Coal Flow Research Articles

The use of plasma technologies to optimize fuel combustion processes and reduce emissions of harmful substances

The latest information technologies and 3D computer modeling methods were used to introduce new technology of plasma fuel ignition and stabilization of combustion processes. Numerical studies of the physicochemical processes occurring during the combustion of pulverized coal fuel flows in areas of real geometry (combustion chambers of thermal power plants) have been carried out. The main regularities of the influence of thermochemical plasma activation of pulverized coal flows on the process of fuel combustion in the combustion chambers of Kazakhstan boilers have been established. The conducted studies of the systems of thermochemical plasma activation of pulverized coal flows have shown the possibility and efficiency of their application at real thermal power facilities. This makes possible to solve both: economic problems (reducing the consumption of fuel oil) and environmental problems (reducing harmful dust and gas emissions from the combustion of low-grade coal fuels from Kazakhstan deposits). This will optimize the processes that occur during the combustion of energy fuel, reduce emissions of harmful substances into the atmosphere (carbon oxides, nitrogen oxides), create and implement in the future a new way to produce "clean" energy.

Coal Flow Foreign Body Classification Based on ESCBAM and Multi-Channel Feature Fusion.

Foreign bodies often cause belt scratching and tearing, coal stacking, and plugging during the transportation of coal via belt conveyors. To overcome the problems of large parameters, heavy computational complexity, low classification accuracy, and poor processing speed in current classification networks, a novel network based on ESCBAM and multichannel feature fusion is proposed in this paper. Firstly, to improve the utilization rate of features and the network's ability to learn detailed information, a multi-channel feature fusion strategy was designed to fully integrate the independent feature information between each channel. Then, to reduce the computational amount while maintaining excellent feature extraction capability, an information fusion network was constructed, which adopted the depthwise separable convolution and improved residual network structure as the basic feature extraction unit. Finally, to enhance the understanding ability of image context and improve the feature performance of the network, a novel ESCBAM attention mechanism with strong generalization and portability was constructed by integrating space and channel features. The experimental results demonstrate that the proposed method has the advantages of fewer parameters, low computational complexity, high accuracy, and fast processing speed, which can effectively classify foreign bodies on the belt conveyor.

Dynamic behavior of outburst two-phase flow in a coal mine T-shaped roadway: The formation of impact airflow and its disaster-causing effect

The study of the dynamic disaster mechanism of coal and gas outburst two-phase flow is crucial for improving disaster reduction and rescue ability of coal mine outburst accidents. An outburst test in a T-shaped roadway was conducted using a self-developed large-scale outburst dynamic disaster test system. We investigated the release characteristics of main energy sources in coal seam, and obtained the dynamic characteristics of outburst two-phase flow in a roadway. Additionally, we established a formation model for outburst impact flow and a model for its flow in a bifurcated structure. The results indicate that the outburst process exhibits pulse characteristics, and the rapid destruction process of coal seam and the blocking state of gas flow are the main causes of the pulse phenomenon. The outburst energy is released in stages, and the elastic potential energy is released in the vertical direction before the horizontal direction. In a straight roadway, the impact force oscillates along the roadway. With an increase in the solid–gas ratio, the two-phase flow impact force gradually increases, and the disaster range extends from the middle of the roadway to the coal seam. In the area near the coal seam, the disaster caused by the two-phase flow impact is characterized by intermittent recovery. In a bifurcated roadway, the effect of impact airflow on impact dynamic disaster is much higher than that of two-phase flow, and the impact force tends to weaken with increasing solid-gas ratio. The impact force is asymmetrically distributed; it is higher on the left of the bifurcated roadway. With an increase in the solid-gas ratio, the static pressure rapidly decreases, and the bifurcated structure accelerates the attenuation of static pressure. Moreover, secondary acceleration is observed when the shock wave moves along the T-shaped roadway, indicating that the bifurcated structure increases the shock wave velocity.

A Faster and Lighter Detection Method for Foreign Objects in Coal Mine Belt Conveyors.

