Carbonation-calcination Reaction Research Articles

CO2 capture from waste-to-energy plants: Techno-economic assessment of novel integration concepts of calcium looping technology

In Waste-to-Energy (WtE) plants, municipal solid waste (MSW) is combusted while power and/or heat are produced. This approach will largely remain as a promising option to handle the MSW capacities in the future. Due to the organic waste fractions present in MSW, net negative CO2 emissions are feasible when integrating carbon capture and storage (CCS) processes into WtE plants. The calcium looping (CaL) process represents one option to capture CO2 from WtE plant exhaust gases. Hereby, CO2 is separated by a circulating limestone-based sorbent being exposed to cyclic carbonation-calcination reaction regimes. Within this study, a techno-economic analysis of a CaL retrofit on a generic 60 MWth WtE plant is conducted. The analysis considerers three different types of supplementary fuel for the CaL process, namely coal, natural gas (NG) and solid recovered fuel (SRF). Based on a detailed process model, economic key performance indicators were calculated by means of a bottom-up approach. Additionally, different heat integration concepts were proposed and assessed. The techno-economic results are discussed in comparison to a benchmark MEA scrubbing process. It was found that levelized cost of electricity increases quite significantly, which leads to cost of CO2 avoidance in the range of 119 EUR/tCO2,av (CaL-SRF) up to 288 EUR/tCO2,av (MEA). It is important to note, that the supply of negative CO2 emissions from a CCS equipped WtE plant enables a cost-efficient solution to at the same time treat MSW in a carbon neutral way while clean heat and/or power as well as negative CO2 emissions are delivered.

Combustion of solid recovered fuels within the calcium looping process – Experimental demonstration at 1 MWth scale

The calcium looping (CaL) process is an efficient post-combustion CO2 capture technology based on the reversible carbonation-calcination reaction of natural lime. This work presents the results obtained during long-term operation at the 1 MWth CaL pilot plant at Technische Universität Darmstadt. During more than 230 h of representative CaL operation, the calciner was heated by oxy-fuel combustion of waste derived fuels. During the experimental investigation, two types of solid recovered fuels (SRF) were utilized. Both types of SRF were fed to the process in the form of raw fluff, similar to typical industrial applications. The flue gas to be decarbonized in the carbonator, was supplied by an on-site combustion chamber. The CO2 concentration was kept between 9.5 and 10.5 vol% as typical value for waste-to-energy (WtE) plants fueled by municipal solid waste (MSW). Over a wide range of operation conditions, CO2 absorption rates of 80% and total CO2 capture rates over 90% were achieved. Within this work, exemplary long-term data plots of relevant CaL process parameters are shown for each type of SRF. A chlorine balance for a representative operation period is established based on the relevant effluent streams from the CaL system. Thereby, it was found that the calciner fly ash represents the major chlorine effluent. Furthermore, the retention rate of chlorine was above 82% throughout all test points, respectively. When taking into account the organic waste fractions typically contained in SRF and MSW, this work successfully demonstrates the feasibility of net negative CO2 emissions by means of the CaL process at semi-industrial scale.

Evaluation of the effect of inert support on the carbonation reaction of synthetic CaO-based CO2 sorbents

Calcium oxide has been proved to be a suitable sorbent for high temperature CO2 capture processes based on the cyclic carbonation-calcination reaction. In this work several synthetic sorbents have been prepared with CaO contents between 40 and 95% wt. on to two different inert supports MgO and Ca12Al14O33. The effect of CaO content and inert nature on materials CO2 carrying capacity and reactivity towards carbonation reaction has been assessed. The materials have been texturally characterised. A complete kinetic study has been performed and the Random Pore Model has been applied to determine the intrinsic rate parameters for the carbonation reaction. Suitable particles for operation in fixed bed reactor have been produced from some selected powdered materials, and a complete particle reaction model that incorporate the intrinsic kinetic data has been developed and validated.

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.

