AU1355702A - Method of evaporation of solutions accompanied by crystallization of salts - Google Patents

Description

-1-

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: Actual Inventor/s: Address for Service: Russian National Aluminum and Magnesium Institute (VAMI) Vladilen M. Tirtishnyi BALDWIN SHELSTON WATERS MARGARET STREET SYDNEY NSW 2000 3710000352 'METHOD OF EVAPORATION OF SOLUTIONS ACCOMPANIED BY CRYSTALLIZATION OF SALTS'

CCN:

Invention Title: The following statement is a full description of this invention, including the best method of performing it known to us:- File: 34370AUP00 e ceivedon ~ic;tm8T~gS oNl

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~a Urc -la- METHOD OF EVAPORATION OF SOLUTIONS ACCOMPANIED BY CRYSTALLIZATION OF SALTS The invention relates to the field of production of alumina, soda, potash and other salts and specifically it relates to the method of evaporation of solutions in evaporating units having substantially tubular processing elements.

Background of the Invention 1 *A method of evaporation of solutions in evaporation units having processing elements of tubular configuration and accompanied by crystallization of salts is known in the art (see L. P. Pertsev "Tubular evaporating units for the crystallization of solutions" M. Mashinostroenie 1982, p. 29 and 66). This method consists of heating of *.i the solution by steam, accompanied by removal of condensate and evacuation of evaporated slurry containing crystals of salts and vapors from an apparatus.

This method is affected by the following major drawbacks. About 20 to percent of the inner space of the heating tubes are clogged by solids of salts which are *.i broken off from the walls of the processing tubes and other elements during operation of the apparatus. Such condition requires stoppages of the apparatus every 3-4 days for washing of each individual tube with water. The encrustation of the most efficient drip pans and clogging of the heating tubes result in the reduction of the evaporation unit capacity and steam utilization ratio. Installation of sophisticated and expensive drip pans leads to a substantial increase in the cost of the equipment. Evaporation of water and other liquids used for washing of the individual heating tubes causes further increase in the consumption of the heating medium such as steam.

-2- A method and apparatus adapted for prevention of deposits formation on the inner walls of crystallizing evaporation units are also known in the art (see, for example, German patent application N 1619806 filed 1972). According to this prior art method, a non-saturated solution is supplied on the internal walls of the unit. Another solution capable of dissolving the solid deposits is poured down in the form of a film along the internal walls of the apparatus.

°ooooThe following important drawbacks are common for this method. This method *:is applicable for dissolving of the solid deposits situated only on vertical or substantially inclined walls capable of supporting the poured film-type solution. It is quite difficult to use the dissolving film according to the German patent application for the removal of deposits accumulated on a ceiling or other upper horizontally positioned sections of the S" unit. There are also major problems with applying this method for the removal of solids accumulated in the commonly used drip pans of grid-type or shutter-type. Another drawback of this method is in utilization of the complex and sensitive spraying devices used for the formation of the film-type solutions which become clogged very easily.

One of the main objects of the invention is to minimize formation of solids in the separator and other parts of the processing units and to minimize clogging of heating tubes by the solid pieces separated from the walls and other structural elements of the apparatus.

Brief Description of the Drawings FIG. 1 shows a processing unit utilizing the method of the invention.

-3- Description of the Preferred Embodiment As illustrated in FIG. 1, a device 10 consists of a heating section 1 which is positioned between the separation chamber 2 and a receiving chamber 7. A plurality of substantially hollow heating elements 5 and at least one substantially hollow circulation element 6 are situated within the heating section 1, so as to provide fluid *.oo communication between the receiving chamber 7 and an interior space of the separation chamber 2. Although, any conventional configuration of the heating and circulation elements is contemplated, in the preferred embodiment of the invention these elements are formed having substantially tubular configuration. A condensate of a heating medium or heating steam is removed from the heating chamber 1 by means of a drain line 9. As will be discussed below, a portion of the condensate is diverted from the drain 9 by means of the line 3 and introduced into the interior space of the separation chamber 2 through a nozzle 4.

tt The heating medium in the form of the heating steam is directed into the inner space of the heating section 1, so as to surround the heating elements 5. A solution is drawn from the receiving section 7 into the heating elements 5. Upon reaching the boiling temperature, the solution in the form of a vapor-liquid mixture enters the interior space of the separator 2. In the separation chamber 2 cooling occurs and an equilibrium between the liquid and vapor phases is achieved. This results in deposits of the suspended crystals of salts on the inner walls of separation chamber 2. The liquid phase containing the crystals of salts is recirculated to the receiving chamber 7 by means of a return or circulation element 6, and the vapor phase is evacuated from the separator through the line 8. After being returned into the receiving chamber 7 and mixed with the solution, the liquid phase containing crystals of salts re-enters the heating elements 6, thus providing continuous circulation of fluids in the apparatus of the invention. The vapor phase, after being separated from the liquid phase, is evacuated from the separation chamber 2 through the line 8.

