High-ash Coal Research Articles

CO2 enhanced in-situ oxy-coal gasification based carbon-neutral conventional power generating systems

UCG (Underground coal gasification) is an economic and a viable in-situ clean coal technology in exploiting deep underground coal resources. Sustaining a combustion front in the in-situ gasification of high ash coal is difficult if steam acts as a gasifying medium. In addition, the use of superheated steam causes the transportation problem for deep coal seam. Conversely, these problems could be avoided if CO2 is used as the gasifying medium. In order to implement a CCS ready system in existing plants, the present study investigates the feasibility of integration of CO2/O2 gasification of in-situ coal with conventional power generating systems such as steam turbine and combined cycle power plants performing in a CO2/O2 mode of combustion. The effect of operating pressure and the ratio of CO2/O2 input to an UCG system on the net thermal efficiency of the IGCC system are evaluated. A detailed energy analysis of the CO2 enhanced IUGCC (UCG integrated with the combined cycle) shows a high net thermal efficiency of 41% with CCS (carbon capture and storage) at the UCG operating pressure of 27 bar. IUGST (Integration of low pressure UCG with a steam turbine cycle) system shows a net thermal efficiency of 27% with CCS.

Recovery of Combustibles from Fine Coal through Controlled Air Fluidization over Inclined Deck

The segregation pattern for dry beneficiation of fine coal (–1.0 + 0.1 mm) in an air table was investigated. The feasibility of cleaning a high ash (~49%) coal to the ash level specified for application in a thermal power plant (34%) was established. The density (ash) distribution pattern on the deck surface at steady state established the progress of segregation under various operating conditions. The operating regimes for a desired product at suitable mass yield were identified. A strategy was developed to process the high ash thermal coal and the flow scheme was established through which around 47% mass yield of the clean coal was obtained at 34% ash level. A second product was generated which was suitable for application in a fluidized bed combustion unit. A completely rejectable tailing was also obtained with 69% ash having a mass yield of 33%. Thus, it was established that high ash coal fines can be treated efficiently by controlled air fluidization over an inclined porous deck. The present study also brought out the features of separation and how segregation progresses over the deck as the material moves towards the discharge end. The effects of important process variables on the separation performance as well as on the segregation pattern were also established.

Kinetics of steam and CO 2 gasification of high ash coal–char produced under various heating rates

Abstract Char particles of high ash Indian coal with different sizes are produced using thermogravimetric method at different heating rates. Particle diameter and porosity changes during devolatilization significantly affect char gasification rates. The effect of coal particle size on char production under various heating rates is reviewed. Char gasification is affected by operating conditions such as reaction temperature, char production method, and particle size in addition to chemical composition and physical structure of char. The measurements of the steam and CO2 gasification rate of the produced chars are performed by an isothermal thermo-gravimetric analysis at the temperatures of 900, 950, and 1000 °C under ambient pressure conditions. It is found that the reactivity of char gasification is increased along with heating rate of char. Three kinetic models are applied to describe the varying conversion rate: volumetric model, grain model, and random pore model. The activation energy of the gasification is varied based on the char generation method and particle sizes. The activation energy is varying from 122 to 177 kJ mol−1 for steam gasification and 130 to 214 kJ mol−1 for CO2 gasification to different sized char particles. The effect of char heating rate on gasification is more pronounced in the activation energies of smaller sized particles.

The Deashing of High-ash Coking Coal Fines by Flotation

Coking coal is usually used to produce coke and then coke is applied in the minerals metallurgy. Worldwide, coking coal is relatively exiguous compared with other rank coals, i.e., lignite and anthracite. The high-ash coking coal fines have about 64% ash content in this article. Without the upgrading process, the high-ash coking coal fines can only be used as fuels. It is a waste of the coking coal resource. In this investigation, an attempt was made to float some clean coals from high-ash coking coal fines. Fourier transform infrared was used to indicate the chemical properties of high-ash coking coal fines. Fourier transform infrared results show that the primary mineral is kaolin in the high-ash coking coal fines. Contact angle measurement was also used to indicate the contact angles of coking coal fines at different gravity ranges and it shows that the contact angle decreases with the increase of gravity range. In this article, some clean coals with ash content of 13.48% could be obtained from high-ash coking coal fines based on natural hydrophobicity and low impeller speed.

