Efficient Post-combustion CO2 Capture Research Articles

Recent advances on the modeling and optimization of CO2 capture processes

This work presents a critical review on the recent developments in the design and optimization of efficient post-combustion CO2 capture processes from point sources, focusing on absorption, adsorption, and membrane separations. Emphasis is placed on the efficient modeling and simulation frameworks, synthesis and design studies, and model-based optimization approaches. Furthermore, the interactions between material (solvent, adsorbent, membrane) development and process design and optimization, are explored. Comparison among the different carbon capture processes, shows that absorption is still the most mature technology for post-combustion CO2 capture. Amines are the most appropriate solvents for CO2 absorption, although significant amount of energy is required for solvent regeneration. On the other hand, the development of materials used in adsorption and membrane-based separations has not reached a mature level that can lead to efficient CO2 capture, employing simple process configurations. Consequently, more complex configurations and design specifications are necessary in these processes, which usually result in an increased separation cost.

Development of green solvents for efficient post-combustion CO2 capture with good regeneration performance

CO2 emission from post-combustion causes severe impacts on global environment. Hence, to minimize greenhouse effect, it is urgent to develop green solvents for CO2 capture. Herein, deep eutectic solvents (DES) were prepared using glycine (Gly) and proline (Pro) as hydrogen bond acceptors and monoethanolamine (MEA) and ethyl diethanolamine (MDEA) as hydrogen bond donors. The MEA-based DESs exhibited better CO2 uptake capability than MDEA-based DESs. The introduction of ethylene glycol (EG) to [Gly][MEA]/[Pro][MEA] not only enhances the absorption kinetics but also improves the regeneration ability. [Gly][MEA][EG] shows a better CO2 capture performance than [Pro][MEA][EG], reaching to 0.2485 g-CO2/g-DES after 6 h absorption at room temperature. [Gly][MEA][EG] shows an excellent tolerance to water content and CO2 concentration in flue gases and exhibits a robust performance in regeneration with no sustainable solvent loss after 10 cycles of recycles. NMR, FTIR and DFT results indicate that CO2 interacts with DESs via the formation of carbamate through the amine group in MEA and amino acids and via the formation of CO32-/HCO3- via the –OH group in EG. This study offers a novel green solvent for CO2 capture, which is feasible for industrial applications.

Part-Load Operation of a Novel Calcium Looping System for Flexible CO2 Capture in Coal-Fired Power Plants

The increasing share of renewable energy supply is forcing fossil-fueled power plants to undergo flexible operation, with large load changes during the day and even periods of complete shutdown. Dual circulating fluidized bed (DCFB) calcium looping (CaL) has rapidly emerged as a viable option for efficient post-combustion CO2 capture in baseload coal-fired power stations. However, DCFBs might be unsuitable for flexible carbon capture at very low power plant capacity factors, beyond which the solid entrainment rate becomes insufficient. This work introduces a CaL system featuring the unique option of decoupling the solid circulation from the carbonator flue gas load with a carbonator bottom interlink. The concept has been successfully demonstrated with high CO2 capture efficiency (Hornberger et al. Fuel Process. Technol., 2020, 106557), but not yet regarding its load flexibility behavior. The carbonator performance has been assessed at partial loads as low as 40%, identifying a minimum active space time of 41 s as a basis to achieve an equilibrium normalized capture efficiency of 90%. In addition, the calciner performance has been evaluated for a variety of oxy-fuel cases (31–55 vol %db) and calcination temperatures (850–940 °C). The obtained results endorse the suggested novel CaL system’s suitability for the flexible decarbonization of load-following power plants.

