High-ash Coal Research Articles

Evaluation of pneumatic inclined deck separator for high-ash Indian coals

Application of pneumatic separators in coal beneficiation is increasing rapidly over the last decade primarily due to their low capital and operating costs, and waste handling problems associated with traditional wet processing methods. Large amount of shale/rock that is extracted in coal production can be removed prior to transportation at the mine face by using this methodology. Due to the limited washing facilities in India, most of the thermal power plants burn raw coal from run-of-mine (ROM) to generate electricity. This practice causes poor utilization efficiency, high operating and maintenance costs, and high emission rates for the power plants. One potential method that can be utilized is the air-fluidized inclined vibrating deck technology. The technology was demonstrated on a pilot-scale at different coal washeries in India at a feed rate of 5-ton per hour. The pilot-scale evaluation showed that 20 %–25 % high-ash incombustible material can be eliminated from ROM feed with only minor losses in energy content (<10 %) from respective ROM coal. Furthermore, a feasibility analysis showed significant economic gains in terms of transportation cost, improving power-plant efficiency, and reducing emissions rates by using the technology.

Pre-combustion removal possibility of hazardous trace elements from Indian high-ash coal by coal preparation technologies

ABSTRACTMany of the potentially hazardous air pollutants listed in the 1990 Clean Air Act are elements commonly found in trace amounts in coal. When coal is burned, these elements release into the environment. An option for controlling the release of these elements into the atmosphere is to remove them before combustion. Conventional physical coal cleaning processes are effective in reducing the concentration of many of these trace elements in coal. In addition, advanced cleaning processes directed toward reduction of various elements may perform better than conventional processes. Therefore, current research focuses on the advanced coal cleaning technology which is directed toward reduction of mineral matter and various toxics elements as well. Results of recent studies indicate that the degree to which a specific trace element can be reduced by coal cleaning depends on its distribution in the coal. To quantify the capabilities of a gravity-based coal cleaning process for removing these hazardous air pollutants, a detail study was conducted on a coal sample collected from one mine of Talcher area. Careful analysis of the experimental data indicates that most of the trace elements of greatest environmental concern are strongly associated with the organic matter of the investigated coal, thus during beneficiation these elements are concentrated in the clean coal fraction. Therefore, it makes the situation more complex and the expected pre-combustion removal of these trace elements seems to be not possible for the high-ash non-coking coals of Talcher coal field.

Utilization of coal-flotation wastes at OAO TsOF Belovskaya

Flotation wastes at OAO TsOF Belovskaya are studied with a view to their disposal in systems for the combustion of high-ash coal. Analysis indicates that, if the flotation wastes are mixed with regular coal, they may be used as fuel in low-temperature fluidized-bed furnaces. The introduction of such furnaces in the drying department at OAO TsOF Belovskaya is recommended, for use in the drying of coal concentrates.

Thermodynamic evaluation of integrated gasification combined cycle: Comparison between high-ash and low-ash coals

Summary In the present study, a coal-integrated gasification combined cycle power plant is simulated. A high-ash coal and low-ash coal are considered to compare the performance of the plant. The combined cycle is in typical commercial size with 450 MW capacity. The feeds are Tabas and Illinois #6 coals which approximately contain more than 30% and 10% ash and have higher heating values of 22.7 MJ/kg and 26.8 MJ/kg, respectively. Energy and exergy analyses are done by aspen plus® and ees, respectively. Energy analysis shows that the overall efficiencies of power plants using high-ash and low-ash coals are 33% and 28%, respectively. The result shows that in high-ash case, 52 kg/s coal, 10 kg/s water, and 1050 kg/s air and in low-ash case, 48 kg/s coal and 820 kg/s air are required for providing mentioned power, approximately. Exergy analysis shows that maximum exergy destruction is in heat recovery steam generator unit. Investigating the emissions shows that high percent of ash in the coal composition has slight effects on the IGCC pollution. Finally, from thermodynamic viewpoint, it is concluded that the high-ash coal, like the conventional one, can be used as thermally efficient and environmentally compatible feed of IGCCs. Copyright © 2016 John Wiley & Sons, Ltd.

