Flammable Gas Concentration Research Articles

Analysis of the Difference between the Harm of Coal Dust Explosion and Its Solid Residue Explosion Based on Explosion Grade and Gaseous Residue Flammability

ABSTRACT In this study, the experiments on coal dust explosion (CDE) and solid residue explosion (SRE) at different concentrations were, respectively, carried out by using a 20 L spherical explosive device. Besides, based on characteristic parameters of explosions and gaseous residues, the differences between and the harm of CDE and its SRE were analyzed. The results show that as the concentration increases, the differential rate between the maximum explosion pressure Pm and the maximum explosion pressure rise rate (dP/dt)m of SRE and that of CDE keeps decreasing. When concentration is 700 g/m3, the differential rate reaches the minimum value, namely Δd1 = 5.56% and Δd2 = 20.80%. The minimum concentration is 200 g/m3 at the CDE grade of S4 (severe), while it is 400g/m3 at the SRE grade of S4 (severe). Besides, SRE consumes less oxygen than CDE at low concentrations (100–300 g/m3), while it consumes more oxygen CDE at high concentrations (400–700 g/m3). The φ(CO)/φ(CO2) in the gas residue from SRE is smaller than one-fourth of that in the gas residue from CDE. The hydrocarbon gas in the gas residue from SRE is about three-fifths of that in the gas residue from CDE. The concentration of flammable gases in gaseous residues from CDE at the concentration range of 200–700 g/m3 can burn in air. Different from gaseous residues from CDE, the flammable range of gaseous residues from SRE is reduced to 300–500 g/m3.

Optimal Gas Detection System in Cargo Compressor Room of Gas Fueled LNG Carrier

This study analyzes the optimal location of gas detectors through the gas dispersion in a cargo compressor room of a 174K LNG carrier equipped with high-pressure cargo handling equipment; in addition, we propose a reasonable method for determining the safety regulations specified in the new International Code of the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC). To conduct an LNG gas dispersion simulation in the cargo compressor room-equipped with an ME-GI engine-of a 174 K LNG carrier, the geometry of the room as well as the equipment and piping, are designed using the same 3D size at a 1-to-1 scale. Scenarios for a gas leak were examined under high pressure of 305 bar and low pressure of 1 bar. The pinhole sizes for high pressure are 4.5, 5.0, and 5.6mm, and for low pressure are 100 and 140 mm. The results demonstrate that the cargo compressor room will not pose a serious risk with respect to the flammable gas concentration as verified by a ventilation assessment for a 5.6 mm pinhole for a high-pressure leak under gas rupture conditions, and a low-pressure leak of 100 and 140 mm with different pinhole sizes. However, it was confirmed that the actual location of the gas detection sensors in a cargo compressor room, according to the new IGC code, should be moved to other points, and an analysis of the virtual monitor points through a computational fluid dynamics (CFD) simulation.

Measurement Algorithm for Determining Unknown Flammable Gas Concentration Based on Temperature Sensitivity of Catalytic Sensor

The assessment of the explosion hazard of a combustible gas mixture is not a trivial task if the type of combustible gases is not known precisely. Typically, the concentration of combustible gas is defined as the response of a catalytic sensor to its presence in the air. It has been known that catalytic sensors have different sensitivities to different combustible gases. Usually gas analyzers are calibrated by methane and are not suitable for measuring other flammable gases without additional correction for each gas. In this paper, we have investigated the dependency of catalytic sensor sensitivity on the sensor temperature for the binary mixture of methane, propane, butane, hexane and hydrogen with air in a wide temperature range. Based on the obtained dependencies, a measurement algorithm and an empirical equation were proposed that allow calculating the concentration of unknown combustible gas in % of LEL. The process of measuring and processing data can be automated using a digital processor. The experimental results have shown that the concentration measurement error is in the range 5%–10% for binary mixture.

