Coal Drying Research Articles

Investigation of the effects of coal properties, environmental conditions, and costs on coal drying method selection using multi-criteria decision-making method (AHP)

In this study, coal properties and environmental characteristics were investigated, and the most suitable coal drying method was determined for four different regions (Armutcuk, Afsin, Can, and Soma) where Türkiye's significant coal reserves are located, using the AHP method (Analytical Hierarchy Process). Installation and operating cost, drying rate, environmental risk, and land area parameters were used as selection criteria in the AHP method. After analyzing the physical and chemical properties of coals from four different regions, changes in moisture content and drying costs were calculated according to various drying methods (rotary, microwave, solar, and air). The results indicated that the solar energy data of the regions were determined to be 1315, 1610, 1400, and 1444 kWh/m²-year for Armutcuk, Afsin, Can, and Soma, respectively. Accordingly, solar energy drying systems are expected to be preferred in regions with high solar energy. However, with the effect of other selection criteria, it was determined that although the Can region receives less solar energy than the Soma region, the microwave drying method should be used for the coal of the Soma region, and the solar energy drying method should be used for the coal of Can region. Microwave and solar energy methods should be preferred for drying the coals of the Armutcuk and Afsin regions, respectively. As in many sectors, multi-criteria decision-making methods are necessary for optimum equipment/method selection in the mining sector. In conclusion, this study showed that the AHP method can be used when appropriate criteria are thoroughly determined.

Proposal and comparison of two heat recovery measures for the coal-based Allam cycle: Double expansion and lower turbine backpressure

Improving the thermodynamic efficiency of the coal-fired semi-closed supercritical CO2 cycle (coal-based Allam cycle) can be achieved by implementing self-heat recuperative coal drying and recompression with more syngas heat integrated with the efficient power cycle. To prevent the heat exchanger from overtemperature during syngas heat recovery, two measures are considered: double expansion and lower turbine backpressure. For the double expansion, a portion of the recycle CO2 is fed into an expander and the exhaust is mixed with the flue gas in the main recuperator to raise the recycle flow rate. For the lower turbine backpressure, the turbine backpressure is decreased to reduce exhaust flue gas temperature. Thermodynamic analysis indicated that self-heat recuperative coal drying and recompression could enhance the net efficiency by 4.28 % points compared to the basic cycle, but the heat exchanger for raw syngas heat recovery faces overtemperature problem with the cold stream exceeding 777 °C. Both the measures proposed above can effectively reduce the temperature to 730–760 °C with slightly decreased efficiencies of 46.93 %∼47.68 % for double expansion and 47.12 %∼47.81 % for lower turbine backpressure. Furthermore, economic assessment shows that compared to the basic cycle, the cost of electricity decreases by 2.49 % and 5.04 % for the schemes with double expansion and lower turbine backpressure, respectively. Therefore, the proposed design with lower turbine backpressure demonstrates advantages in both thermodynamic and economic performance.

Review of modern coal drying methods with the evaluation of their efficiency

Review of modern coal drying methods with the evaluation of their efficiency

Bubbling fluidized bed and oven drying for Turkish coal: a comparative study

ABSTRACT The aim of this study is to compare the changes in the heating value of Turkish coal (Konya-Ilgın) with bubbling fluidized bed drying (BFBD) and oven drying (OD). The changes mentioned at three different temperatures (80-95-110°C) and different moisture contents were investigated. In the tests carried out at three different temperatures using BFBD system, coal drying for 60 minutes produced the dried coal samples with the calorific value of 6300 kcal/kg at 80°C. As a result, a calorific value increase of approximately 53.7% based on initial value was achieved. In the OD system, it increased to 4600 kcal/kg under the same conditions, and at 110°C this value increased to 5250 kcal/kg. This means a 28.0% calorie increase. In the BFBD system, at this temperature value, it reached 6450 kcal/kg, an increase of 57.3% compared to the initial caloric value. Coal drying for 60 minutes produced the dried coal samples with the moisture content 8.9% by BFBD at 80°C. As a result, a moisture decrease of approximately 4.40 times based on initial value was achieved. Under the same conditions, the moisture reduction for OD was 1.33 times. When the temperature value reached 110°C, only a 3.07 times decrease in humidity could be achieved.