Stimulation of CO2 solubility in reversible ionic liquids activated by novel 1-(2-aminoethyl piperazine) and bis (3-aminopropyl) amine

The quest of energy efficient post combustion CO2 capture through an integrated process approach leads to the development of various novel solvents which can yield the necessary outputs. In line with this, the current work explores the experimental and simulation analysis of vapor liquid equilibrium of CO2 in novel aqueous 3-aminoproyl triethoxysilane (TESA) solvent blends enhanced by amine activators. Specific amine activators, viz. 1-(2-aminoethyl) piperazine (AEP) and bis (3-aminopropyl) amine (APA) were considered. The experiments were carried out over the temperature range of (303.2–323.2) K and pressure of (4–350) kPa. In order to realize the effect of activator, AEP/ APA concentration was gradually increased from 0.5 to 1.0 mol/kg with a total solvent concentration of ≈3 mol/kg. Along with this, qualitative 13C NMR and FTIR analysis were also performed to assess the proposed reaction scheme. The experimental vapour liquid equilibrium data (VLE) were correlated by modified Kent-Eisenberg equilibrium model considering gas phase non-ideality as well as non-rigorous statistical non-linear model. The equilibrium constants associated to deprotonation of protonated TESA, AEP and APA as well as carbamate formation reactions of these amines with CO2 are function of solvent concentration, temperature and CO2 partial pressure. These are regressed to fit the experimental VLE data. The modified KE model is further prolonged to estimate the concentration profiles of various molecular and ionic species involved in the reactive system.

Sensitivity Analysis of Carbonate Looping Process Using Twin Fluidized Bed Model

ABSTRACT CO2 as the major greenhouse gas plays an important role in environmental problems. Therefore, it is reasonable to find an effective technology for mitigating large CO2 emissions. Carbonating looping is an efficient post-combustion CO2 capture technology using limestone sorbent, which is more energy-saving than traditional technologies. In our research, a carbonate looping process model had been developed using ASPEN PLUS software. In detail, the sensitivity analysis of main parameters were adopted. The simulation results indicated that the CO2 capture rate of the whole process can achieve above 90% and CO2 concentration in the decarbonated flue gas was less than 4% under the carbonation temperature, the calcination temperature, the F0/FCO2 and the gas-solid separation were 630°C, 900°C, 0.04, 1.0, separately. This work gave an potential example for the retrofitting current coal-fired power plant combined with carbonate looping process.

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.

A metal–organic framework with suitable pore size and dual functionalities for highly efficient post-combustion CO2 capture

A novel porous material was realized for highly efficient post-combustion CO2 capture with high CO2 adsorption capacity, high selectivity and moderate heat of adsorption, mainly attributed to the suitable pore size and dual functionalities.

Polyamine-appended porous organic polymers for efficient post-combustion CO2 capture

Carbon capture and sequestration (CCS) has been proposed to reduce CO2 emissions from large stationary sites such as coal-fired power plants. Currently, however, implementing CCS in power plants is not economically feasible due to the high expense of removing CO2 from flue gas. There is therefore an urgent need for cost-effective CO2 capture technologies, such as efficient solid adsorbents. In this study, we develop a facile strategy that converts a cost-effective porous organic polymer (denoted as PP), which is synthesized by Friedel-Crafts alkylation reaction of dichloro-p-xylene, into outstanding CO2 adsorbents through one-step post-synthesis functionalization with polyamines. Among the adsorbents synthesized, PP-2-DETA and PP-2-TEPA show superior high CO2 uptake capacities, excellent CO2 selectivity over N2, and appropriate Qst. Furthermore, the adsorbents show good CO2 uptake capacity and excellent stability toward both water vapor and regeneration cycles under dynamic flow conditions. Significantly, our samples exhibite much faster adsorption-desorption kinetics than mmen-Mg2(dobpdc) and MCM-41-NH2, which are two outstanding amine-functionalized adsorbents.

Ultrahigh Metal-Organic Framework Loading and Flexible Nanofibrous Membranes for Efficient CO2 Capture with Long-Term, Ultrastable Recyclability.

