GB2129918A

GB2129918A - An open-chamber furnace comprising a blow-pipe for the firing of carbonaceous blocks

Info

Publication number: GB2129918A
Application number: GB08329650A
Authority: GB
Inventors: Paul Buis; Philippe Voisin
Original assignee: Aluminium Pechiney SA
Current assignee: Rio Tinto France SAS
Priority date: 1982-11-09
Filing date: 1983-11-07
Publication date: 1984-05-23
Also published as: ES527102A0; NZ206125A; ES8505092A1; AU563080B2; GB2129918B; FR2535834B1; FR2535834A1; CH657695A5; GB8329650D0; BR8306149A; NO834076L; OA07584A; GR78998B; AU2098683A; CA1207960A; IN165232B

Abstract

An open-chamber furnace for the firing of carbonaceous blocks to be used particularly in the electrolytic production of aluminium by the Hall- Héroult process, is formed by a series of chambers delimited by lateral walls (2) which have openings (6) at the top inter-connecting the chambers and which may be sealed by insulation dampers (10). Each chamber is divided into compartments (3) by hollow heating partitions (4) in which the combustion air and gases circulate, and each partition has at the top openings (13) which are termed "vents". The whole furnace, when operational has in the direction of progression of the fire, a cooling zone, an air preheating zone and a full fire zone, characterised in that at least one cooling air blow-pipe (12A, 12B) located in the cooling zone, is provided over the vents (13) of the partitions (4). <IMAGE>

Description

SPECIFICATION An open chamber furnace comprising a blowpipe for the firing of carbonaceous blocks This invention relates to an open-chamber furnace comprising a blow-pipe for the firing of carbonaceous blocks and, in particular, those which are used as anodes in the electrolytic production of aluminium by the Hali-Héroult "prefired anodes" process, are produced by moulding a carbonaceous paste which substantially consists of pitch and ground coke and by firing said paste at from 1 100 to 1 2000C for about a hundred hours.

The firing is carried out in so-called "revolving fire" furnaces, one of the most widely-used types of which is the open-chamber furnace. This furnace is formed by a seriss of chambers which are delimited lengthwise by transverse walls and divided into compartments by heating partitions, inside which circulate the combustion air and gases produced by liquid or gaseous fuel burners.

"Air-vents" are positioned at the top of the heating partitions for the positioning of burners and probes which measure the temperature.

The firing anodes are stacked in the compartments and are fully immersed in a carbonaceous granulated material, for example: petroleum coke, furnace coke or the like. They are thus isolated from the partitions and protected against contact with the gases of combustion which could cause losses by oxidation, and they may also be separated from each other to avoid the risk of agglomeration or sticking together.

In the course of one firing cycle, the burners are moved progressively (revolving fire), so that each anode charge, in a given chamber, is successively preheated (over a period of 2 or 3 days), subjected to firing (for 2 or 3 days) and cooled.

The combustion fumes are extracted from the furnace by a suction pipe connecting, through openings located in the transverse walls, all the compartments of the same chamber to the main fume collector which runs along the furnace and is itself connected to suction ventilating fans. This suction pipe is usually positioned on a transverse wall, which means that a "dead chamber" must be maintained downstream of the heating zone and insulation dampers must be positioned on the transverse wall downstream of this dead chamber between the heating zone and the operational zone. This arrangement means that a considerable amount of cold air is drawn by suction through the dead chamber and this has a detrimental effect on the thermal output of the furnace.

In an attempt to overcome this problem, ever since 1979 in our factory in Saint-Jean de Maurienne, we have omitted the dead chamber by positioning the suction pipe on one heating partition of the preheating chamber. Likewise, in Patent FR-.A 2,488,685, it was suggested that the fume suction pipe should no longer be positioned on the transverse wall, but over the vents in the heating partitions of the chambers of the preheating zone which are adjacent to this transverse wall.

However, this arrangement makes it impossible to modify the structural arrangements which-could improve the mechanical stability, tightness and thermal insulation of the upper part of the transverse walls, because openings must be maintained in these walls in order to introduce, by a blowing system, air which is needed to cool the furnace after firing, and which, when reheated, is used at the same time as combustion air for the fuel in the fire zone. It is known that the upper part of the transverse walls is a fragile part which requires frequent maintenance to the brickwork and is also difficult to make tight.

The present invention provides a blow-pipe which enables cooling and combustion air to be introduced through the vents in the heating partitions.

Figures 1 to 4 illustrate the implementation of the present invention: Figure 1 is a diagram, in top view, of part of a conventional open-chamber furnace (prior art), Figure 2 shows a cross section, along line AA, of the suction pipe (prior art), Figure 3 shows a partially exploded view of two adjacent chambers, and Figure 4 shows a vertical longitudinal section of one part of a firing furnace.

