Flash expansion

This procedure is called flash vaporization, flash liberation, pressure-volume relations, constant composition expansion, or flash expansion. 

Flash expansion Liquid Pressure reduction (energy)... 

Example 2.2.2 In the flash expansion desalination process (also called the flash vaporization process), cold sea water, heated to a temperature of 121 °C at the corresponding saturation pressure in a preheater, is allowed to enter a flash chamber where the temperature is 38 °C and the pressure is much lower at the corresponding saturation pressure. This produces some pure water vapor and a concentrated brine. In practical processes, the vapor mass flow rate produced can be at most 20% (Silver, 1966) of the feed brine mass flow rate. If the brine feed has 3.5 wt% salt, describe the separation achieved with the separation factors, extent of separation, distribution ratio and equilibrium ratio for two vapor flow rates expressed as a percentage of the feed brine mass flow rate (a) 20 wt%, (b) 10 wt%. 

The apparatus used in obtaining experimental data is shown in Fig. 1. It consisted of a vacuum-jacketed container for liquid He at atmospheric pressure mounted within an outer liquid-helium dewar and above the pumped, low-temperature helium bath. The flash-expansion valve, controlled by a rod running through an 0-ring seal at room temperature, was mounted within a second vacuum space enclosing the storage volume. Liquid helium was conveyed from die... 

The pressure used in producing gas wells often ranges from 690— 10,300 kPa (100—1500 psi). The temperature of the inlet gas is reduced by heat-exchange cooling with the gas after the expansion. As a result of the cooling, a liquid phase of natural gas liquids that contains some of the LPG components is formed. The liquid is passed to a set of simple distillation columns in which the most volatile components are removed overhead and the residue is natural gasoline. The gas phase from the condensate flash tank is compressed and recycled to the gas producing formation. 

Benzyl chloride [(chloromethyl)henzene, a-chlorotoluene], CgH CH2Cl, is a colorless Hquid with a very pungent odor. Its vapors are irritating to the eyes and mucous membranes, and it is classified as a powerfljl lacrimator. The physical properties of pure benzyl chloride are given in Table 2 (2—7). Benzyl chloride is insoluble in cold water, but decomposes slowly in hot water to benzyl alcohol. It is miscible in all proportions at room temperature with most organic solvents. The flash point of benzyl chloride is 67°C (closed cup) 74°C (open cup) autoignition temperature is 585°C lower flammability limit 1.1% by volume in air. Its volume coefficient of expansion is 9.72 x. ... 

The simplest continuous-distillation process is the adiabatic single-stage equihbrium-flash process pictured in Fig. 13-25. Feed temperature and the pressure drop across the valve are adjusted to vaporize the feed to the desired extent, while the drum provides disengaging space to allow the vapor to separate from the liquid. The expansion across the valve is at constant enthalpy, and this facd can be used to calculate To (or T to give a desired To). 

Discharge Flow Regimes Upon developing a puncture in either the vessel or a line attached to the vessel, as in Fig. 26-62, the subsequent depressurization can cause a volatile liqmd to flash and develop bubbles in the liquid. These bubbles cause an expansion, or. 9well, which raises the two-phase, or frothy, level. If the puncture is in the vapor space of a vessel or on a line from the vapor space, the discharge will be at least initially all vapor. This is the simplest discharge case and is treated here as a special case. 

This same principle applies also to the expansion of flashing hqnids in which the bnhhles are guided away from the blades. 

One applieation is the expansion of liquids or flashing liquids. Although this does not seem to be a very large power applieation, but all of the power removed from a eryogenie proeess reduees the amount of heat introdueed into the proeess by turbulenee. 

A possible refinement to the proeess ean be made, partieularly to the 4.49 Btu lost on flashing the 200 psia saturated liquid to atmos-pherie pressure. If this were flashed first to 80 psia and then flashed to atmospherie pressure, over half of the flash gas would be released at 80 psia. The expansion of this gas in a turboexpander would reeover almost half of the total flash loss, and the liquid yield would inerease 4.74% plus eontribute 1% of the plant power. 

