Carbon In Coal Fly Ash Research Articles

Carbon removal flotation performance and economic analysis of different coal fly ash using waste fried oil as a collector

Collector consumption in flotation is significant, and petrochemicals like kerosene, being non-renewable and expensive, are commonly used collectors; therefore, finding suitable alternatives to reduce costs is essential. Waste fried oil (WFO) possesses properties similar to those of kerosene, making it a viable substitute for flotation processes. In this study, the flotation performance was analyzed and economic analysis of WFO as a collector was performed for circulating fluidized bed furnace fly ash (CFBFA) and pulverized coal furnace fly ash (PCFFA). The interaction mechanism between WFO and fly ash was analyzed using contact angle, Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) tests. The findings revealed that the optimal WFO dosage for coal fly ash closely correlates with the combustion technology used to obtain it. The study also established well-fitted curves for the loss on ignition (LOI) of CFBFA and PCFFA with changes in WFO dosage. FTIR and XPS analyses revealed that the interaction of WFO carbon chains with nonpolar regions on the surface of unburned carbon in coal fly ash resulted in an increase in hydrophobic carbon chain groups on the surface of unburned carbon, and the combination of oxygen-containing groups in WFO with the hydrophilic sites on the surface of unburned carbon were the main reasons for the enhancement of hydrophobicity of unburned carbon particles. Moreover, the economic analysis revealed that flotation of 1 t of CFBFA and PCFFA with WFO can yield profits of 1.91 USD and 1.11 USD more, respectively, compared with kerosene, which has practical applications in industry.

Hydrothermal synthesis of zeolites from residual waste generated via indirect carbonation of coal fly ash

Indirect carbonation, a technology to store CO2 and produce stable CaCO3 and MgCO3, involves elution of Ca and Mg from industrial waste and subsequent carbonation. Although substantial residual waste is generated after the elution of Ca and Mg, its recycling attributes have not been adequately scrutinized. The residual waste has lower Ca and Mg contents and higher Si and Al contents than those of the raw material (i.e., industrial waste). This study involves the hydrothermal synthesis of zeolite-P using residual waste from indirect carbonation, conducted at both 100 and 180 ℃. The properties of these zeolites are compared with those synthesized from coal fly ash (CFA). The synthesized zeolites were characterized by X-ray diffraction, field emission scanning electron microscope, thermogravimetric analyzer, and Brunauer–Emmett–Teller (BET). A high zeolite conversion efficiency was achieved through a hydrothermal reaction (up to 87%), even though Si and Al were not added to the residual waste. Additionally, the cation exchange capacity and BET specific surface area of the synthesized zeolites were high (200 cmol kg−1 and 73 m2 g−1, respectively). These findings highlight the possibility of synthesizing zeolites using the residual waste from indirect carbonation as an alternative to conventional zeolite synthesis using industrial waste such as CFA. The synthesized zeolite-P is expected to be effective in wastewater treatment, detergent manufacturing, and water softening.

Environmentally-friendly emulsion-like collector prepared from waste oil: Application in floatation recovery of unburned carbon in coal fly ash

The decarbonization of waste coal fly ash (CFA) and the reuse of waste oil are concerned in this study. The waste oil in kitchen waste was purified and emulsified into emulsion-like collector to reduce the dependence of CFA flotation on non-renewable collector. The feasibility of preparing microemulsion from waste oil by using OP-10 as surfactant, n-pentanol or n-hexanol as co-surfactants was studied. The pseudo ternary phase diagram was used to analyze the emulsification performance. Emulsification results show that waste oil can be prepared into microemulsion under harsh conditions. The concept of an emulsion-like, which does not require water, was proposed because the flotation process was carried out in an aqueous environment. Three emulsion-like (M waste oil:SAR = M2:8, M5:5, M8:2) were used to verify the effect of the ratio of surfactant on the decarburization efficiency. The flotation results show that the carbon removal rate can reach 94.64% under the conditions of appropriate reagent ratio and dosage. In addition, the flotation kinetic analysis was verified, nonlinear fitting results show that the classical first-order model can more accurately explain the flotation kinetic characteristics of CFA flotation by emulsion-like collector. XPS analysis results show that the content of carbon-based hydrophobic groups in CFA is only 59.9%, which indicates that the assistance of collector is necessary to improve the flotation efficiency. The present study realizes the goal of “treating waste with waste” and provides an innovative idea to realize the reuse of CFA and waste oil.

