Technologies to Capture CO2_2 directly from Ambient Air

Building a carbon-neutral world needs to remove the excess CO$_2$ that has already been dumped into the atmosphere. The sea, soil, vegetation, and rocks on Earth all naturally uptake CO$_2$ from the atmosphere. Human beings can accelerate these processes in specific ways. The review summarizes the present Direct Air Capture (DAC) technology that contribute to Negative Emissions. Research currently being done has suggested future perspectives and directions of various methods for Negative Emission. New generations of technologies have emerged as a result of recent advancements in surface chemistry, material synthesis, and engineering design. These technologies may influence the large-scale deployment of existing CO$_2$ capture technologies in the future

Direct capture of CO2 from air using amine-functionalized resin - Effect of humidity in modelling and evaluation of process concepts

Direct air capture (DAC) using adsorbents is a promising negative emissions technology if coupled with CO2 storage and is a viable option as a CO2 source for producing truly carbon-neutral synthetic fuels. However, if this technology is to become a serious climate change mitigation tool with the capture potential of several GtCO2/year, the cost needs to decrease significantly. To achieve this, the material and energy requirements of the process need to be minimized by adsorbent development and process design. Most of the developments in the field of DAC have focused on the synthesis of novel adsorbents, while some of the other aspects of the process have been less studied. This thesis aims to fill some of these gaps in DAC process research. In this work, the performance of an amino resin for CO2 capture was studied experimentally in a wide range of conditions. Humidity and cold conditions were found to nearly double the experimental CO2 adsorption capacity of the studied amino resin in some cases. Based on a working capacity analysis using isotherm modelling, the typically proposed DAC process using temperature and vacuum swing adsorption (TVSA) with a closed inlet is severely limited in terms of CO2 working capacity. Using an improved fixed-bed experimental setup with automatic operation, a detailed comparison of DAC regeneration processes was carried out. By using a purge gas such as air in TVSA, CO2 productivity was significantly increased. This method was also advantageous in terms of the specific energy requirement and adsorbent stability compared to the TVSA process with closed inlet. Therefore, in applications that do not require pure CO2 such as greenhouses or microbial cultivation, using inert purge gas or air is beneficial in adsorbent regeneration. A novel kinetic model was developed that takes into account the effect of humidity in CO2 adsorption on amine-functionalized adsorbents. Using this model, humid CO2 isotherms and adsorption column dynamics were accurately modelled. The kinetic model can be expected to be generally useful in DAC process modelling, and ultimately in DAC process design and optimization

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

Amine–functionalized kenaf as carbon dioxide adsorbent in pressure swing adsorption system

Kenaf (Hibiscus Cannabinus L.) that belongs to the family of Malvaceae is abundantly grown in Malaysia since 2006 to replace tobacco plantation as it is inexpensive, easy to grow, and biodegradable. The use of kenaf as adsorbent is seen as an attractive and innovative method, and it has been used for various adsorptions. Adsorption is a promising technology that has the ability to capture carbon dioxide (CO2), the predominant contributor of global climate change. Inspired by the established and well–known amine–based absorption process of carbon capture and storage technology, the development towards new adsorbent by introducing amine functional group has been studied. Therefore, this study explores the potential of modified kenaf as adsorbent by incorporating amine functional group on the surface and investigates the CO2 adsorptive characteristics of amine–modified kenaf adsorbent using pressure swing adsorption system (PSA). The preparation of amine–modified kenaf was conducted via the incipient wetness impregnation technique. The physical and structural characteristics of amine–modified kenaf were determined via micromeritics 3 flex, field emission scanning electrons microscopy, energy dispersive x–ray, Fourier transform infrared spectroscopy, and thermogravimetric analyzer. The results show that the types of amine, amine loading concentration, and impregnation time affect the physical and structural properties of kenaf and thus affecting the capability for capturing CO2. Screening of various types of amines via PSA revealed that tetraethylenepentamine (TEPA) has recorded the highest CO2 adsorption (0.914 mmol/g). Further examination on amine loading divulged that kenaf to TEPA ratio of 1:2 presents the highest CO2 adsorption (2.086 mmol/g) with 5 hour impregnation time. To examine the utilization of amine–modified kenaf adsorbent in PSA system, pressure bed, adsorption time, and feed flowing rate were evaluated. The result revealed that these parameters affect the gas adsorption of amine–modified kenaf adsorbent. The regeneration study had shown that kenaf adsorbent could sustain the repeated adsorption/desorption cyclic operations. This study also found that physical and chemical adsorption occurred during the adsorption of CO2 on raw kenaf and amine–modified kenaf. Thus, amine–modified kenaf adsorbent has high potential to be used as low–cost CO2 agro–based adsorbent hence inducing towards innovative material in the field of gas adsorption

Impregnation of activated carbons for pre- and post-combustion CO2 capture in a fixed bed pressure swing adsorption reactor: a modelling and experimental comparison

