Coal Grinding Research Articles

Understanding FABA composition in coal-fired power plants: Impact of operating conditions and combustion efficiency on ash characteristics – A case study in PT Bukit Asam, South Sumatra, Indonesia

Coal-fired power plants are integral to global electricity production due to their cost-effectiveness and widespread availability of coal. This research investigates the operational dynamics of these plants, emphasizing the production of fly ash and bottom ash (FABA) as crucial by-products. The study focuses on three power plants in South Sumatra, Indonesia, operated by PT Bukit Asam Tbk. Fly ash and Bottom ash (FABA) and feed coal samples were collected to determine how the operational conditions of a power plant impact the composition of FABA. The mineralogical composition of FABA has been determined accurately with X-Ray diffraction analysis. Significant feed oxides in coal and FABA were identified using inductively coupled plasma atomic emission spectroscopy (ICP-AES). The primary characteristics of FABA mostly consist of unburned carbon, which may exceed levels as high as 76.05 %. The existence of unburned carbon residues is evidence of an inefficient coal grinding operation and low combustion efficiency of carbon in the boiler. The abundance of quartz in the FABA corresponds to its condition of being unmelted when heated to a temperature of 850 °C. A decrease in operating temperature results in a lower percentage of amorphous glass. The presence of quartz and reduced plagioclase concentration in FABA components correspond to the utilization of boiler-incompatible sand as bed material. In addition a consequence of a decrease in combustion temperature, pyrite exhibits partial decomposition, resulting in the formation of a tiny amount of hematite, while the other pyrite is still into its original form. A relatively small amount of spinel was associated to a mineral composed of Fe-oxide. Spinel is formed as a secondary mineral through the decomposition of Fe sulfides and other Fe-bearing minerals that exist in coal. This study evaluates the combustion efficiency and operational characteristics of power plants by applying the shrinking reactive core model by the assistance of Matlab®. The results demonstrate that since the efficiency of coal combustion increases, the concentration of unburned carbon in the FABA decreases. The modeling corresponds with the current findings in the field.

Prediction of HGI of South African coalfields: a comparative application of ANN, SVR and LSTM models

ABSTRACT Hardgrove grindability index (HGI) is a significant index used to determine a mill’s capability and overall efficiency in the grinding of coal. There are several factors that affect HGI due to the complex nature of coal. The influence of proximate analysis, calorific value, total sulfur, and pyrite content on the HGI values of 292 coal samples from South African coalfields were examined. Predictive models of HGI are developed by using soft computing techniques such as Long Short-Term Memory (LSTM), support vector regression (SVR), and Artificial Neural Network (ANN). This study shows that ANN is the most effective predictive model for all the three coalfields, with SVR models being second and LSTM models being the least effective. The correlation between the predicted value and the input data is established by using the cosine amplitude method (CAM). It was found that HGI is most influenced by the fixed carbon content, calorific value, ash content and volatile matter content while pyrite has the least influence.

Influence of the Degree of Loading of a Ball Drum Mill with Grinding Balls on the Intensity of Coal Grinding

There is a direct relationship between the degree of loading of a ball drum mill with grinding balls and the intensity of coal grinding. With an increase in the degree of loading of the ball mill, the intensity of coal grinding also increases. This is due to the fact that with an increase in the number of grinding balls inside the mill, coal is exposed to more intense friction forces and impacts, which leads to more efficient grinding of the material. However, it should be borne in mind that if the mill is loaded too much, there may be a problem with insufficient circulation of the material, which can lead to a decrease in the efficiency of the mill. Thus, the optimal degree of loading of the ball drum mill with grinding balls should be selected depending on the characteristics of the material and the operating conditions of the mill to achieve maximum efficiency of grinding coal

Technology for Producing Composite Solid Fuel From Coals of Kyzyl-Bulak and Kozho-Kelen Deposits and Heated Bitumen

