Heat exchange element profile with enhanced cleanability features

Abstract

A stack of heating surface elements includes a first heating surface element (4) having first (10), second (12) and third (14) zones arranged sequentially along a primary gas flow direction (A). The first zone (10) includes a herringbone structure, the second zone (12) includes a flat structure, and the third zone (14) includes a plurality of corrugations extending in the primary gas flow direction (A). The corrugations have flat peak and trough regions. The stack also includes a second heating surface element (36), where the second heating surface element includes a plurality of corrugations extending in the primary gas flow direction (A).

Claims

1. A stack of heat transfer elements with a primary gas flow direction, said stack comprising: a first heat transfer element having zones arranged sequentially along the primary gas flow direction, a first zone disposed proximate to a first end of the stack of heat transfer elements, the first zone including a herringbone structure, the herringbone structure having a plurality of undulations arranged laterally side by side, a longitudinal extent of said plurality of undulations being non-parallel to said primary gas flow direction; and a second zone disposed proximate to a second end of the stack of heat transfer elements, the second zone including a plurality of castellated corrugations extending in the primary gas flow direction, the plurality of castellated corrugations having a series of repeated and adjacent flat peaks and troughs; and a second heat transfer element, said second heat transfer element including a plurality of undulating corrugations extending in the primary gas flow direction, said plurality of undulating corrugations having a different structure from said plurality of castellated corrogations, wherein the first heat transfer element is disposed over the second heat transfer element in the stack, such that the plurality of castellated corrugations of the first heat transfer element are configured to contact the plurality of undulating corrugations of the second heat transfer element along the primary gas flow direction.

2. The stack of claim 1, wherein the herringbone structure comprises a first region having a plurality of undulations arranged laterally side by side, a longitudinal extent of said plurality of undulations in said first region being greater than 0 and less than 90 to said primary gas flow direction, said herringbone structure further comprising a second region, adjacent to said first region, said second region having a plurality of undulations arranged laterally side by side, a longitudinal extent of said plurality of undulations in said second region being less than 0 and more than 90 to said primary gas flow direction.

3. The stack of claim 1, wherein a width of each of the flat peaks and troughs of the first heat transfer element is from 0.5 to 1.5 times a distance between adjacent troughs of said undulating corrugations of said second heat transfer element.

4. The stack of claim 1, wherein said stack comprises a plurality of first heat transfer elements and a plurality of second heat transfer elements, each first heat transfer element being adjacent to at least one of said second heat transfer elements.

5. The stack of claim 1, further comprising a third zone disposed between said first zone and said second zone, wherein the third zone includes a flat structure.

6. The stack of claim 1, wherein the contact of the plurality of castellated corrugations of the first heat transfer element with the plurality of undulating corrugations of the second heat transfer element along the primary gas flow direction creates closed channels.

7. The stack of claim 1, wherein a height of the plurality of castellated corrugations of the first heat transfer element is equal to a height of the plurality of undulations in the herringbone structure of the first heat transfer element, such that in the stack, continuous contact between the stacked first and second heat transfer elements forms closed channels.

8. The stack of claim 7, wherein the third zone comprises a first transition region adjacent said first zone, the first transition region comprising a shape that transitions between said plurality of undulations of said herringbone structure of said first zone and said flat structure of said third zone.

9. The stack of claim 8, wherein the third zone comprises a second transition region adjacent said second zone, the second transition region comprising a shape that transitions between said flat structure of said third zone and said plurality of castellated corrugations of said second zone.

10. A stack of heating surface elements with a primary gas flow direction, said stack comprising: a first heating surface element having zones arranged sequentially along the primary gas flow direction, a first zone disposed proximate to a first end of the stack of heating surface elements, the first zone including a herringbone structure, said herringbone structure having a plurality of regions, said plurality of regions being arranged such that a boundary of regions is along said primary gas flow direction, said plurality of regions including a first region having a plurality of undulations arranged laterally side by side, a longitudinal extent of said plurality of undulations in said first region being greater than 0 and less than 90 to said primary gas flow direction, said plurality of undulating corrugations having a different strucutre from said plurality of castellated corrugations, said plurality of regions further including a second region, adjacent to said first region, said second region having a plurality of undulations arranged laterally side by side, a longitudinal extent of said plurality of undulations in said second region being less than 0 and more than 90 to said primary gas flow direction; and a second zone disposed proximate to a second end of the stack of heating surface elements, the second zone including a plurality of castellated corrugations extending in the primary gas flow direction, said plurality of undulating corrugations having a differnt structure from said plurality of castellated corrugations, the castellated corrugations having a series of repeated and adjacent flat peak and trough regions; and a second heating surface element, said second heating surface element including a plurality of undulating corrugations extending in the primary gas flow direction, said plurality of undulating corrugations having a different structure from said plurality of castellated corrogations, wherein the first heating surface element is disposed over the second heating surface element in the stack, such that the plurality of castellated corrugations of the first heating surface element are configured to contact the plurality of undulating corrugations of the second heating surface element along the primary gas flow direction.