The mitigation of greenhouse gases, such as carbon dioxide, is of timely concern in the energy sector, requiring new techniques and process options to treat acidic gases and develop solutions for capture and reuse. Solid adsorbents are potentially viable for application as the next generation carbon capture technology. Activated Carbon Norit® RB1 and Cabot Norit® R2030 were selected for this study, owing to their potentially high adsorption rates and affinity with carbon dioxide molecules. The purpose of thesis was to modify the adsorbent using chemical and amine solutions via an impregnation process to provide high adsorption capacity and performance, focusing on surface area modification and attachment of primary amine groups to improve the solid/gas interaction. Diverse characterisation techniques were used to examine and explore the essential properties and parameters of the modified adsorbents developed. Specifically, scanning electron microscopy (SEM) was used to investigate the surface morphology, thermogravimetric analysis (TGA) was applied to test the adsorption capacity with a pure CO2 flow, a high-pressure volumetric analyser (HPVA) was used to measure the gas volume adsorbed at the pre-combustion condition, producing adsorption-desorption isotherms under nitrogen and carbon dioxide binary mixtures, and the textural properties were determined by Brunauer-Emmett-Teller (BET) analysis, allowing comparison of the pore size and the volume adsorbed per sample. The dynamic adsorption behaviour of the activated carbons (ACs) was studied in a fixed bed reactor using a carbon dioxide concentration range of 10–50% combined with a nitrogen flow. The original and modified adsorbents were tested under pre and post-combustion conditions, with the highest uptake of carbon dioxide found to be for MEA+MDEA+AMP Norit® RB1 AC II under pre-combutions and MEA (20%) Norit® RB1 AC under post-combustion conditions. The introduction of amine groups into the sample lead to the enhancement of chemisorption, while the treatment with KOH modified the surface area of the adsorbents, thereby improving uptake behaviour. Additionally, a Pressure Swing Adsorption (PSA) model using a fixed bed reactor was developed for carbon dioxide capture at pre-combustion conditions (25oC and 25 bar) using gPROMS® ModelBuilder software [version 4.1; developed by Process System Enterprise, PSE]. A parameter estimation was executed using similar conditions as applied in the fixed bed reactor rig at the laboratory scale. Nitrogen and carbon dioxide were applied to this model taking into account the physical behaviour of the PSA unit. The estimations demonstrated an excellent approximation to the experimental breakthrough curve for both adsorbents, which also validated the model supported by the sum of squared residuals (SSR) values. Furthermore, the parameter estimation confirmed the novelty of the two amine modified adsorbents for pre-combustion carbon dioxide adsorption, due to their high potential to capture the desired gas in a binary mixture in the PSA fixed bed reactor process

Novel synthetic calcium oxide based sorbent for carbon dioxide capture

This thesis focuses on studying the synthesis of calcium oxide- (CaO-) based sorbents for carbon dioxide (CO2) capture in the post-combustion process. Calcium oxide has been regarded as one the most promising candidates for carbon capture in the last decade due to its high capturing efficiency, low running cost, and abundance in the natural world. However, the main drawback of this category of sorbents (natural limestone and modified CaO) is the rapid decay of the CO2 uptake capacity during the cycles of carbonation and decarbonation reactions. Therefore the target of this research is to enhance sorbent sustainable performance in long-term carbon capture utilisation, for the purpose of reducing the total budget of carbon capture in fossil-fuel power industries. To obtain the optimal CaO-based sorbent, different sacrificial particles were used in the sorbent modification experiment, including hydrophobic polymers and non-ionic surfactants. Among the combinations, modified CaO sorbents prepared with polyethylene glycol (PEG) and Tween80 (also called Polysorbate 80) delivered the best performance. Using sacrificial particles resulted in changing the properties of CaO particles, both physically and chemically: particle size, morphology, surface area and porosity were carefully controlled under specific synthesis conditions, and positively affected the sorbents’ reactivity. A more important factor, which has been ignored by most researchers, the polymorph of sorbent precursor, was also investigated in this thesis. Repeatable results proved that of the sorbents derived from all the three polymorphs of calcium carbonate (calcite, aragonite and vaterite) vaterite-derived sorbent has the best CO2 capture capacity and reversibility. We found that the fraction of vaterite would influence the sorbent particles’ reactivity proportionally in the first-cycle carbonation process. In order to study the sorbent’s physical/chemical properties and its CO2 uptake performance, standard laboratory characterisation methods and a thermal-gravimetric analyser were employed, respectively. A combined gas sorption experiment under controlled conditions using a self-built high pressure reactor also revealed the mechanism of CO2 sorption on different types of porous materials. The existing equipment used to achieve this purpose usually requires a very large scale and involves a rather complicated micro-mechanical structure. A novel measurement methodology based on micro-cantilever design and laser detector was introduced in order to reduce this complexity. Physisorption of CO2 gas molecules by porous materials, such as Zeolite and MCM41, was measured kinetically with the help of this setup. A comparison between chemisorption and physisorption provides useful insights in regard to the search for the best solution for CO2 capture.Open Acces

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

Electrically conductive composite sorbents for CO2 capture from industrial effluents