Kinetic analysis and mathematical modeling of low-rank coal drying by using swirl fluidized bed dryer on varied angles of guide vane and temperatures

ABSTRACT Low-rank coal is currently widely used as fuel to cover the increasing needs of boilers. This kind of coal must be upgraded due to its high moisture content to increase its quality. The drying using a fluidized swirl bed has not been studied to reduce the moisture content of Low-Rank Coal. In contrast, the drying kinetic model has never been found. This study used the angle of guide vanes (AGV) 10°, 20°, and 30° to produce swirl flow. Experiments with varying temperatures used temperatures of 40°C, 45°C, and 50°C. The purpose of this work was to determine the drying characteristics, the best-drying kinetics models, the effective moisture diffusion value, SMER, MER, and SEC on swirl fluidized bed drying. The study results show that the Khazaei and Rational drying kinetic model was the most suitable for the two experimental variations. For experiments with varying AGV, the R2 values obtained are 0.9989–0.9992 and 0.9980–0.9983, while for the variable temperature, the values are 0.9990–0.9992 and 0.9983–0.9992 for each model. The research also found that the smaller AGV angle and higher temperature result in a faster drying rate and consume less energy.

Study on coarse-grained coal water removal characteristics via steam flash drying for low-rank coal upgrading

Low-rank coal drying plays a crucial role in achieving clean and efficient coal utilization. This study introduces steam flash drying, a novel method specifically designed for upgrading low-rank coal. Unlike conventional drying techniques, steam flash drying utilizes steam as the heat medium, generating a certain amount of condensation. This paper presents a comprehensive analysis of the calculated condensate quantity and the experimental measurement of coal particles' water-holding capacity to determine the initial moisture content before drying. Furthermore, the study investigates the steam flash drying effect on different-sized coal particles at a temperature of 497 K. The findings demonstrate that particles above 3 mm have lower water-holding capacity. The initial moisture content is determined by the particles' water-holding capacity and the combined raw coal water content and condensate content. The research reveals a diminishing flash-drying effect with increasing particle size, characterized by a rapid decrease followed by a gradual decline, observed at a critical point of 6 mm. By strategically adjusting the particle size distribution and employing mixing techniques, the coal drying effect can be significantly enhanced by 22%, ultimately leading to a remarkable 17% increase in processing capacity per unit volume. As a result, this study provides a theoretical foundation and optimization strategies for the clean and efficient utilization of coal through steam flash drying.

Development of a laboratory unit and a solid fuel gasification reactor

The paper investigates the process of gasification of pyrolysis coal and other coal-containing materials A schematic diagram of the installation of the gasification process of pyrolysis coal and other coal-containing materials was developed, the design of the reactor for coal gasification and the methodology for conducting experiments and analysing the gasification process of pyrolysis coal and other coal-containing materials were developed. Research methods - modelling of the coal gasification process using the results of theoretical studies. A detailed analysis of the experimental and theoretical data concerning the feasibility of the pyrolysis coal gasification process was carried out, a schematic diagram of the laboratory installation and the design of the gasification reactor were developed. The main goal is to develop a method of gasification of solid pulverised fuel that will simplify the process control and ensure its stability due to the unity of the drying and gasification processes of pyrolysis coal, which are linked by means of a gasification reactor. Additionally, this method provides for the neutralisation of harmful impurities generated during the coal gasification process. As a result of theoretical studies of the solid fuel gasification process, a design of a coal gasification reactor was proposed, which is an ideal displacement reactor. The length-diameter ratio for the working part of the reactor should be at least 10:1. It is proposed to use a heat-resistant molybdenum steel tube (operating temperature up to 1600 0C) with a diameter of two inches to manufacture the reactor. Also, to study the gasification process of pyrolysis coal and other coal-containing materials, a laboratory installation for gasification of solid crushed fuel is proposed, in which a gas mixture of carbon dioxide and oxygen is fed into the reactor and serves as an activator of the gasification process. The prospects of coal processing by gasification to produce a mixture of combustible gases (H2, CO, CH4) are investigated. It is analysed that coal gasification allows obtaining valuable gas that can be used not only as an energy fuel, but also as a technological raw material for the production of methanol, dimethyl ether, hydrogen production, and use as a reducing agent in metallurgical processes.

CHARACTERISTICS, RANKING, AND POTENTIAL OF COAL ON SEAM H AND SEAM H2

Coal is a complex solid object consisting of several chemical elements and comes from plants that are deposited in a basin. The South Sumatra Basin is a basin with the presence of the Muara Enim Formation which is known as a coal-bearing formation. In this research, secondary data was used in the form of proximate analysis, ultimate analysis, and combustion properties analysis results in determining the characteristics, ranking, and potential of coal in the research area. Based on ASTM D 388 – 05 classification, coal in seam H has a Subbituminous B Coal ranking, while seam H2 has a Subbituminous A Coal rating. Based on the parameters in assessing the coal potential use for coal-fired power plants according to Thomas, 2013 in Suhat, et al., 2020, coal in seam H and seam H2 does not support the utilizations, but solutions can be carried out in the form of rewashing sample, coal drying, and coal blending.

