Dust Deflagration Research Articles

Macroscopic behavior and kinetic mechanism of ammonium dihydrogen phosphate for suppressing polyethylene dust deflagration

In this paper, the inhibition effect of ammonium dihydrogen phosphate (NH4H2PO4) on the deflagration of polyethylene dust (C100H202) is studied by combining experimental tests with reaction molecular dynamics simulation (ReaxFF MD). The mechanism by which NH4H2PO4 inhibits C100H202 deflagration is revealed at the microscopic level. The experimental results demonstrate that the inhibition effect of NH4H2PO4 on C100H202 deflagration is positively correlated with its concentration, and the addition of NH4H2PO4 equivalent to 50 % of the mass of C100H202 can completely suppress the deflagration. The apparent activation energies for the decomposition of C100H202 and C100H202/50 %NH4H2PO4 are calculated using ReaxFF MD to be 97.11 kJ/mol and 124.78 kJ/mol, respectively, which are in agreement with the results obtained from thermogravimetric tests. Furthermore, ReaxFF MD is employed to calculate the types and quantities of deflagration products and free radicals before and after the addition of NH4H2PO4. The results indicate that the number of the main intermediate C2H4 decreases with the increasing addition of NH4H2PO4. Based on this, the generation and consumption pathways of C2H4 are traced. It is found that phosphorous groups such as HOPO and PO2 scavenge active free radicals like ·O and ·OH, thereby altering the formation and consumption pathways of C2H4, leading to a reduction in both its formation and consumption. Additionally, H2O and inert gases produced by the thermal decomposition of NH4H2PO4 also contribute to inhibiting the progression of C100H202 deflagration.

Measuring dust burning velocity for deflagration vent design

Deflagration vent design should be based on the burning velocity in the pressure range below 3 bara, where vent relief devices normally operate, rather than the KSt deflagration index, which is typically measured at pressures >50% of the maximum deflagration pressure, Pmax. Tests using a standardized 1000-L vessel showed that in the pressure range below about 3 bara, niacin and lycopodium burned faster than cornstarch, despite its larger KSt index. We attribute this behavior to the endothermic dehydration of cornstarch during the early stages of deflagration. Deflagration vents for cornstarch and other milled grains may have been oversized while vents for some other dusts may have been undersized. Burning velocities are most relevant in the region of the 2-bara midpoint overpressure and can theoretically be found from the “isothermal pressure rate gradient”, or IPRG, which we define as the gradient of (dP/dt) plotted against P (1-1/P)2/3. However, owing to irregular combustion caused primarily by two 5 kJ igniters, the IPRG is found indirectly from the “pressure rate gradient” or PRG, which we define as the gradient of (dP/dt) plotted against P. The PRG was found to be adequately linear for measurement at 2 bara and the experimental curves passed through the "origin". It was shown mathematically that at 2 bara the PRG is 1.05 times larger than IPRG, permitting the IPRG and turbulent burning velocity to be calculated. Since the calculation of burning velocity from the IPRG requires Pmax, a general extrapolation technique was developed for correcting Pmax values obtained in vessels smaller than 1000-L. We propose that, owing to the greater turbulence in the 20-L vessel, a calibration be made using methane. This would establish the turbulence factors for each vessel at 2 bara, allowing the underlying “reference” burning velocities to be calculated and compared. However, to measure turbulent dust burning velocities in 20-L vessels a smaller and more efficient igniter must be used. Two 5 kJ igniters not only obscure the pressure history but wastefully expend energy far from the vessel core, depleting the unburned mixture and depressing the subsequent pressure rate. An observed “double sigmoid” dependence of dust deflagration rate on particle diameter suggests that routine explosibility testing of organic dusts is usually carried out in a region where pressure rates are relatively insensitive to particle size.