Characterization and co-firing potential of a high ash coal with Bambusa balcooa

Two pre-treatment methods, i.e. torrefaction and low-temperature carbonization, were applied to a bamboo species, “Bambusa balcooa” at a temperature between 250°C and 380°C. The physicochemical characteristics and thermal behavior of the coal, raw bamboo and thermally treated bamboo sourced from South Africa were investigated using thermogravimetric analysis (TGA). The aim was to enhance the fuel quality and to determine the combustion potential of B.balcooa solely, or co-fired with a low rank bituminous coal. The co-firing of the raw and thermally treated bamboo samples with coal of 27.50% ash content was conducted in the absence of oxygen, using a ratio of coal inclusion of 10%, 30%, 50% and 75%.Results obtained from the proximate and ultimate analyses show a considerable difference in the quality of the raw bamboo from the thermally–treated samples. The ash content and fixed carbon “dry basis” of the raw B.balcooa (BB) were found to be 0.49% and 6.01%, respectively, with a calorific value of 18.53MJ/kg. After the BB was torrefied (TBB) at 280°C and carbonized (CBB) at 380°C, a fuel with 3.63% ash content and 38.20% fixed carbon, with calorific values of 24.02MJ/kg and 28.20MJ/kg respectively was produced. The nitrogen content of the raw BB was found to be 0.22% while the sulfur was untraceable.Using the TGA data, activation energy (Ea) of 64.12kJ/mol was obtained from the coal tested, which was higher than that obtained from the raw BB (11.24–31.60)kJ/mol. Higher Ea values were obtained as the thermal treatment temperature increased. The Ea values for the carbonized samples were within the range of (67.33–71.71)kJ/mol compared to the torrefied samples (43.70–44.70)kJ/mol. The TG curves were fitted using the Coats Redfern model. In summary, the results showed that the most effective mechanisms for controlling the combustion process in all samples under stage 3 “carbon combustion” were the chemical reaction models (O1, O2 and O3).

Flow pattern evaluation of the internal circulation gasifying principle

Gasification is a key process for the thermochemical conversion of coal for both energetic utilization and its application as a chemical feedstock. In this regard low grade coal with high-ash content gains in importance. Because of its high availability, production share is increasing. Therefore, adapted gasifiers of novel design are required to meet the demands associated with converting high-ash coals. The internal circulation (INCI) principle is a multi-stage gasification system with the ability to efficiently convert high-ash feedstock.The present paper introduces the test-scale COORVED reactor, which was designed according to the INCI principle. Particle image velocimetry (PIV) and computational fluid dynamics (CFD) simulations are conducted for ambient conditions in a cold-flow test facility to demonstrate the flow pattern according to the INCI principle. The evidence of a recirculation cell is provided by PIV experiments. CFD simulations show similar results in terms of overall flow pattern and size of the recirculation cell. After the intensive investigations of the flow pattern in the cold-flow test facility, first PIV results were obtained in the COORVED reactor. The complex accessibility of the reactor raised the necessity of the validation of the elaborate measurement setup. The reliability of the measurement results is proven by generating a laminar velocity profile at ambient conditions, whose results are comparable to analytical solutions.

Introductory study on Fuel-Slurry Integrated Gasifier/Gas Turbine (FSIG/GT) alternative for power generation applied to high-ash or low-grade coal

This is the first round of studies to verify the technical feasibility of applying the Fuel-Slurry Integrated Gasifier/Gas Turbine (FSIG/GT) concept for thermoelectric power generation consuming high-ash coal (HAC). Such resource is, in most instances, considered unprofitable and usually discarded as a residue. This is part of a series dedicated to the application of FSIG/GT, which has already shown the possibility of increasing the efficiencies of conventional power generation based on sugar-cane bagasse and municipal solid waste (MSW). As before, a water-slurry of fuel particles is injected into pressurized vessels using commercially available pumps. Therefore, it avoids the cumbersome sequential or cascade feeding systems. In addition, the process does not need the application of pure oxygen or hydrocarbons to ignite the particles in the injected slurry. The slurry is prepared to contain fractions of dry-solid fuel near the limit allowed for the operation of slurry pumps. The slurry is injected into a dryer, from which the dry solid particles enter the gasifier. As the dryer and gasifier operate under similar pressures, simple rotary valves and Archimedes’ screws can accomplish the transference from one vessel to the other. The produced fuel gas is cleaned to decrease its particle content and size as well alkaline concentration and reach acceptable limits for injections into standard gas turbines. Power steam turbine cycles are used to recover energy. Having in mind the low quality of HAC as fuel, the overall power generation efficiencies attained in the present study seem reasonable. Nonetheless, unlike conventional processes consuming HAC, the present one does not require de-ashing. Future studies will explore possibilities of improving the values achieved at the present instance.

