DE3626359A1 - Evaporator and method for evaporating a fluid - Google Patents

Abstract

An evaporator is described having tubes 3, for bearing a fluid to be evaporated, running in a liquid bath 6. The liquid bath is heated by a steam injector 11 immersed in the liquid bath. The tubes 3 are coiled in a spiral shape, their outer diameter is between 15 and 50 mm, the distance between neighbouring tubes is at least 5 mm and the ratio of coil height to coil outer diameter is between 1.0 and 3.0. <IMAGE>

Description

The invention relates to an evaporator in one Tubes of liquid bath for guiding a evaporating fluids as well as with one in that Liquid bath immersed steam injector.

Evaporators, whose heat exchange surfaces are in one steam-heated liquid bath are located preferably for evaporating low-boiling, liquefied gases, such as B. nitrogen, oxygen, LNG, Natural gas products etc. used. Depending on the type and amount of The heat content of the fluid to be evaporated is sufficient Liquid bath alone is not enough to prevent evaporation ensure and to prevent that the Excess ice build-up forms on heat exchange surfaces. Around it is therefore in In many cases, the liquid bath is required heat and if necessary circulate the liquid. The heating is advantageous by blowing steam made in the liquid bath, being here at the same time due to the rising steam bubbles a revolution of the Liquid occurs.  

However, due to the steam feed Problems can arise at the cold phase interfaces Steam strikes come when steam condenses suddenly. The forces released by the steam strikes lead to a strong mechanical load. Such evaporators are therefore very sensitive to changes in the Load behavior, d. H. Changes in the amount of steam. It comes especially in the low load area Steam strikes due to backflow of cold liquid in the steam system.

The evaporators are preferred for applications used, where a rapid change of the Load range (often from 0 to 100% load in a few Seconds). It gets through in the apparatus rapid temperature changes to mechanical stresses (so-called thermal shock stress).

The present invention is based on the object to develop an evaporator of the type mentioned at the beginning, which has a low susceptibility to failure in the entire load range having. In particular, steam shocks at the Feed of steam over the entire occurring Load range avoided and controlled, a high one mechanical stability achieved and a high Heat transfer value can be achieved.

This object is achieved in that the Pipes are wound helically, the Pipe outside diameter between 15 and 50 mm, the distance neighboring pipes at least 5 mm and the ratio Winding height / outside diameter between 1.0 and Is 3.0.  

It has been shown that the performance of such Evaporator strongly depends on the geometry selected. Around at the same time the highest possible stability towards mechanical influences and good heat transfer from the liquid bath to the fluid to be evaporated must achieve the dimensioning of the pipes and the Pipe spacing is in the specified range. Although the Requirements regarding stability, heat transfer and Load behavior contradict the appearance, has shown in practice that the Evaporator according to the invention optimally all requirements can be met.

In a preferred development of the invention The tubes are wrapped around a core tube and evaporator the free cross section of the core tube is between the 0.5 and 2 times the free cross-section of the winding.

The use of a core tube increases the stability of the jacket-side liquid flow and reduces the Risk of erosion. In addition, you can define better Set operating states.

In a further preferred embodiment of the The subject of the invention is the steam injector through a or more provided with vapor bubble outlet openings Tubes formed, which are arranged in the region of the winding axis are.

The steam outlet openings are at one vertically aligned winding axis in the lower area of the Winding core or below. The escaping steam condenses within the core tube area, causing it to an upward flow of liquid comes. This creates a natural circulation flow, whereby the pipes from one facing down Liquid flow can be coated.  

In a further advantageous embodiment of the Subject of the invention is the diameter of Vapor outlet openings 4 to 8 mm, preferably 6 mm.

In a preferred development of the subject matter of the invention, a heating surface load for the pipes of a maximum of 50,000 W / m ^{2 is} set.

The heating surface load is provided by the a sufficient heating area, d. H. Number of tubes, each according to the purpose of the evaporator, below this Limit set.