Effect of airflow velocity on flame propagation and pressure of starch dust explosion in a pneumatic conveying environment

To investigate the flame propagation and pressure characteristics of dust explosions during the airflow transportation of dust particles, a 2 m transparent pipeline, supplied with a constant airflow from a fan, was constructed as a dust explosion testing apparatus. The distribution patterns of airflow velocity were measured using an anemometer and subjected to statistical analysis. Dust explosion experiments were conducted with airflow velocities of 5, 10 and 15 m/s, and an ignition energy of 1 kJ was applied to the transported dust particles. The results revealed that the flame propagation of starch explosions undergoes distinct stages: ignition, slow propagation, accelerated propagation. The flame propagation speed and explosion pressure initially increased and subsequently decreased as the airflow velocity was raised. As the airflow velocity increased from 5 m/s to 10 m/s, the maximum flame propagation speed rose from 53.2 m/s to 67.7 m/s, and the maximum explosion pressure increased from 25.62 kPa to 31.96 kPa. At an airflow velocity of 15 m/s, both the maximum flame propagation speed and explosion pressure decreased, reaching 32.6 m/s and 19.67 kPa, respectively. In contrast to conventional closed container powder injections, chemical igniters in the pneumatic conveying environment exhibit elongated flames, with the airflow influencing the timing of dust deflagration flame appearance and accelerating flame propagation. Due to the connectivity of the airflow transport pipeline, the explosion pressure tends to be lower. Influenced by non-uniform airflow and temperature differentials, dust deflagration flames within the airflow transport pipeline manifest a spiral propagation structure.

Experimental and numerical study on suppressing coal dust deflagration flame with NaHCO3 and MPP

In this paper, the flame propagation behavior and free radical reaction mechanism of two powder explosive suppressants, sodium bicarbonate (NaHCO3) and polyphosphate melamine (MPP), at different additions were investigated using Hartmann experimental system and CHEMKIN-PRO numerical simulation. The results showed that NaHCO3 and MPP showed different inhibitory advantages. MPP mainly suppressed the propagation of flame during the development and rapid rise stages, while NaHCO3 had a better suppression effect at the preliminary stage of explosion. The gas phase kinetic analysis also proved that the NaHCO3 reaction was rapid, and it could decompose and endothermy at the beginning of the explosion, and generate gaseous H2O and CO2 to dilute the concentration of volatile components. Meanwhile, NaOH, NaO, and NaO2 produced by decomposition consumed free radicals and reduced the initial reaction rate of the explosion. In the process of gas phase reaction, MPP continuously reduced the amount of flame free radicals through a inhibition cycle of HPO3 ⇔ PO2, and generated a large number of inert products for inerting fixed carbon, exhibiting better long-term effectiveness. This study can provide a reference for the selection and design of explosion suppressants.

Macroscopic behaviors and chemical reaction mechanism for the inhibition of NH4H2PO4 powder in hybrid methane/coal dust deflagrations

In this research, the inhibition effect and microscopic mechanism of NH4H2PO4 on the macroscopic deflagration characteristics of methane (9.5 vol%) mixed with three coal samples were studied. Experimental results show that the higher the concentration of added NH4H2PO4, the more pronounced the inhibition effect on the deflagration of three coal samples mixed with methane. When the mass concentration of NH4H2PO4 reached 90%, the deflagration pressures of anthracite/methane hybrids, coking coal/methane hybrids, and long-flame coal/methane hybrids decreased by 50.80%, 45.59%, and 39.06%, respectively. The time for the flame front to reach the height of 300 mm extended by 39 ms, 30 ms, and 63 ms, respectively. In addition, the microscopic reaction mechanism of NH4H2PO4 inhibiting the methane/coal dust deflagration was revealed using a reaction kinetics model. We found that phosphorus-containing substances mainly absorbed explosive active free radicals through cyclic reactions HOPO2 = PO2 and HOPO = PO2. Through ROP analysis, we found that with an increase in inhibitor concentration, the HOPO radical, which had a better scavenging effect on oxidizer free radicals, was gradually replaced by HOPO2, resulting in a saturation effect. Sensitivity analysis showed that the inhibitory effect of NH4H2PO4 mainly depended on phosphorous substances and free radicals HOPO, HOPO2, and PO2.

