Sorption direct air capture with CO2 utilization

Direct air capture (DAC) is gathering momentum since it has vast potential and high flexibility to collect CO2 from discrete sources as “synthetic tree” when compared with current CO2 capture technologies, e.g., amine based post-combustion capture. It is considered as one of the emerging carbon capture technologies in recent decades and remains in a prototype investigation stage with many technical challenges to be overcome. The objective of this paper is to comprehensively discuss the state-of-the-art of DAC and CO2 utilization, note unresolved technology bottlenecks, and give investigation perspectives for commercial large-scale applications. Firstly, characteristics of physical and chemical sorbents are evaluated. Then, the representative capture processes, e.g., pressure swing adsorption, temperature swing adsorption and other ongoing absorption chemical loops, are described and compared. Methods of CO2 conversion including synthesis of fuels and chemicals as well as biological utilization are reviewed. Finally, techno-economic analysis and life cycle assessment for DAC application are summarized. Based on research achievements, future challenges of DAC and CO2 conversion are presented, which include providing synthesis guidelines for obtaining sorbents with the desired characteristics, uncovering the mechanisms for different working processes and establishing evaluation criteria in terms of technical and economic aspects

A study of catalytic metals and alkaline metal oxides leading to the development of a stable Ru-doped Ni Dual Function Material for CO2 capture from flue gas and in-situ catalytic conversion to methane

Atmospheric CO2 concentrations are at their highest level on record. Scientific evidence has demonstrated a direct correlation between the rise of CO2 levels and an increase of the global median temperature (~1°C higher than compared to the pre-industrial revolution times) due to the greenhouse gas effect. The change in climate due to this rapid increase of CO2 levels is already negatively affecting our ecosystem and lives, with unpredictable consequences in the future. The main source of anthropogenic CO2 emissions is attributed to the combustion of fossil fuels for energy production and transportation. Global indicators signal that carbon-intensive fuels will continue to be utilized as a main energy source despite the rising implementation of renewable energy sources. In order to curb CO2 emissions, several carbon dioxide capture, utilization and sequestration (CCUS) technologies have been suggested. The current state-of-the-art CO2 capture technology utilizes toxic and corrosive aqueous amine solutions that capture CO2 at room temperature but require heating above the water boiling point temperatures to separate CO2 from the amine solution; the latter of which is to be recycled. Once the CO2 is purified, it is necessary to transport it to its sequestration site or an upgrading processing plant. These are complicated schemes that involve many energy-intensive and costly processes. To address the shortcomings of these technologies, we propose a Dual Function Material (DFM) that both captures CO2 and catalytically converts it to methane in-situ. The DFM consists of a catalytic metal intimately in contact with an alkaline metal oxide supported on a high surface area carrier. The process operates within the flue gas at 320°C for both CO2 capture and methane generation upon the addition of renewable H2. The catalyst is required to methanate the adsorbed CO2 after the capture step is carried out in an O2 and steam-containing flue gas. Ruthenium, rhodium, and nickel are known CO2 methanation catalysts, provided they are in the reduced state. All three were compared for performance under DFM flue gas conditions. Ni is a preferred methanation catalyst based on price and activity; however, its inability to be reduced to its active state after experiencing O2-containing flue gas during the capture step was an outcome determined in this thesis. The performance of a variety of alkaline adsorbents (“Na2O”, CaO, “K2O” and MgO) and carriers (Al2O3, CeO2, CeO2/ZrO2 (CZO), Na-Zeolite-X (Na-X-Z), H-Mordenite Zeolite (H-M-Z), SiC, SiO2 and ZrO2-Y) were also studied. Selection of the best materials was based on CO2 capture capacity, net methane production and hydrogenation rates that were evaluated with thermogravimetric analysis and in fixed bed reactor tests. Rh and Ru DFMs were effective methanation catalysts with Ru being superior based on capture capacity, hydrogenation rate and price. Ru remained active towards methanation even after exposure to O2 and steam-containing simulated flue gas. Alkaline adsorbents, in combination with reduced Ru, were tested for adsorption and methanation. Ru – “Na2O”/Al2O3 DFMs showed the highest rates for methanation although CaO is also a reasonable candidate with slightly lower methanation kinetics. To date, we have demonstrated that -Al2O3 is the most suitable carrier for DFM application relative to other materials studied. The Ni-containing DFM, pre-reduced at 650°C, was highly active for CO2 methanation. However, the hydrogenation with 15% H2/N2 is completely inactive after exposure to O2 and steam, in a flue gas simulation, during the CO2 capture step at 320oC. This thesis reports that small amounts of precious metal (≤ 1% Pt, Pd or Ru) enhance the reduction (at 320°C) and activation of Ni-containing DFM towards methanation even after O2 exposure in a flue gas. While ruthenium is most effective, Pt and Pd all enhance reduction of oxidized Ni. Another objective of this thesis was to investigate whether a portion of the Ru, at its current loading of 5%, could be replaced with less expensive Ni while maintaining its performance. The findings show that the main advantage of the presence of Ni is a small increase in CO2 adsorption and increase in methane produced, at the expense of a lower methanation rate. Extended cyclic aging studies corroborate the stable performance of 1% Ru, 10% Ni, 6.1% “Na2O”/Al2O3. Characterization methods were used to monitor physical and chemical changes that may have occurred during aging studies. Measurements of the BET surface area, H2 chemisorption, XRD pattern, TEM images and STEM-EDS mapping were utilized to study and compare the structural and chemical changes between fresh and aged Ru doped Ni DFM samples. While similar BET surface areas were observed for the fresh and aged samples, some redispersion of the Ru and Ni sites was confirmed via H2 uptake and the observed decreases in Ru and Ni cluster size in the aged sample in comparison to the fresh. XRD patterns confirm an almost complete disappearance of the NiOx and RuOx species and the appearance of catalytically active Ru0 and Ni0 peaks on the aged sample compared to the fresh one. Further details of these methods, findings and conclusions are described in this thesis

