Flue Gas Purification Research Articles

Chemical looping CO2 capture and in-situ conversion as a promising platform for green and low-carbon industry transition: Review and perspective

Industrial flue gas and solid waste with the characteristics of large emissions and complicated distributions are two issues for industry, due to that sequential CO2 capture and utilization for flue gas shows high energy-cost penalties and solid waste faces with low reutilization ratio. As a powerful process intensification strategy, chemical looping CO2 capture and in-situ conversion (CL-ICCC) provides an effective solution to handle those two issues. However, current researches on CL-ICCC aim to develop process configurations, design bifunctional materials, and reveal reaction mechanisms, which ignore how to apply CL-ICCC for realizing flue gas purification and solid waste reutilization simultaneously in industry. Herein, after reviewing the current status of CL-ICCC for flue gas upgrade, industrial solid waste reutilization and industrial system integration, a perspective is proposed to highlight CL-ICCC as a promising platform for green and low-carbon industry transition. In the proposed system, industrial flue gas enters the capture reactor and reacts with industrial solid waste derived bifunctional materials to separate CO2 from other impurities. In the conversion reactor, reduction agents are introduced to spill CO2 over bifunctional materials and convert it into value-added chemicals. This review and perspective provide a new pathway to establish a low-carbon and self-digestion industrial system.

Cost Analysis of the Boiler Unit of Coal Power Units Depending on the Initial Steam Pressure and the Availability оf Flue Gas Purification Systems

When designing power plants of a new type or equipping them with new generation equipment, the problem of estimating capital investments is solved with the uncertainty of information on its cost. The lack of reliable methods suitable for use in engineering setting complicates decision-making on the technical development of power units and thermal power plants. When evaluating investments in the equipment of power plant units, it is convenient to use continuous functions. Their use makes it possible to carry out the analysis without cost restrictions. The article proposes a method for estimating capital investments in the boiler island of power units of power plants based on a power parametric function. The method includes an assessment of the cost of a boiler unit with fuel preparation systems within the boiler shop, draught and blast. A specific feature of the method is that the cost of the boiler includes the cost of flue gas purification systems from harmful combustion products in the form of ash, sulfur oxides and nitrogen oxides. The method was developed in an engineering setting. The methodological section demonstrates the performance of the method in assessing capital investments in a boiler island in comparison with the same indicator for the EU countries, the USA and China. When discussing the results of the study, it was found that capital investments in a coal-fired boiler with flue gas purification systems is in the range of US$ 25–200 million, depending on the power and initial steam parameters. The share of the cost of environmental flue gas purification systems is 28–50 % of the total cost of the boiler unit. It is demonstrated that the design of coal-fired power units with flue gas purification systems for supercritical parameters with a capacity of less than 300 MW is inefficient due to low competitiveness in terms of specific investments in the boiler.

Research on the characteristics of flue gas purification reaction in spouted bed

Semi-dry flue gas desulfurization and purification technology is a promising flue gas treatment technique. This study numerically investigated the influence of factors such as nozzle expansion angle, and fluidized particles diameter on the purification of SO2 and HF in the spouted bed. The study showed that in nozzle expansion angles of 5-25°, the 10° expansion angle is optimal for SO2 and HF purification efficiency. The fluidized particles' diameter affects purification efficiency. Desulfurization and defluorination efficiency are optimal when the ratio of fluidized particle diameter to slurry droplet diameter is 15. When Ca(OH)2 accounts for 0.005–0.01 of the slurry, desulfurization and defluorination efficiency are most cost-effective. According to the principle of chemical equilibrium, a higher Ca/S ratio facilitates a complete reaction with SO2 and HF, ensuring effective purification of the flue gas. The optimal Ca/S ratio is 2.5, with a desulfurization efficiency of 93.55% and a defluorination efficiency of 99.79%.

