CONTINUOUS KILNS.
The principle of the continuous kiln is (I) to use the heat contained in the ready-burnt brick for heating the atmospheric air supporting the combustion, and (2) to use the heat passing away from the fire for heating the green brick yet to be burned.
The first attempt to burn brick continuously was the railway kiln exhibited at the Paris Exposition in 1857. It is not cer tain who was the inventor of that kiln, whether Collas, Bovie, or who else. The railway kiln, however, did not prove a suc cess, either in Germany, by Mr. Book, or in England, by Mr. Foster. We also know of cases in America where the railway kiln was tried, but likewise without success, the brick coming out of the kiln being " uniformly pale." This was in 1867, at the brickyard of Barnard & Harvey, at Hestonville, on the Pennsylvania Railroad, Philadelphia, where a railway kiln was in use in connection with a Chambers machine. Again, in 1892, at the works of The Anderson Pressed Brick Co., Chi cago, Ill.
In the railway kiln a train of platform cars loaded with brick was slowly moved by means of a screw (worm), or hydraulic pump through a long straight tunnel, in the middle of which the fire was burning; from the fire the loaded brick moved toward the end of the tunnel, cooling down while in motion. The draught of air in the tunnel went in the opposite direction, the air entering where the burned brick left the tunnel, passing through the fire and escaping to the chimney at the other end, where the cars loaded with green brick entered the tunnel.
In the year 1859 the first Hoffmann kiln was erected in the city of Stettin, Prussia, and in a few years 100 of these kilns were erected in Germany, Austria, England, etc. To-day a very large number of Hoffmann kilns are in operation all over the world, burning brick, including the finest paving-brick, terra-cotta, roofing-tiles, etc. In the United States there are only about a dozen genuine Hoffmann kilns ; the first was erected at Carbon Cliff, Rock Island County, Ill., in the year 1866.
In the Hoffmann kiln the brick are not moved during the process of burning, as in the railway kiln ; on the contrary, they are set into the burning chamber as in old-fashioned kilns, and the fire is passed through them horizontally, leaving burned brick behind. The burning chamber of the Hoffmann kiln
consists of an endless tunnel of an annular shape, either circu lar, or elliptic, or oblong in plan. This endless tunnel is suc cessively filled with green brick, and after the fire has passed through, leaving the burned brick behind, they are successively taken out when sufficiently cooled down ; soon afterward they are replaced by green brick. It takes from ten to sixteen days for the fire to make a round in the Hoffmann kiln ; during the same time the whole kiln is once filled with green brick, and once emptied.
It is not possible in the Hoffmann or any other form of con tinuous kiln to avoid the production of a proportion of soft brick, nor is it possible to obtain satisfactory results in the use of such kilns in burning face and front brick. Continuous kilns are especially adapted fof burning common brick with the least possible expenditure for cost of fuel ; but it is an open question whether the interest on the large amount of capital necessary to build such kilns, together with the greater wear, tear, and depreciation, and the extra cost for loading the brick upon wheelbarrows, and removing them from the chambers of such kilns, does not more than counterbalance the saving of fuel.
This is especially true in the United States, where fuel is not so much an item of cost as it is in England and Continental Europe, in which countries the cost of constructing such kilns is also much less, and where the cost of labor for removing the brick on barrows from the kilns is also less than in America. Another drawback in the use of continuous kilns is the fact, although there is certainty of being able to burn the brick in them during all seasons of the year, there is no certainty that the manufacturer can at all times be able to haul brick from his yard, as the weather may not allow it, and the buildings for which he contracts to furnish the brick may not be in condition to require the material only at certain times.