Coal flow in belt conveyors is often mixed with foreign objects, such as anchor rods, angle irons, wooden bars, gangue, and large coal chunks, leading to belt tearing, blockages at transfer points, or even belt breakage. Fast and effective detection of these foreign objects is vital to ensure belt conveyors' safe and smooth operation. This paper proposes an improved YOLOv5-based method for rapid and low-parameter detection and recognition of non-coal foreign objects. Firstly, a new dataset containing foreign objects on conveyor belts is established for training and testing. Considering the high-speed operation of belt conveyors and the increased demands for inspection robot data collection frequency and real-time algorithm processing, this study employs a dark channel dehazing method to preprocess the raw data collected by the inspection robot in harsh mining environments, thus enhancing image clarity. Subsequently, improvements are made to the backbone and neck of YOLOv5 to achieve a deep lightweight object detection network that ensures detection speed and accuracy. The experimental results demonstrate that the improved model achieves a detection accuracy of 94.9% on the proposed foreign object dataset. Compared to YOLOv5s, the model parameters, inference time, and computational load are reduced by 43.1%, 54.1%, and 43.6%, respectively, while the detection accuracy is improved by 2.5%. These findings are significant for enhancing the detection speed of foreign object recognition and facilitating its application in edge computing devices, thus ensuring belt conveyors' safe and efficient operation.

Research on Hole Collapse Monitoring Technology of Coal Seam Gas Extraction Boreholes

It is difficult to monitor the collapse position of a gas extraction borehole in a coal seam. In order to solve this problem, a fiber-optic grating collapse monitoring technology was proposed. Five kinds of grating arrangements (0°, 45°, 90°, 135°, 180°) were examined to simulate the hole collapse. The relationship model between the center wavelength offset and the amount of collapsed coal and extraction flow was constructed to obtain the distribution curve of the hole collapse position and quality along the length of the hole, and flow decay rates of 80% and 50% were used as the critical values to classify the three levels of hole collapse. The results show that the hole collapse monitoring accuracy is the highest with the grating measurement points located below the substrate material arrangement. Finally, the effectiveness of fiber-optic grating monitoring technology was verified in the 2202 working face of the Changcun coal mine of the Lu’an Group, and the pure amount of gas extraction from the repaired borehole after monitoring was increased by 62.6% compared with that before the repair.

A multiphysics model for biogenic gas extraction from coal seams

Approximately 20% of global natural gas resources, including coalbed methane (CBM), could be microbial in origin. This discovery has attracted great interests in extracting biogenic gas in coal seams. Previous studies have demonstrated that this could be achieved through injecting nutrients solution, either with or without microbes, into a coal reservoir. The injected nutrients transport in coal, stimulate the growth of microbes, and enhance their metabolic activities. Through these complex processes, the organic components in coal are biodegraded into methane gas. The generated biogenic gas may be either in free phase or adsorbed on coal grains and can be extracted as an integral part of the gas-in-place. Although this bio-stimulation technique has been proposed for decades, generating and extracting additional biogenic methane in coal seams is still in a stage of conceptual development. In this study, we develop a modelling tool to validate this concept under the laboratory conditions and upscale to reservoir conditions. The model consists of a complete set of partial differential equations (PDEs) to define: (1) coal deformation, (2) water and gas flow, (3) multispecies reactive transport, and (4) microbial growth/decay and adsorption/desorption. All these processes are coupled through coal porosity and permeability model that links hydrological, mechanical, chemical and biological processes together. The multiphysics model is verified against laboratory coal bioconversion data. The verified model is applied to simulate practical operation in which nutrients solution is continuously delivered into coal seams. Simulation results capture all important processes involved and validate the effectiveness of coal-to-methane bioconversion and its extraction.

