Flash vaporizer

The calculation of single-stage equilibrium separations in multicomponent systems is implemented by a series of FORTRAN IV subroutines described in Chapter 7. These treat bubble and dewpoint calculations, isothermal and adiabatic equilibrium flash vaporizations, and liquid-liquid equilibrium "flash" separations. The treatment of multistage separation operations, which involves many additional considerations, is not considered in this monograph. 

FLASH determines the equilibrium vapor and liquid compositions resultinq from either an isothermal or adiabatic equilibrium flash vaporization for a mixture of N components (N 20). The subroutine allows for presence of separate vapor and liquid feed streams for adaption to countercurrent staged processes. 

Edmister, W.C. and K.K. Okamoto (1959), Applied hydrocarbon thermodynamics. Part 12 equilibrium flash vaporization correlations for petroleum fractions . Petroleum Refiner, Vol. 38, No. 8, p. 117. 

Free Hquid hydrocarbons and water flash vaporize if they contact hot surfaces. A rough estimate of the magnitude of such an event can be made if the free Hquid levels are known. Localized flashing of hydrocarbons and water continues, even iu the absence of free Hquids, whenever particles of waste are suddenly brought iu contact with hot surfaces or exposed to iatense radiation. 

The rich oil from the absorber is expanded through a hydrauHc turbiae for power recovery. The fluid from the turbiae is flashed ia the rich-oil flash tank to 2.1 MPa (300 psi) and —32°C. The flash vapor is compressed until it equals the inlet pressure before it is recycled to the inlet. The oil phase from the flash passes through another heat exchanger and to the rich-oil deethanizer. The ethane-rich overhead gas produced from the deethanizer is compressed and used for produciag petrochemicals or is added to the residue-gas stream. 

Figures 26-63 and 26-64 illustrate the significant differences between subcooled and saturated-liquid discharge rates. Discharge rate decreases with increasing pipe length in both cases, but the drop in discharge rate is much more pronounced with saturated liquids. This is because the flashed vapor effectively chokes the flow and decreases the two-phase density.

It is then easy to calculate what the proportions must be so that d x overhead composition -l- r x flash liquid composition = flash vapor composition. Thus ... 

Before desalters came into common use, crude pipe stills were frequently equipped with flash drums to minimize salt deposition on hot surfaces. In the flash drum system, the crude is heated to about 300°F. under enough pressure to suppress vaporization. The pressure is released as the crude enters the flash drum and all of the water (along with a small amount of crude) is flashed off, leaving the salt as a suspension in the oil. The flashed vapor is recombined with the crude near the furnace outlet or in the flash zone of the fractionating tower. 

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. 

Calculate individually the orifice area required to pass the flashed vapor component, using Equation (5a), (3b), (4), (5), or (6), as appropriate, according to service, type of valve and whether the back pressure is greater or less than the critical flow pressure. 

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

The quantity of fuel in a cloud is calculated by use of release and (flash) vaporization models that have been extensively described by Hanna and Drivas (1987). To account for aerosol formation during vaporization, the flash fraction should be doubled up to, but not exceeding, a value of unity. Pool vaporization is also considered. 

The amount of liquid that will evaporate can be calculated if it is assumed that all heated liquid will be exposed to air (see Section 6.3.3.3). Results of calculations can then be compared with experimental results. When the calculated percentage of flash evaporation exceeded 36%, all fuel became an aerosol for fireball formation. At lower percentages, a portion of the fuel formed the fireball, and the remainder former a pool fire on the ground. Thus, these results imply that, when calculated flash evaporation is less than 36% of the available fuel, fuel in the fireball can be expected to amount to approximately three times the amount of flashed vapor. 

Hasegawa and Sato (1977) showed that, when the calculated amount of flash vaporization equals 36% or more, all released fuel contributes to the BLEVE and eventually to the fireball. For lower flash-vaporization ratios, part of the fuel forms the BLEVE, and the remainder forms a pool. It is assumed that, if flash vaporization is below 36%, three times the calculated quantity of the flash vaporization contributes to the BLEVE. 

Thus, is 20% of the energy calculated for nonideal gases or for flash-vaporization situations. For scaled energies ( ) larger than about 0.8 as calculated by Eq. (9.3.5), the calculated velocity is too high, so method 3 should be applied. 

Flash vaporization The instantaneous vaporization of some or all a liquid whose temperature is above its atmospheric boiling point when its pressure is suddenly reduced to atmospheric. 

Superheat limit temperature The temperature of a liquid above which flash vaporization can proceed explosively. 

Flash vapor pyrolysis of chloroform has been used to effect the... 

Because flashing steam-condensate lines represent two-phase flow, with the quantity of liquid phase depending on die system conditions, these can be designed following the previously described two-phase flow methods. An alternate by Ruskin [28] uses the concept but assumes a single homogeneous phase of fine liquid droplets dispersed in the flashed vapor. Pressure drop was calculated by the Darcy equation ... 

Example 8-7 Flash Vaporization of a Hydrocarbon Liquid Mixture... 

An effort has been made to present the basic understanding of the method as it applies to systems involving unequal molal overflow, open steam distillation and single flash vaporization in Figures 8-42 and 8-43. 

The entrance of a liqmd-flashing vapor mixture into the distillation column feed location requires a specially designed distribution tray to separate the vapors from the liquid, w hich must drop onto the packing bed for that section in a uniform pattern and rate. 

In the design of all parts of a system, special consideration should be given to the large amount of flash vapor liberated on the reduction of pressure. Because of the high ratio of specific heat to latent heat, much more flash vapor is liberated with Dowtherm A than with steam. Consequendy, all constrictions that would cause high pressure drops should be avoided. 

Flash vaporization is another simple delivery design, where the liquid is metered into a vessel heated above its boiling point (at the prevailing pressure). Controlled metering of the liquid into the vaporizer can be accomplished by a peristaltic pump or similar devices. A typical vaporizer to supply TiC is shown in Fig. 5.3. 

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