Flue Gas CO2 Research Articles

Comprehensive investigation of flue gas component separation and CO2 sequestration in water-saturated porous media of subsurface formation

Flue gas poses subsurface direct storage inefficiency due to its high non-CO2 content, while surface separation, desulfurization and denitrification processes require additional equipment and financial resources. To address these challenges, flue gas subsurface component separation and CO2 sequestration within aquifer were proposed in this paper. CO2 migrates notably slower than N2, leading to the gathering of N2 at gas flooding front and the occurrence of CO2 hysteresis during flue gas filtration within the aquifer. The phenomenon, characterized by gas composition deviations from the original injection mole fractions of N2 and CO2, is referred to as the flue gas component separation. Numerical simulation results indicate that the solubility difference between N2 and CO2 is the primary force driving the separation of components, and the asynchronous filtration velocities of the gas and aqueous phases further promote the separation. Thus, simultaneous N2 separation and CO2 storage can achieve by the optimized gas-water alternate injection, and the efficiencies of N2 separation and CO2 storage are inversely correlated. Increasing N2 mole fraction within the injected flue gas enhances the efficiency of N2 separation, while having a slight effect on CO2 storage. Water vapor in flue gas condenses and integrates into the liquid phase, while O₂ component is produced slightly later than N₂, leading to a marginal reduction in N₂ separation efficiency. The synergistic influences of aquifer temperature and pressure exhibit bidirectionality, stemming from the shift between the dominant factors between CO2 dissolution and gas sweep efficiency. Conditions of relatively lower aquifer temperatures and moderate pressures, particularly in medium permeability aquifers, are more favorable for enhancing N₂ separation and CO₂ storage. This proposal method holds the potential for efficient subsurface separation of flue gas components and concurrent underground storage of CO2, thereby contributing to the reduction of greenhouse gas emissions and mitigation of climate change.

The effects of different functional groups in Ni3-cluster MOFs on the efficient capture and transformation for flue gas CO2

As the greenhouse effect continuous increasing, the efficient CO2 capture and conversion into high-value fine chemicals have been necessary and meaningful. However, the CO2 coupling reaction always requires harsh catalytic reaction conditions and focuses on pure CO2 gas. Herein, three nickel-cluster metal-organic frameworks (MOFs) with different functional groups on the bridging-ligands have been synthesized and characterized structurally, presenting unique cages and channels architectural features. Catalytic investigations demonstrated that the amino-functionalized MOFs as a catalyst {[H2N(CH3)2]2[Ni3(µ3-O)(XN)(BDC-NH2)3∙7DMF}n (Ni3-NH2, XN = 6′′-(pyridin4-yl)-4,2′′:4′′,4′′′-terpyridine, H2BDC-NH2 = 2-aminoterephthalic acid) owns higher catalytic activity (96 %) than the other two in the CO2 transformation reaction with aziridine into oxazolidinones under 0.5 MPa within 4 h. Moreover, Ni3-NH2 can be reused at least ten times without significant catalytic activity loss under mild condition. Importantly, Ni3-NH2 catalyst still can be applicable to the simulating flue gas with 15 % CO2 as carbon source. The mechanism has been further revealed by NMR, FT-IR and DFT calculations, in which the Ni-site and the amino group can synergistically activate the substrate and CO2 molecule. This work has enriched the species of cluster-based MOFs and investigated the influence of characteristic functional groups on the catalytic activity deeply.