Statistical optimization study of jigging process on beneficiation of fine size high ash Indian non-coking coal

Non-coking coal is used for metallurgical and cement industries apart from generating energy. Indian non-coking coals are high in ash content because of drift origin. These high ash coals require beneficiation before being used. Jigging is one of the unit operations used for beneficiation of coal. Beneficiation by jigging is carried out for the coarser size of particles. Jigging of fine size coal is limited. However, in present study two fine non-coking coal samples having sizes −3+2mm and −2+1mm were used for jigging study. In present study jigging experiments were performed using laboratory Denver mineral jig by varying feed size, water rate, and feed rate. 23 full factorial experimental design was used to study the performance of jigging operation. The performance of jigging was judged by statistical analysis; where ash content and combustible recovery of concentrate were considered to be responses. In addition to statistical analysis, optimization study was also carried out by Nelder–Mead multidimensional pattern search method. Statistical models developed in the present study could predict ash content and yield of the concentrate accurately. At optimized condition, it was possible to achieve 22.6% ash content with 64.15% combustible recovery.

Synergetic and inhibition effects in carbon dioxide gasification of blends of coals and biomass fuels of Indian origin

The present study investigates the enhancement of CO2 gasification reactivity of coals due to the presence of catalytic elements in biomass such as K2O, CaO, Na2O and MgO. Co-gasification of three Indian coal chars with two biomass chars has been studied using isothermal thermogravimetric analysis (TGA) in CO2 environment at 900, 1000 and 1100°C. The conversion profiles have been used to establish synergetic or inhibitory effect on coal char reactivity by the presence of catalytic elements in biomass char by comparing the 90% conversion time with and without biomass. It is concluded that both biomasses exhibit synergistic behavior when blended with the three coals with casuarina being more synergetic than empty fruit bunch. Some inhibitory effect has been noted for the high ash coal at the highest temperature with higher 90% conversion time for the blend over pure coal, presumably due to diffusional control of the conversion rate.

Composition and structure of the mineral and combustion residues of high-ash coal

Elemental composition and infrared spectra of mineral and cindery residuals of high-ash coal coming from a deposit of northern Kazakhstan is under consideration. New concepts about the structural transformations in mineral substance of coal during combustion are presented. The combustion, as shown, is leading to changes of elemental composition and distortions of symmetry of SiO4-tetrahedrons, which form a basis of silicates.

Integration of pyrolysis and entrained-bed gasification for the production of chemicals from Victorian brown coal — Process simulation and exergy analysis

This paper introduces a novel process for the integration of pyrolysis and entrained-flow gasification for the as-mined Victorian brown coal containing 65wt.% moisture. An initial mild pyrolysis of coal is proposed to reduce moisture content, and produce multiple products including char, tar and hydrogen-rich coal gas. Subsequently, the resulting water-free char is subjected to an entrained-flow gasifier, upon the blending of silica additive or high-ash bituminous coal. The resultant syngas passes through a cleaning unit and water gas shift reactor before mixing with the pyrolysis-derived gas to reach a target H2/CO molar ratio of 2.0 that is essential for the synthesis of a number of chemicals. In this paper, process simulation and exergy analysis were conducted to prove the advantages of the proposed process against the conventional drying–gasification combination. The results show that, the proposed pyrolysis–gasification integration process for Victorian brown coal possesses an exergy efficiency 4.5% higher than the drying–gasification process, and 1.5% higher than the drying case for another lignite containing 25wt.% moisture. A prior removal of 20% of the inherent moisture can further improve the exergy efficiency by 4% for Victorian brown coal. The addition of 20% of black coal is the optimum ratio to improve the ash slagging propensity, as well as improve exergy efficiency compared to the conventional drying–gasification process.

