WO2003012352A2 - Multi-stage condenser-evaporator - Google Patents

Abstract

The invention relates to a circulating condenser with a condenser block, comprising condensing passages (4) for a heating medium and at least one circulating section (100,200,300,400) with vaporising passages (1,11) for a liquid. The inlet openings (2,12) and the outlet openings (3, 13) for each evaporation passage (1, 11) are located on opposite sides of the condenser block, whereby the inlet openings (2,12) for all the evaporation passages (1, 11) in the circulating section (100,200,300,400) are arranged beneath the outlet openings (3,13). Furthermore, first and second evaporation passages (1, 11) are provided, whereby the inlet openings (2) for the first evaporation passages (1) and the outlet openings (13) for the second evaporation passages (11) are on the same side of the condenser block.

Description

 description

Multi-level condenser evaporator

The invention relates to a circulation condenser with a condenser block which has liquefaction passages for a heating medium and at least one circulation section with evaporation passages for a liquid, the inlet opening and the outlet opening of each evaporation passage being located on opposite sides of the condenser block and the inlet openings of all evaporation passages of the circulation section below Exit openings of the evaporation passages of the circulation section are arranged.

In a low-temperature air separation plant with a pressure column and a low-pressure column, liquid oxygen from the low-pressure column is vaporized against gaseous nitrogen from the pressure column in indirect heat exchange in a heat exchanger, the nitrogen condensing. Such a condenser-evaporator system is usually referred to as the main condenser.

The main condenser is manufactured almost exclusively as a plate heat exchanger and is designed as a falling film evaporator or as a circulation condenser. At a

Circulating condenser is the condenser block in the liquid bath from which liquid is to be evaporated. The liquid enters the evaporation passages of the condenser block from below and is partially evaporated against the heating medium flowing through the liquefaction passages. The density of the medium evaporating in the evaporation passages is lower than the density of the surrounding liquid bath, as a result of which a siphon effect is created, so that liquid flows from the liquid bath into the evaporation passages.

Liquid oxygen is evaporated in the main condenser of an air separation plant. It is important to ensure that the evaporation passages of the

Condenser blocks flowing liquid oxygen is evaporated to a fraction. This prevents interfering impurities that may be present in the liquid oxygen from accumulating. So be for example, only about 10% of the amount of liquid oxygen flowing into the evaporation passages evaporates and 90% is conveyed as liquid from the outlet openings of the evaporation passages back to the inlet openings of the evaporation passages. The part of the condenser block in which such a circulation of liquid is achieved is referred to below as the circulation section.

The greater the immersion depth of the condenser block of a circulation condenser in the liquid bath, the higher the mean hydrostatic pressure in the evaporation passages and the worse the liquid evaporates, since the boiling point of the liquid increases in accordance with the vapor pressure curve. The efficiency of a circulation capacitor can, however, be increased by dividing the capacitor block into a plurality of circulation sections arranged one above the other. The advantage of such an arrangement is that the immersion depth of the individual circulation sections is in each case less than in the case of a single high capacitor block. This reduces the hydrostatic pressure in the evaporation passages and the liquid can evaporate more easily.

From DE 199 39294 a multi-storey circulation condenser is known, in which the inlet openings and the outlet openings of the evaporation passages of a circulation section are located on opposite sides of the heat exchanger block. In this way, flow paths of the same length for the liquid oxygen to be evaporated are achieved in all evaporation passages. This has the advantage that the pressure losses and thus the circulation rates are the same in all evaporation passages. On the other hand, this arrangement has the disadvantage that the circulating liquid oxygen quantity always exits on the side of the condenser block opposite the inlet openings and has to be returned to the inlet openings via complex pipelines or channels.

It is therefore an object of the present invention to develop a circulation condenser in which the evaporation of the liquid is as uniform as possible in all evaporation passages and which can be produced with the least possible design effort. This object is achieved by a circulation condenser of the type mentioned at the outset, in which first and second evaporation passages are provided and the inlet openings of the first evaporation passages and the outlet openings of the second evaporation passages are located on the same side of the condenser block.

According to the invention, the liquid enters the first evaporation passages from below, flows upwards in the evaporation passages, partially evaporates and leaves the first evaporation passages on the opposite side of the condenser block. The liquid portion of the liquid-gas mixture emerging from the first evaporation passages flows to the inlet openings of the second evaporation passages arranged on the same side as the outlet openings of the first evaporation passages. The liquid then flows through the second evaporation passages back to the side of the condenser block on which the inlet openings in the first evaporation passages are located. During the flow through the second evaporation passages, part of the liquid is again evaporated.

