DE2322501A1 - DEVICE FOR EVAPORATING LIQUIDS - Google Patents

Description

WM It

Maschinenfabrik Augsburg-Nürnberg AG Z O Z. ζ. ο υ ι

File: PHN 6788
Registration from: 2.5.73

Device · for vaporizing. Liquids.

The invention relates to a device for evaporating liquids with at least one

heatable wall and is provided with means by means of which

the liquid in question is distributed as a thin film over the aforementioned wall. Derartfee devices can be used in the Industry, e.g. used in systems in which a Liquid is evaporated and condensed again at another point (condenser). Due to the good heat transfer in the case of evaporation and condensation, these are the required heat transfer surfaces small. Next are the temperature losses that occur and also the amount of heat circulating. transport medium low. The latter has the advantage that only a small amount of power is required for round pumping.

Because the temperatures at which the processes take place in chemical process engineering and also in power tools are mostly high, the temperature level at which the aforementioned heat transfer takes place should also be high. At these high temperatures of more than 500 ^° C., only metallic heat carriers (for example Na and K) can be used. This is because they can withstand these temperatures and have low vapor tensions. A disadvantage, however, is that the boiling of these liquids due to their high surface tension and the small increase in their vapor density

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the temperature is delayed. This causes undesirable Fluctuations in temperature and pressure. As is known, this can be avoided by using liquids of this type be guided as a thin film over a heated surface, so that evaporation on the film surface is almost without Overheating takes place.

The distribution of the .liquid over the relevant The surface causes difficulties at the very high temperatures.

At low temperatures it is common to adjust the thickness of the liquid layer by wiping or rotating rollers to reduce mechanically. For technological reasons, these processes are difficult to use at higher temperatures. Falling film evaporators are also known in which the liquid is distributed over a wall above and then on the Wall flowing down. However, undisturbed layers of uniform thickness are very difficult to achieve.

The invention aims to avoid the above problems. ^ -

The device according to the invention is therefore characterized

characterized in that the means mentioned by a porous Schichf be formed, of which a first part covers the wall in question and on the upper side via an arch piece in a second Layer part passes over, which extends at some distance from the firstschichttedl and from a liquid container is surrounded, in which a supply line for liquid to be evaporated ability flows.

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In the device according to the invention, said porous layer sucks out liquid via the bend the container and distributes this liquid as an even undisturbed film over the heated wall. The porous layer acts like a lifter.

By changing the liquid level in the container, the amount of liquid sucked in adapts to that of the container supplied amount of liquid. The steady state is the amount of liquid that is drained from the container and fed to the container are equal to each other. In this way, by simple means, is a very satisfactory distribution the liquid over the wall is guaranteed. The mode of operation is explained below with reference to the description of the figures explained in more detail.

In a further advantageous embodiment of the Device according to the invention, said second part of the layer has an increasing in the direction of the bend Cross-section on.

This can be achieved according to the invention in that the second part of the layer has a number of cutouts is provided that taper in the direction of the bow piece. For example, the recesses can be designed triangular.

The above-mentioned change in the cross section of the second layer part ensures that the influence of the Change in the liquid level in the container on the liquid flow supplied to the wall is greater. In other words: the regulation of the flow of liquid supplied to the wall has become more sensitive.

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In a further advantageous embodiment of the Device according to the invention, the porous layer is formed by a number of gauzes with coarse mesh, which is of a Gauze layer are surrounded with finer mesh.

In this way a siphon is obtained, the liquid flow in the siphon not being too strong Resistance is encountered, while due to the fine-meshed gauze the capillary force is so great that the liquid will evaporate, but cannot flow out.

Another embodiment of the device according to The invention is characterized in that the space in which the steam is formed is via a steam line with a condenser is connected, which is connected to the liquid container via a Knndensat line, the condenser being higher is arranged as the liquid container and there is a liquid barrier in the condensation line.

In this way a device is obtained in which the vapor formed heats from the heatable wall to the condenser transported and in which the medium circulates without the use of pumping means.

Furthermore, in this device, such a liquid level "automatically adjusts itself in the liquid container, that the flow of liquid supplied to the wall always corresponds to the amount of medium evaporated.

In a further advantageous embodiment of the device according to the invention, in which the liquid to be evaporated is a metal, e.g. sodium, is the space in which steam

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is formed, via a steam line to the condenser connected, which is connected via a condensate line to a collecting vessel from which the condensate is removed Liquid container is supplied in such a mass that the amount supplied is greater than the amount evaporating.

With this device there is always an excess supplied to liquid of the heatable wall. This Excess will flow out of the porous layer due to gravity on the underside. This has the advantage that no accumulation of metal oxides can result in the porous layer.

Such a build-up would be corrosive

Induce attack on the porous layer and the wall of the evaporator. The fact that an excess of liquid is allowed to flow through the porous layer makes it long Lifetime of the device ensured;

The invention is explained in more detail below, for example with reference to the drawing. Show it:

Fig. 1 shows schematically and not to scale a device for evaporating liquids,

Fig. 2 is a graph showing the relationship between the pressure and the mass flow rate of the liquid in the porous layer.

