Explosion Limit Research Articles

System Design and SVM Identification Algorithm for the Ultrasonically Catalyzed Single-Sensor E-Nose

In this article, a system design method and Support Vector Machine (SVM) gas identification algorithm for the ultrasonically catalyzed single-sensor E-nose is proposed and investigated for the first time. In the aspect of hardware, the E-nose system consists of an ultrasonic module, sensing module, data processing module, personal computer, and power supply module. In the aspect of software, a microcontroller in the data processing module is coded by C programming language for data acquisition and operational control, and a user interface is made on the PC by C# programming language for display and sending commands. Performance of the integrated E-nose is tested and evaluated by methanol, ethanol, acetone, and hydrogen gases, respectively. The experimental results show that the integrated E-nose can achieve up to 100% gas identification success rate in the concentration range greater than 10% LEL (LEL = lower explosive limit), with a concentration measurement error less than 10%, and the SVM algorithm can effectively improve the gas identification ability in the low-concentration range (1%–10% LEL). For 1% LEL methanol target gas, it raises the gas identification success rate from 0% to 90%.

An investigation of maximum experimental safety gap of CH4H2 blended fuel at different initial pressures

AbstractThe MESG (maximum experimental safety gap) of CH4H2 mixtures were measured at different initial pressures (40–140 kPa). With an increase in hydrogen fraction, the classification of CH4H2 mixtures was from Group IIA to Group IIC. The mixtures were classified as Group IIB when the hydrogen fraction was between 25% and 77%, followed by Group IIC with continuous increase in the amount of hydrogen. For calculating MESG of CH4H2 blended fuel, the method based on oxygen amount is feasible at any initial pressure. It is different from Le Chatelier's equation, which is used to evaluate the low explosion limits for flammable mixtures but not suitable for calculating MESG. In this study, a formula calculating MESG‐based laminar flame velocity and initial pressure was proposed to obtain the MESG of CH4H2 mixtures more easily.

Numerical Description of Jet and Duct Ventilation in Underground Garage after LPG Dispersion

Contamination of toxic and odorous gases emitted from stacks in buildings located in an urban environment are potential health hazards to citizens. A simulation using the computational fluid dynamic technique may provide detailed data on the flammable region and spatial dispersion of released gases. Concentrations or emissions associated with garage sources and garage-to-house migration rates are needed to estimate potential exposures and risk levels. Therefore, the aim of the study was to use an original mathematical model to predict the most accurate locations for LPG sensors in an underground garage for vehicles powered with LPG. First, the three-dimensional geometry of an underground garage under a multi-family building was reconstructed. Next, two types of ventilation, jet and duct, were considered, and different sources of LPG leakage were assumed. Then, the Ansys Fluent software was applied as a solver, and the same initial value of released LPG (5 kg) was assumed. As a simplification, and to avoid the simulation of choked outflow, the emission from a large area was adopted. The results showed stagnation areas for duct ventilation in which gas remained for both the jet and duct ventilation. Moreover, it was observed that the analyzed gas would gather in the depressions of the ground in the underground garage, for example in drain grates, which may create a hazardous zone for the users of the facility. Additionally, it was observed that for jet ventilation, turbulence appearance sometimes generated differentiated gas in an undesirable direction. The simulation also showed that for blowing ventilation around the garage, and for higher LPG leakage, a higher cloud of gas that increased probability of ignition and LPG explosion was formed. Meanwhile, for jet ventilation, a very low concentration of LPG in the garage was noticed. After 35 s, LPG concentration was lower than the upper explosive limit. Therefore, during the LPG leakage in an underground garage, jet ventilation was more efficient in decreasing LPG gas to the non-explosive values.

A multi-factor evaluation method for the thermal runaway risk of lithium-ion batteries

To systematically and quantitatively establish a multi-factor evaluation method for the thermal runaway risk of lithium-ion batteries (LIBs), the fuzzy analytic hierarchy process was adopted in this paper. The own hazardous factor of battery, hazardous factor of vented gases, jet fire and high-temperature mixture (JFHM), ejected powder and their corresponding sub-factors were evaluated and analyzed. Combined with literature, the model of multi-factor evaluation method was established and the index system was determined. The pair-wise comparison matrixes for the thermal runaway risk were drawn, the triangular fuzzy method was used to calculate and the evaluation weight was obtained. The factors' ranges of the criteria risk grades were quantitatively determined. The risk of thermal runaway consequences under the selected abuse condition was analyzed with a case study. The result shows that the thermal runaway risk from LIBs under the selected abuse condition is level III: the LIB is more dangerous after thermal runaway. Meanwhile, in this method, the lower explosion limit of gas and the maximum height/ length of the JFHM are the two factors with the greatest weights. In the actual design and use process, people should pay attention to the protection of the runaway gas explosion and the harm of JFHM.

