_Versmann's Machine_[28]--This machine, see Fig. 20, was invented by a German engineer, in London, and was patented there in Sept., 1861. It consists of a funnel or hollow cone _b_, of boiler-plate, from one to two feet in diameter at top, and perforated with 200 to 300 small holes per square foot of surface, within which rapidly revolves an iron cone _a_, carrying on its circ.u.mference two spiral knives. The peat thrown in at the top of the funnel is carried down by the knives, and at once cut or broken and forced in a state of fine division through the holes of the funnel, as through a colander. The fine peat collects on the inclined bottom of the chamber _d_, whence it is carried by means of Archimedean screws to a moulding machine. The coa.r.s.e stuff that escapes pulverization falls through _e_ into the cavity _c_. It may be employed as fuel for the engine, or again put through the machine.

This machine effects a more perfect pulverization of the peat, than any other hitherto described. This extreme division is, however, unnecessary to the perfection of the product, and is secured at great expense of power. Through the opening at the bottom of the funnel, much unpulverized peat finds its way, which must be continually returned to the machine. Again, stones, entering the funnel, are likely to break or damage the spiral knives, which bear close to the walls of the funnel.

The pulverized peat must be moulded by hand, or by a separate instrument.

_Buckland's Machine_[29] is identical in principle with Versmann's, and in construction differs simply in the fact of the interior cone having spiral grooves instead of spiral knives. This gives greater simplicity and durability to the machine. It appears, however, to require too much power to work it, and can hardly equal other machines in the quant.i.ty of product it will deliver for a given expenditure. The ground peat yielded by it, must be moulded by hand, or by other machinery. This machine, we understand, has been tried near Boston, and abandoned as uneconomical.

The machines we have described are by no means all that have been proposed and patented. They include, however, so the author believes, all that have been put into actual operation, at the date of this writing, or that present important peculiarities of construction.

The account that has been given of them will serve to ill.u.s.trate what mechanism has accomplished hitherto in the manufacture of peat-fuel, and may save the talent of the American inventor from wasting itself on what is already in use, or having been tried, has been found wanting. At present, very considerable attention is devoted to the subject.

Scarcely a week pa.s.ses without placing one or more Peat-mill patents on record. In this treatise our business is with what has been before the public in a more or less practical way, and it would, therefore, be useless to copy the specifications of new, and for the most part untried patents, which can be found in the files of our mechanical Journals.

14. _Artificial Drying of Peat._

As we have seen, air-dry peat contains 20 to 30 and may easily contain 50 _per cent._ of water, and the best hot-made machine peat contains 15 _per cent._ When peat is used as fuel in ordinary furnaces, this water must be evaporated, and in this process a large amount of heat is consumed, as is well understood. It is calculated, that the temperature which can be produced in perfectly burning full-dried peat, compares with that developed in the combustion of peat containing water, as follows:--

Pyrometric effect of perfectly dry peat 4000 F.

" " peat with 30 _per cent._ of water 3240 "

" " " 50 " " 2848 "

But, furthermore, moist or air-dried peat does not burn in ordinary furnaces, except with considerable waste, as is evident from the smokiness of its flame. When air-dried peat is distilled in a retort, a heavy yellow vapor escapes for some time after the distillation begins, which, obviously, contains much inflammable matter, but which is so mixed and diluted with steam that it will not burn at all, or but imperfectly. It is obvious then, that when a high temperature is to be attained, anhydrous or full-dried peat is vastly superior to that which has simply been cured in the open air.

Notice has already been made of Weber's drying-house, the use of which is an essential part of his system of producing peat-fuel. Various other arrangements have been proposed from time to time, for accomplishing the same object. It appears, however, that in most cases the antic.i.p.ations regarding their economy have not been fully realized. It is hardly probable, that artificially dried peat can be employed to advantage except where waste heat is utilized in the operation.

A point of the utmost importance in reference to the question of drying peat by artificial warmth is this, viz.: Although the drying may be carried so far as to remove the whole of the water, and produce an absolutely dry fuel, the peat absorbs moisture from the air again on exposure; so that drying to less than 15 _per cent._ of water is of no advantage, unless the peat is to be used immediately, or within a few days. The employment of highly dried peat is consequently practicable only for smelting-works, locomotives, and manufacturing establishments, where it may be consumed as fast as it is produced.

A fact likewise to be regarded is, that artificial drying is usually inapplicable to fresh peat. The precautions needful in curing peat have already been detailed. Above all, slow drying is necessary, in order that the blocks shrink uniformly, without cracking and warping in such a way as to seriously injure their solidity and usefulness. In general, peat must be air-dried to a considerable extent before it can be kiln-dried to advantage. If exposed to dry artificial heat, when comparatively moist, a hard crust is formed externally, which greatly hinders subsequent desiccation. At the same time this crust, contracting around the moist interior, becomes so rifted and broken, that the ultimate shrinkage and condensation of the ma.s.s is considerably less than it would have been had the drying proceeded more slowly.

