EP0394758B1 - Heat exchanger - Google Patents

Description

The invention relates to a heat exchanger with a substantially cylindrical flow space, which is delimited by a jacket, with a number of tubes which run through the flow space in a direction essentially parallel to the cylinder axis, with at least one pair of connecting pieces, which are opposite one another on the cylinder surface of the jacket are arranged and lead into the flow space, and with support plates which are installed substantially perpendicular to the cylinder axis in the flow space.

Such heat exchangers are used for a large number of applications for cooling or heating liquids and / or gases by indirect heat exchange. In this case, a fluid enters the flow space through one of the nozzles, rinses the pipes there with a flow direction that is essentially perpendicular to the cylinder axis, and flows out again through another nozzle. The flow space is often divided into several sections, each with its own pair of filler and drain connections. Such a design, in which the fluid in the flow space flows in cross flow to a second fluid which is passed through the interior of the tubes, offers the advantage that the first fluid experiences only a very slight pressure loss when passing through the heat exchanger. This is achieved through a relatively direct passage through the flow space, which, however, presupposes a fairly open construction without flow-preventing fittings in the flow space.

This in turn reduces the mechanical stability and rigidity of the device, so that such heat exchangers have hitherto only been able to be used in the flow space at relatively low flow velocities. In addition, the problem of distributing the first fluid in the flow space perpendicular to the direction of flow has not yet been satisfactorily solved in such cross-flow heat exchangers.
In addition to the mechanical stability in the longitudinal direction, problems can also arise in the heat exchanger due to acoustic vibrations, which are built up by standing waves in planes perpendicular to the cylinder axis.

The object of the invention is now to improve a heat exchanger of the type mentioned in such a way that its mechanical stability is also sufficient for use at higher flow rates.
In particular, the difficulties due to acoustic vibrations are to be overcome. Favorable heat transfer performance and good distribution of the first fluid in the flow space should be ensured.

This object is achieved by at least one anti-drumming plate which is arranged essentially parallel to the cylinder axis and essentially parallel to the connecting line of the pair of opposing connecting pieces in the flow space. In general, two parallel anti-drumming plates are used on both sides of the cylinder axis, which run the full length of the flow space. Under certain circumstances, an odd number and an asymmetrical one Arrangement of anti-drumming plates can be favorable. In this way, obstacles are built into each cross-sectional area, which counteract the formation of standing acoustic waves.
The interaction with the support plates results in a much more stable and rigid mechanical structure and the rigidity of the cylindrical jacket around the flow space is increased. The heat exchanger according to the invention can therefore withstand flow velocities of up to approximately 10% of the speed of sound in the flow space.

To further increase the stability of the heat exchanger and to facilitate its manufacture, it is expedient if the anti-drumming plates and the support plates are integrally connected to one another, for example by welding the contact surfaces. This creates a particularly stable and rigid honeycomb structure within the flow space.

However, with this type of construction, a transverse exchange of the fluid in the flow space between different honeycombs is no longer possible, so that a uniform fluid distribution is not easily guaranteed. In particular, the exchange between the area divided into honeycombs and the edge area of the flow space is severely hampered, so that the heat transfer performance is not optimal, especially in this edge area.

A further development of the invention has a baffle plate which is arranged essentially perpendicular to the connecting line between two pairs of opposing nozzles and continuously over the entire length of the flow space parallel to the cylinder axis. It is advantageous if there is a space between the long sides of the baffle plate and the casing.

Compared to commonly used baffle plates, which are only attached to a small area below the inlet nozzle and therefore only one represent a rough measure for the distribution of the fluid flowing through the inlet connection, the baffle plate specifically effects a better supply of fluid into the edge regions of the flow space.

Furthermore, it is favorable if the baffle plate is divided into sections in the direction of the cylinder axis, which have different relative hole cross-sectional areas. In this way, a targeted distribution of the fluid guided through the flow space can also be achieved in the direction of the cylinder axis.

It is advantageous if the baffle plate is divided into sections, each of which has a whole number n of sections and is delimited on each side either by one end of the flow space or by a plane lying exactly between two pairs of nozzles perpendicular to the cylinder axis. The nozzles are preferably arranged so that the sections are the same size. A heat exchanger can have several sections or just one. In the latter case there is only one pair of nozzles.

hinsichtlich ihrer Abmessungen a_i, b_i und ihrer relativer Lochquerschnittsfläche L_i identisch aufgebaut sind.In a favorable further development of the invention, a section of the baffle plate has an even number n of successive sections P _i , i = 1,..., N, the sections in each case

${\text{P}}_{\text{i}}{\text{and P}}_{\text{n-i + 1}}\text{, i = 1, ..., n / 2}$

are identical in terms of their dimensions a _i , b _i and their relative hole cross-sectional area L _i .