In the global transition to a sustainable low-carbon economy, CO2 capture and storage technology plays a key role in reducing emissions. Metal-organic frameworks (MOFs) are crystalline materials with ultrahigh porosity, tunable pore size, and rich functionalities, holding the promise for CO2 capture. However, the intrinsic fragility and depressed processability of MOF crystals make the fabrication of the flexible MOF nanofibrous membrane (NFM) rather challenging. Herein, we demonstrate an effective strategy for the versatile preparation of self-supported and flexible HKUST-1 NFM with ultrahigh HKUST-1 loading (up to 82 wt %) and stable and uniform HKUST-1 growth through the combination of electrospinning, multistep seeded growth, and activation process. The loading rate of MOF is the highest level among the reported analogues. Significantly, the HKUST-1 NFM exhibits a prominent CO2 adsorption capacity of 3.9 mmol g-1, good CO2/N2 selectivity, and remarkable recyclability. The CO2 capacity retains ∼95% (3.7 mmol g-1) of the initial value after 100 adsorption-desorption cycles, indicating that the HKUST-1 NFM has long-term and ultrastable recyclability and a significant practical value. Thus, the low-cost and scalable production pathway is able to convert MOF particles into self-supported and flexible NFMs, and thereby, they are better applied to the efficient postcombustion CO2 capture.

Balsam-Pear-Skin-Like Porous Polyacrylonitrile Nanofibrous Membranes Grafted with Polyethyleneimine for Postcombustion CO2 Capture.

Amine-containing sorbents have been extensively studied for postcombustion carbon dioxide (CO2) capture because of their ability to chemisorb CO2 from the flue gas. However, most sorbents are in the form of powders currently, which is not the ideal configuration for the flue gas separation because of the fragile nature and poor mechanical properties, resulting in blocking of the flow pipes and difficult recycling. Herein, we present a novel approach for the facile fabrication of flexible, robust, and polyethyleneimine-grafted (PEI-grafted) hydrolyzed porous PAN nanofibrous membranes (HPPAN-PEI NFMs) through the combination of electrospinning, pore-forming process, hydrolysis reaction, and the subsequent grafting technique. Excitingly, we find that all the resultant porous PAN (PPAN) fibers exhibit a balsam-pear-skin-like porous structure due to the selective removal of poly(vinylpyrrolidone) (PVP) from PAN/PVP fibers by water extraction. Significantly, the HPPAN-PEI NFMs retain their mesoporosity, as well as exhibit good thermal stability and prominent tensile strength (11.1 MPa) after grafting, guaranteeing their application in CO2 trapping from the flue gas. When exposed to CO2 at 40 °C, the HPPAN-PEI NFMs show an enhanced CO2 adsorption capacity of 1.23 mmol g-1 (based on the overall quantity of the sample) or 6.15 mmol g-1 (based on the quantity of grafted PEI). Moreover, the developed HPPAN-PEI NFMs display significantly selective capture for CO2 over N2 and excellent recyclability. The CO2 capacity retains 92% of the initial value after 20 adsorption-desorption cycle tests, indicating that the resultant HPPAN-PEI NFMs have good long-term stability. This work paves the way for fabricating NFM-based solid adsorption materials endowed with a porous structure applied to efficient postcombustion CO2 capture.

Biocatalyzed Accelerated Post-combustion CO2 Capture and Stripping in Monoethanolamine

The existing solvent mediated CO2 capture process is energy intensive due to high temperature requirement for solvent regeneration. Therefore, improvement of solvent systems for optimized and low energy intensive CO2 capture and desorption is of enormous interest. In this regard, we report a novel matrix composed of ZnO/Fe2O3 encapsulated mesoporous silica tethered thermostable carbonic anhydrase (CA) (designated as CA@fn-Zn/Fe/MS). The enzyme coupled matrix was used for efficient post combustion CO2 capture and low energy intensive desorption. It was observed that the use of CA@fn-Zn/Fe/MS (0.5 wt%) in 30% Monoethanolamine (MEA) enhances the CO2 uptake to 0.82 mol/mol of solvent and the regeneration efficiency by 2.6 times as compared to the neat MEA at 30 wt% . The enzyme coupled matrix is stable over a broad range of pH and can be used for several cycles. The development adds values to improve conventional amine based CO2 scrubbing technology.