Technical analysis of CO2 capture pathways and technologies

The reduction of CO2 emissions to minimize the impact of the climate change has become a global priority. The continuous implementation of renewable energy sources increases energy efficiency, while the reduction of CO2 emissions opens new options for carbon capture technologies to reduce greenhouse gases emissions. The combination of carbon capture with renewable energy balancing production offers excellent potential for fuels and chemical products and can play an essential role in the future energy system. This paper includes a critical review of the state of the art of different CO2 capture engineering pathways and technologies including a techno-economics analysis and focusing on comparing these technologies depending on the final CO2 application. The current cost for CO2 capture is in the range of 60–110 USD/t, likely to halve by 2030. This review offers technical information to select the most appropriate technology to be used in specific processes and for the different carbon capture pathways, i.e., Pre-combustion, Post-Combustion and Direct Air Capture. This comparison includes the CO2 capture approach for biomethane production by biogas upgrading to substitute fossil natural gas and other alternatives fuels production routes which will be introduces in future works performed by this review authors.Funding for open access charge: Universidad de Málaga / CBUA

Sorption enhanced catalytic reforming of methane for pure hydrogen production : experimental and modeling

H2 is well perceived as a pollution-free energy carrier for future transportation as well as electricity generation. This thesis presents an experimental and modeling study for an improved process of sorption enhanced catalytic reforming of methane using novel catalyst/sorbent materials for low temperature high purity H2 with in situ CO2 capture. A highly active Rh/CeaZr1-aO2 catalyst and K2CO3–promoted hydrotalcite and lithium zirconate are utilized as newly developed catalyst/sorbent materials for an efficient H2 production at low temperature (400–500oC) and pressure (1.5–4.5 bar) in a fixed bed reactor. Experimental results showed that direct production of high H2 purity and fuel conversion (>99%) is achieved with low level of carbon oxides impurities

