GB2189014A - Segmented ceramic furnace baffle - Google Patents

Abstract

An adjustable baffle 14 consists of a number of interengaging baffle elements 15 which can be freely moved relatively to one another in order to facilitate servicing. The elements 15 may interengage by tongue and groove joints. They may be hollow and may contain radiant heaters, or serve as a flue or heat exchanger. The baffle may extend longitudinally of a continuous furnace or may serve as a door. <IMAGE>

Description

SPECIFICATION Segmented ceramic furnace baffle This invention relates to a segmented ceramic furnace baffle.

The use of a baffle wall is deemed to be possible or advantageous in a chamber or zone of any furnace, kiln or boiler which is used to heat any solid, liquid or gaseous matter that is either resident in or passing through said chamber or zone. General types of furnaces embraced by this definition are re-heat or forge furnaces in the steel industry, and heat treatment furnaces in the metallurgical industries, and these furnaces can be walkingbeam, pusher, mesh-belt, roller hearth, castlink conveyor, split crown, batch, rotary-hearth or bogie-hearth furnaces.Also embraced by the definition are kilns in the ceramic industry, or any heating chamber where the provision of a baffle wall might ameliorate the efficiency of the furnace by improving gas flow (for example, by changing the direction of flow), by increasing the area available for heat transfer or by dividing the chamber up into zones.

Existing baffles for performing the functions (of which only a few have been mentioned above) are either metallic or ceramic. Metallic baffles suffer from the disadvantages, from the users' point of view, of being heavy to manipulate, of being expensive, and of having a susceptibility to a high degree of oxidation if the furnace is oil-fired. These disadvantages, or some of them, can be mitigated by forced cooling by means of water or air but this brings with it so-called cold corrosion and also unacceptably high energy costs. Ceramic baffles can be of five different types: Brick. These are expensive to build and are of an inherently heavy construction which can only be built and which can only be thereafter maintained by access to the interior of the furnace.From the maintenance point of view, this means that the furnace must be coid before maintenance can be carried out and this necessitates a long shut-off or "down" time.

Brick baffles are normally uncooled and do not normally need metallic anchors or supports, but they are sensitive to temperature changes which, if severe enough, lead to spalling or even cracking of the bricks.

Ramming/castable. These must have metallic anchors or supports but they are normally water-cooled because, without such cooling, they become damaged by heavy cracking which is caused by oxygen acting upon the metallic anchors/supports and causing corrosion which, in turn, causes said anchors/supports to expand dramatically. Moreover, these baffles are sensitive to temperature changes and are very often only capable of maintenance by means of access to the interior of the furnance.

Ceramic fibre blanket. These also must have metallic anchors or supports which become heavily corroded as just mentioned above. They are normally uncooled but they are very fragile to handle, maintenance is only possible (in many cases) by means of access to the interior of the furnace, and at high temperatures they shrink and age relatively quickly, particularly as a result of the action of combustion products upon them.

Ceramic fibre castable. Again, these must have metallic anchors or supports with all of the disadvantages due to corrosion, as already described. They work well with electrical heating up to a maximum temperature of 750"C but they are nevertheless fragile and expensive and their maintenance frequently requires access to the furnace interior.

Ceramic fibre boards. Whereas these do not require metallic anchors or supports, do not require cooling and can normally be maintained from outside the furnace, they nevertheless have other concomitant disadvantages which will now be discussed. Being very fragile, extraction of them through the roof slot for maintenance or replacement is very difficult; indeed, attempted extraction often results in the board breaking and'this means not only that the furnance no longer has a complete baffle but also that the furnance must be allowed to cool to enable the broken-off piece of the baffle to be removed. The board is liable to shrink considerably and is also very liable to develop through-cracks under the conditions of use.Lastly, the roof slot previously mentioned gives rise to heat losses and also gas leakage, the first being unacceptable economically and the second bing unacceptable as contributing to environmental pollution.

Summarising these disadvantages, therefore, use of existing baffles requires: 1. Relatively long shut-off or "down" times if maintenance requires human access to the interior of the furnace. Sometimes, these shutoff times are very long.

2. Two or more men are required to handle the baffle if the baffle is heavy and/or if the baffle has to be handled very carefully due to its inherent fragility.

3. In the case of very heavy baffles, lifting equipment (cranage) will be needed.

The principal object of the present invention is to provide a furnace baffle which overcomes the various disadvantages discussed above or which at least improves the existing situation considerably.

Accordingly, the present invention consists in a segmented ceramic furnace baffle which comprises a plurality of individual elongate vertically arranged baffle elements which extend through the furnace roof and which are disposed edge to edge in an interlocking but freely movable fashion which is such that any element can be withdrawn through the furnace roof for maintenance or replacement.

