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Calcium looping is a promising CO2 capture technology due to reduced energy and economic penalties compared to mature solvent scrubbing technologies. It also can enable negative CO2 emissions when biomass is used to drive the sorbent regeneration process in the calciner. However, the trade-off between the energy, economic and environmental performance under different biomass co-firing fractions in the calciner and process operating scenarios has not yet been well understood. This study examined the potential for transforming a 580 MWel coal-fired power plant into a negative CO2 emitter via retrofit of calcium looping with biomass co-firing in the calciner. High-fidelity process models were developed in Aspen Plus and used to analyse the effect of biomass co-firing fraction, CO2 capture rate in the carbonator, and the fraction of flue gas fed to the carbonator on the techno-economic performance indicators. The results revealed that co-firing 30% biomass with coal in the calciner was sufficient for the retrofitted process to achieve negative CO2 emissions (−3.9 gCO2/kWelh). In this scenario, the levelized cost of electricity was 5% lower (81.1 €/MWelh) than that in the reference retrofit scenario without biomass co-firing (85.4 €/MWelh) at a carbon tax of 100 €/tCO2. Further improvement to the techno-economic performance was achieved by reducing the amount of CO2 captured in the carbonator by reducing either the CO2 capture rate (81.1 €/tCO2) or the amount of flue gas processed (80.4 €/tCO2). Although this was achieved at the expense of the increased specific CO2 emissions to 65.2 gCO2/kWelh and 109.0 gCO2/kWelh, respectively, the net specific emissions were still about 90% lower than those of the unabated host plant (792.3 gCO2/kWelh). This study demonstrated that depending on design priorities, biomass co-firing in the calciner can transform the existing coal-fired power plants into negative CO2 emission technologies or improve the process techno-economic viability. [ABSTRACT FROM AUTHOR]

A proof of concept of a novel parallel-flow solid–solid heat exchanger consisting of two L-Valves with concentric vertical tubes, named as Double L-Valve, is presented for the case of the Carbonate Looping process, as a CO2 capture technology. The operational objective of the solid–solid heat exchanger is to heat up the relatively cold solid stream coming from the carbonator reactor by absorbing heat from the hotter stream coming from the calciner. This novel solid–solid heat exchanger concept has been constructed on a small scale to study the hydrodynamic response of the system experimentally at different designs and airflow rates in its cold state. Based on the experimental data from the small prototype, a scaled-up hydrodynamic model is proposed that provides estimations for the operational requirements at an industrial scale. Apart from the cold flow pilot model, the heat exchanger is being assessed in the current work for an industrial case study in terms of the following: (a) the heat transfer via rigorous one-dimensional thermal modelling, (b) the structural integrity of the design through Finite Element Method (FEM) analysis, and (c) a parametric study for its expected cost. The purpose of this work is to provide a holistic approach of this novel solid–solid heat exchanger concept, the main advantage of which is its simple design and relatively low cost. [ABSTRACT FROM AUTHOR]

Lime is an essential raw material for iron and steel production, in construction and agriculture, in civil engineering, in environmental protection, and in manifold chemical manufacturing processes. To address the problem of unavoidable process CO2 emissions associated with the production of lime, efficient capture technologies need to be developed and implemented. The indirectly heated carbonate looping (IHCaL) process is an efficient candidate for this application because it utilizes lime as the sorbent for the CO2 capture. In this work, a retrofit configuration of this process is presented and analyzed for net negative CO2 emissions. This is done considering different fuels that provide the heat required for the regeneration of the sorbent. The different scenarios were simulated with an AspenPlus® model, key performance indicators were calculated, and the process was compared with other post-combustion capture methods. The results show that net negative CO2 emissions as high as −1805 kgCO2/tCaO, calculated with a state-of-the-art coal power plant energy scenario (ηe = 44.2 %; eref,el = 770 kgCO2/MWhel), can be obtained. This represents an equivalent CO2 avoidance of more than 230% with respect to the reference plant without capture (1368 kgCO2/tCaO). A specific primary energy consumption for CO2 avoided (SPECCA) lower than 1.5 MJLHV/kgCO2,av was achieved for the same energy scenario. Particularly promising results can be accomplished when applying fuels with high biogenic fraction and low specific CO2 emissions, such as solid recovered fuels (SRFs) with a high calorific value. [ABSTRACT FROM AUTHOR]

