Hydrocarbon auto-ignition

Hydrocarbon auto-ignition differs from hydrogen auto-ignition in that reactions competing with chain branching ate a function of temperature rather than pressure. Classman (1996) attribntes region B of Fig. 11-2 lb to competition between reactions ... 

The motor fuel under test is compared to two pure hydrocarbons chosen as references. The first is 2, 2, 4-trimethylpentane or isooctane which is very resistant to auto-ignition and to which is arbitrarily given the number 100 /... 

After the ceramic heat transfer beds have reached an operating temperature of 1500 F the unit is ready for the process airstream. As the process airstream enters the ceramic heat transfer beds, the heated ceramic media preheats the process airstream to its oxidation temperature. Oxidation of the airstream occurs when the auto-ignition of the hydrocarbon is reached. At this point the heat released by the oxidation of the process hydrocarbons is partially absorbed by the inlet ceramic heat transfer bed. The heated air passes through the retention chamber and the heat is absorbed by the outlet ceramic heat transfer bed. 

Liquefied petroleum gas (LPG) was involved in 17% of the incidents (see Chapter 8), followed by heavy oils (see Section 12.4), gasoline, hydrogen, and hydrocarbon gases. Heavy oils are involved in so many incidents because they are often handled above their auto-ignition temperature and because they are involved in foamovers. 

The auto-ignition temperatures of various halogenated hydrocarbons in presence of chlorine are considerably below the corresponding values in air. Examples are (in °C) chloromethane 215 (618 in air) dichloromethane 262 (556) 1,2-dichloropropane 180 (555°C). Flammability limits are usually wider in chlorine... 

The extrusion aid must easily coat the resin yet be readily removable from the extrudate. It should also not leave a residue which could alter the color of the product. The volatilization temperature of the lubricant should be lower than the sintering temperature of the polymer. The other requirements of lubricants include high purity, low odor, low polar components, high auto-ignition temperature, low surface tension, and low skin irritation. Common lubricants are synthetic isoparaffmic hydrocarbons available in a wide boiling range. Some of the commercial lubricants include Isopar solvents (available from Exxon Corp.), mineral spirits, and VM P Naphtha (available from Shell Corp.). 

Hydrocarbon liquids will auto-ignite upon contact with hot surfaces above approximately... 

Petroleum products do not undergo spontaneous combustion. In general, they must be heated to 400°F or higher before oxidation occurs. Adsorbed hydrocarbons adsorbed on activated charcoal have been known to auto-ignite. This is most likely to occur when the petroleum product has a significant olefin content and has been on the carbon for a considerable amount of time. Given that activated carbon is fairly frequently used to remove small amounts of hydrocarbon from air to... 

Boiling point, °C >180 Melting point, C <-20 Flash point. "C 55-100 Auto-ignition temperature, ° C 475 Relativs density (waters 1) 0.73-0.87 Relative vapor density (air 1) ca. 4.5 Vapor pressure, mm Hg at 20 ° C < 0.36 Solubility In water none Explosive limits, vol% in air 1.0-6.0 Electrical conductivity. pS/m 10 COLORLESS UQUID WITH CHARACTERISTIC ODOR Mixture of aromatic hydrocarbons with lower boRng point above 180 0. Flow, agitation etc. can cause build-up of electrostatio charge due to liquid s low conductivity. Carbon monoxide, carbon dioxide and water are products of combustion. ... 

In what is called a reheat enhanced gas turbine , the California Energy Commission proposed a decade ago (Anon, 1997c) to reform or partially oxidise a mixture of steam and a combustible hydrocarbon (e.g. methane) to produce a hydrogen-rich fuel used for the primary combustor and a reheat combustor upstream of the turbine final stage. Auto-ignition of hydrogen-rich gas into the gas flow path between the stages is carried out. 

An important issue when handling hydrocarbon/steam/air mixtures are the flammability limits. Auto ignition temperatures were determined for reformulated gasoline by Ellis et al. [75], The auto ignition temperature of the air/fuel mixture was determined to be 360 ° C. Addition of steam increased this value to at least 500 ° C at O/C 1.0 and S/C 1.5. 

The temperature required for ignition of the hydrocarbons over a catalyst, which is termed the light-off temperature, is an important feature when operating an auto-thermal reformer or partial oxidation reactor, because it affects the start-up strategy and time demand. The auto-ignition or light-off temperature under conditions of partial oxidation decreases with increasing carbon number. 

Nolan DP. A study of auto-ignition temperatures of hydrocarbon mixtures as apphed to electrical area classification. Saudi Aramco J Technol 1996 [Summer]. 

Exposed hot surfaces may be a readily available ignition soruce in a process facility. In general, studies by the API on the ignition of hydrocarbons by a hot surface suggest it should not be assumed unless the surface temperature is approximately 182°C (360°F) above the minimum ignition temperature of the hydrocarbon involved. Test data and field experience both indicate that the ignition of flammable hydrocarbon vapors by hot surfaces in the open air requires temperatures considerably above the reported minimum auto-ignition temperature of the hydrocarbons involved. 

Auto-ignition This is the temperature at which materials burn without a source of ignition. Gasoline auto-ignites at 450°R Asphalt auto-ignites at 320°F, methane at 1000°R The heavier the hydrocarbon, the lower the auto-ignition temperature. Iron sulfide (pyrophoric iron) burns at room temperature when it is dry. 

Heavy hydrocarbons, such as vacuum tower bottom products, tar, and pitch, are frequently pumped and stored in tanks above their auto-ignition temperatures. The process reason for this is to prevent these fluids from "setting up" or solidifying in the pipelines or tanks. At ambient temperatures, even in hot climates, these fluids would normally be either solid or extremely viscous. 

A hydrocarbon above its auto-ignition temperature will spontaneously ignite upon exposure to air without any source of ignition. This is why there are often fires on pumps that pump heavy hydrocarbons. If the seal on a pump in such a service begins to leak, the... 

---