WO2011092318A2

WO2011092318A2 - A heat exchange unit

Info

Publication number: WO2011092318A2
Application number: PCT/EP2011/051272
Authority: WO
Inventors: Mark Platts; David Normandale
Original assignee: Tanjung Citech Uk Limited
Priority date: 2010-01-29
Filing date: 2011-01-28
Publication date: 2011-08-04
Also published as: GB201001485D0; WO2011092318A3

Abstract

A heat exchange unit comprising a heat exchange duct for the passage of hot gas therethrough, a heat exchange array located within the heat exchange unit, a bypass duct concentrically arranged with respect to the heat exchange duct to selectively enable at least a portion of the hot gas to bypass the heat exchange duct; a variable position sleeve valve arrangement having a first end and a second end, movable axially such that in a first position the sleeve substantially closes a downstream opening of the bypass duct at the second end and opens an upstream opening at the first end to permit gas to flow past the heat exchange array, the second end being arranged to seal against a plug formation; the plug formation comprising an extension extending upstream towards the first end to define an annular channel between the sleeve and the extension, wherein the upstream end of the extension is torispherical.

Description

A HEAT EXCHANGE UNIT

The present application relates to a heat exchange unit. More particularly the present application relates to a heat exchange unit for use in recovering waste heat or generating steam.

EP1088194 granted to a predecessor company of the present applicant discloses a heat exchange unit primarily intended to recover heat from the exhaust gas produced by gas turbines and gas/diesel engines used on offshore platforms and the like, for use in other processes.

This patent discloses the general layout of a heat exchange unit having an annular heat exchange duct with an array of heat exchange pipes located therein and a bypass duct located concentrically within the heat exchange duct. A cylindrical sleeve valve is located between the two ducts and is movable along its axis to switch the flow of exhaust gas between a duty mode in which the gas flows through the heat exchange duct and a bypass mode which, as the name suggests, causes the gas to flow through the bypass duct and therefore not to transfer heat to the array of heat exchange pipes. Compared to previous heat exchange units used in these applications, this layout has been found to be compact, efficient and safe. In particular, the use of the movable sleeve valve ensures that the flow of exhaust gas can never be blocked, meaning that there is no danger of a back pressure damaging the engine or turbine to which the heat exchange is connected. The present applicant has recognised that it is desirable to produce a consistent and even flow though the heat exchange unit to improve heat exchange efficiency.

The present invention seeks to overcome, or at least mitigate, the problems of the prior art. A first aspect of the present invention provides a heat exchange unit comprising a heat exchange duct for the passage of hot gas therethrough, a heat exchange array located within the heat exchange unit, a bypass duct concentrically arranged with respect to the heat exchange duct to selectively enable at least a portion of the hot gas to bypass the heat exchange duct; a variable position sleeve valve arrangement having a first end and a second end, movable axially such that in a first position the sleeve substantially closes a downstream opening of the bypass duct at the second end and opens an upstream opening at the first end to permit gas to flow past the heat exchange array, the second end being arranged to seal against a plug formation; the plug formation comprising an extension extending upstream towards the first end to define an annular channel between the sleeve and the extension, wherein the upstream end of the extension is torispherical. The torispherical shape of the upstream end of the extension improves evenness of flow.

The radius of the toroid portion of the torispherical end may be between 7% and 30%, preferably between 15% and 25%, of the radius of the spherical portion. The radius of the toroid portion of the torispherical end may be substantially 20% of the radius of the spherical portion, improving consistency and evenness of flow.

The plug formation may flare conically outwards at its downstream end at an angle of between 40° and 50°. The angle may be substantially 45°, further improving consistency and evenness of flow.

In said first position the distance between the upstream end of the plug formation and an upstream edge of said upstream opening may be between 475mm and 525mm, and may be substantially 500mm, improving consistency and evenness of flow.

The radius of the spherical portion may be in the range of 900mm to 1100mm, and may be within the range of 135mm and 275 mm, improving consistency and evenness of flow. The heat exchange array may comprise at least one helically coiled tube. The upstream end of the extension may be axially intermediate the upstream opening and the first end of the sleeve valve. There may be a substantially linear relationship between the position of the sleeve valve and the rate of hot gas flow. A second aspect of the present invention provides a heat exchange unit comprising:

a heat exchange duct for the passage of hot gas therethrough;

a heat exchange array located within the heat exchange duct;

a bypass duct concentrically arranged with respect to the heat exchange duct;

a sleeve positioned between the heat exchange duct and bypass ducts a valve arrangement to selectively enable at least a portion of the hot gas to flow through the bypass duct rather than the heat exchange duct; and

a plug formation comprising an extension extending upstream to define an annular channel between the sleeve and the extension, wherein the upstream end of the extension is torispherical.