Design of retrofit flue gas (CO2) scrubber for dependable clean energy at the Duvha Coal Power Plant

The coal-fired power sector is facing unprecedented pressure due to the shift to low-carbon energy sources and the need to prevent climate change. It is imperative to incorporate advanced technologies into conventional coal-fired power plants to enhance their efficiency, flexibility, and environmental sustainability. One advantage of post-combustion CCS methods is that they may be retrofitted into power plants that are already in place. The goal of this work is to design a CO2 flue gas cleaning retrofit system that will meet the most stringent air quality regulations in an operational coal power station in Southern Africa. It will operate and expedite the removal of undesired gas (CO2) in order to attain ideal requirements for air quality in one of Southern Africa's current coal-fired power plants, the Duvha Coal Power Plant. This study is based on chemical absorption, and explores the mechanistic design of the scrubber, which was accomplished through simple computations and Ansys simulations. The approach for developing a wet CO2 scrubber and LSTG system is based on chemical absorption and is integrated with a pilot plant. The results of the parametric study provide a foundation for a comprehensive industrial system design for South Africa's coal-powered industry. The results show that the scrubber's cylinder height and diameter can be used for an LSTG system and are appropriate for CO2 gas flow and capture. The application of the suggested scrubber design and the LTSG's contributions will allow the coal power station to operate with minimal GHG emissions released into the atmosphere. Instead of shutting down coal power facilities, this cleaning system that completely absorbs CO2 emissions can be used to maintain a robust power infrastructure, rather than being phased out. This will boost the power plant's efficiency over its initial operating efficiency and benefit the nation's economy and the power industry.

Dual Metallosalen-based Covalent Organic Frameworks for Artificial Photosynthetic Diluted CO2 Reduction.

Directly converting CO2 in flue gas using artificial photosynthetic technology represents a promising green approach for CO2 resource utilization. However, it remains a great challenge to achieve efficient reduction of CO2 from flue gas due to the decreased activity of photocatalysts in diluted CO2 atmosphere. Herein, we designed and synthesized a series of dual metallosalen-based covalent organic frameworks (MM-Salen-COFs, M: Zn, Ni, Cu) for artificial photosynthetic diluted CO2 reduction and confirmed their advantage in comparison to that of single metal M-Salen-COFs. As a results, the ZnZn-Salen-COF with dual Zn sites exhibits a prominent visible-light-driven CO2-to-CO conversion rate of 150.9 μmol g-1 h-1 under pure CO2 atmosphere, which is ~6 times higher than that of single metal Zn-Salen-COF. Notably, the dual metal ZnZn-Salen-COF still displays efficient CO2 conversion activity of 102.1 μmol g-1 h-1 under diluted CO2 atmosphere from simulated flue gas conditions (15% CO2), which is a record high activity among COFs- and MOFs-based photocatalysts under the same reaction conditions. Further investigations and theoretical calculations suggest that the synergistic effect between the neighboring dual metal sites in the ZnZn-Salen-COF facilitates low concentration CO2 adsorption and activation, thereby lowering the energy barrier of the rate-determining step.

Dual Metallosalen‐based Covalent Organic Frameworks for Artificial Photosynthetic Diluted CO2 Reduction

Directly converting CO2 in flue gas using artificial photosynthetic technology represents a promising green approach for CO2 resource utilization. However, it remains a great challenge to achieve efficient reduction of CO2 from flue gas due to the decreased activity of photocatalysts in diluted CO2 atmosphere. Herein, we designed and synthesized a series of dual metallosalen‐based covalent organic frameworks (MM‐Salen‐COFs, M: Zn, Ni, Cu) for artificial photosynthetic diluted CO2 reduction and confirmed their advantage in comparison to that of single metal M‐Salen‐COFs. As a results, the ZnZn‐Salen‐COF with dual Zn sites exhibits a prominent visible‐light‐driven CO2‐to‐CO conversion rate of 150.9 μmol g−1 h−1 under pure CO2 atmosphere, which is ~6 times higher than that of single metal Zn‐Salen‐COF. Notably, the dual metal ZnZn‐Salen‐COF still displays efficient CO2 conversion activity of 102.1 μmol g−1 h−1 under diluted CO2 atmosphere from simulated flue gas conditions (15% CO2), which is a record high activity among COFs‐ and MOFs‐based photocatalysts under the same reaction conditions. Further investigations and theoretical calculations suggest that the synergistic effect between the neighboring dual metal sites in the ZnZn‐Salen‐COF facilitates low concentration CO2 adsorption and activation, thereby lowering the energy barrier of the rate‐determining step.

