GB2143629A - Air heater - Google Patents

Abstract

An air heater 1 deriving heat from hot gas comprises a stationary heat transfer element 10 with vertical passages 12 formed therethrough between respective faces 13 and 14. Feed and outlet elements 20, 30 are mounted for synchronous movement over the faces 13, 14 so as to direct air to the passages 12 to be heated and to direct the heated air away while permitting flow of hot gas through others of the passages in sequence thereby to heat them. The feed and outlet elements 13, 14 have sealing means 45, 46 for sliding contact with the faces 13, 14 and which are biased towards the faces 13, 14 by counterweight linkages 50. <IMAGE>

Description

SPECIFICATION Air heater This invention relates to air heaters which derive heat from hot gas and which are of the type comprising a stationary heat transfer element having a plurality of passages formed therethrough between respective faces thereof, and feed and outlet elements mounted for synchronous movement relative to the heat transfer element at respective said faces so as to direct air to some of the passages, to be heated while travelling through these passages and to direct the heated air away while permitting flow of hot gas through others of the passages thereby to heat those other passages, said movement being effective to direct air through substantially all the passages in sequence, the feed and outlet elements each having sealing means for sliding sealing contact with said faces of the heat transfer element to restrict mixing of the air and the hot gas.

A problem with this type of air heater is that the heat transfer element (often known as the matrix) expands thermally as the apparatus heats up.

While the sealing means can be set so that leakage rates of two or three per cent are achievable, the sealing means has to be able to compensate for the variations arising from this thermal expansion.

One method which has been used is to mount each sealing means on spring pins which apply compressive forces in service, but this of course results in rapid wear. This is particularly so with the sealing means of the feed element. Most of the wear occurs during run-up and shut down when these sealing means are in heavy compression and consequently the leakage rate can increase to twenty per cent or more unless the sealing means are reset.

The invention provides an air heater of the said type further comprising counterweight biasing means arranged to act on one or each of the sealing means so as to urge it into said sliding contact with the respective face of the heat transfer element.

The counterweight biasing means preferably comprises a plurality of counterweight linkages mounted on the respective feed or outlet element and arranged about the respectve sealing means.

Each such linkage may comprise a balancing arm pivotally mounted on the feed or outlet element and a thrust pin mounted for movement towards and away from the respective face of the heat transfer element and arranged to act on the sealing means, the arm being arranged to urge the pin towards the heat transfer element.

The pin may advantageously be secured adjustably to the sealing means, and the balancing arm would typically be pivotally connected to the pin.

In the case where the feed or outlet element or each of the feed and outlet elements has a peripheral wall portion inclined generally inwardly of and away from the heat transfer element, at least one of the linkages may be located adjacent the said inclined wall portion with its balancing arm oriented generally parallel to the said inclined wall portion.

Preferably, means is provided to limit the movement of each arm laterally of its pivotal mounting.

One or each of the sealing means may comprise an inner portion for sliding contact with the respective face of the heat transfer element and an outer portion secured to the feed or outlet element, the inner and outer portions being flexibly connected, the counterweight means being arranged to urge the inner portion into contact with the respective face of the heat transfer element.

The invention also envisages a kit for converting an existing air heater of the said type to an air heater as above, the kit comprising counterweight biasing means mountable on the existing air heater so as to act on the one or each of the sealing means so as to urge it into contact with the respective face of the heat transfer element.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows in sectional elevation an air heater of the said type; Figure 2 is an exploded perspective view of some principal components of the heater of Figure 1; Figure 3 is a partially sectional side elevation of a counterweight linkage; and Figure 4 is an end elevation of the counterweight linkage of Figure 3.

Referring first to Figures 1 and 2, the air heater 1 comprises a stationary heat transfer element or matrix 10 mounted within an outer gas-tight casing 11. The interior of the matrix 10 is divided into a large number of vertical passages 12 extending between upper and lower faces 13 and 14 of the matrix 10.

