Vickipedia

SMOKE-NUISANCE, in London, is punishable with fine. The act applies to every furnace employed in working engines by steam, and every furnace in any mill, factory, printing-house, dye-house, distillery, bake-house, &c., which is not constructed so as to consume its own smoke, or which is so negligently used that the smoke is not consumed. The penalty is from two to five pounds. The statute only applies to the metropolis and to the river Thames.—In Scotland, a similar act is not confined to the Scotch metropolis.

Large consumers of fuel are naturally more anxious about how it can be best burned economically than about how the escape of smoke into the atmosphere can best be prevented. The two questions are not at all the same, although plans may be devised which will accomplish both objects at the same time. Thus with ordinary bituminous coal not only may the volatile hydrocarbons which sometimes yield twenty per cent, of the heating-power pass up the chimney unburned, but nearly two-thirds of the coal may be wasted by the conversion of the carbon into carbonic oxide instead of carbonic acid—that is, if the carbonic oxide escapes as such—and yet no smoke may appear. At the same time, it is the fact that the most complete combustion of the coal insures there being no smoke.

There is a great difference of opinion even about the apparently simple question of how the coal should be laid on the furnace bars. The late Professor Macquorn Rankine and others, reasoning on theoretical grounds, say that the fresh coals should be laid on the front of the fire; whilst Dr. Anderson, late of the Woolwich Arsenal, judging from great practical experience, says that, on the contrary, they should be mainly piled up at the hack of the fire. Mr. Wye Williams again, whose name is so famous in connection with such questions, asserts that the coal is best spread evenly over the furnace bars.

Whether the fuel is heaped at the front, at the back, or spread uniformly over the fire, the end in view is the same. It is to secure that the volatile hydrocarbons are burned, and that carbon is converted into carbonic acid, and this can only be done when these gases are conducted over a hot portion of the fire with a sufficient supply of air. If the fresh coal is laid on the front, that of a previous charge having been pushed inwards, the coal vapors will of course pass over the thin layer of burning fuel at the back, and be more or less burned. When on the other hand, the fuel is kept banked up at the back (that is at the bridge), and spread evenly over the rest of the grate, although a little smoke may be given off at first, it would nevertheless appear that by this plan the mass of incandescent fuel at the bridge is yet more effectual in burning these vapors. The balance of opinion would, however, seem to be in favor of the method of rapid, thin, and uniform spreading of the coal over the grate, care being taken that no part of the furnace bars are left bare.

With regard to the admission of air to the furnace, it is necessary, in order to obtain the best result, that it be admitted through small orifices, and at such a point or points where the temperature is sufficiently high for the combustion of the coal vapors, and that it be so regulated that heat is not uselessly absorbed by an excessive supply. It is of course also necessary to have sufficient air passing up between the furnace bars to burn the non-volatile coke. The arrangement recommended by Mr. Wye Williams

will be understood by the help of the annexed drawing, which represents one of his furnaces under a boiler h. The fire is fed, as usual, through the door at d; it slopes downward to the bridge g, which rises much above the firebars, so that the flames have to pass over it. The bridge consists of two parts, the solid masonry or brickwork, g, and the chambered portion behind it, c, called the distributer. Into this a tube, 5, opens, through which a supply of atmospheric air enters, and becoming heated, passes through a number of plates with slits, or with perforations as shown in ee’, into the mixing-chamber, f; here the heated air enters into combustion with the carbon in the smoke-laden flame, deprives it of that element, and greatly increases the heat by its combustion. Smoke prevention arrangements may be classified as follows :

I. Apparatus for the regular addition in small quantities and uniform application of the fuel to the fireplace of the furnace. The chief kinds are : (1.) A hopper kept charged with small coal or slack, and feeding a rapidly rotating horizontal disc. (2.) A hopper and rollers to reduce the size of the coals, and a screw spreader for throwing; them on the fire. (3.) An under grate stoker, which feeds a circular furnace by causing the fresh coal to pass from below through a central orifice into the middle of the incandescent fuel. (4.) A hopper and traveling furnace bars.

II. Arrangements for the admission of air above as well as below the furnace bars. This is usually done either by means of air-holes with slide or slides to cover them; or opening and shutting slits in the furnace door or above it. Another plan is to have a valve at the further end of tubular flues in the furnace to regulate the admission of air. In one or two instances a clockwork arrangement has been introduced for gradually closing the air inlets in the furnace doors after firing.