Carbon capture and storage will play a crucial role in industrial decarbonisation. However, the current literature presents a large variability in the techno-economic feasibility of CO2 capture technologies. Consequently, reliable pathways for carbon capture deployment in energy-intensive industries are still missing. This work provides a comprehensive review of the state-of-the-art CO2 capture technologies for decarbonisation of the iron and steel, cement, petroleum refining, and pulp and paper industries. Amine scrubbing was shown to be the least feasible option, resulting in the average avoided CO2 cost of between for the pulp and paper and for the iron and steel industry. Its average equivalent energy requirement varied between 2.7 (iron and steel) and (cement). Retrofits of emerging calcium looping were shown to improve the overall viability of CO2 capture for industrial decarbonisation. Calcium looping was shown to result in the average avoided CO2 cost of between 32.7 (iron and steel) and (cement). Its average equivalent energy requirement varied between 2.0 (iron and steel) and (pulp and paper). Such performance demonstrated the superiority of calcium looping for industrial decarbonisation. Further work should focus on standardising the techno-economic assessment of technologies for industrial decarbonisation. [ABSTRACT FROM AUTHOR]

Featured Application: Kinetic parameters for the development of CaCO3/CaO reactor systems for carbon capture and storage and thermochemical energy storage. The calcium carbonate looping cycle is an important reaction system for processes such as thermochemical energy storage and carbon capture technologies, which can be used to lower greenhouse gas emissions associated with the energy industry. Kinetic analysis of the reactions involved (calcination and carbonation) can be used to determine kinetic parameters (activation energy, pre-exponential factor, and the reaction model), which is useful to translate laboratory-scale studies to large-scale reactor conditions. A variety of methods are available and there is a lack of consensus on the kinetic parameters in published literature. In this paper, the calcination of synthesized CaCO3 is modeled using model-fitting methods under two different experimental atmospheres, including 100% CO2, which realistically reflects reactor conditions and is relatively unstudied kinetically. Results are compared with similar studies and model-free methods using a detailed, comparative methodology that has not been carried out previously. Under N2, an activation energy of 204 kJ mol−1 is obtained with the R2 (contracting area) geometric model, which is consistent with various model-fitting and isoconversional analyses. For experiments under CO2, much higher activation energies (up to 1220 kJ mol−1 with a first-order reaction model) are obtained, which has also been observed previously. The carbonation of synthesized CaO is modeled using an intrinsic chemical reaction rate model and an apparent model. Activation energies of 17.45 kJ mol−1 and 59.95 kJ mol−1 are obtained for the kinetic and diffusion control regions, respectively, which are on the lower bounds of literature results. The experimental conditions, material properties, and the kinetic method are found to strongly influence the kinetic parameters, and recommendations are provided for the analysis of both reactions. [ABSTRACT FROM AUTHOR]

Abstract Calcium looping combustion (CaLC) is a new class of low CO 2 emission technologies for thermochemical conversion of carbonaceous fuels that can help achieve the emissions reduction targets set out in the Paris Agreement. Compared to mature CO 2 capture technologies, which cause net efficiency penalties higher than 7% points, CaLC results in a net efficiency penalty of 2.9% points. However, a thorough economic assessment of CaLC needs to be undertaken to evaluate its economic viability. The levelised cost of electricity is commonly used to assess the economic performance of clean energy systems. However, this method does not account for commercially important parameters, such as tax, interest, and depreciation charges. This study aimed to improve the reliability and accuracy of economic assessments of clean energy systems by implementing the net present value (NPV) approach. This approach was applied to assess the economic performance of two concepts of the CaLC-based power plant with either the conventional steam cycle (SC) or the supercritical CO 2 cycle (s-CO 2) for heat utilisation along with the bottom-up approach to total capital cost estimation. A parametric study for both concepts was also conducted to assess the impact of the key thermodynamic parameters on the economic performance. Although the s-CO 2 case with revised assumptions was shown to result in a 1%-point lower net efficiency compared to the SC case, its break-even cost of electricity was lower by 0.81 €/MWh. Further improvements of the techno-economic performance can be sought by optimisation of the s-CO 2 cycle structure. Highlights • CaLC-based power plant was assessed using NPV approach. • Bottom-up cost estimation method based on CaLC plant equipment scale was derived. • Bottom-up cost method principals can be used for other clean power systems. • Case study of CaLC plant with steam and supercritical CO 2 cycles was evaluated. • Implementing supercritical CO 2 cycle into CaLC power plant improved the economic performance. [ABSTRACT FROM AUTHOR]

