GB2206682A - A rotary regenerative heat exchanger - Google Patents

Abstract

A rotary regenerative heat exchanger has a cylindrical open ended casing with a heat exchange mass therein having a multiplicity of axially and generally radially extending partitions 16 providing a multiplicity of axial gas flow passages, but substantially precluding circumferential gas flow. A gas feed system includes a pair of axially aligned hoods mounted to overlie corresponding portions only of the ends of the mass to feed a first gas to and from the exchange mass. Ducting overlies the remainder of each axial end of the casing to feed a second gas to and from the heat exchange mass and means are provided to cause relative rotation about the axis of the cylindrical casing between the gas feed system and the casing. Radially extending sealing elements 40, 42, 44, 46 divide the ends of the hoods from the ends of the ducts and have a circumferential extent to overlie at all times of relative rotation at least two adjacent ones of the partitions 16, so that the pressure between these partitions is intermediate the pressures on either side thereof. <IMAGE>

Description

A REGENERATIVE HEAT EXCHANGER The present invention relates to regenerative heat exchangers.

Such exchangers are used to recover heat from gaseous fluids such as the flue gases from a power station so that the incoming combustion air can be preheated, thereby improving the efficiency of the installation.

Regenerative heat exchangers are also beginning to be used in further treatment of the flue gases, in order to remove noxious gases such as nitrous and sulphurous oxides which lead to the formation of acid rain.

There are two basic types of rotary regenerative heat exchanger. One of these involves having a heat exchange mass, usually metal plates, mounted in a rotating casing, the casing rotating relative to a gas feed system which includes, on the one hand, a pair of axially aligned hoods, mounted to overlie corresponding portions only of the axial ends of the heat exchange mass, to feed the first gas to and from said heat exchange mass and ducting overlying the remaining of each axial end of the casing to feed a second gas to and from the heat exchanger.

The other form of rotary regenerative heat exchanger involves having a fixed generally cylindrical open ended casing with a similar heat exchange mass mounted in the casing, and for the gas feed system to rotate relative to this fixed casing.

In either event, pressure of the gas passing through the ducting is significantly higher or lower than the gas passing through the hoods. There is therefore a tendency for the higher pressure gas to leak towards the lower pressure gas and attempts have been made to overcome this by placing the ends of the ducting as close as possible to the heat exchange mass. However, this is not always satisfactory, because of the very bulk of the heat exchanger causing a general bowing of the various parts, this leading to a leak path other proposals have involved the use of magnetic sealing elements which operate under the action of sensors. These are relatively complex and can result in operation difficulties.

It is now proposed, according to the present invention, to provide a regenerative heat exchanger comprising a generally cylindrical, open-ended casing, a heat exchange mass mounted in said casing, said heat exchange mass including a multiplicity of axially and generally radially extending partitions, circumferentially spaced from one another to provide a multiplicity of axial gas flow passages through the heat exchange mass, but substantially precluding circumferential gas flow, a gas feed system including a pair of axially aligned hoods, mounted to overlie corresponding portions only of the axial ends of said heat exchange mass, to feed a first gas to and from said heat exchange mass, and ducting overlying the remainder of each axial end of the casing to feed a second gas to and from the heat exchange mass, means to cause relative rotation, about the axis of said cylindrical casing, between said gas feed system and the casing, and radially extending fixed sealing elements dividing the ends of the hoods from the ends of the ducts, said radially extending sealing elements having a circumferential extent at all times of relative rotation to overlie at least two adjacent ones of said generally radially extending partitions.

By having the radially extending sealing elements so that they have a circumferential extent at all times of relative rotation, to overlie at least two adjacent ones of the generally radially extending partitions, a double sealing effect can be achieved. The pressure between the at least two adjacent partitions which the radially extending sealing elements overlie will always be intermediate the pressure in the hood, on the one hand, and the ducting on the other. This double sealing effect greatly reduces the tendency of the higher pressure gas to leak into the lower pressure gas.