The section or sections are thus symmetrical with respect to their division into sections to the connecting line of the associated pair of nozzles.

It proves to be advantageous if the number n of sections P _i within a section is between 2 and 18 and if the sections P _i apply to the raltive hole cross-sectional areas L _i :

${\text{L}}_{\text{i}}{\text{> L}}_{\text{i + 1}}\text{, i = 1, ..., n / 2-1.}$

N is preferably between 4 and 8.

In a favorable embodiment, the ratio between the largest and smallest relative hole cross-sectional area L ₁ / L _{n / 2 is selected} as a function of the distribution length l _v (= distance between the central axis of the filler neck and delimitation of the corresponding section) and the inner radius r of the filler neck, preferably according to the relationship

$\text{L₁ = f. √}\overline{{\text{l}}_{\text{v}}\text{/ r}}{\text{. L}}_{\text{n / 2}}\text{.}$

The factor f is on the order of 1, approximately between 0.8 and 1.3. The ratio l _v / r is usually in the range of 3; L₁ / L _{n / 2} is generally about 1.5 to 2.0, preferably about 1.7.

Extensive hydrodynamic calculations have shown that with the help of such a design of the baffle plate a favorable distribution of gas which is guided through the flow space and thus a high heat transfer performance of the heat exchanger can be achieved. A value range of L _{n / 2} between 10 and 30% has proven to be particularly favorable.

According to a further variant of the heat exchanger, the tubes running through the flow space are combined into a plurality of bundles lined up along the connecting axis of a pair of connecting pieces, the tubes being connected to one another in such a way that the bundles are separated from those in the tubes flowing fluid are successively flowed through. In this way, a cocurrent or countercurrent effect can additionally be achieved, depending on the operating mode.

Up until about 15 years ago, it was common to use heat exchangers as cracked gas coolers in ethylene plants which, like the type according to the invention, have a cylindrical flow space and cooling water pipes lying parallel to the cylinder axis, but in which the gas to be cooled passes several times over the cross section of the flow space. and is brought here.

However, this results in a significantly higher pressure loss and the process is overall energetically unfavorable.

When energy became scarce and expensive, they were forced to use direct contact coolers and to cool the cracked gas by direct heat exchange with water. Such systems have a low pressure drop; however, this is bought through high expenditure on equipment. On the one hand, this is due to the fact that the cooling water is circulated and therefore has to be cooled again in a separate heat exchanger. On the other hand, it is necessary to separate the water removed from the direct contact cooler and the condensed heavy hydrocarbons in a separator.

The use of the heat exchanger according to the invention as a step cooler for cracked gas in an ethylene plant now combines the advantages of the two types of cracked gas coolers known in ethylene plants, namely, on the one hand, moderate outlay on equipment and thus relatively low capital costs and, on the other hand, very low pressure loss and thus low operating costs. The cracked gas is preferably conducted as the first fluid through the flow space.

The invention is explained in more detail below on the basis of an exemplary embodiment schematically illustrated in the drawings.

Figur 1

einen Längsschnitt in einer vertikalen Ebene,

Figur 2

einen Querschnitt und

Figur 3

einen weiteren Längsschnitt in einer horizontalen Ebene durch einen erfindungsgemäßen Wärmetauscher.

Here show:

Figure 1

a longitudinal section in a vertical plane,

Figure 2

a cross section and

Figure 3

a further longitudinal section in a horizontal plane through a heat exchanger according to the invention.

The jacket 1 of the heat exchanger is essentially cylindrical symmetry about the axis 8. It encloses the flow space 2 together with the partition walls 3A and 3C. This in turn is divided into two part spaces by a further partition wall 3B, between which no gas exchange is possible. To the subspace arranged on the left in FIG. 1 there is a first pair 4 of nozzles, which is formed from inlet nozzle 4A and outlet nozzle 4B. Analogously, the nozzles 5A and 5B of the pair 5 can be seen on the right side.