CONVERSION OF ANTHRACITE BOILER UNITS OF CHP PLANTS FOR COMBUSTION OF SUB-BITUMINOUS COAL IN THE WAR CONDITIONS

The work describes the task of urgently converting the boilers of anthracite-burning combined heat and power plants to sub-bituminous coal, which arose in the conditions of Russian aggression in connection with the complete cessation of supplies of project fuel. The developed methods of solving it in a short time with the maximum use of available equipment are given, using the example of boilers with a steam capacity of 220 t/h of CHPP «EURO-RECONSTRUKTSIA» LLC (Darnytska CHPP, Kyiv). On the basis of calculation justification it is shown, and the tests and operation have confirmed, the safety and effectiveness of the technical solution with preservation of coal drying by hot air while limiting the temperature at the exit of the mill and with pulverized coal transport to the burners by half-heated air taken after the first stage of the air heater, while reducing the diameter of the pulverized coal pipes. Measures are proposed and implemented to equalize the distribution of pulverized coal and air among the burners, to operate the mills in alternating mode with the aim to increase the use of hot air, correspondingly to increase the coal jet temperature, to improve the conditions of molten slag removal and to reduce the temperature of flue gases, etc. Uninterrupted operation of the Darnytska CHPP became an important factor in ensuring the functioning of the critical infrastructure of heat and energy supply of Kyiv in conditions of enemy shelling. Bibl. 18, Fig. 5, Tab. 4.

A novel method for low-rank coal drying using steam transient flash evaporation

Low-rank coal drying is essential for clean and efficient coal utilization. In this study, a novel method, steam transient flash evaporation, is proposed for moisture removal from coal. The drying process comprises three stages: heating, flash evaporation, and residual heat drying. A multi-stage energy model is established to elucidate the moisture removal mechanism. The results show that the transient drying effect improves with increasing temperature/pressure. Larger particle sizes exhibit superior drying effectiveness compared to the 6–0 mm samples. A semi-empirical model is developed to calculate the product's moisture content, which shows reasonable agreement with experimental data. Material moisture content decreases during the residual heat drying stage and positively correlates with the moisture content of the product after transient release. Based on these findings, steam transient drying can be used as a safe and rapid method for coal drying.

Converting Slovianska TPP with the central coal pulverizing plant from anthracite to sub-bituminous coal

Purpose. To develop scientific foundations and technical solutions and to implement the converting of the anthracite boiler of the 800 MW unit of Slovianska TPP with central coal pulverizing plant to sub-bituminous coal combustion with maximum use of existing equipment, without stopping the unit’s operation. Methodology. Theoretical and calculational studies on the processes of coal drying and pulverizing at the central coal pulverizing plant. Calculational justification of technical solutions to eliminate the risk of pulverized coal ignition in the pulverized coal supply system and in the boiler unit burners. Trial tests at the coal pulverizing plant and boiler unit. Findings. The technological features of coal pulverizing plant with steam panel dryers designed for anthracite and the peculiarities of the drying process of an individual coal particle were analyzed. It is substantiated that coal drying at the first stages takes place according to the “wet bulb thermometer” mechanism, and safe conditions for sub-bituminous coal pulverizing are determined and confirmed by tests. Technical solutions to eliminate the risk of pulverized coal ignition in the pulverized coal supply system and in the boiler burners were calculated and implemented, which allows the combustion of different coal grades (anthracite, sub-bituminous coal and their mixtures) without changing the composition of the air duct equipment and burners, using only operational measures. Originality. For the first time, it was proved that coal drying at the first stages takes place according to the “wet bulb thermometer” mechanism, and safe conditions for sub-bituminous coal pulverizing at the central pulverizing plant with steam panel dryers and unventilated ball drum mills were determined. Practical value. Technical solutions were developed and implemented to convert the anthracite boiler of the 800 MW unit of Slovianska TPP with a central coal pulverizing plant to sub-bituminous coal burning with maximal use of existing equipment, without stopping the unit’s operation, including safe modes of sub-bituminous coal pulverizing, as well as pulverized coal of various coal grades and their mixtures feeding and combustion. As a result of the implementation of the developed technical solutions, the 800 MW power unit of Slovianska TPP became the first unit in the world capable of using anthracite and sub-bituminous coal separately or in the form of mixtures of a wide range of compositions.

