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Coal ash (CA) is not only one of the most solid wastes from combustion, easily resulting in a series of concerns, but it is also an artificial deposit with considerable metals, such as iron and rare earth. The variation in the coal ash characteristics due to the origins, combustion process, and even storage environment has been hindering the metal utilization from coal ash. In this study, three ash sample from lab muffle, circulating fluidized bed (CFB), and pulverized coal (PC) furnace was derived for the discrepancy study from the combustion furnace, including properties, iron, and rare earth recovery. The origins of the coal feed samples have more of an effect on their properties than combustion furnaces. Magnetic separation is suitable for coal ash from PC because of the magnetite product, and the iron content is 58% in the Mag-1 fraction, with a yield of 3%. The particles in CA from CFB appear irregular and fragmental, while those from PC appear spherical with a smooth surface. The results of sequential chemical extraction and observation both indicated that the aluminosilicate phase plays an essential role in rare earth occurrences. Rare earth in CA from muffling and CFB is facilely leached, with a recovery of approximately 50%, which is higher than that from PC ash. This paper aims to offer a reference to easily understand the difference in metal recovery from coal ash.

Scientific bases and peculiarities of conversion of CHPP anthracite boilers to sub-bituminous coal combustion Print EmailUser Rating: / 0 PoorBest Category: Content №1 2024 Last Updated on 29 February 2024 Published on 30 November -0001 Hits: 1 SocButtons v1.4 Authors: M.V.Chernyavskyy*, orcid.org/0000-0003-4225-4984, Thermal Energy Technology Institute of National Academy of Sciences of Ukraine, Kyiv, Ukraine, e-mail: mchernyavski@gmail.com O.Yu.Provalov, orcid.org/0000-0002-5191-2259, Thermal Energy Technology Institute of National Academy of Sciences of Ukraine, Kyiv, Ukraine, e-mail: eproval@ukr.net Ye.S.Miroshnychenko, orcid.org/0000-0003-2487-6886, Thermal Energy Technology Institute of National Academy of Sciences of Ukraine, Kyiv, Ukraine, e-mail: yevhenmi@gmail.com O.V.Kosyachkov, orcid.org/0000-0002-9445-8738, Thermal Energy Technology Institute of National Academy of Sciences of Ukraine, Kyiv, Ukraine, e-mail: alexkosoy@ukr.net * Corresponding author e-mail: mchernyavski@gmail.com повний текст / full article Naukovyi Visnyk Natsionalnoho Hirnychoho Universytetu. 2024, (1): 041 - 049 https://doi.org/10.33271/nvngu/2024-1/041 Abstract: Purpose. Development of scientific foundations and generalization of experience in development and implementation of technical solutions for conversion of CHPP anthracite boilers with steam productivity up to 250 t/h for combusting sub-bituminous coal with maximum use of existing equipment. Methodology. Consumption and heat calculations of pulverizing systems, aerodynamic calculations of pulverized coal pipes and burners, thermal calculations of boilers and combustion chambers. Calculation justification of technical solutions to eliminate the risk of coal ignition in pulverizing systems and in the burners. Industrial tests on CHPP boiler units. Findings. Different types of pulverizing systems of anthracite CHPP boilers with ball-drum mills, an intermediate pulverized coal hopper and with hot air as a drying agent were considered, and a classification of pulverizing systems by the method of pulverized coal transport to the burners (with drying agent or hot air), and boilers – by the type and location of the burners and the geometry of the furnace, was performed. The problems were analyzed, the calculations of pulverizing systems, pipes, burners, and boilers were performed according to the applied technical solutions, and the experience was summarized of conversion from anthracite to sub-bituminous coal in the boilers of Myronivska, Darnytska CHPP and of the first line of Slovianska TPP. Recommendations are given on methods of conversion of anthracite boilers with a steam capacity of up to 250 t/h with different types of pulverizing systems for burning sub-bituminous coal with maximum use of existing equipment. Originality. For pulverizing systems with ball-drum mills and an intermediate hopper for pulverized coal with hot air as a drying agent classification was made for the first time by the type of transporting agent, and it was shown that when converting from anthracite to sub-bituminous coal with the air transport of pulverized coal to the burners, it is necessary to use the selection of slightly heated air from the first stage of the air heater. It is substantiated that maintaining the temperature conditions of molten slag removal while reducing the share of hot air consumption to the furnace requires the preferential operation of pulverizing systems in a single-mill mode, which is possible due to the greater grindability of sub-bituminous coal. Practical value. Based on the experience of approving technical solutions at Myronivska, Darnytska CHPPs, and at the first line of Slovianska TPP, recommendations are given on how to transfer anthracite boilers with a steam capacity of up to 250 t/h with different types of pulverizing systems for burning sub-bituminous coal with maximum use of existing equipment.

