Carbonation Calcination Cycles Research Articles

Modeling of carbonation reaction for CaO-based limestone with CO2 in multitudinous calcination-carbonation cycles

In the cyclic carbonation-calcination reaction processes, CaO-based solid sorbents have been substantiated to be the effective sorbents for CO2 capture at high temperature. The carbonation reaction has been depicted the carbonation reaction by several kinetic models. Some kinetic models are capable to calculate the intrinsic carbonation rate in the cyclic carbonation-calcination reaction, but the mathematic equation of those models is basically complicated. In this work, a modified model was proposed to delineate the carbonation reaction in multitudinous carbonation-calcination cycles, and was qualified to characterize the whole progression of carbonation reaction in highly cycled particles. The sharp corner is inexistent simultaneously. Additionally, the mathematic equation of this model is apparent simplified. The disconnected pore size distribution is expressed by the log-normal function, and the time evolution of pore structure was also discussed.

Development of Synthetic Ca-based CO2 Sorbents for Sorption Enhanced Reforming Coupled to Ca/Cu Chemical Loop

Sorption Enhanced Reforming (SER) is a very promising option that allows H2 production coupled with capturing CO2 by sorption. The present research work focus in the sorbent point of view and several synthetic materials with a high CO2 absorption capacity and chemically and mechanically stable during multi-cyclic operation (at least 40 calcination-carbonation cycles and 100 cycles in some cases) under the typical SER process conditions have been developed. Two different synthesis routes (co-precipitation and mechanical mixing) have been followed trying to evaluate the effect of two different inert supports (magnesium oxide and mayenite) on the evolution of the CO2 carrying capacity of the materials. Also, sorbents have been synthesized with different morphologies (powder and particles) and sizes (from 100 microns up to 2mm) in order to test their reactivity and mechanical suitability for large scale reactor system operation. Synthetic dolomite with a molar CaO/MgO ratio of 2:1 synthesized by co-precipitation method exhibited very stable performance for 100 consecutive carbonation/calcination cycles and a residual CO2 carrying capacity of 0.29 grCO2/grcalcinedsorbent. Also a very promising result has been obtained for this sorbent mixed with a commercial catalyst in a preliminary SER experiment that yield a H2 production of 92% vol. (d.b.).

Evolution of the CO2 carrying capacity of CaO particles in a large calcium looping pilot plant

Post-combustion calcium looping is an emerging capture technology that uses CaO particles as CO2 sorbent. This work analyses the average maximum CO2 carrying capacity of the sorbent (Xave) in a continuous large-scale calcium looping (CaL) pilot plant, which is believed to adequately represent the lifetime of CaO particles in larger CaL systems based on the regeneration of CaO by oxyfuel combustion in the calciner. The CO2 carrying capacity is a key variable in designing the CO2 capture carbonator reactor and for optimizing the performance of the system. Several experimental campaigns have been carried out in La Pereda 1.7MWth pilot plant both under oxy-fired and air-fired combustion conditions, in which the evolution of Xave with time has been measured under a wide range of conditions in the calciner. A methodology based on a closure of mass and particle population balances has been used to estimate Xave. Closure of the sulphur balance was found to be very accurate as an internal calibration tool to quantify the make-up flow of limestone that effectively participates in the CO2 capture process in any given set of conditions. When the calciner reactor was operated in conditions far from the equilibrium of CO2 on CaO, a good agreement was found between the experimental Xave values and those calculated from population mass balances which account for the number of carbonation-calcination cycles of each particle. However, a CO2 carrying capacity lower than expected was observed in some tests in oxy-combustion mode when the calciner was operating close to equilibrium. Departure from ideal sorbent behavior and more intense deactivation was found to increase with longer residence times in the calciner (∼3min). This deactivating effect may be due to the effective increase in the number of carbonation-calcination cycles of the particles, caused by switching between carbonating and calcining conditions inside the calciner when the reactor operates close to equilibrium. The results obtained in this study indicate that optimum operation of the calciner for sorbent activity is achieved in conditions sufficiently far from equilibrium and with low bed inventories (short particle residence time in the calciner).