CO2 capture through sorption onto activated carbons derived from biomass

In this study, activated carbons (ACs) were synthesized and tested as CO2 sorbents. In-house ACs were prepared starting both from a traditional biomass (i.e. oak wood) and from an unconventional macroalgal seaweed (i.e. Laminaria hyperborea). In addition to this, a biomass-derived commercial AC was studied as a sorbent on which polyethylenimine (PEI) was impregnated. Biochars were produced both by pyrolysis at 800 °C and by hydrothermal carbonization (HTC) at 250 °C. Pyrolysis chars generally had higher fixed carbon and lower volatile content compared to hydrochars. Moreover, seaweed-derived chars exhibited significantly larger ash content than that measured for oak wood-based chars. Pyrolyzed and HTC-treated biomass were then activated either by physical (CO2) or chemical (KOH) treatment. Limited texture development of the biochars was observed after CO2 activation, yet this treatment proved to be more suitable for the creation of narrower micropores. By contrast, KOH activation, followed by HCl washing, led to a more dramatic texture enhancement (but to lower narrow micropore volumes) and higher purity of the ACs due to a significant demineralization of the chars. The morphology of all materials was examined by Scanning Electron Microscopy (SEM) which revealed the creation of larger pores after KOH activation, whereas chars and CO2-ACs generally showed an undeveloped porous matrix along with particles anchored onto the carbon structure. Furthermore, Energy-Dispersive X-ray spectroscopy (EDX) analyses corresponding to the SEM micrographs proved that these particles were inorganic. In particular, Ca compounds predominated in oak wood-based samples. For macroalgae-derived materials, a significant proportion of alkali (i.e. Na, K), alkaline-earth (i.e. Ca, Mg) metal ions and Cl was detected, along with high levels of Cl. Conversely, reduced or negligible levels of inorganic fractions were detected for all KOH-ACs, which confirmed that demineralization occurred upon HCl washing. The identity of inorganic species was revealed by X-Ray Diffraction (XRD) patterns. In particular, calcium oxalate and Ca(OH)2 were identified in oak wood chars, whereas CO2-activated derivatives had CaCO3 as their main crystalline phase. For macroalgae-based materials, KCl and NaCl were found to be the dominant crystalline phases. In addition, MgO was also identified in pyrolyzed seaweed and in its CO2-activated counterpart. By contrast, a partial or total lack of crystalline phases was found for all KOH-ACs, thus offering further evidence of the loss of inorganic species after HCl rinsing. The intrinsic alkalinity of biomass-derived chars and CO2-ACs was corroborated by the great amount of basic surface groups, whose number was lower for KOH-ACs. CO2 sorptions by chars and ACs were initially measured at T=35 °C, PCO2=1 bar, and Ptot=1 bar by using Thermogravimetric Analysis (TGA). Sorbents showing promising behaviour were then tested for capture of CO2 under simulated post-combustion conditions (T=53 °C, PCO2=0.15 bar, and Ptot=1 bar). Unmodified ACs showed relatively high sorption capacity (up to 70mg CO2∙g-1) at higher partial pressure and lower temperature. Nonetheless, the ACs’ sorption capability dramatically decreased at lower partial pressure and higher temperature. However, the biomass feedstocks included in this work proved to be advantageous precursors for sustainable synthesis of CO2-selective sorbents under post-combustion conditions. In particular, Ca(OH)2 and MgO intrinsically incorporated within the raw materials enabled production of highly basic “CO2-philic” sorbents without applying any chemical modifications. The best virgin ACs also exhibited fast adsorption kinetics, excellent regeneration capacity and good durability over ten Rapid Temperature Swing Adsorption (RTSA) cycles. On the other hand, the CO2 uptake of optimally-PEI modified commercial AC was up to 4 times higher than that achieved by the best performing unmodified AC. PEI impregnation was optimized to maximize post-combustion uptakes. In particular, the influence of various parameters (i.e. PEI loading, stirring time of the PEI/solvent/AC mixture, solvent type and sorption temperature) on the post-combustion capture capacity of the PEI-modified ACs was assessed. Interestingly, longer agitation engendered efficient dispersion of the polymer through the porous network. Additionally, a more environmentally friendly (i.e. aqueous) impregnation enabled uptakes nearly as large as those attained when the impregnation solvent was methanol, despite using lower amounts of polymer and shorter impregnation runs. In addition, when measuring uptakes under simulated post-combustion conditions but at 77 °C, optimization of aqueous PEI impregnation led to a sorption capacity larger than those achieved by the best performing PEI-loaded ACs impregnated using methanol as solvent. The use of an oak wood-derived carbon support or monoethanoloamine (MEA) as impregnating agent did not lead to any significant improvement of the CO2 sorption capacity. On the other hand, tetraethylenepentamine (TEPA)-impregnated AC slightly outperformed the optimally-PEI loaded sorbent, but the use of PEI was preferred because of its thermal stability. The addition of glycerol to the PEI/solvent/AC blend resulted in lower CO2 uptakes but moderately faster adsorption/desorption kinetics along with comparable “amine efficiency”. In addition, PEI-loaded AC showed larger CO2 uptakes and faster kinetics than those attained, for comparison purposes, by Zeolite-13X (Z13X). Furthermore, amine-containing ACs were found to be durable and easy to regenerate by RTSA at 120 °C. This CO2 desorption required ca. one third of the energy needed to regenerate a 30% MEA solution (i.e. the state of the art capture technique), thus potentially implying a lower energy penalty for the PEI-based technology in post-combustion power plant. Overall, at higher partial pressure of carbon dioxide, textural properties were the dominant parameter governing CO2 capture, especially at lower temperatures. This CO2 physisorption appeared to be governed by a combination of narrow microporosity and surface area. In contrast, at increased temperature and lower partial pressure, basic (alkali metal or amine-containing) functionalities were the key factor for promoting selective chemisorption of CO2

