Design and operation of pilot plant for CO2 capture from IGCC flue gases by combined cryogenic and hydrate method

This project is a trial conducted under contract with CO₂CRC, Australia of a new CO₂ capture technology that can be applied to integrated gasification combined cycle power plants and other industrial gasification facilities. The technology is based on combination of two low temperature processes, namely cryogenic condensation and the formation of hydrates, to remove CO₂ from the gas stream. The first stage of this technology is condensation at −55 °C where CO₂ concentration is expected to be reduced by up to 75 mol%. Remaining CO₂ is captured in the form of solid hydrate at about 1 °C reducing CO₂ concentration down to 7 mol% using hydrate promoters. This integrated cryogenic condensation and CO₂ hydrate capture technology hold promise for greater reduction of CO₂ emissions at lower cost and energy demand. Overall, the process produced gas with a hydrogen content better than 90 mol%. The concentrated CO₂ stream was produced with 95-97 mol% purity in liquid form at high pressure and is available for re-use or sequestration. The enhancement of carbon dioxide hydrate formation and separation in the presence of new hydrate promoter is also discussed. A laboratory scale flow system for the continuous production of condensed CO₂ and carbon dioxide hydrates is also described and operational details are identified.     

Cyclic calcination/carbonation looping of dolomite modified with acetic acid for CO2 capture

The dolomite modified with acetic acid solution was proposed as a CO₂ sorbent for calcination/carbonation cycles. The carbonation conversions for modified and original dolomites in a twin fixed-bed reactor system with increasing the numbers of cycles were investigated. The carbonation temperature in the range of 630 °C–700 °C is beneficial to the carbonation reaction of modified dolomite. The carbonation conversion for modified dolomite is significantly higher than that for original sorbent at the same reaction conditions with increasing numbers of reaction cycles. The modified dolomite exhibits a carbonation conversion of 0.6 after 20 cycles, while the unmodified sorbent shows a conversion of 0.26 at the same reaction conditions, which is calcined at 920 °C and carbonated at 650 °C. At the high calcination temperature over 920 °C modified dolomite can maintain much higher conversion than unmodified sorbent. The mean grain size of CaO derived from modified dolomite is smaller than that from original sorbent with increasing numbers of reaction cycles. The calcined modified dolomite possesses greater surface area and pore volume than calcined original sorbent during the multiple cycles. The pore volume and pore area distributions for calcined modified dolomite are also superior to those for calcined unmodified sorbent during the looping cycle. The modified dolomite is proved as a new and promising type of regenerable CO₂ sorbent for industrial applications.     

Preliminary analysis of process flow sheet modifications for energy efficient CO2 capture from flue gases using chemical absorption

The energy penalty associated with solvent based capture of CO₂ from power station flue gases can be reduced by incorporating process flow sheet modifications into the standard process. A review of modifications suggested in the open and patent literature identified several options, primarily intended for use in the gas processing industry. It was not immediately clear whether these options would have the same benefits when applied to CO₂ capture from near atmospheric pressure combustion flue gases. Process flow sheet modifications, including split flow, rich split, vapour recompression, and inter-stage cooling, were therefore modelled using a commercial rate-based simulation package. The models were completed for a Queensland (Australia) based pilot plant running on 30% MEA as the solvent. The preliminary modelling results showed considerable benefits in reducing the energy penalty of capturing CO₂ from combustion flue gases. Further work will focus on optimising and validating the most relevant process flow sheet modifications in a pilot plant.     

Partial O2-fired coal power plant with post-combustion CO2 capture: A retrofitting option for CO2 capture ready plants

In the work presented in this paper, an alternative process concept that can be applied as retrofitting option in coal-fired power plants for CO₂ capture is examined. The proposed concept is based on the combination of two fundamental CO₂ capture technologies, the partial oxyfuel mode in the furnace and the post-combustion solvent scrubbing. A 330 MW_el Greek lignite-fired power plant and a typical 600 MW_el hard coal plant have been examined for the process simulations. In a retrofit application of the ECO-Scrub technology, the existing power plant modifications are dominated by techno-economic restrictions regarding the boiler and the steam turbine islands. Heat integration from processes (air separation, CO₂ compression and purification and the flue gas treatment) can result in reduced energy and efficiency penalties. In the context of this work, heat integration options are illustrated and main results from thermodynamic simulations dealing with the most important features of the power plant with CO₂ capture are presented for both reference and retrofit case, providing a comparative view on the power plant net efficiency and energy consumptions for CO₂ capture. The operational characteristics as well as the main figures and diagrams of the plant’s heat balances are included.     

