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For the production of high-strength lump coke from non-baking coals the processing, agglomeration and gentle coking of the agglomerates are essential steps. In previous studies the influence of the processing regime and the briquetting and coking parameters were systematically analysed. The current investigations combined the intensive processing of German and Indonesian brown coals in a twin-screw extruder and a swing mill with the addition of 5 wt% draff as a coking additive. Briquetting the mixture of coal and draff leads to an increasing briquette compressive strength. This binding capability of the draff is probably caused by the denaturation of protein during the processing in the twin-screw extruder and the swing mill. The produced coke as well offers a high mechanical strength. During the coking process the protein and cellulose material could be partially converted to solid bridges between the particles causing a higher coke compressive strength.

The characteristics and mechanisms of inorganics and mineral transformation, particle agglomeration and ash deposition during Zhundong lignite combustion in a 0.2 t/d lab-scale circulating fluidized bed (CFB) furnace were experimentally investigated. A sample of Zhundong lignite with particle size

Additive water is usually needed to preserve 9–11% moisture content of blended coal in the stamp-charging coking process, which in fact is unfavorable for coking property. An insight into the improvement of coking property of coal blends with much low-rank coal (long flame coal SFC, lignite HLH) by regulating additive water was proposed in terms of its effects on the metaplast fluidity and the particle agglomeration behavior. The results indicate that the cohesiveness of gas coals (GC) can be properly enhanced by adding water. The restrictions on the condensation of aromatic structures and the break-up of –CH2– structure and the development of the polyhydroxy groups in aromatic structures are favorable to increase the fluidity of metaplast after adding water, as demonstrated by the optical texture and FTIR analysis of the semicoke (450 °C). The great difference in the hydrophilic properties for various rank coals leads to the particle agglomeration of gas coal and fat coal (GC and FC), which makes them difficult to mix uniformly with SFC after adding water, thus reduces the coking property. A reasonable approach of adding water suggests that H2O and SFC should be well mixed prior to blending with caking coals, which can lead to a uniform particle distribution and a better coking property. This approach promotes the direct and efficient utilization of low-rank coal (especially lignite) by the blending coking with no or less drying and dewatering processes.

A comprehensive analysis of coal quality factors affecting coal agglomeration characteristics was carried out. The influence weight of seven main coal quality indices on agglomeration was calculated by the entropy method. Furthermore, a reliable and comprehensive coal quality index was obtained to evaluate the characteristics of coal agglomeration by the agglomeration experiment results. The proximate analysis, ultimate analysis, and petrographic analysis results were applied for the analysis of organic constituents. The XRF and ash fusion temperatures were applied for the analysis of inorganic constituents. Results show that there is an absolute positive correlation between the C/H, FC/V and the characteristics of coal agglomeration. Both of the vitrinite content and the average reflectivity of the vitrinite have a positive effect on the coking ability of coal. Alkali oxides not only have a low melting point but also can react with Si and Al to form low melting point eutectics. Both of these characteristics result in coal ash slagging. The entropy method was adopted to analyze the effect weight of C/H, FC/V, vitrinite content Vi, vitrinite average reflectivity Rave, ash deformation temperature (DT), Base/Acid ratio (B/A) and Silicon ratio (G) on the agglomeration characteristics of coal. The weights are 11%, 10%, 26%, 12%, 9%, 14% and 18%, respectively. Among them, vitrinite content had the largest effect, and DT had the least effect. In addition, an empirical index of coal agglomeration characteristics is proposed, and the discriminant limits are provided. The results are helpful to the evaluation of coal agglomeration, and useful to the safe and efficient operation of boilers.

The co-combustion of sewage sludge and woody biomass is a key issue in coal power plants. Different combustion and ash behaviors of sewage sludge and woody biomass cause unpredictable operating concerns. In this study, the combustion and ash agglomeration behavior of blended fuel of sewage sludge and woody biomass (BSW) were investigated while coal co-combusted with it. Thermogravimetric analysis (TGA) revealed that adding a high amount of BSW into the coal lowered volatilization, ignition, and burn-out temperature. The char combustion reactivity of coal differed from that of BSW. The shrinking core model (SCM) and volumetric reaction model (VRM) were used to fit the char combustion reactivity of coal and BSW. In the case of ash agglomeration behavior, BSW addition led to increasing particle agglomeration at fouling temperatures. In particular, phosphorus composition influenced particle growth, which was verified using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM–EDX) analysis. Furthermore, the ash mixture ratio of BSW and coal changed the intensity of the phosphorus-bearing mineral phase from X-ray diffraction (XRD) analysis, and finally influenced the melting temperature of the ash.

Oil agglomeration can be a promising technique to recover fines and ultra-fines coal particles from the discarded tailing generated from coal preparation plants. In the present study, an artificial neural network (ANN) and response surface methodology (RSM) was used to predict the behavior of coal oil agglomeration in terms of % ash rejection (% AR) and % combustible matter recovery (% CMR). A three layered Feed Forward Neural Network was developed by varying process variables such as solid concentration (SC), oil dosage (OD) and agglomeration time (AT). Waste soybean oil was used as bridging liquid. An approach of Multilayer Forward Back Propagation Neural Network has been used in conjugation with the hyperbolic tangent sigmoid (tansig) as transfer function. The network is well trained (learning) with Levenberg-Marquardt (LM) algorithm. For further improvement in the generalization of the developed ANN model Bayesian regularization technique has been adopted. Sensitivity analysis was performed using Garson’s algorithm, Pearson correlation coefficient and Connection weight approach. The % CMR values predicted from ANN have been in good agreement with the obtained experimental values (R2 0.9965) and shows better correlation between predicted and observed values than RSM (R2 0.9892). Also, for % AR the correlation (R2 0.9965) obtained using ANN found to be higher than RSM (R2 0.9956).