• Acceleration of the development of a the indirectly heated carbonate looping process. • Detailed process description of the 300kWth pilot plant. • Demonstration in close by semi-industrial conditions for cement and lime. • First-of-a-kind application of waste derived fuels in an IHCaL facility for delivering heat for calcination. The indirectly heated carbonate looping process (IHCaL) is a promising technology for decarbonizing the lime and cement industry. Advantages of the IHCaL are the synergy with these industries using same solid materials and the avoidance of an air separation unit (ASU), since no technical pure oxygen is necessary in this capture process. Former pilot tests showed the feasibility of the IHCaL for applications in the power plant sector. However, the integration of the IHCaL into cement and lime plants, as well as the usability of spent sorbents as educts in these processes, has not yet been proven in industrially relevant conditions. In this study, the modification of an existing 300 kW th pilot plant for demonstrating the IHCaL process are described, aiming in accelerating the demonstration in an industrially relevant environment for cement and lime industries. A flue gas circulation system and a solid fueling system into the combustor, allowing the heat generation for the calcination with e.g. waste derived fuels, have been designed and installed. Results gained during the operation with the modified reactor configuration, are presented in order to assess the performance of the new components in the framework of the IHCaL configuration. The external combustor was operated while co-firing propane with either dried lignite or waste derived fuels. The carbonator was fluidized with a real flue gas from the external combustor, having CO 2 concentrations between 11 and 18 vol-% dry. The results, obtained within more than 200 h of continuous testing with modified reactor configuration, show a good hydrodynamic behavior and adequate reactor performance, while providing a sound basis for further improvement and up scaling of the technology. [ABSTRACT FROM AUTHOR]

The calcium carbonate looping cycle is an important reaction system for processes such as thermochemical energy storage and carbon capture technologies, which can be used to lower greenhouse gas emissions associated with the energy industry. Kinetic analysis of the reactions involved (calcination and carbonation) can be used to determine kinetic parameters (activation energy, pre-exponential factor, and the reaction model), which is useful to translate laboratory-scale studies to large-scale reactor conditions. A variety of methods are available and there is a lack of consensus on the kinetic parameters in published literature. In this paper, the calcination of synthesized CaCO3 is modeled using model-fitting methods under two different experimental atmospheres, including 100% CO2, which realistically reflects reactor conditions and is relatively unstudied kinetically. Results are compared with similar studies and model-free methods using a detailed, comparative methodology that has not been carried out previously. Under N2, an activation energy of 204 kJ mol−1 is obtained with the R2 (contracting area) geometric model, which is consistent with various model-fitting and isoconversional analyses. For experiments under CO2, much higher activation energies (up to 1220 kJ mol−1 with a first-order reaction model) are obtained, which has also been observed previously. The carbonation of synthesized CaO is modeled using an intrinsic chemical reaction rate model and an apparent model. Activation energies of 17.45 kJ mol−1 and 59.95 kJ mol−1 are obtained for the kinetic and diffusion control regions, respectively, which are on the lower bounds of literature results. The experimental conditions, material properties, and the kinetic method are found to strongly influence the kinetic parameters, and recommendations are provided for the analysis of both reactions.

Reaction kinetics is an important field of study in chemical engineering to translate laboratory-scale studies to large-scale reactor conditions. The procedures used to determine kinetic parameters (activation energy, pre-exponential factor and the reaction model) include model-fitting, model-free and generalized methods, which have been extensively used in published literature to model solid-gas reactions. A comprehensive review of kinetic analysis methods will be presented using the example of carbonate looping, an important process applied to thermochemical energy storage and carbon capture technologies. The kinetic parameters obtained by different methods for both the calcination and carbonation reactions are compared. The experimental conditions, material properties and the kinetic method are found to strongly influence the kinetic parameters and recommendations are provided for the analysis of both reactions. Of the methods, isoconversional techniques are encouraged to arrive at non-mechanistic parameters for calcination, while for carbonation, material characterization is recommended before choosing a specific kinetic analysis method.

For effective operation of high-temperature sorption of carbon dioxide from the flue gas in industrial scale, it is necessary to ensure an adequate supply of affordable sorbent having suitable technical parameters. For a given technology, natural limestones meet the condition of low cost. Due to current needs to solve the issue of carbon dioxide capture in power as well as other branches of industry, this study is focused on evaluating different types of natural limestones. A set of laboratory methods for evaluation of the physicochemical properties of limestones was proposed. A laboratory apparatus, based on the principle of fixed bed tubular reactor made of quartz glass, represented the main method for measurement sorption capacities. Within the sample base, a wide spread of sorption capacities was determined in the range of 18.0 - 84.6 % of the theoretical values, based on chemical composition. After six cycles the sorption capacity decreased to 3.5 - 35.6 %, compared to the theoretical value, mainly due to sintering. It was verified that appropriate selection of limestone can significantly reduce degradation of the capacity during cyclic use. [ABSTRACT FROM AUTHOR]