Effect of elevated temperature and pressure on the leaching characteristics of Indian coals

The Indian coal washing circuits are cursed with the availability of high ash coals having poor liberation characteristics as feed material. This result in unacceptably very low product yield (i.e. 10–15%) when aspiring for low ash clean coal (around 8–10%) for efficiently utilising it in iron making process in the form of coke. In this context, a chemical beneficiation route has been explored for demineralising high ash Indian coals. In this work, the effect of aqueous alkali leaching followed by acid washing on the removal of mineral matter from two different captive coals of Tata Steel at elevated temperature and pressure have been explored. The research study revealed that it is possible to reduce the ash content up to 70% by this method. The effect of process conditions such as alkali concentration, temperature and pressure upon the demineralisation kinetics have been investigated. The alkali content of the product coal does not increase whereas the silica and alumina content reduces by nearly 51.3% and 58.8% respectively. Significant reduction in the phosphorus content is observed after the acid treatment. The process does not significantly affect the crucible swelling number index for coking property of coal.

EFFECTIVE REAGENTS FOR FLOTATION OF HIGH-ASH COALS AT PECHORA CENTRAL CONECTRATING FACTORY

In the article the questions on the development of effective reagents for flotation of refractory and high-ash coal with a high content of husenovich elements. Presents research results of physico-chemical properties of this coal sieve and fractional composition, petrographic and reflectograms analyses of the studied coal and ash. Obtaining concentrates by flotation with ash satisfying coke production using known flotation agents difficult. Studied reagent regimes with the use of flotation reagents on the basis of petrochemical intermediates. It is established that the introduction of the DT to 50 volume % diethylbenzene fraction (BPA) and the cubic residue of ethylbenzene (CORE) allows not only to reduce reagent costs by 20-40 % wt., but also to increase the output of concentrate on 15-30 % of the mass. Based on the results of quantum-chemical calculations of possible transformations of alkylaromatic hydrocarbons in the alkylation process (CORE, BPA) hypothesized that the high activity of 1,3,6 - triethylbenzene (the main component of CARE), compared with 1,2-diethylbenzene (the main component BPA), is associated with more favorable spatial orientation of the ethyl group, which facilitates the efficient adsorption of triethylbenzene on the surface of the coal due to the spatial structure. It is established that the application of the recommended reagent conditions (a mixture of diesel fuel with CORE 50/50 wt%.) also allows you to increase the rate of flotation of fine coal. At the equal time, the output of concentrate in the case of using a mixture of diesel fuel with CARE amounted to 68%, and when using DT - 58%, the consumption of diesel fuel 3 times higher.

Determination of the ash content of solid fuel using annihilation γ-rays

The possibility of the instrumental determination of the ash content of solid fuel using annihilation γ-rays was demonstrated. Analytical expressions for the evaluation of sensitivities were obtained. The method was recommended for the analysis of high-ash coals in large masses without special sample preparation.

Experimental Research of Roughing and Cleaning Column Flotation of Difficult-to-Float High Ash Coal

Coal slime in Zhongcheng coal preparation plant in Baotou, Inner Mongolia, was analyzed. It is found that this coal sample is with high inner ash content and very difficult to float. It is hard to obtain low ash concentrate and high ash tailing with primary flotation. The live scale required ash content is 12.00% for total clean coal, 15.00% for flotation concentrate. It is found that the lowest concentrate ash content is 29.24% through exploring flotation experiments, which can not meet the producing requirement. Results of timed release flotation experiment show that when concentrate ash content is 15.00%, the theoretical concentrate yield is 24.36%, with 50.03% of flotation tailing ash content and 35.49% of combustible matter recovery. It can be concluded that the floatable grade of this coal sample is Very Difficult to Float. So flotation column is taken into account. The lowest concentrate ash content of roughing flotation by flotation column is 18.94%, which does not meet the requirement, either. Results of cleaning flotation of roughing flotation concentrate show that when the recycling pressure is 0.14 MPa, the concentrate ash content is 14.15% with a yield of 30.39%, which is satisfactory and can be referred to direct industrial production.

