CO2 Capture Rate Research Articles

Study on MCFC-integrated GSCC systems with SEGR in parallel or series and CO2 capture

In this paper, two new molten carbonate fuel cell (MCFC)-integrated gas–steam combined cycle (GSCC) systems with selective exhaust gas recirculation (SEGR) and CO2 capture are proposed and analyzed. The CO2 concentration in the gas turbine emission is increased because CO2 is selectively recycled with the help of SEGR. Molten carbonate fuel cells (MCFCs) are another way to increase CO2 concentration in the gas turbine flue gas by translating only CO2 from the cathode to the anode. In these two new gas–steam combined cycle systems, SEGR connected with MCFC, either in parallel or series, increases CO2 concentration beyond 11%. A gas–steam combined cycle system combined with MCFC and CO2 capture without SEGR is used as the reference system. Aspen Plus software is adopted to build the system models, and the performances of different systems are discussed and compared. The research results reveal that for the MCFC-integrated gas–steam combined cycle system with SEGR in series and CO2 capture, the CO2 concentration of gas turbine exhaust increases to 11.72% and the thermal efficiency is 56.29% when the overall CO2 capture rate is 88.16%, which is 1.13% higher than that of the reference system; for the MCFC-integrated gas–steam combined cycle system with SEGR in parallel and CO2 capture, the CO2 concentration of gas turbine exhaust increases to 14.15% and the thermal efficiency is 56.62%, which is 1.46% higher than that of the reference system. Furthermore, the economic analysis results show that the economic performances of new systems are mainly influenced by MCFC cost and will be gradually improved with the decrease in the MCFC cost.

A predictive model for the techno-economic assessment of CO[formula omitted] chemisorption processes applicable to a large number of amine solvents

With the growing need to reduce carbon dioxide (CO2) emissions, there have been substantial efforts to identify new solvents that can improve the overall performance of chemical-absorption CO2 capture processes. Given the large number of potential solvents, computer-aided molecular and process design (CAMPD) approaches can play a critical role in accelerating the search for optimal solvents by enabling the systematic exploration of solvent candidates and process conditions. One of the challenges in developing such a framework is the requirement for a process model that can be used to capture the interactions between process performance and solvent structure without significantly increasing its numerical complexity. In the current work, a model for the absorption–desorption of CO2 is developed using the predictive SAFT-γ-Mie group-contribution approach, allowing the performance of numerous solvents to be assessed without the need for extensive experimental data. In order to avoid convergence difficulties when solving this highly nonlinear model, a tailored initialization strategy is established, using an adapted inside-out algorithm to prime a nonlinear equation solver for each column, providing a good initial guess for the whole flowsheet. Tests on three solvents confirm the robustness of the approach. Building on this enhanced numerical stability, the model is validated by comparison against pilot-plant data, showing good accuracy. A detailed parametric study of the effect of the key process variables is undertaken; the important role of the CO2 capture rate, of the lean solvent temperature and loading, and of the desorber pressure is highlighted. The results of the parametric study are used to formulate an optimization problem which is successfully solved for four solvents. A large reduction in total annualized cost and energy requirements is achieved by tuning the operating conditions to each solvent considered. The predictive capability, robustness, and reliability of the proposed model and associated initialization strategy open the way for the evaluation of a large number of novel solvents.

Hydrogen production and CO2 capture from Linz-Donawitz converter gas via a chemical looping concept

