Moreover, the present invention concerns a device in connection with such a method, whereby a flow director is installed inside the connecting duct, which will contribute to reducing the active flow cross-section and which is also designed to minimise problems with uneven gas distribution in the first sections in the furnace rows.

In a ring furnace, two rows of sections are usually built next to each other in parallel rows. At each end of a row of sections, the gas ducts are connected to the parallel row of sections via a connecting duct. In this way, the sections are joined together to form a ring.

Such furnaces have a firing cycle which is gradually moved in relation to the sections as the carbon material is calcined. The firing gases from a section are conducted to an adjacent section in the direction of firing via passages arranged in head walls located between the sections. Each section may be divided into several smaller pits or cassettes by means of partition walls or so-called cassette walls. These walls are provided with ducts for the firing gases, and heat is supplied to the carbon material to be calcined by conducting firing gases through these ducts.

In ring furnaces, a section may be divided into two parts by a barrier wall in the space below the cassettes. The firing gases are then conducted up through one half and down through the other half in the ducts of the cassette walls in the direction of firing.

At the end of the row of sections, the firing gases are conducted from the firing gas passages via a connecting duct to the firing gas passages in the outermost section in the parallel row. One problem associated with prior art connecting ducts is that they may produce uneven gas distribution in the first sections in the furnace rows. US 4.215.982 shows a ring furnace which is used for baking carbon bodies in which the two rows of sections are connected via a transverse duct. The duct connects the firing gas passages in the outermost section in one row to the firing gas passages in the outermost section in the parallel row. Nothing is stated about the inner design of the duct.

One aim of the present invention was to arrive at a method and device for connecting firing gas passages in the outermost section in one row to firing gas passages in the outermost section in the parallel row in such a way that the problems associated with uneven gas distribution and thus undesired temperature variations are minimised.

It is desirable to have a connecting duct which is designed in such a way that the firing gases are distributed as evenly as possible between the gas passages in the head walls. This may be achieved by placing a flow director inside the connecting duct. The flow director may consist of elements as stated in the applicant's own Norwegian patent application no. NO 20012044.

A gradual reduction in the active flow cross-section of the connecting duct will lead to a considerably improved flow pattern into the first section. This will, among other things, contribute to the achievement of a more even temperature distribution in the sections, which, in turn, results in a more even calcining level (lower standard deviation) of the carbon bodies overall in the section. The effects of this are increased production and/or a reduction in the quantity of energy (oil or gas) which must be supplied to the process.

These and other advantageous features are achieved by means of the present invention as it is defined in the attached claims 1 and 4.

The present invention will be described in further detail in the following with examples and figures, where: Fig. 1 shows a plan view of the end of a ring furnace with two rows of sections connected to a connecting duct, where the section is taken just above the base of the sections.

Fig. 2 shows, in perspective from below, a part of a connecting duct with a flow director and an adjacent head wall with firing gas passages.

Figure 1 shows a plan view of the end of a ring furnace with two rows of sections. The section is taken at the lower end of the head wall and just above the base of the sections. The sections are connected to a connecting duct 1. A flow director 2 is placed in the end of the connecting duct 1, and the firing gases FG flow towards it. The firing gases FG flow from the space below the partially shown section K3 through the firing gas passages 3,3'in the head wall 4. For the sake of clarity, only two of the firing gas passages are marked with reference numbers, but there are firing gas passages along the entire head wall. The firing gases FG flow on through the connecting duct 1, and the flow director 2 ensures even distribution of the firing gases FG through the firing gas passages 6 and 6'in the head wall 7 (here too, only two of the passages are marked with reference numbers) and into the space under the partially shown section K2.

Section K2 may be connected to an extraction device (not shown) which contributes to the creation of a vacuum in section K2, which makes it possible for the firing gases to flow in this direction. As examples, sections K3 and K2 are shown here, which may correspond to two of the serially connected sections in a combustion cycle as described in the applicant's own patent, US 5,759,027. The present invention will also apply successively to the other sections in the combustion cycle as the combustion process is moved forwards in the furnace, even though this is not shown in the figure.

Figure 2 shows, in perspective from below, a part of a connecting duct 1 which is designed with an arch, in which a flow director 2 forms an inclined wall by the firing gas passages 6,6'in the head wall 7 above the base of the furnace 5. The firing gases FG flow from the firing gas passages 3,3'in the head wall 4 in the outermost section in one row (not shown), through the connecting duct 1 and in through the firing gas passages 6, 6'in the head wall 7. The flow director 2 may be fixed in the connecting duct 1 at each end in such a way that at least one end fixing allows expansion/contraction of the flow director 2.

The flow director 2 will contribute to making the flow conditions between the outermost sections, here shown as sections K3 and K2, as like the flow conditions between adjacent sections in a row as possible. The length and angle of the flow director are, therefore, adapted to the specific furnace. If the firing direction is changed, the flow director 2 may be moved to the other end of the connecting duct 1 (not shown in the figure).