Surface area of calcium oxide and kinetics of calcium sulfide formation

Borgwardt, Robert H.; Roache, Nancy F.; Bruce, Kevin R.

doi:10.1002/ep.670030215

Cited by 67 publications

(71 citation statements)

References 9 publications

(5 reference statements)

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“…Chemical compositions of various limestones can be found in Chan et al (1970), Chang et al (1984), Borgwardt and Roache (1984), Borgwardt et al (1987), and Fuller et al (1987). The specific· surface area of most of the8.e stones is low (generally less than 1m 2 /g) and the natural porosity ranges from 0 to 8% (Borgwardt and Roache, 1984;Hartman et al, 1978;Borgwardt et al, 1987). Whereas limestones are considered amorphous, Scanning Electron…”

Section: 1) Limestonementioning

confidence: 99%

Structural studies in limestone sulfidation

Fenouil¹

1993

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Section: 1) Limestonementioning

confidence: 99%

Structural studies in limestone sulfidation

Fenouil¹

1993

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“…The first by Borgwardt 47 showed that for micrometer size particles of CaO the rate of CaS formation is most probably limited by diffusion through the product layer surrounding individual CaO grains.…”

Section: Development Of a Model For The Absorption Processmentioning

confidence: 99%

Engineering a New Material for Hot Gas Cleanup

Wheelock¹,

Doraiswamy²,

Constant³

2003

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The overall purpose of this project was to develop a superior, regenerable, calcium-based sorbent for desulfurizing hot coal gas with the sorbent being in the form of small pellets made with a layered structure such that each pellet consists of a highly reactive lime core enclosed within a porous protective shell of strong but relatively inert material. The sorbent can be very useful for hot gas cleanup in advanced power generation systems where problems have been encountered with presently available materials.An economical method of preparing the desired material was demonstrated with a laboratory-scale revolving drum pelletizer. Core-in-shell pellets were produced by first pelletizing powdered limestone or other calcium-bearing material to make the pellet cores, and then the cores were coated with a mixture of powdered alumina and limestone to make the shells.The core-in-shell pellets were subsequently calcined at 1373 K (1100°C) to sinter the shell material and convert CaCO 3 to CaO. The resulting product was shown to be highly reactive and a very good sorbent for H 2 S at temperatures in the range of 1113 to 1193 K (840 to 920°C) which corresponds well with the outlet temperatures of some coal gasifiers. The product was also shown to be both strong and attrition resistant, and that it can be regenerated by a cyclic oxidation and reduction process.A preliminary evaluation of the material showed that while it was capable of withstanding repeated sulfidation and regeneration, the reactivity of the sorbent tended to decline iv with usage due to CaO sintering. Also it was found that the compressive strength of the shell material depends on the relative proportions of alumina and limestone as well as their particle size distributions. Therefore, an extensive study of formulation and preparation conditions was conducted to improve the performance of both the core and shell materials. It was subsequently determined that MgO tends to stabilize the high-temperature reactivity of CaO. Therefore, a sorbent prepared from dolomite withstands the effects of repeated sulfidation and regeneration better than one prepared from limestone. It was also determined that both the compressive strength and attrition resistance of core-in-shell pellets depend on shell thickness and that the compressive strength can be improved by reducing both the particle size and amount of limestone in the shell preparation mixture.A semiempirical model was also found which seems to adequately represent the absorption process. This model can be used for analyzing and predicting sorbent performance, and, therefore, it can provide guidance for any additional development which may be required.

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“…Studies of S O 2 removal at high pressures have been carried out both with carbonates and precalcined solids Newby et al, 1980;Ulerich et al, 1982; Hayhurst, 1984, 1987;Bulewicz et al, 1986. However, because of the aforementioned complexities, with the exception of the general conclusion that favorable desulfurization is possible under PFBC conditions, there is not much agreement in the literature on the e ects of the various -4-parameters on the process.…”

Section: Background Informationmentioning

confidence: 99%

“…Hayhurst 1984, 1987, for example, found that the reaction rate of precalcined limestones in a uidized-bed reactor decreases with an increase in the operating pressure, both in the absence and presence of C O 2 . W orking with a laboratory-size PFBC, Bulewicz et al 1986 observed an increase in the sorption capacity of C a -based sorbents chalk, limestone, and dolomite with an increase in pressure up to 2 atm, but further increase in pressure caused a reduction in the sorption capacity of all samples. Similar observations were made by Jansson et al 1982.…”

mentioning

confidence: 97%

“…4 is the main reaction occurring in the combustor. Similarly, PFBC data from Exxon Hoke et al, 1977 with uncalcined Grove limestone showed that most of the unreacted C ain the bed for C O 2 partial pressures above the equilibrium value existed in the form of C a C O 3 .Studies of S O 2 removal at high pressures have been carried out both with carbonates and precalcined solids Newby et al, 1980;Ulerich et al, 1982; Hayhurst, 1984, 1987;Bulewicz et al, 1986. However, because of the aforementioned complexities, with the exception of the general conclusion that favorable desulfurization is possible under PFBC conditions, there is not much agreement in the literature on the e ects of the various -4-parameters on the process.…”

mentioning

confidence: 99%

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Removal of H2S and SO2 by CaCO3-Based Sorbents at High Pressure

Sotirchos¹

1998

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The theoretical and experimental investigation of the mechanism of S O 2 and H 2 S removal by C a C O 3 -based sorbents limestones and dolomites in pressurized uidized-bed coal combustors PFBC and high pressure gasi ers, respectively, is the main objective of this study. It is planned to carry out reactivity e v olution experiments under simulated high pressure conditions or in high pressure thermogravimetric and, if needed, uidizedbedreactor 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 S O 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 di usivity shrinking-core model and models for di usion, reaction, and structure evolution in chemically reacting porous solids.During the six months of this reporting period, work was primarily done on the study of the behavior of the sul dation of limestones under sequential calcination conditions in the presence of small amounts of oxygen and the development of a stochastic simulation code for determining the extent of pore volume trapping formation of inaccessible pore space in gas-solid reactions accompanied by pore volume reduction such as the sulfation and sul dation of calcined limestones and dolomites.The incentive for carrying out sul dation experiments in the presence of oxygen was provided by the observation that some sul dation experiments that were conducted as oxygen was accidentally leaking into the feed mixture of the reactor showed completely di erent 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. The two C a C O 3 solids Greer limestone and Iceland spar that we employed in our previous experiments were used in the sul dation -iiiand calcination experiments, and the concentration of oxygen that was introduced in the H 2 S-containing stream that was fed to the reactor ranged from 0.2 to 2.5. The obtained results showed that the behavior of the sul dation of limestone depended strongly, in both a qualitative and a quantitative sense, on the level of the oxygen concentration in the feed. For small oxygen concentrations, the weight gained by the calcined sample during sul dation in a N 2 -H 2 S atmosphere went through a maximum, whereas for oxygen concentrations above 0.5-0.6, it increased continuously. A constant weight value was reached at large reaction times in both cases. The value of the weight gain at the maximum increased with increasing concentration of oxygen in the feed, and the same behavior was manifested by the constant value reached at large times. When a maximum was present in the weight gain vs. time curve, the constant value was lower than that expecte...

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Surface area of calcium oxide and kinetics of calcium sulfide formation

Cited by 67 publications

References 9 publications

Structural studies in limestone sulfidation

Structural studies in limestone sulfidation

Engineering a New Material for Hot Gas Cleanup

Removal of H2S and SO2 by CaCO3-Based Sorbents at High Pressure

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