11. The stack of claim 10, wherein a width of each of the flat peaks and troughs of the first heating surface element is from 0.5 to 1.5 times a distance between adjacent troughs of said undulating corrugations of said second heating surface element.

12. The stack of claim 7, wherein said stack comprises a plurality of first heat transfer elements and a plurality of second heat transfer elements, each first heat transfer element being adjacent to at least one of said second heat transfer elements.

13. The stack of claim 10, further comprising a third zone disposed between said first zone and said second zone, wherein the third zone includes a flat structure.

14. The stack of claim 13, wherein the third zone comprises a first transition region adjacent said first zone, the first transition region comprising a shape that transitions between said plurality of undulations of said herringbone structure of said first zone and said flat structure of said third zone.

15. The stack of claim 14, wherein the third zone comprises a second transition region adjacent said second zone, the second transition region comprising a shape that transitions between said flat structure of said third zone and said plurality of castellated corrugations of said second zone.

16. A stack of heating surface elements with a primary gas flow direction, said stack comprising: a first heating surface element having zones arranged sequentially along the primary gas flow direction, a first zone disposed proximate to a first end of the stack of heating surface elements, the first zone including a herringbone structure, and a second zone disposed proximate to a second end of the stack of heating surface elements, the second zone including a plurality of castellated corrugations extending in the primary gas flow direction, the castellated corrugations having a series of repeated and adjacent flat peak and trough regions; and a second heating surface element, said second heating surface element including a plurality of undulating corrugations extending in the primary gas flow direction, said plurality of undulating corrugations having a different structure from said plurality of castellated corrogations, wherein the first heating surface element is disposed over the second heating surface element in the stack, such that the plurality of castellated corrugations of the first heating surface element are configured to contact the plurality of undulating corrugations of the second heating surface element along the primary gas flow direction.

17. The stack of claim 16, wherein a width of each of the flat peaks and troughs of the first heating surface element is from 0.5 to 1.5 times a distance between adjacent troughs of said undulating corrugations of said second heating surface element.

18. The stack of claim 16, further comprising a third zone disposed between said first zone and said second zone, wherein the third zone includes a flat structure.

19. The stack of claim 18, wherein the third zone comprises a first transition region adjacent said first zone, the first transition region comprising a shape that transitions between said plurality of undulations of said herringbone structure of said first zone and said flat structure of said third zone.

20. The stack of claim 19, wherein the third zone comprises a second transition region adjacent said second zone, the second transition region comprising a shape that transitions between said flat structure of said third zone and said plurality of castellated corrugations of said second zone.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings illustrate preferred embodiments of the disclosed method so far devised for the practical application of the principles thereof, and in which:

(2) FIG. 1 is a top plan view of an exemplary preheater assembly incorporating the disclosed heat transfer elements;

(3) FIG. 2 is a plan view of an exemplary heat transfer element according to the disclosure;

(4) FIG. 3 is an isometric view of an exemplary stack of heat transfer elements including the heat transfer element of FIG. 2;

(5) FIG. 4 is a detail isometric view of a portion of the stack of FIG. 3;

(6) FIG. 5 is an end view of the stack of FIG. 3;

(7) FIG. 6 is an isometric view of an exemplary stack of heat transfer elements including an alternative disclosed heat transfer element;

(8) FIG. 7 is a detail isometric view of a portion of the stack of FIG. 6;

(9) FIG. 8 is an end view of the stack of FIG. 6;

(10) FIG. 9 is an isometric view of an exemplary stack of heat transfer elements including an alternative disclosed heat transfer element;

(11) FIG. 10 is a detail isometric view of a portion of the stack of FIG. 9; and

(12) FIG. 11 is an end view of the stack of FIG. 9.

