DD201019A1 - METHOD FOR TEMPERATING SODIUM CYANIDE CRYSTAL POWDER - Google Patents

Abstract

The invention relates to a process for the continuous dewatering of NaCN crystal pulp at solids contents greater than 20%. In this case, a low residual moisture in the centrifuge stage and the advantages of a continuous procedure, a reduction in energy and operating costs to be achieved. According to the invention, a NaCN crystal slurry is fed to a multi-stage Schuben centrifuge and reduced to a moisture content of 3-6% water. The centrifuged 4-6% solids mother liquor is placed in a settler which separates them into a crystal break phase at a temperature of 318-333K. The two phases are returned to the process. The invention finds application in processes for the production of NaCN. Fig. 1

Description

Title of the invention Process for dewatering NaCN crystal pulp

Int. Cl. C 01 c 3/10

Field of application of the invention

The invention relates to a process for the continuous dewatering of NaCN crystal pulp with pesticide contents greater than 20 <$>, -

Characteristic of the known technical solutions

Most known processes for the production of JSaCET salt are divided into the neutralization stage in which HCF and sodium hydroxide solution react with one another, the crystallization, the dewatering mostly carried out as centrifugation but also as filtration, and the drying. The separated in the dewatering step mother liquor with a ca 3-5 fo above the soluble NaCN content is usually attributed to the neutralization in the process.

H ¹ Ur the dewatering step are known both centrifuges and filters are used. In order to keep the content of impurities after the subsequent drying process as small as possible and to avoid interference due to caking product, a residual moisture content of max. 6.5 #> can be achieved.

The lower the moisture content after the dehydration stage, the less contaminants

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# 973346

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Katronlauge, sodium formate and carbonate are in the final product. For this purpose, filter centrifuges are used. The small particle sizes of NaCN with a spectrum of. 10 to 80 μm, however, hitherto only the use of discontinuous filtration centrifuges, for example peeler centrifuges, whereby the filtering effect is achieved by a filter aid layer forming on the filtering device (sieve). Both centrifuges with horizontal and vertical drum are known. The emptying is done either manually or by Ausschälvorrichtungen.

This discontinuous procedure has significant disadvantages compared to a desired continuous. The large number of startup and shutdown requires a lot of energy and leads to increased wear of the machines. Furthermore, in the case of discontinuous processes, a higher filter cake layer is used, whereby a greater expenditure of energy is necessary in order to spin off the same volume of mother liquor and to achieve low best moisture values. Using a modern continuous drying technology also requires a complicated intermediate storage of centrifuge wet NaCN salt (.3.5 - 7 ⁰ Io water), since the salt at these moisture values and storage is prone to caking and lumping.

DE-OS 1 592 329 mentions the use of a rotary filter for the dehydration of NaCIT, the filter not forming part of the invention. The use of a vacuum drum filter is described in DE-PS 1 150 367, wherein the filter even

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if not part of the invention. With this method, "residual moisture values of 11-13.5 # water are achieved even under the best technical working conditions, but this alkali cyanide salt is produced by the barrel process.

"Filters have the disadvantage that they have a much lower separation effect on the residual moisture than filtration centrifuges.With filters, residual moisture values of less than 11 $ can not be achieved with NaCN, but this leads to the caking of the moist salt, the formation of lumps and blockages of Lines and NaCN drying devices of the known type.

The end product quality, i. the content of impurities is extremely high. As is known, it is also energetically more favorable to evaporate the water in the crystallizer than in the dryer.

Object of the invention

The aim of the invention is to develop a process for the continuous dewatering of NaCN crystal pulp, in which a low residual moisture in the centrifuge stage and the advantages of continuous procedure in terms of reducing the energy and operating costs are achieved, and allows a continuous continuous NaCN production process ,

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Explanation of the essence of the invention;

The object of the invention is to combine the advantages of centrifugation in the case of UaCT dewatering and the advantages of a continuous procedure.

According to the invention this is achieved in that a NaCli crystal slurry is fed with at least 20 1o plague a centrifuge with horizontal screen drum in which pushed by periodic horizontal movement of a piston of the forming filter cake on the sieve to -zum the free end of the drum, as well as the thrown off Mother liquor freed in a subsequent settling of most of the beaten pesticide in the form of a Kristallbreies and this in turn is supplied to the centrifuge. In the literature, this type of centrifuge is referred to as a pusher centrifuge.

Due to the small grain size of UaCN crystals, special demands are placed on the pusher centrifuge with regard to filter gap widths, drum length and ejection force, which are critically dependent on the particle size achieved in the crystallizer. It is expedient to use multistage pusher centrifuges.

After the centrifuge less than 6.5% of the final moisture content of HaCN salt, acceleration factors (ratio of centrifugal acceleration to gravitational acceleration) of greater than 650 g are necessary. With increasing acceleration factor and the Eestfeuchten be lower, but a threshold value of about 3.5% Faß can hardly be undershot.

