GB2025013A - A Furnace Chamber Adapted to Form a Continuous Ring Furnace of the Hoffman Type - Google Patents

Abstract

A continuous ring furnace of the Hoffman type comprising: (a) an outer furnace structure (11, 12, 33); (b) hollow partitions; (c) fire pits independent of one another and of tapered shape; (d) a base (34-Figure 10) provided with cooling means (33) to render the thermal efficiency of the furnace chamber (10) independent of the nature of the ground on which the furnace chamber (10) stands; (e) a bottom cavity (35, Fig. 11) in a bottom region of the furnace chamber (10) having an aerodynamic profile that dynamically controls gas flow in the chamber (10); (f) a cover (40- Fig. 11) mounted on a ridge portion of the furnace chamber (10) allowing individual gas flows within the cover which are substantially turbulence free, and (g) sealing means between the cover and the ridge portion to render the connection between the cover (40) and furnace chamber (10) gas-tight. <IMAGE>

Description

SPECIFICATION A Furnace Chamber Adapted to Form a Continuous Ring Furnace of the Hoffman Type This invention refers to an improved furnace chamber adapted to form a continuous ring furnace of the Hoffman type.

As it is well known to those skilled in the art, Hoffman furnaces comprise a number of chambers, usually twenty, identical with and connected to each other to form an endless ring or loop of chambers, wherein the various phases of the furnace operation alternate. Accordingly, each chamber will be in turn a "fire" chamber, a distillation chamber, and so on, according to the furnace cycle.

According to this invention there is provided a furnace chamber adapted to form continuous ring furnaces of the Hoffman type, the furnace chamber comprising: (a) an outer furnace structure; (b) connecting elements and base elements to define hollow partitions serving as interconnecting and spacing elements; (c) fire pits formed by vertically disposed structural elements, the fire pits being independent of one another and having a tapered shape; (d) a base provided with cooling means adapted to render the thermal efficiency of the furnace chamber independent of the nature of the ground by which the furnace chamber is adapted to be supported; (e) a bottom cavity in a bottom region of the furnace chamber, the bottom cavity having an aerodynamic profile that dynamically controls gas flow in the chamber; (f) a cover mounted on a ridge portion of the furnace chamber allowing individual gas flows within the cover which are substantially turbulent free, and (g) sealing means provided between the cover and said ridge portion to render the connection between the cover and furnace chamber gas-tight. There is also'provided a continuous ring furnace of the Hoffman type comprising a sequence of furnace chambers of the invention.

Particularly, this improved furnace chamber, which is generally provided with muffles, essentially comprises walls of different structure; fire pits of different shape and structure; a base of different structure that improves the cooling process of the chamber itself; a smoke collecting and conveying bottom cavity of different shape; and, a cover of different shape.

More particularly, the building structure of the furnace chamber has been significantly modified and renewed in order to obtain a unit that is stearly and economical and, at the same time, adapted to withstand a number of cooling and heating cycles.

The shape and structure of the fire pits have been modified, thus causing the fire pits to become independent of the building structure defining the same and providing them preferably with distributed expansion joints and a preferably octagonal horizontal section that decreases the stresses over the critical areas.

The chamber base structure has been modified providing it in a preferred form with a plurality of transversal air passages, expediently for a force air circulation.

The shape of the gas collecting bottom cavity has been modified preferably by varying the vertical section thereof and giving it an aerodynamic profile allowing firstly the gas flow to be flow-dynamically improved and, secondly, the refractory layer to be thicker in the thermally most critical areas.

Finally, the chamber cover is preferably shaped as a barrel vault rather than a cross vault or a cloister vault as used at present in conventional chambers.

Referring to the obtention of one or more of the possible advantages realisable by the improved furnace chamber of the invention, with respect to conventional chambers of Hoffman furnaces, they can be summarized as follows: higher resistance to thermal stresses, due to the repeated cycles of intense heating and then cooling, together with an improved air tightness and a lower cost of the building structure, a building structure of lesser thickness that conventional structures used at present; an improved gas flow throughout the chamber obtained making use of a bottom and cover having a different shape in respect to the corresponding elements of a conventional furnace chamber.

