Multi-Stage Vacuum

Suitable screw configuration and screw speed ensure compensation of heat loss, particularly after flash and also after the initial forward venting. The vacuums in the individual degassing zones are designed to avoid excessive foaming of the polymer solution or even crumbs in the degassing opening. 

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The partial flow concept is usually used in making the connection of a helium leak detector to vacuum systems with multi-stage vacuum pump sets. When considering where to best make the connection, it must be kept in mind that these are usually small, portable units which have only a low pumping speed at the connection flange (often less than 1 l/s). This makes it all the more important to estimate - based on the partial flow ratio to be... 

The multi-stage vacuum pyrolysis was developed by C. Roy and co-workers, initially at the Universite de Sherbrooke and, currently, at the Universite Laval, in collaboration with Petro-Sun International Inc. there is a pilot demonstration of a single-stage plant at St-Amable, Quebec. The unit has a capacity of 200 kg/hr and is designed for used tires. The technology is based on a multiple hearth vacuum pyrolysis process development unit located near the Universite Laval and operating at a 30 kg/hr biomass capacity. 

Petroleum products may be treated with various solvents for the removal by selective solubility of undesirable constituents or for the recovery of by-products. The solvent and solute must be separated to yield the desired product and to recover the solvent for reuse. The solvents normally boil at a lower temperature than the products from which they are to be removed and so are generally distilled off as overhead products. The pipe stills used for this service may be single-stage or multi-stage units, depending on the service involved. Some solvents can be removed by the use of steam heated stills. In other cases, the high temperature required necessitates the use of fired heaters and vacuum towers. 

Figure 2.5 Possible technological solutions to bioprocess problems a) Fed-batch culture b) Continuous product removal (eg dialysis, vacuum fermentation, solvent extraction, ion exchange etc) c) Two-phase system combined with extractive fermentation (liquid-impelled loop reactor) d) Continuous culture, internal multi-stage reactor e) Continuous culture, dual-stream multi-stage reactor f) Continuous culture with biomass feedback (cell recycling). (See text for further details).

In order to reduce the instrumental background in mass spectrometers, new materials are required or an improvement to the vacuum system. New ion detectors with very low noise should be developed for the measurement of very low isotope ratios. Multi-stage MS-MS instruments could be applied to improve abundance sensitivity. 

In contrast to the decaffeination of coffee, which is primarily executed with green coffee, black tea has to be extracted from the fermented aromatic material. Vitzthum and Hubert have described a procedure for the production of caffeine-free tea in the German patent application, 2127642 [11]. The decaffeination runs in multi-stages. First, the tea will be clarified of aroma by dried supercritical carbon dioxide at 250 bar and 50°C. After decaffeination with wet CO2 the moist leaf-material will be dried in vacuum at 50°C and finally re-aromatized with the aroma extract, removed in the first step. Therefore, the aroma-loaded supercritical CO2 of 300 bar and 40°C will be expanded into the extractor filled with decaffeinated tea. The procedure also suits the production of caffeine-free instant tea, in which the freeze-dried watery extract of decaffeinated tea will be impregnated with the aromas extracted before. 

Description Purified EO or a water/EO mixture is combined with recycle water and heated to reaction conditions. In the tubular reactor (1), essentially all EO is thermally converted into monoethylene glycol (MEG) with diethylene glycol (DEG) and triethylene glycol (TEG) as co-products in minor amounts. Excess water, required to achieve a high MEG selectivity is evaporated in a multi-stage evaporator (2,3). The last evaporator (4) produces low-pressure steam, which is used as a heat medium for other units in the plant. Crude glycol is purified in a series of vacuum columns (5,6,7,8). Selectivity toward MEG can be controlled with the feed composition. 

Custom designed press, vessels <4 D Atm. stg. tanks process vessels Instrument air package Emergency generators Refrigeration packages Multi-stage ejector systems Vacuum pumps Environmental Scrubbers Belt screw conveyors Mills... 

Install pre-condensers cooled with cooling/chilled water. Use multi-stage steam ejectors arranged in series/series-parallel arrangement. Use liquid ring or dry vacuum pumps... 

Retrofit strategy and procedure for minimizing the operating cost of multi-stage SJE, LRVP, DVP, SJE-LRVP and SJE-DVP systems are discussed in this section. They are illustrated with two case studies in the subsequent sections. There are several ways to reduce the energy cost or increase capacity of a vacuum system. Engineers often find it difficult to make correct revamp decisions as most of the information is vendor specific. This chapter illustrates the use of simple techniques, based on available literature, to revamp a vacuum system easily and quickly. 

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