Burning Law Research Articles

Study on the Spontaneous Combustion Law of Coal Body around a Borehole Induced by Pre-extraction of Coalbed Methane.

To address the challenges associated with the high gas content, high pressure, and low permeability coefficient in deep coal seams, strategies such as infilling boreholes and increasing the negative pressure of extraction are commonly implemented to alleviate issues related to coalbed methane extraction. However, long-term mining pressure can lead to the development of cracks in the coal seam near the borehole, thereby creating air leakage channels, which could potentially impact the oxygen supply during the extraction process. This leads to secondary disasters such as the spontaneous combustion of coal and gas explosions, considerably impacting the life and health of underground workers. To solve this issue, a thermal-fluid-solid coupling model for the working surface was constructed based on numerical simulation software, taking into account the multimechanism coupling effect of coal seam gas. The laws of coal oxidation and spontaneous combustion induced by coalbed methane extraction around boreholes were studied. The variation laws of the oxygen concentration, coal temperature, and oxidation heating zone around the borehole under different extraction conditions were simulated and analyzed. The findings demonstrate that the negative extraction pressure enables the gas to penetrate the fracture zone of the borehole, leading to an increase in the oxygen consumption rate and coal temperature around the borehole with an increase in negative extraction pressure. The coal gas leakage surrounding the borehole reduces as the sealing depth increases, and both the heating rate of coal and oxygen volume fraction show a downward trend. The fitting relationship between the negative pressure of drainage, depth of sealing, and temperature change in the coal body surrounding the boreholes was identified. It was determined that the negative pressure of 13 kPa for borehole drainage and a sealing depth >18 m are the optimal extraction parameters. The range of the oxidation zone and the position of the boundary line under this parameter were predicted, and the position function of the dangerous area of oxidation heating was defined. The research results have remarkable implications for the coordinated prevention and control of gas and coal spontaneous combustion in coalbed methane predrainage boreholes, as well as for efficient prevention and control of CO in on-site gas extraction boreholes, thus ensuring efficient and safe gas extraction.

Investigating how oxygen levels and particle size impact the thermodynamics of low temperature coal oxidation: A case study using weakly caking coal

Oxygen concentration and particle size play critical roles in the combustion of coal. Notably, the low temperature oxidation stage is considered pivotal for coal spontaneous combustion (CSC). In this study, we examined the exothermic oxidation of low-temperature weakly caking coal. We used a C80 microcalorimeter to assess the impact of different oxygen concentrations and particle sizes. For weakly caking coal during low-temperature oxidation, the heat flow (HF) curve decreases as oxygen concentration drops. The characteristic temperature increases, and the HF curve shows a noticeable lag. Under identical external conditions, decreasing the particle size of coal results in a reduced minimum floating coal thickness, lowers the oxygen concentration needed for CSC, increases the upper-limit of air leakage intensity, and makes the coal more susceptible to CSC. Reducing the particle size significantly increases the exothermic heat release during low-temperature oxidation, leading to a higher risk of CSC. These research results not only deepen the understanding of the law of coal spontaneous combustion, but also provide a scientific basis for improving the technical level of coal spontaneous combustion fire prevention and control.

Research on the spontaneous combustion of the goaf at different advancing distances based on the dynamic evolution of porosity

Spontaneous combustion of residual coal in the goaf is one of the main disasters in coal mines. Understanding the law of spontaneous combustion of residual coal can effectively prevent coal mine fires. This paper establishes a dynamic evolution model of overburden caving and porosity in the goaf using PFC numerical simulation software, and compares and analyzes the dynamic changes in porosity and the spontaneous combustion zone at advancing distances of 50 m, 70 m, and 100 m. The results show that when the working face advances 100 m, the porosity in the caving zone of the goaf decreases from 0–0.6 to 0.16–0.3. The range of the spontaneous combustion zone on the return air side expands from 42m-50 m to 39m–61 m, and on the inlet side, it expands from 0 to 22m–50 m. With increased exposure time, the spontaneous combustion zone range shifts slightly forward to 32m–55 m on the inlet side and 21m–49 m on the return side. This study reveals the dynamic evolution law of the spontaneous combustion zone in the goaf under the influence of different advancing distances and exposure times, which can assist in preventing goaf fires.