By way of example, preferred forms of the invention will now be described in detail with reference to the accompanying drawings, wherein: Figure 1 is a vertical sectional view generally showing the overall structure of a furnace chamber embodying the invention; Figure 2 is an enlarged similar sectional view of Figure 1 but showing only one of the side walls of the chamber; Figure 3 is an enlarged sectional view taken aiong lines 3-3 of Figure 2; Figures 4A-4D show schematically connections of the inner building structures and hollow partitions of the chamber of Figure 1; Figure 5 is an enlarged perspective view of a hollow brick used in the building structures shown in Figure 4; Figure 6 shows schematically the position of the hollow brick of Figure 5;; Figure 7 is a perspective view of a further hollow brick used in the inner building structures of the chamber of Figure 1 in order to improve the heat-exchange, particularly in the lower portion of the chamber; Figure 8 shows a vertical section through the structure of the fire pit of the chamber of Figure 1; Figure 9 is an enlarged plan view showing the shape of the fire pit of Figure 8; Figure 10 shows the base structure of the chamber of Figure 1; Figure 11 is a vertical longitudinal sectional view of a covered chamber embodying the invention, showing the varying profile of the smoke-flow bottom passage; Figure 12 is an enlarged perspective view showing the cover of the covered chamber of Figure 11; Figures 1 3 and 14 show two forms of possible structures of the barrel vault cover of a chamber embodying the invention;; Figures 1 5 and 1 6 are enlarged views of two forms of fluid-tight connection between the upper ridge and base of the cover of Figure 1 2.

Particularly with reference to Figures 1, 2 and 3, an improved chamber embodying the invention is shown therein and indicated by reference numeral 10.

It can be seen that each chamber has a tublike structure comprising an outer homogeneous containing structure or "box" having two outer side walls 11 and a bottom wall 12. It is to be understood that these outer side and bottom walls extend perpendicularly to the plane of the drawings and they are common to all the chambers embodying the invention and which are intended to define a ring furnace and be arranged in sequence.

Side walls 11 and bottom wall 12 may, for instance, be made from reinforced concrete or steel. Side walls 11 are provided with reinforcing elements, indicated by 11 A, and bottom wall 12 is mounted on a base 33 anchored to the underlying ground.

An intermediate layer of a fibrous heatinsulating material indicated by 13, externally covered by an extremely thin layer of a metal foil, such as of aluminium, indicated by 14, is placed inwardly of each side wall 11 and it is engaged therewith.

Moreover, the "hot" layer, i.e. the layer forming the inner wall of the chamber, which layer is made of bricks of refractory heat-insulating material and is indicated by reference numeral 15, is placed inwardly of intermediate layer 13.

Furthermore, stabilizing hooks 1 6 are inserted into layer 15, which hooks can be made from stainless steel, if desired covered by a ceramic material, the outer end 1 8 of which (Figure 3) is received within vertical slots 19 on side wall 11.

Layer 1 5 is also provided with a plurality of vertical expansion joints, indicated by 20, and filled up with a ceramic fibre.

It will be evident that the above-described structure, which comprises three vertical layers adjacent to and independent of each other, is completely or substantially free from the drawbacks due to cracks and fissures which inevitably occur in the "bound" building structures of conventional chambers. Moreover, hot layer 1 5 can expand by vertically and horizontally sliding with respect to outer wall 11 of the tub-like structure, also due to the presence of layer 13 that, being yieldable, can absorb any residual expansion.

It should be noted that metal foil 14 completely or substantially eliminates the serious drawback resulting from the ambient air introduction, thus definitively solving the problem of the chamber air-tightness.

With reference to Figures 4A-4D, there is shown a top view of separating hollow partitions F which define the muffles from each other and the muffles from the chamber walls.