Below the matrix 10, an air feed element or lower hood 20 is rotatably mounted in bearings 21 for rotation about a vertical axis over the lower face 14 of the matrix 10. As will be appreciated, the lower hood 20 is shown in Figure 2 in underneath perspective, unlike the other components shown in that figure which appear in perspective from above. The lower hood 20 acts to direct air to be heated to the passages 12 in sequence, the air flowing through a number of the passages 12 at any particular time. An air feed conduit 22 cooperates with the lower hood 20 to conyey air to be heated to the hood 20, the junction between the feed conduit 22 and the lower hood 20 being made substantially air-tight by means of a collar seal 23.

Turning vanes 24 mounted in the feed conduit 22 serve to guide the air flow uniformly into the lower hood 20.

Above the matrix 10, an air outlet element or upper hood 30 is also rotatably mounted in bearings 31 for rotation about the same vertical axis as that of the lower hood 20. The upper hood 30 moves over the face 13 of the matrix 10 in the same way as the lower hood 20 moves across the face 14.

The upper hood 30 is rotated synchronously, with the lower hood 20, the latter being always directly below the former, with the drive for such rotation provided by a motor 27. The motor 27 drives a pinion 28 which engages a toothed driving ring 29 secured to the lower hood 20. Drive to the upper hood 30 is transferred through a rigid connection between the upper and lower hoods through the centre of the matrix 10. The upper hood 30 acts to direct the air which has been heated in the passages 12 away from the upper face 13 to an air outlet conduit 32, the junction between the upper hood 30 and the outlet conduit 32 again being sealed against leaks by a collar seal 33. Turning vanes 34 are simiarly provided to regulate the flow of air through the conduit 32.

Hot gas, such as combustion gas from a furnace, for heating the air is admitted to the heater 1 through an inlet 40. The upper hood 30 acts to direct the hot gas into passages 12 not having air travelling through and the lower hood 20 directs the gas away from the matrix 10, the gas exhausting through an outlet 41. It will be appreciated that rotation of the upper and lower hoods in synchronism as described above will cause first hot gas to travel through each passage 12 in a downward direction, thus heating the passage 12, and cause air to travel upwards through the passage 12 which then transfers heat to the air.

In order to minimise mixing of the air and the hot gas, the upper and lower hoods 30 and 20 are each provided with a peripheral seal 45 for sliding contact with the respective face 13 or 14 of the matrix 10. Each seal 45 is attached to its respective hood 30 or 20 by a flexible expansion joint 46.

The other general details of the air heater 1 will not be described here since this type of heater is well known in the art. It will of course be understood that the heater is not restricted to the heating of air but can be used for transferring heat between any two gases.

Referring now to Figures 3 and 4 which show counterweight biasing means in accordance with the invention, the mounting of the lower seal and expansion joint 45 and 46 on the lower hood 20 will be explained in detail. A similar counterweight biasing arrangement, appropriately modified, can be adopted for the mounting of the upper seal and expansion joint 45 and 46 on upper hood 30.

Arranged about the lower seal 45 in spaced relationship is a number (18 in one practicai example) of counterweight linkages 50 mounted on the lower hood 20. Each linkage comprises a balancing arm 51 pivotally mounted on a bracket 52 which is bolted to a base plate 53, the base plate being welded to the hood 20. The pivotal mounting is provided by a pin 54 mounted in the bracket 52 which is a loose fit in hole 55 in the arm 51. A counterweight 56 is threadedly mounted on threaded rod 57 of arm 51 so that the torque of the counterweight 56 about the pivot pin 54 can be varied.

The seal 45 comprises an H section member 47 to which is fixed a thrust pad 48 which makes the sliding contact with the respective face of the matrix 10. The expansion joint 46 comprises upper and lower brackets 42 and 43 secured respectively to the member 47 and hood 20. The brackets 42, 43 are joined by a fully flexible fabric or PVC seal 44 and this seal accounts for the variations in distance between the member 47 and hood 20 due to thermal expansion of the matrix 10, in order to maintain the pad 48 in close fitting contact with the face 14 of the matrix. The seal 45 with bracket 42 can therefore be considered an "inner" portion of the sealing means flexibly connected to an "outer" portion constituted by bracket 43.

