Extended Le Chatelier's formula for carbon dioxide dilution effect on flammability limits

doi:10.1016/j.jhazmat.2006.05.035

Journal of Hazardous Materials

Volume 138, Issue 1, 2 November 2006, Pages 1-8

https://doi.org/10.1016/j.jhazmat.2006.05.035 Get rights and content

Abstract

Carbon dioxide dilution effect on the flammability limits was measured for various flammable gases. The obtained values were analyzed using the extended Le Chatelier's formula developed in a previous study. As a result, it has been found that the flammability limits of methane, propane, propylene, methyl formate, and 1,1-difluoroethane are adequately explained by the extended Le Chatelier's formula using a common set of parameter values. Ethylene, dimethyl ether, and ammonia behave differently from these compounds. The present result is very consistent with what was obtained in the case of nitrogen dilution.

Introduction

Le Chatelier's formula [1] is commonly used to predict the flammability limits of blended gases of various fuels. According to this law, the lower flammability limit L of a blended gas is given by the following equation: $\frac{1}{L} = \frac{c_{1}}{L_{1}} + \frac{c_{2}}{L_{2}} + \frac{c_{3}}{L_{3}} + \dots$ Here, c₁, c₂, c₃, … are mole fractions of component gases in the blend whose lower flammability limits are L₁, L₂, L₃, …, respectively. The sum of the mole fractions, c₁, c₂, c₃, …, is unity. $c_{1} + c_{2} + c_{3} + \dots = 1$ A similar equation is said to be valid for the upper flammability limits. Recently, we have applied the Le Chatelier's formula to newly measured values of flammability limits of various mixtures prepared from nine kinds of compounds [2]. As a result, it has been found that in general Le Chatelier's formula can very well predict the values of lower flammability limits and can reasonably well predict the upper flammability limits. In addition, it has been shown that Le Chatelier's formula can be modified so that the upper flammability limits of various blended gases may be fitted pretty accurately [2].

However, since Le Chatelier's formula is per se for blended gases containing only flammable compounds, it is not applicable as it is to dilution effect of inert gases. In a previous paper, we have developed Le Chatelier's formula to apply to the inert gas dilution effect [3]. As a result, it has been found that the nitrogen dilution effect on the flammability limits of a wide variety of fuel gases can be explained by the extended Le Chatelier's formula using a common set of parameter values.

Dilution with nitrogen is a typical way of ensuring safety in the use of flammable gases. Carbon dioxide is another typical gas to be used for the same purpose. It is of interest whether the carbon dioxide dilution effect on various fuel gases can be explained similarly as in the case of nitrogen dilution. If a similar result is obtained for the carbon dioxide case, we can expect that dilution effects of various inert gases on a variety of flammable gases be explained by the extended Le Chatelier's formula using a common set of parameter values.

Data of carbon dioxide dilution effects on various flammable gases are reported in the literature such as Refs. [4], [5]. However, it is well known that the values of flammability limits are dependent upon the experimental apparatus and condition used for the measurement. In order to make a reliable numerical analysis, it is indispensable to utilize accurate and in particular consistent data of flammability limits in the analysis. In the present study, carbon dioxide dilution effects on the same eight compounds as used in the preceding study [3] were measured carefully, and a similar analysis was carried out using the extended Le Chatelier's formula.

Section snippets

Experimental method

The experimental setup is the same as in a previous study, which basically follows that of the revised version of ASTM-E681 [6], [7], [8]. The explosion vessel is a 12-l spherical glass flask which is enclosed in an air-bath kept at 35 °C. In the present apparatus, the vessel flange is fixed to the top of the vessel, while in the ASTM method the flange is held on the top by spring-loaded clamps. The vessel is connected to a soda lime tower 30 cm in diameter and 50 cm in height through a plastic

Results and discussion

The flammability limits of eight compounds, i.e., methane, propane, ethylene, propylene, dimethyl ether, methyl formate, 1,1-difluoroethane, and ammonia, were measured at various levels of dilution with carbon dioxide. The flammability limits of sample gases themselves were measured in a previous study under the same experimental condition [2]. The result of these measurements is summarized in Table 1. In this table, L_fuel is the concentration of the fuel gas only in the lower flammability

Conclusion

The flammability limits of eight compounds, i.e., methane, propane, ethylene, propylene, dimethyl ether, methyl formate, 1,1-difluoroethane, and ammonia, diluted with carbon dioxide at various levels were measured carefully. The obtained data were analyzed using Eqs. (3) and (4), which are the extended forms of Le Chatelier's formula. At first, the data of individual compounds were analyzed separately. The observed data were explained very well by the equations. Then, the carbon dilution

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Extended Le Chatelier's formula for carbon dioxide dilution effect on flammability limits

Abstract

Introduction

Section snippets

Experimental method

Results and discussion

Conclusion

Limits of flammability of gaseous mixtures

Bull. Soc. Chim. (Paris)

Limits of flammability of gases and vapors

US Bureau Mines Bull.