An effective bed material is crucial to remit slagging/agglomeration for high-sodium lignite during circulating fluidized bed (CFB) gasification. In this study, the exploration of effective bed material for use as slagging/agglomeration preventatives of high-sodium lignite mined from Zhundong district was conducted in a 0.4 T/D CFB test system. Three mineral materials, SiO2-based quartz sand, Al2O3-based corundum and CaO/Fe2O3-rich boiler ash collected from bottom ash of a CFB industrial boiler, were selected as the potential bed material. Their impacts on the de-fluidization tendency, transformation and migration of alkali metals, priority of reactions involving sodium-based species, formation of liquid slags and ash fusibility were investigated through the characterization of ash samples and thermodynamic equilibrium calculation by Factsage 6.1. The particle-size analysis results presented the improvement of three bed materials in the growth of ash particles followed the order of quartz sand > corundum > boiler ash. This order was ascribed to their reaction priority with sodium-based compounds in coal and the chemical property (mainly referring to ash fusibility) of corresponding products. Generally, reactions between sodium-based species and minerals (Al2O3 and SiO2) were the main way of sodium retention within the ash in gasifier. As boiler ash was used, however, Al2O3 and SiO2 preferentially reacted with the CaO enriched in boiler ash rather than sodium-based species in coal, resulting in very low sodium retention. Under such circumstances, computing results suggested the ash in gasifier could withstand higher gasification temperature, consistent with the measured results of ash fusibility. Additionally, the gasification temperature operating range could be largely widened by simply increasing CaO/Fe2O3 content in gasified ash. Therefore, boiler ash is an effective and low-cost bed material for use as the slagging/agglomeration preventative of high-sodium lignite during CFB gasification.

Supercritical water gasification (SCWG) technology is one of the most promising ways to realize efficient and clean utilization of coal because of the special physical and chemical properties of supercritical water. K2CO3 is the most preferable catalyst to improve gasification efficiency. However, K2CO3 leads to ash agglomeration and massive volatility of alkali metals. The accumulation of agglomerated ash prevents the continuous operation of the system, and the volatility of alkali metals weakens the coupling of high-grade H2/CO2/H2O mixture with downstream process. In this study, K2CO3-catalytic SCWG of coal with NaAlO2 loading was firstly investigated in a laboratory-scale continuous reaction system to check whether NaAlO2 can inhibit ash agglomeration and lower the volatility of alkali metals without decreasing the gasification efficiency. The concentration of coal slurry was 20 wt%-35 wt% and the loading content of NaAlO2 was 0 wt%-7.5 wt% of dry coal. By doing GC, PSD, XRD, SEM and ICP-OES analysis for three-phase products collecting from the experiment, it was found that, when NaAlO2 loading increased from 0 wt% to 7.5 wt%, the carbon gasification efficiency of 20 wt%, 30 wt% and 35 wt% coal slurry improved from 90.7% to 93.9%, from 83.8% to 88.6% and from 72.6% to 80.5%, the percentage of H2 increased and the percentage of CO2, CH4 and CO decreased. The addition of NaAlO2 transformed K and Si of coal into K(Na,K)3Al4Si4O16 instead of K2Si2O5, which contributes to the distribution of ash particles into smaller size. 5 wt% NaAlO2 loading decreased the total volatility of alkali metals, and 7.5 wt% NaAlO2 loading will increase the total volatility of alkali metals.

Coal catalytic hydrogasification is an efficient approach to produce CH4. This study investigated hydrogasification characteristic of coal with diverse properties (caking propensity, high rank and sulfur content) in a pressurized fluidized bed. The approaches to realize high CH4 yield and stable fluidization were explored. Experimental results showed that carbon structure and sulfur content in coal were the key factors influencing hydrogasification reactivity. The mechanically mixed CaO/CaCO3 migrated into the interior of coal particle to enhance the activity of Co towards graphite carbon, and capture sulfur adsorbing on Co surface. The caking propensity of coal brought little resistance to the activity of catalyst, whereas, caused serious agglomerating phenomenon. The blending of caking coal with non-caking, low rank coals induced the active hydrogen spill-over and the volatiles-catalyst-coal interactions, which not only in-situ minimized the agglomeration propensity, but also enhanced the overall hydrogasification reactivity. Furthermore, the mechanism of hydrogasification was proposed by taking account of coal property, to broadening the application range of hydrogasification and producing CH4 efficiently (~80.0 wt% in 1.0 h).

Supercritical water gasification (SCWG) technology shows huge advantages to achieve efficient and clean utilization of coal. Ash agglomeration caused by K2CO3 addition makes ash discharging process more difficult and inhibits gasification reaction of carbon in agglomerated ash, which prevents the constant operation of the system and decreases gasification efficiency. This study investigated the formation mechanism of ash agglomeration in potassium carbonate-catalyzed SCWG of coal and find a solution to inhibit this problem. Experiments were conducted in an autoclave to figure out the effect of K2CO3 (0 wt%-10 wt%) and Al2O3 (0 wt%-20 wt%) on ash agglomeration level at 750 °C. After every single experiment, solid residue was dried and classified into different sizes (0–100 μm, 100–1000 μm, >1000 μm). The ash agglomeration characteristics was examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDS). Results indicated that K2CO3 reacted with clay and quartz in raw coal, then formed K2Si2O5, KAlSiO4, KAlSi2O6 and KAlSi3O8. K2Si2O5 plays a cohesive role between different ash particles. Adding Al2O3 can effectively solve this problem by forming KAlSiO4 instead of K2Si2O5. Besides, Al2O3 enhances carbon gasification efficiency by increasing heating rate of feedstock temperature. Simulation work was also done to investigate the boundary condition for ash agglomeration.

