Bourne Archive: Muspratt: Cement: Rüdersdorf kiln
http://boar.org.uk/aaiwxw3Muspratt2Cement.htm Latest edit 17 May 2011
The Bourne Archive
Extracts Concerning Building Cements, 2.
This is part of an article on chemical bonding materials under the heading ‘Cement’. It is presented here in three web pages, respectively dealing with fairly simple lime burning kilns; the present one, dealing with a large lime kiln in Brandenburg; and with mortar.
Vol. 1. pp. 453-6
BUILDING CEMENTS. – [continued]
As an economiser of fuel, the limekiln of RUDERSDORF1 is the best. Fig. 299 is a vertical section of this kiln, which is heated by wood and peat. The Shaft, C, is like the foregoing, formed of two truncated cones, and is about fifty-six Hessian feet [14 m (a Hessian foot was 0.25 m)] in height. It is seven feet in diameter at the top and base, and ten feet in the widest part, opposite where the fires are situated. In the construction of the shaft, limestones may be used in the walls; but that part to which the heat reaches is usually faced with firebrick, the thickness of which increases from half a brick to a brick and a half in thickness as it approaches the seat of the heat. This lining reaches to the height of forty feet, and is shown in the figure at d’; the wall being represented by d d. All these are encased in an exterior wall, e e, built of the same material as d d, leaving a space of a few inches in diameter, which is filled with ashes and other non-conducting material. This serves to retain the heat, and likewise to afford room for the expansion of the firebricks and stones which takes place when strongly heated. An outer wall, B B, encloses the whole, and the intermediate space is divided into several compartments by means of arches, p p p, which serve as receptacles for the lime, and a temporary domicile for the workmen. The fires for heating the limestones are three, and are seen at b b, placed at equal distances from each other. These are arched over and the arches are lined with firebrick. The grates are composed of two perforated tiles, resting in the middle upon the brickwork, f; the perforations of these tiles, by which a current of air, entering by the passage, h, is admitted to the fire, are about one inch wide, and three or four in length. g is closed by an iron door, as also the outlet from i, where the cinders collect at first, and then fall into the channel, whence they are cleared off through the door, z. These doors are left shut until the space, i, is filled, and the cinders have sufficiently cooled to be removed conveniently. The draught-holes where the burnt lime is abstracted are seen at a a; these are closed with iron doors, which are luted [sealed with clay or similar material], except at such times as the content is being taken out, in order that the air may not enter at these orifices to cool the kiln. To facilitate the descent of the lime to these apertures, the sole of the kiln is inclined downwards towards them. As the lime is very hot when the chamber, P, into which the hot air ascends, a current being instituted in this passage by the fires.
Fig. 300 shows the plan of the preceding, at the lines, Z Z, the section being horizontal with the fires, b b, on the one side, and with the draught-holes, a a, on the other. When the kiln is set in operation, the part of the shaft to the level of the fires is filled with limestone, and fires lighted in a a a, which are kept burning till the calcination is completed. A fresh quantity of limestones is now let down by buckets upon that already burned, and continued till the shaft is quite full, when a heap, three or four feet high, is raised over the mouth. The doors at a a a being luted on, so as to shut off the draught, the fires are lighted in b b b, and kept up constantly. Whenever the upper stones are observed to be well burned, the lime under the level of the fires is drawn out; this causes the top column to fall in, upon which a fresh quantity of limestones is thrown on and piled upon the mouth as before. Thus the work progresses without interruption; the lime, however, is drawn out only at periods of twelve hours, when about sixty to seventy-two hundreds, Hessian weight [3,000 to 3,600 kg. (a Hessian Zentner or hundred was 50 kg. i.e. 100 Hessian pounds)], are abstracted.
The time required for burning lime is affected by many causes, such as the size of the stones, their freshness, and density. It is well known that compact limestones are more difficultly burned, than such as are more porous; also, that moisture to some extent facilitates the expulsion of the carbonic acid, even at a lower degree of heat than is required when the limestone is dry. The usual practice of moistening the stones is not so economical as introducing a jet of steam into the kiln; for, in the first case, the heat serves only to evaporate the water before the material can be brought to redness, by which much fuel is wasted; but in the latter, the limestone may be heated to redness, and then the steam admitted, when it will be most serviceable. Where kilns are like the one above described are being constantly worked, there is a great saving of fuel effected by them; but it is evident that they are adapted only for such places as require a very large quantity of lime, and where , consequently, they can be kept in operation without intermission. Theoretically, the consumption of fuel in causticising or burning lime, is only one-tenth of the weight of the limestone; but in ordinary practice, five or six times the quantity which theory shows to be sufficient is used; and where lime is burned for agricultural purposes, and attendance is not very regular, even a much larger amount is consumed.
It is evident, therefore, that those who are engaged in these operations would do well to give the subject their best attention. Much care is required of the lime-burner, especially if the material is of an hydraulic nature; for if he allows the temperature to rise higher than what is required to expel the carbonic acid, the lime in consequence loses its property of setting or hardening.
Such kilns in simpler forms, without the outer accommodation, may be seen today at the Rüdersdorf museum village.