Activation Energy Of Coal Research Articles

The Effect of CO on the Exothermic Characteristics of Low-Temperature Oxidation in Coal

ABSTRACT In recent years, abnormally high concentrations of CO gas have often been detected in goaf areas of coal mines in China, which have posed a serious threat to safe production in coal mines and the life and safety of underground personnel. The effect of CO on the exothermic characteristics of low-temperature oxidation in coal was studied by analyzing the exothermic characteristics, heat release, oxidation stages, and activation energy of coal at different CO concentrations using a C600 microcalorimeter. The experimental results indicated that CO promoted the coal oxidation at low temperature, but inhibited it after reaching 144°C. When the CO concentration is 30%, the exothermic characteristics of coal in low-temperature oxidation adsorption stage were significantly affected, with the heat flow value decreased by 27.0% and the initial exothermic temperature point moved forward by 3.9 K. In the later stage of the oxidation reaction, the heat release of coal was linearly negatively correlated with CO concentration. The higher the concentration, the lower the heat release. These findings contribute to understanding the combustion mechanism of coal in high-concentration CO atmosphere and provide valuable insights for designing and optimizing coal utilization technologies.

Preparation of fully physically crosslinked double-network gel and its fire prevention mechanism

It is important to gain an in-depth understanding of the structure of fire prevention and extinguishing materials during self-heating of coal. In this paper, an Al3+-CMC/PAM-MMT fire prevention and extinguishing gel with double-network was prepared using sodium carboxymethyl cellulose (CMC) and polyacrylamide (PAM) as raw materials, and aluminum citrate (AlCit) and sodium montmorillonite (Na-MMT) as auxiliary materials, by introducing the fully physically crosslinking effect. The optimal amounts of CMC, PAM, AlCit and MMT were determined to be 2 %, 3 %, 8 %, and 3 %, respectively, based on gelation time, stability, and resistance of the gel. The micromorphological image of the double-network gel exhibited a laminar structure of parallel-aligned fibrous networks, where the pores and channels exhibited more complex shapes and became smaller in size, highlighting the superiority of the double-network architecture. The rheological tests showed that the double-network gel had superior structural stability and viscosity under varying shear rates, making it more effective in covering the fire source, enhancing extinguishing efficiency. Additionally, its higher storage and loss moduli indicated stronger elasticity and mechanical properties compared to the single-network gel, emphasizing its advantages in energy storage and recovery. The characterization of active functional groups showed that there was an effective suppression of reactions involving hydroxyl, hydrocarbon, and carbonyl functional groups, during the spontaneous combustion process of coal, following treatment with the gel. Additionally, a proposed mechanism for the gel formation was presented. In the sealing performance test, the pressure-bearing capacity of the double-network gel was approximately twice that of the single-network gel. It indicated that the multi-level structure formed by the gel led to higher density of physical cross-linking points, which provided better sealing performance. Thermogravimetric analysis showed significant decrease in total calorific value and increase in activation energy of coal, after treatment with the gel, rendering it more difficult for spontaneous coal combustion. In the small-scale fire extinguishing performance test, the double network of Al3+-CMC/PAM-MMT gel demonstrated effective suppression of spontaneous combustion of coal and reduced the susceptibility to re-ignition. The fire prevention mechanism of the gel was further explored experimentally.

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.

Study on the experiment and reaction kinetics of sulfur removal from coal by microorganisms.