The capture of CO2 from stationary sources of emission is one of the fundamental approaches of climate change mitigation. One of the main obstacles in the way of implementing many of the introduced technologies for CO2 capture from stationary sources of emission is the associated high cost. For this purpose, dynamic research is focusing on the development of low cost CO2 capture technologies. Knowing that two of the highest cost components of CO2 capture are the capture and the regeneration steps, many research studies are focusing on improving and optimizing CO2 capture and sorbent regeneration to reduce their associated costs. This can be achieved through increasing the amount of CO2 captured by a sorbent, and regenerating the sorbent without using excessive energy. In this context, this thesis targeted the improvement of CO2 adsorption capacity of electrically conductive activated carbon by combining it with materials with a higher adsorption capacity, namely; zeolite type-A and layered double hydroxide. The resulting composite materials can be directly heated and regenerated using Joule effect, potentially reducing the costs of material regeneration using electrical swing adsorption. In this thesis, four types of electrically conductive composite CO2 sorbents were synthesised and characterized: carbonized Purolite® MN200/zeolite NaA composite; carbon supported zeolite NaA composite (zeolite NaA/AC), carbon supported dual-cation containing zeolite type-A composite (ZMG/AC), and carbon supported layered double hydroxide composite (LDH/AC). For the first composite material, a new method was explored for the synthesis of carbonized Purolite® MN200/zeolite NaA composite, where zeolite NaA was synthesised inside the pores of phenolic resin. After synthesis, the composite material was carbonized and activated. The resulting composite material has a unique spherical carbon beads cluster morphology that is expected to reduce pressure drop during CO2 capture. Additionally, the material can easily be shaped and customized according to the shape of the reactor or application requirements. Improving the porosity, mechanical strength, and electrical conductivity of the developed material is expected to make it a suitable material for CO2 capture using electric swing adsorption. Activated carbon beads from MatrixCarbon™ were chosen to be the support material for zeolite NaA, dual-cation containing zeolite type-A (ZMG), and layered double hydroxide (LDH), to synthesise the remaining three composite materials. MatrixCarbon™ activated carbon beads were chosen due to their high porosity and superior electric conductivity. Scanning Electron Microscopy analysis of the internal formation of the composite materials showed the successful growth of zeolites and LDH in the macropores of the carbon beads. The ion exchange process with magnesium in zeolite NaA proved that the material’s CO2 adsorption properties can be modified to work under different sets of operation temperatures. Energy Dispersive X-Ray and X-Ray Diffraction analyses confirmed the formation zeolite NaA, dual-cation containing zeolite type-A, and LDH in the pores of the synthesised composite materials. The amounts of impregnated zeolites or LDH in the composite material was found to range between 4.5 and 6.0 wt% in the composite material. Brunauer-Emmett-Teller (BET) analysis showed that zeolite NaA/AC, ZMG/AC, and LDH/AC composite materials maintained high surface areas of 911, 917, and 1043 m2/g respectively. Temperature Programmed Desorption showed that combining activated carbon with zeolites or LDH crystals not only increases CO2 adsorption capacity but also decreases the desorption temperature of CO2, potentially increasing the cost effectiveness of the materials. Flux response technology was used to investigate CO2 adsorption by the synthesised materials at isothermal and non-isothermal temperatures. The technique proved to be an effective tool for the measurement of CO2 adsorption in solid sorbents. This was demonstrated by the ability to detect the non-linear CO2 adsorption in zeolite NaA and LDH at increasing temperatures (22, 100, 200, and 300 °C), which was reported in previous studies.Open Acces

Capturing CO2 from an integrated steel mill: a techno-economic analysis through process modelling

The increase in global carbon dioxide emission has raised concerns about climate change. This has caused nations to consider different carbon dioxide mitigation pathways to reduce emissions. The iron and steel industry contributes to approximately 30% of total global CO2 direct emission in the industrial sector. It is an energy intense industry. Many steel mills are operating close to thermodynamic limits in efficiency. Therefore decarbonising the steel industry through process improvements is limited. Breakthrough technologies such as carbon capture and storage (CCS) is an alternative and attractive solution. In this research I have explored the application of a retrofit carbon capture technology to an existing steel mill. The steel mill chosen, combusts gases arising from the steel making processes. Different locations within the steel mill were analysed, the in-house power station and the turbo blower house were chosen for retrofit post-combustion carbon capture. Two different separation technologies were process modelled to capture the carbon dioxide from the flue gas of the in-house power station and the turbo blower house. The technologies were chemical absorption and adsorption. The two technologies were techno-economically studied. Chemical absorption, with solvent MEA, showed capability of recovering 86% of CO2 with a purity of more than 99 mol%. Adsorption using sorbent zeolite 13X was able to achieve 82% recovery with purity of 96 mol%. Sorbent activated carbon showed a capability of recovering 67% of carbon dioxide with a purity of 95 mol%. The cost of CO2 avoidance for the process using chemical absorption (MEA) was equal to $44.92/tonne CO2. For the process using adsorption (zeolite 13X) the CO2 avoided cost was equal to$44.90/tonne of CO2. Activated carbon was the most expensive capture process, out of the three processes studied. It costs $45.81/tonne of CO2 avoidance