A Modified Random Pore Model for Carbonation Reaction of CaO-based Limestone with CO 2 in Different Calcination-carbonation Cycles

Abstract In this work, a modified model was presented. The simulation results showed that the modified model was capable to predict the whole conversion-time curve of the carbonation reaction in long series of calcination-carbonation cycles, particularly at short reaction times, including the sudden transition between the first fast regime and the second product layer diffusion controlled slow regime. In comparison with the model of Grasa, to determine the value of conversion corresponding to the transition between regimes ( X k-D ) was unnecessary in the modified model. In addition, compared with the models of Sun and Benedett, the modified model proposed here was capable of predicting with a reasonably good accuracy the carbonation rates obtained in the relevant range of reaction times and conditions in long series of calcination- carbonation cycles, and concept to be successfully applied.

Hydrogen production by sorption-enhanced steam reforming of acetic acid over Ni/CexZr1−xO2-CaO catalysts

The production of high purity hydrogen via the sorption-enhanced steam reforming of acetic acid, a model compound of bio-oil, was investigated in this work. A bi-functional catalyst with stable catalytic activity and CO2-capture ability, Ni/CexZr1−xO2-CaO, was prepared by a sol–gel method and characterized in details by BET, XRD, TPR and SEM-EDX analytic techniques. The characterization of these materials showed that the catalysts were mainly composed of Ni, CexZr1−xO2 and CaO. As CaO loading increased, a new species, CaZrO3, with a perovskite structure was formed. The presence of CaZrO3 in the catalysts acted as a barrier to CaO grain growth at high temperatures and thus improved the CO2-capture stability. These catalysts exhibited good CO2 sorption capacity in 15 consecutive carbonation–calcination cycles, even at a high calcination temperature of 900 °C. Particularly, in case of the Ni/CZC-2.5 catalyst, 98% high purity H2 could be obtained during the prebreakthrough stage when the catalysts were tested in the SESR of acetic acid at 550 °C with an S/C ratio of 4. In addition, high hydrogen purity was maintained over 15 cyclic reaction-calcination operations, which was mainly attributed to the uniform distribution of Ni, CaO, CexZr1−xO2 and CaZrO3 in the catalysts. These results indicated the great potential of the SESR technique for hydrogen production from bio-oil.

A Model to Stabilize CO2 Uptake Capacity during Carbonation-Calcination Cycles and its Case of CaO-MgO.

Nowadays, capturing anthropogenic CO2 in a highly efficient and cost-effective way is one of the most challenging issues. Herein, the key parameters to stabilize CO2 uptake capacity have been studied based on four kinds of pure calcium oxides (CaO) prepared by a simple calcination method with four different calcium precursors. A simple ideal particle model was proposed to illustrate the uniform distribution of pure CaO, in which the CO2 uptake capacity is positively related with surface area of CaO particles and the stability is opposite to the distance between two CaO particles after carbonation. The adsorption capacity of the best sample with a distance of 398 nm between two CaO particles after carbonation only lost 0.344% per cycle, which is originated from the low possibility of the agglomeration between neighboring particles. On the basis of the proposed model, the composite with magnesium oxide (MgO) distributed uniformly in CaO was fabricated by a simple ball milling method, which possessed an excellent stability with a decay rate of only 3.9% over 100 carbonation-calcination cycles. In this case, MgO played as inert to increase the distance between CaO particles for agglomeration prevention.

Performance and Carbonation Kinetics of Modified CaO-Based Sorbents Derived from Different Precursors in Multiple CO2 Capture Cycles

Calcium-based sorbent is a suitable sorbent for the solid looping CO2 capture. The loss-in-capacity due to sintering, however, poses a big problem to the direct utilization of natural/pure CaO in the looping process. The issue of attrition, meanwhile, adds a further obstacle to the long-term cyclic utilization of the sorbent. Additionally, the performance of CaO-based sorbent in the long term solid looping CO2 capture depends to a great degree on the type of precursor used to derive the sorbent. This study aims to systematically study the influence of the various calcium precursors on the sorbent performance in the long term carbonation-calcination cycles. Results of this study indicate that the absorption capacity of CaO sorbents was influenced significantly by the type of CaO precursor. It was found that CaO sorbent derived from calcium acetate gave the best absorption capacity of 0.61 mol-CO2/mol-sorbent after 48 carbonation/calcination cycles. The addition of inert supporting matrix of Al2O3 has enhan...