The paper presents the results of a study of the production of composite solid fuels (CSF) from compositions of coal from the Kyzyl-Bulak and Kozho-Kelen deposits and a bitumen binder. The possibilities of producing CSF from a mixture of bitumen and preheated coals have been studied. To determine the dependence of the quality of the resulting CSF on the grinding size, the above coal was crushed into three fractions: a fraction with a particle size of 0-1mm, a fraction with particles of 0-3 mm and a fraction of 0-5 mm. These 3 fractions of coal were subjected to sieve analysis and the granulometric composition was determined, then each fraction individually was subjected to briquetting on a hydraulic press, in a mold with a diameter of 40 mm. Based on the task, pressing took place at 3 parameters, namely: at a pressure of 10 MPa, 15 MPa and 20 MPa. The use of different pressures made it possible to trace the dependence of the quality of the resulting CSF on the pressing pressure and determine the optimal pressure parameter. Briquetting was also carried out at different concentrations of the charge and the mechanical properties of the CSF were determined at a binder concentration of 6, 8, 10%. It has been established that the use of a bitumen-like product (bitumen) as a binding material, obtained as a result of thermal dissolution of coal with oil waste at a temperature of 320-380°C, produces mechanically strong briquettes that have compression resistance up to 106 kg/cm2 and bending resistance up to 7.5 kg/cm2. It has been shown that the mechanical strength of briquettes increases with increasing degree of coal grinding, and also an increase in pressing pressure increases the mechanical strength of briquettes. As the moisture level of coal increases, the mechanical strength of the briquette decreases. The optimal parameters for producing CHP have been established: coal size 0-3 mm: humidity 6.5%, pressing pressure 200 kg/cm2.

Ecological and technological efficiency of the innovative coal-watercoal cluster of housing and communal serviсes

The possibilities of increasing the ecological and technological efficiency of the innovative coal-watercoal cluster of housing and communal services, including the mechanics of coal destruction in a hydraulic shock installation, are considered. The creation of an experimental coal-watercoal cluster of housing and communal services involves the use of innovative coal-watercoal technology in boilers under construction or in operation, including the processing of solid coal fuels into innovative coal-water fuel suspension with subsequent combustion in specially equipped furnaces. The set tasks of managing environmental and technological qualities in the process of preparing an innovative coal-water fuel suspension based on statistical analysis of the granulometric composition correlate with the tasks of obtaining micro- and ultrafine coal-water suspensions in order to achieve high environmental and technological qualities. The control of an innovative coal-watercoal fuel technology based on automatic control of the granulometric composition using the natural fracturing of coal for the control action during the destruction of coal by the method of water hammer is proposed. Technological patterns of reducing the negative technogenic impact on the geospheres are revealed, including a method for managing the environmental and technological qualities of an innovative water-coal suspension based on automatic control of the granulometric composition during coal grinding by the hydraulic shock method.

The use of Protodiakonov and Hardgrove methods to determine the effect of coal quality on its grinding ability

The factors affecting the mechanical strength of coal and coal charges, deviations of the crushing capacity coefficients' actual values of coal charges from their calculated values, and the possibility of categorizing coal in relation to the degree of its resistance to crushing have been explored. The dependence permitting satisfactory precognition of the HGI value of the coal charge placed on the data of the crushing capacity coefficients of its ingredients was settled. The effect of the grinding ability of coal on its quality indicators, namely the degree of metamorphism, petrographic and elemental composition has been examined in this article. Determination of the coal grind ability was made by means of widely known Protodyakonov and Hardgrove methods, which allow estimating the resistibility of the material to the grind forces. For research 14 samples of coals (Ukraine, USA, and Kazakhstan), and 7 testers of coal charges at the basic coke chemical companies of Ukraine, were applied. The graphical and mathematical dependences are stated to have been developed to enable the predicting of the grinding ability of coals using the Hardgrove (HGI) and Protodyakonov (f) methods, based on determining the indicators of their quality (Cdaf, R0, Oddaf, Vdaf). It is shown that the graphical and mathematical dependencies are polynomials of the second degree, and the values of the coefficients of determination (R2) exceed 0.550–0.930. For the initial time, the coherency between the strength coefficient according to the Protoyakonov method and coal pulverization to the Hardgrove method was established. It was found the f and HGI values of measure are inversely in proportion, and a mathematical and diagram dependence based on one of them for its prognosticate has been established.