Embodiments of the present invention will now be described, with reference to the accompanying drawings in which:

FIGURE 1 is a vertical cross-section through a heat recovery unit according to an embodiment of the present invention in a duty condition;

FIGURE 2 is a similar vertical cross-section to Figure 1 but in a bypass condition;

FIGURE 3 is an end view of a plug end component of the heat recovery unit of the present invention;

FIGURE 4 is a side elevation of the plug end of figure 3;

FIGURE 5A is a computational fluid dynamics (CFD) plot of a heat recovery unit incorporating a hemispherical plug end;

FIGURE 5B is an enlarged view of the region around the plug end of figure 5A;

FIGURE 6A is a CFD plot of a heat recovery unit incorporating a semi-ellipsoidal plug end;

FIGURE 6B is an enlarged view of the region around the plug end of figure 6A; FIGURE 7A is a CFD plot of a heat recovery unit incorporating a 10% torispherical dished end;

FIGURE 7B is an enlarged view of the region around the plug end of figure 7A; FIGURE 8A is a CFD plot of a heat recovery unit incorporating a 20% torispherical dished end;

FIGURE 8B is an enlarged view of the region around the plug end of figure 8A;

FIGURES 9A, 10A, 11A and 12A are CFD plots of a heat recovery unit incorporating the plug end of figure 8A located at different axial positions with respect to the duct entrance;

FIGURES 9B, 10B, 11B and 12B are enlarged views of the region around the plug ends of figures 9A, 10A, 11A and 12A respectively;

FIGURES 13 A, 14A and 15 are CFD plots illustrating a plug end as in figure 8 A and differing angles at the upper section of the plug; and FIGURES 13B and 14B are enlarged views of the region around the plug ends of figures 13A and 14A respectively.

A heat exchange unit 100 of the present invention, shown in Figures 1 and 2, is employed to utilise waste heat from e.g. a gas turbine or diesel engine either for steam generation or to heat liquids for other purposes. Such units are generally cylindrical in shape and are typically used with their major axes orientated vertically.

As indicated in Figure 1, such a unit 100 is intended to receive hot gas 10 through gas inlet duct 34 from a gas turbine engine (not shown) or other type of engine, cool the gas by heat exchange with water passing through a heat exchange array 2, and pass the cooled gas 18 onwards for venting from the gas exit duct 7 to a stack, or for further use. The water is passed in and out of the heat exchange array through inlet and outlet manifolds (not shown).

Referring to Figure 1 and 2 together, the heat exchange unit 100 comprises a generally cylindrical outer casing or shell 1, containing an annular heat exchange array 2, an internal sleeve valve 3, and a valve plug 4. The casing 1 and sleeve valve define a duty passage 22 in which the heat exchange array 2 is located. The sleeve valve 3 is slideable axially within the heat exchange array 2 between two extreme positions. In Figure 1, the sleeve valve 3 is shown at its upper extreme position, so that the valve sleeve's central passage 19, termed a bypass passage, is effectively closed, with substantially all the exhaust gas passing through the heat exchange array 2. In this position, the required gas seal to prevent flow through the bypass passage 19 is provided when an upper "knife edge" 14 of sleeve valve 3 butts against a valve seat 13 provided on the valve plug 4.

The valve plug 4 has a downward extension 8 which extends axially through the bypass passage 19 concentric with the shell. The extension acts as a flow splitter and has a cylindrical upper portion and a shaped plug end portion 26. The upper end of the valve plug 4 flares outwards to form a lower conical portion 29, then inwards to form an upper conical portion 30.

In Figure 2 the sleeve valve 3 is shown at its lower extreme position, such that substantially all of the hot gas 10 passes through the bypass passage 19, so bypassing the heat exchange array 2. In this position, lower valve seat 12 on the bottom of sleeve valve 3 forms a gas seal with a complementary seat 11 attached to the shell 1 below the heat exchange array 2, so causing the hot gas 10 to pass through the bypass passage 19 and out past the valve plug 4 through the annular opening 16 between the plug 4 and the outer components. In operation, the sleeve valve may be positioned in either of the extreme locations discussed above, or intermediate positions in which a proportion of the flow passes through the duty passage 22, and a proportion through the bypass passage 19.

Figures 3 and 4 show an enlarged view of the plug end portion 26 of an embodiment of the present invention where the end portion 26 is torispherical. As shown in figure 4, in this embodiment the end portion 26 is 20% torispherical - that is, the radius of the part-toroid portion 27 is 20% of the radius of the part-spherical portion 28. Specifically, the radius of the part-spherical portion 28 is 1000mm and the radius of the part-toroid portion 29 is 200mm. The overall diameter of the plug extension 8 is in this embodiment 1219.20mm. This diameter can be varied. For the applicant's current product range this would be between from 812.8mm to 1524.0mm, depending on the size of the valve plug 4, but other diameters are envisaged. However, the radii of the part-spherical and part-toroid portions may remain as they are in this embodiment, that is 1000mm and 200mm respectively. Figures 5 A to 15 are CFD plots showing modelled gas flow over various configurations of the valve plug. The bottom, darkest shade of the key on each plot relates to the slowest speed, with speed increasing up the scale. Each shade relates to the shades of the arrows depicted. As well as variations in the shape of the plug end portion 26, the distance x between the upstream tip of the plug end 26 and the upstream surface end of the opening 34 is varied between 500mm and 700mm, and the angle of the lower conical portion 29 to the vertical is varied between 35° and 55°.