“Blue” Hydrogen & Helium From Flare Gas Of The Bakken Formation Of The Williston Basin, North Dakota: A Novel Process

Is it possible to curtail flaring in the Williston basin while simultaneously sequestering carbon dioxide, harvesting economic quantities of natural gas liquids, helium and other valuable products? Utilizing a novel approach described here, diatomic hydrogen and elemental helium, as well as other products, can be profitably extracted from the gas streams produced from horizontal, hydraulically-fractured Middle Bakken Member wells, in the Devonian-Mississippian Bakken Formation of the Williston Basin, North Dakota, USA.However, there are two vastly different methods employed to extract these gasses. Hydrogen is harvested from the gas stream by physically reforming methane (CH4) through the application of one or another of two-stage processes: “Autothermal Reformation + Water Gas Shift (WGS) reaction”, known as ATR; or “Steam Methane Reforming”, SMR. Both yield H2, plus CO (carbon monoxide) in the first phase, and CO2 (carbon dioxide) after the second. Elemental diatomic hydrogen (H2) can be used in fuel cells to generate electricity or directly in certain internal combustion engines; primarily turbines, as primary fuel. The produced CO2 can be captured (CCUS: Carbon Capture, Utilization and Sequestration) and injected downhole for both reservoir energy enhancement and CO2 sequestration, or sold for industrial use because of its purity. Helium, on the other hand, is inert and therefore it is unnecessary to expend the amount of energy required to reformat methane to liberate hydrogen. There are several methods commercially available to economically extract 99.995% pure helium from gas streams where the helium concentration can be as low as 0.010%. The extraction of crude helium from natural gas requires three processing steps. The first step removes impurities through deamination, glycol absorption, nitrogen rejection, and desiccant adsorption, which remove CO2, H2O, N2, and H2S; a typical gas pre-treatment process. The second step removes high-molecular weight hydrocarbons (Natural Gas Liquids), if desired, while the third step is via cryogenics, which removes the final methane. The result is 75-90% pure helium. Final purification, before liquefaction, is accomplished via activated charcoal absorbers at liquid-nitrogen temperatures and high pressure, or pressure-swing adsorption (PSA) processes. Low-temperature adsorption can yield helium purities of 99.99 percent, while PSA processes recover helium at better than 99.9999 percent purity. However, with the advent of selective zeolite or organometallic membranes, the cryogenic extraction of He from the CH4 stream step can be eliminated. Heating the gas stream and passing it through selective semi-permeable membranes allow for the helium, with its much smaller size, and higher energy, pass while excluding the relatively massive CH4 molecule. The helium can be isolated and purified via pressure swing adsorption (PSA) methods to achieve 99.999% purity. The heated methane can then be directly ported to a Steam Methane Reformer unit for extraction of hydrogen. Both H2 and He extraction procedures eliminate the need for gas flaring, as both yield salable products such as LNG and NGLs, and the opportunity to capture and sequester carbon dioxide (CO2) from the produced gas stream. This extracted so-called “Blue Hydrogen” is slated for use in transportation via fuel cells or use in internal combustion engines and sells for approximately $3.00/MCF, depending on the cost of the feedstock natural gas. “Metallurgical helium” or “Grade-A Helium” (i.e., \u3e 99.9999$498/MCF (02-2023). The cost of hydrogen vs. helium extraction is difficult to compare. Hydrogen production depends on the cost of natural gas as a feedstock, which is particularly variable. The cost of helium extraction depends on the volume of gas being processed, as most helium extraction units could handle 10-12 Bakken wells simultaneously. However, as a straight-up market product, helium revenue exceeds hydrogen by a factor of 100. Doing both coincidental from the same gas stream will enhance the revenue of each