Ash limitation of physical coal beneficiation for medium–high ash coal—A geochemistry perspective

Nowadays the industrial coal beneficiation in China could only reduce the ash yield to about 10%, which could not meet the requirement or standard of environment protection. In this work, the possibility of reducing the ash yield was studied from the aspect of geochemistry. The channel samples were collected from two coal seams in Guizhou and Shanxi province, China and then conducted analysis by combining data from coals worldwide. The result reveals that the same coal seam or the coals deposited in the same peat swamp show a significantly positive correlation between ash yield and Al2O3+SiO2 content, and the intercept of regression equation on the ash axis is always less than 5% (generally 2–5%). Overall, the coal from China is featured with a higher intercept compared with that in the other countries. The intercept of 2–5% on the ash axis indicates an original inorganic component in coal-forming peat. The research result also presents a theoretical limitation of coal ash by coal cleaning, because 2–5% of inorganic components in medium–high quality ash coal could hardly be separated by traditional physical coal beneficiation.

Heat integration and exergy analysis for a supercritical high-ash coal-fired power plant integrated with a post-combustion carbon capture process

The International Energy Agency (IEA) has recommended eliminating at least 80% of the CO2 emission from the power sector by 2050 as a response to climate change. Meeting this target is expected to be challenging since a lion’s share of the power generation is based upon coal combustion. A cost effective strategy to decarbonise the power sector would require carbon capture and storage, largely through a post-combustion capture (PCC). In this study, a model of the supercritical coal-fired power plant (CFPP) fed with a high-ash coal was developed and validated, a validated model of a PCC pilot plant using monoethanolamine (MEA) solvent is scaled-up to meet the CFPP capacity, a CO2 compression unit model was developed to fully assess the energy penalty, and the three models were integrated for a 90% capture level. This required determination of the PCC steam requirement and identification of the optimal condensate return location. The performance of the integrated models was compared with the reference CFPP model (with a net efficiency of 39.1%), and the energy penalty was estimated to cause a 25% fall in the CFPP power output. Then, energy saving opportunities were investigated through the heat exchanger network (HEN) analysis. Several HEN designs were analysed, revealing that heat can be recovered from the flue gas leaving the CFPP, and used to heat up boiler feedwater to enhance the plant efficiency. Such a configuration resulted in reduction of energy penalty by 4.15%, improving the performance of the integrated plant. Finally, it is inferred from the exergy analysis that further energy savings can be achieved by reducing the exergy destruction in the PCC.

Use of an Artificial Neural Network to Evaluate the Oleo-Flotation Process to Treat Coal Fines

The results of beneficiation studies of high-ash fine coal using the Oleo-flotation process are presented. The influence of three key variables (diesel oil dosage, wash oil [a product of crude oil obtained during the process of refining at 275 to 300°C] dosage, and impeller speed) of the Oleo- flotation process on yield % and ash % is presented in this article. An attempt is made to develop a three-layer feed-forward artificial-neural-network (ANN) model based on the experimental data set, which was trained using an error-back-propagation algorithm. The results indicated that the predictions from the ANN model are in good qualitative and quantitative agreement with the experimental observations, thereby validating the applicability and accuracy of the developed ANN model.

Fabrication of a complex aluminosilicochrome alloy by a slag-free method

The results of experimental studies of obtaining a complex alloy of aluminosilicochrome from high-ash coals of the Karaganda basin are presented. As a result of carrying out large-scale laboratory studies, a high-quality alloy not subjected to disintegration is formed. A method for melting of refined grades of ferrochrome using aluminosilicochrome as a reducer is suggested.

