DE2846564A1 - Vacuum freezing for recovering sweet from salt water - by alternately freezing and melting very thin falling films - Google Patents

Abstract

A pre-cooled salt soln. is divided into a fine, falling film by means of a contact layer consisting of fillings, vertical plates or hanging synthetic films, in a process for recovering a solvent from a soln., and esp. sweet water from salt water. The falling film is partially vaporised by a pump, the vapour is condensed on an ice layer on a second similar contact layer formed in a previous sequence until these ice layers are melted and sufficiently strong ice layers have formed on the first contact layer. The pre-cooled salt soln. is then fed to the second contact layer and the mode of action of the vapour pump is reversed until the first contact layer is melted and a sufficiently strong ice layer has formed on the second contact layer etc. Used to overcome the disadvantages of known freezing processes, esp. the prodn. of floating ice crystals or ice layers on cooled surfaces such as the necessity for large amts. of rinsing water and the resistance of thick ice layers to the transfer of heat whilst retaining their advantages.

Description

procedure

for the extraction of especially fresh water from salt water by vacuum freezing The invention relates to a method for obtaining fresh water in particular from salt water by vacuum freezing, in which salt water with freezing temperature as a falling film on the icy surface of inert contact material in a vacuum container trickles down, vacuum evaporated by the action of a steam pump and cools down due to the evaporation enthalpy given off, leaving more ice on the contact surface arises. In this process, the one delivered by the steam pump is used at the same time Vacuum vapor is deposited in a second container with the same internals which had sufficiently thick layers of ice in a previous work cycle have formed, which are now melting. By reversing the direction of action of the steam pump and by alternately sprinkling the contact layers, both containers have alternating the function of the crystallizer and the melter.

It is known that in the solution freely swabbing @@@ crystals d @ reh partially Vacuum evaporation of the water supply, which is pre-cooled to vessel temperature was to produce, as well as the produced ice after washing with fresh water in one second container (the smelter) by knocking down what occurs during vacuum evaporation and to melt steam compressed by the steam pump.

It is known that eggs are formed by adding crystallization nuclei on to limit fewer but larger and purer crystals.

It is known to accelerate the growth of floating ice crystals by stirring, spraying or trickling the solution.

It is known to produce layered ice adhering to a wall surface by cooling the back wall surface.

The disadvantage of ice generation due to ice crystals floating in the solution is, as technical experience shows, the small achievable crystal diameter (0.3-0.5mm). As a result, the washing water requirement is already due to the wetting Solution of the crystal surface very high.

The disadvantage of creating layer ice on cooled surfaces is the low thermal conductivity of the ice, which increases with thicker ice layers leads to uneconomically high heat transport resistances.

The object of the present invention is therefore to provide the Disadvantages of the previously known freezing processes, in particular the production of in the solution to floating ice crystals or layered ice on cooled surfaces fix, but keep their benefits.

The solution to the problem is essentially that the pre-cooled Saline solution on a e.g. from packing, vertical plates, hanging foils existing contact layer of a vacuum container is finely distributed, thus its Contact surface wetted as a thin (less than 0.5 to 1 mm) falling film, through the effect of the steam pump partially evaporates and after exiting the contact layer is pumped out again from the lower part of the vacuum container.

So that ice grows on the contact surface is at the time of commissioning expediently to generate a first layer of ice by intensive cooling, which provides the seed crystals for further growth. Furthermore, it must be spontaneous The formation of crystal nuclei in the falling film can be avoided, i.e. hypothermia of the trickle film at the liquid / vapor phase interface opposite the local freezing temperature must remain low.

This is done through small trickle film thicknesses, i.e. through distribution the amount of salt water to a large contact layer cross-section and thus to a Large contact surface There are also any crystallization nuclei that may be present in the salt solution expediently to filter off.

In good time before the gaps in the contact layer blocked the salt water and the suction side of the steam pump must first be on one ice-free contact layer of a second container can be switched, which is now called The crystallizer works. The pressure-side vapor of the vapor pump condenses in the contact layer of the former container and melts the ice formed.

A residual layer of ice is expediently placed on the contact surface left to make it easier for a new layer of ice to grow.

An example of the method according to the invention for seawater is shown in F i g. 1 shown. Sea water 1 of, for example, 20 OC is countercurrent to the Brine 2 and the fresh water 3 produced in the countercurrent heat exchanger 4 to about 2 ° c precooled In a refrigerant evaporator 5, it is further cooled down to -1 0c. The circulation pump 6 conveys the sea water via the three-way valve 7 into the vacuum container 8, where it is atomized over a contact layer as described above and at about -5 ° c vacuum-evaporated. The draining seawater flows through the circulation pump 6 to or is fed back into the sea as brine 2. About the rotary valve 10 promotes the steam jet pump 11 the resulting steam including motive steam 12 in the Vacuum container 13 and a second coolant evaporator 14. In both cases the steam condenses at about 1 OC. in the Containers 13 melt as a result the layers of ice and melt water generated during the previous work cycle can be taken from the process as product 3 via the three-way valve 15. That Condensate of the coolant evaporator 14 can, as shown in the present example, be added to the product 3. The cooling circuit is conventional except from the said coolant evaporators 5 and 14, including from the Compressor 16, the coolant condenser 17 working a little over 20 0c as well as the two expansion valves 18 and 19

Claims (1)

Claim 1. A method for obtaining a solvent from a solution, especially of fresh water from salt water, by vacuum freezing, it is not stated that the pre-cooled saline solution is added to a For example, made of fillers, vertically arranged metal sheets or hanging plastic films existing contact layer is finely distributed as a thin falling film, this falling film is partially evaporated by the action of a steam pump, the steam to the in one previous work cycle formed ice layers of a second identical contact layer is precipitated until these layers of ice have melted and become have formed sufficiently thick layers of ice in the first-mentioned contact layer, whereupon the pre-cooled salt solution is now fed to the second contact layer and the operation of the steam pump can be reversed until the ice layers the first-mentioned contact layer are melted and are sufficiently strong Ice layers have formed in the second-mentioned contact layer, and so on.