Patent Application
20180245844
The invention relates to a heat exchanger, in particular a helically coiled heat exchanger, and a method for distributing a liquid phase over a tube bundle of a heat exchanger.
Such a heat exchanger effects indirect heat exchange between at least a first medium conducted in a tube bundle of the heat exchanger and a second medium conducted in a shell space surrounding the tube bundle which is delimited by a pressure-bearing shell of the heat exchanger.
In such heat exchangers, for example in LNG plants, the coolant entering in biphasic form is generally separated in a pre-distributor of the heat exchanger by gravity separation into a gaseous phase and a liquid phase and the liquid phase is then conducted into a main distributor and from said distributor applied (as a second medium) onto the tube bundle.
Here the liquid phase is for example introduced from the pre-distributor into a central core tube and then guided/diverted into the distributor arms of the main distributor. From there, distribution over the tube bundle is effected. The core tube takes the load of the tube bundle.
However, during the falling of the liquid phase from the pre-distributor into the central core tube gas is entrained and for constructional reasons it is often not possible to dimension the diameter of the core tube sufficiently to ensure that the backflowing gas can escape upward past the newly inflowing liquid phase.
The gaseous phase thus prevented from outflowing in turn impedes the newly inflowing liquid phase, thus forming a biphasic flow which impedes an orderly inflowing of the liquid phase into the distributor arms of the main distributor and thus in the distributor arms dirupts uniform distribution of the liquid phase over the tube bundle. These effects significantly reduce the performance of the heat exchanger.
Furthermore the central feed into the distributor arms of the main distributor leads, particularly during startup of the plant, to an oversupply of the inner layers with coolant (or second medium) which can result in various thermohydraulic problems. For example an increased amount of gas requiring flaring is generated during startup.
Furthermore the use of the core tube as a distributor component has the result that the core tube and the pre-distributor are combined in terms of manufacture. This does not allow independent/simultaneous manufacture.
Proceeding therefrom the present invention accordingly has for its object the provision of a heat exchanger and a corresponding method for distributing a liquid phase which reduce the problems recited at the outset.
This object is achieved by a heat exchanger having the features of claim 1 and by a method according to claim 8. Advantageous embodiments of the heat exchanger are set out in the corresponding dependent claims 2 to 7 and advantageous embodiments of the method are set out in dependent claims 9 and 10. The invention is more particularly described hereinbelow.
A first aspect of the invention provides a heat exchanger for indirect heat exchange between a first medium and a second medium. The heat exchanger has at least the following components: a core tube extending along a longitudinal axis onto which a multiplicity of tubes for receiving the first medium is coiled, wherein the tubes form a tube bundle; a pre-distributor having a liquid space for receiving a liquid phase of the second medium to be distributed over the tube bundle, wherein in correct operation the pre-distributor is not and does not become filled with the liquid phase beyond the liquid space; a feed arranged centrally with regard to the longitudinal axis for introducing the liquid phase into the liquid space; and a main distributor which has a multiplicity of distributor arms for distributing the liquid phase over the tube bundle.
It is provided according to the invention that the distributor arms via at least one flow path proceeding outside the core tube are in fluidic connection with the liquid space of the pre-distributor, wherein the core tube is arranged or sealed off with regard to the liquid space in such a way that in correct operation of the heat exchanger the liquid phase from the liquid space is not introduceable via the core tube into the distributor arms of the main distributor.
In other words: the core tube is arranged separated from the liquid space/fluidically separated therefrom in such a way that the liquid phase (in particular in correct operation) from the liquid space is introduceable/can get into the distributor arms of the main distributor exclusively via the flow path.
The term “liquid space” describes the particular section of the pre-distributor/the particular volume which contains the liquid phase during correct operation of the heat exchanger. The liquid space is thus delimited in the upward direction by the level of the liquid phase.
In the case where a section of the core tube having an outlet opening is arranged in the pre-distributor in correct operation the liquid space extends along the longitudinal axis no further than up to the outlet opening of the core tube, so that the liquid phase cannot ingress into the core tube through the outlet opening. Filling the pre-distributor with the liquid phase beyond the outlet opening is thus not intended in correct operation of the heat exchanger.
The heat exchanger has a central feed for introducing the liquid phase into the liquid space. The pre-distributor is thus in particular not a ring distributor having a feed arranged radially to the longitudinal axis.
Via the at least one flow path routed outside the core tube the free cross section for discharging the liquid phase may advantageously be increased such that a degassing of the liquid phase is possible.
Furthermore, through appropriate number and dimensioning of the flow paths the behavior of the distributor during exceptional modes of operation (for example during startup) may be improved. Thus for example an oversupply of the inner layers of the tube bundle during startup of the plant may be avoided since the liquid phase may be distributed radially further outward through the flow paths outside the core tube. This makes it possible to avoid typical thermal hydraulic problems during startup of the plant which reduces the amount of gas typically requiring flaring during startup in LNG plants.
Since the distributor arms of the main distributor are not connected to the core tube for introduction of the liquid phase it is also advantageously possible to manufacture the main distributor and/or the pre-distributor separately (i.e. not together with the core tube).