To solve the safety problem of spontaneous combustion of high-sulfur coal, applied microbiology, physical chemistry, reaction kinetics theory, combined with the SEM, FTIR and TG-DTG-DSC experiments and analysis of testing methods, the microbial desulfurization experiments were carried out, and the change law of the desulfurization reaction of coal before and after the element composition, main physical and chemical properties, the coal spontaneous combustion point was studied. The results show that when the temperature is 30°C, the coal particle size is 120 mesh, the initial pH value is 2.0 and the bacteria liquid amount is 15 mL, the desulfurization effect of the coal sample is the best, and the maximum desulfurization rate can reach 75.12%. There is obvious erosion on the surface of the coal sample after microbial desulfurization, the pyrite in the coal is obviously reduced, and the molecular structure in the coal is basically unchanged. Under the action of microorganism, part of inorganic sulfur in coal is removed, the spontaneous combustion point of coal is increased by 50°C, the activation energy of coal has increased more than three times, and the possibility of spontaneous combustion of coal is reduced. By analyzing the reaction kinetics of the microbial desulfurization process, it can be seen that the microbial desulfurization reaction is controlled by external diffusion, internal diffusion and chemical reaction, among which internal diffusion is the main influencing factor.

Study the effect of drying on the oxidation thermogravimetric and functional group composition characteristics of immersed lignite

The drying process of immersed lignite has a significant influence on the characteristics and progress of spontaneous combustion. To reveal the influence mechanism of the drying process of immersed coal on the spontaneous combustion characteristics and the change rule of the spontaneous combustion process, in this research, we measured the mass change during coal oxidation with thermogravimetry, and the change of the functional groups with Fourier transform infrared spectroscopy. The influence of the drying process on the coal was analyzed by comparing activation energy, functional group of immersed coal with different drying degrees and raw coal. The results showed that, compared with raw coal, the content of Ar–C–O– and antisymmetric stretching vibration of the carboxylate group (–COO–) as well as the stretching vibration in the quinone group (C=O) and the –OH group increased. For the content of delta s.{text{RCH}}_{{3}},delta as.{text{R}}_{{2}} {text{CH}}_{2}delta as.{text{RCH}}_{{3}}, the value of Asym.CH2/Asym.CH3 decreased. The content of various functional groups changed to be favorable for oxidation and heat release. At different reaction stages, the activation energy was differently affected by the degree of drying. Average values of activation energies at different reaction stages are shown raw coal had the lowest activation energy. After soaking in water and drying, the activation energy of coal is increased to varying degrees, the reactivity is reduced, and the risk of spontaneous combustion is reduced. After soaking in water and drying, the activation energy of coal is increased to varying degrees, the reactivity is reduced, and the risk of spontaneous combustion is reduced. The activation energy of the coal samples dried for 24 h after soaking in water is the lowest among the coal samples dried for different times after soaking in water, and the moisture content is 10.5%.

Characterization and Performance Testing of an Intumescent Nanoinhibitor for Inhibiting Coal Spontaneous Combustion.

Considering disadvantages such as the low thermal stability and environmental pollution of existing gel inhibitors, a green and stable intumescent nanoinhibitor (INI) was prepared and tested. First, polyacrylamide (PAM), nano-silica, and intumescent flame retardant (IFR) were selected as raw materials. The INI was prepared by nanoparticle modification and cross-linking polymerization. Then, the structure and physical properties of INI were tested by Fourier transform infrared spectroscopy, scanning electron microscopy, and rheological experiments. Meanwhile, the inhibition performance of INI was studied through thermogravimetric analysis-Fourier transfer infrared spectroscopy (TGA-FTIR) analysis. The results suggest that the nanomodification improved the dispersibility of INI particles. The addition of modified nano-silica (MNS) and IFR enhances the strength of the reticular structure, thereby improving the transport convenience and covering ability of the INI gel. At high temperatures, IFR can generate a porous foamed carbon layer that further coats the coal. After INI inhibition treatment, the characteristic temperature and activation energy of coal were significantly improved, and the production of carbon monoxide and carbon dioxide decreased. Hence, irrespective of physical properties, physical inhibition performance, or chemical inhibition performance, INI performed well. Research results can provide valuable references for the preparation and performance study of a coal spontaneous combustion inhibitor.

