Post-combustion CO2 Research Articles

Full-plant Analysis of a PSA CO2 Capture Unit Integrated In Coal-fired Power Plants: Post-and Pre-combustion Scenarios

Abstract It is well proven that a general policy to address the worldwide issue of global warming cannot disregard Carbon dioxide Capture and Storage (CCS) in the portfolio of tools. Pressure Swing Adsorption (PSA) processes are believed to be a promising option for achieving more energy and cost-effective capture of CO 2 from large point sources, especially coal-fired power plants. Nevertheless, there is a gap in knowledge with respect to information and approaches for the integration of CO 2 capture using PSA in power plants. The main contribution of this work is to fill this gap, providing a plant-level comparison with other techniques of decarbonization (i.e., state-of-the-art absorption processes) in terms of CO 2 separation performance, energy efficiency and footprint of the technology. Full-plant analyzes were developed based on a dynamic computational model representing coal-fired power plants operating with a Pressure Swing Adsorption (PSA) cycle, both in a post- and pre-combustion configuration. The resulting plant performance is compared to that of absorption-based systems using the same reference power plant assumptions. The post-combustion scenario outputs reveal that the benchmark absorption process outperforms the PSA alternative. Even though the CO 2 separation requirements are met, the relatively large energy penalty and the very large footprint seem to highlight the current unsuitability of PSA for post-combustion CO 2 capture. Conversely, the pre-combustion scenario analysis shows the PSA process as a promising alternative. The performance, in terms of CO 2 separation, energy efficiency and footprint of the technology, results just slightly lower than that of a plant implementing absorption as a CO 2 capture method. However, the novelty of the analysis and the non-maturity of the technology in this application leaves the window open for future improvements.

Investigation of a Hybrid System for Post-Combustion Capture

Abstract This paper investigates an approach for post-combustion CO 2 capture from the pulverized coal power plant “Kleine Kopje” in North-Rheine Westphalia (NRK-NRW). The system combines a single polymer membrane and refrigeration distillation to achieve optimal capture performance. Membrane separation was chosen as an alternative to amine-based separation due to its once-through process, and the refrigeration system was introduced to eliminate the need of multi-stage membranes in order to achieve high separation degree as well as to optimize the end-product purity. Process design and simulation was carried out using Aspen Plus® to determine the energetic and economic performance of the system. The energetic performance of the hybrid system at a feed pressure of 1.5 bar showed that 337.5 kWh/t separated CO 2 was required to separate 90% of CO 2 and capture processes doubled the electricity price from 33.7 €/MWh to 65.5 €/MWh due to high investments for the membrane. Amine-based absorption exhibited slightly better energetic performance at a separation degree of 90%, while the hybrid system was more energy-efficient at lower separation degrees.

Designing Large-scale CO2 Capture Units with Assessment of Solvent Degradation

Abstract Solvent degradation is one of the main operational drawbacks of post-combustion CO 2 capture with amine solvents. Although the different degradation mechanisms have been largely studied in recent years, it is still impossible to predict the solvent losses and the emissions of degradation products that may occur in a CO 2 capture plant depending on its size and on its operating conditions. In the present work, we experimentally study the degradation of MEA (monoethanolamine) under accelerated conditions implying high temperature, continuous gas feed and vigorous agitation. A special focus is set on the oxidative degradation of MEA, which is studied in the absence of CO 2 . Based on the experimental results, we propose a kinetic model to describe both MEA oxidative and thermal degradation pathways. The degradation kinetics is then included into a global model of the CO 2 capture process, enabling solvent losses and emissions of degradation products to be predicted as a function of the process operating conditions. The predicted MEA loss is in the same order of magnitude as reported in degradation measurements from pilot plants, although lower by a factor 3. This kind of model assessing solvent degradation could and should be used for the design of large-scale CO 2 capture plants in order to simultaneously consider the energy consumption of the process and its environmental impact related to the emissions of degradation products and amine solvent. Further developments shall consider the effect of SO x , NO x and dissolved metals on MEA degradation.

Dynamic Operation of Post-combustion CO2 Capture in Australian Coal-fired Power Plants

Abstract Flexible operation of post-combustion CO 2 capture (PCC) plants can improve efficiency through coordinating the balance between consumer demands for electricity and CO 2 emission reductions. This strategy however, will impose process disturbances and the immediate and long term impact is unclear. There is a justified need for the development of accurate dynamic PCC models, as well as practical experience in dynamic operation of PCC pilot plants. This paper presents CSIRO PCC pilot plant data from the 2012 and 2013 dynamic campaigns using MEA solvent. The step-change approach to dynamic plant operation was implemented and the use of density meters to instantaneously measure CO 2 loading instantaneously was investigated.