Linz-Donawitz converter gas (LDG), an important by-product in the steel industry with CO (55–60 vol%) and CO2 (15–20 vol%) as the main components, is usually used as fuel for heating or power generation, releasing massive of diluted CO2 with the concentration lower than 15 % that is difficult to capture. Herein, we propose a method to produce pure H2 via chemical looping water splitting by using LDG as reducing agent, which can easily concentrate CO2 for capture. Fe2O3, one of the most environmentally friendly and low-cost oxides, was chosen as the oxygen carrier to perform this concept. It was found that the addition of small amounts of Ce0.75Zr0.25O2 solid solution could strongly improve the activity of Fe2O3 for CO conversion, especially at relatively low temperatures. Compared with pure Fe2O3, the CO conversion and H2 yield were increased from 39.5 % and 0.34 mmol·g−1 to 100 % and 2.32 mmol·g−1 at 650 °C, respectively, after adding 5 wt% of Ce0.75Zr0.25O2. The strong interaction between the two oxides contributed to the enhanced performance via promoting CO adsorption and lattice oxygen releasing. Water splitting assisted by air oxidation could fully regenerate the reduced oxygen carrier, and the oxygen carrier was stable during the long-term chemical looping process, with the CO2 capture rate at ca. 95.8 %. In situ DRIFTS results showed that CO2 was producedthrough a direct reaction of lattice oxygen with CO, and the decomposition of carbonate species intermediate by adsorption of CO on the surface of oxygen carriers. This study gave full evidence that it was feasible for achieving H2 generation and CO2 capture in one step via chemical looping reforming of reducing exhaust gases (e.g., LDG) from industrial emissions.

Performance analysis of a CO2 near-zero emission integrated system for stepwise recovery of LNG cold energy and GT exhaust heat

Combined cooling, heating and power (CCHP) system can further improve energy utilization efficiency while meeting diversified energy demands, and the rational use of the CCHP system is an effective way to alleviate the energy crisis. An innovative cascaded CCHP system based on the transcritical carbon dioxide cycle (TRCC) and organic Rankine cycle (ORC) has been proposed, which is designed to recover the cold energy of liquefied natural gas (LNG) and the exhaust heat from the gas turbine (GT), while achieving near-zero CO2 emissions. The simulation result demonstrates that the system achieves energy utilization efficiency, exergy efficiency and net electrical efficiency of 87.3%, 56.9% and 55.39%, respectively, with a CO2 capture rate of 79.2 kg/h under the design condition. Compared to the mentioned cogeneration systems that recover LNG cold energy and GT waste heat, the proposed system exhibits improvements in energy utilization efficiency, exergy efficiency and net electrical efficiency by 9.84%, 4.37% and 3.4%, respectively. The parameter sensitivity analysis reveals that increasing the pressure ratio of the TCO2 turbine and ORC turbine or reducing the air compressor feed temperature can improve the overall performance of the system. If the focus is solely on energy utilization efficiency and exergy efficiency, appropriately increasing the air compressor pressure ratio or reducing the gas turbine pressure ratio would be beneficial. The proposed system in the study is environmentally friendly and energy-saving, which especially suggests a direction for cold energy cascade utilization in LNG stations integrated with CCHP.

Flexible operation of Post-combustion CO2 capture process enabled by NARX-MPC using neural network

Post-combustion CO2 capture (PCC) process is expected to serve as the role of a bridge solution during the transition from fossil-based to renewable energy, but extensive energy consumption is a significant hurdle to its widespread commercial adoption. Operating a PCC process economically often requires large operating condition changes in response to power plant load changes and time-varying energy prices. The ‘flexible’ operation requires a controller that aids in such a dynamic operating environment of the PCC process. To balance model complexity with prediction accuracy, we adopt NARX-MPC which employs a neural network-based NARX model as a prediction model for MPC. Under various dynamic operation scenarios, the proposed NARX-MPC is evaluated and compared with a linear MPC (LMPC) controller. Our observations indeed reveal that the NARX-MPC delivers significantly superior closed-loop control performance over the LMPC, especially in scenarios involving large changes in the power plant load or inlet flue gas flow rate and simultaneous changes in the flue gas flow rate and the CO2 capture rate.

Comparative life cycle energy, water consumption and carbon emissions analysis of deep in-situ gasification based coal-to-hydrogen with carbon capture and alternative routes