Particularly, it is seen that a hollow brick 21 having a stepped end 22 is used in the chamber embodying the invention. Hollow brick 21 allows an easy formation of corner interconnections with an S-shaped expansion joint 23A (Figure 4A); cross interconnections with an expansion joint 23B having the shape of a swastika (Figure 4B); and, end interconnections with an Y-shaped expansion joint 23C. Figure 4D shows more particularly an I-shaped joint cover, indicated by 24, that allows two flat or planar expansion joints 23D to be formed, which joints 23D are necessary for forming longer hollow partitions.

The structure of the improved chamber embodying the invention for forming continuous ring furnaces overcomes or minimises also the problem of the "movements" of the walls, made of hollow bricks, with respect to the bottom of the chamber. These movements, indeed, can often cause a disengagement of the hollow bricks from the hollow partitions. This problem is solved or minimised (Figures 5 and 6) by using a special hollow bottom brick, indicated by 25, which has a T-shaped vertical section and operates as a positioning and spacing element. Part 25A of brick 25 between bottom slabs 26 operates as a spacer therefor and a positioning element for the overlying structure 27 made of hollow bricks.

Figure 7 shows a hollow brick 28 used in the chamber embodying the invention to construct the inner building structures (or a part thereof) of the chamber. These building structures must be hollow and they are provided with vertical hot gas-flow passages formed by the aligned cavities of the hollow bricks forming the structures.

Due to the importance of the heat-exchange between hot gas flow and building structures, this hollow brick is provided with cavities having undulating inner surfaces 29 which, both improve the heating process of the chamber and increase the thermal efficiency thereof.

Furthermore, as it is known to those skilled in the art, in most cases each chamber of continuous Hoffman-type ring furnaces is provided with a separate space, normally subdivided into a plurality of cavities, called fire pits, wherein combustion takes place when that chamber becomes the "fire" chamber during the furnace cycle.

The improved chamber embodying the invention is also provided with fire pits having improved shape and structure.

As shown in Figures 8 and 9, pits PZ are defined by vertical building elements 30, independent of longitudinal building structures SM of the chamber, and they are provided with distributed expansion joints 31. Furthermore, pits PZ have an octagonal horizontal section that, tapering to the ends at 32, increases the resistance to possible residual expansion, not accommodated by expansion joints 31, of the building elements defining the pits.

Moreover, as known, the thermal efficiency of the chamber and, accordingly, of the furnace, can vary even significantly depending on the type and nature of the ground on which the furnace is installed and this is a drawback in that it results in a further variable to be considered in devising conventional furnaces.

In order to solve or minimise this problem an improved base 33 is used in the chamber embodying the invention (Figure 10). Bottom wall 12 of the outer structure shown in figures 1 to 3 is anchored to a base 33 and as a result the thermal field of each furnace chamber can be isolated and made independent of the nature of the ground on which the chamber is installed.

Thus, all the materials forming the chamber bottom reliably operate at pre-established working temperatures. To this end, a plurality of parallel air passages spaced apart from one another; indicated by 34, are transversally formed within base 33, in which passages, due to temperature differentials, air circulates for cooling the unit comprising the base 33 and bottom wall 12.

It may be noted that, if necessary, also a forced air circulation can be generated within transversal passages 34, which forced air circulation would allow the unit comprising the base and bottom to be further cooled. Alternatively, passages 34 could also be inclined with respect to the horizontal in order to improve the air draught therein.

Finally, in the improved chamber embodying the invention the gas flow passing therethrough, which gas flow determines the efficiency of the chamber, has been optimized by modifying both the bottom and the cover of the chamber.

Referring to Figure 11, bottom 35 instead of being flat, namely having a constant crosssection, has a variable section of increasing height from input end 36 to output end 37, thus providing bottom 35 with an aerodynamic profile that improves dynamically the gas flow.

Moreover, the thicker refractory material, in the most critical area indicated by 38, protects more efficientiy bottom wall 1 2 of the box-shaped structure against an excessive temperature increase.

With reference to the chamber cover, this cover has the shape of a barrel vault (Figure 12), in order to improve the gas flow within the chamber.