In a generally preferred embodiment of the baffle described in the preceding paragraph, each baffle element is hollow throughout its length.

The interlocking but freely movable fashion described above may be achieved or obtained by means of a tongue-and-groove connection between adjacent baffle elements. In one embodiment, each of a number of said baffle elements may be provided with an elongate groove along two of its opposite edges and each of the others of said baffle elements may be provided with an elongate projecting tongue along two of its opposite edges; in an alternative embodiment, all of the constituent baffle elements are identical with one another, each baffle element being provided ith an elongate groove along a first edge thereof and an elongate projecting tongue along a second edge thereof which is opposite to said first edge.

In a baffle as described in any of the three preceding paragraphs, the constituent baffles need not be of identical lengths.

In a baffle as described in any of the four preceding paragraphs, each baffle element is preferably provided with a member which is secured to that end of the element which will, in use, be the upper end of the element, said member serving not only as a means for supporting the element from the furnace roof but also as a means for lifting the element out of the furnace and lowering the element into the furnace.

Lastly, there may be a gas-tight seal between the furnace roof on the one hand and the constituent baffle elements on the other hand; however, such a gas-tight seal is not essential.

The present invention further consists in a segmented ceramic furnance baffle which is constructed, arranged and adapted to operate substantially as hereinafter described with reference to and as iilustrated in the accompanying drawings which illustrate one embodiment of a baffle according to the present invention, purely by way of example, and in which:: Figure 1 represents one half of a vertical diametral section through a rotary hearth furnace, said one half being equipped with a baffle according to the present invention; Figure 2 represents a top plan view of said furnace; Figure 3 illustrates the make-up of a baffle of indefinite width from adjacent identical interlocking baffle elements; Figure 4 is a cross-section of one of the identical elements; Figure 5 shows the manner in which each element is supported from the furnace roof; and Figures 6 and 7 are front and side views, respectively, of a combined support and lifting means with which each element is fitted.

Referring briefly to the drawings, a furnace 10, having a rotary hearth 11 combined with an inner wall 1 lea, a static outer wall 12 and a roof 13, is provided with a ceramic baffle indicated generally by the reference numeral 14.

The baffle 14 consists of a number of individual elongate vertically extending baffle elements 15 which are tubular and (in this particular embodiment) identical with one another.

Each element 15 has a re-entrant (female) groove 16 along one of its edges and, along the opposite edge thereof, a projecting (male) tongue 17. When a plurality of the elements 15 is assembled to form a baffle, the tongue 17 of one element fits snugly into the groove 16 of the adjacent element and this results in the elements 15 being interconnected in an inter-locking but freely movable fashion. The dimensions and tolerances of the tongue and groove arrangement are specifically designed to allow for deviation from true straightness, said deviation being unavoidable during manufacture.

The furnace roof 13 has a slot 18 therein (Fig. 5) through which all of the elements 15 extend. A baseplate 19 surrounds the slot 18 on the top surface of the roof 13 and a ceramic fibre blanket 20 is placed on said baseplate. The blanket 20 is also provided with a slot through which the several elements 15 extend and, of course, acts as a gasket.

A member 21 (Fig. 6) is inserted into, and secured in, the upper end of each element 15.

The member 21 comprises a rectangular-section tube 22 attached (for example, by welding) to a handle 23 which has a hole 24 therein in order to permit the engagement of each element 15 (either singly or in groups or all at the same time) by a lifting/lowering device. The tube 22 and the top of the element 15 can be detachably secured to one another by a cross-pin extending through holes 25 in the tube 22 and holes 26 in the element 15.

It may be desirable because of temperature tolerance to cast the handle 23.

When all of the constituent elements 15 of the baffle are interconnected, and when all of the members 21 (Fig. 6) have been butted up against one another and are resting on the top of the blanket 20, a cover 27 having a continuous outwardly projecting flange 28 is secured to the roof 13 by bolts 29. When the bolts 29 are tightened up, the blanket edge is compressed between said flange 28 and the baseplate 19 to provide a gas-tight seal. The cover 27 has spaced handles 30.

The ceramic baffle described above provides the following advantages: 1. All of the baffle elements 15 extend through the furnace roof 13 and are provided with lifting means which are outside the roof.

2. Each element 15 is made of a ceramic material and can be made by extrusion and has good mechanical strength, good resistance to thermal shock, and can withstand flames or hot gases. For the ceramic material itself, different mixes and firing temperatures may be used to achieve the qualities required for the different applications.