COAL VS PETROLEUM AS ENERGY SOURCE FOR INDIA

Coal as such has been used in Power Plant as a fuel for long and can be converted to liquid fuel in a coal liquefaction plant to supply Naphtha for Petrochemical Industries and Diesel and Petrol for running vehicles. The cost of producing liquid from coal ranges from $ 35 to $ 60 / bbl whereas crude Petroleum derived similar products’ cost vary anywhere from $ 50 to $ 100/bbl mainly due to crude price variation in International Market since the processing cost of crude in a Refinery is nominal i.e. It varies from $ 1 to $ 1.5 / bbl under Indian scenario. However, under Indian scenario coal ash handling and disposal is a major problem due to high ash coal in a coal Refinery whereas in a petroleum Refinery there is no such problem. Since in India Petroleum Reserve is very little in comparism to demand of Petroleum Products and in order to meet the demand crude petroleum is imported from Middle Eastern countries there is huge drainage of India’s Foreign Exchange. Thus, coal may be an alternative under Indian scenario since coal reserve in India is about 300 billion tons out of which 50% is Bituminous coal that can be easily liquefied to various products as mentioned above. In this article comprehensive discussions on different aspects of a coal refinery and that of a Petroleum Refinery have been presented.

High Ash Char Gasification in Thermo-Gravimetric Analyzer and Prediction of Gasification Performance Parameters Using Computational Intelligence Formalisms

The coal gasification is a cleaner and more efficient process than the coal combustion. Although high ash coals are commonly utilized in the energy generation, systematic gasification kinetic studies using chars derived from these coals are scarce. Accordingly, this paper reports the development of the data-driven models for the gasification of chars derived from the high ash coals. Specifically, the models predict two important gasification performance parameters, viz. gasification rate constant and reactivity index. These models have been constructed using three computational intelligence (CI) methods, namely genetic programming (GP), multilayer perceptron (MLP) neural network (NN), and support vector regression (SVR). The inputs to the CI-based models consist of seven parameters representing the gasification reaction conditions and properties of high ash coals and chars. The data used in the modeling were collected by performing extensive gasification experiments in the CO2 atmosphere in a thermo-gravimetric analyzer (TGA) using char samples derived from the Indian coals containing high ash content. Values of the two gasification performance parameters were obtained by fitting the experimental data to the shrinking unreacted core (SUC) model. It has been observed that all the CI-based models possess an excellent prediction accuracy and generalization capability. Accordingly, these models can be gainfully employed in the design and operation of the fixed and fluidized bed gasifiers using high ash coals.

Modeling of High-Ash Coal Gasification in an Entrained-Flow Gasifier and an IGCC Plant

AbstractGasification of high-ash coal in dry and slurry entrained flow gasifiers is investigated through equilibrium modeling. Effects of oxygen- and steam-to-coal mass flow rate ratios in a dry-fed gasifier and also the effect of water concentration in slurry on composition, temperature, heating value, and cold gas efficiency are studied. It is observed that adding steam to the gasifier reduces oxygen consumption, and the optimum ratio of oxygen-to-coal mass flow (O/F) decreases. At high enough O/F ratios, the steam-to-coal mass flow (S/F) and water-to-coal mass flow (W/F) ratios have no significant influences on gasifier efficiency. It is also observed that for coal, which has a high ash content, dry-fed gasification is preferable. In this type of gasifier, optimum O/F and S/F ratios with respect to cold gas efficiency are determined to be 0.5 and 0.8, respectively. Simulation of the integrated gasification combined cycle (IGCC) in Thermoflow indicates that, for a typical 450-MW combined cycle, 56.6 kg...