Steam Hydration of Calcium Oxide for Solid Sorbent Based CO2 Capture: Effects of Sintering and Fluidized Bed Reactor Behavior

This study reports on the hydration characteristics in the three-step carbonation–calcination reaction (CCR) process with intermediate steam hydration. Specifically, experimental results of sorbent reactivation in a fluidized bed steam hydration reactor are presented along with the effect of the operating gas velocity (Ug) and different calcination conditions on the hydration reaction. The enhancing effect of increasing Ug on the hydration rate is evident but limited with a threshold at 0.3 m/s, above which the bulk phase mass transfer effects are less significant. The highest hydration conversion of 83% is achieved in 30 min at the highest Ug of 0.5 m/s. However, increasing Ug also yields lower steam utilization during hydration; thus an optimal operating condition with respect to both the solid and steam conversions shall be determined via an overall process analysis. In addition, the parametric effect of different calcination conditions, specifically, the calcination temperature, time, and reactor type, on the hydration reaction mechanism is investigated. The sorbent reactivity and morphology is characterized using thermogravimetric and Brunauer–Emmett–Teller analysis as well as scanning electron microscopy imaging. Sorbents produced at lower calcination temperatures and in a reactor with sufficient mixing exhibit a larger surface area and pore volume, and superior reactivity. The effect of calcination time, within the scope of this study, is not as significant. Lastly, sorbent reactivity toward steam hydration depends strongly on its surface kinetics but not to the same extent as carbonation. The hydration and carbonation reactions are compared using a modified Jander’s equation, [1– (1 – ∝)1/3]N = Kt.

Modification of One-Dimensional TiO2Nanotubes with CaO Dopants for High CO2Adsorption

One-dimensional calcium oxide (CaO-) based titanium dioxide (TiO2) nanotubes were successfully synthesized through a rapid electrochemical anodization and chemical wet impregnation techniques. In this study, calcium nitrate solution was used as a calcium source precursor. The reaction time and concentration of calcium source on the formation of CaO-TiO2nanotubes were investigated using field emission microscopy, energy dispersion X-ray spectroscopy, and X-ray diffraction. The adsorption capacity of CO2was determined by thermal gravimetric analyzer. A maximum of 4.45 mmol/g was achieved from the CaO-TiO2nanotubes (6.64 at% of Ca). The finding was attributed to the higher active surface area for CaO to adsorb more CO2gas and then formed CaCO3compound during cyclic carbonation-calcination reaction.

Energy penalty of CO2 capture for the Carbonation–Calcination Reaction (CCR) Process: Parametric effects and comparisons with alternative processes

Process simulations of carbon capture technologies typically examine a limited number of cases and process variables. In many instances, processes are modeled under the most favorable conditions to improve process performance. With no universal standards defined for important parameters such as energy requirements for carbon dioxide compression and air separation, carbon dioxide purity, and base plant efficiency, great variability can exist during process analysis. This publication is presented in sequel to an earlier study on the Carbonation–Calcination Reaction (CCR) Process, which uses a cyclic calcium carbonate–calcium oxide–calcium hydroxide reaction scheme. While the first paper focused on the effect of internal parameters, this follow-up publication focuses on the external parameters of coal rank, base plant efficiency, heat transfer efficiency, compression energy, and air separation energy to determine the contribution of each to the overall energy penalty. In addition, novel integration options are introduced, effect of the CCR Process on boiler performance is analyzed, and a sensitivity analysis is performed. Specifically, the ASPEN Plus simulations focus on the difference between ideal and realistic conditions. The comprehensive simulations allow for a direct comparison of the CCR Process with other processes developed for post-combustion carbon dioxide removal from coal combustion under normalized conditions to remove the effect of external variables. The comparison indicates that the CCR Process always provides a lower energy penalty under similar operating conditions.

Simulations and process analysis of the carbonation–calcination reaction process with intermediate hydration

Several technologies are currently being developed to separate carbon dioxide from large point sources, such as coal-fired power plants. An emerging technology that shows great potential is a calcium oxide–calcium carbonate cycle. A major drawback is the calcium carbonate decreases in reactivity over multiple cycles. The Ohio State University demonstrated in 2008 the first carbonation–calcination reaction (CCR) process that includes intermediate hydration for sorbent regeneration and its feasibility over multiple cycles at the 120kWth scale with actual flue gas from coal combustion. The CCR Process utilizes a calcium-based sorbent to react with the carbon dioxide and sulfur dioxide in a flue gas stream to form calcium carbonate and calcium sulfate, respectively. The carbon dioxide is subsequently released from the calcium carbonate to produce a high-purity, sequestration-ready carbon dioxide stream while regenerating the calcium oxide sorbent. The sulfur dioxide is fixated as calcium sulfate and removed through a purge stream. An intermediate hydration step restores reactivity to the calcium oxide sorbent. Process analysis from computer simulations shows the CCR Process to be highly effective and efficient in removing both carbon dioxide and sulfur dioxide at low energy penalties under realistic conditions. A 20–22% decrease in electricity generation efficiency with the CCR Process is expected, compared with amine scrubbing around 27% and oxy-combustion around 25% energy penalty. A 25–28% increase in thermal energy with the CCR Process is expected to maintain a constant electrical output. Further, the CCR Process consumes half the oxygen necessary for an oxy-combustion plant and 25% less steam necessary for amine scrubbing.