Support plates 12 are installed in the flow space 2, the number of which in the exemplary embodiment is 10, ie 5 per subspace. The support plates 12 are supported by a floor 15. Furthermore, two anti-drumming plates 11 are shown in FIG. 2, which run over the full length of the flow space 2 from the partition wall 3A to the partition wall 3C (see FIG. 1). Support plates 12, anti-drumming plates 11 and partitions 3A, 3B, 3C are welded to one another and form a rigid, honeycomb-like structure in which no lateral gas exchange between the honeycombs and no exchange to the volume between anti-drumming plates 11 and jacket 1 is possible.

For this reason, a baffle plate 10 is provided, which is arranged below the inlet connections 4A, 5A in a horizontal plane over the full length of the flow space 2. The width b of the baffle plate 10 shown in FIG. 10 is approximately equal to the inner diameter 2r of the filler neck 4A, 5A. However, b can also be slightly larger or smaller than 2r (see numerical example below). In the transverse direction, the baffle plate 10 is delimited by the two anti-drumming plates 11 and is integrally connected to them.

As a result of this arrangement, the perforated baffle plate 10 makes the passage of the fluid introduced through the inlet connections 4A, 5A into the central part of the flow space 2 difficult and thus a better distribution through the spaces 14 (see FIG. 2) in the direction of the edge volume between the anti-drumming plates 11 and the jacket 1.

Analogous to the subspaces of the flow space 2, the baffle plate 10 is divided into two parts by the partition 3B. Each of the two sections of the baffle plate 10 consists of sections P₁ to P₆ or P'₁ to P'₆, as shown in Figure 3. In the exemplary embodiment, the number n of sections per section is 6. In a special version, the baffle plate 10 has three different types of perforations, which are distinguished by different relative hole cross-sectional areas. By relative hole cross-sectional areas is meant the ratio between the opening area of the holes and the total area of the sheet. The different types of perforations can be realized by different densities and / or sizes of holes.

$\text{L₂ für P₂, P₅, P′₂, P′₅ und}$

$\text{L₃ für P₃, P₄, P′₃, P′₄.}$

Preferably, three different values L₁, L₂, L₃ of relative hole cross-sectional areas are used in the embodiment, namely

$\text{L₁ for P₁, P₆, P′₁, P′₆,}$

$\text{L₂ for P₂, P₅, P′₂, P′₅ and}$

$\text{L₃ for P₃, P₄, P'₃, P'₄.}$

The perforations are chosen so that the relative hole cross-sectional area (L₃) is the smallest directly below the inlet connection 4A, 5A and the most distant from the inlet connection 4A, 5A, the relative hole cross-sectional area (L₁) is greatest, in order to ensure the most uniform fluid distribution possible to reach in the flow space along the cylinder axis.

The following numerical values were selected in a heat exchanger built for experimental purposes: Diameter of the flow space d _s = 1676 mm Radius of the opening of the filler neck r = 348 mm Distribution length l _v = 999 mm Length of each section a = 333 mm Section width b = 666 mm rel. Hole cross sections: L₁ = 40% L₂ = 30% L₃ = 23% Ratio max. to min. rel. Hole cross section: L₁ / L₃ = 1.74 Hole diameter: d₁ = 8 mm d₂ = 8 mm d₃ = 10 mm Hole division: t₁ = 12 mm t₂ = 14 mm t₃ = 20 mm

It is technically favorable to choose the length a of the sections P₁ to P₆ or P₁ 'to P₆' equal to the distance between two support plates 12. In terms of distribution technology, a higher number of sections with different relative hole cross-sectional areas is of course more favorable; As a practicable compromise between the quality of distribution and the expenditure on equipment, a range of values for the number n of sections per section from 2 to 18, preferably 4 to 8, has been found for the hydrodynamic calculations.

The tubes which pass through the flow space 2 are not explicitly shown in the drawings. In the longitudinal section of FIG. 1, their straight sections lie between baffle plate 10 and support plate 15. At the ends of the heat exchanger, the tubes are either connected to one of the connections 6A, 6B or to one another, as will be explained in more detail below with reference to FIG. 2.

In the cross-sectional view 4 bundles A _1.2 to A _{7.8 are} shown, which are divided into two sub-groups A₁, A₂ to A₇, A₈. The subgroups consist of 50 to 300, preferably 120 to 250 tubes and each fill a volume indicated by two crossed lines on both sides of an anti-drumming plate 11.