Characterization of Some Nigerian Coals for Power Generation

Five coal samples from Odagbo (Kogi State), Owukpa (Benue State), Ezimo (Enugu State), Amansiodo (Enugu State), and Inyi (Enugu State) of Nigerian coal deposits were subjected to proximate analysis, ultimate analysis, calorific value determination, and petrographic and thermogravimetric analysis to determine their suitability for power generation. Based on results of tests carried out, Amansiodo coal is a bituminous, low sulphur, and medium ash coal, while Owukpa coal is a subbituminous A, low sulphur, low ash coal rich in huminites, Odagbo coal is a subbituminous B, medium sulphur, low ash coal rich in huminites, Ezimo coal is a subbituminous C, low sulphur, high ash coal, and Inyi coal is a subbituminous C, low sulphur, high ash coal. Between Odagbo and Owukpa subbituminous coals, Owukpa has a lower ignition temperature (283.63°C) due to its higher volatile matter content (39.1%). However, Ezimo subbituminous coal, which has a lower volatile matter (31.1%), unexpectedly has the same ignition temperature as Owukpa (283.63°C) due to its higher liptinite content (7.2%) when compared with that of Owukpa (2.9%). The ease of combustion of the coal samples in decreasing order is Odagbo &lt; Owukpa &lt; Inyi &lt; Ezimo &lt; Amansiodo.

Flotation behavior of hard-to-separate and high-ash fine coal

The flotation behavior of hard-to-separate and high-ash fine coal was investigated using conventional flotation with constant power input. A new flotation process, based on energy input and distribution, was designed to lower the ash content of concentrate. The results obtained using Fourier transform infrared (FTIR) analysis show that the coal samples have good floatability because of many hydrophobic and few hydrophilic functional groups. Under a constant power input, a large number of ash- forming materials floated into a froth product at the start of flotation. Based on the Fuerstenau upgrading curves, it was determined that the 0.25-0.074 mm size fraction range showed the worst selectivity when compared with 0.50-0.25 mm and -0.074 mm size fractions. The desired concentrate with an ash content of 13.98%, 27.59% of ash recovery, and 80.01% combustible matter recovery could be obtained by transferring the excess energy of the flotation-conditioning stage to the pre-conditioning stage and increasing the power input step-by-step in the flotation-conditioning stage at equal total energy consumption.

COMPLEX REAGENTS BASED ON INDUSTRIAL CONCENTRATES AROMATIC HYDROCARBONS FOR THE FLOTATION OF HIGH-ASH COALS

In article are presented results of investigation of developing of complex reagent based on side product of ethyl benzene formation and light gasoline of catalytic cracking for high-ash coals flotation process in central ore-dressing factory (COF) Pechorskaya JSOC Vorkuta-Ugol. It is discovered that on vat residue of ethyl benzene rectification has 70-90 % vol. in reagent, coal yield increases on 10-16 % wt., extraction of combustible matter increases on 10-17 % wt., accordingly. High activity of flotation reagent, in our view, is connected of the presence of vat residue of ethyl benzene rectification of polyethylbenzenes (bi- and three), with increased adsorption activity and high hydrofobization capacity in compared to paraffin-naphthenic and aromatic hydrocarbons in gasoline fractions. It is established that using complex reagent UKF-1 gets to increase yield of concentrate on 1.4 % wt. in compare with regime with separating entrance collector-reagent and frothing-agent. It is founded that more reliable flow for developed reagent regime is 1.6 kg /ton, coal yield has 59,6 % wt., ash content locates in possible levels and has 9,0-9,1 % wt. A further increasing of the flow rate of the reagent to 2.0 kg/t reduces the selectivity of the flotation process. It is defined main physic-chemical properties for offered reagent according to requirements and standarts for flotation reagents. It is offered principal technological scheme of flotation of coal with complex reagent, characterized with high-economical indicators.