With such a cover, generally indicated by 40, individual gas flows FL from end 40A to end 40B along barrel vault 40C remain parallel to each other, thus avoiding the turbolences generated by the cross vault or cloister vault cover used in conventional chambers, which cross and cloister vaults cause the individual flows to converge towards the centre of the chamber. Furthermore, the shape of cover 40 has no corners and thus it is also free from the drawback of the disconnection of these corners as a consequence of thermal expansion.

A further advantage of the illustrated cover is that it can be made from a variety of highly heatinsulating materials, such as a light heatinsulating refractory material,ncasting of refractory material, plastic refractories, refractory concrete, heat-insulating concrete, ceramic fibres and mineral wools.

To possible forms of the cover structure of the chamber embodying the invention are shown in the sectional detailed views of Figures 1 3 and 14.

Figure 13 shows a structure comprising a lower layer 41 of a light heat-insulating refractory material having a foil 42 of a suitable metal, such as aluminium, applied thereto and an upper heatinsulating layer indicated by 43 (preferably made of bricks) that ensures an effective thermal insulation.

Figure 14 shows a structure formed with a refractory casting 44 and a self-supporting shell 45. Casting 44 is held by a plurality of steel or other metal hooks 46 associated with a supporting net 47, anchored to shell 45 made of metal sheet. This shell has the double function of being both the supporting and the tightening element of the structure.

Figures 1 5 and 1 6 show two possible forms of cover/chamber arrangement for obtaining the necessary gas tightness between an upper ridge portion 147 of the chamber and the base of the corresponding cover. In both cases, upper ridge portion 1 47 is made of prefabricated and prebacked building blocks 48 in a highly refractory casting and bound together by dovetails, instead of being made of simple bricks as in conventional chambers.

In the solution shown in Figure 1 5 the tightness is obtained by means of matelasse ceramic fibre 49 anchored to base 50A of cover 50, while in the solution shown in Figure 1 6 this tightness is obtained through a rectangular groove 51 on upper ridge 47. This groove 51 is filled up with an inert material, such as ceramic fibre, coke grit, sand or the like, and receives an extension 52 protruding from base SOB of cover 50.

A further important advantage of the solutions shown in Figures 1 5 and 16 is that the cover supporting metal structures are kept as far as possible from the heat source, namely the hot gases circulating within the cover.

This results from the fact that the metal structure is not the most internal layer and, accordingly, it is not subjected to extremely high temperatures and then it does not experience the excessive expansions affecting this metal structure when it is an inner element of the cover.

Claims (22)

Claims

1. A furnace chamber adapted to form continuous ring furnaces of the Hoffman type, the furnace chamber comprising: (a) an outer furnace structure; (b) connecting elements and base elements to define hollow partitions serving as interconnecting and spacing elements; (c) fire pits formed by vertically disposed structural elements, the fire pits being independent of one another and having a tapered shape; (d) a base provided with cooling means adapted to render the thermal efficiency of the furnace chamber independent of the nature of the ground by which the furnace chamber is adapted to be supported; (e) a bottom cavity in a bottom region of the furnace chamber, the bottom cavity having an aerodynamic profile that dynamically controls gas flow in the chamber; (f) a cover mounted on a ridge portion of the furnace chamber allowing individual gas flows within the cover which are substantially turbulent free, and (g) sealing means provided between the cover and said ridge portion to render the connection between the cover and furnace chamber gas-tight.

2. A furnace chamber according to Claim 1, wherein the outer furnace structure (a) is boxshaped having two opposite side walls and a bottom wall, an intermediate layer of a fibrous heat-insulating material disposed inwardly of each side wall and in engagement therewith, and a layer of refractory heat-insulating material provided with vertical expansion joints and placed inwardly of the said intermediate layer, wherein connecting means are provided to connect the said intermediate layer to the said refractory layer.

3. A furnace chamber according to Claim 2, wherein the said connecting means comprise stabilizing hooks of steel or other material.

