High CO2 Capture Efficiency Research Articles

Impact of load changes on the carbonator reactor of a 1.7 MWth calcium looping pilot plant

This work analyses the performance of a Calcium Looping (CaL) carbonator reactor that captures CO2 from a power plant operating under large load changes. Several experimental campaigns have been conducted in La Pereda 1.7 MWth CaL pilot plant where the carbonator inlet flue gas velocity varied between 2.0 and 5.3 m/s, leading to large changes in the particles entrainment rate and the solids inventory. These tests showed that CaL systems using circulating fluidized bed reactors are highly flexible. Modest gas velocities translate into high CO2 capture efficiencies because circulation rates equivalent to CaO/CO2 molar ratios ~10–12 can still be maintained, while carbonator solids inventories are relatively large. Under high carbonator gas velocities, a sorbent with high CO2 carrying capacity is necessary to guarantee high CO2 capture efficiencies. In these conditions, the recirculation of a fraction of the exiting particles towards the bottom of the carbonator proved to be useful for moderating the solids circulation rate between reactors, increasing the particles residence time in the carbonator and sustaining high CO2 capture efficiencies. For load increases, staging the flue gas entering the carbonator helped to sustain high CO2 capture efficiencies thanks to maintaining the solids inventory at the bottom of the reactor.

Evaluation of the performance and economic viability of a novel low temperature carbon capture process

A novel Advanced Cryogenic Carbon Capture (A3C) process is being developed using low cost but high intensity heat transfer to achieve high CO2 capture efficiencies with a much reduced energy consumption and process equipment size. These characteristics, along with the purity of CO2 product and absence of process chemicals, offer the potential for application across a range of sectors. This work presents a techno-economic evaluation for applications ranging from 3% to 35%vol. CO2 content. The A3C process is evaluated against an amine-based CO2 capture process for three applications; an oil-fired boiler, a combined cycle gas turbine (CCGT) and a biogas upgrading plant. The A3C process has shown a modest life cost advantage over the mature MEA technology for the larger selected applications, and substantially lower costs in the smaller biogas application. Enhanced energy recovery and optimization offer significant opportunities for further reductions in cost.

Chemical looping with oxygen uncoupling: an advanced biomass combustion technology to avoid CO2 emissions

Bioenergy with carbon dioxide (CO2) capture and storage (BECCS) technologies represent an interesting option to reach negative carbon emissions, which implies the removal of CO2 already emitted to the atmosphere. Chemical looping combustion (CLC) with biomass can be considered as a promising BECCS technology since CLC has low cost and energy penalty. In CLC, the oxygen needed for combustion is supplied by a solid oxygen carrier circulating between the fuel and air reactors. In the fuel reactor, the fuel is oxidized producing a CO2-concentrated stream while the oxygen carrier is reduced. In the air reactor, the oxygen carrier is regenerated with air. Chemical looping with oxygen uncoupling (CLOU) is a CLC technology that allows the combustion of solid fuels as in common combustion with air by means of an oxygen carrier that release gaseous oxygen in the fuel reactor. In the last years, several Cu-based, Mn-based, and mixed oxide oxygen (O2) carriers have been tested showing good CLOU properties. Among them, copper (Cu)-based and Cu-Manganese (Mn) mixed oxides showed high reactivity, O2 release rate, and high O2 equilibrium concentration. The aim of this work is to study the viability of biomass combustion by CLOU process. The combustion of three types of biomass (pine sawdust, olive stone, and almond shell) were studied in a continuous 1.5 kWth CLC unit. Two O2 carriers were tested: a Cu-based oxygen carrier with Magnesium, Aluminum, Oxgen (MgAl2O4) as an inert prepared by spray drying (Cu60MgAl) and a mixed Cu-Mn oxide prepared by spray granulation (Cu34Mn66). These materials are capable of releasing gaseous oxygen when they are reduced in a different range of temperatures. CO2 capture and combustion efficiency were evaluated. Two fuel reactor operation temperatures were used: 775–850 °C for Cu34Mn66 and 900–935 °C for Cu60MgAl. High CO2 capture efficiencies and 100% combustion efficiency were reached with both oxygen carriers and with all the biomasses tested. Therefore, the CLOU technology with the Cu- and Cu-Mn-based oxygen carriers allowed avoiding CO2 emissions maintaining high combustion efficiencies. Results obtained demonstrate that this innovative biomass combustion technology combined with carbon storage lets an efficient BECCS process implementation.

