In _Welkner's Peat Kiln_[30] (fig. 22) the peat, previously air-dried, is exposed to a stream of hot air, until it is completely desiccated, and the arrangement is such, that air-dried peat may be thrown in at the top, and the hot-dried fuel be removed at the bottom, continuously.
In the cut, _A_ represents the section of a wooden cylinder about 10 feet wide and 6-1/2 feet deep, which surmounts a funnel of iron plate _A'_. The mouth of the funnel is closed by a door _n_; about 20 inches above the door the pipe _B_, which conducts hot air, terminates in the ring _a a_, through the holes in which, _e e_, it is distributed into the funnel filled with peat. The air is driven in by a blower, and is heated by circulating through a system of pipes, which are disposed in the chimney of a steam boiler. From time to time a quantity of dried peat is drawn off into the wagon _D_, which runs on rails, and a similar amount of undried peat is thrown in above.
According to Welkner, a kiln of the dimensions stated, which cost, about $1800 gold, is capable of desiccating daily ten tons of peat with 20 _per cent._ of water, using thereby 2000 cubic feet of air of a temperature of 212° F. When the air is heated by a fire kept up exclusively for that purpose, 10 _per cent._ of the dried peat, or its equivalent, is consumed in the operation. At the Alexis Smelting Works, near Lingen, in Hanover, this peat kiln furnishes about half the fuel for a high furnace, in which bog iron ore is smelted. The drying costs but little, since half the requisite heat is obtained from the waste heat of the furnace itself.
[Illustration: Fig. 22.--WELKNER'S PEAT DRYING KILN.]
The advantages of this drying kiln are, that it is cheap in construction and working; dries gradually and uniformly; occupies little ground, and runs without intermission.
Other drying ovens are described in Knapp's _Lehrbuch_ der _Chemischen Technologie_, 3. Aufl. Bd. 1, Theil 1, pp. 178-9; _Jahrbuch der Bergakademien Schemnitz_ und _Leoben_, 1860, p. 108, 1861, p. 55; Wagner's _Jahresbericht der Chemischen Technologie_, 1863, p. 748; Zerrenner's _Metallurgische Gasfeuerung in Oesterreich_; Tunner's _Stabeisen- und Stahlbereitung_, 2. Auflage, Bd. I, pp. 23-25.