Research on the Law of Coal Pillar Spontaneous Combustion and Fire Prevention and Control Technology.

In coal pillar fires, the fire source is hard to be detected and the adjacent goaf is extremely likely to be affected. Such fires would give rise to thermal and dynamic disasters in mines, further causing casualties and environmental disruption. In this study, with the coal pillar spontaneous combustion (CPSC) accident in Chahasu Coal Mine taken as the research object, the oxygen uptake and limit of oxygen concentration of CPSC were explored. Based on the research results, a similar model was constructed, where a control group was used to simulate the hazardous area of CPSC in a bid to investigate the law of CPSC. Moreover, the polymer colloid perfusion system was constructed and the drilling parameters and perfusion process parameters were determined, and practices concerning spontaneous fire control were carried out. Here are the conclusions: First, air leakage in the coal pillar may lead to coal spontaneous combustion due to the impact of rib spalling, threatening 2-6 m above the middle of the coal pillar at a shallow position. Second, coal pillar grouting, injecting polymer colloids for cooling, and coal pillar cement reinforcement prove to be effective ways to prevent CPSC fires and combat recombustion.

Study on the Effect of Bifurcation Position on Spontaneous Ignition and Shock Wave Propagation Characteristics in High-pressure Hydrogen Leakage Tubes

Hydrogen safety issues constrain the development and diffusion of hydrogen energy technologies. The current research on tube types in high-pressure hydrogen storage and transportation links is insufficient. In this paper, the spontaneous combustion law and the propagation characteristics of the shock wave in the tube after accidental leakage of high-pressure hydrogen in a bifurcated tube with a blocking structure are investigated by experimental means. By changing the relative position of the bifurcation structure, it is found that moving the bifurcation position upstream can effectively reduce the intensity of the shock wave at the nozzle of the tube, the propagation velocity of the shock wave inside the tube and the critical ignition pressure. There are three ignition possibilities in the bifurcated tube with blocking structure, and quenching can be realized in the tube under lower pressure.

Determination of Coal Spontaneous Combustion Zone in Overlaying Multilayer Goaf and Its Control Technology of Thickened Slurry

ABSTRACT In order to study the law of coal spontaneous combustion and prevention methods in the overlying multilayer goaf, this study combined the situation of 378 working face and overlying multilayer goaf in Anyuan Coal Mine and determined the coal spontaneous combustion zone in the overlying multilayer goaf by overlaying the oxidation zones divided by wind velocity and oxygen concentration, and verified it. Subsequently, a new type of thickened slurry was prepared based on sodium alginate, carboxymethyl cellulose, loess, and water as the main raw materials, and a thickened slurry fire prevention technique suitable for overlying multilayer goaf was proposed. The research results indicated that the coal spontaneous combustion zone was located near the 3117 return air roadway and the 378 return air roadway in 378 working face, as well as the upper part of 3117 return air roadway in 372 (4) goaf. When the water-soil ratio was 8:1 and thickener concentration was 0.3%, the suspension performance of the thickened slurry was better. At this point, the corresponding yield stress was the smallest and the flow ability was better. Through the used of fixed-point grouting and regional sealing of a thickened slurry fire prevention technique, it was found that the CO concentration gradually decreased to zero in the 372 (4) goaf. The oxygen concentration significantly decreased and the pressure difference remained stable in the sealing wall in the return air roadway. The outlet water temperature were below 25°C all boreholes.

Study on the influence of some factors on the high burning rate of energy-carrying materials based on acrylonitrile butadiene rubber with end-chain carboxyl group

Heterogeneous energy-carrying materials possess outstanding advantages compared to other energy-carrying materials, therefore, research and development of this type of material to create propulsion for flying objects is an inevitable trend in the field of military science and space. This paper presents the results of research on the influence of a number of factors on the technological properties and combustion rate of heterogeneous energy-carrying materials based on acrylonitrile butadiene rubber CKH-10KTP and ammonium perchlorate (AP).The research results show that the combustion law depends on the pressure of heterogeneous energy-carrying materials based on CKH-10KTP and ultra-fine AP (specific surface area 2.61÷3.85 m2/g), using a combustion catalyst ferrocene derivative. The study also determined the optimal content of combustion catalyst - plasticiser to be 3.5÷3.8%. The research results are a solid scientific basis for optimally determining the parameters of radioactivity, energy of energy-carrying materials, supplementing the national data source in the design of aircraft engines, meeting requirements in the new context.

