Lower Explosion Limit Research Articles

Study on the Lower Explosion Limit of Ventilation Air Methane at 700–1200℃

ABSTRACT Regenerative thermal oxidation (RTO) of Ventilation Air Methane (VAM) is an environmentally friendly technology for harnessing heat energy. Higher concentrations of methane can improve utilization efficiency, but it suffers from a high risk of explosion. The lower explosive limit (LEL) of methane at temperatures of 700–1200°C is determined using a self-designed experimental apparatus, and the mechanism at the LEL is analyzed using the GRTO (Gas regenerative thermal oxidation) model constructed by our research group. Results reveal that a linear correlation between the LEL and temperature within 700–1200°C. As the temperature rises, the LEL exhibits a consistent decline. Furthermore, the maximum concentration of VAM in RTO process is elucidated, with an average of 95.3% of LEL. The concentration of ·OH determines the explosive severity at the LEL, and methane explosions are dominated by H+O2⇔O+OH and H2+ OH⇔OH+H2O. 2CH3(+M)⇔C2H6(+M) plays a vital role in inhibiting methane explosion, and its inhibitory effect decreases by 59.5% at 1200°C compared to 700°C.

Hydrogen sensing performance and stability of WO3–SiO2 composite film doped with Pt catalyst

AbstractHydrogen energy has attracted attention as a new energy carrier because it does not generate CO2 emissions during combustion. However, numerous problems face the establishment of a hydrogen infrastructure society. One problem is safety when using hydrogen. A fast sensing system for hydrogen at low concentrations will be needed for hydrogen to be used safely. WO3 is expected to be used as an optical hydrogen sensor element because it reacts with hydrogen and changes color. We prepared Pt-doped WO3 films by the sol–gel method using an ion-exchange technique under various experimental conditions and investigated the films’ response properties to hydrogen and their morphology. As a result, a Pt/WO3 film with SiO2 (Pt/WO3–SiO2 film) annealed at 200 °C showed the shortest coloring and bleaching time to 4 vol% hydrogen. The films also showed good reproducibility with respect to their hydrogen response and good long-term stability. In addition, the fast bleaching time led to a stable repeated response, enabling the films to be used in real-time monitoring applications. Moreover, the sensitivity of the Pt/WO3–SiO2 films depended on the hydrogen concentration, which suggested that quantitative sensing of hydrogen at concentrations below the lower explosive limit could be realized. Furthermore, the catalyst Pt active state and the difference in gas diffusivity due to the microstructure of the films were considered through analysis of the surface, cross-sectional structure, and elemental state of the films. Graphical Abstract

Advancements in the Fabrication of Reinforced Proton Exchange Membranes and Exploration of Next-Generation Membrane Technologies

Developing a polymer-electrolyte membrane (PEM) as a water electrolysis (WE) component is crucial for achieving a hydrogen-based economy while reducing CO2 production. Among proton exchange membranes, per-fluorinated sulfonic acid (PFSA) membranes are considered key components due to their high proton conductivity and chemical and thermal stability. Over the next few years, the demand for PFSA membranes in the PEM electrolysis market is expected to rapidly grow, necessitating suppliers to enhance their manufacturing capabilities and membrane quality.Since 1975, AGC has been manufacturing PFSA membranes, contributing significantly to the electrolysis industry, including PEM water electrolysis and chlor-alkali electrolysis, among others. AGC R&D has developed FORBLUETM S-SERIES, a PFSA membrane for PEMWE, using PFSA polymers manufactured in-house from monomers. PFSA membranes possess the following properties: high proton conductivity, high mechanical strength and chemical stability, low gas permeability, and good dimensional stability. PFSA membrane properties can be optimized by adjusting the membrane thickness and the polymer’s ion exchange capacity (IEC). PFSA membrane dimensional stability can be enhanced using reinforcement, which reduces changes in the in-plane dimensions upon the water uptake and facilitates efficient MEA construction. We have developed two reinforced membranes, Sx-0935DH and Sx-1235DH. Sx-0935DH shows high proton conductivity, and Sx-1235DH exhibits low gas permeation ability. For instance, the overpotential of Sx-0935DH was reduced by >80 mV at 3 A/cm2 compared to N115, measured under ambient pressure at 80 °C. Additionally, the hydrogen concentration on the anode side of Sx-1235DH is 20% of that of N115. Currently, we are working on manufacturing the two reinforced PFSA membranes on a large scale via roll-to-roll (RtR) processing.In the water electrolysis industry, there is a demand for thinner membranes to increase proton conductivity and reduce the energy required for hydrogen production. However, thinner membranes tend to have a higher hydrogen permeation ability. Since the lower explosive limit (LEL) for hydrogen in oxygen is only 4 vol%, reducing the hydrogen gas crossover is critical. A gas recombination catalyst (GRC) is used as a membrane component to lower the concentration of hydrogen in oxygen. AGC is developing thinner membranes, incorporating GRC as the next-generation solution.We will present our recent efforts in manufacturing membranes through RtR processing and developing next-generation membranes for water electrolysis.