While in prior constructions it is generally been considered acceptable for there to be some leakage when one is using the regenerative heat exchanger to improve the efficiency of a furnace installation, or the like, such leakage is unacceptable when one is trying to remove noxious gases from the final flue gas discharged to the atmosphere.

The construction of the present invention enables a far better sealing effect to be produced and the leakage can in fact be negligible.

The casing may comprise a plurality of accurately radially extending walls dividing the casing into a plurality of sector shaped zones, in which case the heat exchange mass may include a number of radially spaced annular partitions and generally radially extending partitions within each sector shaped zone.

With such a construction, said generally radially extending partitions in one sector may be arranged to be substantially parallel to one another (and not parallel accurately to the radially extending partitions) , and the circumferentially extent of each extending sealing element is then constructed to be sufficiently wide to overlie at least two adjacent ones of the parallel partitions and where appropriate, radially extending walls, and the adjacent radially extending partition.

The construction of the present invention may be used in the type of heat exchanger wherein the hood of each axial end is semi-circular and the ducting of each end is semi-circular, the radially extending sealing elements being in the form of a diametral plate including two sector shaped portions. However, the construction of the present invention is particularly suitable for the type of regenerative heat exchanger in which the hood at each axial end is in the form of two diametrally opposite quadrant shaped portions and the ducting at each axial end is in the form of two further quadrant shaped portions located between said hood portions, said radially extending elements being in the form of four plates extending along directions approximately at right angles to one another.

In order that the present invention may more readily be understood, the following description is given, reference being made to the accompanying drawings in which: Figure 1 is a side elevation, in section, of one embodiment of regenerative heat exchanger according to the invention; Figure 2 is a section taken along the line II-II of Figure 1; Figure 3 is an enlarged view of a portion of the casing shown in Figure 2; and Figure 4 is a view similar to Figure 3 of a different type of construction of regenerative heat exchanger according to the present invention.

The heat exchanger shown in Figure 1 includes a fixed casing 10 in the form of an open ended cylinder, this cylinder including a number of radially extending walls 12 dividing the casing into a plurality of sector shaped zones 14. Within each of the zones 14 there is included a part of a total heat exchange mass indicated by the reference numeral 16. The same more particularly in Figure 3 consists of a multiplicity of axially and generally radially extending partitions 18 as well as a number of circumferentially extending partitions 20. These define a multiplicity of axial gas flow passages 22 through the heat exchange mass, which substantially precludes circumferential gas flow within the heat exchange mass.

The heat exchanger also includes a gas feed system for heating a first gas, for example a hot gas, upwardly and for feeding a second gas, for example a cold gas, downwardly in counterflow. The gas feed system includes an upper hood 24 and an axially aligned lower hood 26. The upper hood 24 has an inlet 28 and the lower hood 26 has a outlet 30.

The feed system also includes a lower ducting 32 having gas inlet 34 and an upper ducting 36 having a gas outlet 38, the ducting 32 and 36 being mounted to overlie corresponding portions only of the axial ends of the heat exchange mass. This is achieved by the hoods 24 and 26 each comprising diametrically opposite quadrant shaped portions separated by radially extending sealing elements 40, 42, 44, 46. Thus one of quadrant shaped parts of the hood is connected to the sealing elements 40 and 42 and the other quadrant shaped part of the hood 24 is connected to the sealing elements 44 and 46.Similarly the ducting is connected to these radially extending sealing elements, the ducting 36 having two quadrant shaped parts one of which is connected between to the sealing element 46 and the sealing element 40 and the other of which is connected to the sealing element 42 and the sealing element 44. A precisely similar aligned arrangement is provided below the heat exchange mass held by the casing 10.

The whole gas feed systems is rotatable about a vertical axis and is mounted on a shaft 50 carried by bearings 52, 54 and 56. The rotation of the gas feed system is caused by a motor (not shown).

The upper and lower parts of the gas feed system are connected by a peripheral cylindrical wall 58 surrounding the cylindrical wall of the casing 10.