A model-based approach for the evaluation of new zeolite 13X-based adsorbents for the efficient post-combustion CO2 capture using P/VSA processes

This work presents a mathematical modeling framework for the simulation and optimization of pressure/vacuum swing adsorption (P/VSA) processes for post-combustion CO2 capture. A single-stage P/VSA process for CO2 capture from dry flue gas is considered using new zeolite 13X-based adsorbents resulting from perturbation on the 13X zeolite isotherm. A two-bed six-step P/VSA cycle configuration with light product pressurization is employed in systematic simulation and optimization studies. First a zeolite 13X, the current benchmark commercial adsorbent for CO2 capture, is considered. Accordingly, the model is used to study and evaluate new zeolite 13X-based adsorbents for more efficient CO2 capture. The results from systematic comparative simulation studies demonstrate that a modified zeolite 13X-based adsorbent appears to have better process performance compared with the original zeolite 13X. Furthermore, process optimization studies employing the above potential adsorbents are performed to minimize energy consumption for specified minimum requirements in CO2 purity and recovery. The optimization results indicate that the minimum target of 95% in CO2 purity and 90% in CO2 recovery is easily met for the P/VSA process under consideration for both potential adsorbents under different operating conditions resulting in different energy requirements and CO2 productivity.

Design and operation of a 300 kWth indirectly heated carbonate looping pilot plant

Carbonate looping or calcium looping (CaL) is an efficient post-combustion CO2-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 CO2 avoidance costs than an oxy-fired CaL process. The worldwide first indirectly heated CaL pilot plant with a nominal power of 300kWth 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 CO2 pressure and therewith the calcination temperature. Proof of concept was demonstrated within more than 400h continuous testing. The reactor system showed good hydrodynamic stability, and the heat pipe heat exchanger an excellent performance. CO2 capture rates up to 90% in the carbonator were reached.

Highly efficient post-combustion CO2 capture by low-temperature steam-aided vacuum swing adsorption using a novel polyamine-based solid sorbent

A novel amine-based solid sorbent was prepared for CO2 capture, and the CO2 adsorption characteristics were evaluated for simulated flue gas. Furthermore, CO2 capture tests using a lab-scale three-column fixed-bed system were performed. A novel amine compound was synthesized by attaching hindered functional groups to the terminal primary amino groups of a polyamine, followed by impregnation into pelletized mesoporous MSU-F silica. This novel amine-impregnated solid sorbent overcame the problem of limited CO2 diffusion and exhibited extremely high regenerability even at low temperatures. Lab-scale CO2 capture tests suggested that operation conditions such as temperature, cycle time, rinsing time, flow rate, and regeneration method directly affected CO2 capture performance. In particular, direct low-temperature steam stripping desorption drastically enhanced CO2 capture performance. Steam-aided vacuum swing adsorption (SA-VSA) process was feasible for our amine-based solid sorbent and enabled the recovery of CO2 with high purity (>98%) and recovery rate (>93%). The regeneration heat calculated from the amount of recovered CO2 and the amount of supplied steam was considerably lower (1.47 GJ/t-CO2) than that of liquid amine solvents and other amine-based solid sorbents.

Ionized Zr-MOFs for highly efficient post-combustion CO2 capture

In this study, a previously reported Zr-MOF UiO-66(Zr)-(COOH)2 with optimal features for CO2 capture was ionized by neutralization with aqueous MOH solutions (M=Li+, Na+, K+). This post-synthetic modification route has endowed some of the resulting MOFs with higher CO2 uptake capacity. The CO2/N2 selectivity of UiO-66(Zr)-(COOK)2 calculated by Ideal Adsorption Solution Theory (IAST) demonstrates a significant enhancement of 83% compared with the pristine MOF. In addition, dynamic column breakthrough experiments were performed using a binary CO2/N2 mixed gas with a molar ratio of 15:85 to mimic the flue gas composition. The CO2/N2 selectivity of UiO-66(Zr)-(COONa)2 calculated based on breakthrough data is 99.6, which is among the highest CO2/N2 selectivities obtained experimentally using binary mixed gas breakthrough/co-adsorption experiments. Our results strongly confirm that ionization is an effective way of introducing strong CO2 adsorption sites into MOFs for higher CO2-MOF interactions and better CO2 separation performance.