Evaluation of the Performance and Economic Viability of a Novel Low Temperature Carbon Capture Process

A novel Advanced Cryogenic Carbon Capture (A3C) process is being developed due to its potential to achieve high CO2 capture efficiencies using low cost but high intensity heat transfer to deliver a much reduced energy consumption and process equipment size. These characteristics, along with the absence of process chemicals, offer the potential for application across a range of sectors. This work presents a techno-economic evaluation for applications ranging from 3% to 30% CO2 content.

The mOxy-CaL Process: Integration of Membrane Separation, Partial Oxy-combustion and Calcium Looping for CO2 Capture

CO2 capture and storage (CCS) is considered as a key strategy in the short to medium term to mitigate global warming. The Calcium-Looping process, based on the reversible carbonation/calcination of CaO particles, is a promising technology for post-combustion CO2 capture because of the low cost and non-toxicity of natural CaO precursors and the minor energy penalty on the power plant in comparison with amines capture based technologies (4-9 % compared to 8-12 %). Another interesting process to reduce CO2 emissions in power plants is oxy-combustion, which is based on replacing the air used for combustion by a highly concentrated (~95 % v/v) O2 stream. This work proposes a novel process (mOxy-CaL) for post-combustion CO2 capture based on the integration of membrane separation, partial oxy-combustion and the Calcium-Looping process. An oxygen-enriched air stream, which is obtained from air separation by using highly permeable polymeric membranes, is used to carry out partial oxy-combustion. The flue gas exiting partial oxy-combustion shows a CO2 concentration of ~30 % v/v (higher than 15 % v/v typical in coal power plants). After that, the flue gas is passed to the CaL process where the CO2 reacts with CaO solids according to the carbonation reaction. Thermogravimetric analysis show that the multicycle CaO conversion is enhanced as the CO2 concentration in the flue gas stream is increased. Process simulations show that the mOxy-CaL process has a high CO2 capture efficiency (~95%) with lower energy consumption per kg of CO2 avoided than previously proposed post-combustion CO2 capture technologies. Moreover, the overall system size is significantly lower that state-of-the-art CaL systems, which allows for an important reduction in the capital cost of the technology.

Alkyl amine functionalized triphenylamine-based covalent organic frameworks for high-efficiency CO2 capture and separation over N2

High-efficiency absorbent is a prerequisite for CO2 capture from the atmosphere to alleviate environmental degradation. Herein, grand canonical Monte Carlo (GCMC) was used to investigate the CO2 adsorption and separation behaviors in four alkyl anime functionalized triphenylamine-based covalent organic frameworks (TPA-xC-NH2, x = 1–4). Results show that a longer alkyl anime chain has a more remarkable effect on the CO2 adsorption capacity and separation over N2. The alkyl amine chain owning four carbon atoms of TPA-4C-NH2 exhibits the best performance. The CO2 adsorption capacity in TPA-4C-NH2 is 3.41 mmol/g at 298 K and 5.26 mmol/g at 273 K and 1 bar, thereby enhancing the CO2 adsorption capacity by 50.2% and 30.5%, respectively, with a 121% selectivity increase compared with that of the pristine TPA-COF. The pore characteristic, isosteric heat, coulomb/non-coulomb interaction, and selectivity are analyzed to elucidate the enhancement mechanisms.

High-efficiency and pollution-controlling in-situ gasification chemical looping combustion system by using CO2 instead of steam as gasification agent