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The small particle sizes of the NaCF crystals cause a breakdown of up to 5 % solids in the mother liquor during centrifugation.) This solids content, which is returned to the HaCli production process with the mother liquor and again passes through the stages neutralization and crystallization, leads to capacity losses and may cause interference in the crystallization process, thereby creating crystals at up to 30 <fo smaller grain size. Srfindungsgemäß this is prevented by the mother liquor of a depositing device is supplied, and solids is separated into a Kristallbreiphase and a. mother liquor phase with a maximum of 1 ⁰ Io. the settler can be designed both as a settling vessel and as a hydrocyclone or the like.

The clarified mother liquor phase is admixed in a known manner of the neutralization stage, while the crystal slurry is added to the feed of the centrifuge. It was surprisingly found that the purged in the centrifuge, and sedimented in the settler pesticide has a grain size corresponding to the average of the centrifuge feed, whereby a gradual .Steigerung of the solids content in the mother liquor of the centrifuge can be excluded.

With relatively coarse-grained crystal pulp of 50-80 / im, if a drop in capacity is taken into account in the neutralization and crystallization part, it is possible to dispense with a settling device. During the centrifuging and settling process may

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the temperature does not fall below 308 K and should preferably be at least 318 K - 333 K. The advantage of the process according to the invention lies in the use of the continuous mode of operation for the dehydration stage, whereby the effectiveness of this process stage is significantly increased. This is expressed in a reduction in the energy and operating costs, a possible by reducing the mother liquor cycle capacity increase of the crystallization stage and a reduction in susceptibility. Since, when using a continuous centrifuge, the rinsing waters arising from time to time of the sieves are much smaller in quantity than in discontinuous centrifuges, costs are likewise saved here. , "This manifests itself either in low effluent decontamination costs or, if the rinse waters remain in the process, in lesser amounts of water that must be vaporized.

The reduction of the susceptibility is shown e'imal in the crystallization stage, in which by the removal of the solid in the settling made uniformly large grain size can be achieved, and · the second in the absence of the intermediate storage of. centrifuge wet PTaCiT salt, which is necessary when using a discontinuous drying process and is very complicated and prone to failure. '

The continuous centrifugation allows for the first time fully continuous Mach ^- -Herstellungsverfahren in which the steps are carried out neutralization, crystallization, centrifugation and drying in mutually separated devices.

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F ühruri gsbe ispie I

The method according to the invention and a device which is preferably suitable for its realization are described here "and are shown in FIG.

Sine formed in ETeutralisator 1 from sodium hydroxide solution and hydrogen cyanide STaCN solution is evaporated in a crystallizer 2 to about 35% pesticide-containing Kristallbrei 6. 1.5 m / h Kristallbrei 6 with a temperature of 333. K are fed to a two-stage pusher centrifuge 3. The speed of the centrifuge corresponds to a ratio of centrifugal to gravitational acceleration of 890. Here, the crystal slurry 6 is divided into a STaGN salt 7 with 4.5% residual moisture and a mother liquor 7, which still contains 4 % solids. The FaCIT salt 7 is subsequently dried in a dryer 5, for example a vortex dryer or high-frequency dryer.

The mother liquor 8 with about 328 K arrives in a

Settling vessel 4 with a clarifying area of 6 m. The settling vessel is equipped with baffles to calm the flow. The 2 longer side walls are merged into a gutter, in which a transport screw with low speed conveys the collecting crystal pulp for discharge. The crystal slurry 9 is returned to the centrifuge feed 6, while the clarified liquid phase with about 0.5% of the plague back through the Feutralisationsstufe back into the process.

Claims (1)

235 08 6 invention claim A process for the continuous dewatering of a UaCH crystal slurry of more than $ 20, preferably 30-40 %, of a pulp, characterized in that "the" crystal pulp is fed to a continuous centrifuge, preferably a multi-stage pusher (3), having a ratio of from centrifugal acceleration to gravitational acceleration of greater than 650, preferably 750-1000, operates, wherein the moisture content of NaCT SaI ζ es it (7) is reduced to 3 - 6 ⁰ Io water, and the centrifuged mother liquor (8) 4-6 ° h of solids in a settler (4) is added which this in · a- Kristallbreiphase (9) and a liquid phase (10) at a temperature of 318 - separates 333 K, the crystal (9) is recycled to the centrifuge feed, and the liquid phase clarified to 0.1 - 1% pesticide (10) one before the dewatering stage. , Process stage of the HaOT production process is mixed. £ 9 - 235 08 6 Expire after. Point 1, characterized in that in coarse-grained ITaClT -Krisialibrei (6) of 50 - 80 Aim grain sizes, the abseiling device can be bypassed via the line (11). , Dazu.1 sheet drawing