Organo-refining of high-ash Indian coals at bench scale

Organo-refining is a process of solvent extraction through which organic matters are extracted from coal using organic solvents. Indian coals have high mineral matter content ranging from 25 to 45wt.% (dry basis). The ash in coal is highly disseminated, which makes it difficult to remove by physical beneficiation. Thus, chemical beneficiation is needed to remove the mineral matter. This study was conducted for high ash Indian coals at bench scale. The capacity of the bench scale plant was 40kg/batch feed basis. Coking coal, washery discards and thermal coals of bituminous origin were used as feed material. The mineral matter of these coals varied in the range of 27–36wt.% (db). The feed size of the particle was below −0.5mm. N-methyl-2-pyrrolidone (NMP) and ethylenediamine (EDA) were used as main solvent and co-solvent respectively. The extraction was done at 200°C with 1:6 coal to solvent ratio (by mass, wt./wt.) for 60min. Extraction was followed by solid–liquid separation, solvent recovery and washing of products. The feed and product materials were subjected to proximate analysis, ultimate analysis, and Free Swelling Index (FSI) tests. Organo-refining process produced clean coal yield in the range of 30–45% and clean coal mineral matter was less than 10% for coking as well as non-coking coals. Free Swelling Index (FSI) also improved from 1–5 range for feed coals to 7–8 for product clean coals. Two types of filter (basket and centrifuge) were also tried for separation of solid and liquid from different types of slurries. It was observed that cake moisture can be reduced by 6–12% points for these slurries using decanter centrifuge. The cake moisture reduced to 70% from 76% for clean coal slurry and 60% to 48% for reject slurry. The clean coal yield increased by 5 units (from 35% to 40%) with decanter centrifuge filter. In order to have better filtration and precipitation, the extraction was carried out by mixing of two different raw coals (TL and TC) in a certain ratio (1:1 to 1:3). Also, the extraction was done separately for TL and TC coals and then the clean coal extracts were mixed in 1:1 to 1:3 proportions. Mixing of two raw coals gives better results (36wt.% yield with 6.4% ash clean coal) than mixing of their extracts (30wt.% yield with 6.7% ash clean coal).

Thermogravimetric and evolved gas analyses of high ash Indian and Turkish coal pyrolysis and gasification

High ash coals from India and Turkey are investigated in this study. A coupled thermogravimetric analyzer and mass spectrometer system is used for the thermal decomposition characterization of the coal samples and the identification of the volatiles evolved during the various reaction regions. Coal samples are heated in argon, air, oxygen, steam and blended gas mixtures at the temperature range from 25 to 1250 °C. The experiments are performed to study the pyrolysis, combustion and gasification characteristics of typical Indian and Turkish high ash coals. Thermogravimetry and derivative thermogravimetry studies are applied to measure the conversion level and half-life time of the coals/chars during and after pyrolysis. The maximum mass loss occurs during the devolatilization stage of coals at the temperatures from 350 to 700 °C, where O2, CO2, CO, H2 and a small amount of CH4 are released. Coal particles start to react with steam and produce CO2, CO and H2 when the temperature is increased above 750 °C. The gasification reactions are completed around 950 °C in steam and steam blended ambience. The reactivity of high ash coal chars mainly depends on reagents’ and surrounding gases concentration and also the reaction temperature. The results indicate that the size effect of the char particles is minimal at high gasification temperatures. Char gasification rates determined by TG techniques under isothermal conditions in different reagent flow rates and size effect contribute to enhance the knowledge on high ash coal thermal characterization and gasification and, therefore, to establish the optimum operational conditions for syngas production from high ash coals.