Research on the effect of thermal runaway gas components and explosion limits of lithium-ion batteries under different charge states

The combustion and explosion of thermal runaway gases from lithium-ion batteries may accelerate the propagation of thermal runaway from lithium-ion batteries and pose a serious threat to surrounding people and property. Therefore, the research of thermal runaway gas composition and explosion limits of lithium-ion batteries is of great significance for the prevention and control of thermal runaway of lithium-ion batteries. In this paper, we use experiments combined with empirical formulas to investigate the composition of gases generated by the thermal runaway and the explosion limit of 18,650 lithium-ion batteries. The analysis of the thermal runaway gas components of lithium-ion batteries by using gas chromatography-mass spectrometry (GC-MS) shows that as the SOC increases, the number of thermal runaway gases increases. With the increase of SOC, the change of lower explosion limit (LEL) shows the same trend as that in alkanes content, which increases and then decreases; while the change of upper explosion limit (UEL) shows the same trend as that in unsaturated hydrocarbons content, which decreases and then increases. In addition, 50% SOC battery shows the lowest exhausted gas combustion explosion danger.

Change Law of Lower Limit of Gas Explosion at Ultra-High Temperatures.

During coal seam mining, a large amount of low-concentration mine gas will be produced, and it is the main utilization way to pass it into a thermal storage oxidation device to obtain heat energy. The thermal storage oxidation process is carried out in an ultra-high temperature environment. The excessive gas concentration not only reduces the production efficiency but also presents an explosion hazard. To solve the abovementioned problems, the lower explosion limit of a low-concentration gas at ultra-high temperatures (900–1200 °C) was studied through a self-developed high-temperature explosion experimental device. Fluent software was used to simulate the reaction of a low-concentration gas in a high-temperature environment, and the experimental results were verified according to the maximum explosion pressure. Through analysis and discussion, the following are found: (1) the relationship between the instantaneous explosion pressure of the low-concentration gas and the gas concentration as well as the relationship between the maximum explosion pressure near the lower explosion limit and the gas concentration are in accordance with the Boltzmann function. (2) When the temperature rises from 900 to 1200 °C, the lower limit of gas explosion obtained from experiments is reduced from 2.33 to 1.36%. (3) The lower limit of gas explosion decreases with increasing temperature at ultra-high temperatures and the downward trend slows down, this is similar to the change rule of the lower limit of gas explosion at temperatures below 200 °C. These findings have certain practical significance for improving the utilization efficiency of the low-concentration gas in heat storage oxidation.

Methods to predict variations of lower explosion limit associated with hybrid mixtures of flammable gas and dust

In order to study variations of the lower explosion limit associated with hybrid mixtures of flammable gas and dust, four hybrid mixtures of methane/lycopodium, methane/polyethylene, ethylene/lycopodium, and ethylene/polyethylene with various concentration ratios were constructed. The lower explosion limits of these mixtures were measured in a 20 L spherical explosion vessel. According to the experimental results, it was obtained that the lower explosion limits of these hybrid mixtures were decreased by increasing the flammable gas concentration. The two-dimensional coordinate system was divided into explosion area and non-explosion area using the lower explosion limit curve. For different hybrid mixtures, the proportions of the explosion area were different in the two-dimensional coordinate system. The larger the proportion, the greater the explosion sensitivity. Based on this proportionality relationship, a dimensionless parameter called sensitivity index was defined as the ratio of the explosion area to the non-explosion area. The greater the sensitivity index, the greater the explosive sensitivity of the hybrid mixture. According to the relationship between the sensitivity indices of different hybrid mixtures, the influencing factors for the sensitivity index were established, including combustion heat of the flammable gas and dust, chemical reactivity of the flammable gas, as well as dimensionless parameters of dust decomposition characteristics. Considering these influencing factors, a calculation method for the sensitivity index was established using maximum explosion pressure as well as explosion indices of the flammable gas and dust. Through this comprehensive study, a new predictive approach for determining variations of the lower explosive limit of hybrid mixtures with the newly proposed sensitivity index was established. The predictive performance of this newly developed approach was verified using data from other hybrid mixtures.