Although the global focus is shifting towards clean energy to replace coal, an immediate technological transition is not yet feasible due to the widespread prevalence of the existing coal combustion technology. The main objective of the present work is to investigate the characteristics of pulverized coal combustion by using Ansys Fluent. This study describes the fluid flow and combustion reactions in the 2D axisymmetric computational fluid dynamics (CFD) model for the 300 kW cylindrical swirl pulverized coal burner. The study was conducted to analyze the combustion process including the volatilization and char combustion models, while varying the ratio of air inlet velocity, and examining the effect of swirl number on pulverized coal combustion. The numerical modeling results for burner′s operating conditions are validated with the steady‐state temperature measurement in the burner. The significant outcome of the associated parameters found that the flame in the burner formed a spiral before converging into the flame line in the main combustion chamber. As a result, increasing the primary airflow rate led to a decrease in the axial temperature in the preliminary combustion chamber and decreasing the primary airflow showed the highest temperature in all three cases. While the secondary airflow increases, the swirling flow will be induced inside the chamber, which affects the highest temperature profile in the preliminary combustion chamber. Changing the tertiary airflow rate did not significantly affect the combustion. However, increasing the tertiary airflow rate improved the completeness of combustion. The swirl numbers also influenced the phenomena of combustion, the volatile released, and combustion reactions which could occur more rapidly with a higher swirl number due to a higher concentration of vortex region. Similarly, the highest swirl numbers resulted in the lowest excess O 2 at the exit and the least amount of CO formation.

In order to alleviate the energy crisis and respond to the “dual carbon strategy”, a new energy substance is needed to replace pulverized coal as the new blast furnace blowing fuel. Hydrochar is a clean and renewable carbon resource with high calorific value, good transportation and storage properties, and low ash content. Numerical simulation is used to study the combustion process of co-blown pulverized coal and hydrochar inside the cyclone zone. In this study, a three-dimensional physical model was constructed based on the actual dimensions of the direct-blowing pipe, tuyere, coal gun, and swirl zone of a large blast furnace in China. Numerical simulation methods were used to study the combustion process of coal powder and hydrothermal carbon co-injected into the swirl zone, and to investigate changes in the swirl zone of the tuyere under different conditions. The results show that increasing the proportion of hydrochar in the blended coal is conducive to improving the combustion rate of the blended coal, the temperature inside the gyratory zone increases significantly with the increase in the oxygen enrichment rate, and the high temperature zone is gradually enlarged. For every 1% increase in the oxygen enrichment rate, the maximum temperature of the centerline of the coal plume increases by 28 K, and the burnout rate increases by 1.12%; the increase in the blast temperature makes the combustion of pulverized coal slightly advance and promotes the increase in the internal temperature of the gyratory zone. The change of the blast temperature to 1559 K is more obvious, and the increase in the blast temperature after it is greater than 1559 K is not significant for the improvement of the burnout rate and the temperature of the gyratory area, and it will increase the cost; the lower the proportion of the small particle size is, the bigger the high temperature area of the gyratory area is, and the higher the temperature of the centerline of the coal strand is. If the content of the volatile matter remains unchanged, the increase in the ratio of the hydrochar has little influence on the temperature field of the gyratory area and the temperature of the centerline of the coal strand. The temperature difference is kept at 20 K. With the increase in the hydrochar ratio, the overall burnout rate of pulverized coal gradually increases. Therefore, hydrochar can replace bituminous coal as blast furnace blowing fuel to a certain extent, which can reduce costs and carbon emissions.

