments were also carried out on the effects of pressure on the reaction of calcined CaCO 3 with SO 2 or H 2 S, and conclusions similar to those reached for the indirect reactions were derived.The experiments on the simultaneous occurrence of the calcination and sulfuration (...

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Small pore closure and the deactivation of the limestone sulfation reaction

Cited by 83 publications

References 26 publications

Removal of H{sub 2}S and SO{sub 2} by CaCO{sub 3}-based sorbents at high pressures. Semiannual report, August 1995--January 1996

Removal of H{sub 2}S and SO{sub 2} by CaCO{sub 3}-based sorbents at high pressures. Semiannual report, August 1995--January 1996

REMOVAL OF H{sub 2}S AND SO{sub 2} BY CaCO{sub 3}-BASED SORBENTS AT HIGH PRESSURES

REMOVAL OF H2S AND SO2 BY CaCO3-BASED SORBENTS AT HIGH PRESSURES

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