Effects Of Synthesis Methods And Parameters On Sodium Zirconate For High-Temperature Co2 Sorption

Carbon dioxide (CO2) emission is among the causes of global warming. CO2 capture by CO2 adsorption has been one of the methods to reduce CO2 emission. Moreover, an adsorbent with high efficiency is needed for high-temperature CO2 capture from industrial hybrid processes. Sodium zirconate (Na2ZrO3) is one of the potential solid sorbents with high and stable cyclic CO2 sorption performance, but CO2 adsorption capacity closer to its ideal capacity is still desired. Furthermore, the effects of different methodologies on its CO2 capture performance were not reported previously. The main aim of this research work is to improve the synthesis and thus CO2 capture capacity of Na2ZrO3 for high-temperature CO2 sorption. Effects of carbonation and calcination conditions, different sodium (Na) precursors, and addition of citric acid (CA) and ethylene glycol (EG) on high-temperature CO2 sorption performance of synthesised Na2ZrO3 were investigated. Characterisation and CO2 sorption performance of samples were tested using thermogravimetric analysis, X-ray diffraction, N2 adsorption and SEM. All the above-mentioned parameters significantly affect the CO2 adsorption performances of the prepared Na2ZrO3 sorbents. The use of different Na precursor and CO2 adsorption temperature influenced the CO2 adsorption capacity of the samples. Different calcination conditions also affected the purity of Na2ZrO3. Addition of CA and EG resulted in producing purer Na2ZrO3 with more porous morphology and hence better regeneration stability than the sample prepared without the addition of CA and EG. The best CO2 adsorption capacity of 4.902 mmol CO2/g Na2ZrO3 was achieved at carbonation temperature of 550 °C, for the sample synthesised with sodium citrate as the Na precursor and CA:EG molar ratio of 2:1, and calcined at 900 °C for 4 h. Hence, this sorbent is suitable for high-temperature CO2 capture. It is recommended to test the functionality of this improved Na2ZrO3 sorbent under industrial conditions

Characterisation of torrefied carbon For carbon dioxide capture and cofiring application