Potential of V2O5-WO3/TiO2 catalyst usage as the secondary measure for household heating combustion unit

The active substance used in oxidation honeycomb catalysts determined for real flue gas purification usually consists of precious metals such as platinum or palladium, while the most common is the mixture of the two mentioned elements, however high prices and limited availability of these elements encourages producers for the search for new, equally or better effective alternatives. In this study V2O5-WO3/TiO2 honeycomb catalyst was tested during the combustion test with commonly sold manually loaded stove. The catalyst was installed in the flue gas duct at the stove outlet. The experimental comparison of the flue gas composition at the catalyst inlet and at the catalyst outlet was performed. Flue gas sampling took place for whole combustion periods. Relatively high conversion rates by catalyst of CO (up to 87.1%), C3H8 (up to 61.3%) and TSP (up to 17.7%) were reached, which meant that the limit values of Commission regulation for mentioned kind of equipment were met during four, not only one period (in case of non-use of the catalyst). The V2O5-WO3/TiO2 catalyst has a great potential as the secondary emission control device for achieving low mass concentration of the certain pollutants in the flue gas.

Main problems in the operation of metal gas discharge pipes

This paper considers the main problems of operation of metal gas discharge pipes on the example of research and survey work on the examination of building structures of the exhaust tower with three gas discharge trunks 180 m high, flue gas purification unit of the sintering shop of LLP "NDFZ" in Zhambyl region. Analysis of the actual technical condition, considered in this article exhaust tower with three gas discharge shafts, according to the results of the survey, its volume-planning and structural solutions, showed its generally unrepairable, due to the mass of characteristic critical and unacceptable damage to the load-bearing elements of the frame, physical fatigue of materials, significant corrosion wear of metal structures, which will require a significant amount of proposed repair and maintenance work to eliminate them. The conducted complex of researches has shown that the service life of chimneys built before the 1960s and after has practically expired. Repair or reconstruction of chimneys using previously mastered technologies and materials does not solve the issues of reliability improvement. Rational solutions to these problems are periodic technical expertise by highly specialized organizations and implementation on its basis of methods of overhaul of both gas-exhausting trunks and building structures and interface units, wide implementation of which will solve the problem of extending the life of chimneys.

Density functional studies on the thermal decomposition of H2O2 and heterogeneous oxidation of benzene on the Cu surface

The related research of volatile organic compounds (VOCs) is of great significance to atmospheric governance. Benzene is extremely harmful to humans and the environment as a representative substance in VOCs. In recent years, H2O2, a highly effective oxidant, has seen usage in flue gas purification. However, the purification efficiency remains limited due to the low utilization rate of hydroxyl radicals (·OH), which are derived from H2O2 decomposition. This research primarily focuses on catalyst selection. Density functional theory (DFT) was employed to investigate the characteristics of H2O2 adsorption and decomposition on Cu-based catalysts, as well as the ineffective consumption reaction of·OH on the Cu surface. Concurrently, the interaction mechanism between benzene and·OH on Cu surface was investigated. The findings demonstrate that Cu-based catalysts can enhance the decomposition of H2O2 molecules, and that H2O2 can dissociate to·OH on the surface. Moreover, these catalysts exert a pronounced inhibitory effect on the ineffective consumption reaction between·OH, H2O2 molecules, and the HO2·. The degradation process of benzene under the influence of·OH was analyzed, and the critical step of the reaction, along with the specifics of the ring-opening reaction, were determined. These reactions mechanisms were elucidated, thereby providing theoretical support for the development of novel catalysts.

Optimization of CO2 Capture Efficiency in a Flue Gas Treatment System: Assessing the Impact of Flow Rates, Absorbent Concentrations, Nanoparticles, and Temperature

This study focuses on improving the efficiency of flue gas purification systems for carbon dioxide (CO2) capture. The researchers investigated various factors, including flow rates, absorbent concentrations, nanoparticles, and temperature, to optimize the CO2 capture process. They conducted experiments using a polytetrafluoroethylene (PTFE) hollow fiber membrane contactor to separate CO2 from nitrogen. The presence of titanium dioxide and silica nanoparticles in a potassium carbonate solution facilitated the separation process. The findings indicate that optimizing flow rates and absorbent concentrations can enhance CO2 capture efficiency. The use of nanoparticles in the absorbent solution was found to improve material capture effectiveness. The study also revealed that higher temperatures contribute to increased CO2 capture efficiency. The research aims to advance CO2 capture techniques to mitigate the release of industrial greenhouse gases, particularly in flue gas treatment systems. The researchers determined optimal settings for CO2 capture in these systems, emphasizing the importance of absorbent concentration for stability and absorption, as well as the role of nanoparticles in enhancing reaction kinetics and CO2 collection. The objective of the analysis is to maximize removal efficiency, although specific lower and upper bounds and a target value were not provided. The proposed solution suggests specific values for the independent variables, including temperature, gas flow rate, liquid flow rate, and the concentrations of K2CO3, PZ, SiO2, and TiO2, to optimize CO2 capture.

