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.
Process fluids are capable of forming aerosols when they leak under high pressure and high temperature. Mist or aerosol fire/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 can 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.
For aerosol generated from high pressure orifice, the droplet size distribution is usually wide. To better understand the fundamental properties of aerosol flammability, electrospray is utilized to generate near-monodisperse aerosol. The droplet size is mainly controlled by voltage, liquid flow rate, electric conductivity and other properties. Aerosol is characterized by Malvern Laser Diffraction Particle Analyzer continuously to measure its droplet size and concentration. The laser technology can provide us in-situ data without intervention. Aerosol is further ignited to observe its combustion phenomenon, including flame speed, flame size, ignition delay time and combustion mode. Flame propagation is recorded by high speed camera and image processing and analysis is used to obtain its combustion properties. An example of flame propagation is shown here. The trend of flame propagation as a function of fluid properties will be established by using empirical equations and theoretical models.
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.