JPS6110009A - Improvement of evaporation method of mechanical compression type - Google Patents

Abstract

PURPOSE:To economize heat energy, and to concentrate an aqueous solution of sulfuric acid containing an inorganic salt, by subjecting a concentrated solution to flash distillation, raising temperature and pressure of vapor by a heat and a mechanical compressor, preheating and heating a stock solution by the amount of heat. CONSTITUTION:An aqueous solution of sulfuric acid containing an inorganic salt is sent through the pipe 10, preheated by the first preheater 1 and the second preheater 2, degased by the degasing can 22, added to the solution chamber 3''' of the evaporator 3, fed to the top part of the heating can 3' by the pump 19, and made to fall on the inner wall of a heat exchanger tube. On the other hand, a stock solution is heated with vapor whose temperature and pressure and raised from the outside of the heating can 3' by the mechanical compressor 4 and it is concentrated. The produced vapor is fed through the separator 3'' to the alkali scrubber 23 to remove acidic mist, etc., and sucked in the compressor 4. On the other hand, condensates of the preheaters 1 and 2, and the can 3' are subjected to flash distillation by the flash can 6, drain is discharged, and produced vapor is sucked in the compressor 4. The concentrated stock solution of the evaporator 3 is made to flow into the self evaporating can 7, the concentrated solution after flash distillation is taken out, and the produced vapor is sucked in the heat compressor 5.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an improvement in a method for evaporating and concentrating an aqueous sulfuric acid solution containing an inorganic salt.

! ! As a way to make the thermal energy of the prison evaporator more economical,
The evaporative vapor generated from the evaporator is compressed using a mechanical compressor, such as a rotary blower or a tar compressor, to increase the enthalpy, and this is used as heating vapor by incorporating a so-called heat pump. A mechanical compression method that repeatedly reuses the latent heat of steam has been proposed and implemented.

However, an aqueous sulfuric acid solution containing an inorganic salt and, in some cases, an acidic gas, such as a spinning bath acid used in a rayon and sufu factory, is an aqueous sulfuric acid solution with a concentration of about 10% by weight that contains mirabilite and zinc sulfate as inorganic substances. When the mechanical compression method is applied to evaporative concentration, the acid mist and acid scum containing inorganic salts accompanying the generated vapor may cause adhesion of solids, wear, and corrosion to the casing, rotor, impeller, etc. of the mechanical compressor. The industrial implementation of mechanical compaction has been largely difficult due to the short term loss of efficiency and the constant need for maintenance.

In view of these circumstances, the present inventors have previously filed a
No. 10092 (l\1 1987-216901, mechanical compression evaporation concentration method), proposed an invention to overcome the above-mentioned difficulties.

In other words, the gist of this prior invention is ``After preheating the raw liquid by heat exchange with the concentrated liquid, a heater is attached to the front stage and an evaporation ejector is attached to the rear stage, and the discharged steam of the steam ejector is heated by the heater. 1.0 to 3.0% by weight of the total amount into a vacuum degassing can configured to be used as a source.
The evaporated vapor is then sent to an evaporator to be concentrated to a predetermined concentration, and the evaporated vapor is further led to an alkaline washer, where it is washed with an alkaline cleaning solution having a temperature approximately the same as the saturation temperature of the evaporated vapor, and then is washed with a mechanical compressor. This was a mechanical compression evaporation concentration method J for rayon and staple fiber spinning bath acid, which is characterized by compressing and raising the temperature and using it as a heating source for the evaporator.

As mentioned above, the conventional technology solves the problem of corrosion by cleaning the generated steam with alkaline, but in order to recover sensible heat from the concentrated liquid and drain, heat exchange is performed with the feed liquid, and the The heat exchangers used were liquid-liquid and liquid-drain heat exchangers.

However, in this heat exchanger, the U value (heat transfer coefficient) decreases in a short period of time due to scale generation. Therefore, it is necessary to perform chemical cleaning in a short period of time to remove scale from the heat transfer surface of the heat exchanger, and as the U value decreases due to scale generation, the amount of auxiliary steam used increases, which reduces the evaporation efficiency of the evaporator. There was a problem of decline. (Heat exchange between liquid and drain is not illustrated in the prior patent.) In the present invention, a flash can is provided at the latter stage of the evaporative concentrator, and the flash vapor (penoya) generated by self-evaporation of the concentrated liquid is collected. Condensate of steam that is suctioned and pressurized by a thermal compressor using steam as a driving source, and the discharged steam is used to raise the temperature of the feed liquid.The steam is then heated and pressurized by a mechanical compressor, and condensed in a heater, preheater, etc. (drain) is introduced into a flash can and flash evaporated, the generated vapor (paper) is sucked directly into the mechanical compressor again, and the pressurized vapor is used to raise the temperature of the feed liquid. The conventional method of recovering sensible heat from drains has been improved so that heat is recovered in the form of latent heat. In this case, the auxiliary steam is used as a driving source for the thermal compressor.