The firing furnace which is usually constituted by two parallel bays, is formed by a series of chambers (1), one of which, for example is defined by the dotted line on the left hand side of Figure 1.

Each chamber is surrounded by transverse walls (2) and is divided into compartments (3) by hollow heating partitions (4), provided with baffle plates (5) to ensure that hot (or cold) gases are distributed into the total volume. The compartments are interconnected by openings (6) which may be sealed by shutters, and are open at the top. Anodes (7) are stacked in each compartment (3) and are covered with a carbonaceous granulated material (8).

Burners, which are not shown, are attached to a mobile bridge (20), which moves progressively during the firing cycle.

The combustion fumes are extracted from the furnace by a suction pipe (9) connecting, through the openings (6) located in the transverse walls (2), the various compartments (3) to the main fume collector 1) which runs along the furnace.

In this arrangement, the chamber which is located downstream of the pipe (9), with respect to the direction of progression of the furnace, indicated by the arrow in Figure 1, is a "dead" chamber, as has previously been explained.

It is possible to overcome this disadvantage by positioning the suction pipe over the vents in the heating partitions of the chamber of the preheating zone which is adjacent to this transverse wall (FR-A-2,448,685 mentioned above).

The improvement which is an object of the present invention, comprises providing at least one blow-pipe (1 2A, 1 2B), enabling cooling air and combustion air to be introduced through the vents (13) in the heating partitions (4), omitting the top orifice of the openings (6) which constituted a fragile point and replacing it by a single slit (1 5) which is narrower than the width of the wall (2) at right angles to the opening (6). This slit (15) allows the shutters (10), also termed "dampers" to be inserted or withdrawn, thus closing or opening the passage between the adjacent chambers.

A blow-pipe (1 2A) is usually positioned in the cooling zone, and a blow-pipe ( 1 2B) is usually positioned in the air preheating zone, which is at one and the same time a cooling zone.

In Figure 3, the two openings (6) of the wall (2A) are shown in the arrangement of the prior art.

The upper part (14) is, for the most part, open.

This gives rise to a certain fragility and the tightness of this opening can only be maintained at the cost of frequent maintenance work.

As soon as the fumes have been drawn up by suction and, according to the present invention, cold air has been blown in through the vents (13), the upper part (14) may be closed, as shown on the left-hand side of Figure 3 in (2 B), and it has only a single slit (1 5). This modification, small though it may seem, has far-reaching effects on the life-span of the furnace and on the maintenance costs thereof. The slit (15) which allows the insulation dampers (shutters) (10) to pass between the compartments, is made tight by a simple lid. Moreover, this arrangement makes it possible to precisely control the quantities of air which are introduced into the fire zone in order to ensure optimum combustion.

Finally, in terms of construction, it is possible to reduce the width of the walls (2) which no longer have to support the weight of the suction and blow-pipes. Thus, the width may be reduced to a size which is strictly necessary for positioning and sliding the insulation dampers (10), and this results in an appreciable advantage in terms of investment and maintenance costs as well as a reduction in heat losses which were caused in the prior art, at right angles to the walls and, in particular, at the open top part (14) of the openings (6).

The implementation of the present invention may thus be regarded as constituting a notable technical advance in open-chamber furnace technique.

Claims

1. An open-chamber furnace for the firing of carbonaceous blocks (7), to be used particularly in the electrolytic production of aluminium by the Hall-Hbroult process, formed by a series of chambers which are delimited by lateral walls (2) which have openings (6) at the top, interconnecting the chambers and which may be sealed by insulation dampers (10), each chamber being divided into compartments (3) by hollow heating partitions (4) in which the combustion air and gases circulate, and each partition has at the top openings (13) which are termed "vents", the whole furnace, when operational, comprising in the direction of progression of the fire, a cooling zone, a preheating zone and a full fire zone, characterised in that at least one cooling air blow pipe (1 2A, 1 2B) is positioned over the vents (13) in the partitions (4).

2. An open-chamber furnace according to claim 1, characterised in that one blow-pipe (1 2A) is provided in the cooling zone and one blow pipe (1 2B) is provided in the cooling and air preheating zone.

3. An open-chamber furnace according to claim 1 or 2, characterised in that the openings (6) in the lateral walls (2) pass outside through a narrow slit (1 5), the width of which is less than the thickness of the wall (2) at right angles to the opening (6) and through which it is possible to insert or withdraw the insulation dampers.

4. An open-chamber furnace according to any one of claims 1 to 3, characterised in that the width of the lateral walls (2) is reduced to a width which is strictly necessary to ensure the positioning and sliding of the insulation dampers (10)

5. An open-chamber furnace according to claim 1 substantially as herein described with reference to the accompanying drawings.