Besides Weber's drying oven, the fuel for firing which is derived without cost from the stumps and roots of trees that are abundant on the moor, at Staltach, and which are thus conveniently disposed of, we have briefly to notice several other drying kilns with regard to all of which, however, it must be remarked, that they can only be employed with profit, by the use of waste heat, or, as at Staltach, of fuel that is comparatively worthless for other purposes.

[Ill.u.s.tration: Fig. 21.--CARINTHIAN PEAT DRYING-KILN.]

The _Peat Kilns_ employed at Lippitzbach, in Carinthia, and at Neustadt, in Hanover, are of the kind shown in fig. 21. The peat with which the main chamber is filled, is heated directly by the hot gases that arise from a fire made in the fire-place at the left. These gases first enter a vault, where they intermingle and cool down somewhat; thence they ascend through the openings of the brick grating, and through the ma.s.s of peat to the top of the chamber. On their way they become charged with vapor, and falling, pa.s.s off through the chimney, as is indicated by the arrows. The draught is regulated by the damper on the top of the chimney. To manage the fire, so that on the one hand the chimney is sufficiently heated to create a draught, and on the other waste of fuel, or even ignition of the peat itself is prevented, requires some care.

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 quant.i.ty 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.

[Ill.u.s.tration: 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.

15. _Peat Coal, or c.o.ke._

When peat is charred, it yields a coal or c.o.ke which, being richer in carbon, is capable of giving an intenser heat than peat itself, in the same way that charcoal emits an intenser heat in its combustion than the wood from which it is made.

Peat coal has been and is employed to some extent in metallurgical processes, as a subst.i.tute for charcoal, and when properly prepared from good peat, is in no way inferior to the latter; is, in fact, better.

It is only, however, from peat which naturally dries to a hard and dense consistency, or which has been solidified on the principles of Challeton's and Weber's methods, that a coal can be made possessing the firmness necessary for furnace use. Fibrous peat, or that condensed by pressure, as in Exter's, Elsberg's, and the Lithuanian process, yields by c.o.king or charring, a friable coal comparatively unsuited for heating purposes.

A peat which is dense as the result of proper mechanical treatment and slow drying, yields a very h.o.m.ogeneous and compact coal, superior to any wood charcoal, the best qualities weighing nearly twice as much per bushel.

Peat is either charred in pits and heaps, or in kilns. From the regularity of the rectangular blocks into which peat is usually formed, it may be charred more easily in pits than wood, since the blocks admit of closer packing in the heap, and because the peat coal is less inflammable than wood coal. The heaps may likewise be made much smaller than is needful in case of wood, viz.: six to eight feet in diameter, and four feet high. The pit is arranged as follows: The ground is selected and prepared as for charcoal burning, and should be elevated, dry and compact. Three stout poles are firmly driven into the ground, so as to stand vertically and equi-distant from each other, leaving within them a s.p.a.ce of six or eight inches. Around these poles the peats are placed endwise, in concentric rows to the required width and height, leaving at the bottom a number of air-channels of the width of one peat, radiating from the centre outwards. The upper layers of peat are narrowed in so as to round off the heap, which is first covered with dry leaves, sods, or moss, over which a layer of soil is thrown. Dry, light wood being placed at the bottom of the central shaft, it is kindled from one of the ca.n.a.ls at the bottom, and the charring is conducted as is usual in making wood coal. The yield of coal ranges from 25 to 35 _per cent._ of the peat by weight, and from 30 to 50 _per cent._ by volume.

Gysser recommends to mould the peat for charring in the form of cylinders of 3 to 4 feet long, which, when dry, may be built up into a heap like wood.

A great variety of ovens or kilns have been constructed for c.o.king peat.

At the Gun Factory of Oberndorf, in Wirtemberg, peat is charred in the kiln represented in the accompanying figure. The chamber is 9 feet high, and 5-1/2 feet in diameter. The oven proper, _b b_, is surrounded by a mantle of brick _a a_, and the s.p.a.ce between, _c c_, is filled with sand. Each wall, as well as the s.p.a.ce, is 15 inches in thickness, and the walls are connected by stones _d d_, at intervals of three feet.

Above the sole of the kiln, are three series of air holes, made by imbedding old gun barrels in the walls. The door, which serves to empty the kiln, is a plate of cast iron, the sides of its frame are wider than the thickness of the wall, and by means of a board _e_, a box _m_ can be made in front of the door, which is filled with sand to prevent access of air. The peat is filled in through _i_, a channel being arranged across the bottom of the kiln, from the door _f_, for kindling. When the firing begins, the lowest air-holes and _i_ are open. When, through the lower gun barrels, the peat is seen to be ignited, these are corked, and those above are opened. When the smoke ceases to escape above, all the openings are closed, _m_, is filled with sand, _i_ is covered over with it, and the whole is left to cool. It requires about 8 to 9 days to finish the charring of a charge. Several kilns are kept in operation, so that the work proceeds uninterruptedly.

