DTB crystallizers

FIG. 18-67 Direct-contact-refrigeration crystallizer (DTB type). (Swenson Process Equipment, Inc.)... 

In the growth types of crystallizers, DTB and Oslo-type, these interrelationships have all been taken into account. In the designs intended to produce coarser granularity via the longer retention times, these measures are taken in order to keep the energy input into the suspension smaller than that in the FC crystallizer with its short retention time. For this reason, the crystallizer designs differ from one another mainly with respect to the layout and location of the circulation pumps (whether these are inserted in the suspension or in clarified solution cf. Figure 11.2). 

Figure 3.3 Agitated crystallizers (/) Swenson DTB Draft tube and baffle), (ii) Forced circulation (a) with and (b) without external heat exchange, in) Krystal Oslo a) circulating liquor b) circulating slurry...

The DTB, crystallizer has a relatively slow-speed propeller agitator located within a draft-tube which draws a fine-crystal suspension up to a boiling zone of wide cross-sectional area, as shown in Figure 3.3(i). The fine-crystal magma then passes through an annular zone in which an additional baffle is located. Liquor flow continues upwards at low velocity while crystals settle out and fall to the base of the vessel. Liquor from the external pumped loop provides an up-... 

Figure 9.18 Continuous crystallizers, a) draft-tube and baffle (DTB), (b) single effect forced-circulation evaporative, (c) Oslo or Krystal type after Rohani, 2001)...

In this section the model for a continuous evaporative crystallizer is discussed. The crystallizer is of the draft tube baffled (DTB) type and is equiped with a fines removal system consisting of a large annular zone on the outside of the crystallizer (see Figure 1). In order to vary the dissolved fines flow without changing the cut-size of the fines removal system, the flow in the annular zone is kept constant and the flow in the dissolving system is varied by changing the recycle flow rate. The model assumptions are ... 

Table III. Stationary values of G and for a DTB crystallizer operated with a fines r oval system and a size dependent growth regime. The values are given before and 35000 second after a step in the heat input of the crystallizer from 120 to 170 kW. The simulation has been performed with kOO gridpoints...

All the CSD data examined in this work are those obtained by CEC (Crystal Engineering Corp.) style Krystal-Oslo type crystallizer (Figure 5), except sample no.22 by DTB type crystallizer. Figure 6 and Table III illustrate some examples of... 

The origin of this concept is that the fraction of the total area under a normal distribution curve between the 16 and 84% points is twice the standard deviation. The smaller CV, the more nearly uniform the crystal sizes. Products of DTB crystallizers, for instance, often have CVs of 30-50%. The number is useful as a measure of consistency of operation of a crystallizer. Some details are given by Mullin (1972, pp. 349, 389). 

Natural circulation evaporators like those shown on Figure 8.16 may be equipped for continuous salt removal and thus adapted to crystallization service. For large production rates, however, forced circulation types such as the DTB crystallizer of Figure 16.10(g), with some control of crystal size, are the most often used. The lower limit for economic continuous operation is l-4tons/day of crystals, and the upper limit in a single vessel is 100-300 tons/day, but units in parallel can be used for unlimited capacity. 

A crystal structure determination of [Pd(dtb)2] showed a distorted tetragonal arrangement of sulfur atoms about the palladium atom. The Pd—S distances in the square plane are 2.32-2.34 A, while the Pd—S (apical) distance is 3.46 A, suggesting some interaction. 47 The nickel complex [Ni(dtb)2] can be readily oxidized to [Ni dtbhSj], which was postulated to be a NiIV complex,136 but it is more likely that the complex contains Ni11 with the structure (42).146... 

In comparison with existing crystallizers, including DTB, DP and Standard-Messo... 

Special devices for classification of crystals may be used in some applications. Figure 14 shows a draft-tube-baffle (DTB) crystallizer that is designed to provide preferential removal of both fines and classified product. As shown, feed is introduced to the fines circulation line so that any nuclei formed upon introduction of the feed can be dissolved as the stream flows through the fines-dissolution heat exchanger. The contents of the crystallizer are mixed by the impeller, which forces the slurry to flow in the indicated direction. A quiescent zone is formed between the... 

In DTB and DT crystallizers the circulation rate achieved is generally much greater than that available in a similar forced-circulation crystallizer. The equipment therefore finds application when it is necessary to circulate large quantities of slurry to minimize supersaturation levels within the equipment. In general, tliis approach is required to obtain long operating cycles with material capable of growing on... 

OSLO crystallizers because MSMPR crystallizers operate with much higher slurry densities and lower levels of supersaturation. Forced circulation and DTB crystallizers are examples of MSMPR crystallizers. An OSLO crystallizer operating at high slurry densities with the slurry circulated to the vaporizer will perform like an MSMPR crystallizer. 

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