Activation Strategies for Calcium-Based Sorbents for CO2 Capture: A Perspective

The chemical looping process (CLP) using calcium-based sorbents to capture CO2 through cyclic carbonation–calcination reaction (CCR) before, during, or after the conversion of carbonaceous fuel occurs, is a viable CO2 control technology. With extensive past and current research efforts, the basic process concept has been found to be attractive at larger scales. Additionally, process simulations based on experimental results indicate that the parasitic energy consumption for this high temperature process is relatively low compared to low temperature processes such as the amine-based process. The ability of the calcium-based sorbents to maintain stable reactivity and physical integrity in cyclic reaction under severe operating conditions is one of the most important criteria for the success of the calcium looping technology. Despite being abundant and cheap, calcium-based sorbents derived from naturally occurring precursors, such as limestone and dolomite, suffer from rapid reactivity deterioration after hi...

Experimental Study of HCl Capture Using CaO Sorbents: Activation, Deactivation, Reactivation, and Ionic Transfer Mechanism

Experimental study of dry HCl removal from synthesis gas or flue gas using CaO sorbents, in the context of CaO-based chemical looping processes, is reported. The study was first conducted in a TGA and a fixed-bed reactor to test the effects of chloridation temperature, sorbent particle size, HCl concentration, and space velocity on the HCl capture capacity. The chloridation reactivity deterioration of CaO sorbents with multicyclic carbonation−calcination reaction (CCR) and/or at high calcination temperatures, which are of notable relevance to the CaO-based chemical looping processes, was also investigated. In addition, precipitation (activation) and hydration (reactivation) were used to enhance initial sorbent reactivity and to reactivate the deactivated sorbents, respectively. The effects of deactivation, activation, and reactivation were explained by the morphological property change of the sorbents. To further elucidate the solid phase reaction mechanism of CaO and HCl, ionic transfer behavior during c...

Subpilot Demonstration of the Carbonation−Calcination Reaction (CCR) Process: High-Temperature CO2 and Sulfur Capture from Coal-Fired Power Plants

Increasing concerns over growing CO2 levels in the atmosphere have led to a worldwide demand for efficient, cost-effective, and clean carbon capture technologies. One of these technologies is the Carbonation−Calcination Reaction (CCR) process, which utilizes a calcium-based sorbent in a high-temperature reaction (carbonation) to capture the CO2 from the flue gas stream and releases a pure stream of CO2 in the subsequent calcination reaction that can be sequestered. A 120 KWth subpilot-scale combustion plant utilizing coal at 20 pph along with natural gas has been established at The Ohio State University to test the CCR process. Experimental studies on CO2 capture using calcium-based sorbents have been performed at this facility. Greater than 99% CO2 and SO2 capture has been achieved at the subpilot-scale facility on a once-through basis at a Ca:C mole ratio of 1.6. In addition, the sorbent reactivity is maintained over multiple cycles by the incorporation of a sorbent reactivation hydration step in the carbonation−calcination cycle.

Cyclic Carbonation Calcination Studies of Limestone and Dolomite for CO2 Separation From Combustion Flue Gases

