DISCONTINUOUS CRYSTALLIZATION UNIT FOR THE PRODUCTION OF BALL-SHAPED CRYSTALS

Abstract

The invention introduces a discontinuous crystallization unit for the production of ball-shaped crystals comprising a crystallizer (1) that consists of a metallic cylindrical vessel with its inner surface of a hard material, with an oval or circular cross-section with a conical or vaulted bottom (12), fitted along its length with a duplicator (4) for cooling of the solution and/or suspension of the solution and crystals and a high-speed agitator (8) of a hard material with a drive (9) enabling speed control and thus the rate of the impact of the mechanical action of the agitator on roundness of crystals inside the vessel together with the inner surface of the vessel containing at least 2 baffles (5) of a hard material while the vessel is fitted with at least 1 orifice (10) at the top that at least independent branch of the circulation circuit (11) is connected to from the outside for the inlet of a heated solution and/or heated suspension of the solution and crystals by means of at least 1 circulation pump (2) and through at least 1 heat exchanger (3) and together with the duplicator (4) ensuring controlled periodic changes of temperatures of the crystal suspension around the cooling curve while an interconnection (13) pipeline is connected to the bottom (12) of the crystallizer (1) vessel that is connected to at least one branch of the circulation circuit (11).

Claims

1. A discontinuous crystallization unit for the production of ball-shaped crystals, characterized in that it comprises a crystallizer (1) that consists of a metallic cylindrical vessel with its inner surface of a hard material, with an oval or circular cross-section with a conical or vaulted bottom (12), fitted along its length with a duplicator (4) for cooling of the solution and/or suspension of the solution and crystals and a high-speed agitator (8) of a hard material with a drive (9) enabling speed control and thus the rate of the impact of the mechanical action of the agitator on roundness of crystals inside the vessel together with the inner surface of the vessel containing at least 2 baffles (5) of a hard material while the vessel is fitted with at least 1 orifice (10) at the top that at least 1 independent branch of the circulation circuit (11) is connected to from the outside for the inlet of a heated solution and/or heated suspension of the solution and crystals by means of at least 1 circulation pump (2) and through at least 1 heat exchanger (3) and together with the duplicator (4) ensuring controlled periodic changes of temperatures of the crystal suspension around the cooling curve while an interconnection (13) pipeline is connected to the bottom (12) of the crystallizer (1) vessel that is connected to at least one branch of the circulation circuit (11).

2. The discontinuous crystallization unit in accordance with claim 1, characterized in that the interconnection pipeline (13) before the connection to the circulation circuit branch (11) contains a branching element (14) with a branching pipe (6) with stop valve (7), preferably automatic for discharge crystals for further processing.

3. The discontinuous crystallization unit in accordance with claim 2, characterized in that the branching element (14) is a T-piece and that the stop valve (7) is a valve, cock, flap valve or slide valve.

4. The discontinuous crystallization unit in accordance with claim 1, characterized in that the hard material is stainless steel, enameled metal or glass.

5. The discontinuous crystallization unit in accordance with claim 1 or claim 4, characterized in that the hard material is a material with a hardness of at least 120 HB, preferably at least 200 HB.

6. The discontinuous crystallization unit in accordance with claim 1, characterized in that the exchanger(s) is(are) a tubular heat exchanger(s).

7. The discontinuous crystallization unit in accordance with claim 1, characterized in that the circulation pump(s) is(are) a centrifugal pump(s) with an open impeller of a hard material.

8. The discontinuous crystallization unit in accordance with claim 1, characterized in that the ball-shaped crystals are ammonium perchlorate crystals of a medium size from approx. 100 micrometers to approx. 300 micrometers, preferably approx. 200 micrometers.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0040] FIG. 1is a schematic drawing of the crystallization unit in accordance with the invention with one circulation circuit.

[0041] FIG. 2is a schematic drawing of the crystallization unit in accordance with the invention with two circulation circuits.

