RU2117630C1 - Method of dehydrating magnesium chloride solutions - Google Patents

Abstract

FIELD: technology of dehydration of magnesium chloride solutions. SUBSTANCE: claimed method comprises dehydrating Mg Cl₂ solution is single chamber fluidized bed apparatus in which original solution is sprayed in bed through pneumatic nozzles at gas rate in bed of 2.0-3.0 m/s. In this case, granulometric composition of dehydrated product is regulated by degree of spraying, and number of nozzles should be at least 2 by 5 square m of gas distribution lattice. EFFECT: better guality of the resulting products and improved properties thereof. 4 ex, 2 tbl

Description

 The invention relates to techniques for dehydration of alkaline earth metal chloride solutions. Known methods of dehydration in the apparatus of the spray-boiling layer - RKGS (AS USSR N 218135, class C 25 C 3/04, 1967).

 The method turned out to be difficult, because when it is implemented under industrial conditions, the walls of the apparatus and gas treatment paths are overgrown with dehydrated magnesium chloride, uncontrolled growth of granules with the formation of cakes and lumps in the furnace, as well as the removal of a finely divided dry product from the apparatus, which is difficult to realize.

 A known method of heat treatment of sintering materials, for example chloromagnesium raw materials in a fluidized bed, in accordance with which to prevent sintering of the material, the gas distribution grill is cooled (A.S. USSR N 784386, class C 25 C 3/04, 1979).

 The method is characterized by the complexity of the design of the fluidized bed apparatus and requires fine adjustment of the temperature regime in the process of dehydration of the material. Moreover, as our studies have shown, does not exclude the enlargement of the material during its dehydration with the formation of lumps and cakes. Probably, therefore, in the examples of the method, the dehydration mode of magnesium chloride solutions is not given without the simultaneous supply of bulk materials, such as carnallite.

 A known method of dehydration of solutions of magnesium chloride is the prototype (a. With. The USSR N 268396, class C 01 F 5/34, 10.04.70).

In accordance with the well-known method, dehydration of magnesium chloride solutions is carried out at a gas velocity in the layer of 3.5-4.0 m / s with the addition of 100-500 g of amines per ton of Mg Cl ₂ • 2H ₂ O in the solution, which is added to prevent the formation of layer of speck and lumps.

 The method is difficult because involves the use of toxic amines, which, when dehydrated, do not decompose and contaminate commercial products.

 Adopted in accordance with the known method, the relatively high speed of gases in the layer leads to the removal of a significant amount of fine fractions of the product, the addition of which to the main product reduces its consumer properties. In addition, loads on blowing equipment, smoke exhausters and gas cleaning paths are increasing.

 The invention allows to simplify the process and improve the quality of the resulting product by improving its physical and mechanical properties.

This is achieved by the fact that, in contrast to the known method, including dehydration of solutions in a single-chamber apparatus of a fluidized bed at a gas velocity in the layer of 3.5 - 4.0 m / s with the addition of amines in the initial solution, according to the proposed method, the initial solution is sprayed in a fluidized bed through pneumatic nozzles at a gas velocity in the layer of 2.0 - 3.0 m / s, while the degree of atomization controls the particle size distribution of the dehydrated product, and the number of nozzles should be at least 2 per 5 m ^{2 of the} grate.

 The essence of the method is as follows.

 In contrast to the known method, where the dehydration of aqueous solutions of magnesium chloride is carried out after adding amines at a gas velocity in the layer of 3.5-4.0 m / s, according to the proposed method, amines are not added to the initial solution, and the gas velocity in the layer is maintained at the level of 2.0 - 3.0 m / s, depending on the desired particle size distribution of the target product. As our studies showed, at a gas velocity of less than 2 m / s, the intensity of the "boiling" of the material sharply decreases and the formation of stagnant zones and cakes was observed on the distribution grid.

 When the gas velocity in the layer is more than 3 m / s, as proposed in the known method, the product of the class less than 1 mm is removed from the drying zone. As a result, without the addition of amines, the stabilization of the particle size distribution of the fluidized bed due to the removal of particle growth centers is disturbed, the average particle size distribution of the particles is constantly growing, the "boiling" of the layer damps, which ultimately leads to the formation of lumps, cakes, the lattice is melted and the furnace stops.

 In the table. 1 shows data on the dehydration of a solution of magnesium chloride at a gas velocity in the layer in the range of 1.5 - 3.5 m / s.

 Measurements were made at steady state after 12 hours of continuous operation of the apparatus.

 However, in regime 1, they worked for no more than 4 hours, since the intensity of the “boiling” of the layer decreased, and when the product was unloaded from the furnace, material sticking was observed on the grate. In mode 5, they also worked for no more than 5 hours in connection with the continuous strengthening of particles, while in the boundary layer and on the lattice, an accumulation of particles larger than 15 mm and their melting on the lattice were observed.

 In mode 5, an increased removal of fine fractions of the dehydrated product into the gas purification path was also observed.

Another difference of our proposed method is the spraying of an initial solution of magnesium chloride in a fluidized bed through pneumatic nozzles, while the granulometric composition of the dehydrated product is regulated by the degree of atomization, and the number of nozzles must be at least 2 per 5 m ^{2 of the} gas distribution grid.