In this study, vinasse, a by-product of sugar industry, was analysed for its behaviour during combustion in a fluidised bed combustor. Due to potential agglomeration problems owing to its high potassium content, the vinasse was first pre-assessed using agglomeration indices and muffle furnace tests. Subsequently it was co-fired with Thoresby singles coal in a bubbling fluidised bed of 25 kW thermal capacity. It is found that the agglomeration indices are good indicators of agglomeration tendency of biomass fuels and should be used to pre-analyse the material before firing in a fluidised bed. It was observed during cofiring in fluidised bed that agglomeration occurred very quickly due to high alkali content of vinasse. It is found that not only the alkali content of the material but its feed rate and combustion temperature are also controlling parameters for agglomeration. Vinasse can be used as potential fuel source by carefully controlling operational parameters or by adding alkali getters such as kaoline.

Oil agglomeration is an alternative technique for the cleaning and upgrading of low-rank coal or high-ash content coal slimes. Therefore, this approach was used to beneficiate coal slime with high-ash content of 31.34% in this work. The single-factor tests of oil agglomeration were performed to determine the appropriate ranges for various operational factors, including pulp concentration, reagent concentration, and agitation speed. The separation results suggested that considering the yield and ash content of clean coal, and combustible material recovery, the optimal pulp concentration and reagent concentration should be adjusted as 12%–16%, and 20%–24%, respectively, and the optimal agitation speed should be controlled as 800–1200 r/min. The Response surface methodology (RSM) based on Box–Behnken design (BBD) was adopted to investigate the significance of various operational factors, and the interactions between various operational factors on the response of combustible material recovery. A mathematical model was established to predict the response, and the results indicated that the established model was proved to be highly accurate in the prediction of response. The optimization of the solutions suggested that the maximal combustible material recovery of 97.49% was obtained with the pulp concentration of 12%, reagent concentration of 20%, and agitation speed of 1200 r/min. This work provides an experimental foundation for the operation design and process optimization in the oil agglomeration of coal slimes.

Agglomeration in fluidized beds begins locally by the sticking of slag–liquid-covered particles. Analysis of the composite fuel is not adequate in predicting agglomeration problems. Separation of the high rank Pittsburgh seam coal into particle classes based on specific gravity (SG1: 3 ; SG2: 1.3–1.6 g/cm 3 ; SG3: 1.6–2.6 g/cm 3 and SG4: >2.6 g/cm 3 ) and particle size (PS1 through PS7) helped to identify important particle-level slag–liquid formation tendencies. Slag–liquid formation tendencies under fluidized bed operating temperatures were determined both computationally and experimentally. Particles rich in certain iron and calcium phases melt at very low temperatures that are well within fluidized bed operating conditions. The iron rich particle classes (SG3 and SG4) showed the presence of several phases containing iron in different oxidation states. The presence of these iron phases was not detected in the composite bulk fuel. The possibilities of equilibrium liquid phase formation in the presence of different ratios of these iron and calcium oxides to alumino-silicates were determined. Presence of hematite was found to delay slag–liquid formation. Each of the particle classes showed distinct slag–liquid formation tendencies that indicate initiation of agglomeration around SG3 and SG4 particles. The study revealed the importance of particle class-level differences in mineral matter composition for the prediction of agglomeration during fluidized bed gasification. A novel integrated ash agglomeration model that accounts for particle hydrodynamics as well as particle class level ash chemistry has been outlined to predict agglomeration kinetics.

During initial drawdown in coal bed methane (CBM) production, the coal permeability declines due to partial fracture closure. The recently proposed technique for stimulation of natural coal fractures and cleats by the graded proppant injection targets a uniform cleat filling by the proppant. It provides maximum opening and conductivity during pressure depletion. The technique for graded particle injection below the fracturing pressure has been experimentally evaluated using injection of micro-sized ultra-light high-strength particles into coal cores. The laboratory tests on one-dimensional injection of different size particles into coal cores have been conducted under different effective stress conditions. Calculation of electrostatic interactions results in determining physico-chemical conditions that are favourable for particle–particle and particle–coal repulsion. The repulsion condition prevents particle attachment to the coal surface, particle agglomeration and also formation damage due to external and internal cake formation on the fractures’ surface. Particle placement in repulsion condition with low-salinity water results in almost three-time increase in coal permeability. Implementation of an empirical permeability shape factor allows matching the laboratory data by the mathematical model. The laboratory-based mathematical modelling as performed for the field conditions shows that the proposed method can yield up to six-time increase in productivity index.

Coal–oil agglomeration has been a prominent fine coal processing technique, which involves agitation of coal–water slurries in presence of immiscible oil forming coal–oil agglomerates. The present study investigates this technique using Taguchi (L16) design of experiments (DoE) methodology. Further, the process parameters like oil dosage, agitation speed, agglomeration time, pH and temperature were optimized using Analysis of Mean (ANOM) statistical approach and the percentage contribution of each of these parameters towards organic matter recovery (OMR) was determined by Analysis of Variance (ANOVA) statistical approach. The optimum conditions for maximum OMR (91.38%) were identified as oil dosage of 30%, agitation speed of 2500 rpm, agglomeration time of 2 min, pH of 12 and temperature of 30 °C. The contribution of each of the above process parameters towards the OMR was found to be in the following order: pH (30.38%) > agitation speed (23.06%) > oil dosage (20.63%) > agglomeration time (13.72%) > temperature (10.61%). Multiple linear regression analysis carried out using SPSS 19.0 ascertained a similar order of influence on the OMR. The highest contribution of suspension pH further establishes the fact that oil agglomeration process is a surface property based technique, as pH affects the surface charge on coal/mineral matter/oil droplets. A mathematical model was also developed using SPSS 19.0 to predict the OMR by oil agglomeration under the given set of experimental conditions. The developed model could predict the OMR to a significant extent, which can be further improved by a DoE technique of higher order.