Design of Combustible Gas Automatic Detection and Alarm System

With the social development, gas has been widely applied to various aspects of social life. However, the combustible gas has brought us great convenience, but also there is a considerable risk. Based on this, we designed a kind of "prevention" as the characteristics of the combustible gas automatic detection and alarm systems. The system is the choice of technology is mature and low-cost entry-level 52 series microcontroller as the control center, the whole system is divided into classification sensor detection, alarm distinguishes between sound and light alarm, force control bodies of three parts. The system will detect concentrations of flammable gases, scientific classification, for different grades of police intelligence, the appropriate device driver to send a loud sound and light alarm signal. When you reach the highest level but no one to lift the danger, the system will automatically cut off the gas supply to open the ventilation exhaust and other devices to prevent the occurrence of major accidents, to achieve "prevention first, combining prevention and control" of the human and automatic alarm control system. The automatic alarm control system available in the field of gas alarm has been widely used, it has certain extensibility, compatibility, and stability.

Increased flammability hazard when ionic liquid [C6mim][Cl] is exposed to high temperatures.

Industrial use of ionic liquids may require exposure to high temperatures. We demonstrate that such applications may result in an increase in flammability hazard due to chemical decomposition. The ionic liquid, 1-hexyl-3-methylimidazolium chloride ([C6mim][Cl]), was selected as the study sample. The flash point and other properties were measured using a commercially available flash point analyzer, a thermogravimetric analyzer (TGA), Fourier transform infrared spectroscopy (FTIR), an integrated TGA-FTIR system, and pyrolysis-gas chromatography-mass spectrometer. We found that thermal decomposition occurred with the release of chloromethane, 1-chlorohexane, 1-hexene, 1-methylimidazole, and 1-hexylimidazole as [C6mim][Cl] was heated. Such decomposition changed the components of the residual liquid phase. Vaporization of the [C6mim][Cl] decomposition products increased the mass loss rate on TGA as [C6mim][Cl] was heated to high temperatures, resulting in a high concentration of flammable gases and a decrease in the flash point, which increased the flammability hazard.

Experimental investigation of a smouldering fire in an under‐ventilated silo

An experimental bench was built and run to investigate the behaviour of a smouldering fire in an under‐ventilated silo. This smouldering fire was initiated by placing an electrical resistance at a given depth in the tested grain. The grain was successively corn, wheat, barley, oilseed rape, and sunflower. None of the tests resulted in an open fire but they all showed that the smouldering fire could generate an explosive atmosphere in the top part of the silo. When the venting conditions were kept unchanged within the silo, the tests also showed that the smouldering fire could become dormant resulting in no longer flammable gas concentration being measured in the silo. This phenomenon is associated with the formation of a carbonised rock around the heating resistance. © 2018 American Institute of Chemical Engineers Process Saf Prog 38: e12012, 2019

Long-term emission measurements at a floating roof tank for gasoline storage

In our paper we present the results of a long-term emission measurement of volatile organic compounds emitted by a single-hull floating-roof tank. The tank has a capacity of 12,000m3 and is used to stock commercially available gasoline. Due to imperfect seals and the formation of lubricating films during withdrawal, subsequent emissions of volatile compounds have to be expected. Therefore, a non-zero probability has to be assumed for the formation of ignitable concentrations of flammable gases, resulting in according an explosive gas area classification. Here a representative single-hull floating-roof tank is monitored using an appropriate network of infrared (IR) detectors, accompanied with measurements using a high resolution photoionization detector (PID). Measured values have been compared to the expectations estimated applying the API 2517/2519 and the VDI 3479 standards.The aim is to record data for an explosive gas area classification based on actual emissions, potentially allowing for a regrading of zone 1 to zone 2 classified locations.

Synergistic Effect of Hexaphenoxycyclotriphosphazene and Aluminium Tri-Hydroxide on Flame Retardancy and Smoke Suppression of Epoxy Resin

Flame retardancy and smoke suppression of polymer materials are key problems to be considered for applications that have a potential fire hazard. This study selected hexaphenoxycyclotriphosphazene (HPCTP) and aluminium tri-hydroxide (ATH) powder as an integrated flame retardant treatment in epoxy resin (EP) which is usually used as the matrix of a composite. The characteristics of flame retardancy and smoke suppression were investigated. The results showed that when treated with HPCTP and ATH, the resin exhibits superior properties, resisting flame development and smoke release. Based on analysis of the surface structure of the burned materials by scanning electron microscopy–energy dispersive spectroscopy and X-ray photoelectron spectroscopy, it was confirmed that HPCTP and ATH can attract a lot of heat to slow down decomposition of the resin and produce a comprehensive protection system consisting of a non-flammable gas and solid phases during burning. Non-flammable gas can reduce the concentration of flammable gas to inhibit combustion. In addition, H2O vapour can also reduce the concentration of flammable gas to inhibit combustion. Meanwhile, solid phase films can insulate air to slow down combustion and smoke release.