 Our studies have shown that, along with the speed of gases in the layer, the degree of dispersion of the initial solution in the layer also has a large effect on the growth of particles formed during the dehydration of magnesium chloride solutions. During the tests, mechanical and pneumatic nozzles were tested, while using the mechanical nozzles it was not possible to carry out continuous operation of the fluidized bed furnace due to the build-up of “icing” on the nozzles and the inhomogeneity of particles in the spray zone.

When using pneumatic nozzles, which are a nozzle with the supply of air around its circumference under pressure into the annular gap, it was possible to obtain a uniform spray pattern of the initial solution. In this case, the degree of atomization is determined at a constant flow rate of the supplied solution by the air flow rate in the annular gap, which is reliably regulated by the air pressure in the manifold. Studies have also shown that when spraying a solution in industrial furnaces with a grating surface of more than 2.5 m ² it is impossible to supply the entire solution through one nozzle, because this causes the formation of speck and lumps in the layer. In this regard, it is necessary to install several nozzles above the grate with a surface of more than 2.5 m ² , introducing the solution into the fluidized bed zone towards the movement of the coolant.

 By changing the pressure in the manifold of the air supplied to the nozzles at a gas velocity of 2.0 - 3.0 m / h, it was possible to eliminate the formation of cakes and lumps on the grate of the fluidized bed furnace and to obtain a granular product with an average particle size of 1.6 - 2.9 mm

 In the table. Figure 2 shows the effect of air pressure in the collector (air flow) on the size of the particles formed during drying of magnesium chloride solutions.

 From the above data it can be seen that by changing the air flow rate and, consequently, the degree of spraying of the supplied solution, it is possible to effectively influence the granulation process of the material obtained during dehydration.

 Thus, the proposed technical solutions can significantly simplify the method of dehydration of magnesium chloride solutions and obtain a granular product.

 The method is as follows.

Aqueous solutions of magnesium chloride, for example, Uralsky JSC bischofite solution in accordance with TU 2152-006-00203944-94 with MgCl ₂ content _of 32.0 - 33.9%, are fed through a pneumatic nozzle to the fluidized bed apparatus, which is preliminarily dehydrated bischofite or dry inert material (potassium chloride, sodium chloride, carnallite, etc.) is loaded as a “pillow”.

The gas velocity in the layer is maintained in the range of 2.0 - 3.0 m / s, and the temperature of 120 - 170 ^o C - depending on the requirements of consumers to the residual content of crystalline water in the final product. The solution in the layer is fed through pneumatic nozzles installed in an amount of at least two per 5 m ^{2 of the} gas distribution grill. The solution is sprayed directly in the "fluidized" layer in opposition to the movement of the coolant flow. The flow rate of the solution is regulated depending on the desired temperature of the layer, increasing the flow rate if the temperature rises and lowering if the temperature drops.

 The granulometric composition of the dehydrated product is controlled by the degree of atomization of the initial solution supplied to the fluidized bed.

 If the average particle diameter grows, the air pressure on the collector is increased to 3-4 ati, and in the case of grinding particles in the layer - reduced to 1.5 - 1.7 ati. To obtain a granular product with an average diameter of 2.0 - 2.5 mm, it is necessary to maintain the air pressure in the collector at the level of 2.5 - 3.0 ati.

 The dehydrated product is removed from the apparatus through an unloading device and cyclones, the efficiency of which reaches 98%.

Example 1. In a heated apparatus of a "fluidized" layer with a lattice area of 5 m ² loading as a "pillow" dehydrated bischofite with a content of MgCl ₂ - 63.4% until a layer resistance of 600 mm of water is reached. Art., then through two nozzles with a nozzle diameter of 25 mm and an annular gap for supplying air for spraying 4 mm, a bischofite solution with a content of MgCl _{2 of} 32.8% in an amount of 11 t / h at a temperature of 127 - 135 ^o C. was continuously fed.

 The air pressure in the manifold was maintained at a level of 2.8 - 3.0 bar. The gas velocity in the fluidized bed was maintained at 2.5 m / s.

Received ≈ 6.3 t / h of the final product with a MgCl ₂ content of 57.9% and MgO 0.5% with an average particle size of 1.9 mm.

 After 24 hours of continuous operation of the apparatus, the entire product is unloaded from the furnace. No material sticking to the grate; oven clean.

 Example 2. In accordance with example 1, the dehydration of a magnesium chloride solution was carried out, which was supplied to the apparatus through 1 nozzle. After the furnace stopped after 12 hours, specs were found on the grate under the nozzle, and lumps of material were found in the layer.

Example 3. In accordance with example 1, the solution was dehydrated at a temperature of 150 - 160 ^o C.

A product was obtained with a MgCl ₂ content of 71% and MgO 2.5% with an average particle size of 2.2 mm.

 Example 4. In accordance with example 1, the solutions were dehydrated, but the pressure in the air manifold was maintained at 1.7-1.9 ati.

 Got a product with an average particle diameter of 2.9 mm.

Claims (1)

A method of dehydration of magnesium chloride solutions, including dehydration of solutions in a single-chamber fluidized bed apparatus, characterized in that the initial solution is sprayed in a fluidized bed through pneumatic nozzles at a gas velocity in the layer of 2.0 - 3.0 m / s, while the granulometric rate is regulated by the degree of atomization the composition of the dehydrated product, and the number of nozzles should be at least 2 per 5 m ^{2 of the} gas distribution grid.

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