Artificial Intelligence-based Modeling of High Ash Coal Gasification in a Pilot Plant Scale Fluidized Bed Gasifier

The quality of coal—especially its high ash content—significantly affects the performance of coal-based processes. Coal gasification is a cleaner and an efficient alternative to the coal combustion for producing the syngas. The high-ash coals are found in a number of countries, and they form an important source for the gasification. Accordingly, in this study, extensive gasification experiments were conducted in a pilot-plant scale fluidized-bed coal gasifier (FBCG) using high-ash coals from India. Specifically, the effects of eight coal and gasifier process related parameters on the four gasification performance variables, namely CO+H2 generation rate, syngas production rate, carbon conversion, and heating value of the syngas, were rigorously studied. The data collected from these experiments were used in the FBCG modeling, which was conducted by utilizing two artificial intelligence (AI) strategies namely genetic programming (GP) and artificial neural networks (ANNs). The novelty of the GP formalism is ...

Thermal characterization, gasification and kinetic studies of different sized Indian coal and char particles

Four different sizes of Indian high ash coal and char are investigated. A simultaneous thermal analyzer and mass spectrometer is used for the characterization of the coal and char samples and the identification of the volatiles evolved during the heating of the sample upto 1,050 °C under combustion cum gasification related conditions. The TG and DTA results are discussed for the investigations under air, oxygen, steam and blended gas atmospheres. The thermogravimetry—mass spectrum profile of the coal provides information on combustion performance (ignition, peak combustion and burnout temperatures) and on chemical changes to the volatile matter (H2, O, CO and CO2), char and minerals. The size effects of the coal and char during pyrolysis, combustion and gasification are discussed. The appropriate temperature ranges to the high ash coal gasification in the steam and steam blended gases are evaluated. The Arrhenius model is applied to determine the kinetic parameters from TG/DTG curves.

Limits to co-combustion of coal and eucalyptus due to water availability in the state of Rio Grande do Sul, Brazil

Brazil has favorable edaphoclimatic conditions for the cultivation of biomass for energy. On the other hand, the country plans to expand its thermal power park using fossil fuels, including Brazil’s high ash coal. This study estimates the potential of co-firing biomass from energy forests in power plants fired with Brazilian coal in the state of Rio Grande do Sul, Brazil, focusing on the limits given by biomass and water availability. Results show that the state holds coal reserves that could support a potential of approximately 8GW. Referring to limits due to water availability, different outcomes were found for the various coal fields in Rio Grande do Sul. The Candiota coal field, which represents the most important coal field, holding a capacity of 4GW, shows severe restrictions for water availability that would be aggravated by intense eucalyptus cultivation.

Heat-affected zone analysis of high ash coals during ex situ experimental simulation of underground coal gasification

Underground coal gasification (UCG) is a transient and evolving phenomenon in which many chemical and physical changes occur simultaneously and/or sequentially in various regions throughout the coal seam. Heat affected zones of dry and volatile depleted porous zones are formed up to a certain depth of the coal block leading to coal spalling. In the present work, we present a proximate analysis of the coal samples from various locations of the heat-affected zone (HAZ) during borehole combustion and gasification studies which simulate experimentally underground coal gasification. Results from HAZ studies of wood and four coals show that there is a considerable change in the volatiles to fixed carbon ratio in the depth direction and that the extent of variation depends on the coal as well as on the conditions prevailing during the experiment. These results have a potential bearing on the reactivity of the coal and the product gas composition.

Control of Harmful Emissions Concentration into the Atmosphere of Megacities of Kazakhstan Republic

Solid fuel plays significant role in the development of civilization as the main fuel source. Use of low-grade (ash content ∼ 40-45%) coal is partially offset environmental problems also affect human health when it is burned. As the main industrial corporations use coal, in particular low-grade high-ash content coal from Ekibastuz coal basin because of its cheap cost the atmosphere of megacities like Almaty is polluted by noxious volatile. In this study were developed a mathematical model of turbulent heat and mass transfer process occurring in the combustion chamber of SB-39 of Aksusskaya TPP for control the concentration of volatile and to recommend the optimize methods for burning process. Based on 3D computer modeling investigated formation of harmful dust and gas emissions during the combustion of low-grade coal and offered cost-effective methods of burning.