Laminar Burning Velocities of Hydrogen-Blended Methane–Air and Natural Gas–Air Mixtures, Calculated from the Early Stage of p(t) Records in a Spherical Vessel

The flammable hydrogen-blended methane–air and natural gas–air mixtures raise specific safety and environmental issues in the industry and transportation; therefore, their explosion characteristics such as the explosion limits, explosion pressures, and rates of pressure rise have significant importance from a safety point of view. At the same time, the laminar burning velocities are the most useful parameters for practical applications and in basic studies for the validation of reaction mechanisms and modeling turbulent combustion. In the present study, an experimental and numerical study of the effect of hydrogen addition on the laminar burning velocity (LBV) of methane–air and natural gas–air mixtures was conducted, using mixtures with equivalence ratios within 0.90 and 1.30 and various hydrogen fractions rH within 0.0 and 0.5. The experiments were performed in a 14 L spherical vessel with central ignition at ambient initial conditions. The LBVs were calculated from p(t) data, determined in accordance with EN 15967, by using only the early stage of flame propagation. The results show that hydrogen addition determines an increase in LBV for all examined binary flammable mixtures. The LBV variation versus the fraction of added hydrogen, rH, follows a linear trend only at moderate hydrogen fractions. The further increase in rH results in a stronger variation in LBV, as shown by both experimental and computed LBVs. Hydrogen addition significantly changes the thermal diffusivity of flammable CH4–air or NG–air mixtures, the rate of heat release, and the concentration of active radical species in the flame front and contribute, thus, to LBV variation.

Effects of Initial Turbulence on the Explosion Limit and Flame Propagation Behaviors of Premixed Syngas-Air Mixtures.

Syngas with important industrial applications has explosive hazards because of its flammability. It is necessary and valuable to study the combustion and explosion characteristics of syngas under actual working conditions. To explore the effects of initial turbulence on the explosion limits and the flame propagation behavior of the syngas–air mixtures, the explosion limits were tested by the explosive limit instrument, and the flame propagation process in the spherical pressure vessel was recorded by a high-speed camera. By adjusting the rotating speed of the stirrer to obtain turbulence of different intensities, the explosion limit and flame propagation behavior of syngas under different turbulent conditions were analyzed. The explosion limit of syngas in the macro-static state was 9.5–76.1%, and its flame front was relatively smooth. However, with the increase in turbulence intensity, both the upper and lower explosion limits of syngas decreased. The disturbance of turbulence made the flame shape change. The flame front was wrinkled, and the flame boundary was blurred, which became more and more obvious with the increase in turbulence intensity. The maximum velocity and duration of flame propagation increased with the increase in turbulence intensity. Under the same turbulence intensity, the flame propagation velocity generally augmented first and then lessened.

Modeling the environmental, health, and safety aspects of xylene isomer emission from storage tanks in petrochemical industries, Iran.

The release of xylene isomers from storage tanks poses a significant threat to petrochemical industries, and their safe transportation and storage is a widely researched topic. This paper focused on modeling the environmental, health, and safety effects of P-xylene and O-xylene leakage from storage tanks via Areal Locations of Hazardous Atmospheres (ALOHA) and Wireless Information System for Emergency Responders (WISER). The meteorological data of the area, characteristics of the tanks, and the roughness of the land surrounding the tanks were used to run the ALOHA model. The dispersion distances of P-xylene and O-xylene toxic and flammable vapor clouds were estimated according to the Immediately Dangerous to Life or Health (IDLH) and lower explosive limit (LEL) criteria. Also, the levels of thermal radiation due to the burning of P-xylene and O-xylene were estimated. The results showed that in the cold seasons, the IDLH was a maximum distance of 62m and 45m for P-xylene and O-xylene, respectively. The LEL criteria were 10% with a magnitude of 1100ppm for a maximum distance of 54m and 35m for P-xylene and O-xylene, respectively. The maximum distance of 20m for O-xylene based on the results of the LEL criteria of 60% (6600ppm) was attained in the warm seasons. They are potentially lethal within 60s at 21m (10.0kW/m2) when burned. The WISER software predicted the protective distance for xylene isomers to be about 300m. The results show that creating a protective zone around the P-xylene and O-xylene tanks with a radius of 54m is necessary to reduce hazards.