According to the invention, the liquid is conveyed back and forth between the two opposite sides of the condenser block by means of the first and second evaporation passages and thereby evaporates increasingly. Elaborate constructions such as return pipes or return channels for the liquid are therefore no longer necessary.

The evaporation passages are designed in such a way that all inlet openings of a circulation section are located below the outlet openings of this circulation section. In this way, a liquid level can be selected in front of the inlet openings such that the liquid enters all evaporation passages via the inlet openings, but the outlet openings end in the gas space. This has the advantage that the ascending in the evaporation passages

Liquid-gas mixture experiences the same back pressure in all evaporation passages, which in turn prevents different circulation rates in the individual evaporation passages. If, in addition, the liquid level in front of the inlet openings is chosen so high that the static pressure at the individual inlet openings differs by less than 20%, preferably less than 10%, particularly preferably less than 5%, almost the same circulation rates are achieved through all evaporation passages.

All of the first and / or all of the second evaporation passages of a circulation section are preferably each of the same length. All evaporation passages of a circulation section are particularly preferably of the same length. In this way the circulation rate is the same in all evaporation passages, i.e. the same ratio of non-evaporated liquid to evaporated gas quantity is set in each evaporation passage. As a result, the liquid to be evaporated is always mixed well and any impurities do not accumulate in the liquid.

In a preferred embodiment, a circulation section has as many first as second evaporation passages. It is also advantageous if all evaporation passages have the same cross section. This measure ensures that as much liquid is conveyed through the first evaporation passages as through the second evaporation passages.

The circulation condenser according to the invention is particularly suitable as the main condenser of a low-temperature air separation plant.

The invention and further details of the invention are explained in more detail below with reference to the exemplary embodiments shown schematically in the drawings. Here show:

Figure 1 shows the evaporation passages of an inventive

Revolving section, Figure 2, the view A of Figure 1,

FIG. 3 shows view A of an alternative embodiment from FIG. 1,

Figure 4 shows a circulation capacitor with four arranged one above the other

Revolving sections, FIG. 5 the top view of FIG. 4, 6 shows a condenser evaporator system with four arranged in parallel

Capacitor blocks, each consisting of four superimposed

Circulation sections exist, FIG. 7 shows a section along the line A-A in FIG. 6,

FIG. 8 shows the top view of the capacitor blocks according to FIG. 6,

Figure 9 is a section along the line A-A in Figure 6 with an alternative

Arrangement of the evaporation passages and FIG. 0 shows the top view of the arrangement of the evaporation passages in accordance with

Figure 9.

In Figure 1, a circulation section of a circulation condenser is shown schematically, the main condenser of a double column in one

Cryogenic air separation plant is used to evaporate oxygen. The circulating condenser has a plurality of heat exchange passages arranged in parallel, in which gaseous nitrogen in the indirect

Heat exchange with liquid oxygen is condensed, the oxygen evaporating.

The liquefaction passages for the nitrogen (not shown in FIG. 1) extend from top to bottom over the entire height of the circulation condenser. to

Conduction of oxygen are two different types of evaporation passages

1. 11 provided. In the drawing, the boundaries of the first evaporation passages 1 are shown with solid lines, those of the second evaporation passages 11 with dashed lines.

1, the first evaporation passages 1 have their inlet openings 2 at the lower left end of the circulation section and their outlet openings 3 at the upper right end. The second evaporation passages 11 run in the opposite direction from bottom right to top left. The individual evaporation passages 1, 11 run from the respective inlet opening

2. 12 first horizontally, then vertically upwards and finally horizontally to the outlet openings 3, 13. This embodiment ensures that all evaporation passages are each of the same length. FIG. 2 shows the view of the side of the circulation section designated by “A” in FIG. The liquefaction passages 4 for the nitrogen and the evaporation passages 1, 11 for the oxygen alternate in order to achieve the best possible heat exchange between the nitrogen and the oxygen. The first evaporation passages 1 are located in one half of the circulation section, the second evaporation passages 11 in the other half. Correspondingly, the inlet openings 2 of the first evaporation passages 1 can be seen in the right half of FIG. 2 and the outlet openings 13 of the second evaporation passages 11 can be seen in the left half of FIG.