In order to clarify the competitiveness of deep in-situ gasification based coal-to-hydrogen (deep IGCtH) in the context of carbon-constrained development, based on simulation results, the energy, water consumption and carbon emissions were quantitatively assessed and compared with large-scale fossil energy based routes, using life cycle assessment model from feedstock to hydrogen that covers process energy production and utilization. The results indicate when producing 1 kg of hydrogen, deep IGCtH requires 349.55 MJ of external primary fossil energy input and generates 30.47 kg CO2-eq of emissions, which are 24.88% and 16.32% lower than 465.34 MJ and 36.41 kg CO2-eq of Lurgi surface gasification based coal-to-hydrogen (Lurgi SGCtH), and also 7.38% lower than 377.39 MJ of coke-oven gas-to-hydrogen (COGtH). Furthermore, deep IGCtH can not only reduce coal consumption by 19.7% compared with Lurgi SGCtH, but also reduce oil consumption required to obtain process energy by 81.84%, which also reaches 80.09% compared with COGtH. Due to the high methane content, the exhaust gas and flue gas of deep IGCtH contributes 9.78 kg and 8.84 kg of CO2 emissions, and under the CO2 capture rate of 80%, the carbon emissions adopting exhaust gas and flue gas simultaneous capture reach 25.88 kg CO2-eq, higher than the 23.1 kg CO2-eq adopting exhaust gas single capture, of which waste gas only contributes 3.87 kg of emissions, but electricity consumption causes 15.11 kg CO2-eq of emissions, indicating the key to adopting such scheme to achieve further emissions reduction lies in reducing emissions caused by electricity consumption.

Achieving near-zero emission and high-efficient combined cooling, heating and power based on biomass gasification coupled with SOFC hybrid system

Extensive studies on coupling biomass as a fuel to power systems for clean and efficient energy conversion provides a realistic path towards carbon neutrality. Therefore, a novel system was proposed, which featured biomass CO2 gasification, solid oxide fuel cell (SOFC) with carbon capture, and ammonia Rankine cycle. A thermodynamic model of the system process was developed and used to comprehensively assessment of the performance in terms of thermodynamic, CO2 reduction potential, and economic. The results indicate a net electrical efficiency of 50.41%, a net electrical output of 9124.5 kW, a CHP efficiency of 70.2%, and an exergy efficiency of 45.6%. The key sources of irreversibility identified through exergy analysis were found to be the gasifier, SOFC, and afterburner. Moreover, in this system, an impressive maximum CO2 capture rate of 99.9% was achieved, and a low CO2 specific emission of 0.64 kg/MWh was recorded, highlighting its emission reduction potential compared to conventional CCHP systems. Economic analysis further supports the feasibility of this system, revealing the levelized cost of electricity at 58.17 $/MWh and the swift initial investment recovery period of 4.34 years. This novel system signifies a promising pathway towards a sustainable and economically viable energy conversion.

Analytical first-principles-based model for sprays-based CO2 capture

CO2 removal from flue gases or air is directly proportional to the overall contact area between the solvent and gas flow. Spraying the solvent offers possibilities for large area/volume ratios resulting from the small size of solvent droplets. The overall mass transfer (KGAv) is a crucial indicator of the performance of the system and indicates the overall CO2 capture rate per unit volume at given working pressure. The maximum capture rate of spray systems considered in this study is 608 kmol/m3-hr. This study develops an analytical model to predict mass transfer in spray-based systems for CO2 capture by evaluating KGAv and capture efficiency. Model predictions are validated using two experimental studies for a range of liquid flow rate, inlet solvent loading, different nozzle types, and inlet CO2 partial pressure. The relative importance of the incorporation of equilibrium partial pressure of CO2 (P*) into amine with respect to CO2 partial pressure is also studied. It is found that its effect on KGAv is prominent in high liquid flow rate and low solvent loading regimes where the overall CO2 capture is high. Finally, the variation of key parameters such as KGAv, total mass transfer coefficient (KG), effective area (Av), solvent loading (α), and mole fraction of CO2 in the gas stream (XCO2) along the channel height is studied, which gives insights on optimization of the channel height for specified operating conditions.

Sub-ambient membrane process for CO2 removal in the industrial sector: Iron and steel, cement, and refinery

With the growing interest in net-zero emissions worldwide, the focus on CO2 capture technologies has changed from fossil fuel-combusted power plants to industries such as steel and iron, cement, and oil refining. In this study, a sub-ambient membrane process is applied to representative industrial fields that emit large amounts of CO2 into the atmosphere. In particular, a low-temperature operation for the membrane module is used to improve CO2/N2 selectivity. Additionally, the methodology of heat integration with the propane refrigeration system and the residual refrigeration energy from the retentate of the membrane and the top side of the CO2 liquefaction column is utilized to minimize the refrigeration energy. The genetic algorithm is incorporated to optimize equipment size and operating conditions, subject to capital and operating cost parameters. The CO2 capture cost is observed to have reduced with increasing CO2 concentration in the feed stream. Furthermore, a sensitivity analysis is conducted to examine the effect of the change in the CO2 capture cost at different CO2 capture rates with various carbon tax costs.

