We shall describe one type of this kiln used by MM. Schneider et Cie. in their refractory product works at Perreuil, near Creusot. It is shown in Figs. 230, 231, 232.
The kiln has an outside diameter of 20 metres and possesses fourteen compartments, each measuring: depth, 2.9 m.; mean breadth, 2.5 m.; height, 2.6 m.; this corresponds to a cubic content of about 19 cubic metres. They are separated by walls (Fig. 232) pierced with three openings making communication between them (Fig. 230). The gas arrives below the floor and penetrates into the firing compartment by three vertical openings placed below those connecting the compartments with one another.
In stacking, an empty space is kept between the separating wall and the products (Fig. 230); it is in this chamber that combustion is begun, by the mixture of the gas and the air which has been heated in passing over the cooling fired products.
Circular Continuous Gas And Hot-Air Kiln By Schneider ET. CIE. (Scale of 3.1 millimetres to the metre).
Fig. 230. Section C D.
Fig. 231. Section A B.
Fig. 232. Horizontal Section of the Kiln and Generators.
The combustion when once begun spreads itself through the channels left in the stacks, the hot gases continue their way, heating the products stacked in the following compartments, and finally reach the chimney, 30 metres high, placed in the centre.
The gas generator has 3 gridirons, 1 metre by 1.3 metres. The temperature of this kiln rises to 1500o C.; hence the inside is built of refractory bricks. The firing of a compartment requires from 12 to 16 hours according to the nature of the stacked' refractory products, and its cooling requires 3 to 4 days.
In this kiln we have again the parallel galleries of the rectangular continuous kilns. The distribution of gas is effected by two parallel galleries placed in the centre; the gas passes through vertical conduits under the flooring of the kiln and issues by "chandelles" placed below the orifices of the conduits. This was the arrangement of the first gas kilns; it had to be abandoned in favour of a distribution of gas from the roof on account of obstruction of the conduits by tar. This obstruction need not be feared with purified water gas.
Fig. 233. Continuous Water-gas Kiln - Transverse Section. (Scale of 8.3 millimetres to the metre).
Each conduit is closed by a valve which is worked from outside; in the kiln shown (Fig. 233), there are three conduits placed side by side and corresponding to each row of "chandelles." The conduits are made simply of earthenware pipes encased in masonry. The stacking and the management of the fire are precisely the same as in a generator-gas kiln.
We shall make this estimate for a kiln capable of firing from 5 to 6 million bricks annually and having as dimensions: length, 49 metres; breadth, 11.35 m.; and height, 10.55m. The chimney is 35 metres high and has a diameter at the summit of 1.40 m.
Brick masonry for interior...
270 cub. m.
Rubble or mill-grit for exterior...
795 cub. m. at 30 fr. =
Cast-iron for generator and kiln...
9000 k. at 30 fr. =
Sheet-iron and accessories...
"Chandelles" of refractory clay and sundries
We must add for the chimney...
„ „ „ building ....
The estimate of a kiln like that in Figs. 230 to 232 is thus calculated -
Concrete of crushed stones and hydraulic mortar...
135 cubic metres
Total: 1167 cubic metres at an average price of 30 fr. per cubic metre =
Stoneware and brick masonry ....
540 ,, „
Brick masonry for chimneys ....
82 ,, ,,
Refractory brick masonry...
410 „ „
Iron, cast-iron, steel, and sheet-iron ; 26,050 kilog. at an average price of
30 fr. per 100 kilog...........=
Building (42 cub. m. of timber and 663 sq. m. of roofing), about...
These figures are only intended as a rough indication; they may increase or diminish, according to the cost of labour and materials in the district where the kiln is built.
For the same reasons as we have already stated, it is difficult to fix this cost exactly for want of exact experiments which are capable of comparison. It is certain, however, that with a well-managed kiln, the cost is no greater than with a solid-fuel continuous kiln; M. Fillard states that, in his factory at Fresnes, he has reached a lower cost. He estimates the consumption at 50 kilog. of ordinary coal per 1000 kilog. of fired products.
In the Schneider kiln baking refractory products at 1500° C, the consumption is as much as 110 - 115 kilog. of coal per 1000 kilog. of products.
But the manifest superiority of gas firing consists in the beauty and quality of the results obtained, advantages which are much appreciated for delicate articles such as facing bricks, tiles, squares, etc.