Pre-combustion CO2 Capture Research Articles

On steam hydration of CaO-based sorbent cycled for CO2 capture

The reversible reaction of CaO with CO2 can be used for post- and pre-combustion capture of CO2; however, the reactivity of CaO particles is found to reduce upon repeated use. Hydration has been shown to be an effective method of increasing the reactivity of (or reactivating) CaO to CO2 for CO2 capture. Here, a lab-scale fluidised bed reactor was used to investigate reactivation of sorbent using steam at two different hydration temperatures of 473 and 673K. Prior to hydration, the sorbent was cycled at three different calcination temperatures of 1123, 1173 and 1223K; the carbonation temperature was kept constant at 973K. Following hydration, the sorbent was either carbonated directly or carbonated indirectly via a CaO intermediate. The hydration extent was found to decrease with increasing calcination temperature before hydration and with increasing hydration temperature. The carbonation extent following hydration was found to increase linearly with hydration extent – depending on the method of carbonation – with direct carbonation resulting in higher conversions. Mass loss from the fluidised bed was found to be higher for lower hydration temperatures and increased calcination temperatures before cycling. The hydration behaviour of sorbent was subsequently investigated using a TGA at three different steam hydration temperatures of 483, 578 and 678K. Material for the TGA tests was prepared using the lab-scale fluidised bed reactor, with a calcination temperature of 1173K and a carbonation temperature of 973K. In this case, the number of cycles was varied from 0 to 13, in order to provide a wider range of sorbent properties. Data from the TGA were used to project subsequent carbonation conversions and relative increases in carrying capacity across hydration. The TGA hydration tests emphasise the importance of hydration temperature and prior cycling conditions and length on the increase in carrying capacity following hydration.

Load-following performance of IGCC with integrated CO2 capture using SEWGS pre-combustion technology

The performance assessment of an Integrated Gasification Combined Cycle (IGCC) integrated with the Sorption Enhanced Water Gas Shift (SEWGS) technology for pre-combustion CO2 capture at full-load and part-load modes of operation is investigated. Syngas from a coal gasifier is sent to the SEWGS system after going through solids and H2S removal units. A H2-rich stream is produced by the SEWGS system and used in a gas turbine (GT) for combustion. A control strategy including a buffer tank followed by a control valve, between the SEWGS system and the GT is implemented to smooth out the fluctuations in the H2-rich fuel flow rate, resulted from the cyclic operation of the PSA-based SEWGS system. Simulation of the IGCC integrated with the SEWGS system is first performed at full-load operation of the GT. For evaluating part-load performances, four different cases, introducing various load change strategies for the GT and gasifier are studied. Step/ramp changes of the GT and gasifier, unplanned/planned GT load changes and same/different GT and gasifier load change occurrence time are all addressed through these four cases. Simulation results indicate that the designed control strategy is able to minimize the H2-rich fuel flow rate fluctuations and dampen the fuel composition variations, while keeping the buffer tank pressure within the desired range. Dynamic characteristics of the SEWGS system are revealed and compared with those of the gasifier and the GT. Using the buffer tank between the SEWGS and the GT, improves part-load operation flexibility of the GT. Smooth operation and load following capability of the IGCC integrated with the SEWGS system are achievable, depending on the GT part-load level and load change strategy, taking into account the limited load gradient of the gasifier and the SEWGS units compared to the GT.

Surface-modified spherical activated carbon materials for pre-combustion carbon dioxide capture

Carbon beads exhibiting potential in practical pre-combustion CO2 capture were prepared.

Mixed matrix membranes composed of two-dimensional metal–organic framework nanosheets for pre-combustion CO2 capture: a relationship study of filler morphology versus membrane performance

Mixed matrix membranes containing metal–organic frameworks were fabricated for pre-combustion CO2 capture.