Evaluation on explosion characteristics and parameters of pulverized coal for low-quality coal: experimental study and analysis

Fully utilizing the energy generated by the explosion of pulverized coal will contribute to realize the clean and efficient exploitation of coal resources. The pulverized coal explosion characteristics will be a far-reaching and important task to explore. In this paper, ten kinds of low-quality coals such as high sulfur, high ash, and low metamorphic degree coals were investigated and the minimum ignition energy (MIE), lower explosion limit (LEL), and explosion intensity (EI) parameters under different particle sizes and coal powder concentration conditions were also analyzed combined with a 1.2-L Hartmann tube and a 20-L explosion sphere experimental system. Finally, the morphological characteristics of the exploded coal powder surface were evaluated by scanning electron microscopy (SEM). The results show that the particle size is positively correlated with MIE. LEL shows an inverted "U"-shaped trend with the increasing degree of coal deterioration. The low-rank coal is more flammable and explosive. The maximum pressure PMax at the LEL concentration and maximum pressure rise rate (dP/dt)Max overall value is small. Here, optimum pulverized coal particle size (75μm) for explosive utilization of low-quality coal was determined. Within 50-225 g/m3 of pulverized coal concentration range, the explosion intensity increases with increasing concentration. The smaller the particle size of pulverized coal, the greater the possibility of agglomeration of pulverized coal particles. The surface of the exploded coal particles produces more developed pores. They are irregularly shaped and have more rounded edges than the original coal.

The Fire and Explosion Hazard of Coloured Powders Used during the Holi Festival.

During the world-famous Holi festival, people throw and smear each other with a colored powder (Holi color, Holi powder, Gulal powder). Until now, adverse health and environmental effects (skin and eye irritation, air pollution, and respiratory problems) have been described in the available literature. However, the literature lacks data on the flammable and explosive properties of these powders during mass events, despite the fact that burns, fires, and explosions during the Holi festival have taken place many times. The aim of the article is to present the fire and explosion parameters of three currently used Holi dust and cornflour dust types as reference dust. The minimum ignition temperature of the dust layer and dust cloud, the maximum explosion pressure and its maximum rate of growth over time, the lower explosion limit, the limit of oxygen concentration, and the minimum ignition energy were determined. Tests confirmed that the currently available Holi powders should be classified as flammable dusts and low-explosive dusts. The likelihood of a fire or explosion during mass incidents involving a Holi dust-air mixture is high.

Ideal Positioning of a Pt-Interlayer for H2-O2-Recombination in Polymer Electrolyte Membrane Water Electrolysis

