Scraped Surface Equipment

SSEs and SSCs are used in incremental dewaxing and SSCs in DILCHILL dewaxing. SSEs and SSCs are double pipe exchangers with slurry inside the central tube and the cooling media (filtrate or relfigerant) in the annular area aroimd the inside tube (pipe). Tubes are t5q)ically stacked in groups of 8, 10 or 12 and internal flow may be in parallel or series. Internal pipe diameters are t3 ically 6, 8, 10, 12 inches. 

Borsig GmbH and Armstrong International, Inc. are the leading designers of scraper internals. Both use blades that are softer than the pipe, so that the blades will wear down first. Each uses a spring to apply pressure on the scraper blade to push it against the tube wall so that it scrapes the wax off the wall as the internal shaft is turned. 

Both designs attempt to accomplish wax removal from the wall by scraping while maximizing open cross sectional area in the tube. Wax will tend to accumulate on cold internals like the Spider bearing and other surfaces affixed to the shaft. The build up of wax will increase the pressure drop. When pressure drop becomes limiting, the equipment will either be taken offline and cleaned with hot solvent or cleaned on-line. Various methods have evolved to optimize the cleaning with minimum impact on the process. 

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In one continuous method (17), the waxy oil charge—for example, in the case of a topped crude—is diluted with an equal volume of propane and the mixture is chilled to about —25° F. by means of heat exchange with cold filtrate in double-pipe scraped-surface equipment. This chilled mixture is then mixed with propane which has been chilled by autorefrigeration to —45° F. to bring the ratio of propane to oil to about 5 to 1. Ninety per cent of the refrigeration required is accomplished in this manner the remaining 10% is obtained by evaporating propane from the diluted mixture. 

Technical and product information is also available from the three main suppliers of scraped-surface equipment in Europe, namely Gerstenberg and Agger (Denmark), Schroder (Germany) and Johnson (UK) who fabricate Perfector, Kombinator and Votator equipment, respectively. Numerous patents on fat spreads have also been published, but their review is outside the scope of this chapter. 

Excessive water may drop out of solution and form ice in the slurry or on the inside of the scraped surface equipment. It may also flow downstream to the filters where it may be captured in the wax cake or on the filter cloth. 

Figure 29. Scraped Surface Equipment (photos reprinted courtesy Borsig )...

The scraped-surface ciystallizer provides an effective and inexpensive method of producing slurry in equipment which does not require expensive installation or supporting struc tures. 

Brodie Crystallizer-Purifier [Fig. 1414(c)]. This equipment combines a horizontal scraped surface crystallizer with a vertical purifying section. The capacity and performance of the purifier... 

The high-pressure pumps are normally supplied with a pressure relief valve and associated product piping to protect the scraped-surface heat exchanger equipment downstream and the pump itself, should a blockage of the production line occur. 

Brodie Crystallizer-Purifier [Fig, 16.15(c)], This equipment combines a horizontal scraped surface crystallizer with a vertical purifying section. The capacity and performance of the purifier depends strongly on the sizes of the crystals that enter that zone. In order to ensure adequate crystal size, residence times in the crystallizing zone as long as 24 hr may be needed. No data of... 

Double-Pipe Scraped-Surface Crystallizer This type of equipment consists of a double-pipe heat exchanger with an internal agitator fitted with spring-loaded scrapers that wipe the wall of the inner pipe. 

Fmit) preparations are manufactured by either continuous systems (e.g. Ohmic heating, tube or plate heat exchanger, scraped surface heat exchanger) batch or microwave systems. The plant environment, the plant itself and the C.I.P. (Cleaning in Place) equipment are subjected to an intensive quality management. 

Scraped surface heat exchanger A class of equipment designed to remove heat from viscous liquids. Scraped surface heat exchangers normally consist of a cylindrical barrel, the outside of which is cooled. The inside of the barrel is scraped to remove solidifying material and thereby increase the heat flow. 

In another method of classification of crystallizers, the equipment is classified according to the method of suspending the growing product crystals. Examples are crystallizers where the suspension is agitated in a tank, is circulated by a heat exchanger, or is circulated in a scraped surface exchanger. 

Fig. 8.15. Cut-away drawing of a Votator scrape-surface heat exchange unit used for making plasticized shortening. By permission of Cherry-Burrell Process Equipment A United Dominion Company, Louisville, KY.)...

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