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“The best test of the construction of a steam engine furnace, will be in the greatest quantity of water evaporated under a given pressure with the least quantity of fuel; from the experiments of Mr. Dalton, Count Rumford, Dr. Black, and Mr. Watt, it appears that the heat generated in the combustion of 1 lb. of coal should be sufficient to reduce from 6 to 8 lbs. of boiling hot water to steam, and if more than this weight is used, there is a proportionate quantity of heat lost.
“ To ascertain therefore, experimentally, the effect of the construction of the chimnies now under consideration, a steam engine boiler, of the form most generally used, was seated and worked in the usual manner; there was a very quick consumption of the fuel; the heat of the chimney averaged 440 of Fehrenheit; and 1 lb. of Hartley's Newcastle coal, reduced 5lb. 8oz. of boiling hot water to steam, under a pressure of 4 inches of mercury ; and it is here necessary to state, that the heat of the flues seldom boiled away in cooling more than two gallons of water for every bushel of coals used in the day. But when the same boiler was seated, according to the annexed drawing and description, for which a patent has been obtained, the heat of the chimney was reduced to 250°, and ilb. of the same coal reduced 7lb. 12oz. of boiling hot water to steam, under a pressure of four inches of mercury; thus approximating to the greatest possible quantity that can be practically effected, and making the saving in fuel of 30 per cent. over the common methods; besides which, the heat that was retained in the flues evaporated from 6 to 10 gallons of water, in cooling, for each bushel of coals that had been used.
“ In the common method, the boiler soon cooled; but in the patent way, it retained heat much longer. In the common way, the usual thick dense smoke issued from the top of the chimney: in the patent way, the smoke was three parts consumed, and the little that was discharged rendered of a light yellow brown. If these are advantages worthy of attention, an inspection of the plan will show them to be the natural consequences of the improved arrangement.
“ First. By not allowing the cold air to pass between the fire and the bottom of the boiler, when the furnace door is open, the heat of the fire is not driven down between the bars, so as to melt them, nor the boiler cooled, thus making a considerable saving in wear and tear, as nothing is more destructive than sudden changes of temperature, and the action of air and moisture, on the hot surfaces of metallic bodies; for the draft of cold air that usually passes between the fire and the boiler, on opening the furnace door, is far more powerful than that which ever enters the ash-pit.
“ Secondly. As the intensity of the heat, is in proportion to the consumption of oxygen gas, so that is generally increased when the wind blows favourably to the ash-pit, and is as much diminished when the reverse happens; but by supplying the furnace with air from the shaft Z, all the effects that naturally arise from the variations of the velocities and courses of the wind, and its action
on the fire and chimney are completely counteracted. In all small fires, and in many large furnaces, these united effects are found very considerable. The shaft, chimney, flue, or tunnel for the regular passage of permanently elastic bodies, should increase in dimensions from the orifice at which it is either to be received or discharged; thus, if A was contracted at the top, the elastic smoke would be confined in the body of the chimney, and operate against the draft of the fire at B, and if Z was no larger than the aperture X, an adequate supply of air would not be received.
“ Thirdly. By causing the smoke to descend until it comes again into contact with the heat of the fire, through the small aperture at the bottom of D, two objects are attained. One, that of igniting and consuming the inflammable vapours distilled from the coal, and not burnt in the furnace. The other by retaining in the furnace all the heat above the aperture B.
“Fourthly. This construction of the chimnies alone will scarcely be sufficient in furnaces consuming a chaldron of coals per day, without attention is paid to the constantly supplying it, for which the contrivance shown in the plate becomes necessary, and can be applied to furnaces where the descending flue could not, as in salt pans and all shallow boilers.
“From particular attention paid to the various trials of which the above is the result, it was found that no advantage was gained or lost in the evaporation of water under the various changes of the barometer, for when standing high, it increased the briskness of the fire as much as it pressed on the water; and when low, the contrary.
“There was also more water constantly evaporated when under a pressure of four or six inches of mercury, than when in the open air, arising from the increased heat being above the increased pressure; and, Lastly, That when the furnace and boiler had attained the maximum of temperature, no proportionate effect was produced by even doubling the quantity of fuel.
Reference to the Plate. Fig. 1. Section and elevation of the chimnies, and the method of supplying the fire with fuel.
Fig. 2. Plan of the apparatus.
D. The back of the fire, generally of Welsh lumps, but this may be made a part of the boiler, and taken away at pleasure; at the bottom of this back is left a small aperture, not two inches deep, and the width of the grate through which a strong draft, but not the smoke, passes, being closed with the red embers.
E. A flat bed plate the width of the fire bars and placed above. F. The door as usual for making and raking the fire.
G. A spring made of steel or wood attached to a stationary block M, at one part, and fastened to K at L, in the other.
H. The brick or frame work to support E.
K. A sliding rail with shelf at top, the length of which, if one or more, should be equal to the width of the fire bars.
N. The perforated end of the coal box.
Q. A notched snail wheel; this wheel may be placed above the coal box, or in any other more convenient part; so, that by means of levers and chains, or other connections, similar motions be given to the box and springs.
R. A filling up piece of cast iron, with a branch or shoe at bottom, to take the small coals off the shelf K.
S to T. Enclosures on all sides, leaving only sufficient space for the apparatus to work, the whole of which being in constant motion, and screened from the fire, by the constantly falling crude fuel, is not subject to being burnt away.
U. A double lever working on a pivot, having V. A bearing piece working on the wheel Q. W. The connecting rods or chains from the lever U to the sliding shelf K.
Z. An air shaft, for receiving a supply of external air, from every quarter from which the wind
blow. Y. Any convenient height at which the same may be terminated above the roof or adjacent buildings.
I. The connecting branch carried to X.
X. Apertures for supplying the fire with air, and regulated by valves or dampers, the size of which, when open, are equal to B. Nothing is found more effectual to damp the fire than preventing a supply of air.
5. Brick work placed in the mouth of the flue to preserve the boiler and inflame the smoke.
22. An aperture for the admission of cold air if requisite for the final combustion of the smoke.
23. A door for taking out the ashes or cinders from the bottom of A.
24. The damper to regulate the aperture B; this and X should be regulated at the same time to the same size.
“From an inspection of the above application to the boiler of a steam engine, it will be seen, that the smoke comes to, and rises at the front, returns along the sides, and descends behind, and that a current of cold air cannot pass between the fire and the boiler, even if the door should be left open, while the brick-work at 5, becomes of such a heat, as to inflame the smoke, and which is finally consumed as it descends and mixes with the heat of the fire coming from the aperture at the bottom of D, consequently, the heat is retained in the fire and furnace above the aperture B.