In a further embodiment the core tube has an outlet opening arranged in the pre-distributor at an upper end of the core tube, wherein the outlet opening is arranged above the liquid space in the direction of the longitudinal axis, so that the liquid phase from the liquid space is not introduceable via the core tube into the distributor arms of the main distributor.
In particular the heat exchanger has an impingement plate arranged below the central feed with regard to the longitudinal axis, wherein the outlet opening of the core tube is arranged below the impingement plate with regard to the longitudinal axis, so that the liquid phase from the central feed cannot fall directly into the outlet opening.
In one embodiment the at least one flow path is formed by a downtube extending along the longitudinal axis, so that the liquid phase to be distributed is introduceable via the downtube from the liquid space into the distributor arms.
Such downtubes are also known as downcomers.
In particular each distributor arm is in fluidic connection with the liquid space of the pre-distributor by means of one or more downtubes.
In particular the number and dimensioning (for example the tube cross section) of the downtubes vary based on the entire heat exchanger and/or based on a distributor arm.
In a further embodiment at least one of the distributor arms is formed by a lower section of a shaft which extends from the pre-distributor along the longitudinal axis, so that the liquid phase to be distributed is introduceable via the shaft from the liquid space into the respective distributor arm. In particular all distributor arms of the main distributor are formed by corresponding shafts.
For example the corresponding shaft may extend in a radial direction between the core tube and a shell of the heat exchanger, wherein the shaft has a maximum radial extension at least equal to the maximum radial extension of the respective distributor arm with which the corresponding shaft is in fluidic connection.
In particular the shaft in cross section (perpendicular to the longitudinal axis) has the same shape as the corresponding distributor arm which forms the lower section of the shaft. The cross section may for example have a pie-slice-like shape.
In a further embodiment the distributor arms are in fluidic connection via at least one equalization conduit, so that the liquid level of the liquid phase present in the distributor arms is equalizable via a flow of the liquid phase via the at least one equalization conduit.
The at least two distributor arms are thus in hydraulic communication. In particular the at least one equalization conduit is a ring conduit proceeding in the circumferential direction (with regard to the longitudinal axis) of the heat exchanger.
The equalization conduit advantageously makes it possible to achieve a more uniform distribution of the liquid phase inside the main distributor.
In a further embodiment the distributor arms proceed in a radial direction between the core tube and a shell of the heat exchanger and in an axial direction along the longitudinal axis, wherein the distributor arms each have a roof which seals off the respective distributor arm in the axial direction at the side facing the pre-distributor and wherein the respective roof drops down in the radial direction toward the shell, i.e. outwardly.
This advantageously allows a better degassing since the gaseous phase transported into the distributor arms can collect at the (centrally positioned) highest point of the distributor arm.
In a further embodiment the distributor arms are in fluidic connection with the core tube, so that the gaseous phase present in the distributor arms is withdrawable from the distributor arms via the core tube.
This advantageously allows an effective degassing of the distributor arms through the central core tube.
In a further embodiment the core tube has an outlet opening, wherein the core tube at the outlet opening is in fluidic connection with a gas space of the pre-distributor, so that the gaseous phase present in the distributor arms is introduceable via the core tube into the gas space. In particular the gaseous phase may be withdrawn from the gas space of the pre-distributor.
In particular in correct operation of the heat exchanger the gas space is arranged above the liquid space of the pre-distributor. In particular the core tube ends in the gas space, wherein in particular the outlet opening is arranged at the front face of the core tube and wherein the core tube having the outlet opening projects beyond the liquid space of the pre-distributor, so that the liquid phase cannot get from the liquid space into the core tube.
A second aspect of the invention provides a method for distributing a liquid phase over a tube bundle of a heat exchanger according to the first aspect of the invention. In the method the first medium is conducted through the tubes of the heat exchanger, wherein the liquid phase is introduced into the liquid space of the pre-distributor and wherein exclusively via at least one flow path proceeding outside the core tube the liquid phase is introduced into the distributor arms of the main distributor and from there applied onto a tube bundle of the heat exchanger.
In one embodiment of the method the liquid phase forms a continuous liquid column between the distributor arms and the liquid space of the pre-distributor.
In this operating mode of the heat exchanger the at least one flow path, in particular the downtubes or the shafts, is submerged and the liquid level is in the liquid space of the pre-distributor.
This has the advantage of better degassing since the gas bubbles present in the at least one flow path can ascend right up into the liquid space of the pre-distributor.
In a further embodiment of the method the liquid phase forms a first liquid column in the flow path and a second liquid column in the liquid space of the pre-distributor, wherein the first liquid column is separated from the second liquid column by a gas volume present in the flow path.
The gas volume present between the first and the second liquid column may in particular contain fluid droplets which rain down from the liquid space of the pre-distributor onto the first liquid column standing in the flow path.
Such an operating mode with non-submerged flow paths has the advantage that the fill height of the liquid phase in the pre-distributor varies less severely between different operating conditions, so that the build height of the pre-distributor may advantageously be reduced.
