Carbon In Ash Research Articles

The influence mechanism of mechanical modification on fly ash carbonation to solidify heavy metals

Dry and wet milling, were selected to carry out modification experiments. The influence of mechanical modification pretreatment on fly ash carbonation to solidify heavy metals was explored, and its influence mechanism was revealed. Mechanical modification can improve the physical properties, and the continuous application of mechanical energy can activate the active sites which strengthen fly ash carbonation. The carbonation efficiency was obtained by 500–800 °C thermogravimetric analysis before and after carbonation. The average carbonation efficiency improved by dry milling is 2.28 %, and that improved by wet milling is 8.11 %. Carbonation has a good curing effect on Cr, Cd, Pb and As, especially when the CO2 is raised to supercritical. At 8 MPa pressure, the leaching concentrations of Cr, Cd, Pb and As decrease by 34.94 %, 7.00 %, 15.28 % and 35.85 %. The stabilization effect of fly ash carbonation on heavy metals is significantly improved after mechanical modification pretreatment. Comparison experiments on characterization of fly ash before and after mechanical modification shows that ball milling significantly increases the specific surface area. The crushing effect of wet milling is better, because the presence of water weakens the agglomeration of fine particles caused by van der Waal force. Mechanical modification can effectively improve the pore structure of fly ash and activate active sites which promote carbonation to form a larger physical wrapping area and strengthen stable carbonate formation. so mechanical modification effectively improves the solidification of heavy metals by carbonation.

Characteristics of Combustion and NOx Emission in a 600 MWe Wall-Fired Boiler Under Varying Coal Mill and Burner Damper Configurations

ABSTRACT To accelerate China’s transition toward providing capacity support and prioritizing electricity generation, detailed research is necessary regarding the continuous peak output of coal-fired boilers during peak periods. However, high-load operation of coal-fired boilers may lead to issues such as NOx emission and increased flue gas temperature. This study conducted industrial experiments on a 600 MWe wall-fired boiler operating under peak conditions (500 MWe), using different pulverized coal mill operating modes. The boiler was optimized by adjusting the damper openings of the burners. Experimental results showed coal powder ignited within 0.2 m of burner outlets, indicating good performance. With the reduction in the damper openings of the burners, the concentration of NOx decreased, and the flue gas temperature gradually dropped, with the maximum temperature differential being 179°C. The ABCEF pulverized coal mill case had high water consumption and flue gas loss, unfavorably affecting economic operation. The ABDEF case delayed temperatures by 100°C, with the lowest NOx concentration at 277 ppm, enhancing environmental friendliness. In addition, the ABCDE case exhibited optimal coal burnout, with 0.838% fly ash carbon content, and the lowest flue gas temperature at 111.49°C, reducing flue gas loss by 5.9% compared to the ABDEF case, showing good economic performance.

Report of RILEM TC 281-CCC: outcomes of a round robin on the resistance to natural carbonation of Portland, Portland-fly ash and blast-furnace cements and its relation to accelerated carbonation

Report of RILEM TC 281-CCC: outcomes of a round robin on the resistance to natural carbonation of Portland, Portland-fly ash and blast-furnace cements and its relation to accelerated carbonation

Lysine-coupled fly ash accelerated CO2 mineralization: Feasibility and reaction mechanism

CO2 mineralization using alkaline solid waste is a promising technology for integrated pollution reduction and carbon sequestration. This paper proposed an efficient and environmentally friendly method for lysine-coupled fly ash accelerated CO2 mineralization. And the feasibility of this process was preliminarily explored. The results showed that under mild operating conditions, the promotion of lysine achieved a carbon sequestration capacity of approximately 122.60 g-CO2/kg-FA, with a CO2 mineralization efficiency of 72.84 %. Additionally, lysine acted as a crystal form regulator for CaCO3, resulting in vaterite CaCO3 at an appropriate lysine concentration. Using 13C nuclear magnetic resonance (NMR), the carbamates, bicarbonates/carbonates, and Lys/protonated Lys at different reaction stages were considered to propose a novel reaction mechanism for the Lys-FA-H2O-CO2 system. It indicates that lysine accelerates key reaction steps in the fly ash carbonation process. Lysine, acting as a proton acceptor and promoting carbamate formation, accelerates the mass transfer of CO2 from the gas phase to the liquid phase. Meanwhile, the presence of lysine enhances the leaching capacity of Ca2+ by three times compared to H2O.