Enhancement of reactivity in surfactant-modified sorbent for CO2 capture in pressurized carbonation

The calcination/carbonation loop of calcium-based (Ca-based) sorbents is considered as a viable technique for CO₂ capture from combustion gases. Recent attempts to improve the CO₂ uptake of Ca-based sorbents by adding calcium lignosulfonate (CLS) with hydration have succeeded in enhancing its effectiveness. The optimum mass ratio of CLS/CaO is 0.5 wt.%. The reduction in particle size and grain size of CaO appeared to be parts of the reasons for increase in CO₂ capture. The primary cause of increase in reactivity of the modified sorbents was the ability of the CLS to retard the sintering rate and thus to remain surface area and pore volume for reaction. The CO₂ uptake of the modified sorbents was also enhanced by elevating the carbonation pressure. Experimental results indicate that the optimal reaction condition of the modified sorbents is at 0.5 MPa and 700 °C and a high conversion of 0.7 is achieved after 10 cycles, by 30% higher than that of original limestone, at the same condition.     

Techno-economic evaluation of a PVAm CO2-selective membrane in an IGCC power plant with CO2 capture

Published data for an operating power plant, the ELCOGAS 315 MWe Puertollano plant, has been used as a basis for the simulation of an integrated gasification combined cycle process with CO₂ capture. This incorporated a fixed site carrier polyvinylamine membrane to separate the CO₂ from a CO-shifted syngas stream. It appears that the modified process, using a sour shift catalyst prior to sulphur removal, could achieve greater than 85% CO₂ recovery at 95 vol% purity. The efficiency penalty for such a process would be approximately 10% points, including CO₂ compression. A modified plant with CO₂ capture and compression was calculated to cost €2320/kW, producing electricity at a cost of 7.6 € cents/kWh and a CO₂ avoidance cost of about €40/tonne CO₂.     

Calcium oxides for CO2 capture obtained from the thermal decomposition of CaCO3 particles coprecipitated with Al ions

Calcium-carbonate powders were coprecipitated with Al³⁺ and then decomposed in air and/or under a CO₂ flux between 590 °C and 1150 °C. The data were analysed using a consecutive-decomposition-dilatometer method and the kinetic results were discussed according to the microstructure analysis done by N₂ adsorption isotherms (78 K), SEM and FT-IR measurements. Below 1000 °C, CaCO₃ particle thermal-decomposition was pseudomorphic, resulting in the formation of a CaO grain porous network. When the CaO grains were formed, the Al³⁺ diffused among them, producing AlO₄ groups that promoted the CaO grain coarsening and reduced O²⁻ surface sites available to CO₂ adsorbed molecules to form CO₃²⁻. In pure CaO, CO₃²⁻ diffused through the grain boundary, enhancing Ca²⁺ and O²⁻ mobility; AlO₄ groups reduced CO₃²⁻ penetration and CaO sintering rate. Above 1000 °C, the sintering rate of the doped samples exceeded that of the undoped, likely because of Al³⁺ diffusion in CaO and viscous flow.     

Experimental and modeling of CO2 capture by dry sodium hydroxide carbonation

In this work, CO₂ capture from the air using dry NaOH sorbents has been studied. The influences of the main operating parameters such as temperature, air humidity, and NaOH loading on the CO₂ removal rate have been experimentally investigated using Taguchi method. The results revealed that the appropriate value of the temperature to maximize the rate was in the range of 35–45 °C. A multilayer artificial neural network (ANN) was also used to model the process in order to find the optimal conditions. A procedure reported in the literature was modified and applied to design the ANN model. The model predictions were validated by conducting some more experiments. The experimental results proved the accuracy of the model to predict the optimal conditions. The effects of NaOH particle size and multiple carbonation cycles have also been investigated.     