Circular indirect carbonation of coal fly ash for carbon dioxide capture and utilization

Mineral carbonation of alkaline wastes is a promising route for carbon dioxide (CO2) capture and utilization. An exploration of the carbonation potential of relatively inert alkaline wastes is important to develop mineral carbonation. Large amounts of coal fly ash are generated from coal-fired power plants and must be treated. A fundamental study of the circular indirect carbonation of coal fly ash was proposed and fly-ash leaching, calcium carbonate (CaCO3) precipitation, and solution regeneration with bipolar membrane electrodialysis (BPED) stages were investigated. In the leaching stage, the nitric acid/calcium ratio affected the solution pH and impurity concentration. The leaching behavior of impurities was related mainly to colloidal precipitation. Approximately 97.3% calcium in solution reacted to form precipitated CaCO3, and a higher-purity CaCO3 precipitate was obtained when a lower nitric acid/calcium ratio was used in the leaching stage. The CO2 conversion was 92.9% and the CO2 uptake efficiency was ~0.011 g-CO2/g-fly ash, which can be improved by optimizing the liquor purification process. Fundamental liquor purification was performed. Solution regeneration by BPED was evaluated by investigating the effect of electric potential and current density on the regeneration yield, current efficiency, and power consumption. A comprehensive assessment, including cost and CO2 balance, was conducted, and future interesting research on circular indirect carbonation was suggested.

Experimental investigation of the attachment of unburned carbon in coal fly ash to a stationary air bubble in aqueous solutions

Separating unburned carbon (UC) from coal fly ash (CFA) via froth flotation may be quantitatively characterized by the bubble–particle attachment angle (BPAA), susceptible to operational factors. This study established a novel experimental system to directly observe attachment behaviors between irregularly shaped UCs and a stationary air bubble. The independent and coupling effects of the main operational factors on the BPAA, including solution temperature, pH value, and collector dosage, were investigated via high-speed photography. The BPAA increased rapidly at the beginning of magnetic stirring for each factor, and then grew steadily when agitation time exceeded 180 s, gradually leveling off at its maximum value. The maximum BPAAs were 195°, 176°, and 169° at solution temperatures of 35, 30, and 25 °C, respectively. They were 169°, 144°, and 166° for pH values of 7, 9, and 11, respectively, and 169°, 189°, and 184° at collector dosages of 0, 1, and 2 mL/L, respectively. An overhigh dosage of collector kerosene resulted in oil agglomeration that hindered collision and adhesion. Response surface methodology (RSM) was adopted to analyze and optimize interactions between various factors, indicating that the predicted model that correlated the BPAA and the independent variables were in good agreement with the experimental data. The results show that the importance degree in BPAA decreases in a certain order. Moreover, several optimum solutions were obtained to achieve a maximum BPAA (~196°) under suitable conditions. The outcomes of this study strengthen bubble–particle attachment during the recovery of UCs from CFA by froth flotation, contributing to the comprehensive utilization of CFA.

CO2 sequestration and simultaneous zeolite production by carbonation of coal fly ash: Impact on the trapping of toxic elements

Coal-fired power plants are main contributors to atmospheric CO2 emissions. They also produce huge amounts of coal fly ash (CFA) waste, which is typically landfilled, posing significant environmental risks due to its high content of potentially toxic elements (PTE). However, CFA is an alkaline aluminosilicate-rich waste, which offers the possibility of CO2 mineral capture and the production of economically-relevant mineral by-products such as zeolites. Yet, the combined carbonation and zeolite production from CFA resulting in PTE trapping has never been explored. Here we show that under mild hydrothermal conditions (150 °C) and depending of various process parameters such as pH and background alkali metal ion in (bi)carbonate solutions, a carbonation efficiency of up to 79 %, with a net CO2 mineral capture of 0.045 g/g CFA can be achieved, even when using a low Ca and Mg (3.72 wt% CaO, 1.74 wt% MgO) Class F fly ash. Moreover, amorphous zeolitic precursors and different crystalline zeolites (yield up to 60 wt%) are simultaneously obtained, and PTE in CFA are effectively trapped into the newly formed calcite, zeolitic precursors, and zeolite phases. This is the first time that a combined study of carbonation, zeolitization and PTE trapping in newly formed phases has been developed. These results have important implications for carbon capture and storage, as well as for the safe reutilization and disposal of CFA waste.