Hybrid numerical methods for modelling multi-physics mass transport in coal

It is a challenging task to predict and analyse the transient flow physics in unconventional complex geological formations such as coal seams. This is due to the multi-scale multi-physics nature of processes taking place in coal seam gas reservoirs. Therefore, numerical tools allowing the incorporation of various flow physics inherent to coal into the simulation routine are of particular importance. At the pore-scale, the rock images obtained by micro-computed tomography are frequently used for flow modelling in porous or fractured media by direct numerical simulations (Lattice Boltzman method or by solving Navier Stokes equations) or by utilising so-called pore-network modelling. Both methods have advantages and drawbacks, while their hybridisation may allow us avoid some of the major pitfalls. Due to a limited number of research dedicated to image-based pore-scale modelling in coal, we develop a hybrid numerical model that combines the Hagen-Poiseuille analytical solution and the volume of fluid advection scheme for fluid flow in fractures with the continuum Darcy flow in the coal matrix. The explicit coupling of fluid flow across the fracture-matrix domains is implemented via corresponding source terms in the governing equations. Besides, additional physics including sorption and matrix swelling-shrinkage phenomena are introduced into the numerical model. The hybrid solver is validated against analytical solutions and a previously developed Darcy-Brinkman-Stokes framework, which has similar functionality for modelling fluid flow in coal seams. To validate the developed model and show its capability to capture multi-scale multi-physics flow in coal, several illustrative simulations are conducted using synthetic and realistic digital images of coal. As a result, the accuracy of the hybrid solver was within 4% when compared to the Darcy-Brinkman-Stokes framework for flow simulation on realistic geometry. Besides, the non-parallelised hybrid model outperformed the parallelised direct numerical simulation, being more than 90 times faster in terms of computational time. The findings are beneficial for conducting larger core-scale simulations of multi-scale multi-physics flow in coal seams with potential applications to natural gas production, hydrogen storage, and carbon dioxide geosequestration.

Multi-task allocation framework of coal gangue sorting robot system for the time-varying raw coal flow

ABSTRACT The multi-task allocation has become the key to be solved urgently in applying a coal gangue sorting robot system (CGSRS) in raw coal with high throughput. This paper constructs a multi-task allocation framework of CGSRS for time-varying raw coal flow (TVRCF), including task decomposition, task allocation, and collaborative strategy. Establish the TVRCF decomposition model using the tumbling time window method to obtain the gangue model. A multi-task allocation model based on M/M/s queuing model with impatient customers is proposed because arrival time, granularity, and spatial position of the gangue model are uncertain. By introducing trajectory function and designing benefit function, to solve environment states of sorting area. Creating an iterative mechanism for environment states based on the infinite Markov process, using service time and arrival time interval. An adaptive weights rule based on the greedy algorithm (GAW) is proposed to improve the benefit of multi-task allocation. Simulating 18 groups of TVRCF with 9 productivity. Experimental results show that the proposed framework suits the multi-task allocation of CGSRS to TVRCF. The GAW rule always ensures the optimal sorting rate, the near-optimal task completion success rate, and the manipulator utilization rate. In addition, the stability of the GAW rule is best.

Numerical and Experimental Investigation of the Decoupling Combustion Characteristics of a Burner with Flame Stabilizer

In order to integrate renewable electricity into the power grid, it is crucial for coal-fired power plant boilers to operate stably across a wide load range. Achieving steady combustion with low nitrogen oxide (NOx) emissions poses a significant challenge for boilers burning low-volatile coal in coal-fired power plants. This study focuses on developing a decoupling combustion technology for low-volatile coal-fired boilers operating at low loads. A three-dimensional numerical simulation is employed to analyze and optimize the geometrical parameters of a burner applied in a real 300 MW pulverized coal fired boiler. Detailed analysis of the burner’s decoupling combustion characteristics, including stable combustion ability and NOx reduction principles, is conducted. The results indicate that this burner showed three stages of coal/air separation, and the flame holder facilitates the stepwise spontaneous ignition and combustion of low-volatile coal. By extending the time between coal pyrolysis and carbon combustion, the burner enhances decoupling combustion and achieves low nitrogen oxide emissions. Based on optimization, a flat partition plate without inclination demonstrates excellent performance in terms of velocity vector field distribution, coal air flow rich/lean separation, combustion, and nitrogen oxide generation. Compared with the initial structural design, the average nitrogen oxide concentration at the outlet is reduced by 59%.