Polymer electrolyte membrane water electrolysis (PEMWE) is a promising technology for the production of hydrogen in future energy scenarios.[1] The main electric voltage loss in PEM electrolysers is caused by the ohmic losses of the polymer electrolyte membrane. However, the reduction of the membrane thickness not only reduces the cell voltage, but also leads to lower faradaic efficiencies, which can be accompanied by severe safety issues. The crossover of the produced hydrogen gas through the membrane into the anodic compartment can lead to explosive gas mixtures (lower explosion limit (LEL) of H2 in O2 is ~ 4 % [2]).[3, 4] Typically, PEM electrolysers operate only up to 2 % H2 in O2 (50 % of LEL). An elevation of the hydrogen pressure during electrolysis enhances the crossover of hydrogen even more.[5] For realizing high market penetrations of PEMWE, a safe operation is essential.In order to meet the safety requirements, mitigation strategies for the reduction of the hydrogen in oxygen content are necessary. When increasing the membrane thickness and reducing the operation temperature are not desired, other mitigation strategies need to be evaluated. The integration of a Pt-interlayer in the polymer electrolyte membrane is one possibility.[6] When hydrogen and oxygen permeate through the membrane, they recombine to water at the platinum particles.Klose et al. proposed that the method of incorporating a recombination layer can be optimized further by evaluating its position.[7] The concentration of oxygen at the interlayer must be high enough to let a sufficient amount of hydrogen recombine. However, the oxygen concentration towards the cathode is much lower than a full recombination of hydrogen requires, which is mainly due to the lower oxygen permeation rate (lower diffusivity, lower gradient). Therefore, it is assumed that a Pt-interlayer close to the anode catalyst layer yields higher recombination rates than an interlayer close to the cathode.In this contribution, the influence of the Pt-interlayer position on the H2 in O2 content was investigated. Catalyst coated membranes (CCMs) based on spray-coated Nafion with Pt-interlayers with a loading of 0.01 mg/cm² at three positions (close to anode, centred, close to cathode, see Figure 1a)) and a reference type (without interlayer) were fabricated. The CCMs were examined with regard to their polarisation behaviour and hydrogen crossover characteristics in a 4 cm² cell. The hydrogen crossover was investigated during electrolysis operation at ambient pressure and at elevated cathode pressures (p c = 10 bar).The resulting membrane thicknesses of the CCMs were ~ 100 µm (in dry state). Since commercial Nafion membranes for water electrolysis applications are available in thicknesses between 25 and 183 µm (N211 and N117, respectively), the present membranes correspond to the state of the art. The electrochemical polarisation behaviour of the CCMs shows that the integration of a Pt-interlayer does not lead to additional voltage losses. At current densities as high as 3.5 A/cm², cell voltages below 2 V were achieved.With regards to H2 crossover, each CCM with interlayer reduced the measurable anodic H2 content in comparison to the reference CCM (Figure 1b)). Additionally, the position of the interlayer affected the resulting H2 content. The H2 content decreased with positioning the interlayer closer to the anode. Thus, a higher recombination rate of hydrogen and oxygen is observed when placing the interlayer close to the anode. Since the available oxygen amount in the membrane has obviously to decrease towards the cathode catalyst layer, the experimental findings reflect the aforementioned theoretical situation.In summary, the results of this study confirm that Pt-interlayers are a suitable mitigation strategy to reduce the H2 in O2 content in PEMWE. Further, it was shown that the positioning of the interlayer affects the results. Since the available amounts of hydrogen and oxygen in the membrane depend on the location in the membrane and on the experimental conditions (e. g. operating pressure), the integration of a recombination interlayer at an optimized position within the membrane offers an effective means to safe PEMWE operation with reduced membrane thickness. This improvement will help to consolidate PEMWE as a key technology for hydrogen generation.Literature:[1] K. Ayers, Annu. Rev. Chem. Biomol. Eng., 2019, 10.[2] H. Janssen, Int. J. Hydorgen Energ., 2004, 29.[3] H. Ito, Int. J. Hydorgen Energ., 2016, 41.[4] S.A. Grigoriev, Int. J. Hydorgen Energ., 2009, 34.[5] P. Trinke, Int. J. Hydorgen Energ., 2017, 42.[6] P. Trinke, Int. J. Hydorgen Energ., 2018, 165.[7] C. Klose, J. Elec. Soc., 2018, 165. Figure 1

A step toward lifting the fog off mist explosions: Comparative study of three fuels

Gases, vapors, and dusts are all potential explosion threats; however, mists should also be taken into account. Indeed, dozens of accidents involving hydrocarbon mists were identified in incident surveys. Mist explosions continue to occur, highlighting the need to evaluate and assess the validity of present approaches for assessing mist ATEX risks and to establish reliable standardized safety parameters for fuel mists.In a modified apparatus based on the 20 L explosion sphere, three fluids of industrial interest were investigated. A new siphon injection system comprising a Venturi junction was installed, offering a wide range of dispersion performances. This system was controlled by a specifically developed program, ensuring the apparatus's versatility and adaptability to various tested liquids. It enables precise control of the gas carrier flow, liquid flow, and injection and ignition durations, allowing modification of the dilution rate of a particular droplet size distribution (DSD). The mist cloud dispersed in the 20 L sphere was characterized by determining its DSD using an in-situ laser diffraction sensor and by performing Particle Image Velocimetry (PIV). Mists of kerosene, diesel and ethanol were then subjected to tests to assess their lower explosive limit (LELmist), minimum ignition energy (MIE), maximum explosion pressure (Pmax), and rate of pressure rise (dP/dtmax). For instance, it was found that the LELmist of ethanol, kerosene Jet A1, and diesel fuel for a DSD averaged at 8–10 μm reach 77, 94, and 93 g/m3 respectively. This LELmist was also shown to increase with increasing DSD in the case of Jet A1 mists. A sensitivity study was also performed to emphasize the impact of parameters such as the fuel type, the DSD, and the mist temperature. Findings showed that the explosion severity is strongly influenced by the chemical nature and the volatility of the dispersed fuel. Moreover, controlling the sphere temperature was proven to be a crucial step when using such apparatus for the evaluation of the explosibility of mists. An evaporation model based on the d2 law was also developed to visualize the vapor-liquid ratio before ignition. These findings have already led to the development of a new procedure for determining safety standards for hydrocarbon mists, as well as tools to assess mist explosion risks. They have proven that it is possible to evaluate the ignition sensitivity and explosion severity of fuel mists using a single well-known apparatus.