Closed-Loop and Precipitation-Free CO2 Capture Process Enabled by Electrochemical pH Gradient.

Carbon dioxide (CO2) capture is a crucial negative-emission technology for the mitigation of climate change and global warming. The urgent need of combating climate change motivates the research and development of economical, effective and environmentally benign processes for CO2 capture. Herein, we design and report a flow cell for the CO2 capture from air or flue gas in a precipitate-free and closed-loop manner. No ion-exchange membrane is used in the electrolyser. The water electrolysis produces acidic solution near the anode and alkaline solution near the cathode, while generating valuable hydrogen and oxygen byproducts. The dilute CO2 in air or flue gas is captured by the alkaline solution, which is then mixed with the acidic solution to release the concentrated CO2. The process operates in a cyclic manner as driven by the water electrolysis and the mechanical pumping. No precipitation of calcium carbonate is involved for fixing CO2, which may simplify the separation process and minimizing the materials loss. The simple process enabled by electrochemical pH gradient shows promise for efficient CO2 capture on both small and large scales.

Simulation and optimization for flue gas CO2 capture by energy efficient water-lean ionic liquid solvent

Ionic liquids (IL) are treated as advanced materials for energy-saving carbon dioxide (CO2) capture from flue gas but suffer from serious challenges in energy and mass management. Herein, a water-lean IL-based deep eutectic solvent with 1,8-diazabicyclo [5.4.0] undec-7-ene imidazole ([DBU] [IM]) and ethylene glycol (EG) blends was prepared with a screened proportion of IL:EG=7:3. The CO2 loading and saturated solvent viscosity were 1.89 mol/L and 95 mPa·s, respectively. The foundational properties of the IL-EG solvent were determined by experimental measurements and thermodynamic modeling. The vacuum flashing desorption technology was innovatively adopted for energy-saving solvent regeneration. Industrial-scale process simulation of multistage flashing was used to explore the energy consumption during solvent regeneration. Meanwhile, the segmented cooling paved a route for water separation from water-lean solvent. A comprehensive analysis was performed out to optimize the operating parameters for CO2 absorption and desorption. For the recommended 3-stage flashing configuration, the specific process regeneration energy consumption amounted to only 1.54 GJ/tCO2. Consequently, the total capture cost reduced to 48.1 $/tCO2, marking a decrease of 31.28 %, 16.55 % and 10.25 %, compared with MEA solvent, water-lean solvent and biphasic solvent, respectively. This work offered insights for future endeavors in the development of IL-based CO2 capture process from industrial flue gas.

A Perspective on Electrochemical Point Source Utilization of CO2 and Other Flue Gas Components to Value Added Chemicals.

Electrochemical CO2 reduction reaction (eCO2RR) has been explored extensively for mitigation of noxious CO2 gas generating C1 and C2+ hydrocarbons and oxygenates as value-added fuels and chemicals with remarkable selectivity. The source of CO2 being a pure CO2 feed, it does not fully satisfy the real-time digestion of industrial exhausts. Besides the detrimental effect of noxious gas mixture leading to global warming, there is a huge capital investment in purifying the flue gas mixtures from industries. The presence of other impurity gases affects the eCO2RR mechanism and its activity and selectivity toward C2+ products dwindle drastically. Impurities like NOx, SOx, O2, N2, and halide ions present in flue gas mixture reduce the conversion and selectivity of eCO2RR significantly. Instead of wiping out these impurities via separation processes, new strategies from material chemistry and electrochemistry can open new avenues for turning foes to friends! In this perspective, the co-electroreduction will vividly discussed and supporting role of different heteroatom-containing impurity gases with CO2, generating highly stable C─N, C─S, C─X bonds, and highlight the existing limitations and providing probable solutions for attaining further success in this field and translating this to industrial exhaust streams.