Jetting pre-oxidation was proposed to destroy the caking property of bituminous coal in a fluidized bed (FB) gasifier. By defining an index omega to characterize the degree or realized effect of caking destruction, experiments were conducted in an electrically heated laboratory FB reactor under different conditions to investigate the feasibility and required conditions for effectively destroying the caking propensity of a kind of bituminous coal. The tested major parameters were the equivalence air ratio (ER) of jetting gas and the temperature in the jetting zone. At relatively lower temperatures it was hard to completely destroy the caking propensity of the tested coal particles. Without oxygen inside the jetting gas, it was also impossible to fully destroy the caking propensity of the coal even at sufficiently high temperatures. Thus, oxidation of coal particles at suitably high temperatures was essential to the expected good destruction of their caking propensity. For the tested bituminous coal this was achieved at temperatures above 1000 degrees C in the jetting zone and an equivalent oxygen ratio above 0.1 for the jetting gas (up to 0.3 considering gasification applications). For coal pre-oxidation in a FB, the agglomeration state of char particles due to caking adherence in the reactor could be anticipated via the unsteady variations in the bed temperature and H-2/CO concentrations in the effluent gas with reaction time. (C) 2014 Elsevier Ltd. All rights reserved.

Bergius process for coal liquefaction was patented one century ago. It constituted the first application of dispersed phase catalysts in slurry reactors, considered as once-through disposable solids. Starting from waste materials as additive, the role of catalysts in the conversion of heavy carbonaceous feeds like coal of petroleum residues was progressively identified. Cracking activity was initially considered as necessary, but it was later recognized that hydrogenation activity is essential. The desired properties were established: small particle size, resistance to agglomeration and low cost. Synthesis methods for the production of dispersed phase catalysts are reviewed. Based on historical developments, prospective ways are proposed for improving efficiency of existing conversion processes.

Emulsification is one of the most important stages in coal cleaning by using oil agglomeration. Reduction in size of oil droplets and increase in total surface area provided by emulsification result in coverage of entire coal surface with oil, thereby reducing the oil dosage and affecting rapid agglomeration. Ultrasonic emulsification which has been used recently in many sectors such as pharmaceutical, cosmetic, food, chemical industries may be a beneficial and promising operation in oil agglomeration of coal. In the present study, an oxidized fine coal with high ash and pyritic sulfur content was cleaned by oil agglomeration process after ultrasonic emulsification and the effects of power level and time of ultrasonic treatment on the performance of the agglomeration process were determined. Ash and pyritic sulfur rejections that was found to be 50.38% and 85.28%, respectively, at agglomeration test without ultrasonic emulsification was increased to maximally 56.89% and 88.69% by using ultrasonic emulsification before agglomeration. While increase in power of ultrasonic treatment did not affect ash and pyritic sulfur removals considerably, ultrasonic treatment time had positive affect at higher power levels. Contrary to expectations, ultrasonic emulsification affected the combustible recovery and separation efficiencies adversely.

Spherical agglomeration is a size enlargement process in which the disperse medium is held together in aggregates by liquid bridges of an immiscible agglomerating agent in the dispersion medium in general, an aqueous environment. Extensive studies on the process have shown that the process is affected by a number of process parameters. In the present paper, a large number of process parameters such as agitation speed, oil dosage, agglomeration time, coal particle size, slurry pulp density, pH and temperature of the dispersion medium, oil type, surfactant (anionic) use, and sea water usage as pulping medium. affecting the oil agglomeration of Indian bituminous coal procured from North-Eastern region of the country were investigated. Initially, the process parameters were optimized for maximum coal recovery with significant ash rejections. Subsequent experiments to study the effect of surfactant, oil type and sea water usage as pulping medium were performed under the optimized conditions. All the experiments were performed under batch mode of operation. The coal–oil agglomerates were recovered by screening using a standard test sieve whose pore size was same as the maximum size of feed coal particle. The overall agglomeration performance was studied in terms of efficiency index which took into account both combustible recovery and ash rejection, the two important process estimates of the agglomeration process. The experimental results showed that the Indian bituminous coal used in the study was quite receptive to oil agglomeration process and significant recovery of coal fines with considerable ash rejections was possible through this clean coal technology.

The present study was undertaken to optimize the oil agglomeration process parameters for maximum recovery of coal fines using analysis of mean (ANOM) statistical approach based on the Taguchi parameter design methodology. The various operational parameters considered during the current study were the type of coal, type of oil, coal particle size and pulp density. The study reported a maximum recovery of 91.03% under the following optimum conditions: low ash high sulphur coal, Karanja oil, coal particle size of +75–200 μm and pulp density of 3% (wt./vol.). The percentage contribution of each process parameter towards the agglomerate yield determined using Analysis of Variance (ANOVA) approach was found to be of the following order: coal particle size (55.35%) > type of coal (17.84%) > pulp density (16.50%) > type of oil (8.41%). The most influential process parameter appeared to be coal particle size which has been the primary criteria used for selection of particular process for coal washing. Linear regression analysis carried out using the SPSS 19.0 statistical software further supported the same. Further, a mathematical model was also developed to predict the agglomerate yield by oil agglomeration under the given set of boundary conditions. The experimentally obtained yields were in close agreement with the predicted yield of the model. The agglomerate yield (91.03%) obtained during the confirmation experiment carried out under optimum conditions was much higher than that observed in all the test runs and thereby, the authenticity of optimization was checked.