Carbonate looping or calcium looping (CaL) is an efficient post-combustion CO 2 -capture technology particularly suited for retrofitting existing power plants. Limestone, an inexpensive and highly available natural product, is utilized for the CaL process. A new concept with an indirectly heated calciner is presented, where the heat for calcination is transferred by means of heat pipes from an external combustor. This process modification offers higher plant efficiencies and lower CO 2 avoidance costs than an oxy-fired CaL process. The worldwide first indirectly heated CaL pilot plant with a nominal power of 300 kW th has been erected at Technische Universität Darmstadt. This paper presents the layout of the pilot plant and first operational results using a natural limestone as sorbent and propane as fuel for the external combustor. The calciner was fluidized with air to support self-fluidization of the sorbent during calcination and to lower the partial CO 2 pressure and therewith the calcination temperature. Proof of concept was demonstrated within more than 400 h continuous testing. The reactor system showed good hydrodynamic stability, and the heat pipe heat exchanger an excellent performance. CO 2 capture rates up to 90% in the carbonator were reached. [ABSTRACT FROM AUTHOR]

Carbonate looping promises low energy penalties for postcombustion CO2-capture and is particularly suited for retrofitting existing power plants. To further improve the process, a new concept with an indirectly heated calciner using heat pipes was developed, offering even higher plant efficiencies and lower CO2 avoidance costs than the oxy-fired standard carbonate looping process. The concept of the indirectly heated carbonate looping (1HCL) process was tested at sufficient scale in a 300 kWth pilot plant at Technische Universität Darmstadt. The paper presents a technical overview of the process and shows first test results of the pilot plant. Furthermore, the concept is economically evaluated and compared to other carbon capture processes. [ABSTRACT FROM AUTHOR]

The characteristics of CO2 reacting with CaO in a molten eutectic mixture of CaF2 and NaF has been investigated. Calculations of the Gibbs free energy, temperature analysis of the decomposition of the formed carbonates, and XRD analyses of quenched samples taken during CO2 absorption or desorption were employed to identify the phases present in the melt. Efficient CO2 absorption from a simulated flue gas was observed, due to a combined reaction where CaO initially reacts with CO2 and forms CaCO3. Subsequently, Na2CO3 is formed by an ion exchange reaction between CaCO3 and NaF. It was found that the CaO activity is highest in the temperature range 826-834°C. Increasing the CaO concentration from 5 to 20 wt% in the molten salt resulted in reduced CO2 reactivity efficiency, probably because of precipitation and agglomeration of the sorbent. The total carbonation conversion was independent of the CO2 concentration in the inlet gas, and the sorbent carrying capacity was in the range 0.722-0.743 g CO2/g CaO corresponding to 0.037-0.144 g CO2/g total liquid. Decarbonation was conducted by raising the temperature. 40% conversion back to CaO was recorded at 1160°C. The recorded curves for the CO2 concentration in the outlet gas exhibited a rapid desorption step followed by a slow step. [ABSTRACT FROM AUTHOR]

Alstom is a pioneer and industrial leader in the development of post combustion CCS technologies. Alstom's Regenerative Calcium Cycle (RCC) is a 2 nd generation post combustion CCS technology utilizing a calcination/ carbonation loop to capture CO 2 from flue gas at high temperatures. The CO 2 capture cycle is driven by introducing heat required to regenerate sorbent at 900 °C (4.0 GJ/t CO 2 , chemically bound CO 2 ) the regenerated sorbent is then used for CO 2 capture from flue gas where the exothermic heat of the reverse reaction (-4.0 GJ/t CO 2 captured) is recovered in a power cycle. Due to the option of using natural sorbent materials (limestone), RCC also provides attractive integration opportunities with industrial processes such as cement production. Recently indirectly fired RCC calcination concepts also open the door for game changing performance gains using natural or even synthetic materials. However, the wide range of performance variability characteristic of natural sorbents contributes to uncertainty in defining process performance. Reliable sorbent deactivation models, which describe both cyclic and chemical deactivation, in combination with mechanistic reactor models which predict gas and solids phase conversions are required to lower the uncertainty associated with new reactor concepts and larger geometries required for commercialization for retrofit power-plant flue gas or for integrated solutions for the cement industry. Parallel to RCC process development, Alstom is currently executing a “Derisking” or risk-mitigation study for Norcem, a Norwegian cement producer, who seeks to take a leading position in the development of technologies for CO 2 -capture from cement production facilities. Norcem is currently heading up a project on behalf of the European cement industry (partners are Norcem, HeidelbergCement and the European Cement Research Academy) investigating various technological options at the pilot scale. In relation to this project, Alstom's RCC technology was selected with the objective to define process performance and the associated uncertainty. Pilot testing was conducted at the Institute of Combustion and Power Plant Technology at the University of Stuttgart (IFK) planned by Alstom focusing on the validation of process models and less the targeting of pilot plant performance, which is often limited by reactor geometries. This paper discusses the characterization of sorbent performance and the gap between the performance expected from thermo- gravimetric analysis (TGA) and that realized during steady state pilot testing under representative operating conditions. Operational stability, material balance closure and the confirmation of sorbent attrition characteristics from pilot testing are also discussed and steady-state operational data, gained from pilot testing are applied to initialize mechanistic process models which allow prediction of reactor performance for larger more efficient designs. [ABSTRACT FROM AUTHOR]