Classification performance analysis of a louver classifier with a tilted sidewall and its application to the separation of unburned carbon from biomass combustion ash

Separating unburned carbon (UC) from biomass combustion ash is necessary to achieve high-quality ash as recyclable raw material and improve energy efficiency by reburning the UC in the furnace. In this study, a novel louver classifier geometry with tilted sidewall was proposed to separate the UC from biomass ash and its classification performance was analyzed via experiments and simulations. The louver classifier with a tilted sidewall provided a smaller 50% cut size and classification accuracy index indicating that the separation performance is improved. The CFD simulations revealed that tilted sidewall in the louver increased gas flow downward velocity in the classification region, increasing the inertia of the particles, and causing more particles to leave gas flow and deposit into the collection box as coarse ash. The UC of classified combustion ash increased with a decrease in the median mass diameter, indicating that the classification process for combustion ash produced coarse ash with a lower UC. The tilted sidewall in the modified louver classifier increased the reduction of unburned carbon (RUC) in ash up to 83.8%. The RUC increased with a cut size of the classified ash which was achieved when a high inlet flow velocity and high blow-up ratio are applied.

Assessing the carbonation potential of wood ash for CO2 sequestration

Wood ash, a byproduct of wood combustion, poses environmental challenges when disposed of in landfills. This study explores a sustainable alternative by investigating the carbonation of wood ash, a process converting CO2 into stable carbonate minerals. With increasing concerns about waste management, this research aims to identify optimal carbonation conditions by varying relative humidity, liquid-to-solid ratio (L/S), and temperature. Results demonstrate that the ideal conditions for wood ash carbonation involve a moderate relative humidity of 55%, room temperature at 25 °C, and a lower L/S ratio. Thermogravimetric analysis (TGA) indicates that extended curing times increase CaCO3 formation. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) confirm the presence of carbonate phases. Mechanical strength tests reveal that samples with lower porosity and higher carbonation products exhibit superior strength. This study contributes to the understanding of wood ash carbonation but also emphasizes its potential practical applications in construction materials as light aggregates in cement concrete. The research explores the implications for sustainable waste management, offering insights into environmentally and economically viable solutions for wood ash recycling.

Effect of ultrasonic-hydraulic coupling cavitation pretreatment on carbon extraction from coal gasification coarse slag by flotation

Coal gasification coarse slag represents a type of low-value solid waste produced in coal gasification. This study investigated how the pretreatment of the pulp obtained from coal gasification coarse slag affects carbon extraction by flotation. Ultrasonic treatment can promote carbon ash separation. Flotation results revealed that at an ultrasonic action time of 15 min, the ultrasonic power was 90 W and the microbubble generator flow rate was 300 ml/min. Moreover, the best flotation effect was observed under these conditions. Compared with the results obtained for conventional flotation, the concentrate ash content decreased from 36.88 % to 25.51 % and the combustible substance recovery index increased from 79.84 % to 92.91 %. After coupled cavitation treatment, coal gasification coarse slag exhibited a reduced particle size, an increased specific surface area, a smooth and clean surface, a reduced number of surface inorganic elements, an increased number of pores and a remarkable carbon ash separation effect. This study can provide a reference for special methods such as ultrasonic-hydraulic coupling cavitation to strengthen the flotation of coal gasification coarse slag.