Preparation of Nano-CaCO3 from Phosphogypsum by Gas–Liquid–Solid Reaction for CO2 Sorption

Nano-CaCO3 was prepared from phosphogypsum (PG) through reactive crystallization in the gas (CO2)–liquid (NH3·H2O)–solid (PG) three-phase system. The effects of temperature, CO2 flow rate, and reaction time on the CaCO3 particle size distribution (PSD) were investigated. The results show that PG-derived nano-CaCO3 with an average particle diameter of 86–104 nm can be obtained under a 251–138 mL/min CO2 flow rate at a corresponding temperature of 30–40 °C. Research indicates that the CaCO3 particle size is subjected to the mutual influences of temperature, CO2 flow rate, and reaction time. A relatively low CO2 flow rate with increasing temperature and a strictly controlled reaction time are advantageous to the formation of nanosized CaCO3 grains. Additionally, PG-derived nano-CaO maintains a CO2 sorption capacity of 0.27 g of CO2/g of CaO after 10 calcination–carbonation cycles, which is the same as for commercial nano-CaO.

The effects of refractory zirconium-based ceramic dopants on the stability performance of synthetic Ca-based sorbents prepared by co-precipitation method in cyclic CO2 capture operations

Calcium (Ca) based sorbents utilized in the carbon dioxide (CO2) capture process at high temperatures have displayed considerable activity loss during extended use, due to sintering. Refractory zirconium-based ceramics, however, have shown excellent performances as thermal barrier coatings in many high-tech applications; and, the recent doping of zirconia in Ca-based sorbents has exhibited excellent sustainability in the activity stability in cyclic CO2 capture operations. In this work, we doped sorbents, at loadings of 10 wt%, with a few zirconium-based ceramics, such as alkaline earth metal zirconate (calcium zirconate, CaZrO3), which has the chemical structure of perovskite, and rare earth metal zirconates, which have the chemical structure of pyrochlore. These materials were prepared through the wet co-precipitation method, in order to achieve the optimal uptake capacity and stability in cyclic CO2 capture operations. Among the sorbents tested, the CaZrO3-doped sorbents exhibited excellent performance, remarkable thermal stability and sintering resistant. Therefore, the sorbents were stable though 30 carbonation–calcination cycles. The sorbent showed a CO2 capture capacity of 12 mol CO2/kg sorbent, with an activity loss of 19.6% through carbonation at 675 °C for 10 min and calcination at 850 °C for 10 min. Among the rare earth metal zirconate ceramics, samarium zirconate (Sm2Zr2O7) exhibited the best stability with an activity loss of 23.4% loss, but at a lower uptake of 7.2 mol CO2/kg sorbent at the same carbonation–calcination conditions. In comparison, Cadomin (a natural calcium carbonate) at the same conditions resulted in a capture capacity of 13.5 mol CO2/kg sorbent and an activity loss of 69%. Surface area characterizations showed that incorporation of the ceramics to the calcium based sorbents significantly improved the surface morphology and textural properties of the sorbents. X-ray diffraction results indicated that the improved resistance of the sorbent could be due to forming of ceramic structures such perovskite-type CaZrO3 at a relatively low temperature (around 850 °C compared to higher temperatures required for pyrochlore-type ceramic formation), which made a stable sorbent structure for the carbonation process.

Effect of Coal Combustion on the Reactivity of a CaO-Based Sorbent for CO2 Capture

CaO is usually decomposed from limestone to capture CO2. CaO regeneration (limestone decomposition) is an endothermic reaction and needs a lot of heat, which could be from coal combustion through mixing the coal particles and limestone particles. However, the effect of coal combustion on the CaO sorbent reactivity for CO2 capture needs to be clarified. In this study, the reactivity of the sorbent decomposed from the limestone/coal mixture under various conditions was investigated using thermogravimetric analysis. The results show that the sorbent reactivity decreases with carbonation–calcination cycles because of sorbent sintering under a high temperature. Although coal combustion could supply heat for limestone decomposition, it is also found that sorbent reactivity decreases after adding the coal particles to the limestone particles. Evidently, coal ash remains in the CaO sorbent after coal combustion, but the results show that coal ash does not react with CaO or CaCO3 in a fixed-bed reactor. Coal ash h...

High Temperature CO2 Capture on Novel Yb2O3-Supported CaO-Based Sorbents

Incorporation of CaO in inert solid support has been identified as an effective approach to improve the cyclic CO2 capture performance for CaO-based sorbents. In this work, Yb2O3-supported CaO-based sorbents were fabricated via the wet-mixing technique. Elemental dispersion observed by FSEM-EDS showed that the ultrafine active species of CaO particles was finely separated by Yb2O3. Different amounts of Yb2O3 were introduced and 10−15 wt% was found to be the optimal content range for the support to function as the metal skeleton. In comparison with pure CaO, the improved CO2 capture performance was observed for CaYb10 over prolonged carbonation-calcination cycles under a severe test condition. This improvement could be ascribed to the enriched macropores within 50–100 nm, which was identified by the N2 adsorption–desorption analysis. In addition, the microstructure of the synthetic sorbent (analyzed through TEM images) indicated that CaO particles of ∼160 nm were formed with the Yb2O3 nanocrystallines (∼15...