Highlights: [•] Overview of the R&D work done at IFK, Uni Stuttgart with Calcium Looping (CaL). [•] Economic, simulation, demonstration, hydrodynamic and kinetic studies of CaL performed. [•] In house design and construction of DFB pilot plants based on CaL. [•] Successful demonstration of CaL in the 10kWth and 200kWth DFB pilot plants. [•] Carbonator and regenerator characterization from 10kWth DFB plant. [Copyright &y& Elsevier]

Highlights: [•] Simulations of NGCC cycle with post-combustion CO2 capture by carbonate looping. [•] Sorbent review with respect to sorption capacity and semi-empirical model fit. [•] Calciner energy requirement investigated for natural and synthetic sorbents. [•] Power cycle simulations including CO2 capture and compression units. [•] Prerequisites for high efficiency quantified on material and process level. [Copyright &y& Elsevier]

A promising way to reduce CO2 emissions of fossil-fired power plants is the carbonate looping process with the reversible carbonation-calcination reaction of limestone. The focus is on the gas release in an indirectly heat pipe-heated calciner. Experiments in an electrically heated lab-scale batch calciner demonstrated that transition from a fixed bed to a bubbling fluidized bed is possible without an external fluidization agent only by heating up limestone. Several indirectly heated calciner concepts are presented. [ABSTRACT FROM AUTHOR]

Carbon capture with subsequent compression and storage is a promising possibility for the reduction of CO2 emissions from coal-fired power generation. A very efficient post-combustion CO2 capture technology is the carbonate looping process. To further increase the process efficiency, a new concept is considered where the heat for calcination is transferred from an external combustor to the calciner by means of heat pipes. Some thermodynamic evaluations for a retrofit of a coal-fired host plant with the indirectly heated carbonate looping process and cold flow model tests of a 300-kWth test facility that will be erected in 2013 in Darmstadt are presented. [ABSTRACT FROM AUTHOR]

Abstract: The development of Calcium-Looping for CO2 capture has made vast progress in recent time. The technology has become a serious option for CO2 capture from fossile fuel fired power plants. Calcium-Looping is a highly efficient process which uses broadly available natural limestone as a CO2 sorbent. The process uses the reversible reaction (CaCO3 ↔CaO+CO2) between calcium carbonate and calcium oxide in the temperature range of 650 and 900°C. This publication presents the results of the work done at IFK to demonstrate the Calcium-Looping process in pilot scale at realistic process conditions. The first experimental campaings with the 200 kWth Dual Fluidized Bed (DFB) Facility have shown hydrodynamic stability as well as high flexibility in operation. CO2 capture efficiencies above 90% were achieved consistently over a broad range of process conditions during multiple hours of operation. The presence of water vapor, which is found naturally in flue gas, was found to significantly improve the CO2 capture efficiency. Sorbent attrition measurements fell within a reasonable range, giving confidence that attrition will not be a major restraint for Calcium Looping. [Copyright &y& Elsevier]