The presence of large amounts of alkali metals, chlorine and sulphur in most biomass fuels – compared to coal – can create serious ash-related problems such as deposition, agglomeration and/or corrosion. This paper discusses the viscosity characteristics of fly ash from the co-combustion of various coal/biomass blends in a pilot scale pf-boiler. The produced data provide information on the melting of the ash and its flow characteristics, as a function of temperature, which may be used to modify the temperature profile of the boiler in order to avoid slagging. Straw co-firing lowers the ash viscosity leading to higher stickiness of the ash particles. Wood co-firing has only minor effects, due to the composition of wood ash and the low percentage of wood in the coal/biomass blend.

The significance of coking coal in the metallurgical sector as well as the meager coking coal reserves across the globe increase the necessity to recover coking coal fines from the fine coking coal slurries generated from coal preparation and utilization activities. Oil agglomeration studies were carried out by varying the experimental conditions for maximum recovery of coking coal fines i.e., yield of the agglomerates. The various operational parameters studied were oil dosage, agitation speed, agglomeration time and pulp density. By using Taguchi experimental design, oil dosage (20%), agitation speed (1100 rpm), agglomeration time (3 min) and pulp density (4.5%) were identified as the optimized conditions. A confirmation experiment has also been carried out at the optimized conditions. The percentage contribution of each parameter on agglomerate yield was analyzed by adopting analysis of variance (ANOVA) statistical method as well as multiple linear regression analysis. The order of influence of the parameters on the agglomerate yield is of the following order: pulp density > oil dosage > agitation speed > agglomeration time. A mathematical model was developed to fit the set of experimental conditions with the yield obtained at each test run and also at the optimized conditions. The experimentally obtained yield was compared with the predicted yield of the model and the results indicate a maximum error of 5% between the two. A maximum yield of 90.42% predicted at the optimized conditions appeared to be in close agreement with the experimental yield thus indicating the accuracy of the model in predicting the results.

WOS: 000262877300012, In this study, the optimization of some parameters on agglomeration performance of Zonguldak bituminous coal by oil agglomeration was discussed. A three-level Box-Behnken design combining with a response surface methodology (RSM) and quadratic programming (QP) were employed for modeling and optimization some operations parameters on oil agglomeration performance. The relationship between the responses, Le., grade and recovery, and four process parameters, i.e., amount of oil, agitation time, agitation rate and solid content were presented as empirical model equations for both grade and recovery on oil agglomeration. The model equations were then optimized individually using the quadratic programming method to maximize both for grade and recovery within the experimental range studied. The optimum conditions were found to be 14.61% for amount of oil, 8.94 min for agitation time, 1554 rpm for agitation rate and 5% for solid content to achieve the maximum grade. The maximum model prediction of 0.650 grade at these optimum conditions is higher than any value obtained in the initial tests conducted. Similarly, the conditions for maximum recovery were found to be 20.60% for amount of oil, 5 min for agitation time, 1800 rpm for agitation rate and 19.48% for solid content with a prediction of 96.90% recovery, which is also higher than any other recovery obtained in the initial tests conducted. (C) 2008 Elsevier Ltd. All rights reserved.

WOS: 000235648600033, The objective of this work is to obtain high calorific value/low ash content products from fine bituminous coals by aggloflotation with petroleurr oils such as hexane, heptane, toluene and pentane. The two methods used were agglomeration and aggloflotation for cleaning fine bituminous coal Oil agglomeration experiments first were carried out followed by aggloflotation at the optimum conditions obtained from agglomeration. The effects of fundamental parameters such as oil type and dosage, pulp density, conditioning time; pH and Na2SiO3 amount were studied. The combustible recoveries and ash content of concentrates for optimal aggloflotation test conditions were with hexane: 92.17% combustible recovery (dry basis), 10.87% ash (dry basis) and lower calorific value (LHV) 5864 kcal/kg

WOS: 000234129700003, In this study, the Box-Wilson statistical experimental design method was employed to evaluate the effects of important variables such as bridging liquid (oil) concentration, salt (CaCl(2)(.)2H(2)O) concentration and stirring speed on the agglomeration of bituminous coal. Response function coefficients were determined by the regression analysis of experimental data and the predictions were found to be in good agreement with the experimental results. The optimum kerosene concentration, CaCl(2)(.)2H(2)O concentration and stirring speed were determined as 30 wt%, 1 M and 1683 rpm, respectively, when considering combustible recovery and ash content. In addition, contact angle and solution surface tension measurements were carried out to evaluate of agglomeration success with the contact angle values and surface tension values. The surface tension of CaCl2 2H(2)O solutions and the average contact angle increased with increasing CaCl(2)(.)2H(2)O concentration. (c) 2005 Published by Elsevier Ltd.

Five Australian black coals were studied in a bench scale pressurised fluidised bed combustor (PFBC) to investigate the agglomeration propensity. It was found that coals with higher proportions of calcium aluminosilicate showed higher propensity for agglomeration and defluidisation. The pressure-drop sintering technique can predict the agglomeration propensity for coals. Samples with a sintering temperature lower than the operating temperature of the PFBC showed agglomeration. The laboratory ash can be a good representative of the PFBC ash when studying agglomeration and defluidisation.

