FI77005B - FOERFARANDE, ANORDNING OCH MEDEL FOER KONCENTRERING AV AGGRESSIVA LOESNINGAR. - Google Patents

Description

1 77005

Method, apparatus and spacer for concentrating aggressive solutions

The invention relates to a method, an apparatus and a spacer for concentrating aggressive solutions such as lyes, e.g. NaOH or KOH, to the highest possible concentration before solidification, up to a concentration of 80-99.8%, depending on the desired product.

When concentrating the in aggressive solutions boiling-10 at its point the temperature rises sharply. Thus, e.g.

when the NaOH solution is concentrated from about 50% to about 99% (limits not precise), the boiling point of the liquor at atmospheric pressure rises from about 140 ° C to about 430 ° C. Thus, aggressive solutions 15 are generally initially concentrated with steam at a higher pressure than normal. With high pressure steam, NaOH can be concentrated in practice up to about 75%. Concentration to a higher concentration, i.e. evaporation using indirect steam heating due to the above temperature and pressure rise, is not practically possible, economical and sensible, so special arrangements have had to be made for heating.

For indirect heat transfer in higher temperature ranges, up to about 400 ° C, it is known to use organic heat exchangers, which are often eutectic mixtures of organic compounds with good thermal stability and which evaporate and condense like water vapor. Such is the case, for example, with Dowtherm (The Dow Chemical Company, cf. "Thermal-liquid Systems", Chemical Engineers Handbook, eds. Perry, H.R. and Chilton, C.H. pp. 9-41).

However, known organic heat exchangers generally do not reach sufficiently high temperatures for the final concentration of the aggressive solutions in question, e.g. NaOH.

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It is also known to use molten salt as the heating medium, which is recycled on the jacket side of the heat exchanger. The heated NaOH solution flows on the pipe side of the heat exchanger. The solution is concentrated by the generally known principle of falling film as the water contained in the solution evaporates. The production of molten salt used for heating requires its own equipment, e.g. heating boiler. In addition, a separate recycling piping and pumping system is required to recycle the salt. Such a sys-10 system requires expensive investments, in addition, the maintenance of the system is expensive due to the complexity of the equipment as well as the problems caused by corrosion.

It is also known, by a previously commonly used method, to concentrate NaOH in a pot which was then heated with a direct flame to obtain a high temperature. In such a method, operating and maintenance costs are high. Also, the life of the pot is very limited, often only one year.

The object of the present invention is to provide a process for the indirect concentration of agg-20 reactive solutions, such as steep, e.g. NaOH and KOH, using indirect heat transfer, which avoids the above-mentioned disadvantages, and in particular avoids the use of a falling film or forced circulation device. associated additional investment and additional operating costs and corrosion and the like problems, and which allows the above solutions to be concentrated up to a concentration of 80-99.8%, or even more, in a more advantageous manner and by simpler means than known methods. This object is achieved by the method according to the invention using indirect heat transfer, which is characterized in that the solution to be concentrated is pumped to the flue gas evaporator to pass through the heating elements arranged in the flue gas duct. through tubes arranged from the coldest to the hottest relative to the concentrated solution, the last element having the highest temperature and concentration of the solution.

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According to the invention, the liquid to be concentrated passes through a plurality of heating elements, which are descended stepwise in height so that the liquid passes from the coldest to the hottest, the temperature of the last element being above the solidification point of the solution to be concentrated,

The use of the method according to the invention, in which the liquid to be concentrated passes through a multi-element, staggered apparatus, eliminates practical problems, e.g.

10 minimizes local temperature rises that cause severe corrosion problems. The multi-element solution helps to prevent the formation of local temperature peaks that contribute to the formation of corrosion.

The invention also relates to an apparatus for concentrating aggressive solutions such as lyes, e.g. NaOH or KOH, comprising - heat generating devices - concentrating liquid supply and conveying devices 20 - concentrated liquid removal devices - evaporator devices.

The apparatus is characterized in that it comprises a plurality of blocks of heater elements arranged in descending order from coldest to hottest, the evaporating elements being arranged so as to eliminate the hydrostatic overpressure caused by the increasing specific gravity as the lye concentrates.

In the apparatus according to the invention, there is no need for lye transfer pumps or shut-off devices between the heater elements, which would be in constant contact with the lye. In the solution according to the invention, the emptying devices are only exposed to a hot, solidifying solution at the moment of emptying.

The invention also relates to a heater element suitable for carrying out the method, characterized in that it is provided with a vertical drain pipe of the element, which is connected to the drain piping of the apparatus. The structure of the heating element contributes to the fact that the evaporation equipment can be emptied without separate transfer pumps or shut-off devices, which facilitates the use and maintenance of the equipment.