Study on the carbon evolution laws and carbon accounting methods of coal-fired boilers under deep peaking

The power grid needs to rapidly modify its power output to counterbalance the variable nature of new energy generation. This necessitates enhanced deep-peaking capabilities in coal-fired boilers. This research investigates the CO2 emission evolution in a 330 MW tangentially fired pulverized coal boiler under varying loads, secondary air distributions, and coal blending to elucidate the CO2 emission evolution dynamics of coal-fired boilers. A comprehensive three-dimensional model of the gas-solid two-phase flow in the furnace, coupled with the coal-firing chemical reactions, is established. Finally, a novel carbon accounting method is proposed, which enhances the accuracy of carbon emission results under various conditions. Results indicate that as the load decreases, combustion becomes progressively less complete. At a 30 % load reduction, carbon conversion into CO2 is minimized, and the amounts of CO and unburned carbon in the fly ash peak. Using equal air distribution and layering coal blending—inferior in layers A, B, and C; general in D; and superior in E—across five burners enhances CO2 production under low-load conditions. Consequently, the levels of CO and unburned carbon in the fly ash are reduced. These research findings serve as a reference for precise accounting of boiler carbon emissions.

Composition and Structural Characteristics of Coal Gasification Slag from Jinhua Furnace and Its Thermochemical Conversion Performance

Gasification technology enables the clean and efficient utilization of coal. However, the process generates a significant amount of solid waste—coal gasification slag. This paper focuses on the Jinhua furnace coal gasification slag (fine slag, FS; coarse slag, CS) as the research subject, analyzing its composition and structural characteristics, and discussing the thermochemical conversion performance of both under different atmospheres (N2 and air). The results show that the fixed carbon content in FS is as high as 35.82%, while it is only 1% in CS. FS has a large number of fluffy porous carbon on its surface, which wraps around or embeds into smooth and variously sized spherical inorganic components, with a specific surface area as high as 353 m2/g, and the pore structure is mainly mesoporous. Compared to the raw coal (TYC), the types of organic functional groups in FS and CS are significantly reduced, and the graphitization degree of the carbon elements in FS is higher. The ash in FS is mainly amorphous and glassy, while in CS, it mainly has crystalline structures. The weight loss rates of TYC and FS under an inert atmosphere are 27.49% and 10.38%, respectively; under an air atmosphere, the weight loss rates of TYC and FS are 81.69% and 44.40%, respectively. Based on the analysis of the thermal stability of FS and its high specific surface area, this paper suggests that FS can be used to prepare high-value-added products such as porous carbon or high-temperature-resistant carbon materials through the method of carbon–ash separation.

Mitigating CO2 emissions through an industrial symbiosis approach: Leveraging cork ash carbonation

This study explores for the first time the potential use of carbonation as a method for managing cork ash, a byproduct of biomass waste incineration. Additionally, the cork ash was combined with fly ash from municipal solid waste incineration to leverage the carbonation reaction's ability to stabilize heavy metals. The findings suggest that subjecting biomass ash to carbonation can lead to the formation of mineral carbonates, effectively capturing CO2 and reducing its release into the atmosphere. The combination of various alkaline wastes and the stabilization of leachable heavy metals through carbonation reactions also opens opportunities for synergies between different industrial sectors. Finally, the study proposes a route for the obtained materials valorisation via ‘end of waste’: the reuse of the resulting materials as substitutes for natural resources, particularly in applications like building materials and polymer composites, can further enhance carbon dioxide savings.