Modeling of Oxidative MEA Degradation

Considerable amount of work had been recently done researching the degradation of solvents for CO2 post combustion capture, especially for the benchmark solvent MEA. The degradation of the solvent can cause plant corrosion and losses in the process performance since the solvent might loses its capacity to absorb CO2. Thus, a better understanding of this phenomena is important for the overall process performance. Oxidative degradation is likely to occur at absorber conditions due to the presence of oxygen in the flue gas. Differently from the thermal degradation, the oxidative degradation is not well understood. This work presents a preliminary attempt to rigorously model the degradation of solvents for CO2 capture. Experimental data available in the literature were used to regress some of the model parameters. Several assumptions had to be made due to the lack of knowledge. The model, however, does a reasonable job of representing the dynamic trends of the oxidative degradation in the MEA system. This model is still under further development and new components, experiments and reactions are being implemented in the model.

Modeling and Parameter Identification for CO2 Post-Combustion Capture by Amines Supported on Solid Sorbents

A recently proposed technique for post-combustion CO2 capture in fixed-bed reactors is based on an absorption procedure carried out by amine supported on pelleted solid substrates. This procedure is one of the most promising technologies, in particular because it is less energy intensive than absorption by amines in aqueous solutions. With reference to a laboratory diabatic tubular reactor, a dynamic lumped-parameter model is worked out with physical reasoning. The main two unknown parameters in the model are the CO2 absorption and desorption coefficients. These two parameters are identified by a two-step white-box technique. Identification is performed thanks to real data collected in laboratory experiments.

Postcombustion CO2 Capture in Functionalized Porous Coordination Networks

Motivated by recent experimental reports of zirconium porous coordination networks (PCNs) [J. Am. Chem. Soc. 2012, 134, 14690–14693], which have demonstrated a good stability and CO2 adsorption capacity, we investigate the influence of flue gas impurities and functional groups on the performance of PCN frameworks in selective CO2 capture. Using a combination of grand canonical Monte Carlo (GCMC) simulations and first-principles calculations, we find that O2 and SO2 impurities in flue gas have a negligible influence on CO2 selectivity in all PCN frameworks. However, because of strong electrostatic interaction between H2O molecules and the framework, CO2 selectivity decreases in all PCN structures in the presence of water impurities in the flue gas. Our studies suggest that the PCN-59 framework can be a good candidate for selective CO2 separation from a predehydrated flue gas mixture.

The role of water on postcombustion CO2 capture by vacuum swing adsorption: Bed layering and purge to feed ratio

The influence of water vapor on the adsorption of CO2 in carbon capture by vacuum swing adsorption (VSA) was described. VSA experiments with single and multilayered columns using alumina and zeolite 13X were conducted to understand the migration of water. The penetration depth of water in the column could be controlled by maintaining the purge‐to‐feed ratio above a critical value. At high water content in the feed (>4%), employment of a water adsorbing prelayer was essential to prevent failure of the carbon capture process. A simple axial working capacity model predicts the penetration depth of water in the column for a given feed temperature and adsorption isotherm, and the layering ratio can be selected accordingly. Although water is detrimental to CO2 capture with polar adsorbents, long‐term recovery of CO2 is still possible by appropriate layering and ensuring an adequate purge‐to‐feed ratio. © 2013 American Institute of Chemical Engineers AIChE J 60: 673–689, 2014

Life cycle assessment of natural gas combined cycle integrated with CO2 post combustion capture using chemical solvent

In light of global warming consequences and the need to take drastic steps to reduce its impact by capturing the CO2 from stationary sources, environmental performance assessment of CO2 capture processes is vital for deploying existing or innovative capture technologies. Life cycle assessment (LCA) methodology was used in this study to evaluate the impacts associated with CO2 capture from a natural gas combined cycle power plant, by using a scientific approach of process design and sizing of important unit operations. The environmental assessment was conducted for 90% and 80% CO2 capture efficiencies, using conventional monoethanolamine (MEA) and advanced solvent (KS-1), at various CO2 compression configurations. The results show a major reduction in greenhouse gas emission (GHG) for both capture efficiencies. For the 90% CO2 capture efficiency with conventional MEA, a reduction of 76% in GHG emission was achieved for the entire compression configuration. The 80% CO2 capture efficiency with conventional MEA, on the other hand, showed a 65% reduction in GHG emission. Using the KS-1 solvent resulted in a 78% reduction in GHG emission due to reduction in energy required for CO2 regeneration.However, the assessment shows that CO2 capture operations has led to an increase in other environmental impacts such as human toxicity potential, abiotic depletion, marine eutrophication potential, fresh water aquatic ecotoxicity, marine aquatic ecotoxicity, acidification, terrestrial ecotoxicity and photochemical oxidant formation potential. These impacts are mainly due to the additional energy required for the CO2 capture, infrastructures and chemical solvent used. The advantage of using the novel solvent (KS-1) is clear at 90% CO2 capture compared to the conventional MEA solvent.