Gas Box Exhaust Design Modification for Accidental Hazardous Gas Releases in Semiconductor Industry

Hazardous substances such as hydrogen and chlorine are used in semiconductor manufacturing. When these gasses are discharged, they are mixed with outside air and are connected to a treatment facility through a duct inside a gas box. This study investigated an optimal exhaust design to prevent fire explosions and toxic exposure by optimizing the exhaust volume when hazardous substances leak from the gas box of semiconductor manufacturing equipment. In this study, carbon monoxide was used for modeling. A 75 mm duct was used, and the tracer gas was released into the gas box at 15.4 LPM. The concentrations were measured at nine points inside and outside the gas box. According to the test results, in an experiment designed with 0% air intake, the internal leakage concentration was measured to be more than 25% of the LEL (lower explosive limit) for 10 min when leakage occurred due to stagnant flow, and the outside toxicity concentration was also measured to be more than 50% of the TWA (time-weighted average) value. When the air intake ratio was designed to be 100%, there was a point on the outside that exceeded 50% of the TWA, confirming that excessive air intake could also cause gas to leak outside. Finally, when the intake ratio was designed to be 50% in both directions, it was confirmed that the airflow was maintained smoothly, and the hazardous gasses were safely diluted and discharged through the duct. This study was conducted to improve the safety of workers in the field in the event of leakage of flammable and toxic gasses by testing the location and area of the air intake hole in the gas box exhaust port. Through this effort, the aim is to present specific standards for gas box design and to assist in establishing a legal framework or standardized guidelines.

Effect of CO2 on the explosion limit parameters and kinetic characteristics of ammonia-hydrogen-air mixtures

Effect of CO2 on the explosion limit parameters and kinetic characteristics of ammonia-hydrogen-air mixtures

Consequence modeling and analysis of ethanol leakage from storage tank using the ALOHA program

Chemical spills pose a significant threat to the safety of people living nearby, as well as to air quality and occupational safety. Therefore, preventing chemical spills has become a key issue in environmental protection and process safety. This study aims to evaluate the effects of ethanol released from a tank at a chemical plant in Istanbul, Türkiye. The Areal Location of Hazardous Atmospheres model (ALOHA) version 5.4.7 estimates the storage tank's leakage radius and spread risk under three scenarios. ALOHA can assess the area affected by chemical hazards. The model shows that if the spill occurs 10 centimeters from the base of the tank, the toxic concentration of ethanol exceeds the Immediately Dangerous to Life or Health (IDLH) threshold (i.e., 3300 parts per million) at a distance of 31 meters from the place of release. In addition, when the ethanol concentration exceeds 60% of the Lower Explosive Limit (LEL) (i.e., 19800 parts per million), the flammable vapor cloud extends up to 31 meters from the place of release. For a Boiling Liquid Expanding Vapor Explosion (BLEVE), the mass of the fireball is assumed to be 100%, resulting in the worst possible scenario. During BLEVE, it is estimated that the fireball's diameter and time duration, determined by the amount of Ethanol present, would be 141 meters and 10 seconds, respectively. The results show that the thermal radiation effects caused by Ethanol BLEVE are extremely dangerous.