고온 고압 조건하의 기포유동층 반응기에서의 입자 마모특성

Attrition characteristics of PKM1-SU particles, CO2 absorbents for pre-combustion CO2 capture process, and FCC particles, catalytic particles for hydro cracking of crude oil, were investigated at high temperature and high pressure conditions. Particle attrition tests were executed at various kinds of temperature (0-400 ℃) and pressure (0-20 bar) conditions in a cylinder type bubbling fluidized bed with 15.1 cm diameter, 120 cm height and 1 mm orifice-sparger tube. Attrited particles before and after tests were analyzed by BET, optical microscopy, and particle size analyzer. Effects of bed material height (solid inventory) and steam injection were also verified by using ASTM D5757-95, conventional attrition test method.

Feasibility Study of Employing a Catalytic Membrane Reactor for a Pressurized CO2and Purified H2Production in a Water Gas Shift Reaction

The effect of two important parameters of a catalytic membrane reactor (CMR), hydrogen selectivity and hydrogen permeance, coupled with an Ar sweep flow and an operating pressure on the performance of a water gas shift reaction in a CMR has been extensively studied using a one-dimensional reactor model and reaction kinetics. As an alternative pre-combustion CO2 capture method, the feasibility of capturing a pressurized and concentrated CO2 in a retentate (a shell side of a CMR) and separating a purified H2 in a permeate (a tube side of a CMR) simultaneously in a CMR was examined and a guideline for a hydrogen permeance, a hydrogen selectivity, an Ar sweep flow rate, and an operating pressure to achieve a simultaneous capture of a concentrate CO2 in a retentate and production of a purified H2 in a permeate is presented. For example, with an operating pressure of 8 atm and Ar sweep gas for rate of 6.7 × 10 -4 mols -1 , a concentrated CO2 in a retentate (~90%) and a purified H2 in a permeate (~100%) was simultaneously obtained in a CMR fitted with a membrane with hydrogen permeance of 1 × 10 -8 mol m -2 s -1 Pa -1 and a hydrogen selectivity of 10000.

Evaluation of Pd composite membrane for pre-combustion CO2 capture

Carbon capture with hydrogen-selective Pd membranes can be realized as highly integrated process and CO2 can be separated at high pressure without employing environmentally harmful sorption agents. This study investigates the technical viability of using ultrathin Pd/ceramic composite membranes with innovative ceramic-to-metal connections under conditions that are practically interesting for natural gas-fired power stations, i.e. high feed and permeate pressures and high H2 recovery at elevated temperature. The 90% CO2 capture target was well exceeded during a 150 day test in water gas-shifted reformate at 673K. After system stabilization 98% carbon were held back by the membrane while 98% H2 were separated at nominally 99.5% H2 purity. Special attention has been paid to long-term operation effects on the 2–4μm thick Pd layer. These include the development of a striking, cavernous Pd morphology which increases mechanical stability of the composite membrane, a somewhat reduced but steady H2 permeability, and the disappearance of most membrane defects. The latter is attributed to carbon deposits as exit flow analyses point to CO2 reduction preserving effectively membrane selectivity. Altogether, carbon capture with supported Pd membranes projects as feasible from a technological vantage point.

Potassium-Promoted γ-Alumina Adsorbent from K2CO3 Coagulated Alumina Sol for Warm Gas Carbon Dioxide Separation

This paper provided a practical synthesis method of K-promoted γ-alumina for CO2 precombustion capture integrating adsorbent pelletting and catalytic active component promotion into one single process. The precursor of the absorbent, K-promoted pseudo-boehmite (PB), was synthesized from alumina sol and K2CO3 powder by mixing, aggregating, drying, and aging. Potassium-promoted γ-alumina was obtained after calcination at 400 °C from K-promoted PB. Characteristic crystallines of several stages of products in the synthesis process have been detected by X-ray diffraction. The optimal Al:K ratio in view of CO2 capacity and cyclic performance of K-promoted γ-alumina was obtained by a thermal gravimetric analyzer. The optimal ratio of K-promoted γ-alumina showed a capacity of 0.67 mmol/g (dry base) for the first cycle and 0.34 mmol/g (wet base) after 30 pressure swing adsorption (PSA) cycles at 300 °C. K-promoted γ-alumina adsorbent could be favorable for a low energy penalty precombustion CO2 capture application. It showed a variety of advantages such as low adsorption heat, good mechanical strength, low cost in synthesis, and fair stable capacity.