An alternative arrangement of the evaporation passages 1, 11 is shown in FIG. The evaporation passages 1, 11 alternate with the liquefaction passages 4. In contrast to the arrangement according to FIG. 2, however, the first evaporation passages 1 and the second evaporation passages 11 are now also arranged alternately, a liquefaction passage 4 being located between a first evaporation passage 1 and a second evaporation passage 11. In other words: in the illustration according to FIG. 1, the following passage arrangement is repeated several times in a direction perpendicular to the sheet plane: a plane with nitrogen passages 4, followed by first evaporation passages 1 running from bottom left to top right, followed by a further plane with nitrogen passages which are finally followed by second evaporation passages 11 running from bottom right to top left.

Figure 4 shows a section through a circulation condenser according to the invention, which is used as the main condenser of a double column of a low-temperature air separation plant. The circulation condenser consists of four circulation sections 100, 200, 300, 400 arranged one above the other. At the openings with inlet and outlet openings, e.g. 402, 403, 412, 413, provided sides of each circulation section 100, 200, 300, 400, liquid containers 120, 220, 320, 420 are respectively attached.

The liquid containers 120, 220, 320, 420 are connected to one another by means of an overflow line 21 on one side of the condenser block. The overflow line 21 has an inlet opening 122, 222, 322, 422 at the level of each circulation section 100, 200, 300, 400, so that liquid enters the overflow pipe 21 into the respective liquid container 120, 220, 320, 420 at a certain fill level in the liquid container 120, 220, 320 of the underlying circulation section 100, 200, 300 is passed.

The inlet openings 122, 222, 322, 422 in the overflow line 21 are provided at such a height that during operation the maximum fill level in the liquid containers 120, 220, 320, 420 between 50 and 90%, preferably between 60 and 80% of the Height of the respective circulation section 100, 200, 300, 400 is. The inlet openings 122, 222, 322, 422 are particularly preferably arranged in the overflow line 21 such that the maximum liquid level in the liquid containers 120, 220, 320, 420 is below the outlet openings 3, 13.

The arrangement according to the invention of all inlet openings 2, 12 below the outlet openings 3, 13 of the respective circulation section allows a liquid level in the liquid containers 120, 220, 320, 420 to be selected which lies between the uppermost inlet opening 2, 12 and the lowest outlet opening 3, 13 , This ensures that all evaporation passages 1, 11 are in liquid at their inlet 2, 12 and in the gas space at their outlet 3, 13. The back pressure at the outlet end 3, 13 is therefore the same for all evaporation passages 1, 11, so that an approximately equal circulation rate is achieved in all evaporation passages 1, 11.

The liquid containers 120, 220, 320, 420 are also traversed by two gas collecting lines 23, so that the oxygen gas which arises during evaporation in the evaporation passages 1, 11 and flows into the liquid containers 120, 220, 320, 420 from the liquid containers 120, 220, 320, 420 can be withdrawn via the gas manifold 23.

In Figure 5, the arrangement of the gas manifolds 23 and the overflow pipe 22 is shown in plan view. The first and second evaporation passages 1, 11 are arranged in each circulation section 100, 200, 300, 400 as explained above with reference to FIG. 2. 5, the first evaporation passages 1 are in the lower half of the drawing, the second evaporation passages 11 in the upper half of the drawing. Accordingly, liquid is transported from left to right through the first evaporation passages 1 and from right to left through the second evaporation passages 11. The gas collecting lines 23 are arranged such that they are not in front of the outlet openings of the evaporation passages 1, 11. Due to the lateral displacement of the gas collecting lines 23 relative to the outlet openings 3, 13 of the evaporation passages 1, 11, the gas-liquid mixture emerging from the evaporation passages 1, 11 is first deflected, the flow rate of the gaseous oxygen being reduced and the gaseous being separated from the liquid oxygen. The entrainment of liquid oxygen into the gas manifold 23 is largely avoided.

In a circulation section 100, 200, 300, 400, the entire liquid is always conveyed from one side to the other side of the circulation section 100, 200, 300, 400 and back again and is optimally mixed. A liquid overflow 21 is therefore only necessary on one side of the condenser block. This overflow 21 is preferably arranged on the side of the condenser block on which the supply 25 of the liquid oxygen takes place at the top.