The tubes are connected to each other so that a fluid which is fed via the nozzle 6A, first flows parallel through the tubes of subgroup A₁ and then successively through the tubes of the other subgroups and bundles in the order A₂, A₃, A₄, A₆, A₇ , A₈ and then to the outlet port 6B.

Claims (10)

1. A heat exchanger with a substantially cylindrical flow chamber (2) which is delimited by a casing (1), with a number of tubes which pass through the flow chamber (2) in a direction substantially parallel to the cylinder axis (8), with at least one pair (4, 5) of connection pipes which are arranged opposite one another on the cylindrical surface of the casing (1) and lead into the flow chamber (2) and with support plates (12) which are installed in the flow chamber (2) substantially at right angles to the cylinder axis (8), characterised by at least one anti-noise plate (11) which is disposed in the flow chamber (2) substantially in parallel to the cylinder axis (8) and substantially in parallel to the line connecting the pair (4, 5) of connection pipes disposed opposite one another.
2. A heat exchanger as claimed in Claim 1, characterised in that anti-noise plate(s) (11) and support plate(s) (12) are materially connected to one another.
3. A heat exchanger as claimed in one of Claims 1 or 2, characterised by a baffle plate (10) which is arranged substantially at right angles to the connecting line between two connection pipes (4A, 4B; 5A, 5B) disposed opposite one another in pairs and is arranged continuously along the full length of the flow chamber (2) in parallel to the cylinder axis (8).
4. A heat exchanger as claimed in Claim 3, characterised in that an interspace (14) is provided between the longitudinal sides (13) of the baffle plate (10) and the casing (1).
5. A heat exchanger as claimed in one of Claims 3 or 4, characterised in that in the direction of the cylinder axis (8) the baffle plate (10) is divided into sections (P₁ to P₆, P'₁ to P'₆) which comprise holes having different relative hole cross-sectional areas L₁ to L₆, L'₁ to L'₆.
6. A heat exchanger as claimed in Claim 5, characterised in that the baffle plate (10) is divided into sub-portions which each comprise a whole number n of sections (P₁ to P₆; P'₁ to P'₆) and on each side are delimited either by one end (3A, 3C) of the flow chamber (2) or by a plane (3B) extending precisely between two pairs (4, 5) of connection pipes (4A, 4B; 5A, 5B) at right angles to the cylinder axis (8).
7. A heat exchanger as claimed in Claim 6, characterised in that a respective sub-portion of the baffle plate (10) possesses an even number n of consecutive sections
   
   ${\text{P}}_{\text{i,}}\text{i = 1,...,n,}$

   

   
   
      where the respective sections
   
   ${\text{P}}_{\text{i}}{\text{and P}}_{\text{n-i+1}}\text{, i = 1,...,n/2}$

   

   
   
   are constructed to be identical in respect of their dimensions a_i, b_i and their relative hole cross-sectional area L_i.
8. A heat exchanger as claimed in Claim 7, characterised in that the number n of sections P_i (P₁ to P₆; P'₁, to P'₆) within a sub-portion amounts to between 2 and 18 and that the relative hole cross-sectional areas L_i of the sections P_i are governed by the equation:
   
   ${\text{L}}_{\text{i}}{\text{> L}}_{\text{i+1}}\text{, i = 1,..., n/2-1}$

   

   
   
   applies to.
9. A heat exchanger as claimed in Claim 8, characterised in that the maximum relative hole cross-sectional area L₁ is governed by the equation:
   
   ${\text{L₁ = f . (l}}_{\text{v}}{\text{/r)}}^{\text{1/2}}{\text{. L}}_{\text{n/2}}\text{,}$

   

   
   
   wherein

   f:   factor, 0.8 < = f < = 1.3

   l_v:   distribution length (= distance between connecting axis of a pair (4, 5) of connection pipes and delimitation of the corresponding sub-portion)

   r:   radius of the opening of the inlet connection pipe (4A, 5A).
10. A heat exchanger as claimed in one of Claims 1 to 9, characterised in that the tubes are combined in a plurality of groups (A_1,2 to A_7,8) lined up along the connecting axis of a pair (4, 5) of connection pipes (4A, 4B; 5A, 5B), where the tubes are connected to one another in such manner that the groups (A_1,2 to A_7,8) are passed through consecutively by the fluid flowing in the tubes.

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