Facilitated Transport in Hydroxide‐Exchange Membranes for Post‐Combustion CO2 Separation

Hydroxide-exchange membranes are developed for facilitated transport CO2 in post-combustion flue-gas feed. First, a correlation between the basicity of fixed-site functional groups and CO2 -separation performance is discovered. This relationship is used to identify phosphonium as a promising candidate to achieve high CO2 -separation performance. Consequently, quaternary phosphonium-based hydroxide-exchange membranes are demonstrated to have a separation performance that is above the Robeson upper bound. Specifically, a CO2 permeability as high as 1090 Barrer and a CO2 /N2 selectivity as high as 275 is achieved. The high performance observed in the membranes can be attributed to the quaternary phosphonium moiety.

The role of membranes in post-combustion CO2capture

There are several technological options for post-combustion CO2 capture. Absorption with novel solvents, adsorption, conversion of CO2 into chemical products, calcium looping, and membrane technology are the main alternatives to the conventional absorption process based on amines. In this review, an overview of these technologies is presented and the role that membranes play is evaluated considering two approaches: (i) processes based on selective membranes (gas permeation and supported liquid membranes), and (ii) processes based on non-selective membranes (membrane contactors). The process performance demonstrated by recent research shows that membrane technology can fulfi ll the technical requirements for CO2 capture but a closer interaction with the industrial partners and membrane manufacturers is needed to implement this technology in the industry.

Cycle synthesis and optimization of a VSA process for postcombustion CO2 capture

A systematic analysis of several vacuum swing adsorption (VSA) cycles with Zeochem zeolite 13X as the adsorbent to capture CO2 from dry, flue gas containing 15% CO2 in N2 is reported. Full optimization of the analyzed VSA cycles using genetic algorithm has been performed to obtain purity‐recovery and energy‐productivity Pareto fronts. These cycles are assessed for their ability to produce high‐purity CO2 at high recovery. Configurations satisfying 90% purity‐recovery constraints are ranked according to their energy‐productivity Pareto fronts. It is shown that a 4‐step VSA cycle with light product pressurization gives the minimum energy penalty of 131 kWh/tonne CO2 captured at a productivity of 0.57 mol CO2/m3 adsorbent/s. The minimum energy consumption required to achieve 95 and 97% purities, both at 90% recoveries, are 154 and 186 kWh/tonne CO2 captured, respectively. For the proposed cycle, it is shown that significant increase in productivity can be achieved with a marginal increase in energy consumption. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4735–4748, 2013

Stability of Supported Amine Adsorbents to SO2 and NOx in Postcombustion CO2 Capture. 1. Single-Component Adsorption

Flue gases from coal-fired power plants typically contain not only CO2 but other acid-gas impurities such as SOx and NOx that can dramatically influence the CO2 capture efficiency. Whereas postcombustion CO2 capture by aminosilica materials has been extensively studied over the past few years because of their high equilibrium CO2 capacities, the performance of these materials under realistic conditions (in the presence of SOx, NOx, and O2) remains relatively unexplored. In this study, the degree of irreversible binding of SO2, NO, and NO2 to four supported amine adsorbents is evaluated to assess the SO2, NO, and NO2 adsorption capacities of aminosilica sorbents and their effects on the CO2 adsorption capacities. Adsorbents constructed using poly(ethyleneimine) and three different silane coupling agents (based on propyltrimethoxysilane linkers) with primary, secondary, and tertiary amines are evaluated. Under the experimental conditions used in this investigation, it is found that primary amines with high amine loadings displayed more affinity toward NO than their secondary and tertiary amine counterparts. However, overall, NO adsorption on the aminosilica adsorbents is low, and therefore, the CO2 capacities of the adsorbent materials exposed to NO remained almost unchanged after the exposure. In contrast, all materials showed a very high nitrogen dioxide adsorption capacity upon exposure to NO2. As a result, all adsorbents treated with NO2 exhibited a dramatic reduction in CO2 capacity, which corresponds to the deactivation of amine groups due to the irreversible binding of NO2. In addition, our results indicate that SO2 adsorbed significantly on supported amine adsorbents, resulting in a dramatic loss in CO2 capacity during CO2 capture from flue gas. With similar amine loadings, although secondary amines exhibited higher affinity to SO2, their CO2 capacity loss after exposure to SO2 is lower than that of primary amines, indicating that these materials are more stable in the presence of SO2, which implies that more SO2 desorbs from secondary amines during the desorption step. These results suggest that for silica-supported amine materials to be useful in practical CO2 capture applications, it is necessary to significantly reduce the SO2 and NO2 concentrations of the flue gas prior to the CO2 capture process. On the other hand, the capture efficiency of these materials does not change significantly in the presence of NO. This suggests that such materials might be promising for postcombustion CO2 capture from flue gas streams derived from natural gas combustion, as these streams typically contain reduced SO2 concentrations but can still have significant NOx concentrations.

