Derivation of Le Chatelier\u27s mixing rule for flammable limits

In 1891 Le Chatelier first proposed an empirical mixing rule for predicting the flammable limit of lean fuel air mixtures - this method is still widely used today. This paper presents a proof to Le Chatelier\u27s mixing rule based on thermodynamics. A number of assumptions are required to produce the proof. These assumptions are: The product heat capacities are constant. The number of moles of gas is constant. The combustion kinetics of the pure species are independent and unchanged by the presence of other combustible species. The adiabatic temperature rise at the flammability limit is the same for all species. These assumptions were found to be reasonably valid at the lower flammability limit and less so at the upper flammability limit. This paper also considers experimental data that support some of the assumptions made to arrive at the Le Chatelier mixing equation

Application of the Flammability Diagram for Evaluation of Fire and Explosion Hazards of Flammable Vapors

The safest method to prevent fires and explosions of flammable vapors is to prevent the existence of flammable mixtures in the first place. This method requires detailed knowledge of the flammability region as a function of the fuel, oxygen, and nitrogen concentrations. A triangular flammability diagram is the most useful tool to display the flammability region, and to determine if a flammable mixture is present during plant operations. This paper describes how to draw and use a flammability diagram. A procedure to estimate the flammability region using the available and sometimes limited data is discussed. The paper also shows how to use the flammability diagram with plant operations involving inerting and purging, and from bringing vessels into and out of service. A compilation of flammability diagrams for 30 materials, based on previously published data is provided. An automated apparatus for acquiring data for a flammability diagram is described. The apparatus consists of a 20-L sphere with an automated gas mixing system, a fuse-wire ignition system, and a high speed pressure measurement and data acquisition system. Data derived from the apparatus includes flammability limits, maximum pressure during combustion, and the maximum pressure rate. The effect of fuse-wire ignitor dynamics on the results is studied. A flammability diagram for methane drawn from data obtained from the apparatus, is presented

Flammability zone prediction using calculated adiabatic flame temperatures

This paper describes our work to predict the flammability zone for any mixture of fuel, oxygen and nitrogen. The method utilizes a commercially available equilibrium program to determine the calculated adiabatic flame temperature (CAFT). The model is compared with our extensive experimental data obtained in a 20 L sphere at an initial pressure of 1 atm and 298 K. The data and model compare well over the entire flammability zone for two pure species, methane and ethylene, and not as well for a 50/50 mixture of methanelethylene. Our results show that a good prediction of the flammability zone is obtained using a CAFT criterion of 1200 K. Furthermore, the intermediate species and solid carbon must be included in the equilibrium calculation to fit the fuel rich part of the zone. The intermediate species were selected by the equilibrium program using a built-in species selection criteria. For a gas mixture of methane and ethylene, we were unable to identify mixing rules for estimating KG and Pmax from pure component data. This method provides a direct approach to full flammability zone prediction

Thermokinetic Investigation of o-Nitrotoluene Using Reaction Calorimetry

PresentationO-nitrotoluene (2-NT) is an important chemical widely used in the chemical industry. However, in the past 25 years, severe incidents have killed 10 people and injured more than 200 due to its thermal decomposition. This research focus on the thermal behavior of 2-NT decomposition. Advance Reactive System Screening Tool (ARSST) and the Automatic Pressure Tracking Adiabatic Calorimeter (APTAC) have been used to better understand the mechanisms that result in the explosion hazard of 2-NT. Key parameters such as observed onset temperature, onset pressure, self-heat rate, and pressure rate have been reported. Furthermore, the APTAC data is used in the calculation of Arrhenius data, reaction order, and self accelerating decomposition temperature (SADT). The results show that the 2-NT decomposition reaction has potentially severe consequences and is sensitive to the conditions like sample size and initial pressure. Also, there are two peaks in self-heat rate profile in the ARSST tests which indicate a minimum two different reactions that may be occurring during the decomposition. This study also focuses on the kinetics of the decomposition reaction which is nearly zero-order reaction and SADT prediction of the 2- NT of UN 25 kg package storage