Influence of steam addition during carbonation or calcination on the CO2 capture performance of Ca9Al6O18[sbnd]CaO sorbent

Calcium looping process, on the basis of the reversible reaction between CaO and CO2, is a promising technology for capture of CO2 from different gas streams. The performance of CO2 sorbents could be easily influenced by the gas stream composition. As the exhaust gas stream generally contains a considerable amount of steam, a good understanding of its side effects on the performance of CaO-based sorbents is essential. However, there is not consensus on the mechanism with which the presence of steam during carbonation influences the CO2 capture performance and contradictory results have been reported regarding the effect of steam addition during calcination. This work aims to investigate the effect of steam addition during either carbonation or calcination on the reactivity of a home-made synthetic CaO sorbent containing 78 wt% CaO and 22 wt% Ca9Al6O18. Various concentrations of steam up to 9.5 vol% were provided during either carbonation or calcination for 15 carbonation-calcination cycles (carbonation: 650 or 550 °C; calcination: 800 °C). The morphology changes of the sorbent after cyclic carbonation-calcination experiments were studied in detail at different operating conditions. It was concluded that the sorbent reactivity was significantly increased for all concentrations of steam injected during carbonation step, due to the accelerated solid-state diffusion and steam catalysis. In case of steam addition during calcination, the carbonation performance was affected negatively or positively depending on the concentration of steam in the gas stream. For 2.3 vol% steam injection, the sorbent reactivity was worsened, while the presence of 9.5 vol% steam increased the CO2 capture capacity during 9 initial cycles. Such behavior was attributed to the intensified material sintering in the presence of steam during calcination step, which results in the formation of large pores and the decrease of specific surface area.

Effect of steam on CaO regeneration, carbonation and hydration reactions for CO2 capture

CaO sorbent is one of the most promising sorbents for CO2 capture. However, the reactivity of CaO sorbent decreased rapidly with carbonation-calcination cycles. Steam activation is a feasible approach to improve the sorbent reactivity. In this study, the effects of steam on CaCO3 calcination (CaO regeneration), CaO carbonation and CaO hydration were both investigated. Compared with pure CO2 calcination atmosphere, introducing steam into calcination atmosphere enhanced CaCO3 decomposition rate, which was because that (1) the partial pressure of CO2 decreased; (2) the absorption of H2O by active site CaO* weakened the binding ability between CO2 and CaO*; (3) the amount of heat-transfer between steam and CaCO3 was higher. Lower decomposition temperature in steam/CO2 calcination atmosphere resulted in lower sorbent sintering and higher sorbent reactivity. Besides, the carbonation reactivity of CaO sorbent was over doubled when steam was introduced into carbonation atmosphere, which was due to the formation of OH–. In CaO hydration reaction, sorbent particle pore structure was also developed by hydration treatment. The hydrated Ca(OH)2 sorbent reactivity as well as cyclic reactivity of CaO sorbent was therefore enhanced.

Sol-gel-derived, CaZrO3-stabilized Ni/CaO-CaZrO3 bifunctional catalyst for sorption-enhanced steam methane reforming

Sorption-enhanced steam methane reforming (SESMR) that combines steam reforming of methane with in situ CO2 removal is a promising technology for H2 production, and bifunctional catalysts that integrate catalytic and absorptive sites into one body are believed to have reduced mass transfer resistances. However, it is still a challenge to prepare bifunctional catalysts with high stability. Here, we used a sol-gel technique based on the formation of citrate complexes to prepare a series of Ni/CaO-CaZrO3 bifunctional catalysts in which Ni, CaO and CaZrO3 acted as catalyst, sorbent and stabilizer, respectively. The stabilizer, Ni loading and CaO content had a direct effect on the structure and morphology of the catalyst, which in turn influenced its CO2 uptake and SESMR performance. Compared to Ni/CaO, the CaZrO3-stabilized Ni/CaO-CaZrO3 had smaller and fluffier grains, showing not only higher CO2 uptake and better stability in 50 carbonation-calcination cycles, but also higher stability during cyclic SESMR process. In particular, the catalyst with a Ni loading of 15wt%, CaO content of around 60wt% and CaZrO3 content of 25wt% presented the best SESMR performance by taking into account the catalytic activity and stability as well as the duration of the prebreakthrough period. However, the best catalyst was still subject to slow deactivation during a long-term stability test (up to 90 SESMR cycles), which was mostly due to the smooth and compact shell formed on the catalyst surface. The partially deactivated catalyst can be effectively reactivated by an additional carbonation step during the cyclic SESMR operation.