Study on staged heat transfer law of coal spontaneous combustion in deep mines

The environmental conditions in the mining region were severely impacted by the high temperature and buried depth of residual coal, which considerably enhanced the likelihood of spontaneous coal combustion and worsened the coal's pyrolysis behavior. Therefore, the change laws of mass and heat during coal oxidation were investigated using industrial analysis and synchronous thermal analysis, and reaction models of coal samples at various phases of oxidation were derived using the Bagchi technique. The findings indicated that the activation energy during the stage of water loss and weight loss increased with the coal's water content, while the activation energy of coal in the early stage of oxidation combustion increased with lower ash percentage and higher carbon content. Additionally, the stages of water loss and weight loss and the stage of oxygen absorption and weight increase in the stable exothermic process of coal samples showed a positive correlation between DTG and DSC. The reaction models for the oxidation and combustion stages were both consistent with the number 7 reaction mechanism. The study's findings may serve as a theoretical roadmap for the further investigation and development of flame retardant avoidance strategies for residual coal oxidation in deep mines.

Thermal Characteristics Analysis of Conveyor Belt During Ignition

ABSTRACT Conveyor belt fires are the most serious fires that occur exogenous mine fires. To study the thermal characteristics of the PVC conveyor belt during the fire process, the softening characteristics of the conveyor belt underground in the mine were simulated by using the temperature rise oxidation system. Based on the C600 microcalorimeter, the oxidation heat release law of the PVC conveyor belt and pulverized coal with different softening temperatures was studied at an environmental range of 40–500°C, and the combustion law, heat release and heat absorption, HRR,combustion stages and activation energy were analyzed. The results show that with increasing softening temperature, the law of heat absorption and heat release of the PVC conveyor belt in the initial stage of the independent reaction is opposite, while the heat absorption and heat release in the coupling with pulverized coal increase gradually, and 106% and 107% more heat is released in the rapid development state than in the independent reaction state. The change rule of the heat release acceleration of the PVC conveyor belt remains basically the same whether it is alone or coupled with pulverized coal. The maximum difference in heat release acceleration increases with increasing softening temperature. According to the division of the combustion stages of the conveyor belt according to the heat flow value, when the PVC conveyor belt reacts alone, the temperature range of the heated softening zone is approximately 140°C smaller than when it is coupled with pulverized coal, and the temperature range of the melting pyrolysis zone is expanded by 100°C.It shows that when the conveyor belt is coupled with pulverized coal, fire is more likely to occur and the fire risk is greater. The average HRR at the softening temperature of 100°C is the largest, the ignition time is the shortest, and the danger is the greatest. The activation energy decreases with increasing softening temperature when it is coupled with pulverized coal, indicating that the higher the softening temperature is, the more likely an oxidation reaction will occur. The heat release characteristics and combustion stages division of the conveyor belt proposed in this paper have certain guiding significance for the replacement and maintenance of mine conveyor belts and the prevention and control of mine fires.

Oxygen-Lean Combustion Law of Briquetted Coal Under Stress in Coal Field Fire Zone

ABSTRACT Coalfield fires have become a major hidden danger in mining operations. In order to analyze the laws of coal oxidation and combustion under stress, a uniaxial pressurized experiment was conducted on briquettes. The results show that as the temperature rises, the oxygen consumption rate of the oxidative combustion of the coal sample increases. This rate is higher in the active stage (120–200°C). CO and CO2 gases begin to be generated in the awakening stage (60–70°C), while hydrocarbon gases are gradually generated in the active stage. Additionally, the index gas escape rate is relatively high under a specific axial pressure (4MP). The cross point temperature of the coal sample at 4MP is lower (86.9°C), and the maximum heating rate is higher (0.117°C/s) compared to other coal-oxygen samples with axial pressure applied. The application of axial pressure has two functions including opening pore channels and compacting particle space, which affect the oxidative spontaneous combustion of coal samples. The research results provide a strong scientific basis and theoretical guidance for the detection and prevention of coalfield fires.

