Steam injection vacuum

Fig. 3. Pasteurization by various methods (8) A, HTST B, quick time C, vacuum D, modified tubular E, small-diameter tube and F, steam injection.

Other Continuous Processes. Various pasteurization heat treatments ate identified by names such as quick time, vacuum treatment (vacreator), modified tubular (Roswell), small-diameter tube (MaHotizer), and steam injection. The last three methods are ultrahigh temperature (UHT) processes (see Fig. 3). Higher treatment temperatures with shorter times, approaching two seconds, are preferred because the product has to be cooled quickly to prevent deleterious heat effects. 

The prevacuum technique, as its name implies, eliminates air by creating a vacuum. This procedure faciUtates steam penetration and permits more rapid steam penetration. Consequendy this results in shorter cycle times. Prevacuum cycles employ either a vacuum pump/steam (or air) ejector combination to reduce air residuals in the chamber or rely on the pulse-vacuum technique of alternating steam injection and evacuation until the air residuals have been removed. Pulse-vacuum techniques are generally more economical vacuum pumps or vacuum-pump—condenser combinations may be employed. The vacuum pumps used in these systems are water-seal or water-ring types, because of the problems created by mixing oil and steam. Prevacuum cycles are used for fabric loads and wrapped or unwrapped instmments (see Vacuum technology). 

This system requires direct steam injection into the still with the liquid, all the steam leaves overhead with the boiled-up vapors (no internal condensation) in a steady-state operation, and system at its dew point. Steam is assumed immiscible with the organics. Steam distillation is usually applied in systems of high boiling organics, or heat sensitive materials which require separation at vacuum conditions. 

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The steam-enhanced recovery process (SERF) is an in situ technology designed to remove and treat volatile and semivolatile organic compounds (VOCs and SVOCs) in contaminated soils by using steam injection and vacuum extraction. The technology is based on the idea that added heat (thermal enhancement) increases the volatility and mobility of SVOCs and VOCs and thus facilitates the extraction of soil contaminants. The process works by injecting high-quality steam... 

Steam injection and vacuum extraction (SIVE) is a patented, commercially available in situ technology. SIVE has been used to remove non-aqueous-phase liquids (NAPLs), diesel fuel, jet fuel, semivolatile and volatile organic compounds (SVOCs and VOCs), chlorinated solvents, acetone, and benzene, toluene, ethyl benzene, and xylenes (BTEX) from soil and ground-water. 

The older tall oil distillation columns used bubble cap trays. In new columns, structured packing is preferred. Because of the low pressure drop of structured packing, steam injection is no longer necessary. The low liquid holdup of this packing minimizes the reactions of the fatty and resin acids. A specific distillation sequence for vacuum columns using structured packing of Sulzer has been described (26). Depitching is carried out at a vacuum of... 

Fluid milk is commonly subjected to a combination steam injection/in-fusion and vacuum flash evaporation process to remove volatile off-flavor compounds. The process is designed to remove the same amount of water by the flash treatment as is added during steam injection/infu-sion, so that the composition of the milk remains unchanged. This treatment is most effective for removing volatile, water-soluble flavor compounds, such as those from weeds and feed consumed by the cow. The additional heat from this process usually provides further improvement in product shelf life. 

The overhead product from the primary tower is divided into an overhead and a bottom product in the secondary tower, which operates under a partial vacuum with steam injected into the bottom of the tower to assist in the fractionation. The overhead and bottom products are finished aliphatic solvents, or if the feed to the primary tower is light naphtha instead of heavy naphtha, other aliphatic solvents of different boiling ranges are produced. 

Dynamic Vacuum. Once the maximum initial vacuum has been reached, the vacuum pump is kept running while a 5-10 min. steam-injection is performed from the side of the chamber that lies opposite the vacuum drain point. Modern autoclaves can perform both methods depending on the load to be sterilized. 

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