[Ill.u.s.tration: Fig. 23.--OBERNDORFER PEAT CHARRING KILN.]

[Ill.u.s.tration: Fig. 24.--WEBER'S CHARRING FURNACE.--TRANSVERSE SECTION.]

[Ill.u.s.tration: Fig. 25.--WEBER'S CHARRING FURNACE.--LONGITUDINAL SECTION.]

At Staltach, Weber prepares peat coal in a cylinder of sheet iron, which is surrounded by masonry. Below, it rests on a grating of stout wire.

Above, it has a cover, that may be raised by a pulley and on one side is attached a small furnace, figure 24, the draught of which is kept up by means of a blower, or an exhauster, and the flame and hot gases from it, _which contain no excess of oxygen_, play upon the peat and decompose it, expelling its volatile portions without burning or wasting it in the slightest degree. The construction of the furnace, see fig.

24, is such, that the sticks of wood, which are employed for fuel, are supported at their ends on shoulders in the brick-work, and the draught enters the fire above instead of below. The wood is hereby completely consumed, and by regulating the supply of air at _a_ (fig. 25) by a sliding cover, and at _b_ by a register, the flame and current of air which enters the cylinder containing the peat, is intensely hot and accomplishes a rapid carbonization of the peat, but as before stated, does not burn it. In this furnace the wood, which is cut of uniform length, is itself the grate, since iron would melt or rapidly burn out; and the coals that fall are consumed by the air admitted through c. The hot gases which enter the cylinder filled with peat near its top, are distributed by pipes, and, pa.s.sing off through the grating at the bottom, enter the surrounding brick mantle. Before reaching the exhaustor, however, they pa.s.s through a cooler in which a quant.i.ty of tar and pyroligneous acid is collected.

Weber's oven is 15 feet in diameter, and 3-1/2 feet high; 528 cubic feet of peat may be c.o.ked in it in the s.p.a.ce of 15 hours. The wood furnace is 2 feet in section, and consumes for the above amount of peat 3-1/2 cwt.

of wood. So perfectly are the contents of the iron cylinder protected from contact of oxygen, that a rabbit placed within it, has been converted into coal without the singeing of a hair; and a bouquet of flowers has been carbonized, perfectly retaining its shape. The yield of coal in Weber's oven is nearly 50 _per cent._ of the peat by weight.

Whenever possible, charring of peat should be carried on, or aided by waste heat, or the heat necessary to c.o.king should be itself economized.

In manufacturing and metallurgical establishments, a considerable economy in both the drying and c.o.king may often be effected in this manner.

On the bog of Allen, in Ireland, we have an example of this kind. Peat is placed in iron ovens in the form of truncated pyramids, the bottoms of which consist of movable and perforated iron plates. The ovens are mounted on wheels, and run on a rail track.

Five ovens filled with peat are run into a pit in a drying house, in which blocks of fresh peat are arranged for drying. Each oven is connected with a flue, and fire is applied. The peat burns below, and the heat generated in the c.o.king, warms the air of the drying house.

When the escaping smoke becomes transparent, the pit in which the ovens stand is filled with water slightly above their lower edges, whereby access of air to the burning peat is at once cut off. When cool, the ovens are run out and replaced by others filled with peat. Each oven holds about 600 lbs. of peat, and the yield of coal is 25 _per cent._ by weight. The small yield compared with that obtained by Weber's method, is due to the burning of the peat and the coal itself, in the draught of air that pa.s.ses through the ovens.

The author has carbonized, in an iron retort, specimens of peat prepared by Elsberg's, Leavitt's, and Aschcroft and Betteley's processes.

Elsberg's gave 35, the others 37 _per cent._ of coal. The coal from Elsberg's peat was greatly fissured, and could be crushed in the fingers to small fragments. That from the other peats was more firm, and required considerable exertion to break it. All had a decided metallic brilliancy of surface.

16.--_Metallurgical Uses of Peat._

In Austria, more than any other country, peat has been employed in the manufacture of iron. In Bavaria, Prussia, Wirtemberg, Hanover, and Sweden, and latterly in Great Britain, peat has been put to the same use. The general results of experience, are as follows:--

Peat can only be employed to advantage, when wood and mineral coal are expensive, or of poor quality.

Peat can be used in furnaces adapted for charcoal, but not in those built for mineral coal.

Good air-dry peat, containing 20 to 30 _per cent._ of water, in some cases may replace a share of charcoal in the high furnace.