Inhibition evaluation of modified-fly ash inhibitors in methane/coal dust deflagrations

The inhibitory efficiency of modified-fly ash inhibitors MFAC and PMFAC on methane/coal dust deflagration was experimentally evaluated. Results suggested that PMFAC was superior to MFAC because of the phosphorus-containing substances and abundant reactive radicals. The composite inhibitor first inhibited the gas-phase reactions of the homogeneous combustion in the hybrid explosion field to decrease the maximum rate of explosion pressure rise (dP/dt)max in the period 0–t1, while reducing the maximum explosion pressure (Pmax) by inhibiting the chain combustion reactions in the period t1–t2. Additionally, the impacts of MFAC and PMFAC on the microscopic reactions of hybrid methane/coal dust deflagration were numerically investigated. Results indicated that the inhibitors significantly prolonged the explosion process and decreased the peak rate of productivity (ROP) for each key reactive radical. Subsequently, the inhibition mechanism by which the PMFAC molecules interacted with the deflagration reactions of methane/coal dust was elucidated in detail. Results revealed that the elementary reactions concerning the key free radicals O, H, and OH were considerably inhibited in the gas-phase reactions. The competition for key radicals in the explosion reactions by the inhibitors indirectly inhibited the surface-phase reactions, and the synergistic effect of the radicals significantly decreased the sensitivities of the key reactions.

TGA-FTIR for kinetic and evolved gas analysis of the coal particles in dust deflagration

The common approach in the dust deflagration simulations ignores the temperature gradient inside of the particles. Therefore, the reaction rate of the particle at one temperature remains constant. In order to explore the mass loss and evolve gas characters during the coal particle decomposition procedures, a single-particle model was created using OpenFOAM tool kit. In this study, the pyrolysis characteristics and gas properties of the coal sample were determined by TGA-FTIR. The evolution of gases in real-time was investigated and implemented as kinetic models in the dust deflagration. To solve the heat and mass transfer of the single-particle, a two-phase solver based on the Eulerian method was developed based on reactingFoam. The porosity of the coal particle was included with respect to the coal mass. The result of the heat and mass transfer of the single-particle model agrees well with the experiment. In order to simulate the particle behavior in the dust explosion, new boundary conditions extracted from dust explosion simulations will be implemented. The final goal of the single-particle model is to implement the new particle decomposition behavior into the full scale of dust explosion simulations.

Study on the preparation of novel NiB/Hβ-Al2O3 micro-mesoporous suppressant and its inhibition mechanism of coal dust explosion flame

Coal dust explosion is one of the serious accidents in the coal industry. It is of great significance to study the flame suppression of coal dust explosions. In this paper, a novel active component NiB with amorphous structure for explosion suppression was synthesized by the chemical reduction method. Furthermore, the novel explosion suppressant NiB/Hβ-Al2O3 was prepared through the kneading method by loading novel amorphous NiB nanoparticles on Hβ-Al2O3 with the micro-mesoporous structure as the carrier. The morphology and structure of NiB/Hβ-Al2O3 were characterized by XRD, BET, SEM, and FTIR, which showed that the NiB/Hβ-Al2O3 has proper pore structure and NiB nanoparticles are uniformly distributed as active components for explosion suppression in suppressant. Hartmann tube was used to evaluate the inhibition of coal dust deflagration. The results showed that the flame propagation distance and velocity decreased with the increase of the explosion suppressant. When the addition of explosion suppressant was 30 wt%, the explosion of coal dust was suppressed effectively. Furthermore, combing with the analysis results of the products after coal dust deflagration, the physical and chemical inhibition mechanism of the novel NiB/Hβ-Al2O3 explosion suppressant on coal dust deflagration was put forward.