Performance Evaluation of Water Mist with Mixed Surfactant Additives based on Absorption Property

Abstract The leaking of hazardous, flammable hydrocarbons, such as methane, possesses potential risk to generate accidents of fire or explosion. The conventional technique is water mist which can reduce the environment concentration of flammable gas and manage accidents of fire caused by hazardous hydrocarbons leaking, but pure water mist extremely restricts its popularization and application due to the poor solubility of hydrocarbons. Therefore, the mixed surfactant is used as water mist additive for its excellent physical and chemical nature, and its performance is investigated and evaluated experimentally. A formula of mixed surfactant additive has been developed and the physicochemical properties of water mist with mixed surfactant additive were measured. Additionally, the present work establishes a series of lab-scale experiments to study absorption capacity and gasoline pool fire suppression performance of water mist with mixed surfactant additives and the effect factors. The concentration transient within the test chamber has been evaluated during the absorption experiment. Results showed that water mist with mixed surfactant additives is shown to be efficient in absorbing methane, especially under the condition of low methane concentrations, water mist with 5% mixed surfactant, absorbing time less than 150s had best absorption capacity. Furthermore, the addition of mixed surfactant in water mist can shorten fire suppression time and restrain fire enhancement effectively at the beginning when extinguishes the oil pool fire. The water mist with mixed surfactant additives will greatly promote the large-scale application of water mist technology used to manage accidents of hazardous hydrocarbons leakage or fire.

Non-contact Human Body Electrostatic Voltmeter Based on MEMS Technology

The vibrating or rotating parts of the traditional non-contact voltmeters are exposed, thus they can not be used in high-risk areas, and can hardly measure moving bodies. To solve the above problems, this paper develops new non-contact voltmeters based on MEMS electric field sensors. A new detecting electrode, which connects to the sensor chip, is brought out and effectively enhances the sensitivity. Eleven electrodes are placed on a door frame, and measure the charge distribution of head, shoulder, arm, hand, leg and foot at the same time. By means of a metal human body model, a new calibration method for application is proposed. The voltmeter built in this paper is accurately calibrated. The voltmeters have significant advantages, such as no exposed moving components, safety, high environmental adaptability, and therefore can be used under high dust concentration, high concentration of flammable gas and other harsh environments. Test results show that the measurement range is -30~30 kV, the volt resolution is better than 50 V, and the uncertainty is better than 3%.

Experimental investigation of flame propagation characteristics in the in-line crimped-ribbon flame arrester

An experimental system that consisted of gas mixing equipment, a sensor detection system, a data acquisition device, and an electric spark ignition device was set up to investigate fuel/air deflagration flame propagation and quenching processes through a crimped-ribbon flame arrester in an enclosed horizontal pipe. Deflagration suppression experiments showed that when the concentration of flammable gas was close to the stoichiometric ratio, the evolution processes of explosion pressure for the propane-air and ethylene-air premixed gases in the pipe diameter (DN32–DN400) were similar and could be divided into four stages: isobaric combustion, slow pressure rise, quick pressure rise, and pressure oscillation. However, the explosion duration of the hydrogen-air premixed gas was relatively short, and the peak explosion pressure was high. The pressure rose quickly after the isobaric combustion stage. Therefore, the process can be divided into three stages in the pipe diameter (DN15–DN150). Deflagration speed results indicated that the propane-air flame speed initially increased and eventually decreased along with increases in the pipe diameter (DN32–DN400); however, the ethylene-air flame speed gradually increased with the increase of the pipe diameter (DN80–DN400). No notable pattern of change in the hydrogen-air flame speed was observed in the pipe diameter (DN15–DN150). The maximum propane-air flame speed occurred at 5% concentration. The maximum flame speed for ethylene-air and hydrogen-air happened when the mixture was close to stoichiometric ratio. Under the conditions of the same size of experimental tube configuration and the same ignition distance but different pipe lengths, or the same pipe length but different ignition distances, experimental results showed that the flame arrester successfully stopped the flames at high flame speed and low explosion pressure, but failed at low flame speed and high explosion pressure.