3D porous polymers for selective removal of CO2 and H2 storage: experimental and computational studies.

In this article, newly designed 3D porous polymers with tuned porosity were synthesized by the polycondensation of tetrakis (4-aminophenyl) methane with pyrrole to form M1 polymer and with phenazine to form M2 polymer. The polymerization reaction used p-formaldehyde as a linker and nitric acid as a catalyst. The newly designed 3D porous polymers showed permanent porosity with a BET surface area of 575m2/g for M1 and 389m2/g for M2. The structure and thermal stability were investigated by solid 13C-NMR spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA). The performance of the synthesized polymers toward CO2 and H2 was evaluated, demonstrating adsorption capacities of 1.85mmol/g and 2.10mmol/g for CO2 by M1 and M2, respectively. The importance of the synthesized polymers lies in their selectivity for CO2 capture, with CO2/N2 selectivity of 43 and 51 for M1 and M2, respectively. M1 and M2 polymers showed their capability for hydrogen storage with a capacity of 66cm3/g (0.6wt%) and 87cm3/g (0.8wt%), respectively, at 1bar and 77K. Molecular dynamics (MD) simulations using the grand canonical Monte Carlo (GCMC) method revealed the presence of considerable microporosity on M2, making it highly selective to CO2. The exceptional removal capabilities, combined with the high thermal stability and microporosity, enable M2 to be a potential material for flue gas purification and hydrogen storage.

Mn/Ce@HKUST-1 for Efficient Removal of Gaseous Thallium: Insights from Kinetic and Experimental Studies.

Gaseous thallium (Tl) pollution events, primarily caused by non-ferrous mineral refineries and fossil fuel combustion, have increased over the past few decades. To prevent gaseous Tl distribution from flue gas, MnO2/CeO2@HKUST-1 (MCH) was synthesized and found to achieve a gaseous Tl(I) removal level of up to 90% at 423 K, a weight hourly space velocity (WHSV) of 2000 h-1/mL with an Mn dose of 10%, maintained over 10 h. The best Mn/Ce ratio was found to be 9:1. To further investigate surface kinetic behavior, four commonly used kinetic models were applied, including the Eley-Rideal (ER) model, Langmuir-Hinshelwood (LH) model, Mars-van Krevelen (MVK) model, and pseudo-first-order (PFO) model. While the ER and LH models had the slightest deviation, the MVK model was the most reliable. The CatMAP software was also used to match the simulation deviation. This work demonstrated the Tl removal mechanism and provided insights into the accuracy of kinetic models on minor-radius heavy metal. Thus, this research may help promote the design of reactors, heavy metal removal rates, and flue gas purification technology selection.

Deoxygenation of CO<sub>2</sub> Solvent Based on Monoethanolamine in Gas–Liquid Membrane Contactors Using Composite Membranes

This work is devoted to the removal of dissolved oxygen from a model solvent based on monoethanolamine (MEA) to prevent its oxidative degradation during the absorption purification of flue gases from carbon dioxide. Composite membranes based on porous ceramic and polymer substrates with a thin selective layer of poly[1-(trimethylsilyl)-1-propyne] and its mixture with polyvinyltrimethylsilane have been developed. Gas-liquid membrane contactors have been created on their basis. It is shown that with their use in the vacuum mode, up to 60% of dissolved oxygen can be removed from the model solvent.

Synergistic Adsorption and In Situ Catalytic Conversion of SO2 by Transformed Bimetal-Phenolic Functionalized Biomass.

SO2 removal is critical to flue gas purification. However, based on performance and cost, materials under development are hardly adequate substitutes for active carbon-based materials. Here, we engineered biomass-derived nanostructured carbon nanofibers integrated with highly dispersed bimetallic Ti/CoOx nanoparticles through the thermal transition of metal-phenolic functionalized industrial leather wastes for synergistic SO2 adsorption and in situ catalytic conversion. The generation of surface-SO32- and peroxide species (O22-) by Ti/CoOx achieved catalytic conversion of adsorbed SO2 into value-added liquid H2SO4, which can be discharged from porous nanofibers. This approach can also avoid the accumulation of the adsorbed SO2, thereby achieving high desulfurization activity and a long operating life over 6000 min, preceding current state-of-the-art active carbon-based desulfurization materials. Combined with the techno-economic and carbon footprint analysis from 36 areas in China, we demonstrated an economically viable and scalable solution for real-world SO2 removal on the industrial scale.