DESCRIPTION OF EMBODIMENTS

(13) An improved heat transfer element profile is disclosed. The disclosed heat transfer element profile comprises a composite element profile having a first profile at a hot end of the element and a second profile at a cold end of the element. In one embodiment, the heat transfer element profile includes a transverse herringbone element towards the hot end of the deep undulated element and a notched flat profile towards the cold end of the profile.

(14) FIG. 1 is a top view of an exemplary preheater 1 including a plurality of individual heater baskets 2, each of which can include a plurality of heat transfer elements 4. In the illustrated embodiment the hot end of the heat transfer elements 4 are visible. The cold end of the heat transfer elements 4 are positioned on the opposite side of the preheater.

(15) Referring now to FIG. 2, an exemplary first heat transfer element 4 is shown. The heat transfer element 4 may have first and second ends 6, 8, which may be referred to generally as hot and cold ends, respectively. The first heat transfer element 4 may include a plurality of discrete profile zones. In the illustrated embodiment first, second and third zones 10, 12, 14 are provided. The first zone 10 is disposed adjacent to the first (hot) end 6 of the first heat transfer element 4. The third zone 14 is disposed adjacent to the second (cold) end of the first heat transfer element 4. The second zone 12 serves as a transition zone, and thus is disposed between the first and third zones 10, 14. In use the heat transfer element 4 may have a primary gas flow direction identified by arrow A such that gas will generally flow from the first end 6 to the second end 8.

(16) The first zone 10 comprises a herringbone profile. The herringbone profile can include a plurality of alternating first and second regions 16, 18. Each of the first and second regions 16, 18 can be arranged such that the boundary 20 between regions is oriented along the primary direction of gas flow A. In the illustrated embodiment, the first region 16 includes a plurality of undulations 22 arranged laterally side by side, where the longitudinal axis B-B (FIG. 3) of the undulations in the first region 16 is oriented at an angle with respect to the primary direction of gas flow A. In some embodiments, the angle is between about 0 and 90. The second region 18 can be positioned adjacent to the first region 16, and can include a plurality of undulations 24 arranged laterally side by side, where the longitudinal axis C-C (FIG. 3) of the undulations 24 in the second region 18 may be oriented at an angle with respect to the primary direction of gas flow A. In some embodiments, the angle is between about 0 and 90. As can be seen, the first zone 10 may include a plurality of alternating first and second regions 16, 18.

(17) The third zone 14 can be a corrugated sheet in which the undulations 26 are oriented substantially parallel to the primary direction of gas flow A. In the illustrated embodiment the undulations 26 have flat peaks 28 and troughs 30 (see FIGS. 3 and 4). Disposed between the first and third zones 10, 14 is a second zone 12 which may be referred to as a transition zone. The second zone 12 is a generally flat profile without undulations, as can best be seen in FIG. 3. The second zone 12 may include first and second transition regions 32, 34 that convert the shapes of the first and third zones 10, 14, respectively, to the flat profile of the second zone 12. Thus, these first and second transition regions serve to provide a smooth conversion of the profiles of the first and third zones 10, 14 to the flat profile of the second zone 12.

(18) Referring again to FIG. 2, the first, second and third zones 10, 12, 14 may have respective lengths L.sub.1, L.sub.2, L.sub.3. In some non-limiting exemplary embodiments, the length L.sub.1 may be between 600 to 900 millimeters (mm), the length L.sub.2 may be between 5 to 25 mm, and the length L.sub.3 may be between 200 to 300 mm. It will be appreciated that these lengths are not critical, and that other lengths can be used.

(19) Although the illustrated embodiment includes three discrete profile zones, it will be appreciated that the specific number of zones is not critical, and thus, the first heat transfer element 4 may have as few as two zones, or more than three zones.

(20) FIG. 3 shows a stack of interposed first and second heat transfer elements 4, 36. It will be appreciated that the arrangement of FIG. 3 is for illustrative purposes, and that in practical application a typical heater basket 2 may include a large number of interposed first and second heat transfer elements. In the illustrated embodiment, the second heat transfer elements 36 include a corrugated profile having a plurality of undulations 38 oriented substantially parallel to the primary direction of gas flow A.