Performance of Regenerative Air Preheater of Pulverized Coal Fired Boilers

Abstract: The air preheater (APH) is the final heat trap in the boiler's flue gas path. Effective pre-combustion coal drying and efficient combustion in the boiler are required for APH to operate efficiently. The effectiveness of heat transfer in APH is significantly influenced by the characteristics of relative humidity and ambient air temperature (AAT). Relative humidity (RH) and air density are also impacted by variations in AAT, which in turn alters the heat capacity of the air. If there is insufficient reserve heat exchange capacity in APH, an increase in AAT will diminish the possibility of waste heat recovery. Additionally, a change in AAT will affect the power consumption of the fans and the leakage through various seals.

Study of the Effect of Drying on the Pore Structure and Rate of Oxygen Consumption and Heat Release of Immersed Lignite

To reveal the influence mechanism of the drying process of immersed coal on the spontaneous combustion characteristics, we measured the pore structure of coal with low-field nuclear magnetic resonance and conducted the temperature-programmed spontaneous combustion experiment. The results showed that the pore volume content of the pores with pore sizes of less than 100 nm was significantly reduced. The diameter range of 100–1000 nm was gradually generated after 8 h of coal drying, and the proportion of large pores and cracks larger than 1000 nm increased significantly during the drying process of the immersed coal. The oxygen consumption rate and the heat release rate were significantly affected by the degree of dryness and the temperature of coal samples in the temperature-programmed process. The turning point temperature was 140°C; below the turning point temperature, the raw coal had the fastest oxygen consumption and maximum heat release. When the coal temperature was higher than 140°C, the oxygen consumption rate and the heat release rate of the coal sample that was dried for 24 h were higher than those for the raw coal, followed by the samples that were dried for 8 h and dried for 48 h. The main reason is that the water content of the coal sample decreases to 11.4% and the porosity increases to 16.5% after drying for 24 h, while the proportion of pores or cracks larger than 1000 nm increases significantly to 87.17%, the largest increase range and the pore connectivity will reach the maximum.

Design of a Coal Drying System with Solar-Assisted Heat Pump and Waste Heat Utilisation

The increase in global energy demand has directed researchers towards making low-quality coals into an environmentally friendly energy source by reducing their high moisture content. Drying coal is a high-energy and time-consuming process, so reducing the required energy and drying time is crucial for drying technology. Coal drying increases the thermal value of coal and makes it easier to transport. In this study, a coal drying system was designed using waste heat recovery systems, R-134a refrigerant as working fluid, air source heat pumps, and vacuum tube solar collectors to provide hot air. Firstly, the moisture content of the coal and the desired moisture content after drying were determined, and then the heat required to dry the coal was calculated. Next, the capacity of the solar collector required to provide the necessary heat to the heat pump was determined, and the type and capacity of the heat pump that could produce the required heat were selected. Finally, the coal dryer was designed based on the specific requirements of the power plant and the type of coal used. As a result, the coal drying system designed with solar-assisted heat pumps and waste heat utilization can increase the efficiency of coal-fired power plants by reducing the moisture content of coal before combustion.

Acoustic Drying of Coal in a Rotating Drum

Acoustic Drying of Coal in a Rotating Drum

Study on fluidization characteristics and drying characteristics of fine coal in thermal vibration separation fluidized bed

By studying the fluidization characteristics of the granular bed in the separation process of fine coal, this paper explores the effect of coal particles on the distribution and evolution of the fluidization behavior of the bed, and analyzes the separation and drying characteristics of fine coal. The results indicated that the stable value of pressure drop curve of bed with medium particles is larger than that of mixed particle bed of medium and coal. Meanwhile, with the increase of the coal particle size, the stable value of pressure drop gradually decreases, as well as the drying rate of lignite increases first and then decreases with the increase of gas velocity, vibration frequency and amplitude. Contrarily, the drying time of fine-grained coal decreases and then increase with the increase of vibration amplitude. Under the conditions of N = 1.4, f = 20 Hz, A = 2 mm, the contact efficiency between the gas–solid phases is good, and the bed pressure fluctuation is stable. After the separation of −6 + 3 mm and −3 + 1 mm fine coal, the ash content of clean coal is 13.4 % and 9.1 % respectively, and the gangue ash reached 43.7 % and 63.5 % respectively. With the increase of gas velocity, vibration frequency and amplitude, the activation energy Ea of fine coal drying process decreases first and then increases, and then the activation energy Ea in the separation process of fine coal is the lowest under the conditions of N = 1.4, f = 20 Hz, A = 2 mm.