REDUCTION OF OCCUPATIONAL RISKS FOR THE HEALTH OF WORKERS AND IMPROVEMENT OF ECOLOGICAL SAFETY OF THE ENVIRONMENT DURING CLEANING OF INDUSTRIAL EMISSIONS OF METALLURGICAL ENTERPRISES

Purpose: prevention of occupational risks and reduction of the negative impact on the health of workers of industrial flue gases, along with the improvement of environmental safety thanks to mathematical modeling regarding the rationalization of technological indicators of sulfur removal at production enterprises. Design / methodology / approach: the use of regression analysis is implemented as the main research method. Conclusions: a multifactorial mathematical model of the dependence of the degree of reduction of the content of sulfur dioxide in gaseous products on the technological parameters of flue gas filtration was built using industrial data. This makes it possible to rationalize the technological parameters of production with further regulation of the sulfur dioxide purification process to increase its efficiency. Achieving a reduction in flue gas pollution with sulfur dioxide contributes to reducing the harmful effects on the health of workers, preventing occupational risks, and increasing the level of environmental safety. Limitations / implications of the research: the interrelationship of desulfurization production parameters was investigated in certain intervals according to the features of the technological process, which determines the corresponding limitations of the use of the constructed mathematical model. Practical consequences: the interrelationship of technological indicators of industrial production is determined, which allows adjusting the value of the degree of purification of flue gases from sulfur dioxide when changing the technological parameters of filtration with the establishment of the most favorable conditions. The obtained results can be used to improve the production process of enterprises whose activities are accompanied by gaseous emissions: metallurgical plants, thermal power plants, etc. Originality / value: a multifactorial mathematical model of the dependence of the degree of purification of flue gases from sulfur dioxide on the technological parameters of the industrial process was built. The obtained results were presented in the form of a multivariate regression equation. On the basis of the obtained dependence, for a better visual perception, graphs were constructed in the form of surfaces, respectively, for some of the studied technological parameters.

Construction of microporous polycarbozole frameworks for flue gas purification by increasing connected numbers of external linkers

The development of porous adsorbents to address the trade-off between physical adsorption capacity and selectivity has attracted extensive research interest due to their potential applications in gas separation and purification, but remains a daunting challenge. Herein, we report a new strategy involving increasing connected numbers of external linkers (from di-connected DCM to tri-connected TCM) to crosslink nitrogen-rich carbazole derivatives, thereby improving the microporosity of microporous polycarbozole frameworks and promoting CO2 adsorption capacity and selectivity. This is mainly attributed to tri-connected linker can make carbazole-based monomers more closely packed than di-connected linker, resulting in higher microporosity in tri-connected polymers constructed from the same monomer than that of di-connected polymers. Meanwhile, the dynamic breakthrough experiments show that tri-connected polymers have better CO2/N2 separation abilities than di-connected polymers.

Capture and migration of particulate matter in activated carbon sintering flue gas purification system based on ultra-low emission target

By using alkali metal K as the tracer component of sintered ash, the particulate matter (sintered ash and activated carbon powder) in the industrial two-stage moving bed purification project of sintered flue gas was studied. First, the distribution of K element in the gas phase and each link of the purification system was investigated. The material flowing direction as well as the trapping and releasing mechanism of sintered ash in the purification system were analyzed by BET, XRD, and SEM-EDS techniques. The migration and release rule of activated carbon (AC) powder from moving bed to gas phase was investigated, and the contribution of AC powder to flue gas particles and the key release link were clarified. The results showed that the sintered ash capture rate in the primary adsorption tower of AC was as high as 99.7%, while 65.92% of the sintered ash was captured in the middle chamber of the primary adsorption tower. Sintered ash is trapped by AC at 0–0.5 mm on the surface, which suggested the main trapping mechanisms are inertial collision and interception diffusion settling. The trapped sintered ash is recycled through the system with the AC, and eventually 99.9% ash is discharged with the sieved carbon powder from the desorption tower. The percentage of charcoal powder in the exit flue gas particulate matter is 55.45% and the release of activated charcoal powder to the gas phase in the secondary adsorption tower. Which is the key link affecting the exit flue gas particulate matter concentration. This study elucidates the capture and migration law of particulate matter in AC flue gas purification system, and provides a strong basis for the improvement of technology to achieve stable ultra-low emission of particulate matter from AC system.