In the invention, as a result of evaporation of sodium carbonate, sulfates, etc., the concentration of soluble salts is increased accompanied by crystallization thereof in the separation chamber 2. The resulted mixture is constantly removed from the separation chamber 2 through the circulation element 6 at the level above the upper *q .0region of heating elements In the heating section 1, the heating medium or heating steam is isolated from the processed fluids passing through the heating elements 5 and circulation element A condensate developed as a result of the heat exchange between the heating medium and the processing elements 5, 6 is accumulated within the interior space of 15 the heating section 1 and removed through the drain line 9. An important feature of the invention is that the condensed portion of the heating medium including steam is diverted from the drain line 9 into the separator 2 by means of the line 3. The fine particles of spray of the condensed heating medium including steam are introduced into the interior area of the separator 2 through the nozzle 4. In the preferred embodiment of the invention about 0.3 to 2 percent of the condensed portion of the heating medium or condensate in the form of a fine spray is introduced into the separation chamber 2. In the separator the fine particles of condensate are combined with the particles of the liquid phase washing and diluting the same. Mixing of the fine spray of condensate with the particles of liquid phase causes enlargement of the latter particles within the evaporator. This significantly reduces the formation of solids on the interior wall of the separation chamber 2 in general, and specifically provides protection from excessive formation of undesirable solid deposits on the interior walls.

Because of evaporation of the fine particles of condensate, the method of the invention practically excludes undesirable overheating of the vapor phase in the separation chamber. This prevents forming precipitants on the walls of the separator and minimizes formation of solids.

The above discussed introduction of the fine particles of condensate also o ooeexcludes over-saturation of the particles of the solution which are present in the steam space and precipitated on the separator walls with salts. This approach also prevents over-saturation of the drops of the solution situated on the structural elements of the apparatus and drip pans as a result of mixing with the drops of condensate. All this prevents clogging and encrustation.

In the separation chamber, when the fine particles of condensate are merged with the particles of the liquid phase, the vapor phase is cleaned and purified forming drops of larger size. The cleaning of the vapor phase also accelerates precipitation and the increases in the efficiency of the drip pan operation.

As indicated above, the recommended amount of the fine particles of condensate introduced into the separation chamber should be between about 0.3 and percent of the amount of condensate developed within the heating compartment.

Increase of the amount of the fine particles above the 2 percent level will not result in increasing the efficiency of the method. On the other hand, the reducing the amount of the fine particles below the 0.3 percent level of the produced condensate is technologically difficult to achieve.

-6- The largest amount of non-reacted fine particles of condensate is supplied along with evacuated vapors into the inter-tubular space of the heating chamber of the next unit and removed together with condensate. A part of the fine particles of condensate introduced into the separator is evaporated by the overheated vapors. The above practically excludes any dilution of the liquid phase in the separation chamber.

Example ~During the industrial trial of the method of the invention, an evaporating apparatus consisting of four units was utilized. About 0.4 0.6 percent of the condensed heating medium from the first unit was introduced through the ejectors into the hollow separators (without drip pans). The results of the trial were compared to the operation of the available most powerful evaporating units having the working space of about 800 m 2 and utilized in the sodium carbonate -potash production accompanied by crystallization of anhydrous sodium carbonate. This prior art evaporating unit operates i without introduction of the condensed heating medium into the working space of the apparatus. After utilization of the method of the invention, time between the maintenance shut downs for washing/cleaning of the processing tubular elements was increased up to 40 days. Simultaneously, the clogs in the tubular elements of the processing equipment was substantially reduced. In view to the increase in the efficiency of the heat transfer process and reduced resistance of the drip pans due to the encrustation, the ratio of steam use/utilization was substantially increased. The specific consumption of steam per ton of evaporated water was reduced from 0.62 to 0.33 t/t.

Claims (4)

1. A method of evaporation of solutions accompanied by crystallization of salts in an apparatus consisting of a heating section containing a plurality of substantially tubular processing elements and at least one circulation element, the heating section being positioned between a receiving chamber and a separation chamber, the method comprising the steps of: heating of a solution contained in the substantially tubular processing elements by a heating medium avoiding direct contacts between the solution and the heating medium; evacuation from the heating section of a condensed portion of the heating medium formed during the step of heating; and removal of an evaporated solution containing crystals of salts el and evacuation of vapors from the separation chamber, 15 wherein a portion of the condensed heating medium in the form of a fine spray is introduced into the separation chamber.

2. The method of claim 1, wherein the amount of the condensed heating medium introduced into the separation chamber in the form of the fine spray is from about 0.3 to 2 percent of the total condensed heating medium evacuated from the heating section.

3. The method of claim 1, wherein the condensed heating medium is steam.

4. The method of claim 1, wherein the fine spray of the condensed heating medium is introduced into the separation chamber for mixing with the particles of evaporated solution containing the crystals of salts. A method of evaporation of solutions accompanied by crystallization of salts substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawing and/or examples. DATED this 24th Day of January, 2002 RUSSIAN NATIONAL ALUMINUM AND MAGNESIUM INSTITUTE (VAMI) Attorney: PAUL G. HARRISON Fellow Institute of Patent and Trade Mark Attorneys of Australia of BALDWIN SHELSTON WATERS oo**o *oo