Experimental and Theoretical Method for Determining the Law of Constant-Volume Combustion of a High-Density Propellant

Experimental and Theoretical Method for Determining the Law of Constant-Volume Combustion of a High-Density Propellant

Study on Spontaneous Combustion Law and Prevention Technology of Abandoned Coal in Goaf of Coal Mine

The spontaneous combustion of coal in goaf areas is a significant natural disaster encountered during coal mining operations. To investigate the oxygen consumption characteristics of different coal types, we conducted TG experiments and closed oxygen consumption experiments using seven coal samples exhibiting various degrees of metamorphism. The findings revealed the following key observations: During the oxidation combustion process of coal, the absorbed heat originates from the physical and chemical adsorption of coal and oxygen. The first exothermic peak on the DSC curve represents the maximum combustion temperature of volatile matter and signifies the initiation of coal burning. Coal with higher ignition temperatures is less prone to spontaneous combustion. Analyzing the thermogravimetric curves, we observed that the ignition temperatures of 15# coal and 8+9# coal predominantly extracted from Duanwang Coal Mine are higher compared to the ignition temperature of the 4# coal seam (known for its susceptibility to spontaneous combustion) in Jiudaoling Coal Mine, Liaoning. This observation aligns with their nonspontaneous combustion characteristics. In the closed oxygen consumption experiment, we determined the volume oxygen consumption attenuation coefficients for the main mining areas’ 8+9# and 15# coal seams as 3.9001 × 10 − 4 and 3.83559 × 10 − 4 , respectively. Additionally, the critical oxygen consumption concentrations were measured as 15.71% and 16.78%. The shortest spontaneous combustion periods were determined to be 119.24 days and 121.25 days, respectively, for the aforementioned coal seams. To mitigate spontaneous combustion, the addition of inhibitors is necessary. The selection of an appropriate inhibitor depends on the increase in ignition activation energy. Notably, coal samples treated with a 15% MgCl2 inhibitor exhibited the highest increase in ignition activation energy. Hence, we concluded that a 15% MgCl2 inhibitor is the most suitable ratio for preventing spontaneous combustion.

Effects of pore size, water content, and oxygen-containing functional groups on oxygen adsorption in bituminous coal

To further explore the mechanism of coal spontaneous combustion and better grasp the laws of spontaneous combustion, this article studied the adsorption behavior of O2 in coal. Materials studio software was applied to study the adsorption of oxygen under different water content, different pore sizes, and different oxygen-containing functional groups by means of grand canonical Monte Carlo and molecular dynamics simulation methods. The results show that the adsorption capacity of O2 decreases with the increase in water content. With the increase of molecular pore size of coal, the adsorption capacity of O2 increases, and the tight adsorption amounts decrease. The equivalent adsorption heat is less than 42 kJ/mol, indicating that the adsorption of O2 in coal pores is physical adsorption. The smaller the physical adsorption energy and charge transfer value of the hydroxyl group for O2, it indicates that the hydroxyl group is the active group for the physical adsorption of O2.

Experimental and numerical investigation of aluminum particle combustion driven instability in solid rocket motors