Analysis of the National Annual Emission of Pollutants from Road Transport in Poland in the Years 1990–2020

This article presents the official results of the inventory of pollutants in Poland from road transport, developed in the National Centre for Emissions Management of the Institute of Environmental Protection–National Research Institute in Warsaw as part of the reporting of national pollutant emissions. Considerations concern pollutants harmful to the health of living organisms. Source information is available in official reports. The national emission of pollutants covers the years of balancing 1990–2020. The aim of the work is to assess the dynamic properties of the processes of national emission of pollutants. The list of substances whose emission is examined in the article is consistent with the list of substances in accordance with the European Monitoring and Evaluation Programme/European Environment Agency (EMEP/EEA) procedure. These are pollutants harmful to the health of living organisms. The inventory of pollutants contributing to the intensification of the greenhouse effect in the atmosphere is carried out as part of separate reports. The energy consumption of road vehicles was presented. The ratio of national annual emissions of pollutants in 2020 and in 1990 is the lowest for sulfur oxides and lead, followed by non-methane volatile organic compounds and carbon monoxide. The analysis of the national pollutant emission concerned the energy emission factor, which characterizes the ecological level of the accumulated category of road vehicles. This is an original element, not seen before in world literature and official reports of research institutes. An unambiguous trend of decreasing the energy emission factor of pollutants, apart from ammonia, was found, which is related to the use of catalytic flue gas purification systems. This is confirmed by the analysis of the ratio of the energy emission factor in 2020 and 1990, as well as the relative derivative of the energy emission factor in relation to the national annual emission of pollutants.

Research on migration and transformation behavior of selenium during the dual-alkali wet flue gas deacidification process in the simulated flue gas

Selenium easily escapes from the existing air pollution control devices (APCDs) used in municipal waste solid incineration (MSWI), which poses a threat to both the ecosystem and human health. Dual-alkali wet flue gas deacidification (DAWFGD) has been recently applied in MSWI power plants to improve the purification of flue gas. This technology provides a new route for the coordinated control of selenium in the DAWFGD device, which removes acidic gas simultaneously. In this study, a laboratory-scale DAWFGD system was constructed to investigate the migration and transformation behavior of selenium during the absorption and regeneration process in the DAWFGD system. The results showed that the Na2CO3 solution could effectively absorb SeO2, and the absorption efficiency could reach up to 97.09% by increasing the Na2CO3 concentration. High-concentration CO2 has less of an absorption inhibition effect on gaseous selenium compared to low-concentration HCl and SO2. The absorption of SeO2 was adversely affected by the decrease in pH value of the absorption solution caused by an increase in SO2 concentration. However, the addition of a small amount of alkali solution (OH–) into the absorption solution could well recover its absorption performance for SeO2. During the regeneration process, the precipitation ratio of selenium from the aqueous phase to the solid phase increased with the molar ratio of Ca/S increasing. Besides, selenium was found to be in the form of selenite during both the absorption and regeneration processes. This study helps to evaluate the potential of DAWFGD in MSWI power plants for removing SeO2 from flue gas and provides a theoretical reference for the treatment of gas-phase selenium in the waste incineration process.

A comprehensive review of aluminium electrolysis and the waste generated by it.

Aluminium is produced by electrolysis using alumina (Al2O3) as raw material and cryolite (Na3AlF6) as electrolyte. In this Hall-Héroult process, the energy consumption is relatively large, and solid wastes such as spent anodes and spent pot liner, flue gas and waste heat are generated. Therefore, this article discusses from the perspective of high energy consumption and high pollution and summarizes the methods to reduce energy consumption and solve pollution problems. The functions of carbon anode, carbon cathode, refractory material and sidewall in aluminium electrolysis cells are discussed in detail. The process of aluminium electrolysis and the ways to improve the current efficiency of aluminium electrolysis cells and reduce their energy consumption are outlined. The causes and treatment methods of spent anodes, spent cathodes, spent refractories and spent spot liner are reviewed. The research progress of waste heat recovery and aluminium electrolysis flue gas purification are analysed. And the future research directions of aluminium electrolysis flue gas are provided.