Highlighting the Role of Activated Carbon Particle Size on CO2 Capture from Model Flue Gas

CO2 adsorption onto two particle size classes of the commercial activated carbon Filtrasorb 400, namely 600–900 μm (sample F600–900) and 900–1200 μm (sample F900–1200), was investigated at 293 K under model flue gas conditions in a fixed-bed column. Equilibrium adsorption capacity for a typical 15% CO2 postcombustion effluent was 0.7 mol kg–1 for both investigated adsorbents. In both cases, CO2 breakthrough curves showed a reduction of the characteristic breakpoint time and faster capture kinetics at higher pollutant concentration in the feed (in the range 1–15%). Dynamic adsorption data highlighted the important role played by wider micropores in determining a quicker adsorption process for finer particles. Mathematical modeling of the 15% CO2 breakthrough curve allowed identifying intraparticle diffusion as the limiting step of the adsorption process. Numerical analysis provided values of the intraparticle mass-transfer resistances equal to 1.7 and 3.3 s for F600–900 and F900–1200, respectively.

Post-Combustion CO2Capture by Vacuum Swing Adsorption Using Zeolites – a Feasibility Study

Simulation results in the literature suggest that Vacuum Swing Adsorption (VSA) processes using physisorbents might largely outperform the current state-of-the-art post-combustion CO<sub>2<sub/> capture technologies based on amine solvents in terms of energy consumption. Most studies consider the zeolite NaX as adsorbent. NaX has a very strong affinity for CO<sub>2<sub/> but is difficult to regenerate and very sensitive to the presence of water in the flue gas. By tuning the polarity of the adsorbent, it might be possible to find a better compromise between adsorption capacity, regenerability and sensitivity to H<sub>2<sub/>O. In the present contribution, we therefore screen the performance of a series of zeolites as physisorbents in a VSA process for CO<sub>2<sub/> capture. The adsorbents are tested by breakthrough experiments of a dry and wet model flue gas, in once-through and cyclic operation. The most interesting material, zeolite EMC-1, is selected for numerical simulations of a full VSA cycle, in comparison with zeolite NaX. Both solids satisfy the performance targets in terms of recovery (> 90%) and purity of CO<sub>2<sub/> (> 95%) but the very low pressure required for regeneration of the adsorbents will be a serious handicap for the deployment of this technology on a large scale.

Hollow Fiber Membrane Contactors for Post-Combustion CO2Capture: A Scale-Up Study from Laboratory to Pilot Plant

Membrane contactors have been proposed for decades as a way to achieve intensified mass transfer processes. Post-combustion CO2 capture by absorption into a chemical solvent is one of the currently most intensively investigated topics in this area. Numerous studies have already been reported, unfortunately almost systematically on small, laboratory scale, modules. Given the level of flue gas flow rates which have to be treated for carbon capture applications, a consistent scale-up methodology is obviously needed for a rigorous engineering design. In this study, the possibilities and limitations of scale-up strategies for membrane contactors have been explored and will be discussed. Experiments (CO2 absorption from a gas mixture in a 30%wt MEA aqueous solution) have been performed both on mini-modules and at pilot-scale (10 m2 membrane contactor module) based on PTFE hollow fibers. The results have been modeled utilizing a resistance in series approach. The only adjustable parameter is in fitting the simulations to experimental data is the membrane mass transfer coefficient (km), which logically plays a key role. The difficulties and uncertainties associated with scaleup computations from lab scale to pilot-scale modules, with a particular emphasis on the km value, are presented and critically discussed.

