Boiling liquid-evaporating vapor

Unconfined Vapor Cloud Explosions (UVCEs) and Boiling Liquid Evaporating Vapor Explosions (BLEXT s)... 

A vaporizing liquid is considered next. If a tank initially under high pressure ruptures, it is possible that as a result of the sudden depressurization the liquid or liquid-vapor mixture initially in the tank may partially or completely vaporize. Such explosions are known as boiling liquid-evaporating vapor explosions (BLEVEs). Here we estimate the energy released on a BLEVE. 

Figure 5.3-2 Boiling liquid-evaporating vapor event. The dashed line indicates the system for which the mass and energy balances are being written.

To a first approximation we may think that boiling occurs at constant temperature especially because for a number of processes evaporation heat is enough to polymerization completion (at monomer initial concentration 1,5-3,0 mole/1). Reaction mixture temperature rises up to Tbou and then process proceeds at constant temperature until all solvent and/or monomer part boil away [60]. When total transformation of boiling liquid into vapor occurs one can observe significant temperature rise in reaction zone due to polymerization of either liquid (if monomer in system doesn t boil) or gas monomer [61]. 

The liquefied gas must be maintained at or below its boiling point. Refrigeration can be used, but the usual practice is to cool by evaporation. The quantity of liquid evaporated is minimized by insulation. The vapor may be vented to the atmosphere (wasteful), it may be compressed and reliquefied, or it may be used. 

The LT evaporator shown in Fig. 11-122/ is typical of those commonly used, especially for black hquor. Feed enters at the bottom of the tube and starts to boil partway up the tube, and the mixture of liquid and vapor leaving at the top at nigh velocity impinges against a deflector placed above the tube sheet. This deflector is effective both as a primary separator and as a foam breaker. 

Material stored at or below its atmospheric pressure boiling point has no superheat. Therefore there will be no initial flash of liquid to vapor in case of a leak. Vaporization will be controlled by the evaporation rate from the pool formed by the leak. This rate can be minimized by the design of the containment dike, for example, by minimizing the surface area of the liquid spilled into the dike area, or by using insulating concrete dike sides and floors. Because the spilled material is cold, vaporization from the pool will be further reduced. 

Convective heat exchange, natural or forced Radiant heat transfer, e.g. furnaces Evaporation, e.g. in evaporators Condensation, e.g. in shell and tube heat exchanges Heat transfer to boiling liquids, e.g. in vaporizers, boilers, re-boilers ... 

Vessel mptures can also occur when a higher-temperature liquid or solid is combined with a cooler low boiling liquid, transferring sufficient heat from the hotter material to the colder material such that the colder material rapidly vaporizes. No chemical reactions are involved instead, the explosion occurs because the cooler liquid expands as it is converted to vapor, creating high pressures. These are called physical explosions. A common example is a steam explosion, which occurs when liquid water is accidentally introduced into a process vessel operating at an elevated temperature. If the hotter material is above the superheat limit temperature of the evaporating liquid, initial confinement by a vessel is not required to create an explosion pressure wave. 

Distillation is the process by which two or more liquids, or a solution of liquids and solids, are separated as a result of differences in vapor pressure and boiling points through the evaporation and condensation of the mixture components above the boiling liquid mixture. 

Alcohols. Methyl alcohol, and to a lesser extent ethyl alcohol, were used as freezing point depressants for many years. Their use now is minimal. When properly inhibited, alcohol-water solutions can be satisfactory coolants only under restricted conditions. Alcohol antifreezes fell into disuse because of their low boiling point (lower than that of water) and the danger of loss from boiling or evaporation. Alcohol volatilizes from hot surfaces much more readily than glycol coolant and can be a potential fire hazard. Methyl alcohol liquids are both flammable and poisonous. Methyl alcohol vapors are toxic when inhaled at high concentrations. 

Vaporization (evaporation or boiling) Liquid Condensation Gas to liquid... 

Ebullition consists mainly to the conversion of tho liquid into vapor, and so far is synonymous with evaporation whioh differs from it, however, inasmuch as the latter takes place at ull temperatures—whereas a certain range of heat is required, under every circumstance, before the former phenomenon Is observed. This may be proved by allowing a shallow vessel containing water to remain exposed for some time upon examination it will be found that a portion will have disappeared—or, to other words, it will have evaporated to tho extent of the loss. Most fluids are susceptible of this change, hut those which boil at a low temperature are more volatile than others thus alcohol is evaporated much quicker than water, and for the same reason ether is converted into vapor much more readily than even alcohol. 

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