Fig. 3a shows the manner in which the porous layer may be provided with triangular recesses _r

3 for the manner in which the cross-section of the porous Layer decreases from the bend,

FIG. K is a graph showing the relationship between the pressure and the mass flow rate of the liquid in the porous layer of FIG. 3;

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5 shows an evaporation device in which the steam, after it has been passed over a condenser, flows back into the liquid container via a condensate line,

6 shows a vaporizer device for vaporizing sodium, in which the sodium is circulated by pumps with IfiLfe and FIGS. 7 and 8 show other embodiments of FIG Evaporation devices, in Fig. 1, 1 denotes one Evaporation tank that is on the top with a vapor discharge pipe 2 and on the underside with a steam discharge line 2 and on the underside with a line 3 for discharge any remaining liquid is provided.

On the outside, the container 1 is surrounded by an electrical heating coil 4. On the inside, the wall of the container 1 is covered with a first porous layer part 5, which merges via an arched piece 6 into a second porous layer part 7, which extends parallel to the layer part 5 and is surrounded by a liquid container 8. Liquid to be evaporated can be fed to the container 8 via a line 9 by means of a pump.

The porous layer 5 »6, J consists of a number of gauze layers with coarse meshes, which are covered by a gauze with fine meshes. The operation of this device is as follows.

Because current is passed through the heating coil 4, the wall of the container 1 and the porous Layer part 5 supplied heat.

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With the aid of the pump 10, the supply line 9 the container 8 supplied to be evaporated liquid. By capillary action, the liquid in the container 8 rises into the porous layer part 7 up to the cross section 11 of the arch piece 6 up. From this point on, the liquid flows down through the layer part 5 under the action of gravity. the porous layer 7 »6» 5 acts like a lifter, whereby the Liquid is passed as a thin even layer over the heated inner wall of the container 1, the Liquid stream completely or partially evaporated.

The balance of forces in the porous layer is given by the equation:

β -

at H = height of layer part 5, h = height of layer part 7 above the liquid - level,

/ P = specific gravity of the liquid uiid g S = gravity.

Δ P and; - "■ ρ are the pressure losses in part 5 and in part 7, respectively due to the friction encountered by the liquid flow in the porous layer.

Δ : P "= CH. -7 and AP. = Ch. ^ P, HA h A

where C = constant

A = the area available for liquid flow

the porous layer and
.-> - »■> = mass flow rate of the liquid.

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The above forms are graphed in Figure 2, and it can be seen that an equilibrium between ascending and flowing down the wall Liquid is reached at ftK.

When the liquid level in the container 8 drops so that the distance h is changed to h, the pressure becomes in 'the ascending liquid', along the dashed line Line run in FIG. 2 Mass flow fH_ reached, which is smaller. So this is what goes on shows that by changing the liquid level in the container 8 the led over the wall of the container 1 Liquid flow adapts to the amount to be evaporated.

In the case of very rapid changes either in the steam requirement or in the heat supplied, it will be desirable to adapt the supplied liquid flow as quickly as possible.

This can be achieved, for example, by designing the container 8 to be narrow, so that it is relatively small Changes in the supply of liquid quickly, relatively large changes in level in the container, and thus one Change of h, can be brought about.

Even faster regulation can be achieved by using the cross section available for the liquid A of the layer part 7 is reduced from the arcuate piece 6 downwards.

This can be done with a shape according to FIG. 3a or a Realize the shape according to Fig. 3b.

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e-9-

In Fig. 3a, the layer part 7 has a from Elbow 6 to a pointed shape.

In Fig. 3t), a reduction of the cross section of the layered part 7 is obtained in that triangular training savings ¹ to 17 is attached.

Any combination of these two forms is also possible.

This change in the cross section A of the layer part

7 has the consequence that At? now both through the change

/ η

of h as well as by changing A.

The effect is shown in Fig. 4, from which it can be seen that with the same change h -> h in the liquid level the change in the liquid flow m - ■> m ", where a state of equilibrium exists, is much greater than in the situation shown in FIG.

In this way, the liquid supply can be adapted very quickly to changing operating conditions will.

The evaporation device according to FIG. 1 can be used in chemical process engineering for the evaporation of substances will.

The device can also be used in systems in which an evaporating and condensing medium is heat transported.

Such a system is shown schematically in FIG. The device of Fig. 1 is with the en reference numerals.

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The vapor discharge line 2 connects the space in the container 1 with a space 1h in which a condenser structure 12, for example the heater of a hot gas motor, is arranged. The bottom of the container 1 is now closed; no condensate needs to be discharged and there is a filling line 13 via which a sufficient amount of medium can be introduced into the device.

The space 14 is connected via a condensate line 15 the liquid container 8 connected. In the line 15 there is a liquid barrier 16. When operating There is such an amount of medium in the device that there is liquid at the bottom of the container 1 that contains the lower end of the layer part 5 used.

The operation of this device is as follows.