In the following, the invention and the advantages obtained by it will be described with reference to the figures of the accompanying drawings, in which Fig. 1 shows a flow diagram of a concentrating unit as a basic diagram. an embodiment of the apparatus according to the invention from a side, through-sectional view.

As shown in Figure 1, the apparatus includes gas production and recirculation devices 1, a burner 3 with combustion chambers 3, a piping 21 for supplying fuel, and a gas circulation circuit 4, 4 'and a circulating gas fan 5 for circulating gas. The gas recirculation devices 1 are provided with a cooled gas outlet pipe 6. The apparatus further comprises evaporative condensing devices 7, which include an indirect or direct condenser 8, as well as a condensing tank 9 acting as a condensing lock and, if necessary, devices 10 for creating a vacuum.

In addition, the apparatus comprises an evaporator unit 2 and a solution piping 11 for the solution to be concentrated and an outlet piping 12 for the concentrated product, which is preferably provided with a heat output 13 to prevent the product from solidifying.

The apparatus of Figure 1 is further provided with a solution emptying apparatus 14 for evacuating the apparatus by means of a vacuum from solution. The discharge device 14 includes, for example, a drain tank 15, drain pipes 16, a solution pump 17 and devices 18 connected to the drain tank 15 for creating a vacuum (such as a steam tank).

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5 77005 ejector or vacuum pump).

The apparatus is further provided with the necessary cooling water pipes 19 for conveying cooling water to the necessary objects, such as the condenser 8 and the vacuum-5 devices 10, 18, and further with the piping 20 for conducting the evaporator to the condenser 8.

The modular concentration unit according to the invention comprises several, in Fig. 2 four and in Fig. 3 eight pieces, preferably substantially identical 10 "tube packages", heat exchanger or heater elements 22, which are thus interchangeable. In the solution of Fig. 3, the heat-nin elements 22 are staggered in the height direction so that the hydrostatic overpressure and local overheating caused by the increasing specific gravity are eliminated as the liquor concentrates (Fig. 3).

Fuel is supplied to the burner 3 (Figures 1 and 2) via the fuel pipe 21. The flue gases from the burner 3 are led, for example, by recirculating gas blower 5 through circulating gas circuits 4 through pipe circuits 22 suspended in the flue gas duct 23 of the heating ground 20. The flue gases thus pass through the pipes of the elements 22 indirectly

The operating temperature of the flue gases is controlled by returning part of the flue gas used for heating the evaporators 2 back to the circulation of the hot flue gases to cool the flue gases to the desired temperature.

After the process, part of the cooled flue gas is led to the outside air via the gas outlet pipe 6.

Figure 2 shows a schematic diagram of the apparatus 30 on which the test runs have been performed. In this case, 320 kg / h of NaOH to be concentrated were fed to evaporator 2, which had been evaporated to about 48% by weight in a pre-evaporator and heated to about 53 ° C. The apparatus used in the experiment comprised four heat exchanger-heater elements 22, 35 in which the liquid was heated to a final temperature of about 378 ° C.

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From the first heating element, the solution passed as an overflow to the second heating element, where the liquid was heated to about 151 ° C. Approximately 54% of the solution passed overflow to the third heater element. In the third heater element, the liquid to be concentrated was heated to about 201 ° C and about 76% of the liquid passed overflow to the fourth heater element. The temperature of the fourth element was about 378 ° C and it was concentrated to about 98.2% by weight. From the fourth element, the product passed as an overflow and was subjected to further processing. The parameters for concentrating KOH in a similar four-element element apparatus are: temperature of the first element approx. 148-152 ° C, concentration approx. 51%, temperature of the second element approx. 188-192 ° C, concentration approx. 62%, temperature of the third 250-254 ° C, concentration about 74 ° C and fourth temperature about 278-382 ° C, concentration about 89%.

The concentrated solution may be subjected to a vacuum or vacuum expansion treatment prior to solidification and / or packaging. Since the liquid in the apparatus according to the invention is transferred as an overflow from one element to another, no lye transfer pumps or shut-off devices are required between the heating elements.

Evaporation can take place at atmospheric pressure or under-25 pressure. The process parameters, temperature, pressure and concentration used depend on e.g. the number of heating element paths and the size of the heating surface.

The surfaces in contact with the solution to be concentrated in the heating elements can be made of nickel. When hydrogen is used as a fuel, the outer surfaces of the elements can also be nickel. If the fuel contains sulfur, the nickel pipes must be fitted with a protective layer or pipe, the material of which depends on the fuel used.