Development of membrane bioreactor for conversion of flue Gas-CO2 to C1 and C2 biomolecules

The capture and utilization of CO2 (CCU) from flue gases constitute a novel carbon feedstock for producing renewable chemicals and fuels. To lower the energy demand of CCU, Bio-Integrated Carbon Capture and Utilization (BICCU) was recently presented, where CO2-consuming microorganisms simultaneously desorb and convert CO2 captured from flue gas by methyl diethanolamine (MDEA) with H2 from water-electrolysis as the electron donor. The limiting factor is the microbial toxicity of MDEA, which restricts the capacity of the process. Furthermore, producing soluble molecules like the C2 platform molecule acetate is not possible without contaminating the product with capture agent. To resolve both challenges, we here propose a three-phase membrane system, where the MDEA and microorganisms are separated by a CO2-permeable membrane. Biological batch experiments with a mixed mesophilic culture confirmed the increased capacity of the BICCU-process for producing both methane and acetate when introducing a CO2-permeable membrane to the system to alleviate microbial inhibition by the capture agent and avoid contamination of soluble bioproducts. When using O2-rich flue gas from a biogas combustion engine, the CO2 conversion rate decreased by 18.0 % compared to a clean 20:80 CO2:N2 gas mixture, yet anaerobic metabolisms were still active in the mixed inoculum. Abiotic experiments furthermore showed that the microbial CO2 consumption maintained the gradient across the membrane and enhanced the CO2-flux by a factor of 3.1 ± 0.3. The membrane-based BICCU concept is expected to hold great promise particularly for producing acetate from flue gas-CO2, as the in situ separation eliminates the need for costly downstream separation.

Multicomponent adsorption mechanism of CO2, SO2, NO, and C7H8 from flue gases on nitrogen-doped biochar: Experimental and computational insights

The comprehensive control of CO2 and gaseous pollutants in coal-fired flue gas is urgent and difficult. As a green low-cost adsorbent, nitrogen-doped biochar has potential application in the control technology of flue gas pollutants. Still, its multi-component adsorption characteristics for flue gas are unclear. In this study, the multi-component adsorption characteristics of CO2, SO2, NO, and C7H8 on nitrogen-doped biochar were explored at different temperatures (25–120 °C), and the competitive mechanism of multi-component adsorption was revealed through continuous adsorption experiments and numerical calculation. The adsorption capacities of CO2, SO2, NO, and C7H8 by nitrogen-doped biochar can reach 38.1, 78.9, 3.1, and 245.2 mg/g, among which CO2, SO2, and C7H8 show strong competitive effects. Their adsorption capacities are decreased by 42 % (CO2), 28 % (SO2), and 27 % (C7H8) respectively compared with the single-component adsorption. This is because there are not only more C7H8 adsorption sites on nitrogen-doped carbon, but also C7H8 can partially occupy the adsorption sites of SO2 and CO2 during multi-component adsorption. Combined with the calculation results of density functional theory, the competitive ability of the three gases can be ranked as follows: C7H8 > SO2 > CO2.

High stability and strong hydrophobic hindrance effect of core–shell NaX/polyacrylate composite for CO2 capture

It is well known that zeolite NaX excels at capturing CO2 in dry flue gas, but maintaining its excellent CO2 adsorption capacity in the presence of water remains a huge challenge. In order to significantly reduce the water adsorption of NaX while ensuring its high CO2 adsorption performance, a millimeter-sized spherical NaX/polyacrylate composite with a core–shell structure has been successfully developed through the structural modulation strategy. Here, NaX was uniformly crystallized inside the hydrophobic polyacrylate, and the crystal structure was in situ modulated using functionalized tetraethylenepentamine, so that the unique coupling of the two structures and functions achieves strong hydrophobic hindering performance. Compared with the pristine NaX, NaX/polyacrylate shows a 64.77 % reduction in water adsorption (25 °C, 11 % RH) of 5.20 mmol·g−1. The modulated nanocrystals expose more accessible adsorption active sites, so that the CO2 working capacity of the composite increases to 1.3 times that of NaX. To the best of our knowledge, this is the best case of a material that can retain excellent adsorption performance even after hydrophobic modification. More importantly, the CO2 capacity hardly declined in 100 adsorption–desorption cycles. This work provides a generalized solution to enhance the surface hydrophobicity of zeolite-like materials while maintaining their high CO2 adsorption capacity in practical applications.