Example The present invention will be explained based on a specific example shown in FIG. 1 below.

In FIG. 1, 1 is a first preheater, 2 is a second preheater, and 3 is a first preheater.
Reference numeral 4 indicates an evaporation device consisting of a heater 3', a cenometer generator 3'', and a lower liquid chamber 3'', and 4 a mechanical compressor.

The stock solution to be evaporated and concentrated is fed through a tube 10 to a first preheater 1, then through a tube 11 to a second preheater 2, and then through a tube 12 to a degassing can 22 to degas most of the dissolved gas. rear,
At the head, the liquid flows down through the pipe 12' into the liquid chamber 3''. As the first and second preheaters, for example, a shell-and-tube heat exchanger or a polyblock heat exchanger is used.

The stock solution after preheating is poured into the lower liquid chamber 3'', and the pump 19
The liquid passes through the tube 18, is supplied from the top of the heater 3', and flows down the inner wall of the heat transfer tube. During this time, P/4', which is pressurized and heated from the outside by a mechanical compressor, is heated and evaporated, and the stock solution is concentrated and flows down.

The generated shitabe flows into the separator 3''K, and after separating the mist, is introduced into the alkaline scrubber 23 via the pipe 13.In this embodiment, a liquid film falling type evaporator is adopted as the evaporator @3. Other types of evaporators such as , forced circulation, film rise, natural circulation, etc. may also be used.

The base 4) introduced into the alkaline scrubber 23 is turned into base A?4 by contact with the alkaline cleaning solution. Trace amounts of acidic mist and/or acidic gas contained therein are removed by reaction absorption. In the illustration, a tower type scrubber is shown, which is equipped with a liquid dispersion device 23', a packed bed 23'', a bottom liquid chamber 2311, a liquid circulation pipe 231, etc. Exiting the alkaline scrubber 23, it passes through a pipe 4', It is sucked into the mechanical compressor 4, pressurized and heated, and used as heating paper for the first preheater 1 and heater 3'.In this case, the first and second preheaters 1, 2 and the heating can 3' The condensate passes through pipes 15 and 16,
The water flows into the flash can 6, undergoes flash evaporation, and is then discharged as drain. The vapor generated in the flash can 6 passes through the pipe 17, mixes with the vapor discharged from the heating can (alkaline scrubber), is sucked into the mechanical compressor 4, and is used as its own heat source. The gas 74' sucked into the mechanical compressor 4 in this way also sucks condensate flash vapor in addition to the evaporation vapor in the evaporator 3, and the additional heat generated by the power of the compressor is added to the vapor at the outlet of the compressor. Since excess heat is generated, this is consumed as heating energy for the first preheater 1. Since the condensate from the compressor outlet vapor is recovered in the form of latent heat, a liquid or
A drain heat exchanger becomes unnecessary.

On the other hand, the stock solution concentrated in the evaporation bag f13 flows into the self-evaporator T through the pipe 20, and after flash evaporation, the concentrated solution is discharged out of the system. Further, the vapor generated in the self-evaporator T passes through a pipe 21 and is sucked into a heat compressor (steam ejector K) using auxiliary steam as the driving steam, and after being pressurized, is used as heating vapor for the second preheater 2. . In this case as well, the sensible heat of the concentrated liquid is recovered in the form of latent heat, so the liquid
A liquid heat exchanger is not required.

The pipes 24, 25, and 26 are bleed pipes that are connected to a vacuum generator (not shown) to discharge noncondensable gas and maintain each device at a predetermined degree of vacuum. Further, the gas degassed in the degassing can 22 and the accompanying penoch are introduced into a condenser and a vacuum generator (not shown), and non-condensable gases are discharged.

[Brief explanation of the drawing]

FIG. 1 is a process flow sheet showing an actual MfJ embodiment of the present invention. In the figure, 1...first preheater, 2...second preheater, 3...evaporator, 4...mechanical compressor, 5...thermal compressor, 23
...Alkaline scrubber.

Claims (1)

[Claims] In a mechanical compression evaporator that evaporates and concentrates an aqueous sulfuric acid solution containing inorganic salts, the concentrated liquid is flash-evaporated, and the sensible heat of the concentrated liquid is converted into latent heat by suction and pressure increase with a thermal compressor powered by steam. At the same time, the condensate is heated and pressurized by a mechanical compressor, and condensed in a heating can and preheater. The condensate is then flash-evaporated, and the steam is sucked into the compressor to recover heat from the condensate in the form of latent heat. An evaporative concentration method characterized by using the excess heat at the outlet of the mechanical compressor for preheating the supplied stock solution.