Determination of the Critical Product Layer Thickness in the Reaction of CaO with CO2
16 Jun 2005-Industrial & Engineering Chemistry Research (American Chemical Society)-Vol. 44, Iss: 15, pp 5608-5615
TL;DR: The critical thickness of the product layer of CaCO3 has been measured in this work on real sorbent materials, using different limestone precursors and submitting them to many repeated carbonation calcination cycles (up to 100) Mercury porosimetry curves of the calcines and their carbonated counterparts have been obtained and their differences interpreted with a simple pore model, from which the thickness of a product layer is derived as discussed by the authors.
Abstract: Calcium oxide can be an effective CO2 sorbent at high temperatures When coupled with a calcination step to produce pure CO2, the carbonation reaction is the basis for several high-temperature separation systems of CO2 The formation of a product layer of CaCO3 is known to mark a sudden change in the reaction regime, from a very fast CO2 uptake to very slow carbonation rates The critical thickness of this product layer of CaCO3 has been measured in this work on real sorbent materials, using different limestone precursors and submitting them to many repeated carbonation calcination cycles (up to 100) Mercury porosimetry curves of the calcines and their carbonated counterparts have been obtained and their differences interpreted with a simple pore model, from which the thickness of the product layer is derived An average value of 49 nm (±19% standard deviation) has been obtained, which is quite insensitive to the type of limestone and to the texture of the calcine as long as the model is fulfilled The i
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TL;DR: The CO(2) adsorption behavior of several different classes of solid carbon dioxide adsorbents, including zeolites, activated carbons, calcium oxides, hydrotalcites, organic-inorganic hybrids, and metal-organic frameworks are described.
Abstract: Since the time of the industrial revolution, the atmospheric CO(2) concentration has risen by nearly 35 % to its current level of 383 ppm. The increased carbon dioxide concentration in the atmosphere has been suggested to be a leading contributor to global climate change. To slow the increase, reductions in anthropogenic CO(2) emissions are necessary. Large emission point sources, such as fossil-fuel-based power generation facilities, are the first targets for these reductions. A benchmark, mature technology for the separation of dilute CO(2) from gas streams is via absorption with aqueous amines. However, the use of solid adsorbents is now being widely considered as an alternative, potentially less-energy-intensive separation technology. This Review describes the CO(2) adsorption behavior of several different classes of solid carbon dioxide adsorbents, including zeolites, activated carbons, calcium oxides, hydrotalcites, organic-inorganic hybrids, and metal-organic frameworks. These adsorbents are evaluated in terms of their equilibrium CO(2) capacities as well as other important parameters such as adsorption-desorption kinetics, operating windows, stability, and regenerability. The scope of currently available CO(2) adsorbents and their critical properties that will ultimately affect their incorporation into large-scale separation processes is presented.
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TL;DR: In this paper, the authors classified solid CO2-adsorbents into three types according to their sorption/desorption temperatures: low-, intermediate-and high-temperature adsorbents with temperatures ranging from below 200 °C, between 200-400 °C and above 400 °C.
Abstract: In the last few years there has been a rapid growth in governmental funding and research activities worldwide for CO2 capture, storage and utilization (CSU), due to increasing awareness of the link between CO2 accumulation in the atmosphere and global warming. Among the various technologies and processes that have been developed and are emerging for CSU of CO2, solid CO2-adsorbents are widely applied. In this review, these solid CO2-adsorbents are classified into three types according to their sorption/desorption temperatures: low-, intermediate- and high-temperature adsorbents with temperatures ranging from below 200 °C, between 200–400 °C and above 400 °C, respectively. For each type of solid CO2-adsorbent, the synthesis, interaction mechanism with CO2 and sorption performance, potential applications and problems are reviewed. In the last section, several representative CO2-sorption-enhanced catalytic reactions are discussed. It is expected that this review will not only summarize the main research activities in this area, but also find possible links between fundamental studies and industrial applications.
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Cites background from "Determination of the Critical Produ..."
...The major challenge of this cycle in practical applications is the sharp decay of total reversibility with cycles (Abanades and Alvarez, 2003; Alvarez and Abanades, 2005a, b)....
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TL;DR: The reversible reaction between CaO and CO2 is an extremely promising method of removing CO2 from the exhaust of a power station, generating a pure stream of CO2 ready for geological sequestration.
880 citations
TL;DR: In this paper, a long series of carbonation/calcination cycles (up to 500) varying different variables affecting sorbent capacity have been tested in a thermogravimetric apparatus.