The choice of fuel to be used depends on the local conditions which are taken into account when applying the method and apparatus according to the invention in practice.

Il 7 77005 In this case, for example, hydrogen from chlorine electrolysis is often available for such a purpose.

In the apparatus according to the invention, the elements 22 are substantially identical, which reduces the number of spare parts to be stored, in principle one spare element is sufficient. Each evaporator element can be removed separately for maintenance and is interchangeable, e.g. by moving the heater element used at the highest temperature for use at the lowest temperature, i.e. the service life of the elements can thus be extended.

Each element is provided with a drain pipe passing through the element, which can be connected to a drain device 14. This allows the evaporator unit 15 to be easily emptied by means of a vacuum, which facilitates e.g. maintenance of the device and reduces corrosion and operating problems. Due to the stepwise fitting of the elements from one element of the concentrated liquid upstream and the drain pipe and the drainage device 20, the apparatus according to the invention does not require lye transfer pumps or shut-off devices between the evaporation elements. Conventional equipment is emptied from below, which causes difficulties in known solutions, because the concentrated solution easily solidifies due to even a small drop in temperature and clogs the pipes. In the apparatus according to the invention, the drain pipe significantly facilitates the use of the apparatus.

The drawings and the related description are only intended to illustrate the idea of the invention. The details of the method and apparatus / elements according to the invention may vary within the scope of the claims according to the conditions of use.

Claims (16)

A method for concentrating aggressive solutions, such as liquors, e.g. NaOH or KOH, using indirect heat transfer, characterized in that the solution to be concentrated is pumped to a flue gas evaporator, passing through pipes of heating elements arranged in the flue gas duct, the elements being arranged from coldest to hottest, with the temperature and concentration of the solution being the highest in the last 10 elements. Process according to Claim 1, characterized in that the liquid to be concentrated passes through a plurality of heating elements, the temperature of the last or hottest element being higher than the solidification point of the solution to be concentrated, but preferably not more than about 400 ° C. A method according to claim 1 or 2, characterized in that the concentration of the product in the last block 20 is about 80-99.80%. Method according to Claim 1, 2 or 3, characterized in that the liquid to be concentrated passes through a plurality of heating elements which are descending stepwise from the coldest to the hottest in the height direction. Method according to Claim 1, 2, 3 or 4, characterized in that the thermal energy required for the flue gas evaporator is obtained from the flue gas of the combustion of hydrogen, natural gas or oil or similar fuels. Method according to one of the preceding claims, characterized in that the temperature of the flue gas (combustion gas) is lowered before it hits the thermal surfaces of the element blocks. Il 9 77005 Method according to one of the preceding claims, characterized in that the temperature of the flue gases is reduced by passing the cooled flue gases which have undergone the process into the hot flue gases 5. Method according to one of the preceding claims, characterized in that the combustion gases flow countercurrently to the flow of the liquor. Method according to one of the preceding claims, characterized in that there are 3 to 10, preferably 4 to 8, element blocks. A method according to claim 8, characterized in that when the number of blocks (22) is four and the temperature of the NaOH feed is about 47-52% by weight at about 50-55 ° C, the temperature of the first block at atmospheric pressure is about 120 -140 ° C, the temperature of the second block is about 148-152 ° C, the temperature of the third block is about 190-220 ° C and the temperature of the fourth block is about 20 370-380 ° C, whereby the final concentration of the product is about 98 weight. -%. 11. Apparatus for concentrating aggressive solutions such as lyes, eg NaOH and KOH, comprising - heat generating equipment (1), 25. concentrating liquid supply and conveying equipment, - concentrated liquid removal equipment, and - evaporator equipment, characterized in that the equipment includes a plurality of blocks of heater elements (22) arranged sequentially from the coldest to the hottest with respect to the feed to be concentrated, with the last element having the highest temperature and concentration of the solution. Apparatus according to Claim 11, characterized in that the heater elements are arranged in stages from coldest to hottest so that, as the liquor is concentrated, the hydrostatic overpressure caused by the increasing specific gravity is eliminated. 10 77005 Apparatus according to Claim 11, characterized in that the apparatus comprises 3 to 10 element blocks, preferably 4 to 8 element blocks. Apparatus according to Claim 11, characterized in that the element blocks (22) are substantially identical in structure. Apparatus according to Claim 11, characterized in that the heater element blocks are provided with a drain pipe (16) running vertically through the element block (22) which can be connected to the draining device. A heating element for an apparatus for concentrating aggressive solutions, comprising a piping for the passage of the liquid to be concentrated, characterized in that the heating element (22) is provided with a filling pipe and a heating element length 11 connectable to the draining device (14). II 11 77005