Abstract: CO2 capture by solid sorbents through uptake–regeneration cycling is a promising option for high temperature removal of CO2 from combustion gases and synthesis/fuel gases. The present study investigates the influence of regeneration atmosphere and temperature on the CO2 uptake capacity during repeated cycling of CaO-based solid sorbents. The sorbents were synthesised to contain 75 and 85% w/w of active phase (CaO) and binder (Ca12Al14O33) and were then subjected to cycling tests with repeated CO2 uptake and release in a thermogravimetric analyser TGA for up to 200 cycles. Test conditions were chosen to test high temperature CO2 capture at 600°C in an atmosphere containing 14 and 25% v/v CO2 (N2 balance). Three different regeneration conditions were tested: [(a)] mild condition: regeneration at 900°C in 14% CO2 or 100% N2; [(b)] moderate condition: regeneration at 1000°C in 14% CO2; and [(c)] severe condition: regeneration at 1000°C in 86% CO2. Hydration of the sorbent during synthesis and prolonged carbonation prior to the cycling tests significantly improved the stability of the uptake capacity. Interestingly, the pretreated 75% w/w CaO synthetic sorbent maintained a good uptake capacity up to the 150th cycle under severe regeneration conditions and even showed continuously increasing CO2 uptake capacity throughout the 150 cycle test with 25% CO2. The 75% w/w CaO sorbent is thus an interesting candidate for future work on high temperature CO2 capture. [Copyright &y& Elsevier]

Abstract: Hydrogen is expected to be one of the most important energy carriers in the future. Gasification process may be used to produce hydrogen when joined with carbon capture technologies. Furthermore, the combination of biomass gasification and carbon capture presents a significant technical potential in net negative greenhouse gas emissions. Lime enhanced biomass gasification process makes use of CaO as a high temperature CO2 carrier between the steam biomass gasifier and an oxy-fired regenerator. Important energy penalties derive from the temperature difference between the reactors (around 250–300 °C). A cyclonic preheater similar to those used in the cement industry may improve the energetic efficiency of the process if the particles entering the regenerator reactor are heated up by the gas leaving this reactor. A lime enhanced biomass gasification system was modelled and simulated. A cyclonic preheater was included to evaluate the improvement. Results show an increase of the gasification chemical efficiency and a reduction of the energy consumption in the regenerator. [Copyright &y& Elsevier]

Abstract: A novel process for conversion of hydrocarbons to H2 has been examined. The process, sorption enhanced chemical-looping reforming, involves three interconnected reactor vessels. In the reforming reactor, hydrocarbon fuel is partially oxidized with oxygen provided via a solid oxygen carrier such as NiO. Resulting CO is shifted instantly to CO2 via sorption enhanced water–gas shift, facilitated by the capturing of CO2 with a solid CO2 sorbent such as CaO. Ni and CaCO3, are regenerated downstream in separate reactors. The process produces H2, CO2 and N2 of reasonable purity in separate streams, without need for additional gas separation equipment. The characteristics of the process have been examined by thermodynamic calculations and by process modeling. At 1bar it could produce >2.8mol H2 with a purity of >98vol.% for each mol CH4 added as fuel, while capturing >95% of added carbon as CO2. Increasing the pressure reduces the performance due to lower conversion of CH4. Involved reactions have also been examined in a fluidized-bed reactor at 600–750°C, with particles of NiO and CaO as bed material and CH4 mixed with steam as fuel. The CH4 conversion was incomplete but the results fitted with theory and gas with a H2/(H2 +CO+CO2) ratio of more than 98% was produced at 600°C. [Copyright &y& Elsevier]

Abstract: The calcium-looping process is a promising technique for CO2 capture from coal-fired power plants and for reducing GHG emissions from the power generation sector. This paper presents a calculation model of the carbonator, the key reactor of the Ca-looping process, where CO2 is captured as a result of its reaction with CaO. The model presented is based on the Kunii–Levenspiel theory for circulating fluidized bed and on the recent findings on the properties of CaO as a CO2 sorbent, while taking into account the effects of coal ash and sulfur species. This model can be used for process optimization and for the prediction of the performance of power plants based on the Ca-looping process. Also presented in this paper are the results of a sensitivity analysis of the primary parameters that influence the performance of the carbonator. These results confirm the feasibility of the Ca-looping process with reactors of reasonable size for industrial applications and highlight the importance of the properties of the Ca-based sorbent as they highly affect the carbonator''s performance. [Copyright &y& Elsevier]

Abstract: Environmental degradation due to large emission of pollutants including green house gases from conventional coal based power plants is presently of great concern. On the other hand, existing dependence on the coal based power plants to meet the increasing electricity demand cannot be changed abruptly. Hence developing efficient coal based power plants with low emissions is of great demand. IGCC plants are established technologies for this purpose. However, CO2 capture still causes substantial reduction in efficiency. In this paper, a novel IGCC plant integrating oxygen separation from air by ceramic membrane and post combustion CO2 capture by a twin fluidized bed carbonation–calcinations loop has been proposed. A simulation of this conceptualized plant shows significant increase in efficiency than a comparable IGCC plant with conventional pre-combustion capture. The new IGCC concept reached a net efficiency of 43.2% based on LHV for hard coal. Furthermore, the concept allows CO2 recovery of almost 98% resulting in substantially lower specific CO2 emissions of 22.1g/kWh. A complete description of the plant and detailed simulation results in comparison with the previous IGCC plant are discussed. Additionally, a short parametric study is performed to demonstrate basic process interaction and further thermodynamic potential. [Copyright &y& Elsevier]