Abstract Using CO2 as gasification agent instead of steam in in-situ coal gasification chemical looping combustion (iG-CLC) power plant can eliminate energy consumption for steam generation, thus obtaining higher system efficiency. In this work, a comparative study of iG-CLC power plant using steam and CO2 as gasification agent is concentrated on. The effects of steam to carbon ratio (S/C) and CO2 to carbon ratio (CO2/C) on the fuel reactor temperature, char conversion, syngas composition and CO2 capture efficiency are separately investigated. An equilibrium carbon conversion of 88.9% is achieved in steam-based case as S/C ratio increases from 0.7 to 1.1, whereas a maximum conversion of 84.2% is obtained in CO2-based case with CO2/C ranging from 0.7 to 1.1. Furthermore the effects of oxygen carrier to fuel ratio (φ) on system performances are investigated. Increasing φ from 1.0 to 1.4 helps to achieve char conversion from 75.9% to 88.9% in steam-based case, by contrast the char conversion can achieve 66.3%–84.2% in CO2-based case within the same φ range. In terms of iG-CLC power plant, recycling partial CO2 to the fuel reactor improves the overall performance. Approximately 3.9% of net power efficiency are increased in CO2-based plant, from steam-based plant. Higher CO2 capture efficiency and lower CO2 emission rate are observed in CO2-gasified iG-CLC power plant, expecting to be 90.63% and 85.18 kg·MW− 1·h− 1, respectively.

Power Generation from Coke Oven Gas Using Chemical Looping Combustion: Thermodynamic Simulation

AbstractA chemical looping combustion (CLC) combined cycle with coke oven gas as fuel and NiO/NiAl2O4 as an oxygen carrier is proposed. The system was simulated by Aspen Plus® and the oxygen carrier circulation ratio was calculated. The effects of key operational temperatures and different gas turbines on the system performance were investigated. Under optimized conditions, a high CO2 capture efficiency could be achieved. To capture CO2 thoroughly, the PG6561B gas turbine can be employed, allowing for nearly 100 % CO2 capture efficiency.

Development of robust fluorinated TiO2/PVDF composite hollow fiber membrane for CO2 capture in gas-liquid membrane contactor

Gas-liquid membrane contactor (GLMC) is a promising method to attain high efficiency for CO2 capture from flue gas, biogas and natural gas. However, membranes used in GLMC are prone to pore wetting due to insufficient hydrophobicity and low chemical resistance, resulting in significant increase in mass transfer resistance. To mitigate this issue, inorganic-organic fluorinated titania/polyvinylidene fluoride (fTiO2/PVDF) composite hollow fiber (HF) membranes was prepared via facile in-situ vapor induced hydrolyzation method, followed by hydrophobic modification. The proposed composite membranes were expected to couple the superb chemical stability of inorganic and high permeability/low cost of organic materials. The continuous fTiO2 layer deposited on top of PVDF substrate was found to possess a tighter microstructure and better hydrophobicity, which effectively prevented the membrane from wetting and lead to a high CO2 absorption flux (12.7 × 10−3 mol m−2 s−1). In a stability test with 21-day operation of GLMC using 1M monoethanolamine (MEA) as the absorbent, the fTiO2/PVDF membrane remained to be intact with a CO2 absorption flux decline of ∼16%, while the pristine PVDF membrane suffered from a flux decline of ∼80% due to membrane damage. Overall, this work provides an insight into the preparation of high-quality inorganic/organic composite HF membranes for CO2 capture in GLMC application.

Biomass-facilitated production of activated magnesium oxide nanoparticles with extraordinary CO2 capture capacity

Discovering sustainable materials that can efficiently capture and store CO2 is a crucial step towards mitigating anthropogenic greenhouse gas emissions. The current materials used in post-combustion scenarios have significant drawbacks, including high cost and resulting hazardous byproducts. This study developed a simple and cost-effective method of producing activated MgO nanoparticles that have high CO2 capture efficiency. To optimize CO2 capture, we incorporate biomass during the production to ensure complete and dispersed MgO nanoparticle formation from the decomposition of MgCl2 hydrate. Materials are characterized by SEM, XRD, BET/DFT, ICP, and TGA analysis. Resulting carbon-supported activated MgO nanoparticles efficiently captured CO2 at low temperature, by physisorption and magnesium carbonate formation. Without the incorporation of biomass, MgCl2 hydrate decomposed via low temperature pyrolysis, is still capable of CO2 capture; however, the efficiency is enhanced with the addition of biomass, as this helps support the formation and distribution of MgO nanoparticles. The carbon-supported MgO nanoparticles produced with a 5:2.5 (w/w MgCl2:biomass) ratio was capable of greatest CO2 capture capacity on both a g−1 material (up to 235 mg g−1) and g−1 magnesium (733 mg g−1) basis after 3 h. The carbon-supported MgO nanoparticles have potential to be applied in inexpensive large-scale CO2 capture, as the production can be adjusted based on capacity, resource, or energy constraints.