(21) FIG. 4 shows the interaction between a first heat transfer element 4 and an exemplary second heat transfer element 36 near the second end 8 (i.e., the cold end) of the stack. In this embodiment, the width FW of the flat peaks 28 and troughs 30 of the first heat transfer element 4 is about 0.5 times the distance TW between adjacent troughs 42 of the corrugations 38 of the second heat transfer element 36. As can be seen, in certain places 40, the troughs 42 of the second heat transfer element 36 have good line contact with the flat-topped peaks 28 and troughs 30 of the third zone 14 of the first heat transfer element 4. In other places 44, the troughs 40 of the second heat transfer element have poor or no line contact with the flat-topped peaks 28 and troughs 30 on the third zone 14 of the first heat transfer element 4. The interrelation between the features of the first and second heat transfer elements 4, 36 can also be seen in FIG. 5, which is an end view taken from the second end 8 (i.e., the cold end) of the stack shown in FIG. 3.

(22) Referring to FIGS. 6-8, an alternative stack arrangement is shown. This embodiment may include first and second heat transfer elements 104, 136 having some or all of the features of the first and second heat transfer elements 4, 36 described in relation of FIGS. 3-5, with the exception that the first heat transfer elements 104 may have a different geometric relationship between profile elements at the second end 108.

(23) Thus, the first heat transfer element 104 may have first, second and third zones 110, 112, 114 aligned sequentially in a primary gas flow direction A. The first zone 110 may comprise a herringbone profile substantially as previously described. The second zone 112 may comprise a flat transition zone and the third zone 114 may comprise a corrugated profile as previously described, including flat peaks 128 and troughs 130.

(24) In this embodiment, however, in the third zone 114 of the first heat transfer element 104 the width FW of the flat peaks 128 and troughs 130 may be equal to the distance TW between adjacent troughs 142 of the corrugations 138 of the second heat transfer element 136. As can be seen in FIG. 7, in certain places 140, the troughs 142 of the second heat transfer element 136 have good line contact with the flat-topped peaks 128 and troughs 130 of the third zone 114 of the first heat transfer element 104. In other places 144, the troughs 140 of the second heat transfer element have poor or no line contact with the flat-topped peaks 128 and troughs 130 on the third zone 114 of the first heat transfer element 104. The interrelation between the features of the first and second heat transfer elements 104, 136 can also be seen in FIG. 8, which is an end view taken from the second end 8 (i.e., the cold end) of the stack shown in FIG. 6.

(25) Referring to FIGS. 9-11, a further alternative stack arrangement is shown. This embodiment may include first and second heat transfer elements 204, 236 having some or all of the features of the first and second heat transfer elements 4, 36 described in relation of FIGS. 3-6, with the exception that the first heat transfer elements 204 may have a different geometric relationship between profile elements at the second end 208.

(26) Thus, the first heat transfer element 204 may have first, second and third zones 210, 212, 214 aligned sequentially in a primary gas flow direction A. The first zone 210 may comprise a herringbone profile substantially as previously described. The second zone 212 may comprise a flat transition zone and the third zone 214 may comprise a corrugated profile as previously described, including flat peaks 228 and troughs 230.

(27) In this embodiment, however, in the third zone 214 of the first heat transfer element 204 the width FW of the flat peaks 228 and troughs 230 may be equal to 1.5 times the distance TW between adjacent troughs 242 of the corrugations 238 of the second heat transfer element 236. As can be seen in FIG. 10, in certain places 240, the troughs 242 of the second heat transfer element 236 have good line contact with the flat-topped peaks 228 and troughs 230 of the third zone 214 of the first heat transfer element 204. In other places 244, the troughs 240 of the second heat transfer element have poor or no line contact with the flat-topped peaks 228 and troughs 230 on the third zone 214 of the first heat transfer element 204. The interrelation between the features of the first and second heat transfer elements 204, 236 can also be seen in FIG. 11, which is an end view taken from the second end 8 (i.e., the cold end) of the stack shown in FIG. 9.

(28) Each of the described embodiments illustrate novel heat transfer elements incorporating three separate zones along the depth/height of the elements. The deeper hot end zone 10 of these element sheets 4, which may be about 600 mm deep comprise of undulations arranged in a transverse herringbone arrangement. The main purpose of these transverse herringbones is to restrict skew flow though the elements as the gas flows from hot end 6 to the cold end 8 of the element pack on traverse through the gas side of the rotary air preheater 1 and as the air flows from cold to hot end of the air preheater during the transit of the element basket 2 through the air side of the rotary regenerative air preheater.

(29) As shown in the figures, at the opposite, cold end 8 of the element pack there is a third zone 114 of flat topped undulations that run longitudinally along the depth of the element in the flow direction and typically constitute the lower 300 mm of the element depthalthough that dimension can vary.