Ultrasonication Improves the Flotation of Coal Gasification Fine Slag Residue

Coal gasification fine slag (CGFS) is a significant source of solid waste requiring improved treatment methods. This study primarily investigates the mechanism of ultrasonic treatment in optimising flotation-based decarbonization of CGFS and its impact on CGFS modified with surfactants. The objective is to maximise the carbon ash separation effect to support the clean and efficient utilisation of CGFS. Flotation experiments revealed optimal conditions at an ultrasonication power of 180 W for 2 min and a slurry concentration of 60 g/L, resulting in a residual ash content of 82.59%. Particle size analysis, scanning electron microscopy (SEM), and Brunner−Emmet−Teller (BET) measurements demonstrate the efficacy of ultrasound in extracting inorganic minerals from the surface and pores of residual carbon, consequently reducing both pore and particle sizes. Fourier transform infrared spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) analyses indicate alterations in the surface chemistry of CGFS induced by ultrasound treatment. The content of hydrophilic groups decreased from 31.64% to 29.88%, whereas the COO- group content decreased from 13.13% to 8.43%, consequently enhancing hydrophobicity. Adsorption experiments demonstrate an increase in surfactant adsorption capacity following ultrasonic treatment. Furthermore, ultrasonic treatment facilitates the desorption of surfactants previously adsorbed onto the surfaces of CGFS residue. Therefore, optimal flotation is obtained by applying ultrasonic pretreatment to CGFS before adding flotation chemicals. Upon the addition of Polysorbate (Tween-80), the residual ash content increased 90.17%.

Study on the physical encapsulation mechanism of heavy metals in fly ash carbonation solidification based on synthetic pellets

The physical encapsulation mechanism prevents the leaching of heavy metals by forming calcium carbonate-encapsulated fly ash through the reaction of carbon dioxide and calcium oxide. However, current research in this area primarily involves qualitative analysis, focusing on various methods to enhance the fixation effect of heavy metals. There is a lack of quantitative description regarding how physical encapsulation solidifies heavy metals, and the solidification mechanism of heavy metals is challenging to verify through macroscopic experiments. In this paper, a method for synthesizing small fly ash particles into pellets is proposed to quantitatively study the mechanism of physically encapsulating heavy metals. The data from the carbonation reaction and leaching reaction are fitted using the shrinking core model. The depth of carbonation increases with the lengthening of carbonation time, and the physical encapsulation strengthens the immobilization of heavy metals. The leaching of heavy metals after carbonation can be categorized into three stages based on the shrinking core model: external diffusion, internal diffusion, and chemical reaction control. Synthetic pellets enhance all three stages, especially the external diffusion, which is not detectable with fly ash powder. The fitting results of the experimental data for the carbonation reaction of the enlarged synthetic pellets and the shrinking core model are both above 0.9. This indicates that the primary barrier to leaching of heavy metals is the physical encapsulation formed by the carbonation reaction following the shrinking core model. The physical encapsulation serves as the primary mechanism for the solidification of heavy metals during the carbonation process.

Application of ultrafine bubbles for enhanced carbonation of municipal solid waste incineration ash during direct aqueous carbonation

Municipal solid waste incineration fly ash was selected as the alkaline Ca-bearing solid waste, and a series of direct aqueous carbonation experiments using 10% CO2 gas were conducted to showcase the capability of ultrafine bubbles (UFBs) in enhancing carbonation efficiency. Results from the experiments, conducted using a one-pass water flow system, revealed that carbonation without UFBs increased the CO2 content of the ash from 59 to 200 mgCO2/g (an increase of 141 mgCO2/g), while the presence of UFBs elevated it to 237 mgCO2/g (an increase of 178 mgCO2/g). Consequently, the introduction of UFBs led to a 26% increase in CO2 content in ash [(178−141) / 141]. This improvement was primarily attributed to the enhanced carbonation efficiency for particles ≥ 46 µm. The positive impact of UFBs was more evident (62% increase in CO2 content in ash) in experiments using a water circulation system, where carbonation proceeded at a faster rate compared to the one-pass water flow system. In terms of the mechanism, X-ray diffraction and scanning electron microscopy analyses indicated that UFBs facilitated the removal of CaCO3 deposition, which inhibited Ca(OH)2 dissolution. To the best of our knowledge, this study is the first to demonstrate the favorable influence of UFBs on fly ash carbonation efficiency.