Dual functionality of cathode microporous layers: Reducing hydrogen permeation and enhancing performance in proton exchange membrane water electrolyzers

Dual functionality of cathode microporous layers: Reducing hydrogen permeation and enhancing performance in proton exchange membrane water electrolyzers

Ultra-sensitive liquefied petroleum gas (LPG) sensor based on monometallic Ag nanospheres synthesized via microwave-assisted facile approach

Ultra-sensitive liquefied petroleum gas (LPG) sensor based on monometallic Ag nanospheres synthesized via microwave-assisted facile approach

Acquisition Study of Downhole Explosion Limit in Air Drilling

Summary Downhole explosions adversely affect air drilling; however, the explosion limit can facilitate the adjustment of the flow rate to prevent downhole explosions. The downhole explosion limit, comprising lower and upper limits, can be determined through diverse methodologies. In this study, the interrelation between absolute enthalpy and adiabatic flame temperature (AFT) enabled the deduction of the lower explosion limit (LEL) prediction method, and an equilibrium between heat generation and heat transfer formed the basis for the upper explosion limit (UEL) prediction method. Additionally, a variable-volume apparatus was established to measure the explosion limit and adjust the pressure precisely without changing the amount of gas. The explosion limit of methane in the air was determined using both predicted and experimental methods, mirroring the scenarios of natural gas entering the wellbore during air drilling. The theoretical model exhibited the same reliability as the experimental results, and the prediction method for the explosion limit proved more efficient. Moreover, the effects of initial temperature and pressure on the explosion limit are discussed. The LEL decreased by an average of 15.5% when the initial pressure increased from 0.1 MPa to 2 MPa, while the UEL experienced a significant increase by an average of 152%. The UEL exhibited a logarithmic dependence on the initial pressure. The effect of the initial temperature on the explosion limit was noticeably less pronounced than that of the initial pressure. This study provides the essential theoretical basis and experimental results for avoiding downhole explosions during air drilling.

Time-dependent variations in desorbed gas composition: methodological analysis of asphaltite vein investigation results

Time-dependent variations in desorbed gas composition: methodological analysis of asphaltite vein investigation results

Thermal energy propagation characteristics and hazard effects of hydrogen cloud explosion

Thermal energy propagation characteristics and hazard effects of hydrogen cloud explosion

Numerical Study on the Influence of Various Design Variables on the Behavior Characteristics of Oil and Gas in Internal Floating Roof Tanks

With the development of the petrochemical industry, the number of storage tanks has continuously increased, exacerbating the issue of oil evaporation losses. Therefore, it is urgent to find efficient and economical measures to reduce oil evaporation losses. This paper establishes a diffusion model for internal floating roof tanks (IFRTs) and uses numerical simulation methods to study the mass fraction distribution, pressure distribution, and the variation patterns of oil vapor inside the tanks at different floating roof heights. The results show that the closer to the top of the tank, the lower the oil vapor mass fraction, and the mass fraction distribution is almost symmetrical. As the floating roof height decreases, the vapor mass fraction in the mixed gas region inside the tank gradually decreases, showing a distribution below the lower explosive limit (LEL), indicating improved safety. Furthermore, the study found that in the benchmark model, the behavior characteristics of gasoline vapor are reflected in the changes in mass fraction, velocity, and pressure distribution, where the oil vapor concentration in the upper part is lower but evenly distributed. By comparing the behavior characteristics of oil vapor inside the tank at different floating roof heights, it was found that the floating roof height significantly affects the diffusion and accumulation of oil vapor. The presence of vents effectively reduces the accumulation of oil vapor concentration, improving the stability and safety inside the tank. For different floating roof height scenarios (such as CASE 1, CASE 2, and CASE 4), the oil vapor behavior characteristics are similar. The study results provide important theoretical support for the future development of oil vapor recovery technologies and the design of enclosed energy-saving recovery devices inside tanks, indicating that optimizing the floating roof height and vent system design can significantly reduce oil evaporation losses.