Abstract: The capture and purification of carbon dioxide (CO2) from flue or fuel gas underlies the cost efficiency of carbon capture and storage (CCS) applications in the power and industrial sectors and there is considerable scope for cost reduction with the development of novel capture technologies. High-temperature sorbents are seen as a “next-generation” technology and a promising candidate is calcium oxide (CaO) derived from natural limestone, which is used in a process known as carbonate looping. This process exploits the reversible reaction between CaO and CO2 to form calcium carbonate (CaCO3). Unfortunately, sorbent derived from natural limestone loses its capacity to capture CO2 through long-term cycling, and a large amount of fresh limestone is required to maintain an acceptable CO2 capture efficiency. This work describes the development and characterisation of synthetic CaO-based sorbents, such as those incorporating a mixed calcium-aluminium oxide binder—in this case produced by precipitation in a slurry bubble column. Reactivity tests using a thermogravimetric analyser (TGA) demonstrate the improved long-term CO2 uptake of the synthetic sorbent. The highest CO2 uptake observed after 30 cycles was achieved with 85 wt.% CaO and binder, which was three times higher than the observed capacity of a natural limestone (Havelock). However, contrary to TGA results, experimental results for reactivity tests conducted using a bench-scale fluidised bed reactor (FBR) showed the highest uptake for the precipitated sorbent with no binder. A decrease in uptake was observed corresponding an increase in binder loading from 0–25 wt.%, which was coupled with an increase in mass loss owing to elutriation, attributed to decrepitation during cycling. [Copyright &y& Elsevier]

Abstract: Post-combustion carbonate looping processes are based on the capture of carbon dioxide from the flue gases of an existing power plant in a circulating fluidized bed reactor (CFB) of calcium oxide (the carbonator) particles. The calcination of calcium carbonate in a new oxy-fired CFBC power plant regenerates the sorbent (calcium oxide particles) and obtains high purity carbon dioxide. This communication presents experimental results from a small test facility (30kWt) operated in continuous mode using two interconnected CFB reactors as carbonator and calciner. Capture efficiencies between 70 and 97% have been obtained under realistic flue gas conditions in the carbonator reactor (temperatures around 650°C). The similarity between process conditions and those existing in CFBC power plants should allow a rapid scaling up of this technology. The next steps for this process development are also outlined. [Copyright &y& Elsevier]

Abstract: Carbonate Looping is a promising post-combustion capture process involving the separation of CO2 from the flue gas of a coalfired power plant at high temperatures (600–700 ∘C) using the reversible exothermic CaO carbonation reaction and the endothermic calcination reaction of CaCO3. The core of the carbonate looping process is a dual fluidized bed reactor in which the CO2 acceptor material (CaO) is transported between the carbonator (CO2 absorption) and regenerator (CO2 desorption). Due to the heat requirements for the regenerator, the carbonate looping acts as a CO2 separation unit and an add-on power plant, thereby offering the opportunity for increasing the site electricity production while inflicting only a low electric efficiency penalty on the total power plant. However, the quantity and quality of the Carbonate Looping heat sources differ significantly from a conventional coal-fired power plant. This paper presents the design and simulation of the carbonate looping steam cycle for a large coal-fired plant. The simulation involves the coupling of the carbonate looping reactor model from Aspen Plus with the steam cycle in EBSILON Professional code which is a mass and energy balance cycle calculation program specifically tailored for steam cycle calculations. The resulting simulation includes penalty deduction for the Air Separation Unit and the CO2 conditioning unit, resulting in a net efficiency of 39.2% and while increasing the net power input from 1052 MWe to 1533 MWe, an addition of 481 MWe for the retrofitted power plant. [Copyright &y& Elsevier]

Abstract: The Carbonate Looping process is a promising technology for post-combustion CO2 capture from power plants by means of CaO in a system of two fluidized bed reactors. The present study focuses on the retrofit with re-powering of an existing 1052 MWel coal-fired power plant. Material and energy balances of the process have been performed using ASPEN PLUS. The effect of make-up mass flow on circulating flow, coal feed to the calciner, electrical output, net plant efficiency, and CO2 capture efficiency is discussed. The energy penalty of 2.75% points is much lower than that of other CO2 capture technologies. [Copyright &y& Elsevier]