The invention also relates to a method for Evaporation of a fluid by heat exchange with one Liquid bath, with the steam in the liquid bath is initiated, which is characterized in that at least two steam supply systems are provided and the steam up to a predetermined maximum amount exclusively through a first steam supply system and if the quantity exceeds the specified maximum Quantity exclusively or additionally by one or several other steam supply systems are supplied.  

The method according to the invention makes it very broad Load range covered. If the steam supply system for large amounts of steam is designed, then this results Problem that with low steam loads, (e.g. in the area between ¹ / ₁₀ and ¹ / ₁₀₀ the maximum load or still below) liquid into the steam supply system penetrates and there are steam strikes. For this The reason according to the invention is at least two such Systems provided, one of the systems for the Steam feed from 0 to an intermediate value while the second or the remaining systems of the Intermediate value up to the maximum value the steam feed take over. It is conceivable that the first System continues to deliver steam, i.e. H. the amount of steam of the individual systems add up, or that with the Intermediate value exceeding demand the first system switched off and at the same time the other system or systems be regulated to the appropriate value.

In a preferred development of the invention The procedure is through the first Predetermined maximum quantity supplied to the steam supply system between 2 and 4 t / h, preferably about 3 t / h.

The invention and further details of the invention are shown schematically using Embodiments explained in more detail. Here shows  

Figure 1 is a schematic representation of an evaporation process according to the invention.

Fig. 2 shows an embodiment of an evaporator according to the invention;

Fig. 3 shows another embodiment of an evaporator according to the invention;

Fig. 4 shows a detail A from FIG. 3.

Fig. 1 shows a flow diagram of a method for vaporizing a low-boiling liquid. The low-boiling liquid, for example nitrogen, oxygen, argon, ammonia, LNG or a natural gas product such as methane, propane, butane or a flare gas, is stored in a container 1 in liquid form. The liquefied gas is removed from the container 1 by means of a pipeline 2 and fed to pipes 3 of an evaporator. The evaporator has a container 4 filled with a liquid 6 . The tubes 3 are wound helically around a core tube 5 and are completely immersed in the liquid bath 6 .

The liquefied gas is fed to the tubes 3 at the lower end. On its way up through the pipe windings, the liquefied gas evaporates by exchanging heat with the water bath 6 . The vaporized gas is removed from the upper end of the pipe windings by means of a line 7 .

To heat the liquid 6 , steam is introduced via a steam introduction system 11 in the lower region of the liquid bath. The steam is supplied inside the core tube 5 near its lower end. In addition to heating the liquid, the introduction of steam causes the liquid to circulate naturally, as indicated by arrows 12 . The rising vapor bubbles cause warm liquid to rise inside the core tube, while at the same time colder liquid flows down the tube.

Excess condensate is removed through a line 8 from the upper edge of the container 4 and pumped into a liquid container 9 . Steam is withdrawn from the head of the container 9 via a line 10 and fed to the steam supply system 11 . The liquid used is preferably water.

Fig. 2 shows an evaporator according to the invention in longitudinal section. The same reference numerals as in FIG. 1 are used for analog components. The evaporator has a nozzle 14 for the supply of the fluid to be evaporated, which is connected via a tube guided downward through the core tube to a tube cup into which the tubes 3 wound around the core tube 5 are inserted. The upper ends of the tubes 3 are combined in a tube cup 15 , through which the evaporated fluid is removed. Another nozzle 16 at the upper end of the evaporator is used to supply steam. The connecting piece 16 is connected to a tube 13 leading downward within the core tube 5 , which tube ends shortly before the lower end of the core tube 5 and the end face of which is closed. At its lower end, the tube 13 has steam outlet openings 17 distributed over its circumference, through which steam bubbles emerge into the liquid 6 .