Design of a Pressure Swing Adsorption Process for Postcombustion CO2 Capture

The adsorption processes for postcombustion CO2 capture are usually based on a temperature or vacuum swing (TSA or VSA). In the present contribution an alternative concept is presented, which is based on the regeneration of the solid sorbent (an immobilized amine) by a purge gas, low pressure vapor, under almost isothermal conditions. Because of the close to isothermal operation, the process consumes significantly less thermal and mechanical energy than conventional TSA and VSA processes, respectively. We present a rough design of such an isothermal concentration swing process based on a simplified, analytical model of a 2-step PSA (pressure swing adsorption) process. The analytical model allows a definition of the range of operating conditions that lead to the best compromise between energy consumption and productivity (size and number of the adsorbers). Moreover, it is possible to define the equilibrium and mass transfer properties of the ideal solid sorbent. The feasibility of the concentration swing p...

Application of Ultraviolet, Ozone, and Advanced Oxidation Treatments to Washwaters To Destroy Nitrosamines, Nitramines, Amines, and Aldehydes Formed during Amine-Based Carbon Capture

Although amine-based CO(2) absorption is a leading contender for full-scale postcombustion CO(2) capture at power plants, concerns have been raised about the potential release of carcinogenic N-nitrosamines and N-nitramines formed by reaction of exhaust gas NO(x) with the amines. Experiments with a laboratory-scale pilot unit suggested that washwater units meant to scrub contaminants from absorber unit exhaust could potentially serve as a source of N-nitrosamines via reactions of residual NO(x) with amines accumulating in the washwater. Dosage requirements for the continuous treatment of the washwater recycle line with ultraviolet (UV) light for destruction of N-nitrosamines and N-nitramines, and with ozone or hydroxyl radical-based advanced oxidation processes (AOPs) for destruction of amines and aldehydes, were evaluated. Although <1000 mJ/cm(2) UV fluence was generally needed for 90% removal of a series of model N-nitrosamines and N-nitramines, 280-1000 mJ/cm(2) average fluence was needed for 90% removal of total N-nitrosamines in pilot washwaters associated with two different solvents. While AOPs were somewhat more efficient than ozone for acetaldehyde destruction, ozone was more efficient for amine destruction. Ozone achieved 90% amine removal in washwaters at 5-12 molar excess of ozone, indicating transferred dosage levels of ∼100 mg/L for 90% removal in a first-stage washwater unit, but likely only ∼10 mg/L if applied to a second-stage washwater. Accurate dosage and cost estimates would require pilot testing to capture synergies between UV and ozone treatments.

Water Effects on Postcombustion CO2 Capture in Mg-MOF-74

Mg-MOF-74, one of the best metal–organic framework (MOF) materials for CO2 adsorption and separation, has been widely explored in CO2 capture. In this work, water effects on postcombustion CO2 capture in Mg-MOF-74 are evaluated by using a combination of Grand Canonical Monte Carlo and density functional theory (DFT) simulations. Our results show that in this MOF the CO2 adsorption capacity is decreased by the presence of water molecules linked to coordinatively unsaturated metal sites (CUMs). This effect is a consequence of the reduction of binding energy between CO2 and the water-coordinated Mg-MOF-74 framework. DFT calculations indicate that such binding energy is much lower than that without coordinated water. More importantly, we find that the difference of the binding energy between CO2 and CUM in a MOF and that between CO2 and CUM-coordinated water are good descriptors to evaluate water effects on CO2 capture in MOFs with CUMs. At the same time, these investigations further demonstrate that the CUMs...

Aminosilane-Functionalized Hollow Fiber Sorbents for Post-Combustion CO2 Capture

Increasing carbon dioxide emissions are generally believed to contribute to global warming. Developing new materials for capturing CO2 emitted from coal-fired plants can potentially mitigate the effect of these CO2 emissions. In this study, we developed and optimized porous hollow fiber sorbents with both improved sorption capacities and rapid sorption kinetics by functionalizing aminosilane (N-(2-aminoethyl)-3-aminoisobutyldimethylmethoxysilane) to cellulose acetate hollow fibers as a “proof of concept”. A lumen-side barrier layer was also developed in the aminosilane-functionalized cellulose acetate fiber sorbent to allow for facile heat exchange without significant mass transfer with the bore-side heat transfer fluid. The functionalized cellulose acetate fiber sorbents were characterized by pressure decay sorption measurements, multicomponent column chromatography, FT-IR, elemental analysis, and scanning electron microscopy. The carbon dioxide sorption capacity at 1 atm is 0.73 mmol/g by using the pres...