GB2129533A

GB2129533A - Rotary regenerative heat exchanger

Info

Publication number: GB2129533A
Application number: GB08322907A
Authority: GB
Inventors: Dr John Scott Stoddart; Satinder Paul Hansrani
Original assignee: Babcock Woodall Duckham Ltd
Current assignee: Babcock Woodall Duckham Ltd
Priority date: 1982-08-26
Filing date: 1983-08-25
Publication date: 1984-05-16
Also published as: GB8322907D0

Abstract

A rotary regenerative heat exchanger includes a ceramic matrix 10 that is rotatable about a horizontal axis. Non- contact proximity seals 16 are provided around the matrix adjacent the front and rear faces. The matrix 10 rests on rollers by which through frictional engagement it may be rotated. The matrix 10 may be made of a sillimanite or mullite material. <IMAGE>

Description

SPECIFICATION Improvements in or relating to rotary heat exchanger of the regeneration type This invention relates to heat exchangers of the rotaty regenerative type in which a matrix rotates continuously through a zone in which it absorbs heat and a zone in which it gives up heat.

In a form of rotary heat exchanger of the regenerative type that has been widely used as an air pre-heater in power stations, a metallic rotor,having passages through which gas can pass, has been arranged to rotate about a vertical axis, with its end faces horizontal, through two adjacent ducts to one of which hot waste gases are supplied and for the other of which the air to be heated is supplied. A disadvantage of such a heat exchanger in situations where the temperature of the hot gas is relatively high is that as the rotor undergoes thermal cyciing through several hundred degrees the resultant expansion and contraction leads to difficulty in maintaining the seals that isolate the higher and lower temperature gas streams.

In the steel industry, the temperatures of waste gases generated in soaking pits and reheating furnaces are typically of the order of between 900" and 1200"C. The glass and aluminium industries also yield waste gases at high temperatures. These gases represent a major and readily recoverable source of energy. Conventionally, this energy is recovered through the use of waste heat boilers from which steam can be generated for steelworks requirements. However, in many cases installation of equipment within the vicinity of the furnaces is not possible. The waste heat boilers therefore have to be installed either some distance away from the furnaces or above the furnaces and in each case, the capital cost for installation may become prohibitive.

Additionally, effective use of the generated steam is necessary to make an energy recovery scheme viable. In some steel plants, the overall energy balance is such that substantial quantities of steam cannot be used internally without making inertially generated waste gases, e.g. blast furnace gas and carbon monoxide, redundant at the boiler plant or elsewhere.

The present invention sets out to provide a rotary heat exchanger of the regenerative type that is capable of operating in higher temperature environments as described above.

According to the present invention there is provided a rotary heat exchanger of the regenerative type which comprise a ceramic heat-transfer matrix rotatable within an annular sleeve about a generally horizontal axis, and non-contact proximity sealing means extending around the matrix and serving to prevent the passage of gas between the matrix and the sleeve.

By way of example, an embodiment of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a section, on the line I-I of Figure 2, of a regenerative heat exchanger; Figure 2 is a section taken along line ll-ll of Figure 1; Figure 3 is a detail, on a larger scale, of Figure 2 of a circumferential seal; and Figure 4 illustrates diagrammatically the heat exchanger shown in Figures 1 to 3 installed within the offtake system of a furnace.

The rotary heat exchanger of the regenerative type shown in Figures 1 and 3 includes a disc-like matrix 10 that is mounted for rotation about a generally horizontal axis. The matrix has a "hot" face 1 0a to which incoming high temperature waste gas is directed and from which outgoing heated combustion air departs, and a "cold" face lOb to which incoming cold air for combustion is directed and from which outgoing cooled waste gas departs. The "hot" face 10a communicates with ducts 1 and 2 each lined with a thermally insulating material and connected respectively to a waste gas offtake of a furnace and a combustion chamber of the furnace.

The "cold" face lOb communicate with ducts 3 and 4 connected respectively to a furnace stack and to a source of air for combustion. Contact seals 5, 6 extending diametrically across the matrix 10 are positioned one at each heat exchanger face; seal 5 forms part of the division between ducts 1 and 2 and seal 6 forms part of the division between ducts 3 and 4.