Pyrolysis characteristics and kinetic study of coal in a novel concentrating photothermal thermogravimetric analyzer: Effect of heating rate

Coal pyrolysis is the initial reaction of vast utilization technologies, and the quantitative description of pyrolysis characteristics and accurate kinetic parameters under the wide range of heating rates are of significant challenges. The effect of heating rate from 5 ℃/min to 1000 ℃/min on coal pyrolysis in a novel concentrating photothermal thermogravimetric analyzer was systematically investigated. A new temperature control scheme especially for the ultra-fast heating process was proposed, guaranteeing the absolute temperature control error was less than 4 ℃ throughout the whole heating process. As the heating rate increased from 5 ℃/min to 1000 ℃/min, the absolute value of maximum mass loss rate increased linearly from 4.18 wt%/min to 66.06 wt%/min, and the specific reaction rate for coal conversion at 20% and 50% also increased linearly by 15.4 times and 16.4 times, respectively. The mean activation energies exhibited the exponential decrease tendency from 235.41 kJ/mol to 28.37 kJ/mol. The transformation rates for functional groups of chars were accelerated with the heating rate, and the char with same conversion rate would be more condensed. The activation energy of coal during pyrolysis under heating rate of 1000 ℃/min was binomially correlated with the ratio of small aromatic rings to large ones in char.

Inorganic Thixotropic Gel for Controlling Coal Spontaneous Combustion Through the Prevention of Air Leakage

ABSTRACT Cracks in coal goaf provide air leakage pathways and therefore increase the likelihood of coal spontaneous combustion, thus strongly affecting the safety of mining operations. Herein, an inorganic thixotropic gel (ITG) was proposed for inhibiting coal spontaneous combustion by blocking this leakage. The orthogonal experiments were designed to examine the effects of gel composition on gelation time and rheological/thixotropic properties. The three interval thixotropy test of the optimal-composition gel (4 wt% sodium bentonite, 3 wt% laponite, and 0.46 wt% silicate cement) revealed its good thixotropic recovery. The viscoelasticity test indicated that this gel retained elasticity-dominated behavior before being completely transformed into a sol and was not easy to break into pieces under pressure. By testing the characteristics of the ITG, it was proven that the ITG had an excellent water retention capacity, and high-temperature resistance and the apparent effects on blocking air leakage and extinguishing coal fire. By the thermogravimetric test, the influence of ITG on coal activation energy was calculated based on the ignition activation energy theory. FTIR was also introduced to analyze the effect of ITG on active groups of coal. In addition, structural characterization showed that ITG featured a tight surface and a stable overall structure, which further agreed with its prominent ability to block air leakage.

Thermogravimetric Analysis of the Combustion Characteristics and Combustion Kinetics of Coals Subjected to Different Chemical Demineralization Processes.

In order to explore the influence of different chemical demineralizations on coal combustion characteristics and combustion kinetics, five coals subjected to different chemical demineralization processes were investigated via thermogravimetric analysis. The ash contents of clean coal was reduced to 0.1–1.55% after different chemical demineralizations. The ignition temperature of coal decreased by 12–69 °C, and the peak temperature decreased by 7–62 °C. The burnout temperature of clean coal increased by 63 °C after demineralization by NaOH. The adsorption of noncombustible NaOH into the porous structure of TaiXi-3 caused an increase in burnout temperature. Alkali-soluble minerals were proven to have a negative effect on the combustion performance of coal, while acid-soluble minerals had the opposite effect. The combustion kinetics of five kinds of coals at a heating rate of 10 °C/min was investigated. The activation energy of coal obviously changes before and after demineralization (58.39–91.39 kJ mol–1). The activation energy of clean coal is obviously lower than that of raw coal.