Immobilization of carbonic anhydrase on poly(ionic liquid) composite membranes for CO2 absorption by gas-liquid membrane contactors

In our current climate crisis, an impressive global effort is being deployed to develop and implement technologies to mitigate CO2 emissions. For instance, CO2 capture and storage/utilization (CCUS) will be fundamental during the energy transition. In the context of CCUS, the enzyme carbonic anhydrase (CA) has gained growing attention because it acts as a green catalyst in CO2 capture by absorption. A few works investigated the preparation of membranes with immobilized CA for CO2 capture by gas-liquid membrane contactors. Although these biocatalytic membranes exhibited improvements in the CO2 capture rate, limited immobilization strategies and carriers have been investigated so far. This work describes the fabrication, characterization, and testing of novel composite membranes with immobilized CA for CO2 capture. The membranes were comprised of a hydrophilic poly(ionic liquid) (PIL) top layer coated on a porous poly(vinylidene fluoride) (PVDF) support. The layer was prepared by in-situ polymerization of an ionic liquid monomer solution cast on the PVDF. CA was easily immobilized on the PIL layer by physical adsorption. The immobilized enzyme's catalytic activity was evaluated to identify the optimum formulation of the PIL layer (monomer and cross-linker concentrations) and immobilization protocol (enzyme concentration in the buffer solution and pH). Despite the immobilization protocol's simplicity, the enzyme was strongly bonded as the enzyme-loaded membranes could be reutilized 10 times while retaining above 90% of their initial activity. These membranes were further characterized by SEM, EDX, ATR-FTIR, TGA, DSC, zeta potential, and water contact angle. Moreover, the biocatalytic composite membranes were tested in a gas absorption set-up to demonstrate their applicability. They showed an increase in the overall mass transfer coefficient with respect to the pristine support by a factor of 2.5, making them interesting candidates for promoting CO2 capture.

A strategy for CO2 capture and utilization towards methanol production at industrial scale: An integrated highly efficient process based on multi-criteria assessment

CO2 capture and utilization are an effective solution to the problem of CO2 emissions, and a combination of ammonia-based CO2 capture and its use for methanol production is a highly feasible strategy. However, the uses of conventional technologies have resulted in a high demand for energy, with limited use of hydrogen. To address these problems, an innovative strategy is proposed and demonstrated in this study that enhances the conventional design, i.e., to use ammonia-based CO2 capture with double tower absorption and solvent split, along with wet hydrogen for methanol production at industrial scale. The process is further improved through a multi-criteria assessment that considered the CO2 capture rate, NH3 loss rate, CO2 conversion rate, and energy saving factors, in which the latter is based on two components, namely the reboiler duty and the condenser duty. Moreover, an exergy analysis method is used to optimize the improved process, and a highly efficient integrated process is finally established. It has been found that the use of a double-tower absorption process ensures high rates of CO2 capture and low rates of NH3 loss. Additionally, adjusting the molar ratio of H2 to CO2 leads to an impressive 8% increase in the CO2 conversion rate, reaching 25%. In terms of energy savings, the average reboiler duty was reduced from 13.39 to 11.85 MJ/kgCO2, i.e., by 11.50%; while the condenser duty was reduced by 11.36%; both contributed to the overall energy savings. In the I-ACCMP process, the total exergy loss is 437.24 kW, of which the exergy loss of the heat exchangers accounts for 16%, and the desorption tower (DES) accounts for 48%. After optimization, the exergy loss of the heat exchangers decreases from 70.02 kW to 40.45 kW, the exergy loss of the DES decreases from 209.29 kW to 180.91 kW, and the reboiler duty is reduced from 10.60 MJ/kgCO2 to 7.71 MJ/kgCO2. The total exergy loss decreases from 437.24 kW to 372.68 kW, which is a reduction by 14.8%.