Efficient multi-objective optimization and operational analysis of amine scrubbing CO2 capture process with artificial neural network

Amine scrubbing processes for post-combustion CO2 capture have been extensively studied and significantly improved via various novel designs. However, the amine scrubbers implemented nowadays were usually not optimized according to a number of different evaluation criteria. This is often due to the fact that, for high dimensional design spaces, the rigorous simulation runs needed to facilitate process optimization always calls for huge numbers of simulation software accesses and overwhelming iterative calculations. Therefore, in this study, the well-trained surrogate model was adopted to replace its rigorous counterpart for the purpose of ensuring efficient optimization runs in practical applications. In current study, two objectives, i.e., the specific equivalent work and the CO2 capture level, were both rapidly and effectively optimized in various practical scenarios with different flue gas CO2 concentrations. The corresponding operational parameters and utility consumptions were also easily obtained without additional effort. The computation results obtained so far showed that the proposed surrogate-assisted approach can be utilized to significantly reduce the computational load in practice.

Unveiling the promoting mechanism of Mo on the performance of CuCeOx catalyst for simultaneously NH3-SCR denitration and CO oxidation under oxygen-rich conditions

NOx and CO coexisted in numerous actual industrial flue gases. The simultaneous removal of NOx and CO had great potential for application but remained still a challenge. Herein, a series of Mo-modified CuCeOx catalyst was developed to simultaneously achieve NH3-SCR denitration and CO oxidation. The results indicated that the CCM3 catalyst displayed the optimal performance with 91.2 % NOx conversion and 100 % CO conversion as well as excellent long-time stability and SO2 or/and H2O tolerance at 225 ℃. It was found that the strong interaction between Cu, Ce and Mo oxides resulted in the particles highly dispersed with smaller size on catalyst surface, which could provide abundant active sites to decreasing the competitive adsorption among reactive gases. Furthermore, the Mo modification promoted the production of more oxygen vacancies, Ce3+ and Oα species, which facilitated the redox recycle and the generation of intermediates. Moreover, the H2-TPR and NH3/CO/O2-TPD analysis illustrated that the reducibility and the capacity for reaction gas adsorption and activation were enhanced, which improved low-temperature activity. The in situ DRIFTS experiment revealed that the E-R and L-H mechanism were existed in NH3-SCR process on CC and CCM3 catalysts. What’s more, the stronger acidity and strengthened E-R mechanism on CCM3 catalyst hindered the adsorption of SO2 and weakened the inhibition effect of competitive adsorption among SO2 and NO. Additionally, both surface lattice oxygen and chemisorbed oxygen could react with Cu+–CO species to produce CO2, the pathway obeyed L-H and MvK mechanism. This work may provide a novel strategy for the treatment of CO and NOx pollutants in industrial flue gas.

Combustion characteristics on ammonia injection velocity and positions for ammonia co-firing with coal in a pilot-scale circulating fluidized bed combustor

Ammonia (NH3) co-firing with coal in thermal power plant offers a viable solution for reducing CO2 emissions. Optimizing the NH3 injection method is crucial to achieving comparable performance and pollutant emissions in NH3–coal co-firing compared to coal only combustion in a circulating fluidized bed combustion system. The impact of NH3 co-firing with coal on the injection velocity and location in related to the NH3 supply method was evaluated. Injection velocity was controlled by varying the number of ammonia supply ports and their heights (0.2 m and 1.8 m from the distributor). Injecting NH3 through one port at a high velocity of 2.4 m/s increases CO emissions while decreasing NO emissions due to the formation of a reducing environment. Conversely, utilizing two ports with low NH3 injection velocity of 1.2 m/s exhibited the opposite trend in CO and NO emissions, achieving the highest combustion efficiency without the formation of N-containing components. This injection velocity promotes better mixing of gases (air and NH3) and solids (bed materials and coal) without hindering coal combustion. Regarding greenhouse gases emissions, the part of CO2 emissions decreased by considering CO2 concentration and flue gas flow rate, while the part of N2O emissions significantly increased due to N-chemistry by > 5 times.