Development of Next Generation Membranes for PEM Water Electrolysis in AGC

AGC’s FORBLUETM product family has over 70 years of experience in ion-exchange membranes (IEMs). S-SERIES, a FORBLUETM member, is a per-fluorinated sulfonic acid polymer (PFSA) membrane utilized in various electrochemical devices and industrial electrolysis. AGC’s IEM technology had a lot of experience in the chlor-alkali application and was further developed for the PEM water electrolysis industry.AGC R&D has developed S-SERIES membranes with a smaller thickness, improved reinforcement, and high ion exchange capacity (IEC) that enhanced not only an electrochemical performance but also dimensional stability.A membrane electrode assembly (MEA) was fabricated using a developed membrane with high IEC polymer (IEC 1.25 meq/g). As a result, IV characterization of a single cell with 25 cm2 electrode area at 80°C showed a significant voltage reduction compared to a commercial membrane in the PEM water electrolysis market. In addition, H2 crossover during the electrolysis was evaluated in a single cell with a 25 cm2 electrode area at 80°C and ambient pressure, and the H2 concentration in O2 at the anode side was compared at a current density of 1.0 A/cm2. The developed membrane showed 0.3 vol% H2 crossover, whereas the commercial membrane showed 0.5 vol%.Furthermore, next-generation membranes with gas recombination catalysts (GRC) and radical scavengers leading to lower gas crossover and higher chemical stability are under development. Recently, high-pressure electrolyzers have been getting more attention and the increase of H2 crossover is a concern against the lower explosive limit (LEL) for hydrogen in oxygen. In general, PFSA membranes are considered to have high chemical durability, however, F ion release is observed, that indicate that this PFSA polymer is attacked by OH radicals generated in the PEM water electrolysis system. AGC has been investigating the application of GRC and radical scavengers to the newly developed membranes. It was evaluated in a single cell with 25 cm2 electrode area at 80°C and 2.0 A/cm2. As a result, the H2 crossover and F ions release rate (FRR) were reduced compared to the membrane without both additives. The data will be presented on these improved performances.

Critical risks with the permeability dimension to describe the hydrogen crossover phenomenon

Critical risks with the permeability dimension to describe the hydrogen crossover phenomenon

Facile Abatement of Oxygenated Volatile Organic Compounds via Hydrogen Co-Combustion over Pd/Al2O3 Catalyst as Onsite Heating Source

Catalytic combustion of volatile organic compounds (VOCs) usually requires external energy input to hold the desired reaction temperature via electric heating. This work presents an example of internal onsite heating of the catalytic active sites via hydrogen catalytic combustion with air over a conventional Pd/Al2O3 catalyst. Hydrogen combustion was ignited by the catalyst at room temperature without electric heating, and thus the temperatures were readily varied with the concentrations of H2. Representative oxygenated VOCs such as methanol, formaldehyde and formic acid can be completely oxidized into CO2 and water by co-feeding with H2 below its low explosion limit of 4% using Pd/Al2O3 as shared catalyst. The catalytic performance apparently is not sensitive to the sizes of Pd nanoparticles in fresh and spent states, as revealed by XRD and STEM. This provides an option for using renewable green hydrogen to eliminate VOC pollutants in an energy-efficient way.