Experimental programme in CIUDEN's CO2 capture technology development plant for power generation

Energy projections made by the World Energy Council, the International Energy Agency (IEA) and the US Energy Information Administration give similar pictures of the dominant role of fossil fuel in the future primary energy global demand and the necessity of incorporating CCS Technologies as part of the portfolio of solutions to reach the target world emission reduction in the coming years. Without CCS, CO₂ emission levels by 2050 are expected to increase by 70%.One of the most relevant initiatives for the deployment of CCS technologies is promoted by the Spanish Government through the institution Fundacion Ciudad de la Energia (CIUDEN). CIUDEN is developing a complete programme focusing on the development of CCT and CCS technologies in Europe.CIUDEN's CO₂ capture programme includes the construction and operation of a Technology Development Plant (TDP) in NW Spain (El Bierzo). The construction of the installation started in November 2008 and incorporates the following technologies: fuel preparation system, pulverised coal boiler (20 MWth), circulating fluidized bed boiler (30 MWth), biomass gasifier (3 MWth), flue gas cleaning train for NO_x, dust and SO_x, and CO₂ processing unit.This paper describes CIUDEN's TDP for CO₂ capture, focusing on the particularities of the installation and design, and especially on the PC unit and equipment required for its operation. The experimental programme currently under way is also described.Results are expected to be an extraordinary advance in the development and strengthening of CCT and CCS technologies, particularly oxycombustion.     

Experimental study on CO2 capture conditions of a fluidized bed limestone decomposition reactor

In this study, the decomposition conditions of limestone particles (0.25-0.50 mm) for CO₂ capture in a steam dilution atmosphere (20-100% steam in CO₂) were investigated by using a continuously operating fluidized bed reactor. The results show that the decomposition conversion of limestone increased with the steam dilution percentage in the CO₂ supply gas. At a bed temperature of 920 °C, the conversions were 72% without steam dilution and 98% with 60% steam dilution. The conversion was 99% with 100% steam dilution at 850 °C of the bed temperature. Steam dilution can decrease not only the decomposition temperature of limestone, but also the residence time required for nearly complete decomposition of CaCO₃. The hydration and carbonation reactivities of the CaO produced were also tested and the results show that both the reactivities increased with the steam dilution percentage for decomposing limestone.     

Thermodynamic performance of O2/CO2 gas turbine cycle with chemical recuperation by CO2-reforming of methane

This paper proposes a novel power cycle system composed of chemical recuperative cycle with CO₂–NG (natural gas) reforming and an ammonia absorption refrigeration cycle. In which, the heat is recovered from the turbine exhaust to drive CO₂–NG reformer firstly, and then lower temperature heat from the turbine exhaust is provided with the ammonia absorption refrigeration system to generate chilled media, which is used to cool the turbine inlet gas except export. In this paper, a detailed thermodynamic analysis is carried out to reveal the performance of the proposed cycle and the influence of key parameters on performance is discussed. Based on 1 kg s⁻¹ of methane feedstock and the turbine inlet temperature of 1573 K, the simulation results shown that the optimized net power generation efficiency of the cycle rises up to 49.6% on the low-heating value and the exergy efficiency 47.9%, the new cycle system reached the net electric-power production 24.799 MW, the export chilled load 0.609 MW and 2.743 kg s⁻¹ liquid CO₂ was captured, achieved the goal of CO₂ and NO_x zero-emission.     

Modelling of a fluidized bed carbonator reactor to capture CO2 from a combustion flue gas

In recent years several processes incorporating a carbonation-calcination loop in an interconnected fluidized bed reactor have been proposed as a way to capture CO₂ from flue gases. This paper is a first approximation to the modelling of a fluidized bed carbonator reactor. In this reactor the flue gas comes into contact with an active bed composed of particles with very different activities, depending on their residence time in the bed and in the carbonation-calcination loop. The model combines the residence time distribution functions with existing knowledge about sorbent deactivation rates and sorbent reactivity. The fluid dynamics of the solids (CSTR) and gases (PF) in the carbonator are based on simple assumptions. The carbonation rates are modelled defining a characteristic time for the transition between a fast reaction regime to a regime with a zero reaction rate. On the basis of these assumptions the model is able to predict the CO₂ capture efficiency for the flue gas depending on the operating and design conditions. Operating windows with high capture efficiencies are discussed, as well as those conditions where only modest capture efficiencies are possible.     

