Vacuum cooling crystallizer

Chemicals, e.g., fumaric acid, which show only a moderate increase in solubility with increasing temperature. A combination of evaporation and cooling may be used to produee the supersaturated solution. Depending upon the )deld required, this operation may be carried out in either a vacuum cooling crystallizer or an evaporative crystallizer (see Fig. 5). 

The elements of design for a vacuum cooling crystallizer are the same as for the evaporative crystallizer except a heat exchanger is not required. The operating features are also similar. In this case, the heat for evaporation is supplied by the sensible heat of the feed and the heat of crystallization. 

Mother liquor is circulated, with or without crystal contem, through a heat exchanger where heat is added or removed from the system. (Adiabsffic vacuum cooling crystallizers do not require this step.)... 

The solid wasfe processing systems include the radwaste volume reduction/snlidifiratinn system and the radwaste incinerator. The systems reduce in volume and solidify low-level radioactive planf wasfes to prepare them for safe storage and/or disposal. The radwaste volume reduction/solidification system employs a vacuum-cooled crystallization process to effect volume reduction, coupled with high speed, higher shear mixing of the waste with cement to achieve solidification. For combustible plant wastes, the radwaste incinerator utilizes a controlled air incineration process. 

Figure 11.3 shows the functional principle of this control method, using vacuum cooling crystallization as an example. Figure 11.3a shows a sketch of a FC crystallizer used for vacuum cooling crystallization. This is the simplest form of basic... 

Figure 11.12 shows the different designs of the simple FC group depending on the crystallization process such FC crystallizers can be used for (vacuum cooling crystallization or vacuum evaporative crystallization), one can find the typical FC , and with and without a tube and shell heat exchanger. These are the simple stirred tank 0, the draft tube (DT) crystallizer (2), and the FC crystallizer ((J), ). 

The suspension is recirculated by stirrers or circulation pumps and the supersaturation created within the suspension. The stirred tank (I) is suitable for vacuum cooling crystallization. The disadvantage of this design is the absence of directed flow recirculation, as only a simple, but inexpensive stirrer is used. This means that the maximum supersaturation is not fully under control, which is why this design should only be used for systems with large metastable zones. 

Use of the FC crystallizer is preferred for evaporative crystallization. The directed and controlled recirculation is carried out with an axial flow pump (elbow-type). This design can also be used for vacuum cooling crystallization, so that then the heat exchanger is no longer required ((J)). The use of this version is recommended if due to the lack of barometric cover in the draft tube crystallizer the incoming solution would boil out of the feed-in point. 

Figure 11.14 DTB crystallizers in the potash industries (vacuum cooling crystallization).

Unlike vacuum cooling crystallization, this method does not depend on the concentration and temperature of the feed solution. Additional heat can be introduced by means of a heat exchanger and thus undersaturated solutions treated in a crystallizer. Furthermore, the concentration factor of the mother liquor can be selected that is, the quantity of solvent to be evaporated is adjustable to the requirements of the mass balance. The mass balance is based on the corresponding... 

Brine containing the dissolved sodium sulfate is separated from the salt crystals in a cyclone. The underflow returns to the leaching tank. The overflow is collected in the feed tank for the Glauber s salt crystallizer. Sodium sulfate is crystallized from the liquor in a continuous vacuum cooled crystallizer. 

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