Numerical study on the influence of temperature on CO2-ECBM

CO2-ECBM can not only improve the production of CBM, but also contribute to CO2 geological sequestration, which has multiple economic effects. In this paper, COMSOL simulation software was used to conduct numerical simulation studies on the 3# coal seams in Qinshui Basin. A fully coupled model of coal deformation, gas flow and migration, and thermal transfer was established to evaluate the effect of temperature on the production of CBM by CO2 injection. The results indicates that temperature is a key factor affecting CH4 production and CO2 storage. Increasing injection temperature can significantly accelerate the process of gas displacement and the CO2 storage is more sensitive to temperature than the CH4 production. In contrast, both the CH4 production and the CO2 storage decrease with the increase of initial temperature of coal seam and the permeability will decrease faster. With the increase of injection time, the effective influence radius of displacement increases, but the increment of influence radius decreases gradually. The lower the initial temperature of the coal seam, the larger the influence radius, the influence radius increases as a whole with the increase of time. Low Young's modulus or high Poisson's ratio can effectively increase CO2 storage and CH4 production.

GUI Development for Economic Dispatch Analysis on Sulselrabar Power Plant

The take or pay contract between PT. PLN (Persero) with Independent Power Producer (IPP), a power plant belongs to PT. PLN (Persero) is no longer operated optimally, for example, the Barru steam power plant. The steam power plant is a power plant that bears the primary load. The actual conditions in the Barru steam power plant field are charged a maximum of only 3-4 hours or only when the peak load is according to the dispatcher's request. This research examines comparing the economy dispatch method to maximize conditions in the Barru steam power plant, which dispatchers no longer order maximally. So that the Barru power plant operator can determine the distribution of the power allocation ordered by the dispatcher to the two power plant units of the Barru steam power plant, the method being compared is the lambda iteration method. The basis for calculating the two ways is to calculate in advance the characteristics of the fuel consumption of the power plant when operating in one day. The primary data is data on the results of electricity production issued by the generator and fuel consumption taken from the coal feeder flow. Based on the research results, it is known that the lambda iteration method can save production costs of Rp. 9.05 per KWH.

Pore-scale modeling of pore structure properties and wettability effect on permeability of low-rank coal

Permeability is a key parameter for coalbed methane development. Although the absolute permeability of coal has been extensively studied, wettability and pore structure properties continue to challenge the microscopic description of water-gas flow in coal. For this purpose, we reconstructed the microstructures of low-rank coal using micro-computed tomography (micro-CT) images. Pore geometry and pore-throat parameters are introduced to establish a relationship with absolute permeability. A dual-porosity pore network model is developed to study water-gas displacement under different wetting and pore structure properties. Results show that absolute permeability is significantly affected by pore geometry and can be described using a binary quadratic function of porosity and fractal dimension. Water-gas relative permeability varies significantly and the residual gas saturation is lower; the crossover saturation first decreased and then increased with increasing porosity under hydrophobic conditions. While the water relative permeability is lower and a certain amount of gas is trapped in complex pore-throat networks; the crossover saturation is higher under hydrophilic conditions. Models with large percolating porosity and well-developed pore networks have high displacement efficiency due to low capillary resistance and avoidance of trapping. This work provides a systematic description of absolute permeability and water-gas relative permeability in coal microstructure for enhanced gas recovery.

Numerical simulation of multiphase flow and co-gasification of biomass and coal for a new test reactor

Numerical simulation of multiphase flow and co-gasification of biomass and coal for a new test reactor

Permeability evolution and gas flow in wet coal under non-equilibrium state: Considering both water swelling and process-based gas swelling

Accurate knowledge of gas flow within the reservoir and related controlling factors will be important for enhancing the production of coal bed methane. At present, most studies focused on the permeability evolution of dry coal under gas adsorption equilibrium, gas flow and gas diffusion within wet coal under the generally non-equilibrium state are often ignored in the process of gas recovery. In this study, an improved apparent permeability model is proposed which accommodates the water and gas adsorption, stress dependence, water film thickness and gas flow regimes. In the process of modeling, the water adsorption is only affected by water content while the gas adsorption is time and water content dependent; based on poroelastic mechanics, the effective fracture aperture and effective pore radius are derived; and then the variation in water film thickness for different pore types under the effect of water content, stress and adsorption swelling are modeled; the flow regimes are considered based on Beskok’s model. Further, after validation with experimental data, the proposed model was applied to numerical simulations to investigate the evolution of permeability-related factors under the effect of different water contents. The gas flow in wet coal under the non-equilibrium state is explicitly revealed.