Increased carbon dioxide (CO2) emissions across the globe, and the resulting atmospheric levels, have become the subject of many scientific studies in recent times. Managing and reducing CO2 emissions has remained a challenge for scientists and researchers in carbon capture science, despite technology advancements. Although recent technologies deployed suggest an improvement from the classical approaches, there is a need to explore other alternatives to optimise process performance and to reduce the cost of carbon capture and sequestration processes. In this study, torrefaction technology was employed to develop ‘torrefied carbon’ using renewable carbonaceous materials, such as Iroko (IR - hardwood) and Scottish Pine (SP - softwood), for CO2 capture from the combustion stacks of coal-powered plants. The study was divided into two parts: (a) developing the torrefied carbon using selected torrefaction conditions, at temperatures of (290 °C, 320 °C, 350 °C and 380 °C), a residence time of 60 min and heating rate (10 °C min-1), under CO2 atmosphere. The second is testing the torrefied carbons for CO2 adsorption potential and cofiring applications. The physicochemical characteristics of the torrefied carbons, such as hydrophobicity, calorific values and ultimate analysis, as well as the torrefaction performance indicators, such as energy gain, energy consumption, mass density and mass yield, amongst others, were assessed, allowing the fuel quality and potential use of the torrefied carbon once entirely spent for CO2 capture in same power plant to be evaluated. Given the results obtained, the torrefaction performance indicators showed there is energy gain for the selected torrefaction conditions. The highest energy gain values of 104 and 102 were found for the SP and IR, respectively, at the torrefaction condition of 320 °C, at a residence time of 60 min. The calorific values of the torrefied carbons developed at 320 °C and 350 °C, where - IR (26.49 MJ kg-1 and 26.75 MJ kg-1) and SP (26.13 MJ kg-1 and 29.12 MJ kg-1), respectively, which were higher than those of the low-ranked coal (23.20 MJ kg-1) investigated. For the adsorption studies, the torrefied carbons developed at 350 °C showed the highest CO2 adsorption capacity for both IR and SP carbons. The thermodynamic study of the CO2 adsorption using the Langmuir and isosteric heat of adsorption suggests the existence of heterogeneous surface sites on the torrefied carbon surfaces. The CO2 adsorption shows low heat of adsorption, given the values of the isosteric heat, for IR320 (-45 KJ mol-1), IR350 (-58 KJ mol-1), SP320 (-28 KJ mol-1) and SP350 (-41 KJ mol-1), an indication that the CO2 adsorption process is governed by physisorption. The kinetics of the CO2 adsorption of the torrefied carbons followed the Double Exponential Model, described by two distinct rate-determining steps. The rate of CO2 adsorption on the torrefied carbons appeared fast, given the equilibration time of an average of < 8 min for the IR and 11 min for the SP carbon, suggesting that the short time of equilibrium based on the Pressure Swing Adsorption process indicates a good potential from the materials on a kinetic basis. Within the study context, it was determined that the torrefied carbons could be employed for cofiring in coal-powered plants following a CO2 capture process. Although the structural features exhibited by the torrefied carbons were not fully explored in this work, due to the research limitations, the study opens up an opportunity into the potentials of torrefied carbon utilisation as a cost-intensive alternative in CCS applications.Increased carbon dioxide (CO2) emissions across the globe, and the resulting atmospheric levels, have become the subject of many scientific studies in recent times. Managing and reducing CO2 emissions has remained a challenge for scientists and researchers in carbon capture science, despite technology advancements. Although recent technologies deployed suggest an improvement from the classical approaches, there is a need to explore other alternatives to optimise process performance and to reduce the cost of carbon capture and sequestration processes. In this study, torrefaction technology was employed to develop ‘torrefied carbon’ using renewable carbonaceous materials, such as Iroko (IR - hardwood) and Scottish Pine (SP - softwood), for CO2 capture from the combustion stacks of coal-powered plants. The study was divided into two parts: (a) developing the torrefied carbon using selected torrefaction conditions, at temperatures of (290 °C, 320 °C, 350 °C and 380 °C), a residence time of 60 min and heating rate (10 °C min-1), under CO2 atmosphere. The second is testing the torrefied carbons for CO2 adsorption potential and cofiring applications. The physicochemical characteristics of the torrefied carbons, such as hydrophobicity, calorific values and ultimate analysis, as well as the torrefaction performance indicators, such as energy gain, energy consumption, mass density and mass yield, amongst others, were assessed, allowing the fuel quality and potential use of the torrefied carbon once entirely spent for CO2 capture in same power plant to be evaluated. Given the results obtained, the torrefaction performance indicators showed there is energy gain for the selected torrefaction conditions. The highest energy gain values of 104 and 102 were found for the SP and IR, respectively, at the torrefaction condition of 320 °C, at a residence time of 60 min. The calorific values of the torrefied carbons developed at 320 °C and 350 °C, where - IR (26.49 MJ kg-1 and 26.75 MJ kg-1) and SP (26.13 MJ kg-1 and 29.12 MJ kg-1), respectively, which were higher than those of the low-ranked coal (23.20 MJ kg-1) investigated. For the adsorption studies, the torrefied carbons developed at 350 °C showed the highest CO2 adsorption capacity for both IR and SP carbons. The thermodynamic study of the CO2 adsorption using the Langmuir and isosteric heat of adsorption suggests the existence of heterogeneous surface sites on the torrefied carbon surfaces. The CO2 adsorption shows low heat of adsorption, given the values of the isosteric heat, for IR320 (-45 KJ mol-1), IR350 (-58 KJ mol-1), SP320 (-28 KJ mol-1) and SP350 (-41 KJ mol-1), an indication that the CO2 adsorption process is governed by physisorption. The kinetics of the CO2 adsorption of the torrefied carbons followed the Double Exponential Model, described by two distinct rate-determining steps. The rate of CO2 adsorption on the torrefied carbons appeared fast, given the equilibration time of an average of < 8 min for the IR and 11 min for the SP carbon, suggesting that the short time of equilibrium based on the Pressure Swing Adsorption process indicates a good potential from the materials on a kinetic basis. Within the study context, it was determined that the torrefied carbons could be employed for cofiring in coal-powered plants following a CO2 capture process. Although the structural features exhibited by the torrefied carbons were not fully explored in this work, due to the research limitations, the study opens up an opportunity into the potentials of torrefied carbon utilisation as a cost-intensive alternative in CCS applications