Development of a multi-scale mathematical model for green hydrogen production via biogas steam reforming process

In this work, a dynamic 2D heterogeneous model for catalytic hydrogen production by biogas steam reforming process was developed, considering both the macroscale and the microscale of the system. The partial differential equations (which describe mass and energy balances) of the mathematical model, have been converted into total differential equations, by spatial discretization and implemented in Matlab/Simulink for process simulation. Based on simulation results, the profiles for mass and concentration of the reactants and products were obtained. The developed model has been validated with available literature data. For the conversion of methane, it predicted 72.43% and for the hydrogen percentage on the dry basis, it gave the value of 72.72%. In this study, a special emphasis was placed on highlighting the influence of a high content of carbon dioxide in biogas on the size of the reactor. The developed model is used to study the effects of step and ramp flow inputs disturbances for the methane conversion and hydrogen percentage on the dry basis and to observe how the reactor design parameters change when the CO2 concentration in the feed flow increases. Furthermore, the developed model for biogas reforming was integrated in a green hydrogen plant with CO2 capture feature for overall performance evaluation (e.g., energy efficiency, CO2 capture rate etc.). The decarbonized green hydrogen plant has promising performance indicators (high overall energy efficiency of 54.5% and a high CO2 capture rate 70%).

A novel contactor for reducing the cost of direct air capture of CO2

Carbon dioxide removal from air, also known as Direct Air Capture (DAC), is gaining more attention due to the importance of negative emissions and their impact on reversing climate change. However, CO2 removal cost remains a major obstacle for widespread DAC adoption. A significant portion of DAC cost is due to its CO2 adsorbent. Here, we present a novel monolithic DAC contactor backed by a validated model displaying enhanced mass transfer, markedly increasing the CO2 capture rate. The contactor employs helical channels, rather than commonplace straight channels, forming a highly convective Dean flow augmenting CO2 transport and release to/from the sorbent layer coated on the monolith channel walls. It is shown that the novel contactor can capture the same CO2 using about 35% less adsorbent when compared to straight channel contactors. Techno-economic analysis shows the new contactor can reduce the overall DAC cost by about 30%.

The prospects of flexible natural gas-fired CCGT within a green taxonomy

Despite increased commitments toward net zero, there will likely be a continued need for natural gas to provide low carbon dispatchable power and blue hydrogen to balance the increased penetration of renewables. We evaluate the CO2 emissions intensity of electricity produced by (i)natural gas-fired combined cycle gas turbine (CCGT) power plants with carbon capture and storage (CCS), and (ii) blue hydrogen CCGT plants which uses steam methane reforming with CCS to supply H2. This study aims to determine whether these assets are able to meet a possible green taxonomy emissions threshold of 100kg CO2 eq/MWh. Key considerations include methane leakage, CO2 capture rate, and the impacts of start-up and shut down cycles performed by the CCGT-CCS plant. This study suggests that, in order for natural gas to play an enduring role in the transition toward net zero, managing GHG emissions from both the upstream natural gas supply chain and the conversion facility is key.

Coupling chemical looping air separation with the Allam cycle – A thermodynamic analysis

The Allam cycle is a class of oxy-fuel combustion power cycles using supercritical CO2 (s-CO2) as the thermal fluid to achieve power generation with inherent capture of CO2. Compared to other conventional CO2 capture techniques, the Allam cycle stands out owing to its high fuel-to-electricity conversion efficiency (55–59%), the elimination of the Rankine cycle and reduced physical footprint. A key source of energy penalty of Allam cycle comes from the air separation unit (ASU), which supplies pure oxygen via an energy intensive cryogenic process. This paper presents a thermodynamic analysis of a novel supercritical CO2-based power generation scheme, in which a natural gas fuelled Allam cycle is integrated with a chemical looping air separation (CLAS) system, which supplies oxygen to the combustor. The modelling results show that the Allam-chemical looping air separation (Allam-CLAS) process can achieve 56.04% net electrical efficiency with a 100% CO2 capture rate, when a Co3O4-based oxygen carrier is used. This is 6% higher than the Allam cycle coupled to a cryogenic ASU. The exergetic efficiency of the Allam-CLAS system driven by the Co3O4-CoO redox cycle is 57.13%, also more favourable than a conventional Allam-ASU system (with reported exergetic efficiency of 53.4%). This newly proposed Allam-CLAS power cycle presents a highly efficient, and simple solution to generate zero-carbon electricity from natural gas.