Via the heating coil k , the wall of the container 1 is again supplied with heat. It should be noted that the heat can be supplied in any other known manner, for example by means of a burner or a chemical heating system, instead of via a heating coil. As a result of the supplied heat, as has been described above, liquid will evaporate from the layer 5, the amount of liquid supplied from the container 8 being equal to the amount of evaporating liquid in the steady state.

The steam flows through line 2 into space 14 ^% and condenses there on condenser 12.

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The condensate flows back into the container 8 via the line 15 and the liquid barrier 16. the Liquid barrier in this line ensures that when the device is started, no steam passes through it Line can flow. During operation, a column of liquid forms, which ensures that a flow occurs in the direction of the container 8.

In the steady state, an amount of steam flows to the condenser which is equal to the amount flowing to the container 8 Liquid is. When the cooling capacity of the condenser 12 increases, the pressure in space 14 decreases, whereby the column of liquid rises in line '15. The liquid required for this is withdrawn from the container 8, so that the liquid level therein decreases. This means that the porous layer 7> 6, 5 of the wall will add a smaller amount of liquid. The amount of liquid now supplied is too small for the original one Condition and thus certainly too low for the required increase in performance. The lack of fluid is caused by the layer 5 from the itself on the bottom of the container the liquid is absorbed. In this way, the system adapts to changes in performance very easily of the condenser.

If the system is to transport heat at high temperatures, e.g. if the condenser goes through the heater a hot gas engine is formed, metals such as Na or K should be used as the medium.

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In this case, there is a risk that the porous layer and the wall of the container 1 will be severely attacked at higher oxygen concentrations. The oxides are not very volatile, which means that they remain in the porous layer 5 during "evaporation" and accumulate there so that the oxygen concentrations there can exceed the permissible value. In order to avoid such an accumulation, the device according to FIG. 6, the condensate is returned from the space Ik via a discharge line 20 to a storage vessel 21. A line 22, in which there is a pump and a closure member 2k, is connected to the storage vessel 21. Above the pump 23 there is a circulation line 25, which for this purpose ensures that when the closure member 2k is closed, the liquid delivered by the pump can flow back into the storage vessel. The line 22 connects to the underside of the container 1. The underside of the container 1 is connected via a line in which a pump 27 is located the container 8 in connection.

The pump 27 is now set in such a way that it always supplies a larger amount to the container 8 than it does from evaporated from the porous layer. The excess liquid will now flow out of layer 5 on the underside and entrain the non-evaporated oxides so that no Accumulation of these oxides in the layer 5 can occur.

In the systems according to FIGS. 5 and 6 there is an evaporator structure according to FIG. 1 with electrical heating applied. Instead, other designs can also be used, e.g. as shown in Figures 7 and 8.

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Claims (4)

are provided. The evaporator contains a number of tubes 30 which are received on the top and bottom in plates 31 and 32, respectively. These plates 31 and 32 divide a container 33 into a vapor space 3k, a heating space 35 and a condensate space 36. A supply line 37 for heat combustion gases connects to the heating space, which gases with the help of guide transverse walls 38 through the space 35 and along the outside of the Pipes 30 are led to a discharge line 39. The tubes 30 are provided on the inside with a porous layer ^ O, which is bent on the top over the edge of the tubes and is used there with condensate in a container kl. The liquid sucked in from the container k1 from the porous layer kO evaporates in the tubes 30, the steam being able to flow via the steam discharge line 2 to the condenser. Condensate flows back into the container 41 via the condensate line 15. In the evaporator according to FIG. 8, the condensate flows back via the line 22 and the line 26 with the pump 27. PATENT CLAIMS; 1. Device for evaporating liquids, which is provided with at least one heatable wall and with means with the help of which the liquid in question is distributed as a thin film over said wall, thereby characterized in that said means are formed by a porous layer, a first part of which is the wall covered and on the upper side passes over an arc into a second layer part, which is some distance away extends from the first layer part and from a liquid 409847/0558 keitsbehält is surrounded, in which a feed line for liquid to be evaporated opens. 2 »Device according to claim 1, characterized in that that said second part of the layer has a cross-section that increases in the direction of the curved piece. 3. Device according to claim 2, characterized in that that the second part of the layer is provided with a number of recesses which taper in the direction of the curved piece 4. Apparatus according to claim 1, 2 or 3 »characterized in that that the porous layer is formed by a number of gauzes with a coarse mesh, which is formed by a gauze layer with are surrounded by finer meshes. 5 » Device according to one or more of the preceding claims, characterized in that the space in which the steam is formed is connected via a steam line to a condenser, which is arranged via a condensate line with the liquid container and a liquid barrier is located in the condensate line is located. 6, device according to one or more of claims 1, 2, 3 or k _t, in which the liquid to be evaporated is a metal, characterized in that the space in which the vapor is formed is connected to a condenser via a vapor line , which is connected to a collecting vessel via a condensate line, from which the condensate is transferred to the liquid. Keitsbehälters is supplied in such a mass that the supplied Flussxgkeitspaket is greater than the amount evaporating. 409847/0558 Blank page