CO2 Capture Performance of Core/Shell CaO-Based Sorbent Using Mesostructured Silica and Titania in a Multicycle CO2 Capture Process

Carbon dioxide (CO2) capture is a process that can significantly reduce the amount of CO2 in the atmosphere. In this study, several solid sorbents were examined for their CO2 capturing performance over 30 carbonation–calcination cycles. The sorbents included natural calcined Cadomin limestone (denoted as CD), hydrated calcined Cadomin pellets (denoted as CP), core/shell sorbets with CD and CP as cores, and mesostructured silica (denoted as CD@Si and CP@Si, respectively) and titania (denoted as CD@Ti and CP@Ti) as shells. The core/shell sorbents were prepared with a protective porous shell using the mesoporous silica and titania layers. The surface morphology and porosity of all sorbents were qualified using scanning electron microscopy and were quantified using nitrogen physisorption. X-ray diffraction was also used to identify the crystal phase composition of the sorbents before and after calcination. The CP@Ti pellets showed the best performance in the retention of CO2 uptake over 30 cycles with an activity loss of 50.9%. This is attributed to the formation of a protective layer of thermally stable mesoporous titania using a sol–gel method, which prevented the aggregation of CaO crystals and sorbent sintering. Although the modified core/shell sorbents exhibited an improvement in maintaining the stability of the cyclic operation compared to natural limestone, further study is needed to understand the core/shell sintering phenomenon at high temperatures using other novel materials.

Catalytic performance of Ni/CaO-Ca5Al6O14 bifunctional catalyst extrudate in sorption-enhanced steam methane reforming

In this work, mm-sized shaped Ni/CaO-Ca5Al6O14 bifunctional catalyst extrudates were prepared by extruding sol–gel-derived Ni/CaO-Ca5Al6O14 powder, and applied to the sorption-enhanced steam methane reforming (SESMR) process. The Ca5Al6O14-stabilized bifunctional catalysts exhibited higher stability and CaO utilization efficiency than that of Ni/CaO when subjected to 50 carbonation–calcination cycles for CO2 capture, indicating the positive effect of Ca5Al6O14 incorporation. The Ni/CaO-Ca5Al6O14 extrudates possessed good activity and stability over 10 SESMR cycles, and showed advantages over the use of catalyst and sorbent mixture, including an extended prebreakthrough time and a higher catalytic activity. In particular, the Ni/CaO-Ca5Al6O14 extrudate consisting of 15wt% (mass fraction) Ni, 61.7wt% CaO and 23.3wt% Ca5Al6O14 provided high activity and stability for the SESMR process, even at a low H2O/CH4 molar ratio of 2 over 20 SESMR cycles. These results clearly demonstrate that the Ni/CaO-Ca5Al6O14 extrudate is an interesting candidate for the SESMR process.

Synthesis of Highly Efficient CaO-Based, Self-Stabilizing CO2 Sorbents via Structure-Reforming of Steel Slag

Capturing anthropogenic CO2 in a cost-effective and highly efficient manner is one of the most challenging issues faced by scientists today. Herein, we report a novel structure-reforming approach to convert steel slag, a cheap, abundant, and nontoxic calcium-rich industrial waste, as the only feedstock into superior CaO-based, self-stabilizing CO2 sorbents. The CO2 capture capacity of all the steel slag-derived sorbents was improved more than 10-fold compared to the raw slag, with the maximum uptake of CO2 achieving at 0.50 gCO2 gsorbent(-1). Additionally, the initial steel slag-derived sorbent could retain 0.25 gCO2 gsorbent(-1), that is, a decay rate of only 12% over 30 carbonation-calcination cycles, the excellent self-stabilizing property allowed it to significantly outperform conventional CaO, and match with most of the existing synthetic CaO-based sorbents. A synergistic effect that facilitated CO2 capture by CaO-based sorbents was clearly recognized when Mg and Al, the most common elements in steel slag, coexisted with CaO in the forms of MgO and Al2O3, respectively. During the calcium looping process, MgO served as a well spacer to increase the porosity of sorbents together with Al2O3 serving as a durable stabilizer to coresist the sintering of CaCO3 grains at high temperatures.