The research into the propagation law of the shock wave of a gas explosion inside a building

Based on the dissipation rate conservation equations of turbulent kinetic energy in the k-ε turbulence model, a complicated three-dimensional finite element model of a kitchen filled with gas mixture is developed by using the open source field operation and manipulation (OpenFOAM). Two representative kitchens were used to investigate the propagation law of the shock wave of a gas explosion inside a building by considering the key characteristics of the blast shock wave. The influence of some crucial parameters, such as initial conditions and kitchen parameters, on the properties of the blast shock wave is investigated. The basic steps to predict the peak pressure of the blast shock wave are given in consideration of the initial condition and the kitchen whilst the injury effect of the blast shock wave on the humans and animals is evaluated. The research results indicate that the pressure time history and the peak pressure space distribution are greatly influenced by the kitchen design layout. The coupled interaction between the initial temperature and gas volume concentration, especially at the upper and lower explosion limits of the gas, significantly affects the peak pressure. The peak pressure varies significantly with the opening and the buffer; however, it has little relation with the width, length, and height of the kitchen. The proposed method can accurately and effectively predict the peak pressure of the blast shock wave inside buildings. In terms of the peak pressure space distribution of the explosion shock wave, the peak pressure is much higher than the threshold of the killing pressure, which is unsafe for the humans and animals in the building.

Analysis of the effect mechanism of water and CH4 concentration on gas explosion in confined space

In order to study the effect of water and CH4 concentration on gas explosion, a 20L spherical explosive device was used to carry out a water-containing gas explosion experiment, and the explosion simulation was carried out with CHEMKIN-PRO, the mechanism of water on gas explosion was analyzed from the perspective of free radicals and energy. The results showed that the upper limit of gas explosion, maximum explosion pressure and temperature decreased significantly with the increase of water content. The higher the concentration of CH4, the more obvious the inhibitory effect of water on gas explosion pressure, and the optimal explosion concentration of CH4 decreased with the increase of water content. As the water content and CH4 concentration increase, the residual CH4 content increases after the explosion, the O2 content decreases, and the CO content produced increases. When the CH4 concentration is lower than the optimal concentration, water promotes the formation of CO2 to a certain extent; when the CH4 concentration is higher than the optimal explosive concentration, the CO2 content decreases with the increase of water content. Overall, water inhibits methane explosion, the addition of water on the one hand reduces the concentration of active free radicals H, O, OH, on the other hand, it interferes with the generation of gas explosion energy and consumes the kinetic energy of the gas explosion flame shock wave through heat absorption, thus inhibiting the intensity of gas explosion.

Effect of component ratio and inert gas on explosion characteristics of binary premixed alkanes

The flammable gases mainly CH4 are released in the process of coal mining, and the ratio of gas formation and distribution has a significant impact on gas explosion characteristics. In this paper, the effects of different components on the explosion characteristics (Explosion limit and Maximum explosion pressure) of the binary premixed alkanes were studied by using the explosive limit experimental device of combustible gas, in which CH4, C2H6 and C3H8 were formed in different proportions. The results show that :(1) with the decrease of H/C composition, the upper and lower limits of explosion of binary premixed alkanes decrease, and the explosion limit domain width also shows a downward trend; (2) By comparing the maximum explosion pressure of binary premix alkanes, the influence ability of different single alkanes on the explosion risk is obtained: C3H8>C2H6>CH4; (3) With the increase of N2 content, the explosion limit range of premixed alkanes becomes narrower, the explosion limit range width and maximum explosion pressure are effectively reduced, and the initial initiation time is delayed, so as to reduce the explosion risk.