WOS: 000184125400010, In this study, the kinetics of agglomerate growth in a batch oil agglomeration process has been studied using bituminous coal. The effect of operating variables such as kerosene concentration, pulp density and speed of agitation on the agglomeration process was investigated. It has been found that the second-order kinetic equation describes the growth of agglomerates adequately. The growth of the agglomerates in the oil agglomeration process shows a self-preserving growth. Using this, a characteristic curve has been developed. For the prediction of the size distribution of the agglomerates, the d(50) values of the agglomerates must be known. Therefore, a model has been developed by using the kinetic equation for estimation of d(50) values of agglomerates for this coal. It was shown that the size distribution of the agglomerates for any levels of the process variables studied can be predicted using the equation of characteristic curve and d(50) values. Knowledge obtained from this study will be helpful for technological advancement of this kind of study. (C) 2003 Elsevier Science Ltd. All rights reserved.

The hydrothermal dewatering of a Loy Yang Low Ash Victorian brown coal has been studied under a wide range of process conditions. The intra-particle porosity ( 50 μm gave products of constant intra-particle porosity but smaller coal particles gave products with higher intra-particle porosities as a result of agglomeration. Milling of the coal reduced the porosity of the dried coal at constant particle size.

In this study, the concentration of coal–pyrite and lignite taken from Yozgat-Ayridam (Turkey) Coal Management was investigated by oil agglomeration. In the previous studies, the agglomeration of coal–pyrite was investigated using different bridging liquids (fuel oil, diesel oil and kerosene) and the combination of reagent (KEX, Acorga M5397)+kerosene. When using only bridging liquids, the agglomeration recovery of pyrite was very low. To increase the hydrophobicity of pyrite, KEX was used. However, the pyrite was not agglomerated with an acceptable recovery. But when using Acorga M5397, which is a chelating reagent, the agglomeration recovery of pyrite was increased. The pyrite was agglomerated with a recovery of 76.70 wt% by single-stage agglomeration. In the optimum conditions which were determined for coal–pyrite, the agglomeration recovery of lignite was investigated. It was found that the lignite could not be agglomerated with an acceptable recovery. To investigate the separation of coal–pyrite and lignite, the artificial mixture of coal–pyrite and lignite was prepared with the weight ratio of 1/4 of coal–pyrite and lignite. It was found that the pyrite could be agglomerated at a recovery of 96.54% with three-stage agglomeration process. The lignite concentrate was produced with a recovery of 73.96 wt% and the pyrite content of 0.86 wt%. These findings showed that the coal–pyrite and lignite could be separated by oil agglomeration using appropriate reagent and bridging liquid.

Development of more effective technologies of utilising low rank coals for power generation has been driven by a demand for higher efficiency, low capital costs and minimal environmental impacts. Fluidised bed systems are regarded as one of the more promising alternative technologies for power generation to overcome the disadvantage of the existing pulverised coal burning power generation plants for low rank coals. However, ash deposition and bed agglomeration are potential problems in fluidised bed processing of coals with high alkali and sulphur contents. In order to gain a better understanding of the mechanism of agglomeration in fluidised beds, a good knowledge of the rheological behaviour of coal ash deposits at high temperatures and under the processing conditions is necessary. Rheological characterisation of materials at high temperatures is difficult due to lack of standard instruments and reliable measurement techniques. We have recently developed a rheometer that has the capability of measuring the rheological properties of coal ash slag over a wide range of temperatures from 600 to 1300°C and under different processing atmospheres. In this paper the features of this unique instrument are described and the experimental technique developed for flow property measurement is outlined. Some typical measured rheological properties of coal ashes from different Australian low-rank coals are presented and discussed to illustrate the potential applicability of the rheometer for high-temperature rheological characterisation. Furthermore, by means of the experimental results obtained it is demonstrated that the alkali content of the coal ash plays a significant role in controlling the rheological characteristics of the ash deposit, which in turn has an important implication on agglomeration in fluidised bed combustion processes.

Froth flotation and selective agglomeration are two techniques, which can be employed for the recovery of fine coals. Short chain volatile fatty acids (VFAs) contained in landfill-derived liquids are similar in structure to many of the organic chemicals employed in both processes. The results from laboratory investigations, based on flotation and selective agglomeration techniques, have demonstrated that VFAs can substitute for some, or all, of the commercial reagents currently used. The results of these investigations, using VFAs and landfill gas condensates, are presented, along with discussion of their potential application to fine coal recovery.

A promising oil agglomeration process has been developed for the beneficiation of fly ash using a six-ft agglomeration column. Carbon concentrates have been isolated in recoveries greater than 60% and purities of 55–70%. The parameters studied include agitation speeds, airflow rates, slurry feed rates, solvent/ash ratios, and the use of various solvents as agglomerating agents. The effects of these variables on the quality of separation are discussed.

The aim of this work was to obtain high calorific value products from coal fines cleaning wastes by agglomeration with vegetable oils. These residues are mainly being disposed of in dumps, causing important economic and environmental problems. Three Spanish coal fines wastes from different coal cleaning plants were agglomerated with crude and refined sunflower and soybean oils over a wide range of oil concentrations. The response of these fines wastes to agglomeration with the oils, was evaluated by the percentages of coal matter recovery, ash rejection and efficiency index. Speaking in terms of products quality, the best results were attained at the lowest oil concentrations, especially when the refined ones were used. In these cases, the agglomeration with vegetable oils allowed the recovery from coal fines wastes of a ready to burn fine coal fuel.