4. A furnace chamber according to any preceding claim, wherein the outer furnace structure is of reinforced concrete.

5. A furnace chamber according to Claim 2 or any claim appendent thereto, wherein a metal foil is disposed between the said intermediate layer and the outer side wall adjacent thereto.

6. A furnace chamber according to Claim 5, wherein the foil is an aluminium foil.

7. A furnace chamber according to any preceding claim, but not appendant to Claim 4, wherein the outer furnace structure is of metal sheet.

8. A furnace chamber according to any preceding claim, wherein the connecting and base elements (b) include as connecting elements hollow bricks having a stepped end, said hollow brick being adapted to form one or more of corner interconnections with S-shaped expansion joints, cross intersections with swastika-shaped expansion joints and end connections with Yshaped expansion joints.

9. A furnace chamber according to any preceding claim, wherein the connecting and base elements (b) include as connecting elements refractory elements having an I-shaped horizontal section with two flat or planar expansion joints.

10. A furnace chamber according to any preceding claim, wherein the connecting and base elements include as base elements T-shaped hollow bricks, the stem of the T-shape being adapted to be received between adjacent bottom slabs and blocked therebetween whereby the T shaped hollow brick is inhibited from moving relatively to the said adjacent bottom slabs and the said adjacent bottom slabs from approaching each other

11. A furnace chamber according to any preceding claim wherein the fire pits (c) are defined by vertically disposed building elements of refractory material provided with vertically disposed expansion joints, independent of the transversal building structures of said chamber, said building elements defining a number of pits having a tapered horizontal section that is larger in the central area and narrower at the ends thereof.

12. A furnace chamber according to any preceding claim, wherein the base (d) of said chamber has a bottom wall anchored thereto and is provided with a plurality of transversal passages parallel to and spaced from each other, open at the ends thereof, in which passages air is adapted to circulate owing to existing temperature differentials when in use.

1 3. A furnace chamber according to Claim 12, wherein mechanical means adapted to generate a forced air circulation within said transversal passages are connected to said transversal passages.

14. A furnace chamber according to any preceding, claim, wherein the gas flow bottom, cavity (e) of said chamber has a variable vertical section of increasing height from the flow input end to the output end, thus allowing an increase of the thickness of the refractory layer protecting said bottom wall of said chamber at said input end.

1 5. A furnace chamber according to any preceding claim, wherein said cover (f) has a barrel vault shape allowing individual gas flows constituting the hot gas flow to flow parallel to each other without causing any substantial turbolence.

1 6. A furnace chamber according to Claim 15, wherein said barrel vault cover comprises a lower layer of a light heatinsulating refractory material; an aluminium or other metal foil applied to the upper surface thereof, and an upper heatinsulating layer.

1 7. A furnace chamber according to Claim 15, wherein said cover (f) comprises a casting of a refractory material and a self-supporting hook of metal sheet to which said casting is connected through a system comprising steel or other metal hooks and a supporting net associated therewith.

1 8. A furnace chamber according to any preceding claim, wherein the-ridge portion of said chamber is made of prefabricated and pre-backed building blocks in a refractory casting and bound together by dovetails.

19. A furnace chamber according to any preceding claim, wherein the sealing means (g) comprises a matelassé ceramic fibre anchored to a base portion of the cover and lying on the said ridge portion.

20. A furnace chamber according to any one of Claims 1 to 18, wherein the means (g) comprises a rectangular groove filled up with a ceramic fibre or other inert material, and adapted to receive an extension integral with a base portion of said cover.

21. A furnace chamber adapted to form continuous ring furnaces of the Hoffman type substantially as herein described and with reference to Figures 1-3 and/or Figure 4 and/or Figures 5 and 6 and/or Figure 7 and/or Figures 8 and 9 and/or Figure 10 and/or Figure 11 and/or Figure 12 and/or Figure 13 or Figure 14 and/or Figure 1 5 or Figure 1 6 of the accompanying drawings.

22. A continuous ring furnace of the Hoffman type comprising a sequence of furnace chambers of the kind claimed in any preceding claim.