Handbook of Railroad Construction; For the use of American engineers. / Containing the necessary rules, tables, and formulæ for the location, construction, equipment, and management of railroads, as built in the United States.

by George L. Vose

The power of fuel depends upon the amount of carbon in it.

Pure coke is solid carbon.

Hence its superior value as a heat generator.

OF THE PROCESS OF COKING.

318. Anthracite coal is used for locomotive fuel in its natural state. It is employed chiefly upon those roads on the eastern slope of the Alleghanies. The bituminous coal lies in the Mississippi valley, and may be found anywhere between the summits of the Alleghanies and the Rocky Mountains. This, in its natural state, contains so much pitchy matter as to render it unfit for locomotive purposes. Upon being heated, it melts, runs into a mass, and clogs the grate; requiring frequent poking and a strong draft. But when the bitumen is burnt off by slow and careful baking, (as described below,) no fuel equals it.

Just as carbonized wood is charcoal, so carbonized coal is coke. Coke is bituminous coal deprived of its bitumen, the raw coal being baked in ovens having vents so regulated as to admit air enough to char, without consuming the coal. The ovens being closed at the proper time, the fire is gradually extinguished, and the coke, compacted into large masses, requiring to be broken up before taken out. Coal may be coked by piling loosely in heaps, covering with earth, and firing through openings, which, after forty or fifty hours, are closed. In preparing coke, however, in the large quantities required for railroads, and that it may be of the very best quality, a good deal of care must be taken.

Probably in no place more or better coke is made, or the operation more skilfully carried on, than at the Camden-town station of the London and North-western Railroad, (England).

The company have built eighteen ovens, in two rows, all discharging their volatile gases into a horizontal flue terminating in a chimney one hundred and fifteen feet high; having an internal diameter of eleven feet, and being three feet thick, (making the external diameter seventeen feet). The ovens are elliptical, 11 × 12 feet inside, with walls three feet thick. The height is ten feet, the first three feet from the ground being solid, and furnished with a fire brick floor, on which the coal is placed. Each oven communicates with the flue by an opening in the top two and one half feet by twenty-one inches; which opening is closed by an iron damper, to regulate the draft. The openings for the doors are three and one half feet square outside, and two and three fourths inside, being closed with iron doors four and one half by five feet, lined with fire brick, and balanced in opening by counterweights. (The object of the chimney and horizontal flue is to carry the smoke and unburned gases so far up that they shall not be a nuisance. In America we might allow the smoke of each oven to escape through a low chimney of its own, (ten or twelve feet high,) and save the cost of a large stack; like the coking ovens in our foundries).

The operation of coking is carried on as follows:—Each alternate oven is charged between eight and ten A. M. every day, with three and one half tons of good coals. A whisp of straw is then thrown in, which takes fire from radiation from the top, and inflames the smoke then arising from the surface, by the reaction of the hot sides and bottom upon the body of the fuel. In this way the smoke is consumed at the very point of the process, where it would otherwise be the most abundant. The coking process is a complete combustion of the volatile principles of the coal. The mass of coal being first kindled at the surface, where it is supplied with an abundance of oxygen, because the doors in front and vents in the rear are open, no more smoke goes from the chimney than from that of a common kitchen fire. The gas generated from the slightly heated coal cannot escape destruction in passing up to the bright flame of the oven. Any deficiency in oxygen for consuming the smoke is supplied by the air entering the grooves of the dampers.

As the coking process advances most slowly from the top to the bottom, only one layer is consumed at a time; while the surface is covered with red-hot cinders, ready to consume any particles of carburetted or sulphuretted hydrogen gases which may escape from below. The greatest mass cannot emit more gases than the smallest heap.