A laboratory scale spouted bed combustor was used to study the effectiveness of various control methodologies in alleviating ash-related problems such as particle agglomeration and bed defluidisation during fluid bed combustion of low-rank coals. The three control techniques investigated are: (i) the use of mineral additives; (ii) alternative bed materials; and (iii) pretreatment of coal. Mineral additives, including dolomite, two clays and gibbsite, were injected into the spouted bed combustor while burning a South Australian low-rank coal at 800°C. Samples of the same coal treated with Al, water washing and acid washing were also tested in the spouted bed combustor. In addition, experiments were also conducted with alternative bed materials including bauxite and calcined sillimanite. Experiments showed that the three techniques reported in this paper are effective to different extents in reducing particle agglomeration and defluidisation. Among the mineral additives tested, gibbsite and a clay additive rich in kaolinite and sillimanite were found to be most effective. The use of calcined sillimanite and bauxite as alternative bed materials extended the combustion time before defluidisation occurred by 7 and 10 times, respectively, compared to silica sand. While Al pretreatment and water-washing were found effective for control of agglomeration and defluidisation, acid-washing did not improve the operation of the bed burning this particular coal. Al enrichment in ash coating of bed particles which suppress the formation of Na and S rich eutectics was identified as the main mechanism for prevention of agglomeration and defluidisation by these control techniques.

The wettability of three Spanish anthracites with a large mineral matter content was studied by measuring the oil/water/coal contact angle with heptane and with crude and refined vegetable oils. The captive drop method was used for this purpose. The contact angle was found to depend on the coal, oil, and an interaction between coal and oil. Particle agglomeration tests were conducted to determine the maximum recovery of organic matter for each combination of coal and oil. The maximum recovery was observed to correlate well with the three-phase contact angle when heptane was employed as an agglomerant for the different anthracites. When vegetable oils were employed as agglomerants, the maximum recovery was also observed to correlate well with the contact angle in half the cases. For the other half the recovery exceeded what would have been predicted by the contact angle. Therefore, for these cases the oil wettability of the coal seemed greater under dynamic conditions than under static conditions.

This paper presents selected results from an extensive on-site measurement campaign where the ash behaviour in a 12 MW CFB boiler was studied during firing of coal, peat and wood. Samples were taken from all in-going (bed material, fuel) and out-going solid material streams (secondary cyclone and bag filter) as well as from the bed and the return leg. Deposit samples were further collected from the cyclone inlet and from two different locations in the convective path. In addition, the boiler operation was monitored, including collection of operational data, flue gas temperature profiles and emissions. The paper discusses the differences in the ash chemistry that were detected between the three different combustion cases and draws conclusions on the impact of the chemistry on the bed agglomeration and fouling tendency for each fuel.

Long-wave fluorescence relative intensity measurements and a vitrinite microelasticity index were used to determine oxidation levels in a suite of artificially oxidized coals. These petrographic parameters were correlated with the agglomeration responses of the coals. Very definite relations were found between the petrographic indicators of oxidation and the agglomeration rates of the coals.

Oil agglomeration is an effective technique for recovering and deashing coal fines. Conditioning is the most important unit operation prior to agglomeration or size enlargement. In this study, the effects of the design and process parameters in the conditioning step, which markedly influences the effectiveness of selective oil agglomeration, on the recovery of agglomerate and the ash and pyritic sulfur content of the agglomerates were investigated. It was found that the success of the process in terms of both recovery and selectivity for a brown coal was highly dependent on the conditioning parameters. In addition, an empirical equation which relates the recovery with all the conditioning parameters was developed. The values calculated by this equation closely matched the experimental values.

The aim of this work was to study the feasibility of using vegetable oils for coal agglomeration. Three Spanish anthracites were agglomerated with refined sunflower and soybean oils. The response of coals to agglomeration with these oils was evaluated by measuring the percentages of organic matter recovery and ash and pyritic sulfur rejections. The influence of oil type and concentration on agglomeration results was investigated. In addition, results were compared with those previously obtained in the agglomeration of these coals with n-heptane. It can be concluded that refined sunflower and soybean oils are suitable for use as agglomerants for these high-rank coals, especially to clean those coals with a high content of mineral matter.

The dilatometric properties and Roga index of two orthocoking coals, subject to extraction with n-pentane, methylene chloride and chloroform, were determined in order to investigate the influence of low-molecular weight substances on coking properties of the coals. With increasing extraction yield, their dilatation and agglomerating capacity were observed to decrease, whereas their softening point was shifted towards higher temperatures. The effect of reduction by potassium in liquid ammonia on dilatometric properties of coals, as well as on their agglomerating capacity, was also studied. This reduction was found to cause a significant increase in coal dilatation, a decrease in softening temperature of the coals, and an insignificant increase in their agglomeration capacity. The extracts obtained from raw and reduced coals are characterized and their role as well as the role of the reduction process in the phenomenon of coal plasticity is discussed.

The response of three high-ash Spanish anthracites to agglomeration with n-heptane was evaluated by measuring the organic matter recovery, ash rejection and pyritic sulfur rejection. The influence of oil concentration and coal particle size on the agglomeration results was investigated. The combustible recoveries of these coals increased to a maximum as the n-heptane concentration is raised, and then decreased. Ash rejection fell as the coal recovery increased. The effect of oil concentration on pyritic sulfur rejection was comparable with that on ash rejection. Regarding ash, pyritic sulfur was removed from one coal with noticeable selectivity. Ash rejection and organic matter recovery were improved by grinding one coal to

The results of 206 batch laboratory tests on selective agglomeration of three coals are reported. The effectiveness of the agglomeration process is analysed with the use of some new indices describing rejection of sulfur and mineral matter as well as recovery of coal matter. The influence of the process variables was examined by multiple linear regression. Correction calculus for measurement errors was used to estimate the accuracy of the experimental results.