Data Driven Modelling and Optimization of MEA Absorption Process for CO2 Capture

Global warming is a rising issue and there are many research studies aiming to reduce greenhouse gas emissions. Carbon capture and storage technologies improved throughout the years to contribute as a solution to this problem. In this work the post-combustion carbon capture unit is used to develop surrogated models for operation optimization. Previous work included mechanistic and detailed modeling of steady-state and dynamic systems. Furthermore, control structures and optimization approaches have been studied. Moreover, various solutions such as MEA, DEA, and MDEA have been tested and simulated to determine the efficiency and the behavior of the system. In this work a dynamic model with MEA solution developed by (Nittaya, 2014) and (Harun, 2012) is used to generate operational data. The system is simulated using gProms v.5.1 with six PI controllers. The model illustrated that the regeneration of the solvent is the most energy-consuming part of the process. Due to the changes in electricity supply and demand, also, the importance of achieving a specific %CC and purity of carbon dioxide as outputs of this process, surrogated models are developed and used to predict the outputs and to optimize the operating conditions of the process. Multiple machine learning and data-driven models has been developed using simulation data generated after a proper choice of the operating variables and the important outputs. Steady-state and transient state models have been developed and evaluated. The models were used to predict the outputs of the process and used later to optimize the operating conditions of the process. The flue gas flow rate, temperature, pressure, reboiler pressure, reboiler, and condenser duties were selected as the operating variables of the system (inputs). The system energy requirements, %CC, and the purity of carbon dioxide were selected to be the outputs of the process. For steady-state modeling, artificial neural network (ANN) model with backpropagation and momentum was developed to predict the process outputs. The ANN model efficiency was compared to other machine learning models such as Gaussian Process Regression (GPR), rational quadratic GPR, squared exponential GPR, tree regression and matern GPR. The ANN excelled all other models in terms of prediction and accuracy, however, the other model’s regression coefficient (R2) was never below 0.95. For dynamic modelling, recurrent neural networks (RNN) have been used to predict the outputs of the system. Two training algorithms have been used to create the neural network: Levenberg-Marquardt (LM) and Broyden-Fletcher-Goldfrab-Shanno (BFGS). The RNN was able to predict the outputs of the system accurately. Sequential quadratic programming (SQP) and genetic algorithm (GA) were used to optimize the surrogated models and determine the optimum operating conditions following an objective of maximizing the purity of CO2 and %CC and minimizing the system energy requirements