Fully utilizing the energy generated by the explosion of pulverized coal will contribute to realize the clean and efficient exploitation of coal resources. The pulverized coal explosion characteristics will be a far-reaching and important task to explore. In this paper, ten kinds of low-quality coals such as high sulfur, high ash, and low metamorphic degree coals were investigated and the minimum ignition energy (MIE), lower explosion limit (LEL), and explosion intensity (EI) parameters under different particle sizes and coal powder concentration conditions were also analyzed combined with a 1.2-L Hartmann tube and a 20-L explosion sphere experimental system. Finally, the morphological characteristics of the exploded coal powder surface were evaluated by scanning electron microscopy (SEM). The results show that the particle size is positively correlated with MIE. LEL shows an inverted “U”-shaped trend with the increasing degree of coal deterioration. The low-rank coal is more flammable and explosive. The maximum pressure P Max at the LEL concentration and maximum pressure rise rate ( dP/dt ) Max overall value is small. Here, optimum pulverized coal particle size (75μm) for explosive utilization of low-quality coal was determined. Within 50–225 g/m 3 of pulverized coal concentration range, the explosion intensity increases with increasing concentration. The smaller the particle size of pulverized coal, the greater the possibility of agglomeration of pulverized coal particles. The surface of the exploded coal particles produces more developed pores. They are irregularly shaped and have more rounded edges than the original coal.

Coal blending has become a common practice in large-scale boilers due to fluctuations in fuel supply, and it has an important impact on combustion and nitric oxide (NO) formation. To clarify these effects, this study numerically investigates the combustion characteristics and NO generation in a 130 t/h tangentially fired pulverized-coal boiler under boiler maximum continuous rating (BMCR) conditions. A three-dimensional furnace model was developed based on the actual boiler geometry, and combustion was simulated using coal combustion sub-models coupled with the discrete phase model (DPM). The results indicate that increasing the proportion of bituminous coal raises the peak furnace temperature from 1856 K under unblended firing to 1959 K at 80% blending and increases the outlet NO concentration from 357 mg/m3 to 457 mg/m3. Furthermore, coal blending shifts flame intensity toward the furnace wall, enhances carbon monoxide (CO) formation in oxygen-deficient near-wall regions, and promotes NO generation in wall-adjacent high-temperature zones. These findings demonstrate that coal blending significantly influences combustion performance and pollutant emissions, highlighting the need for optimized air distribution and blending strategies in tangentially fired boilers.

Coal and gas outburst is one of the major serious natural disasters during underground coal, and the shock air flow produced by outburst has a huge threat on the mine safety. In order to study the two-phase flow of a mixture of pulverized coal and gas of a mixture of pulverized coal and gas migration properties and its shock effect during the process of coal and gas outburst, the coal samples of the outburst coal seam in Yuyang Coal Mine, Chongqing, China were selected as the experimental subjects. By using the self-developed coal and gas outburst simulation test device, we simulated the law of two-phase flow of a mixture of pulverized coal and gas in the roadway network where outburst happened. The results showed that the air in the roadway around the outburst port is disturbed by the shock wave, where the pressure and temperature are abruptly changed. For the initial gas pressure of 0.35 MPa, the air pressure in different locations of the roadway fluctuated and eventually remain stable, and the overpressure of the outburst shock wave was about 20~35 kPa. The overpressure in the main roadway and the distance from the outburst port showed a decreasing trend. The highest value of temperature in the roadway increased by 0.25 °C and the highest value of gas concentration reached 38.12% during the experiment. With the action of shock air flow, the pulverized coal transportation in the roadway could be roughly divided into three stages, which are the accelerated movement stage, decelerated movement stage and the particle settling stage respectively. Total of 180.7 kg pulverized coal of outburst in this experiment were erupted, and most of them were accumulated in the main roadway. Through the analysis of the law of outburst shock wave propagation, a shock wave propagation model considering gas desorption efficiency was established. The relationships of shock wave overpressure and outburst intensity, gas desorption rate, initial gas pressure, cross section and distance of the roadway were obtained, which can provide a reference for the protection of coal and gas outburst and control of catastrophic ventilation.