INCREASE IN THE DENSITY OF CARRIER MEDIUM AS A WAY TO CREATE HYDROTRANSPORT OF MINERALS IN LARGE LUMP FORM

Existing coal hydro-transport technologies require preliminary grinding of coal into powder. The same circumstance prevents the use of pipeline transport for the delivery of granite, limestone and other building materials from mining sites to the consumer. With an increase in the density of the carrier medium it becomes possible to supply through the pipeline coal and other solid materials in lumpy form. After the complete regeneration of the carrier medium, the delivered coal or lump material in such a water-salt liquid is no different from that transported by rail. The regenerated working liquid is completely returned to the head of the process.

Energy consumption model of coal grinding based on energy dissipation fractal dimension

Based on particle size distribution characteristics, this paper explored the energy dissipation law in the coal ultrafine grinding process. By studying the fractal dimension of coal particle size distribution under the multi-domain fractal rule, the truncated particle size was introduced to characterize the energy consumption changes of coarse, intermediate, and fine particles. Combined with macro-energy consumption laws and three-piecewise fractal dimensions, a micro-energy consumption theory considering lattice fracture and agglomeration of ultrafine particles was proposed. On this basis, the energy consumption fractal dimension DE was proposed, and its theoretical calculation value was 2.021. The energy consumption formula of coal ultrafine grinding was established, in which energy consumption was characterized by the DE th power of the added surface area of coal particles. The DE obtained by the specific surface area and the adsorption equilibrium constant of pores were 2.285 and 2.564, respectively, which confirmed the reliability of the above theoretical analysis.

Influence of Grinding Methodology and Particle Size on Coal and Wood Co-Combustion via Injection Flame Opening Angle

Today, more than 61% of the world’s electricity is generated by burning fossil fuels. The search for reducing the negative impact of such thermal power plants on the environment does not stop for a minute, one of the solutions to this problem is the partial replacement of coal with biomass. This method has proven itself most effective over the past five years. Co-pulverized combustion of coal and biomass has not found wide practical application, since the processes of grinding, mixing and subsequent spraying of such mixed fuels have not been fully studied. This study compares the influence of the method of grinding, mixing coal and biomass on the processes of spraying mixtures with a change in the pressure of the atomizing air. The results of the research showed that the joint grinding of coal and biomass contributes to the achievement of the minimum size of coal and wood and, as a result, leads to an increase in the opening angle of the torch, which will significantly improve the efficiency of flame combustion in the furnace space at the station. The most effective spray pressure of the mixed fuels was established, which was 3 bar. An analysis of the results obtained during the course of the research allows us to conclude that the mixing of coal and sawmill waste, followed by joint grinding in a ball mill, contributes to the effective grinding of biomass and coal particles to a finely dispersed state, which subsequently leads to a significant increase in the opening angle of the torch at any concentration of the mixture composition fuels.

Automated system for control and monitoring of explosion safety of the coal grinding process in ball drum mills