On the utilization of waste fried oil as flotation collector to remove carbon from coal fly ash

In this paper, the waste fried oil was used to remove the unburned carbon in coal fly ash during flotation process, and found that the waste fried oil could be a novel collector for the removal of carbon from coal fly ash. The results implied that the wetting rate of the fly ash after treated by waste fried oil was decreased, meanwhile the contact angle was increased. A significant decrease in wetting heat was observed, which indicated a weaker interaction between deionized water and fly ash after treatment with waste fried oil. Flotation tests showed that the content of unburned carbon could be reduced effectively through froth flotation when took waste fried oil as collector. FTIR analysis testified that waste fried oil had abundant oxygen-containing groups that could be adsorbed in a carbonaceous matter to achieve hydrophobization. X-ray photoelectron spectroscopy, scanning electron microscope, and energy dispersive analyses showed that the main compositions of flotation concentrate products were unburned carbon, whereas the tailing products consist of aluminum and silicon, which confirmed the superior separation performance when the waste fried oil was used as a collector in coal fly ash flotation. This investigation provides an approach to remove the unburned carbon in coal fly ash based on the principle of “waste control through waste”, which can solve the environmental problems brought by large amounts of both coal fly ash and waste fried oils.

Effect of the intensification of preconditioning on the separation of unburned carbon from coal fly ash

Coal fly ash is the main by-product in coal combustion power stations. Unburned carbon in coal fly ash indicates energy waste and acts as a potential obstacle to the utilization of coal fly ash. The purpose of the study involves examining the flotation intensification for the separation of unburned carbon from coal fly ash in the presence of preconditioning. Pulp conditioning before flotation using a stirred tank ensuring that the flotation process is effective to the maximum possible extent. In this paper, prospective conditioning-flotation tests were conducted to study the process intensification for the froth flotation of coal fly ash. The interaction behavior of preconditioning on the separation of unburned carbon was investigated by conducting flotation tests. Six flotation kinetic models were used to fit the flotation kinetic test data of cumulative unburned carbon recovery under different conditioning speeds by using the 1stOpt statistical analysis software, and the results indicated that the model 2 of first-order model with rectangular distribution was most reasonable for the data fitted of coal fly ash flotation with preconditioning. Additionally, the microstructure and element composition of concentrates and tailings ash were presented by SEM-EDS and XPS analysis, and indicated that the separation efficiency of unburned carbon from coal fly ash could be improved significantly by the process intensification. The flotation intensification mechanism of preconditioning was discussed based on the surface hydrophobicity and floatability of coal fly ash particles. The contact angle increased with increases in the conditioning speed, while the induction time decreased, and there were significant differences in the state of bubble-particle attachment.

Self-sustaining carbon capture and mineralization via electrolytic carbonation of coal fly ash

This study presents a new electrolytic carbonation process to synergize the treatment of different waste streams generated by power plants, including fly ash, brine wastewater, and CO2. The acidity generated by electrolysis of brine electrolyte directly liberates calcium from fly ash. The metal ions balance the OH− produced at the cathode to form hydroxide, which then fixes CO2 into high purity carbonate precipitates. Results show that electrolysis increased fly ash dissolution by 32.4% compared to the control with spontaneous dissolution of fly ash, and the carbonation process captured 89% more CO2 and increased capture capacity from 9.75 to 18.42kg-CO2/t-fly ash in the NaCl electrolyte. The energy expenditure was 19.4–29.3kJ/mol-CO2, lower than that required for sorbent or solvent based post-combustion carbon capture. The process takes advantage of all waste streams generated on site and can consolidate traditionally separated treatment processes to save costs, produce energy and value-added products, as well as generate carbon benefits.

Chemical forms of the fluorine, chlorine, oxygen and carbon in coal fly ash and their correlations with mercury retention

Fly ashes recovered from the particulate control devices at six pulverized coal boiler unites of China, are studied using an X-ray photoelectron spectroscopy (XPS) with a particular focus on the functionalities of fluorine (F), chlorine (Cl), carbon and oxygen on fly ash. It is found that the inorganic forms of F and Cl are predominant on the ash surface in comparison with their organics, and the proportion of organic Cl is relatively higher than that of organic F. Similar results are also obtained in the bulk by correlating the F and Cl contents with those of the unburnt carbon and other compositions in ash. Strong correlations of mercury retention with surface carbon–oxygen functional groups indicate that the CO, OH/CO and (OCO)O on surface are of significant importance for mercury retention in fly ash. Their surface concentrations are related to coal type. The presence of Cl in fly ash helps with mercury retention. No obvious effect of F is observed.