Technical and life cycle performance comparison between petroleum coke chemical looping combustion and oxy-combustion combining with advanced steam cycles for power generation processes

Inferior petroleum coke is attractive to be used in power generation industry since it has the advantage of high calorific value. To address the environmental problem of petroleum coke combustion for power generation, this paper establishes a process model of petroleum coke chemical looping combustion (CLC) and compares its performance with that of a petroleum coke oxy-combustion (OCB). The results show that CO2 capture rate of the CLC and OCB both reach about 100%. Under the petroleum coke conversion rate of 70%, the net electrical efficiencies of the petroleum coke CLC and OCB are 28.61% and 24.68%. The life cycle energy consumption and GHG emission of the CLC and OCB are 12.08/12.76 GJ/MWh and 338.03/397.91 kg CO2 eq/MWh, respectively. Compared with the sub-critical steam cycle in the above base case, the net electrical efficiencies of the CLC integrated with supercritical and ultra-supercritical cycles are increased by 0.93 and 1.53 percentages points, while their life cycle energy consumption and GHG emission are decreased by 0.31/0.49 GJ/MWh and 5.85/10.34 kg CO2 eq/MWh. When the conversion rate increases from 70% to 95%, the net electrical efficiencies of the CLC process are increased to 39.71/40.97/41.84%, and their life cycle results are decreased to 9.32/9.09/8.95 GJ/MWh and 300.85/296.20/292.07 kg CO2 eq/MWh. Therefore, improving conversion rate of the CLC and its coupling with advanced steam cycles for power generation are important for clean and efficient utilization of inferior petroleum coke.

Comparative techno-economic analysis of the integration of MEA-based scrubbing and silica PEI adsorbent-based CO2 capture processes into cement plants

The objective of this work was to perform the techno-economic analysis for the integration of two post-combustion carbon capture technologies into cement plants, namely monoethanolamine (MEA) scrubbing-based and silica-alkoxylated polyethyleneimine (SPEI) adsorbent-based processes. The key performance indicators were investigated, including emission abatement, energy performance, break-even selling price, CO2 capture and avoidance cost. The technical evaluation showed that the conventional MEA and SPEI-based processes required 3.53 GJ/tonne CO2 and 2.36 GJ/tonne CO2 of regeneration energy when achieving 90% of CO2 capture rate, respectively. In addition, the specific primary energy consumption for CO2 avoided was estimated at 6.5 GJ/tonne CO2 for the MEA-based and 4.3 GJ/tonne CO2 for the SPEI-based process. The CO2 capture costs of MEA and SPEI-based processes were estimated at 61.4 and 49.8 €/tonne CO2, respectively. Meanwhile, the CO2 avoidance cost of MEA and SPEI processes were estimated at 84.7 and 62.2 €/tonne CO2 respectively. The economic evaluation indicated that the cost of clinker production was increased by 108% with the integration of the solvent-based MEA-based and 84% for the SPEI-based processes. However, in the case, the maximum heat of 53.9 MWth is recovered from the reference cement plant, the costs of CO2 capture and CO2 avoidance for both the MEA and SPEI-based processes would be reduced. The CO2 capture costs of MEA and SPEI-based processes would decrease to 48.0 and 35.6 €/tonne CO2, respectively. Additionally, the CO2 avoidance costs for the MEA and SPEI-based processes would be reduced to 57.5 and 44.5 €/tonne CO2, respectively.