Research progress on biomass ash carbon capture and storage

Carbon capture and storage (CCS) technology is an important way to slow down the continuous increase in atmospheric CO2 concentration and to achieve the dual carbon target. Carbon capture and storage through biomass ash is a secure, permanent, and environment friendly way. To better understand the characteristics of biomass ash carbon capture and storage, we summarized progresses on biomass ash carbon capture and storage, clarified the mechanisms of biomass ash carbon sequestration, analyzed the influencing factors, and explored its applications in various domains. The capacity of CCS by biomass ash mainly derived from alkaline earth metal oxides of CaO and MgO. The actual carbon sequestration efficiency is affected by factors such as biomass source, chemical composition, temperature, humidity, pressure, and CO2 concentration. However, the underlying mechanism is unclear. The CCS capacity of biomass ash significantly impacts its potential applications in building materials reuse, soil quality improvement, and adsorbents carbon capture and storage absorbent preparation. Long-term research is critically needed. For future studies, we should strengthen the research on the carbonization efficiency of biomass ash from multiple sources, establish a database related to the impact of biomass ash carbonization, build a methodological system to promote scientific management of biomass ash, develop biomass ash carbon capture and storage technologies, and quantitatively assess its role in carbon sequestration.

Carbonation and permeation behaviour of geopolymer concrete containing copper slag and coal ashes

The current study primarily evaluates the carbonation and permeation resistance of coal bottom ash (CBA) and copper slag (CS) based geopolymer concrete (GPC). The strength parameters along with non-destructive tests were also performed for reference. CS and CBA were used as a 10%, 30% and 50% replacement of natural fine aggregates (NFA). Fly Ash (FA) was used as a binder and all seven mixes were subjected to oven curing at 65 °C for 24 h. The molarity of NaOH was kept constant (12 M) along with Sodium Silicate/Sodium Hydroxide ratio of 2. With inclusion of CS the carbonation depth, initial and capillary absorption has been decreased by 30%, 23% and 19% respectively with respect to control mix. The above-mentioned values have been increased by 28%, 27% and 58% in CBA based GPC. GPC mix containing 30% replacement of CS as sand has been considered to be appropriate for carbonation and permeation aspects.

Alternative sorbents for mercury capture in flue gas from lignite combustion

This paper presents an experimental study of two of alternative sorbents for mercury capture from the lignite combustion flue gas. The sorbents are based on calcium hydroxide and aluminosilicate, using different modifications. A commercially available activated carbon (AC) with bromine impregnation was selected as the reference sorbent. This sorbent is a state-of-the-art solution for mercury removal in industrial combustion facilities. However, its application is costly for power plants because of the market price of the AC and because the presence of carbon in the fly ash can complicate its further use, which gives a strong motivation for exploring new alternatives. Experimental investigation was carried out in a 500 kW pilot-scale bubbling fluidized bed combustor using a lignite with naturally high mercury content. A injection system of our own design and construction was used to supply the sorbents to the flue gas downstream of the combustor at a flow rate in the range of 100–500 mg/m3N of the flue gas. Continuous measurement of mercury concentration was used upstream the sorbent injection and downstream the fabric filter, simultaneously. Different sorbent injection rates and flue gas temperatures at the sorbent injection point were examined.The mercury capture ratio was evaluated considering the Hg balance in the combustor. It was shown that the mercury self-capture by the fly ash in the fluidized bed combustion system varies approximately from 30 to 90 %, depending on the SO2 concentration. The Hg capture ratio for calcium hydroxide was in a range of approximately 15–25 %, while for aluminosilicate it was 25–45 %, determined by the actual conditions of the flue gas and the initial Hg concentration. This is in the range of the reference AC, which typically reaches from 25 – 95%. The increased injection rate of the sorbents was reflected in the Hg capture ratio, but its promotion was observed only in the case of the aluminosilicate sorbent. A correlation of the Hg capture ratio with the flue gas temperature at the injection point was also clearly identified only for the aluminosilicate sorbent, when an increase in the temperature led to increasing in the capture ratio.