Laboratory agglomeration-flotation tests were used to evaluate the recovery of residual bitumen from a sample of Suncor oil sands fine tailings, using ground coal as a bitumen absorbent. To improve its effectivness, the coal was preconditioned with no. 2 fuel oil, subjected to 30 s high-shear mixing and collected by flotation over 3 min. This oil-conditioned coal was then contacted with mature fine tailings for 5 min with low-shear mixing. Flotation for 5 min resulted in the recovery of 93% of the residual bitumen, compared with 85% after 40 min mixing achieved in earlier tests. Equipment to accomplish this separation has already been designed, scaled and operated for fine coal recovery from washery wastes., 1993 Eastern Oil Shale Symposium, 16-19 November, 1993, Lexington, Kentucky, USA

Surface characterization techniques (scanning electron microscopy and X-ray photoelectron spectroscopy) were used to examine toluene-insoluble solids from coprocessing of coal and heavy oil in order to evaluate their physical spearation potential. Washability studies, using float-sink tests, were also carried out to provide an empirical estimate of the ash separation attainable. On the basis of the results, agglomeration tests were performed in an attempt to optimize the beneficiation of the organic matter in the residue pitch. Ash rejection in these tests ranged from 30 to 40%. Analysis of the ash from the agglomerated and reject fractions suggested that most of the iron was retained in the agglomerates.

Demineralization of Blue Creek coal by selective agglomeration using diesel oil involves high-shear mixing to disperse the diesel in a slurry of fine coal and separation of the resulting agglomerates from the tailings. A total of 54 agglomeration trials were made with thickener underflow from the Jim Walters Resources Inc. No. 4 mine preparation plant. Two additional particle size distributions of the thickener underflow were obtained by wet grinding and all three coals were stored under water. All experiments were performed at room temperature. The feed which has less than 1 wt% of total sulfur is suitable for recovery by oil agglomeration. Ash rejection and recovery of combustibles is approximately 80%. The effects of blending the agglomerates with a coal-water fuel are reported.

The degree of surface hydrophobicity of a range of coal types has been previously shown to be dependent on the carbon to oxygen ratio (or coal rank). The surface hydrophobicity of these coals increases during agglomeration due to substantial removal of the mineral matter content of the coals. It has been found that the degree of hysteresis between the advancing and receding contact angles for light gas oil in water against the coal surfaces decreases as the rank of the coal decreases. This is due to the lower rank coals possessing an organic component which is closer in surface free energy to that of the inorganic constituent of the coal compared to that of the higher rank coals.

The role of inorganic matter in causing agglomeration and defluidization during the circulating fluidized-bed combustion of high-sodium, high-sulfur low-rank coals was reported in a previous paper. It was found that the ash formed during the combustion of these coals is transferred to the surface of the bed particles. The ash coating thus formed contains a molten phase at the furnace temperature, which makes the bed particles sticky. During the experiments, the effects of temperature and coal quality on the extent of agglomeration were also measured. The results, reported here, show that the tendencies for agglomeration and defluidization to occur increase markedly at temperatures above the initial ash sintering temperature when the ash coating on the bed particles exceeds a critical thickness. The proportions of the melt-forming inorganic elements and mineral inclusions in the ash also have a pronounced effect on agglomeration and defluidization tendencies. The results are considered to be of significance in the development of mechanistic models for agglomeration and defluidization.

Circulating fluid bed combustion is increasingly being adopted for large scale power generation from low-rank coals. However, these coals often contain alkalis which are known to cause agglomeration and defluidization in CFBC systems through mechanisms that are not yet fully understood. A laboratory-scale fluid bed combustion system has been used to carry out experiments with coals containing various amounts of sodium chloride, organically bound alkali and alkali earth metals. The bed material and fine ash removed from the furnace have been characterized by various analytical techniques. It was found that, in the stirred environment of circulating fluid bed combustors, a portion of the ash is deposited on the surface of the bed particles. This ash coating contains a molten phase which causes the bed particles to stick together and/or defluidize. The ash formation studies reported in a previous paper and the interaction of ash with bed material reported in this paper describe a sequence of events that can explain the role of the inorganic matter in agglomeration and defluidization.

A theoretical model is described for using laboratory batch experimental data to design industrial plant for the upgrading of coal by selective agglomeration. The maximum velocity gradient and the real residence time are used as the two criteria in designing the stirred tanks that are the main components of the plant. The first criterion is determined as the product of impeller diameter and impeller rotation speed. The second criterion is the product of number of impeller wings, impeller wing height and number of parallel operating tanks, divided by the overall slurry flow rate. Formulae for required power and specific energy consumption are derived and recommended for optimization of the plant. As data are not available from large plants, calculations on hypothetical plants are provided to illustrate the use of this technique for scale-up.

Laboratory experiments demonstrated that low-rank coals can be cleaned by agglomeration with distillate coal liquefaction recycle oils. Materials tested included a lignite, three subbituminous coals, a bituminous coal, two petroleum oils, and three coal liquefaction recycle oils. Ash rejections obtained were as high as ~ 50% for Texas lignite and 15–20% for two Wyoming subbituminous coals. A Montana subbituminous coal showed no ash rejection, though physical agglomeration occurred. Organic recoveries for the low-rank coal tests were always > 98%. All three liquefaction recycle distillates tested were effective agglomerating agents for low-rank coals. In the few cases tested, adjustment of the slurry pH to 2.0 or addition of cresylic acid to the slurry had beneficial effects for the lignite agglomeration. Selectively retained in the product ash were Fe (a potential liquefaction catalyst), Ti, Ca, and Mg, whereas Na was selectively rejected.