MESSRS. LILLIE AND SONS' BOILER FURNACE, Sir,-Without desiring to impugn the general correctness of your censure of the late Leed's Smoke Report, I must, nevertheless, make a claim on your candour for the allowance of one (at least) remarkable exception to it. The parties who laid plans before that meeting were not all "smoke doctors;" neither were they all patentees, outbidding one another for the favour of the public. Some there were who simply communicated the results of their own private and personal experience, without hope of fee or reward-who sought to make no traffic of their knowledge or skill, but to make it freely available for the benefit of the public at large. First in this class (according to Mr. West's order of enumeration,) were Messrs. Lillie and Son of this town, and it is in behalf of the plan submitted by them that I beg to enter the present appeal. It appears to me to be an eminently simple and efficacious plan-combining the nearly complete prevention (I suppose we must no longer say combustion,) of smoke with great economy of fuel; but it was before published," and but for this Leeds meeting might never have been published at all. So far, therefore, you must allow the meeting did good. "never The plan, as will be seen from the accompanying engraving, which exhibits a longitudinal section of a forty horse boiler and furnace, erected at Messrs. Lillie and Son's works in Store-street, (a similar one may be also seen at Horrocks and Co.'s, Preston,) consists merely in a regulated admission of air into the furnace through the passage A, at the end of the ash-pit B, (immediately before the bridge). A rod C is connected to a valve by which the air passage is opened and closed. The air is allowed to flow in for four hours after first firing in the morning. This is stated to have the effect of completely consuming the smoke during this period, when it would otherwise be given off most abundantly. By this time the coal is coked, and the valve is shut for the remainder of the day; the air which passes through the bars being then sufficient for the combustion of the carbonized fuel. They supply the furnace with fuel only at starting in the morning, when they put on sufficient to work the engine throughout the day. They make no clinkers, and only a very small proportion of ashes, which are let out by the slide D. The whole of the front of the firing end of the boiler is made perfectly air-tight, there being folding doors under the dead plate, in which are two smaller doors, which are opened and shut at intervals, as the steamgauge requires. These doors regulate the steam, by admitting more or less air. The boiler, set on this plan, has been at work about ten months, to the entire satisfaction of Messrs. Lillie and Son in every respect. In a former furnace which they had with Stanley's feeder, the consumption of coal was 20 lbs. per hour per horse power; they now have a more regular supply of steam, from 13 lbs. of coal per hour for each horse power, so that the saving of fuel is, in this instance, 35 per cent. They estimate it at 20 per cent. on the average. The cost of erection of the furnace itself is pretty nearly the same as on the old principle; but the inventors are of opinion that there is no necessity, where their method is employed, for the expense of erecting the very high chimneys at present generally in use. Their chimney, which is 30 yards high, they consider sufficient for 500 horse power. Relying on your willing co-operation to make this very useful plan as extensively known to the public as it is freely presented to them, I remain, Sir, your constant reader, Manchester, April 7, 1842. ON THE MANAGEMENT OF FURNACES AND MR. WILLIAMS ON FURNACES AND BOILERS. obtain, from any given weight of fuel, all the heat which it is capable of giving out? And secondly, whether the entire, or what portion of the heat so obtained, is turned to evaporative or other purposes; in other words, how much of the available heat is usefully applied, and how much is lost? These are the cardinal points in the inquiry; yet on these we obtain but little information from books. Until, however, these questions shall be satisfactorily answered, it is manifestly idle to draw conclusions as to the efficiency of a furnace or boiler, or the evaporative power of any description of fuel, from the consideration alone of the water evaporated. Much has been written on the subject of the areas, surfaces, and mechanical proportions of furnaces and boilers; and they have been condemned or approved, not from their relation to the degree of perfection in which combustion is effected, or the quantity of heat generated, taken up, or wasted, but by reference solely to what is but a secondary result, namely, the quantity of water evaporated. It is true, the increasing this quantity is the great practical end in view; but we are now speaking of the mode of estimating that quantity in reference to the fuel employed: my object, therefore, is to show that until we have ascertained the quantity of heat wasted or misapplied, we are not in a position to draw any inference from that portion which may be usefully employed. Were we convinced, that all our arrangements and processes are so complete that the coal is enabled to give