Influence of calcination conditions on carrying capacity of CaO-based sorbent in CO2 looping cycles

This study examines the loss of sorbent activity caused by sintering under realistic CO₂ capture cycle conditions. The samples tested here included two limestones: Havelock limestone from Canada (New Brunswick) and a Polish (Upper Silesia) limestone (Katowice). Samples were prepared both in a thermogravimetric analyzer (TGA) and a tube furnace (TF). Two calcination conditions were employed: in N₂ at lower temperature; and in CO₂ at high temperature. The samples obtained were observed with a scanning electron microscope (SEM) and surface compositions of the resulting materials were analyzed by the energy dispersive X-ray (EDX) method. The quantitative influence of calcination conditions was examined by nitrogen adsorption/desorption tests, gas displacement pycnometry and powder displacement pycnometry; BET surface areas, BJH pore volume distributions, skeletal densities and envelope densities were determined. The SEM images showed noticeably larger CaO sub-grains were produced by calcination in CO₂ during numerous cycles than those seen with calcination in nitrogen. The EDX elemental analyses showed a strong influence of impurities on local melting at the sorbent particle surface, which became more pronounced at higher temperature. Results of BET/BJH testing clearly support these findings on the effect of calcination/cycling conditions on sorbent morphology. Envelope density measurements showed that particles displayed densification upon cycling and that particles calcined under CO₂ showed greater densification than those calcined under N₂. Interestingly, the Katowice limestone calcined/cycled at higher temperature in CO₂ showed an increase of activity for cycles involving calcination under N₂ in the TGA. These results clearly demonstrate that, in future development of CaO-based CO₂ looping cycle technology, more attention should be paid to loss of sorbent activity caused by realistic calcination conditions and the presence of impurities originating from fuel ash and/or limestone.     

Calcination and sintering characteristics of limestone under O2/CO2 combustion atmosphere

The O₂/CO₂ coal combustion technology is an innovative combustion technology that can control CO₂, SO₂ and NO_x emissions simultaneously. Calcination and sintering characteristics of limestone under O₂/CO₂ atmosphere were investigated in this paper. The pore size, the specific pore volume and the specific surface area of CaO calcined were measured by N₂ adsorption method. The grain size of CaO calcined was determined by XRD analysis. The specific pore volume and the specific surface area of CaO calcined in O₂/CO₂ atmosphere are less than that of CaO calcined in air at the same temperature. And the pore diameter of CaO calcined in O₂/CO₂ atmosphere is larger than that in air. The specific pore volume and the specific surface area of CaO calcined in O₂/CO₂ atmosphere increase initially with temperature, and then decline as temperature exceeds 1000 °C. The peaks of the specific pore volume and the specific surface area appear at 1000 °C. The specific surface area decreases with increase in the grain size of CaO calcined. The correlations of the grain size with the specific surface area and the specific pore volume can be expressed as L = 744.67 + 464.64 lg(1 / S) and L = − 608.5 + 1342.42 lg(1 / ε), respectively. Sintering has influence on the pore structure of CaO calcined by means of influencing the grain size of CaO.     

Ca-based sorbent looping combustion for CO2 capture in pilot-scale dual fluidized beds