An adaptive focused target feature fusion network for detection of foreign bodies in coal flow

An adaptive focused target feature fusion network for detection of foreign bodies in coal flow

A lattice Boltzmann model for simulating gas transport in coal nanopores considering surface adsorption and diffusion effects

The gas flow in coal is extremely complicated as a combined results of multiple flow mechanisms and complex pore structures. Comprehensive understanding of gas flow behaviors in coal is of great importance for the prediction of coalbed methane (CBM) production and the elimination of gas-induced disasters in coal mines. Based on the lattice Boltzmann method (LBM), this study constructs a LB model considering surface adsorption and diffusion effects, which involves multiple mechanisms of gas flow, including viscous flow, enhanced gas slippage (gas slippage is enhanced by surface diffusion) and surface diffusion. The results show that in micropores (<2 nm) and mesopores (2–50 nm), under the effect of adsorbed gas, bulk gas flow velocity increases at a low pressure but decreases at a high pressure. Adsorbed gas surface diffusion permeability, enhanced gas slippage permeability and viscous flow permeability decrease with the rise of pore pressure. In nanopores in coal reservoirs, surface diffusion more significantly enhances gas slippage at a low pressure and in smaller pores. Besides, in the flow calculation, gas slippage without the considering effect of adsorbed gas and Knudsen diffusion can replace each other. According to the results from the LB model, the apparent diffusion coefficients of gas in coal particles decreases with the increase of pore pressure in smaller pores(<10 nm) but increases in larger pores(>10 nm). The study further investigates flow mechanisms controlling the CBM extraction yield in different extraction stages. In the early stage of extraction, the CBM extraction yield is controlled by Darcy seepage in fractures; in the middle stage, it is controlled by viscous flow in larger matrix pores; in the late stage, it is controlled by gas diffusion induced by the superposition of surface diffusion and enhanced gas slippage in matrix micropores and mesopores.

Experimental investigation on the leakage plugging and fire extinguishment characteristics of industrial solid waste-based composite foam slurry materials

For understanding the leakage plugging and fire extinguishment characteristics of industrial solid waste-based composite foam slurry material (CFSM), the plugging effectiveness, thermal stability, and fire extinguishing and cooling process were analyzed systematically. The experimental device was designed to test the plugging effect of CFSM, when the thermal stability performance monitoring system and fire-extinguishing experimental platform were built to analyze the thermal stability, heat insulation properties, and extinguishment of CFSM, respectively. The results revealed that the surface temperature of CFSM with thickness more than 60 mm would not exceed the critical self-heating temperature of coal (60 °C) before reaching the equilibrium state of condensation heat, thus showing the good thermal insulation effect. The thermal conductivity of CFSM did not exceed 0.098 W/(m·k), indicating the excellent thermal insulation properties. The plugging experiments exhibited that the macroscopic plugging effect of CFSM with thickness more than 40 mm was less different from that of the completely sealed state, and the closed porosity of CFSM reached 74.5%, thus showing the well plugging performance. Moreover, the fire-extinguishing experiments indicated that CFSM could quickly flow and diffuse in burning coal, and exhibiting the well fire-extinguishing properties by covering the fire source, bonding-coating and lasting oxygen insulation. The study would provide an effective basis for the application of fire extinguishment technology using CFSM.

