Читать книгу Description of the Process of Manufacturing Coal Gas - Friedrich Christian Accum - Страница 11

Table of Contents

We have stated already that pitcoal is in this country the cheapest crude natural production from which carburetted hydrogen gas can be obtained in the large way. It is that which yields it in abundance, and which can with the least trouble and expence be subjected to the operation it has to undergo for the production of the gas.[3] Nature has dealt this mineral out to us, with an unsparing hand, and has provided mines of coal which seem to defy the power of man to exhaust.

[3] Other Substances from which carburetted hydrogen gas, may be economically obtained, are animal and vegetable oil, tar, both vegetable and coal tar; pitch, resin, the essential oils obtainable from vegetable and from coal tar, and the compact species of turf. On this subject we shall speak hereafter.

The principal coal mines in England are those near Newcastle and Whitehaven. The town of Newcastle stands on beds of coal which extend to a considerable distance round the place, and which as far as concerns many hundred generations after us, may be pronounced inexhaustible.

Pitcoal like all other bituminous substances is composed of a fixed carbonaceous base in the state of bitumen, united to a small portion of earthy and saline matter, which constitute the ashes left behind when the coal is burnt. The proportions of these parts differ considerably in different kinds of coal; and according to the prevalence of one or other of them, so the coal is more or less combustible, passing by various shades from the most inflammable coal into blind coal, Kilkenny coal, or stone coal, and lastly into a variety of earthy, or stony substances, which although they are inflammable do not merit the appellation of coal.

All the varieties of coal used in this country for fuel may be divided into the following classes.

The first class comprehends those varieties which are chiefly composed of bitumen only, which take fire easily, and burn briskly with a strong and yellowish white blaze, which do not swell or cake on the fire, and require no stirring, which produce no slag, and by a single combustion are reduced to light white ashes. Some of this species of coal when suddenly heated crackle and split into pieces, especially if laid on the fire in the direction of the cross fracture of their laminæ.

Cannel coal, deserves to be placed at the head of this class; next to this, we may rank all those descriptions of coal known in the London market by the names of Hartley, Cowper’s Main, Tanfield Moor, Eighton Main, Blythe, and Pont Tops. It also includes the sort of coals found in several parts of Scotland, called Splent coal, and some of those raised on the Western Coast of England.

Most of the coals raised in Staffordshire ought likewise to be classed among this species of coal, but the line of distinction between these, and the classes subsequently named, cannot be accurately drawn.

The following table exhibits the maximum quantity of gas obtainable from the first class of coal.[4]

[4] Own Experiments, made at the Royal Mint Gas-Works.

One Chaldron of Coal, produces	Cubic feet of Gas.
Scotch Cannel coal	19,890
Lancashire Wiggan coal	19,608
Yorkshire Cannel coal,
(Wakefield)	18,860
Staffordshire coal,[5]
First variety,[6]	9,748
Second variety,	10,223
Third variety,	10,866
Fourth variety,	9,796
Gloucestershire coal,[7]
First variety, (Forest of Dean, High Delph)	16,584
Second variety, (Low Delph)	12,852
Third variety, (Middle Delph)	12,096
Newcastle coal,
First variety, (Hartley)	16,120
Second variety, (Cowper’s High Main)	15,876
Third variety, (Tanfield Moor)	16,920
Fourth variety, (Pontops)	15,112

[5] They require a much higher temperature, than is necessary for the decomposition of Newcastle coal.

[6] For the maximum quantity of gas produced from this and the three succeeding varieties of coal, I am indebted to J. Gostling, Esq. Proprietor of the Birmingham Gas Works.

[7] Most varieties afford a porous, and very friable coke.

The second class of coal, comprehends all those varieties which contain a less quantity of bitumen, and a larger quantity of carbon than the first class. They burn with a flame less bright and of a more yellowish colour, and the last portion of flame they are capable of yielding is always of a lambent blue colour, they become soft after having laid on the fire for some time, swell in bubbles and pass into a state of semi-fusion, they then cohere and coke, puff up and throw out tubercular scoriæ, with a hissing noise, accompanied with small jets of flame.

In consequence of the agglutination and tumefaction, the passage of air, if this sort of coal be burnt in an open grate, is interrupted, the fire burns as it is called hollow, and would become extinguished if the top of the coal were not from time to time broken into with the poker.

The coke formed from this species of coal is more compact than that produced from the first sort of coal, and is well calculated for standing the blast of bellows in metallurgical operations. In respect to weight the second class of coal is considerably heavier than those of the first class, the difference amounts to not less than from twenty-eight pounds to thirty-three pounds in the sack of coal. A chaldron of some varieties of this class of coal, if the coals are in large lumps, weighs upwards of twenty-eight hundred weight.