Dust cloud evolution and flame propagation of organic dust deflagration under low wall influence

The present study discusses experiments on organic dust explosions in a setup with low wall influence. The proposed apparatus decouples the dust dispersion and the deflagration event in two separate compartments. The use of a continuous-wave laser to illuminate the centre plane of the observation chamber allows capturing both, the dust cloud and the flame during the same experiment and eliminates typical problems caused by the limited dynamic range of high-speed cameras. A k-means clustering method is used for image segmentation to obtain the spatial extent and the propagation velocities of the unreacted particle cloud and the flame zone. Spatially resolved velocities are calculated by the additional use of an optical flow method. The main goal of the presented setup and image processing method is to provide high quality validation data for the development of numerical models on dust deflagration.

A novel ATH/SBA-15 suppressant prepared by in-situ synthesis and its inhibition mechanism on PE dust deflagration flame

Recently, polyethylene (PE) dust explosions have become a serious threat to the petrochemical industry. In order to prevent the occurrence of PE dust explosion, a novel aluminum hydroxide (ATH)/Santa Barbara Amorphous type 15 (SBA-15) powder explosion suppressant with the uniform dispersion of ATH was prepared by in-situ synthesis method. For ATH/SBA-15 inhibitor, SBA-15 molecular sieve and ATH was used as the carrier and active component of explosion inhibition, respectively. The inhibition effect on PE dust deflagration was studied by flame propagation experiment. The results showed that when the addition amount of ATH/SBA-15 exceeded 40 wt%, PE dust deflagration flame was almost completely inhibited. Furthermore, the Coats-Redfern method was used to study the thermal decomposition kinetics model. It was found that the thermal decomposition kinetics model of PE before and after the addition of explosion suppressants followed the random nucleation and growth reaction mechanism (A3 model). Further fitting analysis showed the apparent activation energy of PE increased significantly after adding ATH/SBA-15 inhibitor, confirming that ATH/SBA-15 had a significant inhibitory effect on PE deflagration in thermodynamics. Finally, combining with a series of characterization results, it was founded that the ATH/SBA-15 suppressant played the efficient synergy of physics and chemistry, which was efficient in inhibiting PE deflagration. The physical inhibition mainly includes: the free radicals adsorption by SBA-15 molecular sieve, the coating effect of ATH, the endothermic effect and the reduction in O2 concentration by H2O decomposed from ATH. Meanwhile, the chemical inhibition mainly lies in the elimination of the free radicals O· and H· in the explosion process by ATH.

Effects of physical and chemical factors on the suppressant enhanced explosion parameter (SEEP) in flame propagation of metal dust layers

Adding solid inertants to metal dust is an effective means of reducing the risk of dust fires and explosions. However, inertants that can effectively suppress the metal dust deflagration could somehow violently enhance the fire hazard of the same metal dust layer. This severe risk has not been well recognized and discussed in depth. To investigate the physical and chemical factors that cause the SEEP phenomenon, flame propagation experiments on mixed dust layers were performed using three common metal dusts (Mg, micro Ti, nano Ti) and five commonly used inertants (NH4H2PO4, NaHCO3, CaCO3, SiO2, CaO). The results indicate that the physical factors were the vaporization of metal dust and the destruction of the oxide layer by the gas from the decomposition of inertants. The chemical factors behind SEEP were the exothermic chemical reaction of metal dust with inertants, and the combustion of the gases released by the decomposition of inertants. Both factors significantly increased the severity of a fire in the dust layers, and in some cases, the chemical factors increased the likelihood of an explosion. Regardless of physical or chemical factors, the mass percentage of inertants in the mixed dust layers that lead to SEEP has a relatively wide range. Therefore, research on the use of solid inertant technology to prevent or mitigate dust explosions should fully consider the physicochemical properties of metal dust. The results are supposed to be used as a comprehensive guide for selecting suitable inertants for metal dust to prevent fire and explosion incidents.