Analysis of natural gas leakage diffusion characteristics and prediction of invasion distance in utility tunnels

With the continuous development of urbanization, the number of underground supplies and demanded pipelines is increasing. In order to reasonably plan the construction of urban underground space, underground utility tunnels emerge, and show potential to reduce the difficulty of pipeline maintenance and repair. For natural gas pipelines laying in utility tunnels, however leakage accident can result in serious consequences. In this study, the numerical simulation method was used to analyze the leakage and diffusion characteristics of natural gas in utility tunnels under various working conditions, and the single-factor change and multi-factor change of different pressures, leakage diameters, ventilation conditions and leakage locations were investigated. The results showed that: the increase of pipeline operating pressure and leakage diameter could accelerate the diffusion velocity of methane in the utility tunnel. According to the prediction equation of methane invasion distance (MID) under natural ventilation condition, the average error was 8.29%. The mechanical ventilation condition accelerated the methane discharge and greatly reduced the distribution range and concentration of methane in the utility tunnel. In the single-factor change analysis, when the mechanical ventilation frequency was above 15times/h, the methane concentration at each monitoring point was below the lower explosion limit. No matter where the leakage occurs, the mechanical ventilation will prevent methane from diffusing upstream direction, and the downstream was at higher risk for methane distribution. The larger the coordinate value x of leakage location was, the smaller the distribution area of methane in utility tunnel was. When x = 90 m, the methane concentration at each monitoring point was 0. The prediction equation of MID under natural ventilation condition can provide reference for the installation distance of methane leakage alarm device. The research on methane diffusion characteristics under mechanical ventilation conditions provides suggestions for daily maintenance and accident prevention of gas pipelines in the utility tunnel.

Experimental Investigation on the Cleaning Effect and Influence Rule of Hydrogen Peroxide–Acetic Acid on Lead–Bismuth Eutectic Alloy

During the refueling process of lead–bismuth eutectic (LBE)–cooled fast reactors, lead–bismuth alloy can easily adhere to the surface of the fuel rod clads when spent fuel assemblies are unloaded from the reactor core. For some designs, the lead–bismuth alloy attached on the spent fuel rods will be cleaned via physical or/and chemical methods prior to their transportation, storage, and reprocessing. In this article, the cleaning effect of a washing lotion composed of hydrogen peroxide (H2O2) aqueous solution and concentrated acetic acid (CH3COOH) as the main components on LBE was experimentally investigated. By adjusting the composition ratio of the washing lotion and the reaction temperature, the law of their influence on the cleaning effect of LBE was determined. The optimal washing lotion composed of 30 Vol% hydrogen peroxide aqueous solution as oxidant, 40 Vol% concentrated acetic acid as acid, and 30 Vol% ultrapure water as the solvent was proposed based on experimental investigations. The optimal working temperature range was also obtained. The reaction intermediate product was characterized with the XRD analysis in order to understand the reaction mechanism. The composition of the released gas (even in a slight amount) was also analyzed with gas chromatography. The hydrogen concentration in the released gas was found to be lower than the detection limit of gas chromatography (10 ppm). Since the explosion limits of hydrogen at atmospheric pressure are between 3.95 and 75.73 Vol%, the risk of possible hydrogen explosion is concluded to be extremely low. Therefore, no special treatment of the released gas is required even in a large-scale industrial platform. Furthermore, corrosion effect of the washing lotion on austenitic stainless steel components was tested as well and found to be negligibly small. The relative mass loss of the thin-walled stainless steel samples immersed in the washing lotion was found to be less than 0.5% after an experimental duration of 144 h, which facilitates sufficient cleaning time in future industrial applications.

Applying ground gas and gas flux monitoring techniques to low-enthalpy, shallow geothermal energy exploration

Ground gas and gas flux testing has been undertaken in a variety of situations including detecting volcanic and geothermal activity and monitoring landfill and carbon storage. However, there are no documented studies of its application to shallow geothermal investigations, particularly where the water in disused mines will be used as the conduit for heat and the overlying ground has a complex industrial heritage. Background ground gas and gas flux measurements from three separate campaigns at a mine water heat research site in Glasgow, UK did not reveal any concerns regarding mine gas or other potentially harmful gases from previous land uses. The detected CO2 was found to be predominantly of biological origin and reflected the expected quantities based upon land use, seasonal and weather fluctuations and was consistent with other UK sites. One location is recommended for further investigation due to higher-than-expected nitrogen and lower oxygen measurements. Some hydrogen gas was detected, albeit well below explosive limits, which may be present as a result of past industrial site uses, highlighting the need for more investigation into the presence of hydrogen at ex-industrial sites. Apart from this there was very little evidence of the industrial site history in the gas characterisation.A process-based analysis, based upon the stoichiometric relationship of CO2, CH4, O2 and N2, was applied to the results. This complemented, but was not a substitute for, the background survey. There were limitations with the process-based approach when there was not a clear anomalous CO2 signal or where potentially more than one process was occurring simultaneously.