out all its heat, and the water to absorb it all, the amount of evaporation might then be taken as a correct exponent of the areas, surfaces, and proportions of air furnaces and boilers, and the merits or demerits of any system of combustion. Arbitrarily, however, referring certain effects to certain proportions, we assume the very objects of the inquiry, and the very data on which the whole depends, and thus commit the practical error of laying down rules and giving formulæ for calculations (as Tredgold and others have done) which must necessarily be as speculative and uncertain, as the assumed data on which they are based. That these two divisions of the subject are not only distinct, but even frequently opposed to each other in practice, may be proved by showing that the amount of evaporation may continue the same, under 323 processes in which the quantities of heat generated may be essentially different; or, that the same quantity of heat under one arrangement may produce a much larger evaporative effect than under another, The weight of water evaporated, or in other words, the quantity of water taken up by the water, so far, indeed, from being a certain or adequate criterion of efficiency in a furnace or boiler, is in truth but one only of those incidents from which our calculations and inferences are to be drawn, and is not entitled to credit when taken apart from those others which have equal claim to consideration. This lumping sort of process however this estimating the effects of many combining, or even adverse causes, from a single result― has much retarded our progress towards obtaining that correct estimate of details from which alone a safe conclusion may be drawn. Until we are enabled to distinguish and appreciate the several varying results, giving to each its due measure of cause and effect, we are but floundering in the dark, and on a wrong road, without any chance of arriving at the wishedfor end. With respect to the first point-whether we obtain the full measure of heat from the fuel employed, this is a purely chemical question: as, however, the heat developed will be in the ratio of the perfection of the process of combustion, the visible inspection which I suggest will go far to enable us to form a very accurate estimate on this head. If the flame passing from the furnace exhibit a uniform state of activity, and a clear white colour, we may be assured that the combustion of the coal gas is complete; the atmosphere in the flues will then be transparent, and the fuel may be considered as giving out its full measure of heat. On the charge of coal being thrown on, the evolved gases should, at once, become ignited, if the air be properly administered. The interior of the flues will then exhibit an increasing flame (as shown in my last communication) until it is from 20 to 30 feet in length, instead of Tredgold's standard of 6 feet. Mr. Dewrance, engineer of the Liverpool and Manchester rail-road, states, respecting a boiler furnace to which the air is properly admitted, and which is 3 feet square-"We have a clear flame along the flues to the distance of 30 feet from the fire, and the flues at this distance are quite hot previously, this part was quite cold." On the charge being about half exhausted, and when the mass on the bars begins to assume a red glowing appearance, a visible change frequently comes over the whole, which is here worthy of notice, as I have not seen it alluded to by others. This change is caused by the manner in which the charge of coal burns in the furnace. If equally and uniformly, the clear internal atmosphere will continue undisturbed-no smoke will be produced, and the combustion of the gaseous matter will remain perfect to the end. If, however, the coal burn partially, or into holes, leaving parts of the bars uncovered, the flame will then be altered, and from its previous white and flaky character, it will assume a reddish cloudy appearance-the atmosphere in the flues will no longer be transparent, but will become hazy or dark-smoke will be generated-the eliminated carbon will be deposited along the flues and boiler plates, and, by its non-conducting character, seriously influence the evaporative effect. The deposition of carbon will instantly be detected by its coating the bulb of the thermometer. Now this derangement of the process of combustion cannot be detected, or even supposed to exist, except by internal inspection, and by the aid of sightholes and thermometers; for on looking in at the door, the furnace and its contents exhibit an active glowing state-the change I have described, and the production of smoke, only showing itself when the door is shut. The interior appearance, however, of the flues, and the fall of the thermometer, (which we know must be accompanied by a diminished evaporative effect,) at once sets us right, and contradicts the deceptive appearances in the furnace-proving, incontestably, that we are not then obtaining the entire heat which the fuel is capable of giving out. If allowed to continue, the evil consequences rapidly increase. The fuel burns away still more irregularly, and a considerable loss of heating effect will follow, quite sufficient to derange all calculations or results, although no indication of the kind will