Experimental investigation on the inhibition of coal dust deflagration by the composite inhibitor of floating bead and melamine cyanurate

To mitigate the coal dust deflagration caused by leakage during coal gasification, a novel composite inhibitor (FB/MCA) was synthesized from floating bead (FB) and ultrafine melamine cyanurate (MCA) powders. The MCA powder was uniformly loaded on the FB after sufficient impregnation, as observed by scanning electron microscope. And thermogravimetric analysis indicated that FB/MCA composite inhibitor had excellent heat absorption properties. The inhibition performance of FB/MCA composite inhibitor on coal dust deflagration was studied in a vertical combustion tube. The results showed that under the effect of FB/MCA composite inhibitor, the peak flame temperature and propagation velocity of coal dust deflagration decreased by 37 and 23%, respectively. The flame propagation time was prolonged from 132 to 227 ms, and the average value of flame acceleration dropped sharply. Residues analysis showed that the surface of the unburned coal dust was coated with a heat-resistant film produced by FB/MCA composite inhibitor, which hindered its oxidation and preheating by the flame. Besides, the scavenging mechanism of free radicals (O and OH) by FB/MCA composite inhibitor was revealed in depth.

Experimental study on the minimum ignition energy of cornstarch particle-air flows in a horizontal pipeline

Pipelines and process equipment are commonly interconnected in a network of dust extraction or pneumatic conveying in lines industry. History has shown that the severity of a dust deflagration could be much accentuated if the initial fireball is allowed to propagate further through pipelines. However, less is known about the hazard of a primary ignition in a pipeline conveying system with combustible dust and high airflow velocity. This paper presents an experimental study on the ignitability of cornstarch particle-air flow in a lab-scale piping system. The results show that minimum ignition energy (MIE) of dried cornstarch flow at 12–28 m/s was less than 300 mJ, and the minimum explosible concentration (MEC) was less than 100 g/m3. An increase in airflow velocity increased both MIE and MEC, as well as stretching the spark plasma. Moisture in the dust significantly decreased its ignitability, with this being a more marked factor than airflow velocity in influencing the ignition hazard in a pipeline.

Study on inhibition effect and mechanism of micron and nano Al(OH)3 powders on deflagration flame of poplar dust

In this paper, the Hartmann experimental system was used to study the effect of different proportions of micron and nano Al(OH)3 powders on the deflagration flame propagation of poplar dust. In the course of the experiment, a high-speed camera was used to record the flame shape and characteristic parameters in the process of poplar dust deflagration flame propagation. Combined with the SEM images of poplar dust explosion products under different conditions, the pyrolysis characteristic curves of poplar dust, micron and nano Al(OH)3 powders, the inhibition mechanism of micron and nano Al(OH)3 powders on poplar dust deflagration was analyzed. The experimental results show that micron and nano Al(OH)3 powders have obvious inhibition effect on poplar dust deflagration flame, and better inhibition effect can be achieved when 35% nano Al(OH)3 powder is added. And under the condition of adding the same proportion of micron and nano Al(OH)3 powders, the inhibition effect of nano Al(OH)3 powder is better than that of micron Al(OH)3 powder.

Study on the characteristics and influencing factors of micron/nano carbon material dust explosions