A new denitrification strategy based on high-temperature catalytic coatings Y2O3-BaO-ZrO2 without using ammonia in a lab-scale natural gas combustion furnace

Catalytic decomposition of NO at high temperatures without the use of ammonia, offers an eco-friendly and sustainable solution for denitrification in industrial combustion or heating processes. To simulate a complex combustion flue gas, we designed a lab-scale natural gas industrial combustion furnace specifically for assessing the impacts of Y2O3-BaO-ZrO2 catalyst coated on SiC plates on NO emissions. Various factors including the plate number, excess air ratio, combustion power, and coating position were considered. Results demonstrated that arranging the Y2O3-BaO-ZrO2 coated plates shifted the high-temperature zone of the furnace downstream. When the excess air ratio was below 1.05, the catalytic coating significantly reduced NO emission concentration at the furnace outlet by over 40 %. However, this reduction coincided with a substantial presence of unburned CO in flue gases. Placing the coated SiC plates in the constant temperature zone of 1100–1200 °C within the middle of furnace offered significant advantages in NO removal, particularly as the combustion power increased. Based on a 60-h durability evaluation of Y2O3-BaO-ZrO2 coating, the observed good high-temperature thermal and chemical stabilities further enhanced the coating’s potential for industrial application. The possible mechanism of the reduction NO by CO over coating surfaces were analyzed by in situ optical measurements. After calculation, using 12 kg Y2O3-BaO-ZrO2 catalysts might decrease at least 642 kg of ammonia consumption under ideal conditions, and significantly reduce the investment cost on existing flue gas denitrification equipment. Therefore, the investigated technology is a green and sustainable denitrification strategy, which would potentially provide a novel approach towards attaining ultra-low NO emissions.

Evaluation of Na2CO3-doped MCM-48-Li4SiO4 adsorbent for CO2 capture: Performance and DFT mechanism

Efficient CO2 adsorbents are crucial for addressing the global climate crisis. In this study the novel adsorbents were synthesized using an impregnation precipitation method with MCM-48 as the silica source and Li2CO3 as the lithium source. By doping alkali metal carbonate (Na2CO3), the ML-Na2CO3 adsorbent was created for high-temperature CO2 capture. The results showed that the maximum adsorption capacity of 35.63 wt% was achieved at 600℃ in the mixture (15 vol% CO2, the balance being N2)when the adsorbent contained 15 wt% Na2CO3, representing a 4.49 wt% increase compared to the undoped ML adsorbent. The adsorption kinetics analysis confirmed a good fit with the biexponential model. Density Functional Theory (DFT) simulations revealed that the adsorption energy increased by an average of 0.1035 eV and Oslab exhibited high activity in chemisorbing CO2, forming CO32−. Na2CO3 doping modified the electronic structure of Oslab and Lislab, resulting in increased high-energy electrons, reflective activity, and improved CO2 adsorption energy. Overall, incorporating Na2CO3 enhanced carbon dioxide adsorption performance by 114.42 %, indicating a promising potential for real flue gas CO2 adsorption applications.

