Spray burning

The combustion of liquids is a fertile area for further study. Kowledge of the combustion science of individual droplets as well as groups of droplets helps improve performance of devices that rely on spray burning, particularly diesel engines. Understanding of the science of liquid pool fires potentially effects safety during spills. 

C.G. McCreath, N.A. Chigier Liquid-spray burning in the wake of a stabilizer disc, Fourteenth symposium (international) on combustion, The Combustion Institute, Pittsburgh, 1973, pp. 1355-1363. 

Results of analysis and operating experience gained have shown that the large sodium spray leaks are not real as r as the reactor facilities are concerned. Nevertheless, studies on the sodium spray burning are still going on. Leak tight vertical cylindrical chambers with elliptical bottoms and covers are used for the tests. The main objective of the experimental studies is to determine the portion of sodium burnt in drops. The sodium jet is directed straight upwards. The injector is located near the chamber bottom. There is a reflector provided on the jet route in order to break the jet into drops. The distance between the injector and reflector can be varied. 

In wetted-wall units, the walls of a tall circular, slightly tapered combustion chamber are protected by a high volume curtain of cooled acid flowing down inside the wall. Phosphoms is atomized by compressed air or steam into the top of the chamber and burned in additional combustion air suppHed by a forced or induced draft fan. Wetted-waU. plants use 25—50% excess combustion air to reduce the tail-gas volume, resulting in flame temperatures in excess of 2000°C. The combustion chamber maybe refractory lined or made of stainless steel. Acid sprays at the bottom of the chamber or in a subsequent, separate spraying chamber complete the hydration of phosphoms pentoxide. The sprays also cool the gas stream to below 100°C, thereby minimising corrosion to the mist-collecting equipment (typically type 316 stainless steel). 

Burning Pyrites. The burning of pyrite is considerably more difficult to control than the burning of sulfur, although many of the difficulties have been overcome ia mechanical pyrite burners. The pyrite is burned on multiple trays which are subject to mechanical raking. The theoretical maximum SO2 content is 16.2 wt %, and levels of 10—14 wt % are generally attained. As much as 13 wt % of the sulfur content of the pyrite can be converted to sulfur trioxide ia these burners. In most appHcations, the separation of dust is necessary when sulfur dioxide is made from pyrite. Several methods can be employed for this, but for many purposes the use of water-spray towers is the most satisfactory. The latter method also removes some of the sulfur... 

Liquid fuel is injected through a pressure-atomizing or an air-blast nozzle. This spray is sheared by air streams into laminae and droplets that vaporize and bum. Because the atomization process is so important for subsequent mixing and burning, fuel-injector design is as critical as fuel properties. Figure 5 is a schematic of the processes occurring in a typical combustor. 

The vapor cloud of evaporated droplets bums like a diffusion flame in the turbulent state rather than as individual droplets. In the core of the spray, where droplets are evaporating, a rich mixture exists and soot formation occurs. Surrounding this core is a rich mixture zone where CO production is high and a flame front exists. Air entrainment completes the combustion, oxidizing CO to CO2 and burning the soot. Soot bumup releases radiant energy and controls flame emissivity. The relatively slow rate of soot burning compared with the rate of oxidation of CO and unbumed hydrocarbons leads to smoke formation. This model of a diffusion-controlled primary flame zone makes it possible to relate fuel chemistry to the behavior of fuels in combustors (7). 

Special purpose and blended Portland cements are manufactured essentially by the same processes as ordinary Portland cements but have specific compositional and process differences. White cements are made from raw materials of very low iron content. This type is often difficult to bum because almost the entire Hquid phase must be furnished by calcium aluminates. As a consequence of the generally lower total Hquid-phase content, high burning-zone temperatures may be necessary. Past cooling and occasionally oil sprays are needed to maintain both quaHty and color. 

If an ethyl ether fire occurs, carbon dioxide, carbon tetrachloride, and dry chemical fire extinguishers meeting National Eire Prevention Association Code 1 and 2 requirements may be used successhiUy (23). Water may also be effectively appHed (see Plant safety). Hose streams played into open tanks of burning ethyl ether serve only to scatter the Hquid and spread the fire. However, ether fires may be extinguished by a high pressure water spray that cools the burning surface and smothers the fire. Automatic sprinklers and deluge systems are also effective. 

Fire Hazards - Poinr (deg. F).-300-350 OC Flammable limits in Air (%) Not pertinent Fire Extinguishing Agents Water spray, dry chemical, foam or carbon dioxide Fire Extinguishing Agents Not To Be Used Water or foam may cause foaming Special Hazards of Combustion Products Not pertinent Behavior in Fire Not pertinent Ignition Temperature (deg. F) 400 - 700 Electrical Hazard Not pertinent Burning Rate No data. 

Fire Hazards - Flash Point (deg. F) 20 CC Flammable Limits in Air (%) 2.8 - 14.4 Fire Extinguishing Agents Stop flow of gas. Use water spray, carbon dioxide, or dry chemical for fires in water solutions Fire Extinguishing Agents Not to be Used Do not use foam Special Hazards of Combustion Products Vapors are eye, skin and respiratory irritants Behavior in Fire Not pertinent Ignition Temperature (deg. F) 756 Electrical Hazard Data not available Burning Rate 4.5 mm/min. 

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