Because of the wide range of applications of lithium ion batteries, the combustible and explosive carbon material dust of a negative electrode material requires additional attention. Few explosion test data of carbon material dust are available. In this paper, the thermodynamic and explosion parameters of allotropes of carbon dust and the same type of carbon material dust with different particle size distributions were determined. The results showed that the explosion pressure of micron/nano carbon material dust ranged from 0.4 to 0.7 MPa; the maximum deflagration index Kst ranged from 4 to 10 MPa · m/s; and the minimum ignition temperature was approximately 600 °C. The proportion of the small dust particles was an important factor that caused a change in the initial oxidation weight loss temperature and apparent activation energy of the same type of carbon dust. The variation trend among the initial oxidation weight loss temperature, apparent activation energy and particle size distribution of different carbon dust materials was not obvious, and mainly depended on the difference in molecular structures. Different molecular structures resulted in different apparent activation energies of the carbon allotropes. The apparent activation energy played a leading role in the change in the dust deflagration index. The smaller the apparent activation energy was, the smaller the energy required for carbon-carbon chemical bond breaking. The faster the carbon-carbon bond-breaking rate was, the larger the deflagration index. The dust particle size distribution, specific surface area and other characteristics had little influence on the deflagration index. Furthermore, the apparent activation energy had a greater impact on the deflagration index than the explosion pressure. The dust explosion pressure was mainly limited by oxygen in the test equipment, and its maximum value remained relatively constant. The minimum ignition temperature of dust clouds decreased with decreasing activation energy and increasing pre-exponential factor. The lower the initial oxidation weight loss temperature was, the lower the measured dust cloud minimum ignition temperature.

Inerting mechanism of magnesium carbonate hydroxide pentahydrate for coal dust deflagration under coal gasification

To reduce the risk of coal dust deflagration caused by the leakage in the coal gasification process, a semi-closed vertical combustion tube was built with a high speed camera and micro-thermocouples. And the inerting effect of magnesium carbonate hydroxide pentahydrate (MCHP) with different particle sizes was investigated on the coal dust deflagration. The results showed that the initial flame became very faint and the brightness of the flame was greatly weakened after the addition of MCHP powder. And as the inerting ratio increased, both of the flame velocity and temperature decreased. When the particle size of MCHP powder decreased, the flame propagation time extended from 132 to 196, 223, and 228 ms respectively. And the residue analysis revealed that the decomposition of MCHP not only absorbed the highly reactive radicals of combustion, but also formed inert gases and heat-resistant protective film, which greatly reduced the deflagration intensity of coal dust.

Macromorphological features and formation mechanism of particulate residues from methane/air/coal dust gas–solid two-phase hybrid explosions: An approach for material evidence analysis in accident investigation

The present work aimed at acquiring the macromorphological features and formation mechanisms of post-explosion particulate residues from the hybrid explosion of methane/coal dust mixtures. For this purpose, a comparative study on the explosion severity of six mass concentrations of coal dust deflagration in four methane-air atmospheres was firstly experimentally performed, with the post-explosion particulate residues collected after explosion experiments. In addition, the morphological classification and formation rules of the particulate residues for methane/coal dust mixtures were preliminarily proposed based on the SEM observations, theoretical analysis, and qualitative discussions. Moreover, the fractal characteristics in particle size variation of the particulate residues were comparatively studied using the fractal theory. Furthermore, the macromorphology features and morphological structures of the post-explosion particulate residues were explored quantitatively with the aid of SEM results and image processing technique. Results demonstrated that Pmax, (dP/dt)max, and Kst first increased and then exhibited a decreasing tendency with the increase in coal dust concentration for various methane equivalence ratios, and they reached their maximum values as the methane equivalence ratio was 0.9. Whereas the combustion time (tc) showed the opposite tendency with the increasing coal dust concentration under various methane equivalence ratios. Besides, compared with pre-explosion dust samples, seven various types of particulate morphological structures occurred distinctively in the solid residues, indicating the combustion behaviors and explosion severity of the mixtures. Quantitative analysis indicated that the fractal dimension for the particle size variation of the particulate residues was smaller than that of the pre-explosion dust sample, and increased logarithmically as the methane equivalence ratio increased. Moreover, the range of the roundness distribution of the particulate residues deviated significantly from that of the pre-explosion dust sample, and expanded gradually with the increasing concentration of coal dust and then decreased negatively and logarithmically with the increasing particle size. Eventually, the coupling correlations between the particulate residues and explosion severity were established comparatively, and we ulteriorly proposed the potential utilization of qualitative-quantitative analysis on the post-explosion particulate residues in coal-dust-involved explosion accidents. This work would be conducive to disaster investigation and hazard assessment for methane/coal dust explosions.

