- March 17, 2013
- Posted by: essay
- Category: Term paper writing
Hydrocarbon fuels have next significant properties:
”¢ Flammability Limits
”¢ Auto-ignition Temperature
”¢ Minimum Ignition Energy
”¢ Other reflections.
It is also important to take into account probable types and effects of explosive overpressures. The upper and lower flammability limits detect a variety of a gas or vapor concentrations in air that may be lighted and uphold burning. Any formation out of these limits cannot be lighted. The lower flammability limit declines slightly as pressure is grew. Though, the upper flammability limit may grow mainly as pressure grows.
The next graph demonstrates the effect of pressure on the flammability range of methane in air. While these tendencies are consecutive for all hydrocarbons, each fuel has various flammability ranges.
Other factors which expand a flammability range include:
”¢ Grown temperatures
”¢ Grown energy of the ignition source
If pure oxygen, instead of air, mixes up with hydrocarbon
Humidity and other pollutants also will mention the flammability range. A fuel-air alloy may kindle without the insertion of a lighting source. The minimum auto-lighting temperature is the lowest temperature at which the fuel vapors spontaneously lightened. “Hydrocarbons that have been heated can ignite if they are exposed to air” (Choudhuri).
The auto-ignition temperatures of hydrocarbons at atmospheric pressure
“Methane has the highest temperature of auto ignition” (Choudhuri). As the quantity of carbon atoms in the hydrocarbon grows, the auto-ignition temperature drops. To put it differently, heavier hydrocarbons conduce to auto-ignition before lighter hydrocarbons. Grown pressures may curtail the temperature as well. The minimum energy for burning is the minimum ignition energy. Every different fuel is air alloy that will have dissimilar minimum ignition energies. “Factors that impact the minimum ignition energy are:
”¢ The temperature
”¢ The total energy
”¢ The rate at which energy is supplied, or time period over which it is delivered
”¢ The area over which energy is delivered” (Choudhuri).
The minimum power value of ignition is usually given as the energy demanded to light up the most jet mix of fuel and air. The flammable mix which is either is close to top or to low limits can demand higher quantity of energy than the minimum energy of ignition to light up. Except for several jet or changeable substances, liquids do not light up. It is vapors which have been let out from a surface of liquids that light up. Liquids will let out vapors on norm which is proportionate to their temperature. The capacity to let out vapors and the norm on which this occurs identifies the variability of a liquid. The temperature of flash of a liquid is certain as the lowest temperature in which that liquid gives vapors on sufficient norm to support an instant flame across its surface. The temperature of flash is also connected with pressure of vapor of a liquid. Low pressure of vapor conforms to a heat of flash, and the high blood pressure of vapor conforms to low temperature of flash. It is important not to forget, that temperatures of flash are measured in atmospheric pressure; if pressure above, the information appropriating in atmospheric pressure is not precise any more. The temperature of flash should be used only as the approximate link because the liquid can behave in another way in a floor than in the bench tests executed to define flash items. It is probable for an explosive atmosphere to subsist even if environment temperature is below temperature of flash of a liquid. The temperature of auto-ignition for liquid vapors is common to the temperature of gases. A good fog from a liquid of hydrocarbon can operate as pure gaseous substance. These aerosols can turn into an explosive mix at temperatures which are distant below a liquid temperature of flash. The drops should become evaporated but because of their small volume the energy demanded to make it is lowered meaningly. Special-purpose liquids of hydrocarbon, type “frac” liquids or “the poor oil” used in processing means of service with readiness emit other hydrocarbons. So, their properties will transform strikingly when they meet other hydrocarbons, type of composition fluids. Consequently, the potential dangers connected with these liquids can be changed totally. Any reused liquid should be checked up to confirm that its properties are still appropriating for planned use. “The chemicals and hydrocarbon-based liquids typically used by the oil and gas industry also have the potential for creating explosive mixtures including:
”¢ Chemicals used for well servicing and stimulations
”¢ Solvents and cleaning agents
”¢ Specially formulated hydraulic fluids and lubricants” (Little).
In definite circumstances, some industrial “solids” may form explosive mixes. As it is heated, it can undergo paralyses, a chemical worsening which occurs leading release of vapors. The released vapors have capacity to generate an explosive atmosphere and able to light up. For instance, physical explosions occur when vessels are rendered pressing on outside of their limits and break. Inflammable air ferry explosion of a mixture is an example of it. Chemical explosions occur because of reactions between chemical versions. Chemical explosions are stronger in or nearby stoichiometric levels. An explosion in the limits of the tank can cause physical explosion if pressure increase is enough. Explosions are defined by the speed at which the flame front moves as well. The super pressure created during an explosion depends on the capacity of front of a flame to accelerate and reach high speeds. Barriers, equipment, and accumulation cause the flame acceleration. The norm, to which the front of a flame moves through a constant inflammable mixture, is known as its burning speed. Air-hydrocarbon mixes have a maximum burning speed when the thickening of fuel is above stoichiometric. Site of ignition, force of ignition, fuel type, and fuel concentration are significant boundaries that impact gravity of explosions. If the cloud of vapor lightened in its end, front of a flame has all the length long clouds to be accelerated. If ignition occurs in the middle of a cloud, fronts of a flame have only half of distance to be accelerated in both ways. So, the areas that are impacted by the biggest overpressure may be a worthy distance far away from the place where the substance was lightened and released. Unlimited explosions of clouds of vapor can make destructive super pressure when greater sums of fuel are involved. On the contrary, explosion in the limited volume leads to considerable increase of pressure because of a heat of production of combustion and the limited capacity of gases to extend.
Choudhuri A.R., Investigation on the Flame Extinction Limit of Fuel Blends. Combustion and Propulsion Research Laboratory at the University of Texas at El Paso, USA, 2005.
Arthur D. Little Inc. Final Report on an Investigation of Hazards Associated with the Storage and Handling of Liquid Hydrogen. Report C-61092, Cambridge, USA, 1960.