The article presents the results of research on automated systems of control and monitoring of explosion safety of dust and gas mixture during coal grinding in ball drum mills (BDM). The problem of the gas-dynamic factor, which arises at the disintegration of coals of middle stage of metamorphism (gas coals) in the atmosphere of closed or limited space, for example in mine workings, chambers, furnace furnaces, etc., is considered. Earlier, when burning anthracite coals, such a problem did not arise, since anthracite does not have a gas component of hydrocarbons. Therefore, all automated control systems were developed from the condition of grinding quality and optimal loading of the BDM. The work aims to develop an automated system of control and monitoring of explosion safety of coal-gas mixture in ball drum mills in the process of grinding gas coals in preparation for combustion. It is established that the sizes of coal grinding fractions in the BDMs from 50 microns to 250 microns correspond to the sizes of supermelonites from 10 microns to 200 microns to particles that are formed during sudden coal and gas emissions in mines. Coal supermelonites are the main source of gas emission into the atmosphere of mine workings, as at their formation there is the disintegration of the supramolecular organization of coal macromolecule and generation of methane. Crushing of gas coals in the BDM inevitably leads to the formation of the explosive methane-coal mixture, which further enters the furnace of the boiler unit. As a result, a new functional scheme for automatic regulation and optimization of parameters of the BDM with a measuring and computing system for controlling the temperature of the gas medium, pressure drop, and a self-tuning microprocessor controller was developed. A technological scheme for installing control and measuring equipment has been developed for preparing coal for burning in a thermal power plant boiler unit. Explosion safety control in the technological cycle of preparing gas coals for burning is carried out constantly using methane and oxygen concentration sensors. The operability of the control system was confirmed on the industrial mill of the boiler unit BKZ-160-100PT TPP of "Kramatorskteploenergo" TPP. Keywords: ball drum mill, coal grinding, methane, explosion safety, control system.

Study of modes and parameters of mineral raw material grinding process in ball drum mills

The paper presents the results of research on the vibration-acceleration signal of the ball mill drum bearing support depending on its load when grinding mineral raw materials. Investigations of vibration sensor readings, installed on the bearing support of the mill drum, and amplitudes of the vibration-acceleration signal from the volumetric filling of the installation drum have been carried out. The dependences of vibro-acceleration signal amplitudes on the frequency spectrum of Fourier series at different volumetric filling of the mill drum in the interval of loads from 0 t/h to 18 t/h are investigated. In research on the interrelation of a signal of vibro-acceleration and consumed power of an electric drive of a drum depending on the degree of its volume filling, their averaged values are established. According to the values of averaged numerical values of amplitudes of vibro-acceleration signal amplitudes, the graphs of their dependence on the frequency spectrum of Fourier series in the range from 0 to 30000 Hz are obtained, the dependences of the consumed power of the ball mill and the amplitude of the vibro-acceleration signal on the volumetric filling of the drum are established, the algorithm of determining the level of filling of the mill drum is developed, the dependences of the vibro-acceleration signal and consumed power on the level of filling of the ball mill in volumetric units are established. It is established that the filling of the mill drum by the consumed power of the electric drive can be controlled up to 0.7 of the volumetric filling of the mill drum. At the same time, the value of volumetric filling of the mill drum, expressed through the signal of vibration velocity of the bearing support, smoothly grows in the whole range of drum filling from 0.0 to 1.0. In this case the reliability of the received information on vibration acceleration of the mill drum support with deviation from the approximating curve, not exceeding 5–6%. Tracking of the level of filling of the mill drum is provided by the signal of the vibration sensor, which allows to maintain of optimal performance, grinding quality, and power consumption. The obtained results give grounds to use the vibration acceleration signal in the system of automatic control of the coal grinding process as a criterion for evaluating the degree of filling of the mill drum during its operation. Keywords: ball drum mill, grinding, vibration acceleration signal amplitudes, coal.

Application of a Method for Measuring the Grindability of Fine-Grained Materials by High-Speed Milling.

This article deals with the development of an alternative method for determining the grindability index of fine-grained materials. This method is inspired by the commercially used VTI method (also known as RTI after the Russian Thermal Energy Institute), which was widely used in Central and Eastern Europe in coal grinding. The disadvantage of the VTI method is that it uses a specific grinding device that otherwise has no other use and nowadays is no longer commonly available. Through the new method, high-energy grinding was performed using a commercially available planetary mill on silicate materials such as limestone, feldspar, corundum, and quartz. The effectiveness of the method was verified on clinker as a representative of widely used materials. The deviation between the grindability index calculated by the origin VTI method and the new developed method was on average approximately 8%; in the case of clinker grinding, it was only 3%. The results showed that the VTI method could be replaced by a new method that uses a modern available planetary mill and laser granulometry to determine the grindability index. The result is a new classification of materials according to their grindability indexes, which is based on the original VTI method.