Carbonate looping experiments in a 1 MWth pilot plant and model validation

Carbonate looping is an efficient post-combustion CO2 capture technology using limestone based sorbents. A carbonate looping pilot plant consisting of two interconnected circulating fluidized bed (CFB) reactors with a thermal capacity of 1MWth has been designed and erected at Technische Universität Darmstadt. The pilot plant has been operated for>1500h in fluidized bed mode, thereof>400h with CO2 capture. The heat for the endothermic regeneration of CaO in the calciner was provided by combustion of either propane or pulverised coal with O2 enriched air. High CO2 absorption efficiencies of up to 85% in the carbonator were achieved for long periods. Taking the CO2 produced by oxyfuel-combustion in the calciner into account, the pilot plant was operated with total CO2 capture rates above 90%. A process model for the carbonate looping pilot plant has been developed with ASPEN PLUS™. A 1D CFB model has been implemented in the process model to determine the effect of hydrodynamics within a fast fluidized bed on the CO2 absorption rate in the carbonator. Operating conditions of a selected test campaign where used as boundary conditions. The results of process simulations show good agreement of calculated CO2 absorption rate with experimental data. Hence, this process model can be considered as a reliable tool for scale-up of the process.

Efficiency and Flexibility Potential of Calcium Looping CO2 Capture

Abstract The Calcium Looping (CaL) is a proven technology for efficient post combustion CO2 capture from fossil fuel fired power plants. The technology is applied in Dual Fluidized Bed (DFB) systems and offers CO2 capture rates of 90% and above with low electric efficiency penalty. Early process feasibility studies for Calcium Looping were performed to identify the process potential by means of simplified process simulations based on assumptions and experimental data from lab scale. Now, existing experimental data from pilot scale investigations provide a substantial data base for reliable calculation of process efficiency and efficiency penalty for CO2 capture. Therefore the results of parametric investigations at pilot scale were incorporated into the simulations and new findings like the process improvement potential by natural flue gas water vapor considered. Moreover, the process simulation model was extended with a flue gas recycle for a more realistic process design and a CO2 capture model to predict CO2 capture efficiencies based on the operated process parameters. These novelties were used to identify optimum process operating points and further process optimization potential and process efficiency penalty calculated, considering expenditures for oxygen production by an air separation unit and CO2 compression for storage. The process simulation model is capable to be used as a design tool for process scale-up. Besides efficiency improvement, load flexibility is a major challenge for CCS plants of the future. In the second part of this publication, concepts to increase load flexibility of Calcium Looping CO2 capture systems are presented. For small size power plants up to 200 MWel or industrial CCS plants a turbulent carbonator design with a bottom link to the sorbent calciner represents an interesting option for highest plant flexibility. Both, a fast fluidized carbonator and a turbulent carbonator design was tested at IFK with high capture efficiency and flexibility in operation.

Precipitating Carbonate Process for Energy Efficient Post-combustion CO2 Capture

The precipitating carbonate process utilizes the carbonate to bicarbonate reaction for the absorption of CO2 followed by precipitation and concentration of part of the bicarbonate before entering the regenerator. This process can be an attractive alternative for existing carbon-capture post-combustion technologies because of its energy efficiency potential. Screening pilot plant experiments of the precipitating carbonate process have shown sufficiently high cyclic loadings and confirmed the operation at the predicted low stripping steam rates. The CO2 vapour pressure of lean solvent entering the absorber was low enough to supply sufficient driving force for 90% removal of CO2 from flue gas containing 4% CO2. This needs to be further demonstrated in a further improved pilot-plant set-up.