The tube 13 has, for example, a nominal width of 50 mm, 100 openings 17 are provided, each of which has a diameter of 6 mm. The outer diameter of the outermost winding is approximately 1000 mm, the distance from the lowest to the upper winding is, for example, 1500 mm, ie the ratio of the winding height to the winding diameter is 1.50. The free cross-section of the tube winding is approximately 0.21 m ² , that of the core tube is approximately 0.49 m ² , ie the free cross-section of the core tube is 1.7 times as large as that of the winding.

The evaporator also has a nozzle 19 for supplying liquid and an overflow 18 for excess condensate.

FIG. 3 shows a further embodiment of an evaporator according to the invention, in which, in contrast to the evaporator according to FIG. 2, two steam supply systems 20, 21 are provided, both of which open into the liquid 6 below the lower edge of the core tube 5 . The first steam supply system has a connecting piece 20 which is connected to a pipe 22 leading downward through the core pipe 5 . The tube, which has a diameter of 80 mm, has steam outlet openings 17 with a diameter of 6 mm each at its lower end. A second steam supply system has a pipe 23 leading downward from a connecting piece 21 through the core pipe. The tube 23 , the diameter of which is 150 mm, likewise has steam outlet openings 17, each with a diameter of 6 mm, at its lower end.

If the steam requirement is between 0 and 3 t / h, the steam is supplied exclusively through the thinner tube 22 . If a larger amount of steam is required, the steam supply to the nozzle 20 is suddenly interrupted and the steam is instead supplied to the nozzle 21 . A quantity of steam is accordingly supplied via the nozzle 21 , which is between the minimum value of 3 t / h and a predetermined maximum value. Instead, it is also possible to use two steam supply systems of the same type, each of which can supply, for example, between 0 and 3 t steam / h. If there is a demand between 0 and 3 t / h, the steam is only supplied via one of the systems; if there is a higher demand, the first system remains at the maximum value, while for the second system between 0 and 3 t / h of steam as required are fed. Analogously, more than two such systems can also be operated.

FIG. 4 shows a section A from FIG. 3. As an example, six tubes 3 of a winding are drawn out, the outer diameter d of which is between 15 and 50 mm. The distance between adjacent tubes ( l ₁ in the horizontal direction, l ₂ in the vertical direction) is at least 5 mm and is preferably in the range between 10 and 25 mm for l ₁ and between 5 and 20 mm for l ₂ .

Claims (7)

1. Evaporator with pipes running in a liquid bath for guiding a fluid to be evaporated and with a steam injector immersed in the liquid bath, characterized in that the pipes ( 3 ) are wound helically , the pipe outer diameter between 15 and 50 mm, the distance between adjacent pipes ( 3 ) at least 5 mm and the ratio of winding height / winding outer diameter is between 1.0 and 3.0. 2. Evaporator according to claim 1, characterized in that the tubes ( 3 ) are wound around a core tube ( 5 ) and the free cross section of the core tube ( 5 ) is between 0.5 and 2 times the free cross section of the winding. 3. Evaporator according to claim 1 or 2, characterized in that the steam injector is formed by one or more pipes ( 13; 22, 23 ) provided with steam bubble outlet openings ( 17 ), which are arranged in the region of the winding axis. 4. Evaporator according to one of claims 1 to 3, characterized in that the diameter of the vapor bubble outlet openings ( 17 ) is between 4 and 8 mm. 5. Evaporator according to one of claims 1 to 4, characterized in that a heating surface load for the tubes ( 3 ) of a maximum of 50 000 W / m ^{2 is} set. 6. Process for evaporating a fluid Heat exchange with a liquid bath in which steam is introduced into the liquid bath, thereby characterized in that at least two Steam supply systems are provided, and the steam up to a predetermined maximum quantity only through a first steam supply system and at one the quantity exceeding the predetermined maximum exclusively or additionally by one or more other steam supply systems is supplied. 7. The method according to claim 6, characterized in that that supplied by the first steam supply system predetermined maximum quantity is between 2 and 4 t / h.