Double pipe crystallizer

Figure 38. Front elevation of a double-pipe crystallizer.

Figure 39. Vertical cross section of a double-pipe crystallizer showing scraper agitator, adjustable support of shaft bearing, and baffles in the coolitig jacket.

Selection Double-pipe crystallizer, nominal 8 in. diameter. To consist of 4 sections each 20 ft long each section shall be jacketed for 18 ft of its length. Effective heat-transfer area will be 153 ft total volume 24.9 ft process material retention time 3.33 hr. 

No. n 2uired One unit Type Double-pipe crystallizer... 

There are two commercial solvent crystaUi2ation processes. The Emersol Process, patented in 1942 by Emery Industries, uses methanol as solvent and the Armour-Texaco Process, patented in 1948, uses acetone as solvent. The fatty acids to be separated are dissolved in the solvent and cooled, usually in a double-pipe chiller. Internal scrapers rotating at low rpm remove the crystals from the chilled surface. The slurry is then separated by means of a rotary vacuum filter. The filter cake is sprayed with cold solvent to remove free Hquid acids, and the solvents are removed by flash evaporation and steam stripping and recovered for reuse (10). 

Double-Pipe Scrapea-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. The cooling hquid passes between the pipes, this annulus being dimensioned to permit reasonable shell-side velocities. The scrapers prevent the buildup of solids and maintain a good film coefficient of heat transfer. The equipment can be operated in a continuous or in a recirculating batch manner. 

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. 

The organic layer is to be neutralized with 1 per cent HaOH solution and then concentrated to 56 per cent BHC by evaporation of some of the volatile ingredients in a flash still. The overhead from this still is largely benzene and monochlor benzene which are separated by fractionational distillation. The benzene is recycled and the monochlor benzene is to be sold as a by-product. A large fraction of the benzene hexachloride is to be crystallized out in a double-pipe chiller" and the crystals removed by means of a continuous centrifuge. The filtrate is to be recycled to a flash still for reconcentration. 

A robust mechanical unit that can cope with most encrustation problems is the scraped-surface heat exchanger, often referred to as a scraped-surface chiller when used in crystallization operations. The unit is essentially a double-pipe heat exchanger fitted with an internal scraping device to keep the heat transfer... 

High heat transfer coefficients, up to 1 kW m K, and hence high production rates, are obtainable with double-pipe, scraped-surface heat exchangers. Although mainly employed in the crystallization of fats, waxes and other organic melts (section 8.2.2) and in freeze concentration processes (section 8.4.7), scraped-surface chillers have occasionally been employed for crystallization from solution. Because of the high turbulence and surface scraping action, however, the size of crystal produced is extremely small. 

In the double-pipe scraped surface crystallizer, cooling water passes in the annular space. An internal agitator is fitted with spring-loaded scrapers that wipe the wall and provide good heat-transfer coefficients. This type is called a votator and is used in crystallizing ice cream and plasticizing margarine. A sketch is shown in Fig. 4.13-2. 

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