The wear mechanism of mill beaters for coal grinding made-up from high manganese cast steel

Determination of the cause-and-effect relationship regarding the wear of the lining (beater) of a coal beater mill is presented. The type and state of the material used for the aforementioned mill element was assessed. The lining wear mechanism was brought to the state of the aforementioned material. In the analyzed case, excessive wear of the Hadfield steel beater of the fan mill was identified. This study analyzes the chemical composition, macro- and microscopic examinations and hardness tests to find the cause of their unsatisfactory wear resistance. The test results show a significant influence of the carbon content on the process of strengthening the surface layer of the beater and the justification for considering the use of various materials for individual elements of the beaters. The methodology of testing the material's ability to deformation hardening was proposed and the role of the manganese cementite mesh in the decohesion (destruction) of the structure as a result of the coincidence of such precipitates with intense deformation micro-twinning has been presented. Analyzed cast steel has a high tendency to strain hardening (from 190 HBW to 500 HBW). As a result of exploitation, investigated plates were highly worn. The primary mechanism of wear was erosion. The presence of carbides in the microstructure also indicates an incomplete supersaturation of the material.

Optimization of operating conditions on ultra-fine coal grinding through kinetic stirred milling and numerical modeling

This study investigated ultra-fine coal grinding performance of four low- to moderate-cost grinding media in a laboratory stirred mill. Kinetic grinding tests showed that silica beads generated the finest product size with a P80 of 5.9 μm from a feed size of 24.4 μm while having a specific energy (SE) input of 309 kWh/ton. Nonetheless, the least energy consumption of 109 kWh/ton was achieved by alumina beads; however, yielding a coarser product size of 15.5 μm. In addition, test results indicate that optimizing media sizes, solids concentration, and using viscosity modifiers enhance coal ultra-fine grinding performance. Under the optimized testing conditions, a P80 of 2.7 μm was produced with a corresponding SE input of 270 kWh/ton using silica beads ranging from 420 to 850 μm and a dispersant dosage of 14 kg/ton. Moreover, the mathematical models generated based on population balance modeling provided an accurate forecast of the particle-size distribution.

Study of the processes of joint grinding and ignition of coal with wood raw materials

The conditions for obtaining composite fuel “coal-pine sawdust” on a semi-industrial roller mill RM-20 were selected: the rotor speed was varied from 10 (300 rpm) to 40 Hz (1200 rpm). The ignition of the obtained samples was studied, and the optimal composition of the composite was determined.

Improving the efficiency of the coal grinding process in ball drum mills at thermal power plants

Ensuring the reliable operation of the dust fuel preparation system at thermal power plants (TPP) is a topical issue since it determines the energy strategy of any country that fires coals for thermal energy production. This unit is one of the most energy-intensive units in TPP. Those systems are outdated, poorly automated and high energy-intensive. Furthermore, they must ensure efficient and safe operation of the facility while being environmentally friendly. The current work focuses on the process of grinding coals in ball drum mills for further pulverized combustion. An experimental study was performed in order to determine the main factors (rotational speed of the drum mill, the degree of loading with the grinding balls, and the velocity of the supplied air) that affect the efficiency of the fuel preparation system. The obtained experimental data and performed mathematical modeling resulted in regression equations describing the energy performance of the mill. Three regression equations for mill productivity, power consumed, and specific surface area of the final product were obtained and validated. The study reveals that the lowest specific energy consumption is achieved when the relative rotational speed of the mill is between 0.81 and 0.87; the weighted average diameter of the balls ranges from 33.5 up to 34.5 mm; the load factor of the grinding media ranges from 0.325 up to 0.335, the supplied air velocity is between 0.2 and 0.3 m/s. The proposed methodology allows adjustment of the operating parameters of the grinding process to achieve the lowest energy consumption. The power consumption for the preparation can be reduced up to 5 % for the selected operation mode of the grinding facility.