(30) As can be seen in FIGS. 5, 8 and 11, the height FTH of these said flat topped undulations 26, 126, 226 are selected to be the same as the height HTH of the transverse herringbone undulations 22, 24 towards the hot end 6 of the heat transfer element 4, 104, 204. Arranged in such a fashion, it can be seen that these flat-topped undulations 26, 126, 226 provide a relatively wide sealing surface against which one or more peaks of the corrugations 38, 138, 238 in the opposing second heat transfer elements 36, 136, 236 compress, thereby forming a line of continuous contact forming closed channels.

(31) The different embodiments show the typical effect of increasing the width FW of the flat topped undulations 26, 126, 226 in providing contact between the peaks of the corrugations 36, 136, 236.

(32) The closed channels formed by these lines of contact produce a physically closed element profile that acts to contain both normal gas flow patterns and the intermittent sootblowing jets used for cleaning the elements. Indeed, the combination of this physically closed element at the cold end (e.g., second end 8) of the elements 4, 104, 204, combined with the aerodynamically closed profile produced by the transverse herringbone undulations 22, 24 further up the element act to maximize the penetration the sootblowing jets and increase their cleaning effectiveness.

(33) At the same time, it can be noted that this cold end 8 of the disclosed composite profile (the first heat transfer element 4, 104, 204) does not incorporate any angled undulations to promote turbulence and increase the thermal performance of the element. Therefore, this corrugated-flat section (the third zone 14, 114, 214 of the first heat transfer element 4, 104, 204 produces a zone with low heat transfer and pressure drop characteristics analogous to those of conventional low performance notched-flat elements mentioned earlier.

(34) A much shallower intermediate zone (the second zone 12, 112, 212) of the first heat transfer element 4, positioned between the different hot end (first zone 10, 110, 210) and cold end (third zone 14, 114, 214) profiles of the element. This intermediate zone (the second zone 12, 112, 212) is typically only around 25 mm in length and is deliberately not formed into any determinate shape. Instead, its purpose is to produce a natural, free-form transition between the different profiles (i.e, the transverse herringbone profile of the first zone 10, 110, 210 and the flat topped corrugated profile of the second zone), thereby allowing this transition zone 12, 112, 212 to take up its natural shape in a smooth manner. This transition zone 12, 112, 212 is designed to eliminate any sudden transitions between one profile and another, which sudden steps might otherwise promote enhanced, localized erosion rates. In addition, the uninterrupted continuity across the transition zone 12, 112, 212 also ensures that the reduction in the peak sootblower jet velocities and associated peak impact pressure is minimized, thereby ensuring effective cleaning.

(35) The inventor is unaware of any heat transfer element that has been designed specifically with the purpose of producing with different performance characteristics at each end of the same heat transfer element. The inventor also believes that the castellated, flat topped undulations (peaks 28, 128, 228, troughs 30, 130, 230) which are designed to alternately come into line contact with the corrugations of the opposing element sheets on either side of the undulated sheet is a unique approach to producing closed channel elements. Additionally, the inventor believes that the shallow, non-preformed transition zone 12, 112, 212 provides a novel but simple approach to promoting smooth flow patterns between the different hot and cold ends of the element profile, thereby minimizing the erosion rate and promoting smooth transition of flow from one zone of the element to the other and reducing the intermediate pressure drops and energy losses.

(36) Because it will reduce the inter-tier shocks and losses, the applicant also argues that this invention should produce a lower pressure drop than the more traditional two tier arrangement.

(37) Several alternative structure arrangements that might be incorporated without changing the basic invention have been described, in which the width FW of the flat topped undulations (peaks 28, 128, 228, troughs 30, 130, 230) has been varied showing typical arrangements that produce a minimum of one to two lines of contact against single flat topped undulations and, similarly, no more than one to two lines of corrugations at the cold end (the third zone 12) of the first heat transfer element 4 where there is no contact between these corrugations and the adjacent troughs 30, 130, 230 of the flat-topped undulations. It is considered desirable to achieve these constraints in order to maximize the stability of the finally compressed element pack.

(38) It will be appreciated that the disclosed arrangement can be used in a variety of types of heat exchangers, such as plate type heat exchangers, to produce the same combination of benefits as described in relation to the rotary regenerative heat exchanger 1 described herein.

(39) While the present invention has been disclosed with reference to certain embodiments, numerous modifications, alterations and changes to the described embodiments are possible without departing from the spirit and scope of the invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof.