CS204499B1 - Device for cleaning the sublimed substances - Google Patents

Description

The invention relates to an apparatus for the continuous purification of sublimable substances.

Various variants of sublimation purification of substances are described in the patent literature. The sublimation of the substances is carried out either in a stream of hot carrier gas or in a fluidized bed with inert solid particles at a temperature sufficient to evaporate the substances and atmospheric pressure (U.S. Patent 3,526,658) or reduced (U.S. Patent 3,113,140).

The transport of the bulk material into the hot fluidized bed is generally associated with considerable difficulties.

In the dosing container, the loose substance forms vaults, which cause irregular dosing or its interruption. Furthermore, when entering the hot fluidized bed, some of the sublimed substances melt and stick to the walls of the dispensing device, which can lead to clogging of the inlet and interruption of dosing. In order to ensure continuous dosing by a screw conveyor, inert solid particles are sometimes added to the sublimation purification raw material. After sublimation of the substance, a portion of these particles is then removed from the fluidized bed of the sublimator and, after cooling, mixed again with another sublimed feedstock (U.S. Pat. No. 3,113,140). The disadvantage of this method is the transport of a relatively large proportion of inert particles, the need for further operation - mixing these particles with the raw material, heat losses, possible failure of the equipment with hard particles. According to another method, the conveying of the sublimed feedstock by means of a rotating roller with vanes on the housing is combined with pneumatic conveying by means of nozzles located in the mouth of the dispenser (German Patent 1 091 542). This process requires a considerable amount of inert gas for pneumatic transport, which in addition causes a large dilution of the vapor-gas mixture.

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The vapor mixture of the sublimed feedstock and carrier gas from the sublimator is then typically passed through a filter to collect non-volatile particles entrained in the steam gas mixture and further into a condenser (or crystallizer). To enable a continuous sublimation process, vapor condensation devices of sublimed substances are suitable, which prevent their condensation on the walls of the device and condensate respectively crystallize in the volume of the steam-gas mixture. Among the patented devices are: heating the walls of the device above the dew point of the vapor-gas mixture (U.S. Pat. No. 3,362,898, NSR Auslegeschrift 1,108,663), and the device whose walls are wetted by a continuous layer of liquid according to U.S. Pat. No. 154 907, which results in a suspension of the sublimed substance in the coolant fluid and the device according to U.S. Pat. No. 161,505, in which the crystallization is carried out in the space defined by the porous walls through which the auxiliary gas passes and which prevents access of the sublimed substance to the porous walls. No crystal growth rate is regulated in any of these devices. In all cases, the vapor-gas mixture cools rapidly, thereby causing a large supersaturation of the sublimed substance vapor and the formation of large amounts of small crystals. These have a low bulk density, which is disadvantageous for transport and storage and are also less pure than larger crystals.

The disadvantages of the prior art are eliminated by the device for continuous purification of the sub-limiting substances of the present invention. SUMMARY OF THE INVENTION The present invention is based on a dispensing system which continuously transports bulk sublimable substances to be cleaned into a sublimator with a layer of solid nonvolatile particles deposited on a grate and fluidized with a gas heated in a preheater. The dispensing system consists of a dispenser of feedstock for sublimation cleaning, in which at least one bar is mounted in the vertical direction at a distance of 1 to 10 mm from the container wall, ending at a height of 1 to 10 mm above the pair of conveying screws. continuously cuts the column of bulk material from its walls along its entire height, which reliably eliminates the vaulting of the material and ensures its continuous feeding into the pair of screws. The worm housing is housed in a housing through which coolant flows. The screw threads are in focus and closely interlocked and convey continuously the bulk material into the hot fluidized bed in the sublimator. The filter is, for example, a gas-permeable ceramic tube or a sleeve of heat-resistant textile material stretched on a wire basket placed in a jacket heated to a temperature above the dew point of the steam-gas mixture. The filter retains non-volatile impurities entrained by the steam-gas mixture. In special cases, with high demands on product purity, the use of an electrostatic filter is preferred. Downstream of the filter, there is an additional gas supply in the pipeline to adjust the vapor concentration of the sublimed substance in the carrier gas.

In the gas distributor, the vapor-gas mixture is mixed with the additional gas and fed at a uniform rate to the nucleation chamber. In the manifold there is a manifold ring with steam-gas mixture feed openings distributed around its circumference. The bottom of the manifold is perforated and a layer of ceramic or metal bodies is deposited thereon to ensure good heat distribution and uniform distribution of the vapor-gas mixture velocity over the cross section of the nucleation chamber.

The nucleation chamber is formed by a tempered jacket with auxiliary gas inlets, in which a cylinder of gas-permeable material is placed, into which one or more nozzles for the supply of cooling fluid reach. At the same time as the coolant is supplied to the steam-gas mixture, it is gas-permeable3

204,499 mi transparently inert gas heated to the nucleation temperature of the sublimed substance. A temperature-regulated amount of crystalline nuclei is formed in the nucleation chamber, from which crystals grow in the crystallizer by further cooling the steam-gas mixture.

The advantage of the device described above is, in particular, that it allows a continuous process of sublimation cleaning and its regulation as a whole. Its main advantages over the prior art devices are that it eliminates vaulting in the dispenser, continuously feeds the sublimed feedstock into the hot fluidized bed without sticking it to the walls of the device, and does not add inert solid particles to the feedstock or transport it pneumatically with a large amount of inert gas. Other important advantages of the apparatus are the possibility of controlling the growth rate and crystal size in a nucleation chamber equipped with a gas distributor which ensures uniform distribution of the steam-gas mixture throughout its cross-section and in a gas-permeable wall crystallizer with controlled cooling of the mixture by finely atomized liquid.

By way of example, a device is shown schematically in the attached figure. The dispenser 1 is filled with a bulk material to be sublimated. A layer of practically spherical corundum ceramic particles in the sublimator 8 is heated to the sublimation temperature and fluidized with nitrogen heated in the preheater 6. At the same time, a strong stream of water is fed to the sheath 5. After reaching the sublimation temperature in the fluidic layer The dosing of the bulk material into the hot fluidized bed is regular throughout the experiment for 8 hours. The dosing amount is controlled by varying the speed of the pair of screws. The sublimated vapor / nitrogen mixture formed in the sublimator passes through a filter 10 and a distributor 12 to the nucleation chamber 14. Simultaneously, heated nitrogen is supplied to the nucleation chamber 14 through the inlet 15 and the steam-gas mixture is lowered by a small amount of water mist. The inlets 20 and 25 are simultaneously supplied with air, heated in different sections to different temperatures, and water is sprayed through the nozzles 21 in the crystallizer 18. An uncondensed portion of the vapor-gas mixture is passed through the filter assembly 23 and the crystalline product is discharged from the sump 24 via a conveyor 26.

When the steam-gas mixture in the nucleation chamber 14 is partially cooled by the water mist supplied through the nozzle 17, the diameter of the product particles is 20 to 50% greater than when the water mist is cut off.

Claims (4)

SUBJECT OF THE INVENTION 1. A device for continuous cleaning of sublimable substances consisting of a dispenser of loose sublimable substances to be cleaned, a pair of screws with a tempered jacket, a carrier gas preheater, a carrier gas supply line, a sublimator with a layer of fluidized non-volatile particles deposited on the grate separating the non-volatile impurities entrained in the steam-gas mixture from the sublimator, supplying additional gas to adjust the concentration of the steam-gas mixture from the sublimator, a gas distributor, a nucleation chamber for preparing crystalline nucleation substances, tempered jacket crystallizer. cooling fluid4 294 499 tiny, a gas-permeable wall located inside the tempered jacket, a set of filters to remove the non-condensed portion of the steam-gas mixture, a product sump with dry gas inlets, and a product conveyor from the crystallizer. 2) mounted at least one bar (3) vertically at a distance of 1 to 10 mm from the inner wall of the container (1) ending at a height of 1 to 10 mm above a pair of worms (4) with threads interlocking in a tempered jacket ( 5) opening in a sublimator (8) with a layer of solid non-volatile particles connected through a filter (10) to a gas distributor (12), a nucleation chamber (14) and a crystallizer (18) with nozzles (21). 2. Apparatus according to claim 1, characterized in that in the gas distributor (12) there is a distributor ring (13) with openings for the vapor-gas mixture distributed around its periphery and a layer of ceramic or metal bodies is placed on the perforated distributor. Device according to Claims 1 and 2, characterized in that at least one auxiliary gas inlet (15) is arranged in the tempered jacket of the nucleation chamber (14) and inside the jacket there is a cylinder (16) of gas permeable material into which at least one nozzle ( 17) for coolant supply. Device according to Claims 1 to 3, characterized in that the nozzles (17) and (21) are heated externally by resistance heating and a hot gas stream.