The injection of hydrogen into a blast furnace is a promising technology to fulfill the low-carbon ironmaking purpose. A three-dimensional computational fluid dynamic (CFD) model is developed to investigate the effect of hydrogen injection rate and blast oxygen enrichment rate on the tuyere, raceway, and surrounding coke bed behaviors. It was found that hydrogen injection leads to a higher water vapor volume fraction in the raceway and a higher hydrogen fraction in the coke bed. The magnitude of velocity and temperature near the tuyere only increase slightly due to the cold inlet temperature of hydrogen, which also results in lower coke bed temperature. The volume-averaged temperature decreases from 2146 K to 2129 K when the injection rate increases from 0 to 1000 Nm3/h. Oxygen enrichment rate presents a highly positive correlation with temperature in the raceway and coke bed, water vapor and carbon dioxide volume fraction in the raceway, and pulverized coal burnout rate. Because more carbon participates in the raceway reaction with an increase in oxygen enrichment rate from 0% to 10%, the final carbon monoxide fraction in the coke bed increases from 0.29 to 0.40, and the final hydrogen fraction decreases from 0.15 to 0.13. With the increase in hydrogen injection, the temperature of the raceway and the coke bed decreased slightly. Pulverized coal burnout changes little with the hydrogen injection rate increasing from 500 Nm3/h to 1500 Nm3/h, which is because hydrogen combustion promotes pulverized coal at the front part of the raceway but inhibits it at the end due to the relative lack of oxygen. These results will help better understand the combustion behavior in the tuyere and raceway of the blast furnace with oxygen-rich blast and hydrogen injection.

The conditions in the combustion zones, i.e., the raceways, are crucial for the operation of the blast furnace. In recent years, advancements in tuyere cameras and image processing and interpretation techniques have provided a better means by which to obtain information from this region of the furnace. In this study, a comprehensive approach is proposed to visually monitor the status of the pulverized coal cloud at the tuyeres based on a carefully designed processing strategy. Firstly, tuyere images are preprocessed to remove noise and enhance image quality, applying the adaptive Otsu algorithm to detect the edges of the coal cloud, enabling precise delineation of the pulverized coal region. Next, a Swin–Unet model, which combines the strengths of Swin Transformer and U-Net architecture, is employed for accurate segmentation of the coal cloud area. The extracted pulverized coal cloud features are analyzed using RGB super-pixel weighting, which takes into account the variations in color within the cloud region. It is demonstrated that the pulverized coal injection rate shows a correlation with the state of the cloud detected based on the images. The effectiveness of this visual monitoring method is validated using real-world data obtained from a blast furnace of SSAB Europe. The experimental results align with earlier research findings and practical operational experience.

This paper presents the development of a multiphase aerodynamic reactor designed for multi-component systems, focusing on precise catalyst dosing in the combustion chamber. The study aims to underscore the significance of this work by emphasizing the critical role of optimized operational conditions in enhancing the transportation of the modifier for combustion processes. Through comprehensive numerical simulations and experimental tests, this research explores the impact of parameters such as flow rates of the dosed substance and air, dosing nozzle outlet diameter, and conduit diameter on the flow rate and trajectory of the transported modifier. The findings highlight the importance of a minimum droplet diameter of 30 μm, preferably 50 μm, for proper delivery to the combustion chamber. This study not only identifies key differences between analyzed structures but also emphasizes the crucial role of these operational parameters in achieving optimal conditions for modifier transport.