The nitrogen passages, not shown, extend over the entire height of the condenser block, that is to say over all circulation sections 100, 200, 300, 400. The gaseous nitrogen is fed to the nitrogen passages via the feed line 26 and withdrawn as a liquid at the lower end of the block via line 27. The gaseous nitrogen is distributed over the nitrogen passages via a collector / distributor 28 connected to the condenser block.

FIGS. 6 to 8 show a further variant of the invention

Circulating capacitor shown. This consists of four capacitor blocks 61, 62, 63, 64, which in turn each have four circulation sections 100, 200, 300, 400. Two capacitor blocks 61, 62 and 63, 64 are arranged directly next to each other, so that the respective evaporation passages 1, 11 run parallel to one another. The resulting double blocks 61, 62 and 63, 64 face each other with their entry and exit openings 2, 3, 12, 13 (see FIG. 8). The arrangement of the first and second evaporation passages 1, 11 again corresponds to FIG. 2. The capacitor blocks 61 and 62 or 63 and 64 are arranged next to one another in such a way that their block halves provided with the first evaporation passages 1 adjoin one another. The two double blocks 61, 62 and 63, 64 each have a common liquid container 20. In the middle between the capacitor blocks 61, 62, 63, 64 there is a liquid container 30 common to each block for each circulation section 200, 300, 400. The outer ones Liquid containers 20 only collect the circulating liquid which is passed through the second evaporation passages 11 into the liquid containers 20 and convey them back into the central liquid container 30 via the first evaporation passages 1.

Due to the described arrangement of the evaporation passages 1, 11, the gas-liquid mixture emerging from the first evaporation passages 1 is supplied essentially in the middle of the liquid container 30. The gas collecting lines 23 are therefore in the outer region of the liquid container 30 near the inlet openings into the second Evaporation passages 11 arranged. In these zones, the flow rate of the gas-liquid mixture emerging from the first evaporation passages 1 has calmed down to such an extent that practically no liquid is entrained into the gas collecting lines 23.

FIGS. 9 and 10 show an alternative arrangement of the evaporation passages 1, 11 with an arrangement of the condenser blocks 61, 62, 63, 64 according to FIG. 6. As in the system according to FIGS. 6 to 8, a circulation section is composed of the corresponding sections 100, 200, 300, 400 of the four capacitor blocks 61, 62, 63, 64. In this case, however, not each of the blocks 61, 62, 63, 64 has first evaporation passages 1 and second evaporation passages 11.

The flow according to the invention through first evaporation passages 1 and backflow through second evaporation passages 11 is not realized in each individual block 61, 62, 63, 64, but rather in that the two adjacent condenser blocks 61, 62 and 63, 64 are each rotated through 180 ° , be put together. The evaporation passages of the condenser blocks 61 and 63 correspond to the second evaporation passages 11 and the evaporation passages in the condenser blocks 62 and 64 correspond to the first evaporation passages 1.

Claims

claims 1. Circulation condenser with a condenser block, which has liquefaction passages for a heating medium and at least one circulation section with evaporation passages for a liquid, the inlet opening and the outlet opening of each evaporation passage being on opposite sides of the condenser block and the inlet openings of all evaporation passages of the circulation section below the outlet openings of the Evaporation passages of the circulation section are arranged, characterized in that first and second evaporation passages (1, 11) are provided and the inlet openings (2) of the first evaporation passages (1) and the outlet openings (13) of the second evaporation passages (11) are on the same side of the capacitor block. 2. Circulation condenser according to claim 1, characterized in that all first evaporation passages (1) and / or all second evaporation passages (11) are of the same length. 3. circulation capacitor according to one of claims 1 or 2, characterized in that the circulation section (100, 200, 300, 400) as many first as second Evaporation passages (1, 11). 4. Circulation condenser according to one of claims 1 to 3, characterized in that all first and / or all second evaporation passages (1, 11) have the same cross section. 5. circulation condenser according to one of claims 1 to 4, characterized in that between two first evaporation passages (1) no second evaporation passage (11) is arranged. Circulating condenser according to one of claims 1 to 5, characterized in that exactly a second evaporation passage (11) is arranged between two first evaporation passages (1). Use of a circulation condenser according to one of claims 1 to 6 as the main condenser of a cryogenic air separation plant.