In figures 5 A to 8B, the distance between the end portion 26 and the inlet duct 34 remains constant at 500mm and the angle of the lower conical portion 29 is kept at 45°. The shape of the end portion 26 is varied. There are a number of potential shapes for the end portion 26. Figures 5A and 5B show a hemispherical end portion, figures 6A and 6B show an ellipsoidal end portion and figures 7A and 7B show a torispherical end portion where the radius of the toroid portion is 10% of the radius of the spherical portion. Figures 8 A and 8B show the configuration of figure 4, a 20% torispherical end portion.

Variations in gas flow through the heat exchange unit between the figures can be seen. The gas flow velocity of figures 8A and 8B is the most consistent and even, indicating that the 20% torispherical end portion is the optimum shape.

Figures 9A to 12B show models where the end portion 26 is 20% torispherical and the angle of the lower conical portion 29 remains constant at 45°. The distance between the upstream tip of the plug end 26 and the upstream surface end of the opening 34 is varied. Figures 9A and 9B show the gas flow where that distance is 550mm, figures 10A and 10B where it is 600mm, figures 11A and 11B 650mm and figures 12A and 12B 700mm. As the plots show, in no case is the gas flow as consistent and even as it is in figures 8A and 8B, indicating that 500mm is the most advantageous distance of those investigated.

In figures 13A to 15, the angle of the lower conical portion 29 to the vertical is altered whilst the two remaining variables are kept constant. In figures 13A and 13B the angle is 35°, whilst in figure 14 the angle is 55°. In neither case is the gas flow as consistent and even as that of figures 8A and 8B, where the constant conditions are the same and the angle of the lower conical portion is 45°. The optimum angle, therefore, can be seen to be substantially 45°. The advantages of the embodiment of figures 3 and 4 can be seen from the above analysis. The torispherical shape of the plug end has surprisingly been found to have the greatest influence on the evenness of flow, whereas one might expect a hemispherical or other shape to be advantageous. The axial position of the plug end and conical angle have been found to have additional benefits. By providing a valve plug 4 having a 20% torispherical end portion and a 45° lower conical portion, and positioning said valve plug 4 so that the end portion is 500mm from the uppermost point of the inlet duct 34, the gas flow through the heat exchange unit can be optimised. This arrangement also provides a more linear relationship between the position of the sleeve valve and the gas flow rate, in part-bypass conditions, compared to other arrangements, thus improving control of the process.

Optimisation of gas flow through the heat exchange unit enables more efficient heat transfer to take place. It also leads to a reduction in the velocity range, enabling the maximum gas flow velocity to be kept below the point where unwanted levels of vibration and noise are produced.

Claims

1. A heat exchange unit comprising a heat exchange duct for the passage of hot gas therethrough, a heat exchange array located within the heat exchange duct, a bypass duct concentrically arranged with respect to the heat exchange duct to selectively enable at least a portion of the hot gas to bypass the heat exchange duct; a variable position sleeve valve arrangement having a first end and a second end, movable axially such that in a first position the sleeve substantially closes a downstream opening of the bypass duct at the second end and opens an upstream opening at the first end to permit gas to flow past the heat exchange array, the second end being arranged to seal against a plug formation; the plug formation comprising an extension extending upstream towards the first end to define an annular channel between the sleeve and the extension, wherein the upstream end of the extension is torispherical.

2. A heat exchange unit according to claim 1 wherein the radius of the toroid portion of the torispherical end is between 7% and 30% and preferably between 15% and 25% of the radius of the spherical portion.

3. A heat exchange unit according to claim 2 wherein the radius of the toroid portion of the torispherical end is substantially 20% of the radius of the spherical portion.

4. A heat exchange unit according to any one of claims 1 to 3 wherein the plug formation flares conically outwards at its downstream end at an angle of between 40° and 50°.

5. A heat exchange unit according to claim 4 wherein said angle is substantially 45°.

6. A heat exchange unit according to any preceding claim wherein when in said first position the distance between the upstream end of the plug formation and an upstream edge of said upstream opening is between 475mm and 525mm.

7. A heat exchange unit according to claim 6 wherein said distance is substantially 500mm.

8. A heat exchange unit according to claim 2 wherein the radius of the spherical portion is in the range of 900mm to 1100mm.

9. A heat exchange unit according to claim 8 wherein the radius of the toroid portion is within the range of 135mm and 275 mm.

10. A heat exchange unit according to any preceding claim wherein the heat exchange array comprises at least one helically coiled tube.

11. A heat exchange unit according to any preceding claim wherein the upstream end of the extension is axially intermediate the upstream opening and the first end of the sleeve valve.

12. A heat exchange unit according to any preceding claim wherein there is a substantially linear relationship between the position of the sleeve valve and the rate of hot gas flow.

13. A heat exchange unit comprising:

a heat exchange duct for the passage of hot gas therethrough;

a heat exchange array located within the heat exchange duct;

a bypass duct concentrically arranged with respect to the heat exchange duct;

a sleeve positioned between the heat exchange duct and bypass ducts

a valve arrangement to selectively enable at least a portion of the hot gas to flow through the bypass duct rather than the heat exchange duct; and