The quantitative evaluation of two-stage pre-combustion CO2 capture processes using the physical solvents with various design parameters

Integrated Gasification Combined Cycle technology with Carbon Capture Storage has many potential advantages for future power generation system and many pre-combustion CO2 capture technologies have been developed for removing the acid gas and CO2 from the syngas.In this study, redesign and modeling of the two-stage pre-combustion CO2 capture process, using three different physical solvents, was conducted. The quantitative design modeling analysis was performed using the computational software ASPEN Plus®. The Selexol process was evaluated as the most efficient pre-combustion CO2 capture process from the points of electric/thermal energy consumption as a result of ASPEN Plus® modeling. The Selexol modeling process resulted in electric energy of about 3.2 MWe to maintain the operating temperature and pressure by using the pump, the compressor and the chiller. The consumption of thermal energy was also evaluated to be 0.85 MWth for regeneration of the solvent in the H2S stripper. Concomitantly, various comparison and performance results were obtained by changing the key design modeling parameters; Water-Gas Shift conversion rate, operating temperature and CO2 capture rate were varied for their individual effects on energy consumption, solvent and hydrogen loss. As Water-Gas Shift conversion rate increased, the Selexol process consumes the least amount of electric energy among the modeled CO2 capture processes using the physical solvents. On the other hand, changing the operating temperature turned out to be advantageous for the Rectisol process over other CO2 capture processes using the physical solvents. The reboiler heat duty and hydrogen loss with total solvent flow rate can also be reduced by dropping the operating temperature. As CO2 capture rate increased, Selexol process was more efficient than other processes using the Methanol and NMP (N-Methyl-2-Pyrrolidone). This modeling result is explained by the decrease in the reboiler heat duty and electrical energy consumption although the solvent flow rate increased.

Impact of experimental pressure and temperature on semiclathrate hydrate formation for pre-combustion capture of CO2 using tetra-n-butyl ammonium nitrate

TBANO3 (tetra-n-butyl ammonium nitrate) is a promising liquid phase promoter for capturing CO2 via HBGS (hydrate based gas separation) technology. In this study, the impact of experimental pressure and temperature on formation of mixed CO2–H2-TBANO3 semiclathrate hydrate for the optimum 1.0 mol% TBANO3 reported by Babu et al. [1] was investigated. Experimental pressures of 3.0, 4.5 and 6.0 MPa and temperatures of 274.2, 276.2 and 278.2 K were employed. Irrespective of the experimental pressure, shorter induction time was observed for experiments conducted at 274.2 K when compared to the experiments at other temperatures. At a given pressure, the total gas uptake increased with increase in experimental temperature. Similarly at a given temperature, the total gas uptake increases with an increase in pressure. Higher rate of hydrate formation was observed at experimental pressure of 6.0 MPa than at 3.0 and 4.5 MPa irrespective of the experimental temperature. The CO2 composition in hydrate was between 87.5 and 93.2 mol%. Finally, the gas consumption for 1.0 mol% TBANO3 as promoter was much higher than other promoters of quaternary salts like tetra-n-butyl ammonium bromide and tetra-n-butyl ammonium fluoride at comparable concentration and driving force.

Life cycle assessment of a hypothetical Canadian pre-combustion carbon dioxide capture process system

The methodology of life cycle assessment was applied for evaluating the environmental performance of a Saskatchewan lignite integrated gasification combined cycle (IGCC)-based electricity generation plant with and without the pre-combustion CO2 capture process. A comparison between the IGCC systems (with and without CO2 capture) and the competing lignite pulverized coal electricity generating station was conducted to reveal which technology offers more positive environmental effects. The results showed significant reduction of GHG emissions where both post- and pre-combustion CO2 capture processes are applied. With the application of the CO2 removal technology, GHG emissions were reduced by 27–86%. The performances of the IGCC systems were superior to those of the pulverized coal systems. However, in terms of other environmental impacts, multiple environmental trade-offs are involved depending on the capture technology. For the post-combustion CO2 capture process system, it was observed that the environmental impact was shifted from the air compartment to the soil and water compartments. The IGCC systems showed the same tendency of shifting from air pollution to soil and water pollution, but the amount of pollution is less significant. This is likely because the IGCC system operates at higher efficiencies; hence, it requires less fuel and produces fewer emissions.