Effect of Grinding Behavior on Liberation of Coal Macerals

Macerals are the smallest organic constituents of coal. Reactive macerals or vitrinite is mainly responsible for coking potential of a coal during carbonization method. The effect of a novel grinding on coal maceral separation is studied in this work. The alternate method is based on grinding of coals by shearing compared to impact crushing as in other conventional methods like hammer mill. It is found that liberation of vitrinite is better in shearing. Coking properties of such maceral enriched coals showed improvement in laboratory coke making tests.

SHAP-based interpretation of an XGBoost model in the prediction of grindability of coals and their blends

ABSTRACT The Hardgrove Grindability Index (HGI) is a measure of coal’s resistance to crushing. HGI is influenced by many factors due to the complex structure of coal. This study examines the effect of the proximate and ultimate analysis and maceral content on HGI, based on 329 samples of Polish coals. In this study, a machine learning technique XGBoost (Extreme gradient boosting regressor) was used to develop a predictive model of HGI with satisfactory accuracy (R2 = 0.86). The Shapley additive explanations (SHAP) technique was used to explain the relationship between the predicted value and the input data. Studies have shown that the moisture (negative impact), carbon (positive), volatile matter (negative), vitrinite (positive) and liptinite (negative) content have the greatest impact on HGI. Additionally, three experimentally obtained coal blends that differ significantly in the degree of grindability were selected for testing the model. The results confirmed the effectiveness of the method when used also for blends. The influence of individual coal parameters on the predicted grindability of the blends has been thoroughly examined.

Evaluation of Grindability Behaviors of Four Different Solid Fuels Blending by Using the Hardgrove Mill

Grindability measurements are widely used in mineral and coal processing industry to determine resistance of materials to comminution.Grindability measurement as testing methods can be divided into two general categories; the Bond and the Hardgrovegrindabilities. Grinding characteristics of the mineral or coal blending have been studied by several researchers over many yearsand a wide range grinding variables has been investigated. In this study, because of the simplicity and the potential usage of themethod for the determination of the grindability of coals and their blending in a comparative scale, a Hardgrove mill were used toinvestigated the grinding behavior of four different solid fuels and their blending. Grindability of four different solid fuels such as;petroleum coke, coke coal, lignite and bituminous coal and their binary, ternary and quaternary blending were investigated by theHardgrove grindability test. The test results indicated that determine the existence of a very good relation between the Bond andthe Hardgrove grindability of the fuels, and relationship between experimental and calculated HGI values of the fuels blendingwere also shown as a very good. However, there is not obtain a good relation between proximate analysis results of the solid fuelsand HGI values of fuels blending.

Numerical and experimental study on co-firing of low volatile coal in a 330 MW tangentially fired boiler

Burnout related problem occurs in the utility boiler burning low volatile coals. The in-furnace co-firing of low volatile coal (LV) experiments and simulation were carried out in a tangentially fired PC furnace to investigate the effect of co-firing ratio, injection position and particle size on NOx emission and carbon in fly ash (Cfh). The results of full-scale experiment show that Cfh increases from 2.16% to 4.21% as the LV co-firing ratio rises from 33% to 50%, while the NOx emission increases from 356.0 mg/Nm3 to 385.2 mg/Nm3 (@6% O2). The model is validated against the experimental data. The numerical simulation results show that NOx increases from 308 mg/Nm3 to 567 mg/Nm3 when the co-firing ratio of LV increases from 0% to 100%, while Cfh increases from 1.20% to 7.15%. It is found that the contribution of top two layers (E and F) to the total Cfh is significantly higher than that of the other layers. Under the working conditions of burning bituminous coal in the bottom layer and lean coal (particle size 70 μm) in the upper five layers, Cfh is 5.4%. When the particle size of lean coal in the five layers is reduced to 40 μm, Cfh rapidly decreases to 2.0%. And the Cfh can be reduced to 2.5% when only the top two layers feeding lean coal with smaller particle size (40 μm). Only 40% marginal cost of coal grinding is needed to reach the marginal benefit corresponding to 83% Cfh improvement while all layers of LV coal are ground into the small size.