Ethane flammability limits

Flammability limits for pure components and selected mixtures have been used to generate mixing rules. These apply to mixtures of methane, ethane, propane, butane. 

The behavior of flammability limits at elevated pressures can be explained somewhat satisfactorily. For simple hydrocarbons (ethane, propane,..., pentane),... 

Ethane — Fire Hazards Flash Point (deg. F) -211 Flammable Limits in Air (%>) 2.9 - 13.0 Fire Extinguishing Agents Stop flow of gas Fire Extinguishing Agents Not To Be Used Data not available Special Hazards of Combustion Products Not pertinent Behavior in Fire Not pertinent Ignition Temperature (deg. F) 940 Electrical Hazard Class I, Group D Burning Rate 13 mm/min. Chemical Reactivity Reactivity with Water No reaction Reactivity with Common Materials No... 

Use laminar premixed free-flame calculations with a detailed reaction mechanism for hydrocarbon oxidation (e.g., GRI-Mech (GRIM30. mec)) to estimate the lean flammability limit for this gas composition in air, assuming that the mixture is flammable if the predicted flame speed is equal to or above 5 cm/s. For comparison, the lean flammability limits for methane and ethane are fuel-air equivalence ratios of 0.46 and 0.50, respectively. 

Heavy-gas behavior is often dominant close to the point of release and in the near field. It is particularly important when considering large releases of pressurized or refrigerated flammable materials, for which the value of the lower flammable limit is low. Typical hydrocarbons that fall into this grouping are ethane, 2.9% by vol LFL propane, 2.1% by vol LFL and the butanes, 1.8% by vol LFL (Gas Processors Suppliers Association, 1972). Farther downwind, after additional mixing with air, the concentration of the flammable material is less important because it is then less than the lower flammable limit. The other hazard of heavy gases is asphyxiation of personnel who may inadvertently enter or be surrounded by the cloud. 

The behavior of flammability limits at elevated pressures can be explained somewhat satisfactorily. For simple hydrocarbons (ethane, propane,..., pentane), it appears that the rich limits extend almost linearly with increasing pressure at a rate of about 0.13 vol%/atm the lean limits, on the other hand, are at first extended slightly and thereafter narrowed as pressure is increased to 6 atm. In all, the lean limit appears not to be affected appreciably by the pressure. Figure 25 for natural gas in air shows the pressure effect for conditions above atmospheric. 

A gas mixture of methane, ethane, and pentane entering an adsorber has an upper flammability limit of 12.5% and a lower flammability limit of 2.85%. Given a methane concentration of 30%, calculate the concentrations of the other two components of the gas mixture. Flammability limits for methane, ethane, and propane at various concentrations are given in the following table. 

There are two composition limits of flammability for air and a gaseous fuel under specified conditions [76]. The lower limit is the minimum concentration of combustible gas that will support combustion, while the higher limit is the maximum concentration. Table 5.1 shows the lower and higher limits for pure hydrocarbons in air at room temperature and atmospheric pressure (RTP) [76]. For methane in air, the flammability limit is 5—15 mol%. For ethane in air, the limits are 2.9—13.0 mol%. The limits become lower with increasing molecular weight. It also is interesting to note that the limits are the same for n-pentane and isopentane, and also for -butane and isobutane. 

Flammable gases are defined by the U.S. Department of Transportation as those that when mixed with air are flammable in concentrations of 13 percent or less by volume in air or, if the gas has a flammable range wider than 12 percent in air, regardless of its lower flammable limit. Examples of flammable gases include acetylene, butadiene, carbon monoxide, ethane, ethylene, hydrogen, hydrogen sulfide, the liquefied petroleum... 

For most flammable hydrocarbons, the LFL is around 2%—5%. For simple alkanes, such as methane and ethane, the UFL is in the 10%—15% range. Some chemicals, such as hydrogen, ethylene oxide, and acetylene, have much higher values for UFL. Values for flammable limit ranges for many flammable materials are provided by NFPA 704—Standard System for the Identification of the Hazards of Materials for Emergency Response. 

F igure 7-50 shows the effect of pressure on the limits of flammability of an ethane system. 

Figure 7-50. Effects of pressure on limits of flammability of ethane-nitrogen-air mixture at 26°C. By permission, U.S. Bureau of Mines, Bulletin 627 [43],...

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