Non-precious metal (pre-)commercial catalysts for Pd membrane water gas shift

Development of membrane-reactors for use in pre-combustion CO2 capture power schemes is of great interest. The local environment of the catalysts at the catalytic membrane reactor (CMR) conditions is different from conventional applications, inducing changes in demands to the catalyst properties. Here, the use of low-cost base metal catalysts in membrane assisted-water gas shift (MWGS) reaction is studied. A conventional high temperature FeCr-based shift catalyst was studied in a membrane reactor with feed gas mimicking combined-cycle power plant process gas. Combining the catalyst with hydrogen selective Pd membranes, results in approximately 95% hydrogen recovery and CO conversion. No loss of selectivity (through methanation and Fisher–Tropsch reaction) and stability was found during tests, according to expectations, i.e steam/H2 > 0.5 and steam/CO > 2. However, in order to meet these conditions in an ATR + pre-shift based natural gas combined cycle (NGCC) process, steam injection is required at the cost of an efficiency penalty and higher membrane surface area. Using severe conditions representing coal-gasification (IGCC) conditions with high CO concentration and steam/CO < 2, higher hydrocarbons and oxygenates are indeed being formed and catalyst deactivation is unavoidable. For both coal and gas-fired combined-cycle power plants, an alternative catalyst (Topsøe ZnO/ZnAl2O4 type catalyst) was identified with similar hydrogen recovery and activity but superior selectivity and stability to the FeCr type catalyst at steam/H2 < 0.5 and steam/CO < 1.

Influence of the pyrolysis step and the tanning process on KOH-activated carbons from biocollagenic wastes. Prospects as adsorbent for CO2 capture

The present study deals with the influence of vegetable tanning on the chemical composition and textural properties of activated carbons obtained from a mixture of leather solid wastes by KOH activation, with or without a previous pyrolysis stage. A degreased, dehydrated skin and a mixture of commercial tannins were used as reference materials to study the effect of vegetable tanning.The data obtained by thermogravimetry indicated that the interactions between the tannin and collagen increased the thermal stability of the leather wastes, and that H2O, CO, CO2, H2, CH4, CxHy, NxOy, SO2 and toluene, were the principal gases produced during the pyrolysis. The resultant absorbent materials showed a high specific surface area and total pore volume of up to 1602m2g−1 and VTOT: 0.695cm3g−1, respectively. The activated carbons prepared were basically microporous with a certain degree of mesoporosity, and contained a significant amount of nitrogen. Direct chemical activation of the materials increased the volume of medium-sized micropores and the size of the micropores.The activated carbons obtained showed high CO2, low or moderate CH4 and very low H2 adsorption capacities at high pressures, most of the adsorbents being more effective in adsorbing CO2 than a commercial activated carbon used as reference (Chemviron Filtrasorb F400). These results open up the way for applying these adsorbent materials in: (i) precombustion CO2 capture to produce hydrogen in IGCC plants with a PSA process, (ii) separating/concentrating mixtures of CO2/CH4 in natural gas feeds for use as fossil fuel or (iii) natural gas storage.