Conversion of high-ash coal under steam and CO2 gasification conditions

The use of domestic high-ash coal reserves contributes to the security of energy supply, and therefore high-ash coal is expected to remain as a key energy source in several countries (e.g., India, Turkey) for at least the next 30–40years. However, the use of high-ash coals for energy production (currently performed mainly via combustion processes) poses a number of technical and economic challenges, e.g., low efficiency and environmental issues. Gasification is an attractive option, since it allows a more efficient, more environmentally friendly conversion of the coal. In particular, integrated gasification combined cycle (IGCC) offers high efficiency, reduced emissions and potential for the implementation of CO2 capture.With the aim of optimising the design and operation of high-ash coal fluidised-bed gasification processes, this paper studies the effect of temperature and partial pressure on the conversion and reactivity of coke from an Indian high-ash coal under CO2 and steam gasification conditions using thermogravimetric analysis. Moreover, additional steam gasification tests have been carried out in order to determine the conversion rate under realistic fluidised-bed gasification conditions (e.g., coal ash as bed material, coal particle size, heating rate, bed hydrodynamics, gasification atmosphere), thus taking into account the effect of mass and heat transfer phenomena.Results of isothermal TGA tests have shown that coke reactivity increases at higher temperatures and/or partial pressures of gasifying agent. The experimental data have been fitted to two conversion models (shrinking core and volumetric). The determination of kinetic parameters (reaction order b, pre-exponential factor A and activation energy Ea) has been carried out at three conversion levels: X=0.2, X=0.5, and X=0.8. In the case of CO2 gasification, the reaction order b ranges between 0.2 and 0.8, although at temperatures of 850–900°C, the reaction order has a value around 0.6. In the case of steam gasification, the reaction order ranges between 0 and 1.1, and increases with reaction temperature.Fluidised-bed steam gasification tests have shown that approximately 23–27% of the carbon contained in the coal (~40–45% of the overall coal, considering also hydrogen and oxygen released in the gas) is quickly converted during the devolatilisation stage. Between 12 and 22% of the carbon contained in the remaining coke is converted to gas within the first 25min of steam gasification. Finally, 55–80% of the carbon in the coke remaining after steam gasification is converted during the first 25min of oxidation with air. Conversion of the high-ash coal is favoured at higher steam partial pressures and/or higher gasification temperatures. The conversion rate under fluidised-bed conditions is significantly lower than that obtained in TGA tests at similar temperature and steam partial pressure values. Differences in coal particle size, heating rate during devolatilisation, inhibition issues, and other fluid-dynamic effects influence the reactivity of the produced coke as well as the heat and mass transport rates. The overall effect of these phenomena is a shift in reaction regime. Operation under realistic FB conditions has an equivalent effect to a decrease in the gasification temperature under TGA conditions.

Modeling and full-scale tests of vortex plasma-fuel systems for igniting high-ash power plant coal

The processes of supplying pulverized-coal fuel into a boiler equipped with plasma-fuel systems and its combustion in the furnace of this boiler are investigated. The results obtained from 3D modeling of conventional coal combustion processes and its firing with plasma-assisted activation of combustion in the furnace space are presented. The plasma-fuel system with air mixture supplied through a scroll is numerically investigated. The dependence of the swirled air mixture flow trajectory in the vortex plasma-fuel system on the scroll rotation angle is revealed, and the optimal rotation angle at which stable plasma-assisted ignition of pulverized coal flame is achieved is determined.

Production of carbon reducing agents from high-ash coal

Tests are conducted on the production of high-ash coke from Batyr, Kuuchek, and Sary-Adyr coal (Kazakhstan). The mechanical strength of the coke is assessed.

High ash coal pyrolysis at different heating rates to analyze its char structure, kinetics and evolved species

Mass losses of high ash coal and the mole fractions of evolved species were measured during pyrolysis using a thermo-gravimetric analyzer (TGA) and a mass spectrometric analyzer, respectively. Coal samples of three sizes from Bilaspur, India were pyrolyzed using the TGA in an argon atmosphere under dynamic conditions at atmospheric pressure under the heating rates of 40, 100, 500, and 1000°C/min until the furnace temperature reached 1000°C and maintain the temperature to complete the pyrolysis process. The structural properties of the produced char such as pore surface area (BET) obtained by N2 adsorption method and SEM analysis were performed in order to explain the differences in structure based on char generation method. The BET surface area is increased by more than twofold when the heating rate is raised from 40°C/min to 1000°C/min. The kinetic parameters of activation energies (E) and Arrhenius constant (A) of thermal pyrolysis for different sized coal particles at various conversion levels were correlated from the thermogravimetric data under four heating rates. The dependencies of kinetic parameters on particle size and conversion levels during coal pyrolysis were estimated. The results revealed that higher pyrolysis rate of coal would greatly increase the yield of light gases such as CO, H2 when compared to slower pyrolysis process.