Methane in air

Table A-4-1.3a, based on data in [62], shows how the MIE (mJ) of 28 vol% hydrogen and 8.5 vol% methane in air vary with circuit capacitance (pF) and electrode diameter (mm). Points refers to the use of steel gramophone needles. The table shows that MIE is decreased with decreased capacitance and electrode diameter however, as reflected in Figure 3-5.4.1 corona...

From Eq. (4-la) the stoichiometric concentration of methane in oxygen is 1 part in 3 = 33.3 mole percent methane. From Eq. (4-lb) the approximate stoichiometric concentration of methane in air is 1 part in 3 -E (158/21) = 9.5 mole percent methane. Tims, a mixtnre of 15 mole percent methane in oxygen has a stoichiometric ratio (p = 15/33.3 = 0.45 (lean), while the same methane concentration in air has a stoichiometric ratio (p = 15/9.5 = 1.58 (rich). 

Flame radius changes in time for o = 628 s and different methane in air concentrations in the mixture. Closed vessel. (Reproduced from Gorczakowski, A., Zawadzki, A., Jarosinski, J., and Veyssiere, B., Combust. Flame, 120,359, 2000. With permission.)... 

Pt 2 - Specification for safety and performance requirements for Group I instruments reading up to 5% methane in air. 

Methane leaks from a tank in a 50 m3 sealed room. Its concentration is found to be 30 % by volume, as recorded by a combustible gas detector. The watchman runs to open the door of the room. The lighter mixture of the room gases flows out to the door at a steady rate of 50 g/s. The flammable limits are 5 and 15 % by volume for the methane in air. Assume a constant temperature at 25 °C and well-mixed conditions in the room. The mixture of the room gases can be approximated at a constant molecular weight and density of 25 g/mol and 1.05 kg/m3 respectively. After the door is opened, when will the mixture in the room become flammable ... 

FIG. 26-9 Maximum pressure as a function of volume percent concentration for methane in air in a 20-L test sphere. The initial temperature and pressure are 25°C and 1 atm. The stoichiometric concentration is 9.51% methane. [C. V. Mashuga and D. A. Crowl, Application of the Flammability Diagram for Evaluation of Fire and Explosion Hazards of Flammable Vapors," Process Safety Progress, vol. 17, no. 3 copyright 1998 American Institute of Chemical Engineers (AlChE) and reproduced with permission.]... 

In some applications, it is necessary to inject nutrients or other chemicals into the aquifer to effect a more efficient restoration. Most of the time, additives are injected into separate wells. These additives may include surfactants, nutrients, pH adjustment chemicals, or additional carbon sources. Some success has been achieved with injected heated air to improve volatility of the chemicals. Where a small quantity of methane (as a primary substrate) is required, it can be added with the injection air. The lower explosive limit (LEL) of methane in air is 5% thus, extreme care must be used to control the mixture and the methane content of the vapor that reaches the surface. 

FIGURE 8.1 The effect of superequilibrium radical concentrations on NO formation rates in the isothermal reaction of 13% methane in air ( = 1.37). The upper curve is the ratio of the maximum NO formation rate calculated using the detailed reaction mechanism of Ref. [6] to the initial NO formation rate calculated using the Zeldovich model. The lower curve is the ratio of the NO concentration at the time of the maximum NO formation rate calculated using the detailed reaction mechanism to the equilibrium NO concentration (from Miller and Bowman [6]). 

For example, the lower flammability limit of methane in air at sea level is a concentration (by volume or partial pressure) of about 5%. The upper flammability limit is about 15% by volume or partial pressure. Heavier hydrocarbons tend to have lower LFLs. The LFL and UFL of some common hydrocarbons are given in Table B-2. 

An increase in temperature tends to widen the flammable range, reducing the LFL. For example, the LFL for methane in air is commonly quoted as 5%. As the temperature of methane increases to autoignition temperature, the LFL falls to around 3%. Stronger ignition sources can ignite leaner mixtures. Flammability limits also depend on the type of atmosphere. Flammability limits are much wider in oxygen, chlorine, and other oxidizers than in air (NFPA, 1997). 

A mixture of methane in air is flammable only between 5 and 15% so no reaction occurs and the temperature and pressure are unchanged. You might ask the person who turned on the lights to open the window because the room seems a bit stuffy. We will discuss combustion processes and explosions more in Chapter 10. 

Fig. 11. The mechanical valves can be replaced by thermal or chemical modulating devices. In principle, this modification circumvents the need of reliable mechanical valves and offers a more flexible system s . An example is the thermal oxidative modulation of methane in air. Figure 12 shows a concentration profile during 8 days, determined with an experimental modulation CC set up...

However, J. Taylor found that the converse may also hold good on the detonation of an explosive freely suspended in a chamber filled with a mixture of 9% methane in air (i.e. not fired in a mortar), the relationship between the charge limit and the rate of detonation (Fig. 134) is clearly marked in explosives of similar composition. Murata [42] came to the same conclusion. Likewise, if detonation is initia-... 

Fig. 17.9 Selected species profiles in opposed-flow, premixed, twin flames [214]. The solution in the upper panel is at a high strain rate, which is very near extinction, and that in the lower panel is far from extinction. Both are for a mixture of 9% methane in air. The flow is from left to right, with the symmetry plane on the right.

Fig. 17.23 Sampling-probe measurements of CO2 mole fractions in a stagnation-flow boundary layer above a hexaluminate-based catalyst. In all cases the equivalence ratio of methane in air is 4> — 0.3, while the surface temperature varies from 880°C to 1110°C. In all cases the inlet flow that issues though the contraction nozzle is Tin = 400°C and the inlet velocity is U n = 70 cm/s. The separation distance between the nozzle exit and the stagnation surface is /. = 1.65 cm.

An example is the sensor for methane (Stetter and Li, 2008), which also shows sensitivity to several other oxidizable species. The cell current is calibrated against the concentration of methane in air of 75% relative humidity. The key element in this sensor is the low volatility electrolyte, such as y-butyrolactone, propylene carbonate,... 

Fig. 7.18 Response of fuel cell amperometric sensor to methane in air (adapted from Stetter and Li, 2008)...

Information on the content of carbon dioxide and methane in air bubbles contained in ice kerns reflects the important role of these minor gas constituents (MGCs) in climate formation, but it is still unclear what took place first change in temperature or in MGC content. For instance, it was recently shown that during four interglacial periods, changes in temperature in the Antarctic took place about 4,000 years before the changes in C02 concentration. 

Figure 9.2. Generalized trend of the concentration of methane in air extracted from dated ice cores. (After Cicerone and Oremland, 1988.)...

Photochemical air pollution in the troposphere results from a complex interplay between sunlight and primary air pollutants emitted in ambient air that leads to the formation of ozone and other oxidizing and eye-irritating agents. On the other hand, pollutants injected into the stratosphere by such human activities as supersonic transports (SST s) and release ofchlorofiuoro-methanes in air by their use as aerosol propellants and refrigerants may eventually reduce the protective layer of ozone from harsh solar ultraviolet radiation. Although the full impact of injected air pollutants in the stratosphere is not apparent at present, various model calculations show conclusively that the continuous future release of chlorofluoromethanes and NO (NO and N02) would result in substantial reduction of ozone in the stratosphere. 

Lower Limit or Inflammation of Methane in Air. (Burgess and Wheeler, 1911.)... 

Performance requirements for Group I apparatus indicating up to 100% (v/v) methane in air... 

---