Abstract: Post-combustion carbonate looping processes are based on the capture of CO2 from the flue gases of an existing power plant in a circulating fluidized bed (CFB) reactor of CaO (the carbonator) at around 650 ∘C. The calcination of CaCO3 in a new oxy-fired experimental results from a small test facility (30 kWt) operated in continuous mode using two interconnected CFB reactors as carbonator and calciner. Capture efficiencies between 70 and 97% have been obtained under realistic flue gas conditions in the carbonator reactor. The similarity between process conditions and those existing in CFBC power plants should allow a rapid scaling up of this technology. [Copyright &y& Elsevier]

[Display omitted] • Mineral MgO promoted with CaCO 3 and molten salts shows promise for carbonate looping. • Faster sorption rate is enabled with elevated molten salt and lower CaCO 3 contents. • Higher molten salt loadings lead to more severe sintering and cyclic activity loss. • Extended carbonation conversion enhances cyclic operation and counteracts sintering. • Long sorption duration or low temperature with 30 % CO 2 flow improves stability. This study evaluated the CO 2 capture performance of MgO obtained from mineral magnesite and doped with limestone and molten Li, Na and K nitrates under consecutive sorption/desorption cycles via thermogravimetric analysis. Increasing the molten promoter loading resulted in a higher CO 2 sorption rate, while elevated CaCO 3 amounts impeded CO 2 diffusion. When exposed to a 30 % CO 2 flow at 300 °C for 30 min, the sorbent with alkali salts and CaCO 3 to MgO molar ratios of 0.20 and 0.05 respectively attained a capture of 7.2 mol CO 2 /kg of sorbent and a negligible activity loss (∼6%) after 50 cycles. This performance was promising, considering the mineral nature of precursors. In-situ X-ray diffraction revealed the growth of the MgO crystal after each desorption, proving the gradual MgO sintering. However, the morphological transformations occurring during cyclic operation and especially if high conversions of MgO are reached, trigger an alkali salt redistribution that grants high stability. [ABSTRACT FROM AUTHOR]

• A 1 MWth carbonate looping plant was operated in steady state for > 2000 h. • A carbonator efficiency > 80 % was obtained under a variety of operating conditions. • A calciner efficiency > 90 % was achieved 30 K above equilibrium temperature. Carbon capture and utilization/storage is an effective means to reduce CO 2 emissions from power and energy intensive industries. Carbonate looping is a 2nd generation post-combustion CO 2 capture technology using solid sorbents that form carbonates when reacting with CO 2. This technology has economic benefits caused by the low efficiency penalty and the low cost of the sorbent. Autothermal continuous operation of this process at high CO 2 capture rates has been successfully proven in several pilot plants up to 1.7 MW th. The 1 MW th pilot plant in Darmstadt has been operated for more than 2000 h with long periods of steady-state conditions, which allows the evaluation of the performance of the reactor system during long-term operation. This paper presents complementary results of these pilot tests focussing on the performance of the carbonator and calciner reactors. A high carbonator efficiency above 80 % is possible in the temperature range of 650–675 °C with a specific solid inventory above 700 kg/m2 combined with either a high sorbent looping ratio of 16 mol Ca /mol CO2 or a high make-up ratio of 0.13 mol Ca /mol CO2. A calcination efficiency of 90 % can be achieved by a calciner space time above 6 min, if the calciner temperature is 30 K above the equilibrium temperature at the prevailing CO 2 concentration. Heating of the sorbent entering the calciner consumes almost half of the thermal fuel input. [ABSTRACT FROM AUTHOR]

Reaction kinetics is an important field of study in chemical engineering to translate laboratory-scale studies to large-scale reactor conditions. The procedures used to determine kinetic parameters (activation energy, pre-exponential factor and the reaction model) include model-fitting, model-free and generalized methods, which have been extensively used in published literature to model solid-gas reactions. A comprehensive review of kinetic analysis methods will be presented using the example of carbonate looping, an important process applied to thermochemical energy storage and carbon capture technologies. The kinetic parameters obtained by different methods for both the calcination and carbonation reactions are compared. The experimental conditions, material properties and the kinetic method are found to strongly influence the kinetic parameters and recommendations are provided for the analysis of both reactions. Of the methods, isoconversional techniques are encouraged to arrive at non-mechanistic parameters for calcination, while for carbonation, material characterization is recommended before choosing a specific kinetic analysis method. [ABSTRACT FROM AUTHOR]