Screening CO2 Capture Test for Cement Plants Using a Lab Scale Calcium Looping Pilot Facility

This poster presents the first experimental results obtained from a 30 kWth Calcium Looping test facility upgraded to work at conditions closer to those expected in a calcium looping system retrofitted to a cement plant. The main modification in the facility is the use of a second recycle of fine solids (<40 micron) collected in the secondary cylones located after the main calcium loop for CO2 capture. This allowed the operation of the main calcium loop using finer particle size distributions (dp50 around 60-75 micron), which should generate solid purges more suitable to be processed in clinker ovens. High CO2 capture efficiencies have been achieved in preliminary experiments with high make-up flow of limestone and high CO2 concentrations. Further experimental work and modeling activities for an adequate interpretation of results are ongoing within the CEMCAP H2020 project.

Comparative Evaluation of the Performance of Coal Combustion in 0.5 and 50 kWth Chemical Looping Combustion Units with Ilmenite, Redmud or Iron Ore as Oxygen Carrier

Chemical Looping Combustion (CLC) is one of the most promising technologies to achieve the CO2 capture at a low economic and energetic penalty. In CLC the combustion is split in two steps: fuel combustion assisted by an oxygen carrier in the fuel reactor, and oxygen carrier regeneration in the air reactor by oxygen in air. Usually, the air and fuel reactors are interconnected fluidized beds, with the oxygen carrier circulating between them. Thus, the CO2 capture is inherent to the CLC process. The use of solid fuels in CLC is attracting great attention due to coal is the most abundant fuel, and burning biomass with CO2 capture would allow to reduce the atmospheric CO2 concentration. The in situ Gasification CLC (iG-CLC) allows the conversion of the solid fuel by performing both gasification and combustion of gasification products in the fuel reactor. In iG-CLC complete combustion is not reached, and an oxygen polishing step is required downstream by using a small fraction of pure oxygen.In this work, an overview of the operational experience in ICB-CSIC is presented. Results obtained in 0.5 kWth and 50 kWth CLC units burning different coals with ilmenite, redmud or iron ore are compiled and critically compared. Insights were obtained in order to achieve high CO2 capture and combustion efficiency values. Eventually, the use of ring-type internals in the fuel reactor of the 50 kWth CLC unit was accomplished to promote the gas-solid contact, thus increasing the combustion efficiency.

Total Integrated Operation of Gasifier, Hot Gas Desulfurizer, and SEWGS Process for Pre-combustion CO2 Capture Using Real Syngas from Coal

SEWGS (Sorption Enhanced Water Gas Shift) process is one of options for pre-combustion CO2 capture using dry absorbent and water gas shift catalyst. In this process, the thermodynamic equilibrium in the shift reaction can be enhanced to give more hydrogen yield by adding a CO2 absorbent into the shift reactor. Total integrated system consists of coal gasifier, hot gas clean-up process (two interconnected fluidized bed desulfurizer), and one loop SEWGS process. In this presentation, continuous operation results of the hot gas clean-up process and one loop SEWGS process using dry absorbents at high temperature and pressure conditions were discussed. Dry absorbents (for desulfurization, CO2 absorption) were produced by KEPCO RI (Korea Electric Power Corporation Research Institute) by means of spray-drying method. Continuous operation was performed at high pressure (21bar for gasifier, 20bar for hot gas clean-up process, and 18bar for SEWGS process) and reaction temperature was 550oC for desulfurizer and 236oC for SEWGS reactor. Totally integrated operation was maintained up to 50hours. We could get high sulfur capture efficiency (99.6%) in the desulfurizer, high CO conversion (98.9%) and CO2 capture efficiency (98.0%) in the SEWGS reactor.