Dynamics of gas composition and thermal behavior post explosions: An experimental investigation across varied initial concentrations

Dynamics of gas composition and thermal behavior post explosions: An experimental investigation across varied initial concentrations

Inhibition effect of inert gas jet on gas and hybrid explosions caused by thermal runaway of lithium-ion battery

Inhibition effect of inert gas jet on gas and hybrid explosions caused by thermal runaway of lithium-ion battery

The gas production characteristics and catastrophic hazards evaluation of thermal runaway for LiNi0.5Co0.2Mn0.3O2 lithium-ion batteries under different SOCs

The gas production characteristics and catastrophic hazards evaluation of thermal runaway for LiNi0.5Co0.2Mn0.3O2 lithium-ion batteries under different SOCs

Numerical simulation of gas diffusion and explosion limit of VOCs in containment integrated leak rate test

CILRT is an important work in the overhaul of nuclear power plants. VOCs from paints and cleaners used in the containment during the overhaul will migrate inside the containment, and the numerous rooms and compartments inside the containment make the air flow impeded, and the VOCs may be enriched to bring combustion risk. The complete fire risk analysis method includes volatilization kinetics of chemicals, mixture explosion limits, and numerical simulation of VOCs diffusion and migration. The volatilization rate at the lowest room temperature of 20°C is used as a conservative input, the complement of CAITA realistic model is used as the flow domain, and the geometry is appropriately simplified, and the steady ventilation process, the internal flow and the laws of diffusion and agglomeration of 12 kinds of VOCs gases in the 9-h pressure-holding process are investigated by Computational Fluid Dynamics. The simulation results of steady ventilation show that the VOCs gases are almost uniformly carried by the air to all spaces inside the containment, and the explosion risk is low. The concentration field of the steady ventilation process was taken as the initial boundary condition and unsteady state simulation of the 9-h holding pressure process was performed. The results show that the gas flow inside the containment basically stops after 3456 s of pressure holding. With the extension of time, the VOCs gases accumulate at the bottoms of the three lower layers of the containment under the effect of laminar diffusion and gravitational settling, where the total concentration of the mixed gases reaches the highest at the bottom of the lowest layer. The total concentration of the VOCs gas mixture was below the lower explosion limit throughout the 9-h pressure-holding process, and the explosion risk was low.

Unveiling the Air Quality Impacts of Municipal Solid Waste Disposal: An Integrative Study of On-Site Measurements and Community Perceptions

This study examines air quality conditions in and around a classroom located in the Sarıçam/Adana region of Türkiye, near the campus of Adana Alparslan Türkeş Science and Technology University and the Sofulu municipal solid waste (MSW) facility. This academic setting was strategically chosen due to its proximity to the waste facility. The study aims to provide a comprehensive view of the environmental and social impacts of solid waste management through a methodological approach that combines quantitative on-site measurements and qualitative survey studies. Findings from measurements and surveys underline the significant and measurable impacts of MSW facilities on the ambient air quality of university residents. The analysis revealed a marked increase in concentrations of key pollutants, including carbon monoxide (CO), hydrogen sulfide (H2S), dust, and methane (CH4). At sampling point N1, H2S levels rose from 0 ppm in July to 13 ppm in November. Methane increased from 0.2% to 2.5% of the Lower Explosive Limit (LEL) at the same point, although it remained within safety limits. Additionally, CO levels showed a 40% increase, and dust concentration levels rose from 0.21 mg/m3 to 2.36 mg/m3 from summer to winter, indicating a seasonal variation likely influenced by the landfill’s operational dynamics, as well as changes in temperature and relative humidity. In particular, the results indicate high concentrations of CO, H2S and dust, which are directly related to air quality degradation. The study also sheds light on the impacts of these waste disposal facilities on the general well-being and health of the university community, particularly on students and staff. In addition to these findings, the study highlights a general lack of awareness in the university community about the impacts of MSW facilities on air quality. This highlights the need for increased education and information dissemination. The results support the development of comprehensive and effective strategies, including technical solutions and public awareness initiatives, to mitigate the impacts of these facilities on residential areas. In conclusion, the impacts of MSW facilities on air quality should be seen as a multidimensional issue that requires a holistic approach addressing environmental, health, social, and educational dimensions.