Validation of a water–gas shift reactor model based on a commercial FeCr catalyst for pre-combustion CO2 capture in an IGCC power plant

In the Nuon/Vattenfall CO2 Catch-up project, a pre-combustion CO2 capture pilot plant was built and operated at the Buggenum IGCC power plant, the Netherlands. The pilot consist of syngas conditioning, sweet water-gas shift, condensate recovery, bulk CO2 separation by physical absorption using dimethyl-ether of poly-ethylene-glycol (DEPEG) as solvent, solvent regeneration and CO2 compression. The project aimed at verifying the technology performance and at generating knowledge in the form of validated models and operational experience. This paper describes the construction and validation of the model for the WGS reactors. A one-dimensional heterogeneous reactor model was developed. The intrinsic kinetics was measured in the lab at 20bar pressure, 350–450°C and in the presence of 5–20ppm of H2S. The engineering reactor model is successfully validated against a set of 20 steady-state pilot plant operational periods varying in inlet temperature, syngas composition and throughput. A good fit of the pilot plant data was obtained by moderately tuning the relative catalyst activity in the model to the state of the catalyst in the pilot. This indicates that the lab-scale catalyst ageing procedure effectively mimics the initial catalyst deactivation observed in the pilot plant.

Dynamic Modeling and Validation of a Precombustion CO2 Capture Plant for Control Design

In view of the increasing share of electricity produced by renewable energy sources, transient operation of decarbonized power plants is gaining more relevance. This is due to the inherent fluctuating operation of wind or solar plants. Accurate physically based dynamic models are important tools to study the interaction between power plant and CO2 capture unit during dynamic operation. Moreover, such models are indispensable to design appropriate control systems aimed at improvement of dynamic performance. This paper documents the development of dynamic components as well as system models of a precombustion CO2 capture unit applied to integrated gasification combined cycle (IGCC) systems following an object-oriented modeling approach. The models have been implemented by means of the Modelica language into an open source software library. The fluid properties are computed with accurate thermodynamic models implemented within an in-house property package which is interfaced with the Modelica process models. Comprehensive model validation has been performed at component, subsystem, and system level by comparison against experimental measurements obtained from various open- and closed-loop transient tests at the CO2 capture pilot plant situated at the Buggenum IGCC power station. Results are in satisfactory agreement, considering the main process mass flow and temperature variables. To demonstrate the use of validated, dynamic process models, a control design study is presented whereby a control strategy based on feed-forward, feed-back, and cascade control has been implemented and tested with the aim to improve dynamic performance of the capture unit. It can be concluded that prompt syngas load variation is a feasible operating mode for precombustion CO2 capture units featuring sophisticated control systems. The software library containing the validated component and system models serves as a reliable foundation for the development of large-scale precombustion capture unit models.

Biomass integrated gasification combined cogeneration with or without CO2 capture – A comparative thermodynamic study

Fossil fuels presently cater to majority of energy demand of the world. However, due to the climate change problem capture of CO2 emitted from the use of fossil fuels is emerging as a necessity. Alternately, developing technology with CO2 neutral fuels may reduce green house gas emission. Possible even better solution may be combining both of these options, i.e., employing CO2 capture process for energy efficient system using CO2 neutral fuels, say biomass. In this paper, such cogeneration system with CO2 capture using amine solution has been proposed. Thermodynamic modeling for the detail process has been implemented using ASPEN Plus®. Comparative study of performance relative to a similar base case plant without carbon capture has been presented. Results show post combustion CO2 capture process is better than pre-combustion CO2 capture process for such plants with net negative CO2 emission. Also degree of CO2 capture has to be optimized on the basis of the overall performance of the plant as higher CO2 capture affects thermodynamic and economic performance of the plant, specifically beyond certain value. In a net CO2 negative emission plant extent of CO2 capture is quite flexible and may be decided for optimum performance.

Improvements in the Pre-Combustion Carbon Dioxide Sorption Capacity of a Magnesium Oxide–Cesium Carbonate Sorbent

Cesium-carbonate-doped magnesium oxide has been shown to be a prospective candidate for pre-combustion CO2 capture at temperatures between 300 and 410 °C. Materials were synthesized by wet mixing commercially available materials as well as a solvothermal approach using a magnesium methoxide in methanol solution. The materials were activated by heat treatment at 600–610 °C to yield the active CO2 sorbent. The sorbents showed working capacities of around 4 wt % in up to 25 partial pressure swing (12 min of sorption and 24 min of desorption) cycles. If the cesium carbonate was dissolved in the magnesium methoxide solution before solvothermal synthesis, multi-cyclic working capacities were increased to 5 wt %. Brunauer–Emmett–Teller surface area measurements of the activated materials showed that the solvothermal method led to materials with higher surface areas of ∼13 m2/g, as compared to 3.4 m2/g if made from commercial MgO. Transmission electron microscopy showed the morphology of the activated solvotherma...