Application of ASTEC, MELCOR, and MAAP Computer Codes for Thermal Hydraulic Analysis of a PWR Containment Equipped with the PCFV and PAR Systems

The integrity of the containment will be challenged during a severe accident due to pressurization caused by the accumulation of steam and other gases and possible ignition of hydrogen and carbon monoxide. Installation of a passive filtered venting system and passive autocatalytic recombiners allows control of the pressure, radioactive releases, and concentration of flammable gases. Thermal hydraulic analysis of the containment equipped with dedicated passive safety systems after a hypothetical station blackout event is performed for a two-loop pressurized water reactor NPP with three integral severe accident codes: ASTEC, MELCOR, and MAAP. MELCOR and MAAP are two major US codes for severe accident analyses, and the ASTEC code is the European code, joint property of Institut de Radioprotection et de Sûreté Nucléaire (IRSN, France) and Gesellschaft für Anlagen und Reaktorsicherheit (GRS, Germany). Codes’ overall characteristics, physics models, and the analysis results are compared herein. Despite considerable differences between the codes’ modelling features, the general trends of the NPP behaviour are found to be similar, although discrepancies related to simulation of the processes in the containment cavity are also observed and discussed in the paper.

α-Fe2O3 based nanomaterials as gas sensors

Interest in detecting and determining concentrations of toxic and flammable gases has constantly been on the increase in recent years due to increase of modernization, industrialization and high standards of life. Detection of such gases is very important in many different fields such as industrial emission control, household and social security, vehicle emission control and environmental monitoring. Metal oxide gas sensors are among most important devices to detect a large variety of gases. α-Fe2O3, an environmental friendly semiconductor (E g = 2.1 eV), is the most stable iron oxide under ambient atmosphere and because of its low cost, high stability, high resistance to corrosion, and its environmentally friendly properties is one of the most important metal oxides for gas sensing applications. This is the first review about gas sensing properties of α-Fe2O3 nanostructures. In this paper gas sensing properties of α-Fe2O3 are extensively reviewed. After a brief explanation about metal oxide gas sensors and α-Fe2O3, sensors based on α-Fe2O3 nanomaterials have been reviewed. Gas sensing section is divided into five subsections: pure α-Fe2O3 gas sensors, metal/α-Fe2O3 gas sensors, metal oxide/α-Fe2O3 gas sensors, polymer/α-Fe2O3 gas sensors and graphene/α-Fe2O3 gas sensors.

Elimination of flammable gas effects in cerium oxide semiconductor-type resistive oxygen sensors for monitoring low oxygen concentrations.

We have investigated the catalytic layer in zirconium-doped cerium oxide, Ce0.9Zr0.1O2 (CeZr10) resistive oxygen sensors for reducing the effects of flammable gases, namely hydrogen and carbon monoxide. When the concentration of flammable gases is comparable to that of oxygen, the resistance of CeZr10 is affected by the presence of these gases. We have developed layered thick films, which consist of an oxygen sensor layer (CeZr10), an insulation layer (Al2O3), and a catalytic layer consisting of CeZr10 with 3 wt% added platinum, which was prepared via the screen printing method. The Pt-CeZr10 catalytic layer was found to prevent the detrimental effects of the flammable gases on the resistance of the sensor layer. This effect is due to the catalytic layer promoting the oxidation of hydrogen and carbon monoxide through the consumption of ambient O2 and/or the lattice oxygen atoms of the Pt-CeZr10 catalytic layer.

Applying Catalytic Sensor in Non-volatile Wireless Sensor Networks

Fundamental solutions were developed and energy-saving parameters of a catalytic sensor operation were chosen for using a catalytic sensor in non-volatile wireless sensor networks.Energy-saving mode is based on cyclic method, where every cycle includes short current pulse and the pause between pulses does not exceed regulated by normative documents “response time” for sensors working in continuous mode.To reduce current pulse duration, heating and measuring processes are combined. Two-staged pulse shape was chosen for this, the first stage accelerates heating, the second one is measuring, where we reduce sensor supply voltage and heating temperature, form transient cooling of the sensing element, then measure cooling rate, which is proportional to measured concentration of flammable gas in the air.