Carbon-based materials for low concentration CO2 capture and electrocatalytic reduction

The gradual increase in carbon dioxide (CO2) concentration in the atmosphere has been recognized as a significant problem for humankind. CO2 flue gas is one of the most apparent contributing sources of emissions. CO2 capture and conversion are environmental-friendly and efficient ways to reduce atmospheric carbon dioxide emissions from flue gases. Considering the traditional expensive gas purification process of low-concentration CO2, the low-cost capturing and electrocatalytic CO2 reduction (ECR) at low concentration by newly-developed carbon-based materials provide an attractive approach to convert low-concentration CO2 in flue gas into high-value fuels and chemicals. Developing and integrating carbon-based capturing and catalytic materials with an understanding of the mechanism has a promising future and will promote this technology toward practical application. This review describes recent progress in the design, preparation, and structural characterization of existing carbon-based materials for the capture and catalysis of low-concentration CO2. The crucial factors of capturing and catalysis performance of all the carbon-based materials are also summarized. Furthermore, the review identifies existing research problems and challenges, and outlines future research directions. We also discuss the prospects for the industrialization of low-concentration CO2 capture and ECR. The remaining technological challenges and future directions for enhancing and applying of carbon-based materials for CO2 capture and electrocatalytic reduction are highlighted.

Production of eicosapentaenoic acid by Vacuoliviride crystalliferum under 20% CO2 conditions

Utilizing flue gas CO2 to co-produce eicosapentaenoic acid (EPA) with microalgae is considered an ideal approach for combating climate change and reducing cultivation costs. However, microalgal species that can efficiently produce EPA under high-CO2 conditions are scarce. This study identified that the eustigmatophycean strain Vacuoliviride crystalliferum demonstrates rapid growth under 20 % CO2 conditions (0.22 vvm), achieving a biomass concentration and productivity of 3.90 g/L and 229.26 mg/L/d, respectively. The EPA content and EPA productivity were found to be 4.28 % (w/w) and 9.80 mg/L/d, respectively. Additionally, an improved biomass concentration of 3.39 g/L and EPA content and productivity of 4.32 % (w/w) and 11.28 mg/L/d were obtained in a 30 L up-scaled cultivation system. Taken together, these findings suggest that V. crystalliferum is a promising candidate for integrating flue gas sequestration with EPA production.

Supersonic separation benefiting the decarbonization of natural gas and flue gas

Supersonic separation utilizes the cryogenics created by gas expansion to purify the mixture. This method is a novel carbon capture scheme. In this work, the models of N2-CO2 (flue gas) and CH4-CO2 (natural gas) are established to calculate the condensation flow. The condensation behavior of CO2 in natural gas and flue gas is clarified respectively, and the difference between the two is compared for the first time. Under the same conditions, CO2 in flue gas reaches the limit non-equilibrium state first, forming non-equilibrium condensation with limit nucleation rate of 7.78 × 1020 m−3s−1 and maximum droplet growth rate of 8.19 × 10−3 m s−1. However, the maximum droplet growth rate in natural gas is only 2.22 × 10−3 m s−1, which implies that the interphase mass transfer rate in flue gas is larger during the CO2 condensation. In addition, the condensation behavior of CO2 in natural gas is more sensitive to the changes of inlet parameters. This work provides an invaluable contribution to the development of supersonic carbon capture.

Integrating direct air capture with algal biofuel production to reduce cost, energy, and GHG emissions

We investigate the potential to reduce costs and greenhouse gas emissions of the utilization of direct air capture of CO2 (DAC) for the production of algal biofuel. We examine four integrated designs for a DAC system comprised of solid amine monolith adsorbents delivering CO2 at the required level for algae cultivation with a photobioreactor (PBR)-based fuel production facility. We show that the integration of DAC with this biofuel production facility provides cost and greenhouse gas emissions benefits. Heat integration decreases operating expenses by reducing energy demand for heating requirements. Mass integration, utilizing flue gas CO2 as a carbon source for the PBRs, decreases the DAC system scale, resulting in both capital and operating cost savings. The most advantageous option depends on the interplay of heat and mass integration while matching the diurnal rhythm of algal growth with the inherently steady pace and energy requirements of the DAC system and fuel production. For these technologies, the DAC-PBR mass and energy integration provides an 18 % cost reduction and a 50 % reduction in greenhouse gas emissions for the current state of the technology.