A Pilot Plant Study of Coal Dryer: Simulation and Experiment

High moisture content in low-range coal causes low calorific value. To increase the quality, drying by a coal dryer to minimize moisture content is proposed. Here, a case study of a cyclone-like conical tube coal dryer pilot plant was reported. Drying heating uses combustion heat generated from volatile matter combustion. This approach will solve the two problems simultaneously: decreasing moisture content and volatile matter. The computational fluid dynamic (CFD) approach is used to study fluid dynamics inside the coal dryer using ANSYS Fluent 2020R2 software. The CFD simulation results represent the phenomenon of coal drying inside the coal dryer validated by the pilot plant experimental result. The simulation was carried out in steady and unsteady conditions to understand the drying phenomena. The simulation firmly fits the experimental result, especially in an unsteady state system, indicating that the simulation result is promising for further coal dryer design. The optimal condition produces a high moisture content reduction of 86.37%, uniform fluid distribution, and significant volatile matter combustion

Liquid carbon dioxide drying and subsequent combustion behavior of high-moisture coal at high pressure

• LCO 2 drying increases combustion rate by 37% for coal with 20% water at 500 °C. • The faster combustion of LCO 2 –coal slurry produces 35% higher particle temperature. • Both NMR and weight loss data support LCO 2 drying mechanism in high moisture coal. • The high pressure boiler with LCO 2 drying cycle increases power output by 11.3%. In this work, the combustion and radiation characteristics of high-moisture coal treated with liquid carbon dioxide (LCO 2 ) at high pressure were examined. The coal conversion and gas yield were measured to determine the combustion rate constants at four different temperatures. The particle temperature and radiative heat flux emitted from the burning coal bed were measured using a two-color pyrometer and radiometer, respectively. The changes in the moisture content of the coal microstructure after LCO 2 treatment were measured using nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA). The combustion kinetic results showed faster LCO 2 –coal slurry combustion, which frequently occurred at low temperatures. The particle temperature and radiative heat flux of the LCO 2 –coal slurry increased faster to higher steady-state values than those of raw coal. The influence of LCO 2 on the combustion of high-moisture coal was not observed on graphite devoid of water or volatile content. This indicates an effective exchange between LCO 2 and water in coal micropores when coal is exposed to LCO 2 . In addition to the TGA data, the LCO 2 drying mechanism in high-moisture coal was confirmed using NMR relaxation data. The performance of the LCO 2 drying process was compared with that of the conventional boiler with oven drying unit in terms of the water removal effect, combustion, and radiation behavior. An energy analysis was undertaken to calculate the amount of total energy produced from three power cycles occurring in a high-pressure boiler, including one combining the LCO 2 drying cycle with the steam power cycle.

Optimization Design Analysis of Boiler Blowdown Utilization on A Rotary Coal Dryer with Drum Tilt Angle Variations

Lignite coal has dominated the use of steam power plants in recent years. Despite the consequences, which cause many problems, lignite is cheap and easy to obtain. One of the problems was mitigated by reducing the moisture content using a rotary coal dryer. Coal dryer is deemed uneconomical with the current energy sources from turbine extraction steam, electric heaters, and exhaust gas using large-powered fans. The waste energy from boiler blowdown, a water-vapored fluid discharged from the boiler to maintain water and steam quality, is being conducted to improve. Blowdown investigated in a rotary coal dryer type. The compressed air absorbed the heat from the blowdown through the steam coil. The hot air mixed with the coal in the rotary drum. A rotary drum was tested with the tilt angles of 0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, and 90°. The research steps were designing, preliminary modeling, numerical analysis, prototyping, and experimental performing. The result shows that the moisture content has decreased significantly from 35.37% to 21.28%, within an angle of 10°. Based on an economic assessment, this coal dryer also proves that dried lignite coal has increased 4.9% economic value than bituminous coal.

Study of Coal Drying Characteristics Using Boiler Blowdown in a Rotary Coal Dryer

Drying lignite coal to reduce its moisture content has become popular in the last decade. Previously, coal dryers used typical energy such as steam, fuel, or electrical as heat sources. Waste energy had never been implemented in a coal dryer while using it would reduce the cost of production and raise the economic value of the coal itself. An experimental study of drying low-rank coal was conducted using waste energy boiler blowdown in a rotary coal dryer. With variations of 0.595 mm, 1.18 mm, and 4.75 mm coal particle size and the flow's changes of 20 kg/hour, 30 kg/hour, and 40 kg/hour. The hot air temperature of 70 o C, mass flow rate of 36 kg/hour, and pressure of 0,03 MPa were the constant parameters on the 15 rpm rotary drum. The results found that the coal moisture decreased significantly at 0.595 mm particle size and 20 kg/hour of flow. The final coal moisture dropped by 20.685%, and the calorific value increased by 879.6 kcal/kg from its initial value. In addition, the efficiency of the rotary coal dryer is 81.8%.