Further details and advantages of the invention shall be elucidated through the following figure description of an exemplary embodiment by reference to the figures.
The tube bundle 2 has a multiplicity of tubes 20 each of which are helically coiled around a core tube 3 which extends along the longitudinal axis Z and is arranged coaxially to the shell 4 in the shell space 5. The core tube 3 takes the load of the tube bundle 2.
To distribute the liquid phase F over the tube bundle 2 a biphasic mixture is initially conducted from above via a feed 104 proceeding for example along the longitudinal axis Z into a pre-distributor 100 of the heat exchanger 1. The pre-distributor 100 has a floor 101 proceeding transversely to the longitudinal axis Z and a circumferential lateral wall 102 leading off therefrom. The feed 104 further has a feed opening 105 which in the operational state of the heat exchanger 1 points downward and is located opposite an impingement plate 103 which is arranged in the pre-distributor 100 above the floor 101 of the pre-distributor 100. The biphasic mixture can outflow from the impingement plate 103 onto the floor 101 and is collected and calmed there, wherein a gaseous phase G can outgas from the biphasic mixture. The liquid phase F of the biphasic mixture collects in a liquid space 110 of the pre-distributor 100 while the outgassed gaseous phase G collects in a gas space 120 of the pre-distributor 100 arranged above the liquid space 110 and for example may be withdrawn from the gas space 120.
The core tube 3 projects through the floor 101 of the pre-distributor 100 into the pre-distributor 100. The core tube 3 has an outlet opening 31 in the upward direction which is arranged below the impingement plate 103. The core tube 3 projects above the liquid space 110 of the pre-distributor 100 into the gas space 120 of the pre-distributor, so that the liquid phase F present in the liquid space 110 cannot flow into the core tube 3. Thus in correct operation of the heat exchanger 1 the pre-distributor 100 is filled with the liquid phase F only to the extent that the liquid level of the liquid phase F is below the outlet opening 31.
According to the invention the pre-distributor 100 is connected with the distributor arms 201 of a main distributor 200 exclusively via a flow path 30 located outside the core tube 3. The distributor arms 201 proceed from the central core tube 3 in a radial direction R (see
The flow path 30 may for example lead through a multiplicity of downtubes 10 arranged parallel to the longitudinal axis Z, as depicted in the left-hand part of
Via the downtubes 11 and/or the shafts 12 the flow cross section of the flow path 30 is advantageously enlarged compared to heat exchangers of the prior art having a flow path proceeding in the core tube and a better degassing of the liquid phase F is therefore made possible during downflow from the pre-distributor 100 into the distributor arms 201.
The distributor arms 201 are delimited (in the embodiment having downtubes 11) in the upward direction (in the correct configuration of the heat exchanger 1) by a respective roof 203 which in particular drops down in the radial direction R from the central core tube 3 toward the shell 4. As a result the gaseous phase G which outgasses in the distributor arm 201 or which is entrained through the downtubes 11 into the distributor arm 201 can collect at the centrally arranged highest point of the roof 203. Particularly at this position the distributor arm 201 may be connected via a degassing conduit 208 with the interior of the core tube 3, so that the gaseous phase G from the distributor arm 201 can enter the core tube 3 via the degassing conduit 208, can ascend in the core tube 3 and can get into the gas space 120 of the pre-distributor 100 via the outlet opening 31. This has the advantage of an improved degassing of the liquid phase F.
The liquid phase F is distributable from above over the tube bundle 2 by means of the distributor arms 201 of the main distributor 200. As depicted in
The distributor arms 201 also each have two lateral walls 204, 205 located opposite one another which in each case diverge toward the inside 4a of the shell 4 and are connected to one another via a front-face wall 206 which is located opposite the inside 4a of the shell 4 in each case. The distributor arms 201 therefore each have in particular a pie-slice-like shape. The lateral walls 204, 205 and the front-face wall 206 of the respective distributor arm 201 furthermore lead off from the floor 202 of the respective distributed arm 201 in the upward direction along the longitudinal axis Z and in each case connect to the roof 203 of the respective distributor arm 201 which drops down from the core tube 3 toward the inside 4a of the shell 4, so that the gaseous phase G carried into the distributor arms 201 can ascend along the roofs 203 toward the core tube 3.
Furthermore, between every two distributor arms 201 adjacent in the circumferential direction of the shell 4 an intermediate space 6 is in particular present through which tubes 20 of the tube bundle 2 may be routed upward past the distributor arms 201 along the longitudinal axis Z.
The distributor arms 201 adjacent in the circumferential direction are connected to one another at their lateral walls 204, 205, in particular via equalization conduits 209, and the level of the liquid phase F in the distributor arms 201 and optionally in the downtubes 11 or shafts 12 is therefore equalizable between the distributor arms 201 via the equalization conduits 209.
As shown in
Alternatively, the heat exchanger 1 may also be operated as in
| Number | Date | Country | Kind |
|---|---|---|---|
| 17020069.5 | Feb 2017 | EP | regional |