The circumferential extent of the radial sealing elements 40, 42, 44 and 46, in each instance, both above and below the heat transfer mass 16 in the casing 10 is such as to overlie at least two of the generally radially extending partitions 18. As shown, they actually cover rather more than two and indeed are shown covering at least two of the walls 12.

It will be appreciated that as the gas feed system rotates about the axis of the shaft 50, the hot gas indicated by the arrows 60 flows upwardly and through the passages 22 which at that time are positioned between the sealing elements 46 and 40 on one side and between the sealing elements 42 and 44 on the other side. The gas thus heats the heat transfer mass to an elevated temperature.

The speed of rotation is very low, of the order of lrpm giving the heat transfer mass an adequate time for its temperature to be raised.

The provision of the wide sealing elements 40 to 46 prevents or reduces any significant leakage between the hot gas flow 60 and the cold gas flow 62. There will always be a zone under the sealing elements which is at a pressure which is intermediate the pressure in the hood 24 and the pressure in the duct 36 on the one hand, and the pressure in the hood 26 and the duct 32 on the other hand.

If reference is made to Figure 4 an alternative construction is illustrated therein in which the casing 80 is caused to rotate relative to the hoods and ducting (not shown) the latter remaining stationary. A pair of quadrant shaped sector plates 82 and 84 again overlie at least two of the generally radially extending partitions 86, this again reducing the leakage path.

In each of the constructions described above, the pressure zone which is under the center path of the sealing plate will, in each instance, be intermediate the higher pressure appearing in the hood and the pressure appearing in the ducting at that end of the heat exchange mass.

While reference has been made to the casing being generally cylindrical, this need not necessarily imply a curved peripheral wall. In many instances, the peripheral wall of the casing will be polyognal, as viewed in the actual direction of the casing.

Claims (7)

1. A regenerative heat exchanger comprising a generally cylindrical, open-ended casing, a heat exchange mass mounted in said casing, said heat exchange mass including a multiplicity of axially and generally radially extending partitions, circumferentially spaced from one another to provide a multiplicity of axial gas flow passages through the heat exchange mass, but substantially precluding circumferential gas flow, a gas feed system including a pair of axially aligned hoods, mounted to overlie corresponding portions only of the axial ends of said heat exchange mass, to feed a first gas to and from said heat exchange mass, and ducting overlying the remainder of each axial end of the casing to feed a second gas to and from the heat exchange mass, means to cause relative rotation, about the axis of said cylindrical casing, between said gas feed system and the casing, and radially extending fixed sealing elements dividing the ends of the hoods from the ends of the ducts, said radially extending sealing elements having a circumferential extent at all times of relative rotation to overlie at least two adjacent ones of said generally radially extending partitions.

2. A heat exchanger according to claim 1, wherein said casing comprises a plurality of accurately radially extending walls dividing said casing into a plurality of sector-shaped zones, and wherein said heat exchange mass includes a number of radially spaced annular partitions and generally radially extending partitions within each sector-shaped zone.

3. A regenerative heat exchanger according to claim 2, wherein said generally radially extending partitions in any one sector are substantially parallel to one another, and wherein the circumferential extent of said radially extending sealing elements is sufficiently wide to overlie at least two adjacent ones of said parallel partitions and, where appropriate, said radially extending wall and the adjacent radially extending partition.

4. A heat exchanger according to any preceding claim, wherein the hood at each axial end is in the form of two diametrally opposite, quadrant shaped, portions and the ducting at each axial end is in the form of two further quadrant shaped portions located between said hood portions, said radially extending sealing elements being in the form of four plates extending along directions at right angles to one another.

5. A regenerative heat exchanger according to any one of claims 1 to 3, wherein said hood at each axial end is semi-circular and the ducting at each axial end is semi-circular, the radially extending sealing elements being in the form of a diametral plate including two sector shaped portions.

6. A regenerative heat exchanger according to any preceding claim, wherein the casing is fixed and the gas feed system rotates relative thereto.

7. A regenerative heat exchanger substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.