Aluminum particles are extensively employed to enhance the energetic properties of propellants. However, the heat release rate (HRR) fluctuations resulting from aluminum combustion can potentially affect the stability of solid rocket motors (SRMs). Using a self-made high-pressure combustion diagnostics system and laser ignition system, this work investigates the combustion behavior of single aluminum particle under propellant atmosphere and acoustic excitation. An unsteady aluminum combustion model using Ranz-Marshall correlation and involving the heat and mass transfer equation was developed. The D2 law of aluminum particle combustion in a real propellant under 0.5 MPa was fitted as t = D2/0.31. The measured combustion rate of laser-ignited aluminum particles was found to increase from 0.381mm2/s to 0.465 mm2/s when an acoustic excitation of sine wave(200 Hz, 20Pa) was applied to the propellant, which agreed well with the prediction of the proposed unsteady combustion model whose error was 4.7%. Then, the verified correlation was included in the SRM to calculate the HRR fluctuation of the aluminum on acoustic boundary near the propellant burning surface. The effects of particle diameter, gas velocity, oscillation amplitude and frequency on the HRR fluctuation were obtained. It was found that the HRR fluctuation increases with the increasing particle diameter, gas velocity, and oscillation amplitude, and that due to the acoustic boundary effect, the HRR fluctuation is more sensitive under low-frequency oscillation. Based on the HRR fluctuation of aluminum combustion and particle damping, the growth rate of instability resulting from aluminum combustion in an SRM was investigated. The results showed that the growth rate of instability resulting from aluminum combustion were 9.38s-1 and 24.06s-1, while the particle damping (−25.8s-1) caused by combustion residuals, which suggests the aluminum particles play a critical role in SRMs combustion instability.

Research on the Internal Relationship Between Dynamic and Static Combustion Laws of Propellant for a Large-caliber Artillery

In this paper, according to the closed bomb test results of the same formula and different batches of propellant, the static combustion law of the propellant is obtained. Combined with the results of the artillery firing test, the dynamic combustion law of the propellant is obtained through the internal ballistic simulation fitting. The relationship between the static and dynamic combustion laws of the same formula and different batches of propellants is obtained. Using the research results of this paper, for the new batch of propellant, the dynamic combustion law of the new batch of propellant can be determined according to the closed bomb test results. Combined with the internal relationship between the dynamic combustion law and the static combustion law in this paper, the internal ballistic performance prediction accuracy can be improved.

Research on Potential Equilibrium of Dynamic Combustion Performance in Electrothermal-Chemical Launching

The interior ballistic potential equilibrium theory is used to analyse the parameters at the potential equilibrium points of pressure curves of 30mm conventional launching experiment and electrothermal-chemical (ETC) launching experiments. Analysis shows that: compared to the conventional launching experiment, (1) the time for ETC launching experiment to arrive the potential equilibrium point is apparently shortened; (2) the relative burnt percentages of the propellants at the potential equilibrium points are smaller in ETC launching tests. And the curves of gas generation brisance in the three ETC launching experiments are consistent. Then based on the measured pressure curves, the actual gas generation functions in chamber for conventional launching experiment and ETC launching experiments are fitted respectively. Using the average actual gas generation functions to replace the shape functions which are derived from the hypothesis of Geometric Combustion Law, the interior similarity equations of ETC Gun are established with the potential equilibrium point as the reference state. The calculated pressure curve obtained by solving the interior ballistic similarity equations of electrothermal chemical gun is in good agreement with the experimental pressure curve. Therefore, it is expected that the interior similarity equations of ETC Gun could predict the experimental pressure curve.

Oxidative combustion law of water-soaked coal under oxygen-lean condition

ABSTRACT Residual coal is easily submerged and damaged by groundwater. In the course of mining underlying coal seam, coal belonging to the overlying gob area tends to spontaneously combust during draining water. To explore the effect of micro-functional group transformation in immersed coal on the coal spontaneous combustion (CSC) traits during the low-temperature oxidation process (LTO), the migrant law of special functional groups under varying oxygen concentration (Co) of immersed coal was discussed by infrared spectroscopy. The endothermal and exothermal properties of the function group inside of coal were studied via thermal analysis. It is shown that the higher Co, the more oxygenic function groups on the soaked, and by contrasted with the Co of 18% the 14% has a small increase and the chain length is shortened. The temperature increment together with the Co content determines the functional group content, the pyrolysis process produces some function group. The lower the Co, endothermic coefficient decreases and endothermic temperature increases, the higher the ignition temperature of coal oxy-combustion, the lower the total heat release. And the speed of the oxygen-absorbing weight gain and the conversion of the functional group would be improved followed by the burnout temperature rising. Below 14% Co, the oxidative combustion process will be greatly inhibited. Those findings complement a theoretical basis for preventing long-term water-soaked coal oxidative spontaneous combusting in shallow buried coal seams.