To demonstrate process feasibility of in situ CO₂ capture from combustion of fossil fuels using Ca-based sorbent looping technology, a flexible atmospheric dual fluidized bed combustion system has been constructed. Both reactors have an ID of 100 mm and can be operated at up to 1000 °C at atmospheric pressure. This paper presents preliminary results for a variety of operating conditions, including sorbent looping rate, flue gas stream volume, CaO/CO₂ ratio and combustion mode for supplying heat to the sorbent regenerator, including oxy-fuel combustion of biomass and coal with flue gas recirculation to achieve high-concentration CO₂ in the off-gas. It is the authors' belief that this study is the first demonstration of this technology using a pilot-scale dual fluidized bed system, with continuous sorbent looping for in situ CO₂ capture, albeit at atmospheric pressure. A multi-cycle test was conducted and a high CO₂ capture efficiency (> 90%) was achieved for the first several cycles, which decreased to a still acceptable level (> 75%) even after more than 25 cycles. The cyclic sorbent was sampled on-line and showed general agreement with the features observed using a lab-scale thermogravimetric analysis (TGA) apparatus. CO₂ capture efficiency decreased with increasing number of sorbent looping cycles as expected, and sorbent attrition was found to be another significant factor to be limiting sorbent performance.     

Microporous phenol-formaldehyde resin-based adsorbents for pre-combustion CO2 capture

Different types of phenolic resins were used as precursor materials to prepare adsorbents for the separation of CO₂ in pre-combustion processes. In order to obtain highly microporous carbons with suitable characteristics for the separation of CO₂ and H₂ under high pressure conditions, phenol-formaldehyde resins were synthesised under different conditions. Resol resins were obtained by using an alkaline environment while Novolac resins were synthesised in the presence of acid catalysts. In addition, two organic additives, ethylene glycol (E) and polyethylene glycol (PE) were included in the synthesis. The phenolic resins thus prepared were carbonised at different temperatures and then physically activated with CO₂. The carbons produced were characterised in terms of texture, chemical composition and surface chemistry. Maximum CO₂ adsorption capacities at atmospheric pressure were determined in a thermogravimetric analyser. Values of up to 10.8 wt.% were achieved. The high-pressure adsorption of CO₂ at room temperature was determined in a high-pressure magnetic suspension balance. The carbons tested showed enhanced CO₂ uptakes at high pressures (up to 44.7 wt.% at 25 bar). In addition, it was confirmed that capture capacities depend highly on the microporosity of the samples, the narrow micropores (pore widths of less than 0.7 nm) being the most active in CO₂ adsorption at atmospheric pressure. The results presented in this work suggest that phenol-formaldehyde resin-derived activated carbons, particularly those prepared with the addition of ethylene glycol, show great potential as adsorbents for pre-combustion CO₂ capture.     

Evaluation of solid sorbents as a retrofit technology for CO2 capture

Processes based upon solid sorbents are currently under consideration for post-combustion CO₂ capture. Twenty-four different sorbent materials were examined on a laboratory scale in a cyclic temperature swing adsorption/regeneration CO₂ capture process in simulated coal combustion flue gas. Ten of these materials exhibited significantly lower theoretical regeneration energies compared to the benchmark aqueous monoethanolamine, supporting the hypothesis that CO₂ capture processes based upon solids may provide cost benefits over solvent-based processes. The best performing materials were tested on actual coal-fired flue gas. The supported amines exhibited the highest working CO₂ capacities, although they can become poisoned by the presence of SO₂. The carbon-based materials showed excellent stability but were generally categorized as having low CO₂ capacities. The zeolites worked well under dry conditions, but were quickly poisoned by the presence of moisture. Although no one type of material is without concerns, several of the materials tested have theoretical regeneration energies significantly lower than that of the industry benchmark, warranting further development research.     

Modeling and simulation for the methane steam reforming enhanced by in situ CO2 removal utilizing the CaO carbonation for H2 production