All VGCF was graphitized prior to composite consolidation. Composites were molded in steel molds lined with fiberglass reinforced, non-porous Teflon release sheets. The finished composite panels were trimmed of resin flash and weighed to determine the fiber fraction. Thermal conductivity and thermal expansion measurements of the various polymer matrix composites are given in Table 6. Table 7 gives results from mechanical property measurements. 

By trial and error procedure, determine the amount of liquid which flashes by an isoenthalpic (constant enthalpy) expansion to the critical flow pressure (or actual pressure if greater than critical) for the flashed vapor. 

Flash chamber A chamber provided to al low the burning of a flammable gas in a process. In a refrigeration system, it is the separating tank between the expansion valve and the evaporator. 

Choking, or expansion of gas from a high pressure to a lower pressure, is generally required for control of gas flow rates. Choking is achieved by the use of a choke or a control valve. The pressure drop causes a decrease in the gas temperature, thus hydrates can form at the choke or control valve. The best way to calculate the temperature drop is to use a simulation computer program. The program will perform a flash calculation, internally balancing enthalpy. It will calculate the temperature downstream of the choke, which assures that the enthalpy of the mixture of gas and liquid upstream of the choke equals the enthalpy of the new mixture of more gas and less liquid downstream of the choke. 

Overpressure effects due to the vessel failure appear to be determined by gas expansion, not by flash vaporization. 

Another theory of liquid-liquid explosion comes from Board et al. (1975). They noticed that when an initial disturbance, for example, at the vapor-liquid interface, causes a shock wave, some of the liquid is atomized, thus enhancing rapid heat transfer to the droplets. This action produces further expansion and atomization. When the droplets are heated to a temperature equal to the superheat temperature limit, rapid evaporation (flashing liquid) may cause an explosion. In fact, this theory resembles the theory of Reid (1979), except that only droplets, and not bulk liquid, have to be at the superheat temperature limit of atmospheric pressure (McDevitt et al. 1987). 

This section addresses the effects of BLEVE blasts and pressure vessel bursts. Actually, the blast effect of a BLEVE results not only from rapid evaporation (flashing) of liquid, but also from the expansion of vapor in the vessel s vapor (head) space. In many accidents, head-space vapor expansion probably produces most of the blast effects. Rapid expansion of vapor produces a blast identical to that of other pressure vessel ruptures, and so does flashing liquid. Therefore, it is necessary to calculate blast from pressure vessel mpture in order to calculate a BLEVE blast effect. 

Energy here means the work which can be done by the fluid in expansion, ,wo ) This means that energy release during flashing must have been very rapid. 

Assuming that the blasts from vapor expansion and liquid flashing are simultaneous, the total energy of the surface explosion is ... 

Fill Ratio (vol %) Expansion of Vapor Only Combined Expansion of Vapor and Flashing of Liquid ... 

The simplest form of pressurization uses the expansion of the water content of the system to create a sufficient pressure in an expansion vessel to provide an anti-flash margin of, say, 17°C at the lowest pressure (highest point) of the system. The main disadvantage of a naturally pressurized expansion vessel is the ability of water to absorb air and the consequent risk of oxygen corrosion. 

The expln limits of mixts of gaseous Cl azide with Ar, N, and C dioxide are in Ref 3. The shock wave formed by the expansion of the gas into a vacuum is sufficient to cause de-compn (Ref 5) Qe -93.2 l.Skcal/mole, flame temp at 20mm 3380°K (Ref 6). Mixts of Cl azide.N trifluoride H 1 1 2 at 12—24 torr are initiated with a Xe flash lamp to produce explns which excite a H fluoride laser. Q azide, S hexafluoride, H mixts were similarly used (Ref 7)... 

Liquefied Petroleum Gas (LPG) (Cont d) storage, 403 transportation, 483 Liquids density, 49 effluent, 509 flashing, 50 immiscible, 49 thermal expansion, 49, 65 vaporization, 45, 246... 

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