Impact of high capture rates and solvent and emission management strategies on the costs of full-scale post-combustion CO2 capture plants using long-term pilot plant data

Pilot plant campaigns are critical to our understanding of the performance of solvent-based post-combustion capture processes. During the ALIGN-CCUS project, long-term pilot plant runs in the Niederaussem lignite-fired power plant were conducted, that aimed to investigate solvent degradation and emissions management and capture rates beyond 90%. Based on these pilot runs, we here investigated the cost effect of amine degradation and emissions for two solvent systems, MEA and CESAR1, as well as the effect of incorporating degradation and emission mitigation strategies and the effect of higher carbon capture rates. We found that for lignite-fired power plants, CESAR1 is not per se a cheaper solvent system than MEA when actual solvent losses (or their mitigation measures) are considered, contrary to what earlier studies have suggested. It may, therefore, be just as good a benchmark as MEA would be, as long as all degradation and emission (mitigation) costs are included in their cost estimates. Second, MEA reclaiming with ion exchange resins and CESAR1 emission mitigation measures (dry-bed and/or turbulent flue gas pre-treatment) do not increase the cost of CO2 capture or electricity. If anything, our work suggests these measures reduce costs marginally, owing to lower solvent make up, offsetting the additional capital and operational costs. Finally, the cost effect of capture rates beyond 90% proves minimal (the cost of CO2 capture and the levelized cost of electricity increase by 3% and 5%, respectively, when moving from 90% to 98% CO2 capture rate), indicating solvent-based CO2 capture may also be a useful mitigation strategy in societies transitioning towards net-zero-CO2 emissions.

Production of high-purity carbon dioxide and sodium bicarbonate by lime cellar gas cleaning and chemical recycling: Process simulation and techno-economic analysis

The cement industry is responsible for 8% of total global CO2 emissions, which mainly originate from limestone calcination and fuel combustion. In view of the application potential of using CO2 to produce chemicals, this paper developed a novel process based on the Aspen Plus process simulation for the co-production of 99.99% CO2 by means of Methyldiethanolamine (MDEA) absorption/desorption and NaHCO3 by carbonization of CO2, NH3 and Na2SO4. The effects of absorption temperature, NH3 and Na2SO4 feeding amount, crystallizer temperature and pressure on CO2 capture rate and utilization rate were explored. The results showed that the best CO2 capture rate was achieved when the cellar gas inlet temperature of the absorber tower was 37 °C; Saturated Na2SO4 solution was favorable for CO2 absorption, and the CO2 utilization rate increased with the increase of Na2SO4 dosage; NaHCO3 yield decreased with the increase of crystallizing temperature, and the best NaHCO3 yield was achieved when the crystallizer temperature was 35.5 °C; Crystallizing pressure had little impact on the reaction. Economic analysis showed that the project will start to be profitable in 6.48 years with a Net Return Rate (NRR) value of 13.51%. It indicates that the project has economic benefits and provides a new way to reduce CO2 emissions from lime cellar gas.

Enhancing the CO2 capture capacity of natural macroporous carbonized fibers by growing carbon nanotubes on their surface

In this study, a new hybrid material with superior CO2 sorption capacity was prepared by the growth of carbon nanotubes (CNT) into the macroporous structure of acid carbonized fibers (ACF). The growth of CNT was carried out by chemical vapor deposition using acetylene as a carbon source for 3.5 min at 700 °C. Selected materials were characterized by N2 physisorption, FTIR, potentiometric titrations, acid digestions, Raman spectroscopy, scanning and transmission electron microscopy. The CO2 capture was measured in static mode at pressure up to 10 atm in a sorptometer and in dynamic mode in a thermogravimetric analyzer at pressure of 1 atm. CNTs were homogeneously grown on the entire surface of ACF. The surface area of carbonized fibers increased from 2 to 452 m2/g after CNT growth and treatment at 300 °C for 1 min in air. The CO2 capture capacity of the ACF increased from 2.30 to 3.51 mmol/g at 25 °C and 10 atm after CNTs growth and air treatment (ACF3-CNT-AT1). The CO2 capture rate was also higher, from 0.023 to 0.032 mmol/g·min for ACF and ACF3-CNT-AT1 at 25 °C and 1 atm, respectively. These results were mainly attributed to the increase in basic groups and highly reactive edge sites. In addition, regeneration capacities of 99% and 95% were obtained for the first 3 sorption-desorption cycles and an apparent selectivity (QCO2/QN2) of 1.65 and 2.48 for ACF and ACF3-CNT-AT1, respectively. The rapid sorption-desorption kinetics, coupled with the high reversibility of CNT-modified ACFs, makes this hybrid material viable for use in CO2 capture systems.