SU504702A1 - Electrolytic liquor concentration method - Google Patents

Description

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The invention relates to the technology of evaporation of electrolytic liquors obtained by electrolysis of chloride solutions in diaphragm electrolyzers with a solid cathode.

A known method of concentrating electrolytic liquors with a concentration of 8-12% NaOH to strong liquors with a concentration of 42-50 NaOH by two-stage evaporation with intermediate filtration of liquors with a concentration of 25-30% NaOH obtained in the first stage of evaporation from the solid phase and threefold use in a three-body the system of the first stage of evaporation of steam coming from the side under pressure of 5-8 atm. In the second stage, selective steam under a pressure of 2.5-4 atm from the first case of the three-body system of the first stage of evaporation is used once. However, this method has a high steam consumption in the second stage of evaporation and a correspondingly increased flow rate of cooling water supplied to the condenser.

To eliminate the drawbacks, a method is proposed in which the evaporation in the second stage is carried out in two stages, in the first of which electrolytic liquors are evaporated to a concentration of 34-38% NaOH using selected steam under a pressure of 1-2 atm from the second building of the three-body system of the first stage of evaporation , selected steam under pressure of 2.5-4 atm from the first case of the three-body system of the first stage of evaporation is fed to the second stage of the second evaporation stage.

Thus, the steps of the second stage of evaporation are connected to each other, but the solution is sequential, and the selected pair is parallel. Evaporation on both steps x

the second stage of evaporation is carried out under the same vacuum - 70-90%.

The proposed method allows to reduce the steam consumption by 12-15% and, accordingly, the consumption of cooling water supplied to the condenser is reduced.

Example. Electrolytic liquor in the amount of 100 tons per hour, containing 10% NaOH and 16% NaCl, is subjected to a two-stage concentration. In the first stage, the liquor is evaporated to a concentration of 15% NaOH in a three-body system with a primary vapor pressure of 6 atm (saturation temperature 158 ° C) and a vacuum in the last case of 80%. In the first case, 19 t / h of water are evaporated from a solution under a pressure of 2.8 atm, 18 tons / hour in a second case at a pressure of 1.15 atm (4 tons / hour of which are due to self-evaporation of the solution) and 11 tons in a third case / hour (of which 5 tons / hour due to self-evaporation). 5 tons / hour

the juice and heating steam obtained in the first case, having a saturation temperature of 132 ° C, and 12 t / h of juice steam obtained in the second case and having a temperature of 102 ° C, are taken to the second stage of the concentration process.

The middle liquor after the third building is filtered from the crystalline salt precipitated upon concentration in the amount of 12 tons / hour. The filtered middle liquor, containing 25% NaOH and 10% NaCl, is successively passed into the first and second stages of the second evaporation stage, where it is concentrated to 38% and 49% NaOH, respectively. In both steps, evaporation is carried out under a vacuum of 90%. The first stage is heated with selected steam of the second building of the first stage. 10.8 t / h of water is evaporated in it (another 1.2 t / h of steam is used for heating and dehydration of the solution). The boiling point of the solution in the first stage, taking into account the depression, is 88 ° C.

The boiling point in the second stage due to a sharp increase in concentration and temperature depression rises to 105 ° C. Heating of this stage is produced by selected extra steam from the first building of the first stage. In the second stage only 3.5 t / h of water is evaporated, another 1.5 t / h of steam is spent on heating the solution to the boiling point in the step and on its dehydration.

From the second stage of the second stage, strong liquor is evaporated after cooling and storage at the warehouse.

Claims (1)

Invention Formula The method of concentration of electrolytic liquor with a concentration of 8-12% NaOH to strong liquors with a concentration of 42-50% NaOH by two-stage evaporation with intermediate filtration of liquors with a concentration of 25-30% NaOH obtained in the first stage of evaporation from the solid phase, using three times the three-body system of the first stage of evaporation of steam coming from the side under pressure of 5-8 atm and feeding to the second stage of evaporation of selected steam under pressure of 2.5-4 atm from the first case of the three-case system of the first stage evaporated characterized in that, in order to reduce steam consumption in the second stage of evaporation and cooling water, evaporation in the second stage is carried out in two stages, in the first of which electrolytic liquors are evaporated to a concentration of 34-38% NaOH using selected steam under pressure 1- 2 atm from the second building of the three-body system of the first evaporation stage, selected steam under pressure of 2.5-4 atm from the first building of the three-body system of the first evaporation stage is supplied to the second stage of the second evaporation stage.