Transport properties of porous lime and their influence on the decomposition of porous compacts of calcium carbonate
TL;DR: In this paper, special experimental techniques have been developed to measure the thermal conductivity of porous lime and the diffusion coefficient of carbon dioxide through it, and measurements have been made on lime whose porosity varied in the range 0·45
About: This article is published in Chemical Engineering Science.The article was published on 1970-01-01. It has received 49 citations till now. The article focuses on the topics: Lime & Calcium carbonate.
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TL;DR: In this paper, a review of the literature on using lime from limestone to sequester CO 2 from combustion systems is presented, and the physical properties of calcined products after sintering and reaction are reviewed.
494 citations
Cites background from "Transport properties of porous lime..."
...All the models must include the diffusion of reactant or product gas through the internal voids [9,37,73,74]....
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TL;DR: The reversibility of the reaction CaCO3 ⇌ CaO+CO2 has been examined through a large number of cycles (up to 40), mainly at 866 °C as mentioned in this paper.
Abstract: The reversibility of the reaction CaCO3 ⇌ CaO+CO2 has been examined through a large number of cycles (up to 40), mainly at 866 °C. The decomposition to the oxide is always 100% but the reactivity of the oxide so formed to carbon dioxide falls off markedly after a rapid initial reaction. There is a large increase in surface area on going from the non-porous calcium carbonate to the oxide and this is due to the formation of pores, mostly very small (< 4 nm). The fast component of the back reaction is a surface reaction and the subsequent slow reaction is controlled by the slow diffusion of carbon dioxide through the newly formed carbonate layer. The reversibility of the reaction decreases with the number of cycles, rapidly at first and then more slowly: the first effect is probably due to loss of pore volume in the oxide and the second to sintering of the carbonate.
429 citations
TL;DR: Current understanding of fundamental aspects of the cyclic carbonation-calcination reactions of CaO such as its reversibility and kinetics are reviewed, and recent attempts to develop synthetic, CaO-based sorbents that possess high and cyclically stable CO2 uptakes are presented.
Abstract: The enormous anthropogenic emission of the greenhouse gas CO2 is most likely the main reason for climate change. Considering the continuing and indeed growing utilisation of fossil fuels for electricity generation and transportation purposes, development and implementation of processes that avoid the associated emissions of CO2 are urgently needed. CO2 capture and storage, commonly termed CCS, would be a possible mid-term solution to reduce the emissions of CO2 into the atmosphere. However, the costs associated with the currently available CO2 capture technology, that is, amine scrubbing, are prohibitively high, thus making the development of new CO2 sorbents a highly important research challenge. Indeed, CaO, readily obtained through the calcination of naturally occurring limestone, has been proposed as an alternative CO2 sorbent that could substantially reduce the costs of CO2 capture. However, one of the major drawbacks of using CaO derived from natural sources is its rapidly decreasing CO2 uptake capacity with repeated carbonation-calcination reactions. Here, we review the current understanding of fundamental aspects of the cyclic carbonation-calcination reactions of CaO such as its reversibility and kinetics. Subsequently, recent attempts to develop synthetic, CaO-based sorbents that possess high and cyclically stable CO2 uptakes are presented.
283 citations
TL;DR: In this paper, a mathematical model for flash calcination of Ca(OH)/sub 2/ and CaCO/sub 3/ is presented, which describes the decomposition of the parent material at the reactant-product interface.
Abstract: A mathematical model for the flash calcination of Ca(OH)/sub 2/ and CaCO/sub 3/ is presented. The model describes the decomposition of the parent material at the reactant-product interface, the diffusion of CO/sub 2/ or H/sub 2/O through the growing CaO layer, and the sintering of the CaO layer. The model is qualitative, but it provides useful estimates of peak CO/sub 2/ pressures on the CaO layer, relative rates of surface area development and loss for Ca(OH)/sub 2/ and CaCO/sub 3/, the effect of particle size, and the effects of time and temperature.
166 citations
TL;DR: In this article, a differential particle model is applied to a single particle, which includes mass and heat transport, transport through a product layer and chemical kinetics, but heat transport and product layer diffusion are of minor importance.
165 citations
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TL;DR: In this paper, the problem of determining the effective thermal conductivity of a two-phase system, given the conductivities and volume fractions of the components, is examined, and an equation based on a three-element resistor model is proposed.
Abstract: The problem of determining the effective thermal conductivity of a two‐phase system, given the conductivities and volume fractions of the components, is examined. Equations are described which have been proposed as solutions to this problem, including those of Maxwell, de Vries, and Kunii and Smith, the weighted geometric mean equation, and an equation based on a three‐element resistor model found applicable to the analogous electrical conductivity problem. Experimental results are presented for five unconsolidated samples: three quartz sand packs, a glass bead pack, and a lead shot pack. The method of conductivity measurement using the transient line heat source (thermal conductivity probe) is described. Data are reported showing the variation of effective thermal conductivity with porosity, solid particle conductivity, saturating fluid conductivity, and the pressure of the saturating gas. From considerations based on the kinetic theory of gases, it is shown that the characteristic dimension of the pore ...
818 citations
TL;DR: In this article, the authors used a modified thermo-balance to measure the diffusion coefficient and thermal conductivity of the porous lime layer, and the mass and heat transfer coefficients to the surface of the compact.
149 citations