SU1139702A1 - Method of concentrating electrolytic leaches - Google Patents

Abstract

METHOD FOR CONCENTRATING ELECTROLYTIC ALKALES, including sequential evaporation of them in four stages to an alkali concentration in the first stage 11-13%, in the second 15-17%, in the third 25-26% and in the fourth 46-50% vacuum crystallizer, intermediate one discharging sodium chloride suspension from the vacuum crystallizer, separating the suspension and feeding the liquors separated from the sodium chloride precipitate to the subsequent evaporation stage, clarifying the concentrated liquors, cooling and separating them c. obtaining alkali, characterized in that, in order to trace the purity of the sodium chloride precipitate when the content of sodium sulfate in the original liquor is above 0.5%, a thickened suspension of the third stage is fed into the vacuum crystallizer (L of the evaporation stage simultaneously with the electrolytic lye of the second evaporation stage, and the liquors separated from the vacuum crystallizer are sent to the third stage of evaporation.

Description

11 The invention relates to chemical technology, in particular to methods for producing caustic soda by concentrating electrolytic lye diaphragm electrolytic. A known method of electrolytic concentration by multistage evaporation, in which one stripped to 30% of liquor is directed to the separation of salt crystals. After the crystalline liquor is removed from the liquor (the product is sent to the final evaporation to a concentration of 42-50% lye. The stripped liquor is sent to the cooling and separation stages to obtain the desired product 1. The disadvantage of this method is that of saltite salt, salt crystals are significantly contaminated by sodium sulfate, which leads to a decrease in the quality of the reverse brine and additional costs during electrolysis. The desired result is a method of electrolytic alkali concentration, which includes sequential hardening them in four stages to an alkali concentration in the first stage 11-13%, in the second 15-17%, in the third 25-26% and in the fourth 46-50%. After the third stage, an intermediate suspension of the chloride suspension in the ri is carried out with preliminary cooling of the liquor in a vacuum crystallizer. The liquor separated from the precipitate is fed to the subsequent evaporation stage followed by their clarification, cooling by separation and obtaining commercial alkali C23, Ives This method allows to increase the yield of pure sodium chloride salt; however, contamination of the sodium chloride output salt with sodium: sodium fata impurities is observed when the content of the scientific research institute in the initial 10% lye is more than 0.5% sodium sulfate. This also results in fine salt crystals, which worsens the precipitate separation process. In addition, sediment removal is difficult due to the high viscosity of the plant. The purpose of the invention is to increase the purity of the precipitate of sodium chloride 2 when the content of sodium sulfate in the initial liquors is higher than 0.5%. This goal is achieved by the fact that according to the method of electrolytic concentration of liquors, including sequential evaporation in four stages to an alkali concentration in the first stage 11-13%, in the second 15-17%, in the third 25-26% and in the fourth 46-50% , feeding the reaction mixture of the third stage into a vacuum crystallizer, intermediate withdrawal of sodium chloride suspension from the vacuum crystallizer, separating the suspension and feeding the liquors separated from the sodium chloride precipitate to the subsequent evaporation stage, clarifying concentrated liquors in their cooling and separation of alkali to give, in a vacuum crystallizer serves thickened | hydrochloric suspension upari- third step. simultaneously with the electrolytic lye of the second stage of evaporation, and the liquors separated from the vacuum crystallizer are sent to the third stage of evaporation. The drawing shows a flow diagram of an installation for carrying out the proposed method. The installation consists of sequentially connected evaporators 1 and 2, a vacuum crystallizer 3, centrifuges 4 for separating sodium chloride sediment, a tank 5 for collecting salt dissolving, a tank 6 for collecting os-, vetilated liquors, sequentially connected evaporators 7 and 8. Hydro cyclone 9 for classifying a suspension, a disk crystallizer 10 for cooling one stripped off solution, a centrifuge 11 for clarifying caustic soda — the target product, caustic soda collection tank 12, salt collection tank 13, barometric condenser 14, and vacuum Wasp 15. The electrolytic liquor concentration process is carried out as follows. Pre-heated electrolytic liquors with a concentration of 10% alkali are fed to a four-way evaporation plant, where they are subsequently evaporated in an evaporator. devices 1 and 2, respectively, to a concentration of 11.5–13.5% and 15–17% alkali, after which, with a temperature of 140142 ° C, are introduced into a vacuum cristizer 3 for cooling to. A condensed suspension from the evaporator 7 of the second evaporation stage, having a concentration of 25-26% alkali and a temperature of 115120 ° C, and sludge particles larger than 1 mm from the hydrocyclone 9 are sent here, while in a vacuum crystallizer 3 a suspension is obtained a concentration of 18-22% alkali with a temperature of 80-85 ° C. vacuum crystallizer 3; the suspension is fed to a centrifuge 4 to separate the sodium chloride precipitate. The recovered sodium chloride precipitate is sent to dissolve the salt in tank 5, from which the prepared reverse sodium chloride brine is sent to electrolysis. The clarified liquor is collected in the collection tank 6 of the clarified liquor, from where they are sent for evaporation to successive evaporators 7 and 8, where the liquor is concentrated, respectively, 25-26% and 46-50% of alkali at boiling points of the solution 114-116 and 80- 85 0. From the evaporator 8 of the final evaporation, the solution enters the hydrocyclone 9 to separate sediment particles larger than 0.1 mm and then is sent successively for cooling to the disk crystallizer 10 and for clarification to the centrifuge 11. I collect the finished caustic tons in the tank 12 of the collection of the finished caustic soda, and salt is fed into the tank 13 of the collection of salt. In contrast to the known method proposed in vacuum crystallization, a suspension is obtained with a concentration of 18-22% in caustic soda, the dissolving sodium sulfate in which is 1.6 1.55%, which allows to obtain pure reverse salt brine when the content of the original electrolytes is Sodium sulfate lytic liquids are higher than 0.5%. In addition, at a given alkali concentration, the productivity of equipment at the separation of sodium chloride crystals will increase due to a decrease in the viscosity of the solution entering the separation. An example. The initial electrolytic liquor in the amount of 1000 kg containing,%: NaOH 10; NaCJ 16.7; Na2SO 0.8, subjected to evaporation in a high-capacity installation with quadruple use of the heat of heating steam to the concentration,%: NaOH 49; NaCl 2.5; NajSO 0.12. The first case 1 of the evaporator is heated with heating steam having 179С, the subsequent cases 2, 7, 8 are heated with the secondary steam of the previous case, having temperatures of 150, 126 and 99 C, respectively. In the first and second stages electrolytic liquors are concentrated in the first two consecutive cases 1 and 2 to the concentration,%: NaOH 16; NaGI 16 and 0.78 and in the amount of 639 kg / h of solution and 59 kg / h of sodium chloride precipitate with a temperature of 141 ° C are sent to a vacuum crystallizer 3. At the same time, it is fed with a thickened suspension from an evaporator 7 in an amount of 132 kg / h containing 50% of the solid phase and having an alkali concentration of 2b%. In addition, 30 kg / h of slurry with a concentration of 49% alkali with sediment particles with a size of more than 1 mm and containing 50% of the solid phase enters the vacuum crystallizer 3 from a hydrocyclone 9. In the vacuum crystallizer, by displacing and self-evaporating the solution, liquor is obtained having a concentration,%: NaOH 20; NaCl 10; , 2.9 with a temperature and kinematic viscosity of 1.8 10 m / s. From the vacuum crystallizer 3, the suspension enters the centrifuge 4, in which the sodium chloride precipitate is separated in an amount of t40 kg / h and sent to a 5-dp dissolution tank with water. The resulting brine is sent to electrolysis. The clarified liquor from the tank 6 is sent to the third stage of evaporation in an evaporator 7, from "the removed clarified liquor in the amount of 359 kg / h is sent to the evaporator 8. In the last liquor it is concentrated at the boiling point of the solution to a concentration. %: NaOH 49; NaCl 2.5; 0.12 willows in an amount of 228 kg / h are sent to a hydrocyclone 9, after which the suspension in an amount of 30 kg / h, containing sediment larger than 0.1 mm, is sent to a vacuum crystallizer 3, and partially clarified liquor in an amount 188 kg / h of liquid and 10 kg / h of solid phase are sent for cooling to a disk crystallizer 10 with the subsequent separation of sediment in a centrifuge in the amount of 10.5 with the production of finished products 511397026