Naturally occurring limestone and dolomite samples, originating from different geographical locations, were tested as potential sorbents for carbonation/calcination based CO2 capture from combustion flue gases. Samples have been studied in a thermogravimetric analyzer under simulated flue gas conditions at three calcination temperatures, viz., 750°C, 875°C, and 930°C for four carbonation calcination reaction (CCR) cycles. The dolomite sample exhibited the highest rate of carbonation than the tested limestones. At the third cycle, its CO2 capture capacity per kilogram of the sample was nearly equal to that of Gotland, the highest reacting limestone tested. At the fourth cycle it surpassed Gotland, despite the fact that the CaCO3 content of the Sibbo dolomite was only 2/3 of that of the Gotland. Decay coefficients were calculated by a curve fitting exercise and its value is lowest for the Sibbo dolomite. That means, most probably its capture capacity per kilogram of the sample would remain higher, well beyond the fourth cycle. There was a strong correlation between the calcination temperature, the specific surface area of the calcined samples, and the degree of carbonation. It was observed that the higher the calcination temperature, the lower the sorbent reactivity. The Brunauer–Emmett–Teller measurements and scanning electron microscope images provided quantitative and qualitative evidences to prove this. For a given limestone/dolomite sample, sorbent’s CO2 capture capacity depended on the number of CCR cycles and the calcination temperature. In a CCR loop, if the sorbent is utilized only for a certain small number of cycles (<20), the CO2 capture capacity could be increased by lowering the calcination temperature. According to the equilibrium thermodynamics, the CO2 partial pressure in the calciner should be lowered to lower the calcination temperature. This can be achieved by additional steam supply into the calciner. Steam could then be condensed in an external condenser to single out the CO2 stream from the exit gas mixture of the calciner. A calciner design based on this concept is illustrated.

Kinetics and Structural Characterization of Calcium-Based Sorbents Calcined under Subatmospheric Conditions for the High-Temperature CO2Capture Process

The influence of several process parameters on the calcination of a naturally occurring limestone and a precipitated mesoporous calcium carbonate (CaCO3) sorbent structure to calcium oxide (CaO) is detailed in this study. CaCO3 calcination is an integral part of a multicyclic carbonation−calcination reaction (CCR) process that separates carbon dioxide (CO2) from high-temperature gas mixtures into a pure CO2 stream. Maintenance of high sorbent reactivity over repeated CCR cycles reduces the capital and operating cost of the CCR process. A lower calcination temperature, required to maintain high sorbent reactivity, reduces the calcination rate of CaCO3. This study investigates various process conditions such as subatmospheric calcination, sorbent dispersion in a rotary calciner, use of a high thermal conductivity sweep gas, etc. in enhancing the calcination rate at lower calcination temperatures. The high-temperature gas−solid carbonation studies of the resulting CaO sorbent prove the necessity to maintain a high porosity structure during limestone calcination.

Production of hydrogen through the carbonation–calcination reaction applied to CH4/CO2 mixtures

The production of hydrogen combined with carbon capture represents a possible option for reducing CO2 emissions in atmosphere and anthropogenic greenhouse effect. Nowadays the worldwide hydrogen production is based mainly on natural gas reforming, but the attention of the scientific community is focused also on other gas mixtures with significant methane content. In particular mixtures constituted mainly by methane and carbon dioxide are extensively used in energy conversion applications, as they include land-fill gas, digester gas and natural gas. The present paper addresses the development of an innovative system for hydrogen production and CO2 capture starting from these mixtures. The plant is based on steam methane reforming, coupled with the carbonation and calcination reactions for CO2 absorption and desorption, respectively. A thermodynamic approach is proposed to investigate the plant performance in relation to the CH4 content in the feeding gas. The results suggest that, in order to optimize the hydrogen purity and the efficiency, two different methodologies can be adopted involving both the system layout and operating parameters. In particular such methodologies are suitable for a methane content, respectively, higher and lower than 65%.

Study of the carbonation–calcination reaction applied to the hydrogen production from syngas

In the last years the interest in hydrogen as an energy carrier is significantly increased both for vehicle fuelling and stationary energy production by fuel cells. The benefits of a hydrogen energy policy are the reduction of the greenhouse effect and the centralization of the emission sources. Moreover, an improvement to the environmental benefits can be achieved if hydrogen is produced from renewable sources, as biomass. The present study relates the development of an innovative system for hydrogen production and CO2 capture starting from syngas. The plant is based on the carbonation and calcination reactions for CO2 absorption and desorption, respectively. In the carbonation reactor also steam methane reforming and CO-shift take place to enhance the hydrogen production. By means of a thermodynamic analysis, the system has been optimized in terms of the amount of the hydrogen produced and its purity. Different syngas compositions have been tested. The results confirm the effectiveness of the system proposed, which provides 99% H2 purity and zero CO2 emission in the case of the syngas derived from Battelle Columbus Laboratories gasifier.