The microstructure and stability of a Ni-nano-CaO/Al2O3 reforming catalyst under carbonation–calcination cycling conditions

The paper investigated the effect of carbonation–calcination cycling conditions on the microstructure and CO2 sorption property of a sorption complex catalyst. The carbonation operation condition consisted of temperature of 600 °C with 20% CO2–80% N2 and 20% CO2–80% steam atmosphere to simulate the methane reforming reaction conditions; the calcination condition was 800 °C with 100% N2. The Brunauer–Emmer–Teller (BET) surface area and thermogravimetric analysis (TGA) were measured to investigate the microstructure and variation in sorption property of the catalyst after multiple cycles under each condition. Results showed that the microstructure and CO2 sorption capacity of the sorption complex catalyst decayed significantly in the initial carbonation–calcination cycles, especially under a steam atmosphere. X-ray diffraction analysis revealed that a stable compound Ca12Al14O33 formed gradually during the initial carbonation–calcination cycle seven at a temperature of 800 °C. A model is proposed to explain the observed effect of carbonation–calcination cycling on Ca12Al14O33 formation. Furthermore, based on our findings, a new sorption complex catalyst was prepared by pretreating at a high temperature of 900 °C. Evaluation of the catalyst prepared by the ReSER hydrogen production process through 10 circulations revealed significant improvement instability.

Calcium looping process simulation based on an advanced thermodynamic model combined with CFD analysis

Abstract The current study presents a new methodology for the simulation of the Calcium Looping (CaL) process based on the coupling of CFD and advanced thermodynamic models. As a first step, CFD models for the two reactors, i.e. the carbonator and the calciner, of a pilot scale Dual Fluidized Bed system are developed and validated by comparing the numerical predictions with corresponding experimental data for pressure distribution, carbonator capture efficiency and sorbents regeneration in the calciner. For the carbonator modeling, the Two-Fluid-Model (TFM) approach is combined with the advanced EMMS scheme in order to provide results with high accuracy, even for the difficult to model dense bottom zone of the riser. A similar approach is adopted for the calciner; numerical results indicate that CO2 follows an almost linear trend along the bubbling bed height, while the bubbling formations might result in a reduced efficiency for the calcination reaction due to the entrapment of CO2 bubbles inside the emulsion phase. Numerical results related mostly to the hydrodynamics of the reactors, such as the solids distribution and residence time are then used as input parameters in a kinetics-based process algorithm. Process modeling simulations reveal the importance of splitting the carbonator riser into two distinct sections, i.e. the bottom zone with dense solid phase and the upper one (freeboard) with a more dilute solid concentration. The heat balance calculation for these two regions demonstrates a big gap between the heat flux density for the bottom zone (19.26 kW/m2) and the freeboard (0.46 kW/m2), which should be taken into account for the design of an effective heat removal system for scaled-up reactors. As a final step, a sensitivity analysis is performed for the optimization of the parameters governing the operation of the whole carbonation–calcination cycle. Efficient sorbent regeneration and high looping ratio enhances the CO2 capture efficiency in the carbonator, whilst low CO2 concentration in the calciner is suggested for more effective lime regeneration.

Modelling of the kinetics of sulphation of CaO particles under CaL reactor conditions

CO2 capture in a calcium looping (CaL) system is one of the most promising technologies for climate change mitigation. The main reactors in these systems (carbonator and calciner) operate in conditions where the reaction of CaO with the SO2 resulting from the combustion of coal is inevitable. This work reports on the sulphation of CaO under a range of variables that are typical of reactors in CaL systems. Furthermore it is demonstrated that the number of calcination carbonation cycles changes the sulphation patterns of the CaO from heterogeneous to homogeneous in all the limestones tested. For 50 carbonation calcination cycles and for particle sizes below 200μm, the sulphation pattern is in all cases homogeneous. The sulphation rates were found to be first order with respect to SO2, and zero with respect to CO2. Steam was observed to have a positive effect only in the diffusion through the product layer controlled regime, as it leads to an improvement in the sulphation rates and effectiveness of the sorbent. Most of the experimental results of sulphation of highly cycled sorbents under all conditions can be fitted by means of the Random Pore Model (RPM) assuming that the kinetics and diffusion through the product layer of the CaSO4 are the controlling regimes.