Interior ballistic two-phase flow model and its calculation for a mixed charge structure

The mixed charge for guns generally consists of two or more kinds of propellants. Medium and large caliber guns usually adopt the typical combination of tubular and granular propellants, not only meeting interior ballistic indexes but also improving launch safety. However, numerical investigations, charge design, and optimizations of such charge structures rely heavily on classical interior ballistic theory. To gain insight into some crucial phenomena in this complex interior ballistic process, a two-phase flow dynamic model of a 125 mm smoothbore gun with mixed charge (granular propellants, tubular propellants, and a combustible cartridge case) is developed. Unlike the previous form of solid governing equations, the conservation equations, surface temperature and combustion law functions are simultaneously established. The space-time conservation element and solution element (CE/SE) method is used to solve the mathematical model, simplifying the calculations of partial derivatives in source terms. Results show that the model can describe the combustion and flow, and the predicted projectile velocity agrees well with the measured one. In addition, the effects of the mass ratio of mixed propellants on interior ballistic performance are discussed in detail. As the tubular propellant mass decreases, ignition consistency deteriorates, particle accumulation intensifies, and the maximum pressure exceeds the permitted one, all of which may affect launch safety. The work in this paper provides a powerful tool for observing and predicting the interior ballistic process of the mixed charge.

Combustion characteristics and thermal decomposition mechanism of the flame-retardant cable in urban utility tunnel

Although urban utility tunnel act as innovative technique for sustainable development, the cable fire of tunnel should be carefully treated. Extensive studies have usually focused on the combustion or pyrolysis stage of cables by a single test, but comprehensive tests still need to further investigation. Therefore, the cable ignition, expansion charring, pyrolysis and combustion from the macro and micro perspectives were comprehensively explored with cone calorimeter and simultaneous thermal analysis infrared gas chromatography (STA-FTIR-GC/MS). It was found that in addition to the outermost sheath material of the cable, its insulation material and flame retardant material play a non-negligible role in the fire. To more accurately reflect the actual pyrolysis and combustion characteristics of the material, a simplified cable ignition model was established, the combustion laws of typical cables in the urban utility tunnel under different radiation intensities were explored, the quantitative characterization and risk assessment of the toxicity of the gas products were studied.What's more, the pyrolysis characteristics and reaction mechanism of cables under different thermal environments were revealed. The work provides the necessary support for the establishment of database and design standard of fire engineering in urban utility tunnel.

Air Leakage Law and Prevention Technology of Coal Spontaneous Combustion in the Goaf of “Isolated Island” Fully Mechanized Caving Face

ABSTRACT The coal pillar along the goaf of the completely mechanized caving face of “Isolated Island” is severely damaged, with complex air leakage and a high risk of coal spontaneous combustion. In order to research the law of goaf air leakage in “Isolated Island” working face and effectively control the hidden threat of coal spontaneous combustion in goaf, it is necessary to investigate the goaf air leakage law. In this work, the 3302 “Isolated Island” entirely mechanized caving face of Jining No. 2 Coal Mine in Shandong province, China, served as an example. SF6 tracer gas air leakage measurement was utilized to identify the air leaking route in the goaf. In conjunction with the numerical modeling, the air leakage route surrounding the goaf was evaluated to establish the coal spontaneous combustion risk region, and the targeted prevention and controlled ways of coal spontaneous combustion were proposed. The results indicated that the primary source of air leakage was the seepage of air flow through the working face to the rear goaf and the diffusion to the adjacent goaf through the broken coal pillar. The risk area for coal spontaneous combustion was 40–80 m behind the rear goaf and 50 m within the coal pillar of the adjacent goaf. Regarding this region, the comprehensive prevention and control strategies of plugging and oxygen reduction, inerting and cooling, monitoring and forecasting were proposed. In addition, the fire prevention and extinguishing system combining slurry spraying, sodium silicate, and liquid CO2 injection was designed at both ends of the 3302 track and haulage roads. Using field measurements during the working face mining process, the corresponding methods for reducing the CO volume fraction in 3302 return air roadway and air return corner effectively prevented and controlled the hidden danger of coal spontaneous combustion in the goaf and ensured the safety of working face mining. This research developed a new technology for the prevention and management of coal spontaneous combustion in the goaf of the “Isolated Island” working face.