Realizing low life cycle energy use and GHG emissions in coal based polygeneration with CO2 capture

Cogeneration of synthetic natural gas (SNG) and power from coal can realize both high energy conversion efficiency and low energy penalty for CO2 capture (CC). Life cycle energy use and GHG emission assessments are applied to coal based SNG and power cogeneration with CO2 capture. Four typical pathways are considered based on the main applications of SNG in China. Results show that when SNG is produced in a single product plant with CO2 capture and SNG is used for power generation, its life cycle energy use is averagely around 5% lower than that of supercritical coal power with CC and even can be comparable with ultra supercritical (USC) with CC pathway. Such low energy use is mainly due to much lower energy penalty for CO2 capture in a SNG production plant than in a post-combustion coal fired power plant. The life cycle energy use of cogeneration plant with CC is 10–19% lower than that of USC with CC due to system integration, the obvious higher CO2 concentration before separation and the consequent much lower energy penalties for CO2 capture. The life cycle GHG emissions of cogeneration with CC range from 135 to 150 gCO2 eq./MJ, which are obviously lower than those of all coal power pathways including USC units (10–17% lower than USC with CC). For steam and power cogeneration and pure vehicle operation pathways, the cogeneration technology with CO2 capture also shows obvious life cycle energy use and GHG emission advantages over its competitive pathways.

Integration of the Ca–Cu Process in Ammonia Production Plants

In this work, the application of a Ca–Cu process into a state-of-the-art ammonia production plant is assessed through process simulations, aiming at reducing the primary energy needs of the syngas production and purification sections. The proposed process has shown to significantly reduce the specific primary energy consumption, even when accounting for the higher electric consumption in the Ca–Cu process. From an environmental point of view, the proposed process has an inherently high CO2 capture efficiency (about 97%). The encouraging thermodynamic performance along with some simplifications in the syngas conditioning process and the ammonia synthesis loop confirms the potential of the Ca–Cu process as a route for syngas generation in ammonia plants.

Incorporation of monoethanolamine (MEA), diethanolamine (DEA) and methyldiethanolamine (MDEA) in mesoporous silica: An alternative to CO2 capture

Monoethanolamine (MEA), diethanolamine (DEA) and methyldiethanolamine (MDEA) are substances used in the CO2 capture industrial process. The inconvenience of their use is that these species have low thermal stabilities, are volatile, and in the presence of air undergo oxidation processes to form corrosive products. This work proposed the incorporation of MEA, DEA and MDEA in a mesoporous silica substrate as an alternative for CO2 adsorption. The mesoporous materials have a high surface area and a large pore size. The high material porosity enabled the incorporation of a large quantity of ethanolamine. The presence of MEA inside the silica pores promoted the acceleration of the decomposition process. The materials prepared using a mixture of mesoporous silica and DEA and MDEA had an optimal CO2 capture efficiency than the isolated ethanolamines. This increased CO2 capture efficiency was most significant in the sample prepared using MDEA. The increase of CO2 efficiency capture by the incorporated material was 30% higher compared with free MDEA. DEA and MDEA incorporated in mesoporous silica had a higher CO2 capture efficiency in the second and third adsorption cycles than free DEA and MDEA. The study showed that the incorporation of DEA and/or MDEA in mesoporous silica may increase CO2 capture efficiency.

Hydrogen production from heavy fraction of bio-oil using iron-based chemical looping process: Thermodynamic simulation and performance analysis

The purpose of this work is to investigate the overall performance of the iron-based chemical looping hydrogen (CLH) production from the heavy fraction of bio-oil (HFB). The multiple ASPEN models are employed to simulate a two-stage fluidized bed reduction reactor considering the thermodynamic equilibrium limit. Several important factors are discussed to determine the suitable reactor operation conditions for the process simulation of two operation modes. The results show HFB CLH process has a maximum hydrogen efficiency of 73.1% (LHV) and a total thermal efficiency of 59.2% (LHV) at the cost of decreasing the CO2 capture efficiency under the condition of supplementary firing. Within the complete self-sustaining operation range, the highest hydrogen thermal efficiency is 57.8% (LHV) corresponding to a total thermal efficiency of 58.3% (LHV) and a CO2 capture efficiency of nearly 100%. This study indicates the CLH process has significant advantages over the conventional coal gasification (CG) for hydrogen production owing to its high energy conversion efficiency and high-efficient CO2 capture with low cost.