3. The ceramic material used has a high thermal conductivity and, therefore, can quickly reach "steady state" condition when the temperature changes.

4. The ceramic material used is highly resistant to oxidation.

5. All of the elements 15 are of small mass and can therefore be easily withdrawn from and lowered into the furnace.

6. The cross-sectional shapes of the elements 15 and the manner of their interlocking enable a substantially radiation-tight wall or baffle to be built to any width whilst still providing the possibility for the constituent elements to expand during heating up.

7. Maintenance of the baffle can be attended to from outside the furnace and merely needs a decrease of furnace pressure as compared with complete shutdown. Conversion of an existing furnace to utilise the present invention will only necessitate a shut-off in order to make the slot in the furnace roof.

8. All of the parts described above (for example the cover 27 and each of the elements 15) are of low weight and do not necessitate the use of cranage.

9. Assembly and maintenance of the baffle can be carried out by one man.

10. Baffle walls can be used, for example, to divide off completly a bogie-hearth chamber, either along the length of the furnace in order to reduce the effective width of the chamber or across the width of the furnace in order to reduce the effective length of the chamber, whereby fuel usage is limited when smaller loads are required to be heated. When not being used, the baffle can be raised out of the way of the charge, either flush with the roof or to a predetermined height to act as a baffle wall between zones.

11. Any baffle wall may be linked to the charge end door of a continuous furnace to guarantee clearance of the load by the baffle.

12. A baffle wall may be installed into a continuous furnace, either in place of the charge and discharge doors, or as a supplement to them. The use of this arrangement allows individual elements of the baffle to be lowered to a suitable position above the charge, or to be lowered down to just clear the moving hearth of the furnace, thus increasing or reducing the width of the door jambs to suit the stock width. If the baffle is to be used as a door, or where there is a temperature differential between either side of the baffle, ceramic fibre insulation material may be instailed in each tube.

13. It is considered that it would be possible to put power means in a baffle to give a radiant wall e.g. using silicon carbide elements.

14. It is also considered that it would be possible to use the baffle as a flue or as a heat exchanger.

The cross-pin referred to above as being the means of detachable connection of the member 21 to the top of the respective element 15 is shown in Fig. 3, indicated by the reference numeral 31. In one embodiment, the pin has a protuberance secured (e.g. welded) to its outer surface at a location substantially half-way along the length of the pin. The pin 31 also has a slot 32 and a mark 33. In order to assemble the member 21 and the element 15, the pin 31 is slid into the aligned holes 25,26 in such a manner that the protuberance passes through the extension 26a of the slot 26 (Fig. 4) and then the pin 31 is turned about its axis (e.g. by a screwdriver) to bring the mark 33 into alignment with a mark 34 on the element 15; thus aligned, these marks 33,34 provide a visual indication or check that the member 21 is securely connected to the element 15.

Claims (10)

1. A segmented ceramic furnace baffle which comprises a plurality of individual elongate vertically arranged baffle elements which extend through the furnace roof and which are disposed edge to edge in an interlocking but freely movable fashion which is such that any element can be withdrawn through the furnace roof for maintenance or replacement.

2. A baffle as claimed in Claim 1, wherein each baffle element is hollow throughout its length.

3. A baffle as claimed in Claim 1 or Claim 2, wherein the interlocking but freely movable fashion is achieved or obtained by means of a tongue-and-groove connection between adjacent baffle elements.

4. A baffle as claimed in Claim 3, wherein each of a number of said baffle elements is provided with an elongate groove along two of its opposite edges and each of the others of said baffle elements is provided with an elongate projecting tongue along two of its opposite edges.

5. A baffle as claimed in Claim 3, wherein all of the constituent baffle elements are indentical with one another, each baffle element being provided with an elongate groove along a first edge thereof and an elongate projecting tongue along a second edge thereof which is opposite to said first edge.

6. A baffle as claimed in any one of the preceding Claims, wherein the constituent baffles need not be of identical lengths.

7. A baffle as claimed in any one of the preceding Claims, wherein each baffle element is provided with a member which is secured to that end of the element which will, in use, be the upper end of the element, said member serving not only as a means for supporting the element from the furnace roof but also as a means for lifting the element out of the furnace and lowering the element into the furnace.

8. A baffle as claimed in any one of the preceding Claims, wherein there is a gas-tight seal between the furnace roof on the one hand and the constituent baffle elements on the other hand.

9. A segmented ceramic furnace baffle constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

10. Any features of novelty, taken singly or in combination, of the embodiments of the invention hereinbefore described with reference to the accompanying drawings.