The co-combustion of pellets with pistachio shells in residential units additionally equipped by Pt-based catalyst

There are several published studies evaluating the possibilities of thermal and non-thermal utilization of pistachio hard shells in many technical sectors; however, there are no relevant data about the possibilities of usage of this homogenous biomass-based by-product as a fuel for automatic household heating appliances for partial or full substitution of standard ENplus A1 pellets, which is the aim of the presented study. The composition and basic properties of both fuels were compared as well as the flue gas composition formed during the 6 different fuel mixture combustion in two real-scale pellet burners. The mass concentration of observed pollutants (CO, total suspended particles, and C3H8) in the flue gas was strongly affected by increasing of pistachio shell mass fraction in the fuel mixture (from 10 to 100%). In comparison to the combustion of ENplus A1 pellets, CO was increased up to 25.9 times, total suspended particles up to 15.3 times, and C3H8 up to 13.7 times. Based on the results of real combustion tests, the equations were listed, describing the increase of the mass concentration of pollutants for the whole spectrum of pellets/pistachio shell ratios applied on the chosen designs of the pellet burners. The Pt-based oxidation honeycomb catalyst, additionally installed at the combustion unit outlets for flue gas purification, showed conversion rates up to 82.2% in the case of CO and up to 33.1% in the case of C3H8. This enables the reaching of the same or lower mass concentrations of mentioned pollutants in the flue gas, formed during the co-combustion of appropriately selected fuel ratios in comparison to ENplus A1 pellet combustion without the catalyst.

Simultaneous removal of NOx and dust with integrated catalytic filter: Interactions between NH3-SCR and filtration processes

The integrated selective catalytic reduction of nitrogen oxides by NH3 (NH3-SCR) and dust filtration technology can effectively reduce the energy consumption and space of the flue gas purification system. Herein, a novel catalytic filter is fabricated by in situ depositing FeWOx heterogeneous catalyst onto stainless-steel-fiber filter (named as FeWOx/SSFF), which displays excellent deNOx performance (>85 % NOx conversion and 96 % N2 selectivity) with superior H2O and SO2 tolerance, as well as great dedust efficiency (>99.99 % and low residual pressure drop). The suitable oxygen mobility and enhanced charge transfer ability at the crystalline-amorphous interface contribute well to the excellent SCR performance, and the low pressure drop is promoted by the well dispersion of FeWOx species on the SSFF. Notably, a volcanic relationship between dedust process and SCR performance was obtained, due to the boosting of dedust process for the denitrification, which was confirmed by computational fluid dynamics (CFD). Besides, excessive dust-cake could inhibit SCR performance owing to catalytic site being covered by dust particles. Accordingly, SCR process hardly affected dedust efficiency and residual pressure drop. This work reveals the interactions between SCR and dedust processes, and paves a way to design novel catalytic filters for simultaneously removing dust and gas pollutants at practical conditions.

Migration and control of mercury in hazardous chemical waste incineration

This study evaluated the emission and control characteristics of mercury during hazardous chemical waste incineration. Meanwhile, for the complex flue gas conditions generated by hazardous chemical waste incineration, the commercial activated carbon used in the incineration system was modified with CuBr2, and its Hg0 removal performance was tested. The results showed that the major proportion of Hg was in the fly ash, and the content accounted for 74.53 % of the total Hg. The Hg content in the fly ash increased with decreasing fly ash particle size. In the exhaust flue gas, the Hg content was 11.05 % of the total Hg, in which the mass percentages of Hg2+ and Hg0 were 59.08 % and 40.92 %, respectively. The flue gas purification equipment of the incineration system had a removal efficiency of 92.40 % for HgT. The saturated Hg0 removal capacity of the modified activated carbon was improved by 33.51 times. Under simulated incineration flue gas conditions, the modified activated carbon was able to achieve an Hg0 removal efficiency of 92.85 %. The results can contribute to the understanding of Hg emissions from hazardous chemical incineration systems and provide guidance for efficient Hg removal from activated carbon.