The transient behavior of catalytic methane steam reforming (MSR) coupled with simultaneous carbon dioxide removal by carbonation of CaO pellets in a packed bed reactor for hydrogen production has been analyzed through a mathematical model with reaction experiments for model verification. A dynamic model has been developed to describe both the MSR reaction and the CaO carbonation-enhanced MSR reaction at non-isothermal, non-adiabatic, and non-isobaric operating conditions assuming that the rate of the CaO carbonation in a local zone of the packed bed is governed by kinetic limitation or by mass transfer limitation of the reactant CO₂. Apparent carbonation kinetics of the CaO pellet prepared has been determined using the TGA carbonation experiments at various temperatures, and incorporated into the model. The resulting model is shown to successfully depict the transient behavior of the in situ CaO carbonation-enhanced MSR reaction. The effects of major operating parameters on the transient behavior of the CaO carbonation-enhanced MSR have been investigated using the model. The bed temperature is the most important parameter for determining the amount of CO₂ removed by carbonation of CaO, and at temperatures of 600°C, 650°C, 700°C and 750°C, the CO₂ uptake is 1.43, 2.29, 3.5 and -CO₂/kg-CaO, respectively. Simultaneously with the increase in CO₂ uptake with increasing temperature, the corresponding amounts of hydrogen produced are 1.56, 2.54, 3.91 and -H₂/kg-CaO, at the same temperatures as above. Operation at high pressure, high steam to methane feed ratio, and the decreased feed rate at a given temperature are favorable for increasing the degree of the overall utilization of CaO pellets in the reactor bed, and for lowering the CO concentration in the product.     

Reactivation and remaking of calcium aluminate pellets for CO2 capture

CaO-based pellets supported with aluminate cements show superior performance in carbonation/calcination cycles for high-temperature CO₂ capture. However, like other CaO-based sorbents, their CO₂ carrying activity is reduced after increasing numbers of cycles under high-temperature, high-CO₂ concentration conditions. In this work the feasibility of their reactivation by steam or water and remaking (reshaping) was investigated. The pellets, prepared from three limestones, Cadomin and Havelock (Canada) and Katowice (Poland, Upper Silesia), were tested in a thermogravimetric analyzer (TGA). The cycles were performed under realistic CO₂ capture conditions, which included calcination in 100% CO₂ at temperatures up to 950 °C. Typically, after 30 cycles, samples were hydrated for 5 min with saturated steam at 100 °C in a laboratory steam reactor (SR). Moreover, larger amounts of pellets were cycled in a tube furnace (TF), hydrated with water and reshaped, and tested to determine their CO₂ capture activity in the TGA. It was found that, after the hydration stage, pellets recovered their activity, and more interestingly, pellets that had experienced a longer series of cycles responded more favorably to reactivation. Moreover, it was found that conversion of pellets increased after about 70 cycles (23%), reaching 33% by about cycle 210, with no reactivation step. Scanning electron microscope (SEM) analyses showed that the morphology of the low-porosity shell formed at the pellet surface during cycles, which limits conversion, was eliminated after a short period (5 min) of steam hydration. The nitrogen physisorption analyses (BET, BJH) of reshaped spent pellets from cycles in the TF confirmed that sorbent surface area and pore size distribution were similar to those of the original pellets. The main alumina compound in remade pellets as determined by XRD was mayenite (Ca₁₂Al₁₄O₃₃). These results showed that, with periodic hydration/remaking steps, pellets can be used for extended times in CO₂ looping cycles, regardless of capture/regeneration conditions.     

CO2 capture capacity of CaO in long series of pressure swing sorption cycles

One promising method for the capture of CO₂ from point sources is through the usage of a lime-based sorbent. Lime (CaO) acts as a CO₂ carrier, absorbing CO₂ from the flue gas (carbonation) and releasing it in a separate reactor (calcination) to create a pure stream of CO₂ suitable for sequestration. One of the challenges with this process is the decay in calcium utilization (CO₂ capture capacity) during carbonation/calcination cycling. The reduction in calcium utilization of natural limestone over large numbers of cycles (>250) was studied. Cycling was accomplished using pressure swing CO₂ adsorption in a pressurized thermogravimetric reactor (PTGA). The effect of carbonation pressure on calcium utilization was studied in CO₂ with the reactor operated at 1000 °C. The pressure was cycled between atmospheric pressure for calcination, and 6, 11 or 21 bar for carbonation. Over the first 250 cycles, the calcium utilization reached a near-asymptotic value of 12.5-27.7%, depending on the cycling conditions. Pressure cycling resulted in improved long-term calcium utilization compared to temperature swing or CO₂ partial pressure swing adsorption under similar conditions. An increased rate of de-pressurization caused an increase in calcium utilization, attributed to fracturing of the sorbent particle during the rapid calcination, as observed via SEM analysis.