Novel Discrete Fracture Network Model for Multiphase Flow in Coal

Multiphase flow intensely affects the movement and accumulation of other fluids in coal and plays an essential role in predicting the permeability of coal during coalbed methane (CBM) production. Fractures have played a decisive role in the transport of CBM after hydraulic fracturing has occurred. In this study, a multiscale pore network model (PNM) was constructed on the basis of focused ion beam scanning electron microscopy (FIB-SEM) image results. Additionally, a novel discrete fracture network model, fracture–pore network model (F–PNM), was proposed to investigate the effect of fracture density, fracture developing direction, and wettability on multiphase flow. The results reveal that the permeability of F–PNM increases with the increase of the fracture density, which could be the result of the predominance of snap off. The permeability decreases as the angle between the fracture and flow direction increases; initially, the permeability decreases steeply and then it tends to remain stable; and for angles between 0° and 15°, the permeability decreased by as much as 61.8%. Moreover, the wettability of coal has limited impact on its water relative permeability; however, it has a measurable effect on gas relative permeability, which could be owing to water accumulation on the coal surface under different wettability conditions. A good wetting performance would have a negative effect on the CBM production and reduce flowback efficiency.

The influence mechanism of effective stress, adsorption effect and Klinkenberg effect on coal seam permeability

Permeability is an important parameter in the process of coalbed methane exploitation. To improve the production efficiency of coalbed methane and explore the control mechanism of the gas flow law in coal, the permeability of helium and nitrogen in the same coal sample was tested under different effective stress (the difference between external stress and pore pressure of coal mass) and pressure by using the seepage device. Based on the gas flow theory, the interaction mechanism of effective stress, adsorption effect and Klinkenberg effect in controlling the permeability has been analyzed. Increasing the gas pressure will enhance the adsorption and deformation ability of coal, causing the reduction of pore size, while it will also cause the reduction of effective stress and stress deformation. There is a certain competition between them under the same external stress condition, which will lead to the change of pore and then affect the permeability of coal seam. The Klinkenberg effect will lead to more complex change factors of permeability, especially in laboratory experiments. Both adsorption deformation and stress deformation will affect the pore structure of coal body, which will also lead to changes in the influence degree of Klinkenberg effect on apparent permeability. Under the influence of adsorption effect, the Klinkenberg effect may be a variable. The experimental results in this work elaborate the microscopic control mechanism of gas permeability change in coal. It can not only provide important guidance for gas injection technology, but also enrich the theory of coal seam gas flow.

MODELS AND METHODS FOR IMPROVING THE OPERATION OF THE ENERGY FACILITY CONTROL SYSTEM

This article is devoted to improving methods and models for a computer-integrated control system (CICS) that monitors the wear of heat exchange surfaces of pipes in steam boilers at coal-fired thermal power stations (TPP), in particular for coal with unknown abrasive composition. The system uses real-time coal quality data to 1manage the abrasive, optimize coal distribution, and verify coal quality to reduce costs. It is described that the difficulties faced by the global coal industry are related to quality, price and environmental issues, and the transition to sustainable energy is complicated by this diversity. Efficient power generation depends on accurate identification of fuel composition and minimizing damage from abrasive impurities in the fuel of heat exchangers. Despite the existing analytical methods, there is a need for improved diagnostic technology, which involves the integration of automated systems to improve efficiency and sustainability. The paper presents a mathematical model that calculates the effect of different types of coal and impurities on the wear of heat exchange tubes, maximizing service life and minimizing costs. It includes a Cochran sampling rule to improve coal quality control. An automated coal quality management method was also developed to reduce wear from abrasive coal impurities. It includes a stepwise supplier selection and stock utilization method, enhancing wear control using the Cochran stepwise sampling method. In addition, a fuzzy logic-based control device distributes the flow in such a way as to ensure satisfactory coal quality, emphasizing the need for continuous system monitoring. A model-based CICS has been developed that controls coal flow based on real-time impurity identification, resulting in significant cost savings and extended overhaul intervals. Computational experiments confirm that the CICS can more than double the service life of heat exchange tubes by maintaining a satisfactory thickness, thereby postponing repairs and reducing operating costs. Overall, this article presents a comprehensive approach to managing and optimizing heat exchanger tube wear at TPP using modelling, real-time data analysis, and automated control systems to improve efficiency and sustainability.