Amine hybrid aerogel for high-efficiency CO2 capture: Effect of amine loading and CO2 concentration

The objective of this research was to develop a high-performance CO2 adsorbent by a simple, cost-effective and environmental-friendly route based on amine hybrid aerogel. A new amine hybrid titania/silsesquioxane composite aerogel (AHTSA) was prepared by a one-pot sol-gel process followed by supercritical drying (SCD). The wet gel was obtained by orderly mixing all the reactants in a container without adding any catalyst. SCD was conducted without contaminant emission. Effects of amine loading and CO2 concentration on pores structure and CO2 adsorption performance of AHTSA were investigated. Higher amine loading leads to lower specific surface area and mesopore volume of AHTSA, due to the increase of large pores and diminishment of mesopores when increasing the amine loading. Resulting from the sharp decrease of the surface area, overdosing of the amine precursor negatively affects the surface amine content of AHTSA and thus reduces its CO2 adsorption capacity. High CO2 concentration favors the CO2 adsorption capacity and rate as concentrated CO2 favors the CO2 diffusion in the pore space of the adsorbent, enhances the interaction between CO2 and surface amine groups. The dry CO2 adsorption capacity of AHTSA increases from 1.64, 4.19 to 6.66mmol/g when the CO2 concentration of the mixture gas varies from ∼400ppm (air), 1% to 10%. Short adsorption halftime and high amine efficiency of AHTSA with different CO2 concentrations reveal that AHTSA is a dynamic and effective adsorbent for CO2 capture, even direct air capture.

Sorbents with high efficiency for CO2 capture based on amines-supported carbon for biogas upgrading

Sorbents for CO2 capture have been prepared by wet impregnation of a commercial active carbon (Ketjen-black, Akzo Nobel) with two CO2-philic compounds, polyethylenimine (PEI) and tetraethylenepentamine (TEPA), respectively. The effects of amine amount (from 10 to 70wt.%), CO2 concentration in the feed, sorption temperature and gas hourly space velocity on the CO2 capture performance have been investigated. The sorption capacity has been evaluated using the breakthrough method, with a fixed bed reactor equipped with on line gas chromatograph. The samples have been characterized by N2 adsorption–desorption, scanning electron microscopy and energy dispersive X-ray (SEM/EDX). A promising CO2 sorption capacity of 6.90 mmol/gsorbent has been obtained with 70wt.% of supported TEPA at 70°C under a stream containing 80vol% of CO2. Sorption tests, carried out with simulated biogas compositions (CH4/CO2 mixtures), have revealed an appreciable CO2 separation selectivity; stable performance was maintained for 20 adsorption–desorption cycles.

Coal combustion in a 50 kWth Chemical Looping Combustion unit: Seeking operating conditions to maximize CO2 capture and combustion efficiency

In-situ Gasification Chemical-Looping Combustion (iG-CLC) with coal has been proposed as a low-cost process for the capture of CO2 during the energy generation. Previous experimental works have highlighted that high CO2 capture efficiency, close to 100%, can be achieved. However, a certain amount of unburnt gases (mainly CH4, CO and H2) are present in the CO2 stream. These gases can be treated in an oxygen polishing step placed downstream from the CLC unit where they are burnt with pure oxygen, which defines the so-called oxygen demand for the process. The aim of this work was to optimize the performance of the iG-CLC process with coal in order to minimize oxygen demand while maintaining CO2 capture at high levels. Ilmenite was used as the oxygen carrier to burn a bituminous coal in a 50kWth CLC unit, which consisted of a fuel reactor, an air reactor and a carbon stripper unit between them. The fuel reactor temperature, solids inventory in the fuel reactor, solids circulation rate, coal feeding rate and carbon stripper efficiency were varied, and the CO2 capture efficiency and oxygen demand were calculated for each set of operating conditions. The effect of the fuel reactor temperature was higher on the CO2 capture than on the oxygen demand, with a temperature close to 1000°C advisable in order to reach CO2 capture rates higher than 90%. In order to further increase CO2 capture, the efficiency of char separation in the carbon stripper was increased. The solids circulation flow rate and the coal feeding rate -which define the oxygen carrier-to-fuel ratio-, in addition to the solids inventory in the fuel reactor, showed a strong influence on the combustion efficiency. Thus, the total oxygen demand was able to be decreased from 10% to 7% by increasing the oxygen carrier-to-fuel ratio from 1.1 to 1.5 and the solids inventory from 450 to 720kg/MWth. However, an increase in the circulation rate showed a detrimental effect on CO2 capture, which could be offset by increasing the carbon stripper efficiency.