Preparation of hierarchically porous carbon ash composite material from fine slag of coal gasification and ash slag of biomass combustion for CO2 capture

With the spread and development of industrialization, CO2 emissions are increasing dramatically, posing a serious threat to the global ecosystem. Based on coal gasification fine slag (CGFS) pore structure characteristics, CGFS was used to prepare carbon-ash composite hierarchically porous material by chemical activation and hydrothermal methods for CO2 capture. It would achieve comprehensive and high value utilization of CGFS. In addition, the biomass combustion ash slag (BCA) is rich in alkali and metal elements, there are extremely important influence on CGFS pore formation. Therefore, the alkali and potassium sources were extracted in leaching experiments for CGFS-based porous materials preparation. It was found that the prepared porous material had a large specific surface area (1270 m2/g), a graded porous structure and excellent CO2 adsorption capacity (4.06 mol/kg at 0 °C), while the pores of the BCA-impregnated porous material were further developed with a larger specific surface area (1406 m2/g) and more functional groups on porous material surface. All these results indicate the relevance between using BCA impregnates and material performance enhancement. Furthermore, the CGFS-based graded porous composite porous materials have great potential for repurposing in practical and industrial CO2 adsorption applications.

Effect of Minor Oxide and Residual Carbon on Coal Ash Crystallization Behavior and Slag Properties during Coal Gasification: Critical Literature Review and Thermodynamic Simulation.

Coal-ash-associated problems seriously limit the industrial application of entrained flow coal gasification. There have been many studies of this issue. However, many problems still need to be fully understood, especially regarding the effect of minor oxides and residual carbon on the crystallization of slag in coal ash systems. Crystals formed in slag affect the slag properties, especially its viscosity. This article reviews the crystallization behavior of coal ash slag and its impact on ash fusion temperature (AFT) and temperature of critical viscosity (Tcv). A thermodynamic simulation using FactSage 7.3 thermochemical software was performed to study the effect of minor oxides (i.e., Na2O, K2O, and TiO2) and residual carbon at a temperature range of 1000-1700 °C on the phase transformation in the oxide system. The literature review reveals that the minor oxides and residual carbon in coal ash affect the AFT and the coal slag's Tcv. The thermodynamics simulation indicated that Na2O, K2O, and TiO2 tend to decrease Tcv, while the residual carbon increase Tcv.

An investigation of nanobubble enhanced flotation for fly ash decarbonization

Froth flotation is often employed to remove unburned carbon in the fly ash produced as a coal combustion by-product before it can be utilized in the cement or similar industries. However, with the deterioration of coal quality and environmental regulations getting stricter, fly ash has become increasingly more difficult to be purified by the flotation process and the limitations of traditional flotation techniques have become more obvious for ultrafine particles such as fly ash. Nanobubbles have proven effective in enhancing the flotation performance with fine and ultrafine particles. In this study the effect of nanobubbles on fly ash flotation decarbonization and underlying mechanisms have been investigated with a flotation column under various experimental conditions using a Chinese fly ash sample. The results have demonstrated that nanobubbles are able to significantly improve the efficiency of decarbonization of fly ash flotation. Typically the use of nanobubbles increased the recovery of unburnt carbon by 3–15 % and reduced the fly ash LOI by 0.2 %–3.5 %. It has also been shown that nanobubble flotation reduced the required dosages of frother and collector by approximately one half. New mechanisms of nanobubbles improving fly ash decarbonization flotation performance were explored from the perspectives of bubble-particle interactions and solution surface tensions.

Efficient decarburization modification of coal gasification fine ash by microwave field activation

The presence of residual carbon in coal gasification fine ash (CGFA) significantly impacts its subsequent processing and utilization. This paper proposes and investigates the use of microwave field heating to decarburize CGFA, exploiting its favorable microwave absorbing characteristics attributed to its composite structure comprising carbon, iron, and water. The experimental results demonstrate an 81% reduction in the required time and a 74% decrease in energy consumption (based on preliminary calculations) to achieve a decarburization rate of 95% compared to conventional thermal electric furnace calcination methods. The treated CGFA exhibits optimized mineral species, reduced electron binding energy, enhanced solubility, and increased heat release intensity during hydration, leading to improved reactivity of mineral phases in alkaline environments. Furthermore, when used as supplementary cementitious material, the activity index of CGFA shows a remarkable 21% increase in macroscopic performance testing.