Effect of powder inhibitors on ignition sensitivity evolution of wood-plastic mixed dust: Based on thermal decomposition behavior and deflagration residues

The ignition temperature (IT) of the dust cloud is one of the main parameters of combustible dust deflagration risk assessment. Since the previous research focuses on the IT of single dust, in order to reduce the deflagration risk of mixed dust, the effects of dust concentration and dispersed pressure on the IT of wood-plastic mixed dust and the inhibition effects of different powder inhibitors were investigated through experiments. The thermal decomposition behavior of the mixed dust was studied by comprehensive thermal analysis, and the surface characteristics of the deflagration products were analyzed by FTIR spectra, thus revealing the inhibition mechanisms of inhibitors on ignition sensitivity of mixed dust. The results showed that the best ignition conditions for wood-plastic mixed dust were 300 g/m3 and 15 kPa. Ammonium polyphosphate (APP) and aerosil had significant inhibition effects on the ignition sensitivity of wood-plastic mixed dust, and the inhibition effect was better with the increase of inerting ratio. Their inhibition mechanisms are different, and the inhibition effect of APP is better. It was worth noting that APP can promote the initial decomposition of wood-plastic mixed dust, resulting in accelerated dehydration and carbonization rate of mixed dust and improved thermal stability.

Comprehensive investigations on the explosion suppression of biomass fuels: Starch as a representative

Starch is one type of biomass fuel raw material commonly used, but presents deflagration hazards when suspended in the air. Dust deflagration accidents might be effectively inhibited by creating a gas inerting atmosphere. In this work, the evolution of starch deflagration flame in the inhibitory gas atmosphere N2 or CO2 was investigated. Under the action of inerting gas, heterogeneous combustion is strengthened, the flame propagation velocity is reduced and the acceleration trend is smooth. The maximum flame temperature is decreased and fluctuation after reaching the maximum value is weakened. According to the micro characterization of deflagration residues, after injecting inhibitory gas, more amorphous carbon is protected and the carbon layer formed has a smaller crystal size, some easily oxidized functional groups in starch are maintained during the deflagration. Meanwhile, carbon content and the original chemical bond ratio in the residues are also increased. In addition, experimentally measured the maximum limit inerting ratios of CO2 and N2 are chosen as 33% and 54%, respectively. On this basis, safety application for gas inerting technology in practical processes was discussed.

The inhibiting effects of sodium carbonate on coal dust deflagration based on thermal methods

To aid the development of safe procedures, the inhibiting effects of sodium bicarbonate (NaHCO3) on coal dust explosions were investigated by employing a simultaneous thermal analyzer and a standard 20-L spherical chamber. The thermal behaviors and explosion parameters of the coal dust/NaHCO3 mixtures were characterized and the surface morphology, functional groups and chemical composition of the explosive residue were conducted. Finally, the inhibiting mechanism of NaHCO3 on coal dust explosions was proposed. The results demonstrated that the thermal decomposition temperature of coal dust was increased and the thermal decomposition rate, maximum heat flow, and heat release were decreased after the addition of NaHCO3. The apparent activation energies and pre-exponential factors of coal dust were also increased. The maximum explosion pressure and maximum explosion pressure rising rate during deflagration decrease with an increase in the NaHCO3 mass fraction, and the optimal inhibiting ratio of NaHCO3 powder to pulverized coal explosion is 400%. NaHCO3 powder covers the surface of coal dust particles promoting heat absorption and isolation, and the functional groups, such as C=C, C–O and C–H, are protected by NaHCO3, preventing coal dust pyrolysis and inhibiting the explosions. The results provide guidance for the prevention of coal dust explosion.