Experimental research on the characteristics of the secondary oxidation heat of different unloaded coals

The oxidation heat characteristics of coal are key factors affecting the spontaneous combustion of coal. To study the thermal characteristics of the secondary oxidation of unloaded coal, a C600 microcalorimeter was used to test the unloaded coal under different stress conditions (0 MPa, 3 MPa, 6 MPa, 9 MPa, 12 MPa, 15 MPa) at 30–300 °C. The initial heat release temperature, heat release, and activation energy of coal were analyzed. The results shows that the initial heat release temperature of unloaded coal shows a trend of first increasing and then decreasing with increasing stress, and as the degree of oxidation increases, the maximum value of the initial heat release temperature point moves to a lower value. As the stress increases, the amount of heat release shows a fluctuation that first decreases and then increases, and as the degree of oxidation increases, the minimum heat release moves forward from 12 MPa for primary oxidation to 6 MPa for secondary oxidation. Similarly, the activation energy first increases and then decreases with increasing stress, and the maximum activation energy increases with increasing degree of oxidation, which is consistent with the trends of heat release. As the degree of oxidation increases, the overall performance of unloaded coal with increasing stress shows that the preoxidized coal sample is more susceptible to oxidation when it is reoxidized.

Performance of Fire Extinguishing Gel with Strong Stability for Coal Mine

ABSTRACT The spontaneous combustion of coal is one of the main disasters affecting safe production. In order to prevent and extinguish mine fires more efficiently, a new type of fire-suppression polymer gel with strong stability has been developed. The optimal formula was determined by testing the gelation time of different ratios of gel components. The measurement of water retention rate, viscosity and permeability of the gel were also carried out to verify the thermal stability and flowability. The effect of gel on the suppression of CO emission during coal oxidation was tested by the temperature-programming experiments. By the thermogravimetric experiments, the influence of gel on coal activation energy was calculated based on the ignition activation energy theory. FTIR was also introduced to analyze the effect of gel on active groups of coal during coal oxidation. Furthermore, the extinguishing mechanism of the gel was analyzed from forming characteristics. It is proven that the strong stable gel is an excellent fire extinguishing material with the advantages of controllable glue time, good water retention and the obvious effects of sealing.

Effect of Igneous Intrusions on Low-temperature Oxidation Characteristics of Coal in Daxing Mine, China

ABSTRACT In order to investigate the effect of igneous intrusions on low-temperature oxidation characteristics of coal, metamorphic coal samples affected by igneous intrusions and normal coal samples were collected from Daxing Mine. The thermal effect of coal at a low temperature was studied by Thermogravimetric analysis and Differential scanning calorimetry (TG-DSC). The oxidation kinetics experiment was used to analyze the oxygen consumption, the index gas, the crossing point temperature (CPT) and apparent activation energy of coal. Compared with normal coal, the metamorphic coal had lower weight loss rate and higher oxygen absorption rate due to igneous intrusions. At the same time, the metamorphic coal absorbed less heat at low-temperature stage and entered the exothermic stage first, and the total heat release in the whole stage was larger. The author also found that the initial exothermic temperature of coal decreased obviously due to igneous intrusions. In addition, metamorphic coal had lower apparent activation energy because of igneous intrusions, which indicated that the molecular structure of coal became easy to be activated, and the energy needed for activation became lower. Fourier transform infrared spectroscopy (FTIR) analysis suggested igneous intrusions changed the chemical structure of coal and increased the branching degree and short aliphatic chains. Moreover, metamorphic coal consumed more oxygen and produced more carbon monoxide, ethylene and ethane, with lower crossing point temperatures, which concluded that the igneous intrusions accelerated the oxidation reaction of coal at low-temperature stage and increased the spontaneous combustion risk of Daxing coal.

Experimental Study on the Effect of Chemical Composite Additives on Heat Release Characteristics of Coal Oxidation Spontaneous Combustion