[0042] FIG. 3shows round ammonium perchlorate crystals produced by the crystallization unit in accordance with the invention

EXAMPLES

Example 1

[0043] For the production of ball-shaped crystals of ammonium perchlorate a discontinuous crystallization unit has been used that comprised a crystallizer (1) that consisted of a metallic cylindrical vessel of an enameled metal with its inner surface of polished stainless steel, with an oval or circular cross-section with a conical or vaulted bottom (12), fitted along most of its length with a double jacket (4) for cooling of the solution and/or suspension of the solution and crystals and a high-speed agitator (8) of stainless steel with a drive (9) enabling speed control and thus the rate of the impact of the mechanical action of the agitator on roundness of crystals inside the vessel together with the inner surface of the vessel containing 2 baffles (5) of polished stainless steel while the vessel was fitted with 1 orifice (10) at the top that 1 independent circuit of the circulation pipeline (11) was connected to from the outside for the inlet of a heated solution and/or heated suspension of the solution and crystals by means of a circulation centrifugal pump (2) with an open impeller and through a tubular heat exchanger (3) and together with the double jacket (4) ensuring controlled periodic changes of temperatures of the crystal suspension around the cooling curve while an interconnection pipeline (13) was connected to the bottom (12) of the crystallizer (1) vessel that was connected to one circuit of the circulation pipeline (11) as shown in FIG. 1.

[0044] The raw material was rough-grained ammonium perchlorate (APC). It was produced during discontinuous crystallization in a plastic crystallizer fitted with cooling diffusers. APC crystals were separated from the mother liquor (ML) on a process filter and dried with process pressurized air. The moisture content of the crystals varied in the range of 5-10% by weight. Further, ML is used for the preparation of the APC solution, which is removed by filtration after the crystallization process described below.

[0045] 700-1200 kg of rough-grained APC was dissolved in a process filter in 3500-4500 kg of ML, which was preferably heated up by steam using a tubular heat exchanger to a temperature of 50-90 C. This way an APC solution was produced that was saturated at temperatures in the range of 40-60 C. and then was re-pumped to a plastic tank.

[0046] Crystallization was conducted in the crystallizer described above as part of the crystallization unit in accordance with the invention one version of which is schematically illustrated in FIG. 1.

[0047] The APC solution from the plastic tank was pumped to the crystallizer in the quantity of 900-1200 kg. The solution was heated up as necessary in the tubular heat exchangers so that the resulting temperature in the crystallizer could vary in the range of 35-65 C. After filling of the crystallizer 1 the pump 2 was started that ensured the total flow of 30-100 m.sup.3/h of the APC solution and later the APC suspension through the exchanger 3 during the entire crystallization process.

[0048] Then, the agitator 8 was put in operation, the speed of its motor 9 being set with a frequency changer to the value of 60-240 rpm. The agitation also continued throughout the crystallization period.

[0049] Then, cooling of the APC solution followed, when in the first stage the solution was cooled to the initial crystallization temperature at the rate of 40-80 C./h. The initial crystallization temperature was in the range of 30-55 C. From this temperature the cooling rate was reduced to 2-15 C./h and at the same time heating of the solution, later suspension of APC in the exchanger 3 was started to ensure the 0.2-3.5 C. difference between the inlet and outlet APC solution temperature. Steam, water or other heat-carrying media can be used for the heating.

[0050] The crystallization process was completed when the temperature achieved 10-25 C. At this temperature heating of the solution by means of the exchanger 3 was turned off and the circulation pumps 2 and the agitator 8 were switched off.

[0051] The suspension was then pumped with a suitable pump via the interconnection pipeline 13, the T-piece 14 and automatic stop valves 7, which is a closing valve, and the branching pipe 6 for further processing in the process filter. There, ML is separated from APC crystals. Then, crystals are dried by the process pressure filter to the value of 90-98% by weight (related to the total weight with residual water).

[0052] APC crystals whose particle size distribution in accordance with sieve analysis is within the ranges presented in table 1 were prepared in the above mentioned method.

TABLE-US-00001 TABLE 1 Sieve analysis of obtained APC crystals Fraction 0-100 m 100-150 m 150-180 m 180-300 M >300 m Weight 3-10 4-19 12-35 40-75 0-6 %
The size and shape of APC crystals are shown in FIG. 3.

Example 2

[0053] The same discontinuous crystallization unit was used as in Example 1, but it contained 2 circulation circuits 11, 11 for the inlet of the heated solution or heated suspension of solution and crystals with the use of circulation pumps 2, 2 and through heat exchangers 3 3 as shown in FIG. 2.

[0054] This arrangement of the unit made it possible to increase the number of crystallization cycles at the same cooling rate and/or reduce the flow rate in the circulation circuit branch(es). The general APC crystal production process was the same as in Example 1.

[0055] The obtained crystals had a rounder shape; otherwise they exhibited the same purity and particle distribution as compared to Example 1.