Flammability and Combustion Research

Flammability Research

Within industry many manufacturing processes involve flammable chemicals, therefore flash points and flammability limits are information that is essential to maximize safety in process design and operational procedures. Even though there are regulations and standards that use the flash point temperature as a criterion, most of the experimental standard test methods are for pure compounds. Most of the flammability information available in the literature applies to pure fluids. But, because of gaps in information, a complete characterization of the liquid mixture is needed, especially for non-ideal mixtures. For gases and liquid mixtures, flammability limits are needed. These limits are needed for various mixtures over various temperature and pressure ranges as well as over various oxygen atmospheres.

The flammability research at the Center is a combined theoretical and experimental study that will develop methods for predicting flash points (flammability limits) for liquid mixtures, and test those methods using experimental data (Vidal, 2005). This work is important because currently there are no reliable methods to assess the flammability of mixtures. The chemical industry will benefit from this work because most of the chemicals handled in industry are mixtures instead of pure components. The development of theoretical methods to estimate flash points and flammability limits as well as the availability of experimental data will help in the characterization of flammability hazards.

Aerosol Research

Process fluids are capable of forming aerosols when they leak under high pressure. Mist or aerosol explosions have resulted in enormous losses to the chemical process and other manufacturing industry. Such aerosol explosions have been well documented, but little is known about the mechanisms for explosions of heterogeneous mixtures of vapor and droplets in air. Flammability limits for vapors are well defined. However, it has also been recognized that aerosols can explode at temperatures well below their flash points (Sukmarg et al, 2002). It is therefore critical that the hazardous nature of aerosols be studied in depth and strategies developed for reduction of aerosol explosion hazards and increased safety of handling fluids that can produce aerosols.

Research conducted by the Center has established correlations between the operating conditions and the drop-size distributions of heat transfer fluids (HTF) aerosols and has developed predictive models to relate aerosol droplet sizes and formation distances to bulk pressures, temperatures, fluid properties, orifice sizes, and ambient conditions (Sukmarg et al, 2002, Krishna et al, 2003, Krishna, 2003, and Sukmarg, 2000). As potentially hazardous conditions are identified, effective prevention and control measures will be developed. A better understanding of aerosol combustion behavior is vital to the prevention of aerosol explosions. Our vision is that by using correlations that predict aerosol formation as a function of atomization conditions, safety guidelines for selecting less hazardous HTFs and their operation conditions can be established.

Dust Explosion Research

Every process involving combustible finely divided solids or dusts is associated with explosion hazards. Although detailed statistical records of dust explosion are not generally available, it is known that approximately 70% of the dusts or powders processed in the chemical process industry are combustible and ignitable. Data from the Heath and Safety Executive indicate one dust explosion every day in Europe, with damages from each incident in the range of millions of dollars, not including the damage and loss caused by injuries, fatalities, production stoppages, and marketing losses. In the United States, some recent incidents where dust explosions were most likely the root cause include incidents in Indiana (October 2003), Kentucky (February 2003), and North Carolina (January 2003). As stated by the U.S. Chemical Safety Board in regard to the June 18, 2003, dust explosion in Kinston, NC, there is a critical need for research to characterize the explosion behavior of dusts to make possible strategies for handling dusts safely and to minimize the possibility and severity and therefore the risk of industrial dust explosions.

Fundamental research in the field of dust explosions has been classified into dust cloud formation process, dust cloud ignition process, flame propagation in dust clouds, and blast waves generation by burning dust clouds. Preliminary results seem encouraging but there are still a lot unresolved issues that need to be investigated further. On the experimental front, large-scale tests need to be conducted on dusts that are able to mimic typical industrial explosion scenarios.

Flammability of Hydrocarbon and Hydrocarbon Mixtures at Non-standard Conditions

Pure hydrocarbon or hydrocarbon mixtures are used in industry at various temperatures, pressures, oxygen concentrations, and other conditions. Flammability data in the literature, especially at non-standard conditions, is often inadequate for safe use of these liquids at conditions encountered in industrial applications including storage.

Based on previous flammability research in a closed cylindrical vessel with thermal criteria, measurements by the apparatus developed by Wun Wong will continue. From the collected data and revised objectives, the apparatus will be further developed and modifications will be considered. Objectives of the current research include:

Determine flammability Limits (LFL and UFL) for pure hydrocarbon and hydrocarbon mixtures in air at standard and non-standard conditions (e.g., temperatures, pressures, and concentrations of oxygen and water).
Characterize other flammability properties (e.g. minimum ignition energies, flash point, autoignition temperature) for hydrocarbon mixtures in air at standard and non-standard ranges of temperature, pressure, oxygen, and water.
Develop models from the measured data to guide safe handling, storage, and use of liquids and gas mixtures at industrial conditions.