Exhaust circulation into dry gas desulfurization process to prevent carbon deposition in an Oxy-fuel IGCC power generation

Semi-closed cycle operation of gas turbine fueled by oxygen–CO2 blown coal gasification provides efficient power generation with CO2 separation feature by excluding pre-combustion type CO2 capture that usually brings large efficiency loss. The plant efficiency at transmission end is estimated as 44% at lower heating value (LHV) providing compressed CO2 with concentration of 93vol%. This power generation system will solve the contradiction between economical resource utilization and reduction of CO2 emission from coal-fired power plant. The system requires appropriate sulfur reduction process to protect gas turbine from corrosion and environment from sulfur emission. We adopt dry gas sulfur removal process to establish the system where apprehension about the detrimental carbon deposition from coal gas. The effect of circulation of a portion of exhaust gas to the process on the retardation of carbon deposition was examined at various gas compositions. The circulation remarkably prevented carbon deposition in the sulfur removal sorbent. The impact of the circulation on the thermal efficiency is smaller than the other auxiliary power consumption. Thus, the circulation is appropriate operation for the power generation.

Swellable, water- and acid-tolerant polymer sponges for chemoselective carbon dioxide capture.

To impact carbon emissions, new materials for carbon capture must be inexpensive, robust, and able to adsorb CO2 specifically from a mixture of other gases. In particular, materials must be tolerant to the water vapor and to the acidic impurities that are present in gas streams produced by using fossil fuels to generate electricity. We show that a porous organic polymer has excellent CO2 capacity and high CO2 selectivity under conditions relevant to precombustion CO2 capture. Unlike polar adsorbents, such as zeolite 13x and the metal-organic framework, HKUST-1, the CO2 adsorption capacity for the hydrophobic polymer is hardly affected by the adsorption of water vapor. The polymer is even stable to boiling in concentrated acid for extended periods, a property that is matched by few microporous adsorbents. The polymer adsorbs CO2 in a different way from rigid materials by physical swelling, much as a sponge adsorbs water. This gives rise to a higher CO2 capacities and much better CO2 selectivity than for other water-tolerant, nonswellable frameworks, such as activated carbon and ZIF-8. The polymer has superior function as a selective gas adsorbent, even though its constituent monomers are very simple organic feedstocks, as would be required for materials preparation on the large industrial scales required for carbon capture.

Enhanced kinetics for the clathrate process in a fixed bed reactor in the presence of liquid promoters for pre-combustion carbon dioxide capture

In this work, we present enhanced kinetics of hydrate formation for the clathrate process in the presence of two liquid promoters namely THF (tetrahydrofuran) and TBAB (tetra-n-butyl ammonium bromide) in a FBR (fixed bed reactor) for pre-combustion capture of CO2. Silica sand was used as a medium to capture CO2 from CO2/H2 gas mixture by hydrate crystallisation. Experiments were performed at different temperatures (274.2 K and 279.2 K) and 6.0 MPa to determine the total gas uptake, induction time and rate of hydrate formation. The observed trends indicated that higher driving force resulted in higher gas consumption and significantly reduced induction time. For the same driving force, higher gas consumption and shorter induction time was achieved by THF as compared to TBAB. 5.53 mol% THF attained higher gas consumption than 1.0 mol% THF whereas 3.0 mol% TBAB attained lower gas consumption than 0.3 mol% TBAB. A highest gas uptake of 51.95 (±5.183) mmol of gas/mol of water and a highest rate of 51.21(±8.91) mol.min−1.m−3 were obtained for 5.53 mol% THF at 6.0 MPa and 279.2 K. Overall, this study indicated better hydrate formation kinetics with the use of THF in an FBR configuration for CO2 capture from a fuel gas mixture.