The matrix comprises heat storage elements in the form of ceramic blocks 7 having a plurality of gas flow passages 8 extending axially between the "hot" and "cold" faces of the matrix. The blocks are retained within a metallic rim 9. The ceramic may be a sillimanite or mullite material; such materials will operate successfully up to a temperature approximately 1 3500C. The blocks are of substantially rightangled parallelopipedal form and have external grooves that accept support bars 11 by which the blocks are supported and located. The support bars 11 (only one of which is shown) are constructed of a material having a thermal coefficient of expansion similar to that of the blocks.

The matrix is supported with its axis horizontal and rotated about its axis by circumferentially spaced driven friction rolls 12 which bear against peripheral tyres 13 located about the matrix rim 9.

The friction rolls 12 and ancillary gearing are mounted within the lower part of a housing 14which extends around the circumference of the matrix 10 and provides an annular sleeve within which the matrix rotates. With the seals 5 and 6, the annular sleeve effectively provides the ends of the ducts 1,2,3 and 4. Below the sleeve, the housing 14 has a vent 15 and is mounted on a carriage 17.

As will be seen in greater detail in Figure 3, the matrix 10 is provided near each of its end faces with circumferential non-contact labyrinth seals 16 to seal the spaces between the circumference of matrix 10 and the adjacent faces of the annular sleeve. Each seal 16 comprises a plurality of ribs 16a projecting outwardly from the matrix 10, which each lie continuously in a groove 16b in the housing 14.

In operation, the matrix 10 is rotated by the driven friction rollers 12 at a relatively slow speed e.g.

between 0.1 and 0.4 revolutions per minute, so that each part moves first through the gas flowing from duct 1 to duct 3 and then through air flowing from duct 4 to duct 2. Much of the heat of the waste gases entering the matrix from duct 1 is absorbed by the ceramic heat storage elements, to be given up subsequently as the heated matrix rotates to the relatively cold gases entering through duct 4.

Figure 4 illustrates the regenerative heat exchanget that has been described located within the offtake system of a furnace. The matrix housing 14 is supported on a furnace offtake 18 leading waste gases from the furnace to a stack 18a. Ducts 1 and 4 are connected to the offtake 18 through closable ports 19, 20 respectively. Duct 3 is connected to lead combustion air under pressure from a fan 20 to the matrix, and duct 2 to lead heated air from the matrix to a burner 21. Fuel gas is conveyed to the burner by ducting 22 and may be preheated by waste gases upstream of the stack 18 by suitable location of the ducting 22 within the offtake 17. When the heat exchanger is operative, a shutter 23 is moved completely or partially across the offtake 18.

It is to be appreciated that the embodiment illustrated in Figure 4 is merely one example of arrangement in which the heat exchanger is incorporated. In alternatives the matrix may be located in positions other than that illustrated; e.g. the matrix may be positioned within, or adjacent, to the offtake itself.

In a different form from that described, the matrix may be formed by a single block.

Claims

1. A rotary heat exchanger of the regenerative type which comprises a ceramic heat-transfer matrix rotatable within an annular sleeve about a generally horizontal axis, and non-contact proximity sealing means extending around the matrix and serving to prevent the passage of gas between the matrix and the sleeve.

2. A rotary heat exchanger as claimed in claim 1 in which, to constitute the sealing means, near each of its end faces, the matrix is provided with a plurality of outwardly projecting ribs which each lie continuously in a groove in the sleeve.

3. A rotary heat exchanger as claimd in either of the preceding claims in which the matrix rests on rollers,the rollers are provided with drive means, and rotation of the matrix is effected through frictional engagement between the rollers and the matrix by rotation of the rollers.

4. A rotary heat exchange as cliamed in any of the preceding claims in which the ceramic is sillimanite material.

5. Rotating heat exchanger as claimed in any of claims 1 to 3 in which the ceramic is a mullite material.

6. A rotary heat exchanger claimed in any of the preceding claims and connected to receive hot waste gases flowing through the take-off from a steel furnace.

7. A rotary heat exchanger of the regenerative type substantially as described with reference to, and as illustrated by, Figures 1 to 3 of the accom panying drawings.

8. Plant including a heat exchanger of the regenerative type substantially as described with reference to, and as illustrated by, Figure 4 of the accompanying drawings.