Direct mineral carbonation of coal fly ash for CO2 sequestration

Developing countries face the projected scenario of increased CO2 emissions in the coming years as their major dependence for power generation relies on the coal reserves. Mineral carbon sequestration using industrial alkaline solid residues is a promising technology for carbon capture and storage. In this laboratory work, direct mineral carbonation of coal fly ash (CFA) through gas–solid as well as aqueous route has been studied with 100% CO2 gas in a stainless steel reactor at low pressure (<10 bar) and room temperature. The dry route demonstrated to be a slow process, wherein the maximum sequestration capacity was found to be 26.3 g of CO2/kg of CFA at 10 bar for 1 h. In the case of wet carbonation, the maximum capacity achieved was 50.3 g of CO2/kg of waste with the CFA water slurry of 15 as L/S ratio, stirred at 900 rpm at 4 bar for 2 h. The carbonation process was evidenced by the characterization of the carbonated CFA using FT-IR, XRD, SEM and TGA. The results show that CFA can be utilized for carbon capture through the simple, direct carbonation approach and the process parameters play vital role in effective sequestration.

A laboratory-scale study of the aqueous mineral carbonation of coal fly ash for CO2 sequestration

Mineral sequestration of waste materials provides a promising method for CO2 sequestration, due to its potential as a finishing step in industries which produce CO2 and alkaline solid by-products. However, a number of challenges in mineral carbonation that remain to be resolved, including overcoming the slow kinetics of mineral–fluid reactions, dealing with the large volume of source material required, and reducing the energy needed to hasten the carbonation process. In order to overcome the slow reaction kinetics, experiments on accelerated carbonation are being conducted worldwide. As a result, studies of the operational parameters of the carbonation reaction are progressing. The present study examined the effect of two operational parameters on the mineralization of Australian coal fly ashes for CO2 sequestration at laboratory scale. In this study, carbonation tests were carried out for three Australian coal fly ash samples (S1, S2, S3) inside a continuously stirred reaction chamber. Different water-to-solid ratios (from 0.1 to 1) and reaction temperatures (20–80 °C) were tested under a moderate initial CO2 gas pressure of 3 MPa, and the pressure drop due to carbonation with time was recorded until a constant pressure was achieved at the end of each test. The quantity of CO2 stored in each test was estimated by applying ideal gas law to the test conditions. The formation of carbonates during testing was confirmed by performing micro-structural analysis using scanning electron microscopy. According to the results, a 0.2–0.3 water-to-solid mix ratio recorded the highest sequestration potential for all three fly ashes, and was identified as the optimum for mineralization. The increase of reaction temperature resulted in a faster rate of initial CO2 transfer into the fly ash material but did not have a significant impact on the overall sequestration. Of the three tested ashes, S3 ash sample showed the highest sequestration potential of 27.05 kg of CO2 per ton of fly ash under test conditions. The results confirm the possibility of manipulating the water-to-solid mix ratio and the reaction temperature to enhance the carbonation reaction for mineral CO2 sequestration.

A Novel Method for CO2 Sequestration via Indirect Carbonation of Coal Fly Ash

Coal fly ash is a potential candidate for CO2 mineral sequestration. If calcium is extracted selectively from coal fly ash prior to carbonation (namely indirect carbonation), a high-purity and marketable precipitated calcium carbonate (PCC) can be obtained. In the extraction process, recyclable ammonium salt (i.e., NH4Cl/NH4NO3/CH3COONH4) solution was used as a calcium extraction agent in this study. The influence of time, temperature, agent concentration, and solid-to-liquid ratio on calcium extraction efficiency was explored. NH4Cl/NH4NO3/CH3COONH4 are confirmed to be effective calcium extraction agents for the high-calcium coal fly ash investigated, and about 35–40% of the calcium is extracted into the solution within an hour. The calcium extraction performance is best for CH4COONH4, followed by NH4NO3 and NH4Cl. Increasing temperature from 25 to 90 °C and agent concentration from 0.5 to 3 mol/L only subtly increases calcium extraction efficiency for NH4Cl and NH4NO3, while the positive effect of incre...