The usual denomination by which the second class of coal is known in the London market, is that of strong burning coal. The following varieties are sufficiently known, Russel’s Walls-End; Bewick’s and Craister’s Walls-End; Brown Walls-End, Wellington Main, Temple Main, Heaton Main, Killingsworth Main, Percy Main, Benton Main, and some varieties of the Swansea coal.

The smaller kinds of coal of this class are preferred by smiths, because they stand the blast well. They make a caking fire so as to form a kind of hollow, space or oven, as the workmen call it. Some varieties abound in pyrites, and others are intersected with thin layers of slate and lime-stone. They require more heat for being carbonized than the first class, and the fluid obtained from it by distillation, contains a considerable portion of carbonate, sulphate, and hydrosulphuret of ammonia. They are well calculated for the production of coal gas; the coke which they produce is not very brittle, and will bear moving from place to place, without crumbling into dust.

The following table exhibits the maximum quantity of gas obtainable from the second class of coal.[8]

[8] Own Experiments, made at the Royal Mint Gas-Works.

One Chaldron of Coal, produces	Cubic feet of Gas.
Newcastle coal,
First variety, (Russel’s Wall’s End)	16,876
Second variety, (Bewick and Craister’s Wall’s End)	16,897
Third variety, (Heaton Main)	15,876
Fourth variety, (Killingsworth Main)	15,312
Fifth variety, (Benton Main)	14,812
Sixth variety, (Brown’s Wall’s End)	13,600
Seventh variety, (Mannor Main)	12,548
Eighth variety, (Bleyth)	12,096
Ninth variety, (Burdon Main)	13,608
Tenth variety, (Wears Wall’s End)	14,112
Eleventh variety, (Eden Main)	9,600
Twelfth variety, (Primrose Main)	8,348

The third and last class of coals includes those which are destitute of bitumen, being chiefly composed of carbon in a peculiar state of aggregation, evidently combined chemically with much earthy matter. Coals of this class require a still higher temperature to become ignited than any of the former classes, they emit little or no smoke. When laid on a fire they burn away with a feeble lambent flame, indeed some varieties give no flame at all, but burn merely with a red glow, somewhat like charcoal, and at length become consumed without caking. They leave a small portion of heavy ashes.

When submitted to distillation they afford little or no tar; of a consistence almost resembling pitch, and a gaseous fluid chiefly composed of gaseous oxide carbon and hydrogen gas. It is scarcely necessary to add that they are altogether unfit to be employed for the manufacture of coal gas. The Kilkenny, Welch, and stone or hard coal belong to this class. They require a strong draught when burnt in an open fire-grate, and the large quantity of gaseous oxide of carbon which they furnish during their combustion is extremely offensive. This is particularly the case with Kilkenny coal. The Welch stone or hard coal is better adapted for culinary purposes, and there is reason to believe that this species of coal might be rendered useful in the smelting of iron ore, by a slight modification in the metallurgic process employed for extracting the metal from its ore, but to eradicate prejudice, and to alter established practices is a work which nothing but time can effect. This species of coal is sent all over the kingdom; it is well calculated for the operations of drying malt and hops, and its small coal or culm has been found a more economical fuel, than Newcastle and Sunderland coals, for the burning of lime and bricks, and for all other processes where no blazing fuel is required.

The following table exhibits the maximum quantity of gas obtainable from this class of coals.

One Chaldron of Coal, produces	Cubic feet of Gas.
Welch coal. First variety, from Tramsaren, near Kidwelly,[9]	2,116
Second variety, from the yard vein at the same place	1,656
Third variety, from Blenew, near Llandillo	1,416
Fourth variety, from Rhos, near Ponty Barren	1,272
Fifth variety, from the Vale of Gwendrath	1,292
Sixth variety, from ditto	1,486

[9] The coal for these Experiments was supplied gratuitously, to the Gas Works of the Royal Mint, by Sir W. Paxton of Middleton Hall.

When we consider the before mentioned varieties of coal in an economical point of view, as fuel to be used in the gas-light process, for heating the retorts, it appears from a series of experiments that have been made under my direction, that the second class of coal comprehending those varieties which contain a larger quantity of carbon than bitumen (p. 45,) afford the most economical fuel, they act less on the grate bars, and fire bricks of the furnace than those varieties which take fire easily and burn briskly with a strong blaze. A mixture of Welch Stone coal, and Newcastle coal forms an excellent economical fuel, where an intense glowing fire is required.