tic soda in the amount of 187.5 kg / h. The table shows that in contrast

containing,%: NaOH 50; NaCl 1.0; from a known method in a vacuum-crystal NajSQii 0, 3. a crystal there are no crystals

Comparative data obtained from sodium sulfate, which makes it possible to use the proposed half-way and to obtain high-quality reverse-known methods, are given in table.

The performance of the original solution, kg / h

The concentration of the original electrolytic lye,% NaOH

NaCl

Na SO

The first stage of evaporation 1 Concentration,% NaOH

.. Naj SO

Number of crystals separated, kg / h NaCl

Na2.S04

Second stage evaporation Concentration,% NaOH

NaCJ NajSO

The number of leached crystals, kg / h

NaC268.0

Na, j SO,

Vacuum crystallizer Concentration,%

NaOH26,0

NaCl7,4

NajSO 1.0

1000

1000

16.2

15.4 1.33

70.0

20.0 10.5 1.5

Number of required centrifuges, pieces of doC akkichene and ai1mosf (chkma

Claims (1)

METHOD OF CONCENTRATION OF ELECTROLYTIC ALKALI, including sequential evaporation of them in four stages to an alkali concentration of 11-13% in the first stage, 15-17% in the second, 25-26% in the third and 46-50% in the fourth; a vacuum crystallizer, an intermediate withdrawal of a suspension of sodium chloride from a vacuum crystallizer, separation of the suspension and supply of liquors separated from the precipitate of sodium chloride to the subsequent evaporation stage, clarification of the concentrated liquors, their cooling and separation c. alkali production, characterized in that, in order to increase the purity of the sodium chloride precipitate when the sodium sulfate content in the initial liquors is higher than 0.5%, a condensed suspension of the third evaporation stage is fed to the vacuum crystallizer 5 simultaneously with the electrolytic liquors of the second evaporation stage, and the liquors separated after the vacuum crystallizer are sent to the third stage of evaporation.