Abstract: Calcium oxide can be an effective sorbent to separate CO2 at high temperatures. When coupled with a calcination step to produce pure CO2, the carbonation reaction is the basis for several high-temperature CO2 capture systems. The evolution with cycling of the capture capacity of CaO derived from natural limestones is experimentally investigated in this work. Long series of carbonation/calcination cycles (up to 500) varying different variables affecting sorbent capacity have been tested in a thermogravimetric apparatus. Calcination temperatures above T > 950 °C and very long calcination times accelerate the decay in sorption capacity, while other variables have a comparatively modest effect on the overall sorbent performance. A residual conversion of about 7−8% that remains constant after many hundreds of cycles and that seems insensitive to process conditions has been found. This residual conversion makes very attractive the carbonation/calcination cycle, by reducing (or even eliminating) sorbent purge ra...
670 citations
References
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TL;DR: Identifying and building a sustainable energy system are perhaps two of the most critical issues that today's society must address.
Abstract: Identifying and building a sustainable energy system are perhaps two of the most critical issues that today's society must address. Replacing our current energy carrier mix with a sustainable fuel is one of the key pieces in that system. Hydrogen as an energy carrier, primarily derived from water, can address issues of sustainability, environmental emissions, and energy security. Issues relating to hydrogen production pathways are addressed here. Future energy systems require money and energy to build. Given that the United States has a finite supply of both, hard decisions must be made about the path forward, and this path must be followed with a sustained and focused effort.
4,824 citations
TL;DR: A portfolio of technologies now exists to meet the world's energy needs over the next 50 years and limit atmospheric CO 2 to a trajectory that avoids a doubling of the preindustrial concentration as mentioned in this paper.
Abstract: Humanity already possesses the fundamental scientific, technical, and industrial know-how to solve the carbon and climate problem for the next half-century. A portfolio of technologies now exists to meet the world’s energy needs over the next 50years and limit atmospheric CO 2 to a trajectory that avoids a doubling of the preindustrial concentration. Every element in this portfolio has passed beyond the laboratory bench and demonstration project; many are already implemented somewhere at full industrial scale. Although no element is a credible candidate for doing the entire job (or even half the job) by itself, the portfolio as a whole is large enough that not every element has to be used.
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TL;DR: The use of calcines of natural limestones as CO2 regenerable sorbents is investigated in this paper by studying the decay of the maximum carbonation conversion during many carbonation/calcination cycles.
Abstract: The use of calcines of natural limestones as CO2 regenerable sorbents is investigated in this work by studying the decay of the maximum carbonation conversion during many carbonation/calcination cycles. New experimental information is complemented with a compilation of previously published data on this subject. The observed conversion limits in the reaction of CO2 with lime are interpreted in terms of a certain loss in the porosity associated with small pores and a certain increase in the porosity associated with large pores. In the carbonation part of every cycle, the CaCO3 fills up all the available porosity made up of small pores plus a small fraction of the large voids, limited by the thickness of the product layer that marks the onset of the slow carbonation rate. A simple model based on textural changes, observed by scanning electron microscopy, fits equally well all the data from this work and from other authors. The two model parameters are consistent with known mechanism occurring during calcinat...
689 citations
TL;DR: In this article, a new process for CO2 removal from flue gas using the reaction CaO + CO2 ↔ CaCO3 was proposed, which consists of two fluidized bed reactors connected by solid transportation lines.
Abstract: A new process is proposed for CO2 removal from flue gas using the reaction CaO + CO2 ↔ CaCO3. This process consists of two fluidized bed reactors connected by solid transportation lines. In one reactor (absorber), CO2 in the flue gas is captured by CaO at 873 K and the produced CaCO3 is transported to another reactor (regenerator), in which CaCO3 is decomposed to CaO at 1223 K. The produced CaO is transported to the absorber again. The heat of decomposition in the regenerator is supplied by feeding coal and pure oxygen, thus the flue gas from the regenerator is high purity CO2 (>95%, dry base). In this work, a conceptual study is conducted for material balance, heat balance, power generation, and power consumption for O2 production and CO2 liquefaction (compression). Also, a kinetic study of CaO+CO2 → CaCO3 was conducted to design the absorber. The required bed height of the absorber was calculated by use of a bubbling fluidized bed model. The bed height was found to be determined not by the chemical reaction rate but by the arrangement of heat transfer tubes for heat recovery.
661 citations
TL;DR: In this paper, the kinetics of reaction between CO2 and lime are 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.
Abstract: The kinetics of reaction between CO2 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 CaCO3 layer. The magnitude of the estimated product layer diffusivity is in the range of 10−18 to 10−21 m2/s, the corresponding activation energy is 88.9 ± 3.7 kJ/mol below 688 K and 179.2 ± 7.0 kJ/mol above that temperature, suggestive of solid state diffusion. Plausible mechanisms are discussed.
603 citations