Effects of Calcination Conditions on the Properties of Lime

Mullins, Rita; Hatfield, John D.

doi:10.1520/stp41937s

Cited by 5 publications

(5 citation statements)

References 2 publications

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“…Reported experimental measurements of sorption capacities for various types of carbonates are not numerous. Those found in the literature (Potter, 1969;Borgwardt and Harvey, 1972;Mullins and Hatfield, 1970) have been used along with our own experimental data for comparison with the theoretical predictions of eq 9.…”

Section: Resultsmentioning

confidence: 99%

Influence of Porosity of Calcium Carbonates on Their Reactivity with Sulfur Dioxide

Hartman¹,

Pata²,

Coughlin³

1978

Ind. Eng. Chem. Proc. Des. Dev.

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An extended grain theory that takes into account local reductions in porosity of reacting particles has been employed to correlate their capacities to react with sulfur dioxide in flue gas. This approach provides better agreement with experimental results than the application of a simpler structural model based on uniform conditions throughout the particle. Experimental measurements show that the natural porosity persists during the calcination process and that the carbonate rocks already porous prior to their calcination are, in general, better suited for the sulfation reaction than common, dense limestones.

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Section: Resultsmentioning

confidence: 99%

Influence of Porosity of Calcium Carbonates on Their Reactivity with Sulfur Dioxide

Hartman¹,

Pata²,

Coughlin³

1978

Ind. Eng. Chem. Proc. Des. Dev.

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“…Limes with wider pores generally have smaller surface areas and react more slowly (Borgwardt and Harvey, 1972; Ulerich et al, 1978), but show higher ultimate conversion (Ulerich et al, 1978). There is therefore a trade-off to be considered in choosing the proper conditions for limestone calcination, since the choice of conditions is known to influence the pore structure of the lime produced (Mullins and Hatfield, 1970; McClellan and Eades, 1970; Ulerich et al, 1978). Bhatia andPerlmutter (1980, 1981a) and Gavalas (1980) have developed random pore models to correlate reaction behaviour with the internal pore structure.…”

Section: Conclusion and Significancementioning

confidence: 99%

Effect of the product layer on the kinetics of the CO₂‐lime reaction

Bhatia¹,

Perlmutter²

1983

AIChE Journal

609

551

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The kinetics of reaction between COZ and lime is investigated in the range of 673 to 998 K with a view to examining the effects of product layer deposition and variations in the limestone calcination atmosphere. The reaction is initially rapid and chemically controlled and goes through a sudden transition to a much slower regime controlled by diffusion in the product CaCOs layer. The magnitude of the estimated product layer diffusivity is in the range of m2/s, the corresponding activation energy is 88.9 f 3.7 kJ/mol below 688 K and 179.2 f 7.0 kJ/mol above that temperature, suggestive of solid state diffusion. Plausible mechanisms are discussed. to SCOPEThe effect of pore structure and the influence of product layer diffusion on the CO&me reaction has been examined in the temperature range of 673 to 998 K under COz levels varying from 10 to 42% in nitrogen. The data is analyzed by means of the random pore model (Bhatia and Perlmutter, 1980, 1981a), and intrinsic rate constants as well as product layer diifusion coefficients are determined. Product layer diffusion coefficients for calcines prepared under varying levels of COZ in nitrogen are compared, and the role of solid state processes in the product layer diffusion process is examined.

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“…Since the pore structure area and porosity of solids can often be adjusted by sintering, the above analysis should indicate suitable criteriafor selecting conditions for such a pretreatment. This is especially true for limestones since the pore volume distributions of their calcines are strongly dependent on the calcining atmosphere and temperature (Ulerich et al, 1978;McClellan and Eades, 1970;Mullins and Hatfield, 1970). …”

Section: Optimal Pore Structurementioning

confidence: 99%

The effect of pore structure on fluid‐solid reactions: Application to the SO₂‐lime reaction

1981

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The effect of varying pore structures on the kinetics of fluid-solid reactions is investigated through the random pore model developed in prior papers Perlmutter, 1980, 1981). By considering several idealized pore-size distributions it is shown that a solid having a uniform pore size is intrinsically less reactive than one possessing a pore-size distribution. For solids with bimodal pore size distributions optimal structures are shown to exist for which the reactivity is a maximum.Numerical solutions were obtained to the model equations for various values of the parameters characterizing the pore structure, the diffusion, and the chemical kinetics. The results show that the conversion-time behavior and the expected ultimate conversion can be very sensitive to variations in surface area and porosity for reactions accompanied by an increase in volume of the solid phase.These findings are in agreement with experimental literature on the SO 2-1' ime reaction (Ulerich e t al., 1978; Borgwardt and Harvey, 1972;Potter, 1969; Falkenberry and Slack, 1968) and the model is shown to fit the data of Borgwardt (1970), and of Coughlin (1974, 1976). It is seen that this reaction is diffusion controlled under the conditions of Hartman and Coughlin, in consonance with their own finding using the grain model, and a prior Pigford and Sliger (1973) interpretation. The temperature behavior of the diffusion coefficient in the product layer suggests the participation of an activated process, possibly a solid state diffusion step. SCOPEResults are reported on the effects of pore structure differences on the reaction behavior of solids, particularly in terms of variations in surface area, porosity, and dispersion in the pore size distribution. The analysis utilizes the random pore model developed by Perlmutter (1980,1981), representing a further development of these prior treatments.To demonstrate its use the model is applied to the data of Borgwardt (1970) and Coughlin (1974, 1976) on the lime-S02 reaction. The evaluation includes examination of the relative diffusional and kinetic resistances, of the incomplete conversions arising from pore closure in the solid, and of optimal pore distributions. Further comparisons are made with experimental reports of Ulerich et al. (1978), Borgwardt (1970), and Falkenberry and Slack (1968), to relate porestructure to the frequently observed differences in reaction behavior. CONCLUSIONS AND SIGNIFICANCEAn analysis of various simple pore size distributions shows that of all the pore structures with the same surface area and porosity, the one with pores of uniform size offers the least intrinsic reactivity. For bimodal pore size distributions optimal structures exist for which the reactivity is a maximum. Such results may offer guidance in the compaction of microporous solids by suggesting the desired pore structure.As expected, reactivity generally increases with surface area, but such variation can reduce ultimate conversion by more rapidly plugging pores a t the particle surface. Practical...

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Effects of Calcination Conditions on the Properties of Lime

Cited by 5 publications

References 2 publications

Influence of Porosity of Calcium Carbonates on Their Reactivity with Sulfur Dioxide

Influence of Porosity of Calcium Carbonates on Their Reactivity with Sulfur Dioxide

Effect of the product layer on the kinetics of the CO₂‐lime reaction

The effect of pore structure on fluid‐solid reactions: Application to the SO₂‐lime reaction

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Effects of Calcination Conditions on the Properties of Lime

Cited by 5 publications

References 2 publications

Influence of Porosity of Calcium Carbonates on Their Reactivity with Sulfur Dioxide

Influence of Porosity of Calcium Carbonates on Their Reactivity with Sulfur Dioxide

Effect of the product layer on the kinetics of the CO2‐lime reaction

The effect of pore structure on fluid‐solid reactions: Application to the SO2‐lime reaction

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Product

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Effect of the product layer on the kinetics of the CO₂‐lime reaction

The effect of pore structure on fluid‐solid reactions: Application to the SO₂‐lime reaction