粉煤灰未燃碳的深紫外激光诱导击穿光谱分析

粉煤灰未燃碳的深紫外激光诱导击穿光谱分析

Carbon-enriched coal fly ash as a precursor of activated carbons for SO 2 removal

Carbon-enriched coal fly ash was evaluated in this work as a low-cost adsorbent for SO 2 removal from stack gases. The unburned carbon in coal fly ash was concentrated by mechanical sieving and vegetal oil agglomeration. The carbon concentrates were activated with steam at 900 °C in order to develop porosity onto the samples. The performance of these samples in the SO 2 abatement was tested in the following conditions: 100 °C, 1000 ppmv SO 2, 5% O 2, 6% water vapor. A good SO 2 removal capacity was shown by some of the studied samples that can be related to their textural properties. Cycles of SO 2 adsorption/regeneration were carried out in order to evaluate the possibility of thermal regeneration and re-use of these carbons. Regeneration of the exhausted carbons was carried out at 400 °C of temperature and a flow of 25 ml/min of Ar. After each cycle, the SO 2 removal capacity of the sample decreases.

04/01828 Size distribution of unburned carbon in coal fly ash and its implications: Külaots, I. et al. Fuel, 2004, 83, (2), 223–230

04/01828 Size distribution of unburned carbon in coal fly ash and its implications: Külaots, I. et al. Fuel, 2004, 83, (2), 223–230

Adsorption of surfactants on unburned carbon in fly ash and development of a standardized foam index test

The “foam index” test is commonly used for quick evaluation of the suitability, with respect to air entrainment, of pozzolanic additives for concrete. Many foam index test procedures are in common use, and it is difficult to compare results between laboratories. The present paper explores the possibility of standardizing the test for use with coal fly ash pozzolans. It does so by establishing that a series of commercial air-entraining admixtures (AEAs) and pure anionic surfactants all behave in a well-correlated manner, when tested using the same protocol, on a suite of 29 fly ash samples (both class F and class C) obtained from utilities throughout the United States. A pure, reagent-grade surfactant can be chosen as the basis for a standardized test; it appears as though dodecyl benzene sulfonate (DBS) is a good candidate material for such testing. The present results also confirm that it is the carbon in coal fly ash that is the main sink for AEA adsorption in concrete mixtures containing significant amounts of ash. The solution chemistry in the testing mixture is important, and use of cement in the test mix is strongly recommended. Careful attention also needs to be paid to the relative amounts of different components in the mixture to be tested.

Size distribution of unburned carbon in coal fly ash and its implications

A set of nine coal fly ashes, obtained from various US utilities, were fractionated by standard dry-sieving techniques. The carbon contents of the different size fractions were measured, and the nature of the carbon particles was microscopically examined. Significant differences were found in the distribution of carbon in class F and class C ashes. The ‘foam index’ test is commonly used for quick evaluation of the suitability, with respect to air entrainment, of pozzolanic additives for concrete. This test measures adsorption of air entraining admixtures (AEAs) by the carbon in the fly ash. Application of this test to the different ash fractions confirmed that the smallest particle size fractions of ash make the major contribution to AEA adsorption. The carbon from class F ash has a comparable capacity for AEA adsorption as carbon from class C ash, when compared on a surface area basis. What makes the class C carbons apparently ‘worse’ is the fact that they have much higher surface areas than class F carbons (and it is only by virtue of the low carbon mass in most class C ashes that problems with these ashes are not more common). The importance of accessibility of the surface is also clearly seen from these results.

Comparison of the loss-on-ignition and thermogravimetric analysis techniques in measuring unburned carbon in coal fly ash

We have determined, through thermogravimetric analyses (TGA) of seventy fly ash samples obtained from diverse coals and boilers, that loss-on-ignition (LOI) consistently overestimates unburned carbon in fly ash. Experimental results have shown that LOI overestimated unburned carbon by at least 20% in 44% of the fly ashes tested. Although some of these errors may be associated with previously identified thermal decomposition of minerals in fly ash, volatile organic compounds appear to play a role for some of the fly ashes evaluated in this study. This discovery has implications in the use of LOI to calculate combustion losses and monitor fly ash quality by power plant managers. We propose an alternative method to measure unburned carbon based on TGA.

Comparison of the Loss-on-Ignition and Thermogravimetric Analysis Techniques in Measuring Unburned Carbon in Coal Fly Ash

We have determined, through thermogravimetric analyses (TGA) of seventy fly ash samples obtained from diverse coals and boilers, that loss-on-ignition (LOI) consistently overestimates unburned carbon in fly ash. Experimental results have shown that LOI overestimated unburned carbon by at least 20% in 44% of the fly ashes tested. Although some of these errors may be associated with previously identified thermal decomposition of minerals in fly ash, volatile organic compounds appear to play a role for some of the fly ashes evaluated in this study. This discovery has implications in the use of LOI to calculate combustion losses and monitor fly ash quality by power plant managers. We propose an alternative method to measure unburned carbon based on TGA.