ABSTRACT To study the effect of chemical composite additives (CCAs) on the heat release characteristics of coal oxidation spontaneous combustion, this paper develops a CCA comprising multiple chemical reagents that is formulated into different concentrations and used to treat coal samples. Microcalorimetry technology with high precision and high sensitivity was used in this experimental research. The heat release parameters of the oxidation of different treated coal samples were obtained and compared by varying the heating rate. The experimental results show that the general trend for coal is first absorbing heat and then releasing heat with increasing temperature, and there is a “step-like” trend in the heat releasing stage. For the same heating rate, water treatment and CCA treatment delay the temperature increase in the coal in the heat absorbing stage, and in the heat releasing stage, water treatment increases the heat release rate and maximum heat flow. CCA treatment decreases the heat release parameters value of the oxidation of coal, and the effect is increased with the increasing CCA concentration. The thermal analysis kinetics method was used to study the coal oxidation reaction. CCA treatment can increase the activation energy of coal, increase the difficulty of reaction process and reduce the heat release rate, which has an inhibitory effect on the spontaneous combustion of coal. Increasing the heating rate can accelerate the reaction rate of the system, resulting in an increase in the spontaneous combustion tendency of coal.

Analysis on Spontaneous Combustion Characteristics of Adding Associated Sulfur Minerals in Coal

ABSTRACT In order to further study the influence of associated sulfur minerals on spontaneous combustion and ignition characteristics of coal, four coal samples with different sulfur contents were prepared by adding different sulfur minerals to raw coal, and through Thermogravimetric Analysis (TG) experiment, Differential Scanning Calorimeter (DSC) test and X-ray diffraction (XRD) analysis, the influence of associated sulfur minerals on spontaneous combustion and ignition characteristics of coal was studied. Experimental results show that with the increase of associated sulfur minerals, the characteristic temperature of coal decreases, while the oxygen absorption, flammability and incombustibility stability index increase gradually, indicating that the coal is more prone to spontaneous combustion after being mixed with the associated sulfur minerals. Based on Coats–Redfern method to calculate the activation energy of coal during combustion stage with different associated sulfur minerals in coal, the calculation shows that the activation energy of coal combustion stage decreases with the increase of the associated sulfur minerals in coal and makes it easily to burn. Through the XRD and DSC analysis of associated sulfur minerals, it is found that the main components of the associated sulfur minerals are melanterite and copiapite, which can react with water and oxygen at room temperature, and the exothermic reaction makes coal more prone to spontaneous combustion. The associated sulfur minerals are exothermic after 200°C and reach an exothermic peak at 565°C, which makes the activation energy of coal in combustion stage decrease and coal easily to burn.

Prediction of coal stockpile autoignition delay time using micro-calorimeter technique

Spontaneous ignition of coal is one of the major challenges faced by coal industries, which results in a great loss and energy wastage. To evaluate the thermal behavior of coal powder and predict the autoignition delay time (AIDT) of coal stockpile, a C80 micro-calorimeter was employed to detect the thermal behavior of coal at elevated temperature. The reaction heat, reaction order, frequency factor and activation energy of coal were obtained from the experimental data. Based on the Semenov model, the self-heating oxidation temperature (SHOT) and temperature of no return (TNR) were calculated for the 25kg coal stockpile. Assuming that the coal stockpile is under quasi adiabatic conditions, its AIDT was predicted and compared with the experimental result. The comparison indicates that the micro-calorimeter technique is a useful way to access the safety of coal stockpile, which can be widely used in large scale coal storage and transportation.

미분탄 순산소 연소에서 주위 기체와 석탄 특성이 화염전파에 미치는 영향

Oxy-fuel combustion of pulverized coal is one of the promising new technologies to reduce CO2 and NOx from coal combustion. However, the stability of pulverized coal flame is reduced in the oxy-fuel combustion. This flame stability is concerned with the flame propagation that is affected by surrounding gas and coal characteristics, such as gas temperature, gas composition, coal volatile, coal activation energy and coal size. In this paper, a study on the influence of surrounding gas and coal characteristics on the flame propagation velocity in oxy-fuel combustion of pulverized coal was preformed. One dimensional model was used to calculate the flame propagation velocity of pulverized coal clouds. In this model, the radiation is considered to be the main source of heat exchange, and Monte Carlo method was adopted for accurate calculation of radiation heat flux. It was found that the flame propagation velocity become higher with the decrease of coal activation energy and the increase of coal volatile. Also, according to the increase of gas temperature and O2 concentration, flame propagation velocity increased.