The weight of the seal 45 is supported by a thrust pin 60 of each linkage 50, which pin is slidably mounted in a respective hole 61 (in the hood 20). The vertical thrust in the pin 60 is transferred through a clevis 63 welded to the end of pin 60, and then through the shank of a bolt 64 spanning the bracket 63 and held in place by a nut 65. The bolt 64 is a loose fit in hole 65 in the arm 51 in the same way as the loose fit of pin 54 in hole 55. This loose fit is provided to prevent failing of the linkages by fly ash or corrosion since of course the linkages are in the path of the hot gas passing through the heater.

The pin 60 is adjustably secured at its other end to the seal 45 by virtue of a threaded engagement in a collar 66 and passes through a hole in the member 47, the collar 66 being welded to a plate 67 which is bclted to the member 47, as will be seen from Figure 4. The pin 60 is formed at its upper end portion with a longitudinal groove 68 for engagement by a lock bolt 69 threadably mounted in the collar 66. The groove 68 in conjuction with the bolt 69 maintains the pivot bolt 64 in alignment and the bolt 69 can be tightened on the pin 60 anywhere along the groove 68. To avoid damage to the linkages in use, lateral movement of the balancing arm 51 is limited by two gussets 58 welded to the hood 20.

It will be readily understood from Figure 3 that the counterweight linkages will effectively support the seal 45 and maintain the necessary contact pressure between the seal 45 and the matrix 10.

Adjustment of the contact pressure can be made by rotating the counterweight 56 as appropriate so as to move along the threaded rod 57.

The counterweight linkage 50 shown in Figures 3 and 4 is that adopted adjacent to the downwardly and inwardly inclined portions of the hood 20, such portions being indicated at 25 in Figures 1 and 2. As seen in Figure 3 it is convenient to arrange the balancing arms of such linkages generally parallel to those inclined hood portions.

Counterweight linkages adjacent other portions of the hood around the seal 45 will have the shape of their balancing arms and the adjustment of the linkages modified as necessary.

The invention can take the form of an air heater originally constructed as above or alternatively a conversion kit including the necessary number of counterweight linkages can be used to convert an existing air heater of the type in question.

The above embodiment of the invention has the great advantage that despite thermal expansion the counterweight linkages provide a very satisfactory and substantially constant contact pressure between the sealing means and the matrix which is not affected as parts wear out, thus resulting in a very considerable, improvement in the isolation of the air and hot gas in such heaters.

Claims (10)

1. An air heater of the said type further comprising counterweight biasing means arranged to act on one or each of the sealing means so as to urge it into said sliding contact with the respective face of the heat transfer element.

2. A heater as claimed in claim 1 wherein the counterweight biasing means comprises a plurality of counterweight linkages mounted on the respective feed or outlet element and arranged about the respective sealing means.

3. A heater as claimed in claim 2 wherein each counterweight linkage comprises a balancing arm pivotally mounted on the feed or outlet element and a thrust pin mounted for movement towards and away from the respective face of the heat transfer element and arranged to act on the sealing means, the arm being arranged to urge the pin towards the heat transfer element.

4. A heater as claimed in claim 3 wherein the pin is adjustably secured to the sealing means.

5. A heater as claimed in either claim 3 or claim 4 wherein the balancing arm is pivotally connected to the pin.

6. A heater as claimed in any one of claims 3 to 5 wherein the feed or outlet element or each of the feed and outlet elements has a peripheral wall portion inclined generally inwardly of and away from the heat transfer element, at least one of the linkages being located adjacent the said inclined wall portion and having its balancing arm oriented generally parallel to the said inclined wall portion.

7. A heater as claimed in any one of claims 3 to 6 further comprising means to limit the movement of each arm laterally of its pivotal mounting.

8. A heater as claimed in any preceding claim wherein the one or each of the sealing means comprises an inner portion for sliding contact with the respective face of the heat transfer element and an outer portion secured to the feed or outlet element, the inner and outer portions being flexibly connected, the counterweight means being arranged to urge the inner portion into contact with the respective face of the heat transfer element.

9. A kit for converting an existing air heater of the said type to an air heater as claimed in any preceding claim, comprising counterweight biasing means mountable on the existing air heater so as to act on the one or each of the sealing means so as to urge it into contact with the respective face of the heat transfer element.

10. An air heater substantially as hereinbefore described with reference to and as shown in the accompanying drawings.