Numerical Simulation on the Influence of Flammable Gas Concentration on Explosion Peak Pressure

This paper simulates the alternation of the maximum explosion overpressure on the different condition of the concentration based on the fluent software. The results show the maximum explosion overpressure increases in the earlier stage and then decreases in the later stage because of the different flammable gas concentration: the maximum explosion overpressure enhanced in 6% gas concentration and drops in 12% gas concentration; it augments in 6% gas concentration and drops in 12% gas concentration with the joining of the hydrogen; the explosion pressure peaked just at the 9% concentration of the flammable gas.

Research on Modelling and Controlling the Concentration of Combustible Solvent Vapors in Indirect Electrical Heating Circulation Dryer

Abstract Starting with a practical drying process and an explosion case, the significance of modelling the solvent vapor concentration is discussed. With a simple calculating equation and several mathematical and experimental methods used, a model of flammable gas concentration during the drying process is proposed. Key factors that influence the concentration value most are obtained to give a method of controlling the concentration of solvent vapors in order to avoid explosion danger. Practical applications and field experiments have been made to prove the accuracy of the model and the feasibility of the concentration control method. A satisfactory modelling effect is shown in the results and a successful improvement to an actual drying process is also made by reducing the top solvent vapor concentration to 3.7%, which is below the lower explosive limit.

Numeral Simulation on the Venting Explosion Process of Methane and Propane Gas in Closed Cylindrical Vessel

Abstract The mathematical model of the pressure field in the vented explosion process in closed cylindrical vessel containing methane and ethane was built based on the soft-ware fluent. The characteristics of pressure development, flame propagation, gas flow and flammable gas concentration change have been studied in the process of bursting disc open to pressure completely discharge. The results show that the development and change of vessel pressure exhibit different characteristics in the venting explosion process of different flammable gas, and vessel pressure will take on a double-peak phenomenon during the explosion process of highly reactive gas. The turbulent flow produced in the process of venting explosion will elongate the flame along the vessel surface near vent and enhance the burning rate.

Method of test for burning velocity measurement of flammable gases and results

This article describes a test method for measuring the burning velocity of flammable gases with air used as oxidant. Burning velocity is a physical property enabling the classification of flammable refrigerants. A safety standard committee, such as ASHRAE 34 SSPC, requests information about methods of tests capable of improving the classification of flammable refrigerants. The burning velocity is a function of the flammable gas concentration in the total mixture with air, and it can be measured at concentrations ranging from the lower propagation limit (LPL) of the flame in the tube to the upper propagation limit (UPL). The burning velocity reaches a maximum in the vicinity of the stoichiometric concentration. The test method is based on the initiation of the combustion of the gas, or blends of gases, in a homogenous mixture with air contained in a vertical cylindrical tube, and the observation and the recording of the flame propagation. Results for R-290, R-152a, R-717, R-32, and R-143a are presented using the tube method as described and performed at the Center for Energy and Processes.

Measurement of Gas Flow Rates from Small-Scale Reactions

The rate and total volume of noncondensable gas generation are important parameters in the safe, successful scale-up of chemical processes. Information regarding the evolution of noncondensable gas is used to (1) ensure the gas can be vented from the reactor without overpressurization, (2) calculate the concentration of flammable gases (or oxygen) to avoid creating an explosive mixture in the equipment, and (3) size the scrubber to ensure the capacity and heat removal rate are sufficient. The data are used in parallel with information regarding the heat of reaction from the desired chemistry, thermal stability of reaction mixtures/components, and an intimate knowledge of the process to analyze the risk associated with scaling up. If the level of risk is judged to be unacceptable, the analysis can be used to make rational process changes in order to reduce the risk to an acceptable level. Several techniques have been developed to study the gas hazards associated with a particular reaction. In general, these techniques suffer from at least one of two primary limitations: (1) the volume is not measured directly, causing the condition and/or composition of the gas to influence the accuracy of the measurement, or (2) the sensitivity is too low to take reliable measurements from small-scale reactions. The Pfizer Global Process Safety Network set out to develop a new device that could solve both of these problems and be used in conjunction with a microcalorimeter to provide heat of reaction data in parallel. This paper describes a new device that is used in series with a thermal mass flow meter to accomplish this goal. Detailed discussion of the error bounds on the flow rate from this device is also included.