be discovered by looking in at the doors. These injurious effects are occasioned solely by the partial admission of the air through the little craters or holes in the burning mass, and the uncovered bars, in larger quantities than is consistent with the conditions under which the gaseous matter enters into combustion, or these can be chemically disposed of at the moment of its admission. Such unequal quantities of air, though entering in at the hottest part of the furnace, not only carry away much heat, but, by cooling, the evolved gases below the temperature of chemical union and action, convert them into true smoke. The disease being discovered, the remedy at once suggests itself, and is as simple as it is scientific-namely, fill up those holes or cavities in the burning mass with fresh coal, or equalize it on the bats, and thus prevent the partial admission of the air. Either expedient will at once restore the previous clear white flame and transparent atmosphere in the flues, and again raise their temperature. Here we have a further proof of the value of these sight-holes and means of internal inspection; for not only have they indicated the nature and cause of the derangement, but the effectiveness of the remedy. Without this visible proof, indeed, who would have supposed that the throwing a little fresh coals into these holes in the burning mass, would have had the effect of stopping the generation of smoke-checking the fall of the thermometer and raising the temperature of the flues? An observant fireman will soon appreciate and correct these changes: but there can be no law or regulation for preventing such evils, since the irregularity with which the fuel burns will depend on many casual circumstances, as, the peculiar burning quality of the coalthe unequal size of the lumps-a mixture of different sizes and kinds-the irregular formation of clinkers, or careless charging. Attention to these matters will give no trouble, if the means of interior inspection be supplied: but without it, the master, as well as the fireman, will be perplexed by results for which they cannot account-finding the chimney smoking, and the evaporation diminishing at the very moment when they least expected it. Under such circumstances, the evil will be attributed to any thing but the right cause for as well may we pretend to describe what is taking place in a room from which we MR. WILLIAMS ON FURNACES AND BOILERS. exclude all light, as to discover what is taking place in the furnace or flues, without the means of looking in. We have now to consider the second, and equally important point-whether the entire of the heat supplied by the furnace is usefully applied by the boiler? For, even supposing we are satisfied on the first head, and that combustion is absolutely perfect, we are still as far as ever from being in a position to determine the efficiency of boiler, furnace, or fuel, until the amount of escaping, or lost heat, be correctly ascertained, an amount which I have frequently found to be as much as one-third of the entire heat, which might be obtained from the fuel. Under such circumstances of palpable loss, it would be as irrational and deceptive, to measure the evaporative effect of any coal or boiler, without taking into account the quantity of waste heat, as it would be to measure a liquid without noticing the loss by leakage or overflowing of the vessel employed. We have therefore to ascertain the absolute temperature of the escaping products, and the rapidity of their current; yet these are matters which are most neglected in ordinary practice. On the practical bearing of this part of the question, being the proportion of the heat applied or lost, the following table, indicating the temperature of the escaping gaseous matter, will supply us with some useful facts: Thermometric Length of flame 10 14 26 28 325 ing made the circuit of a cylindrical boiler, (see Mech. Mag. No. 971,) 15 feet long, taken at a distance of 48 feet from the furnace. The thermometer had its bulb inclosed in a protecting tin tube, and inserted through an iron plate which covered the flue. The tube was introduced only so far as kept the temperature below 600°-the entire range, as we see in the table, being between 460° and 540° or but 80 degrees. So far as the rate of progression, in two minute time, during à charge which lasted forty minutes is important, the result may be depended on: the absolute temperature of the gaseous escaping current was, however, considerably beyond what could be indicated by the thermometer, and was ascertained to be from 200° to 250° beyond what is stated in the preceding table. This fact was determined beyond all question, by means of the melting points of a series of metallic alloys prepared by Dr. Kane, after an extensive series of experiments specially undertaken for the purpose. By these metallic alloys, inserted into the flue, it was found that the escaping stream of heat was at least 750°. Under such circumstances, could there be a doubt that a body of heat was absolutely lost, quite sufficient to defeat any calculation? And would it not therefore have been deceptive to the last degree, to draw any inferences from the mere weight of water evaporated? One thing was certain, namely, that the fuel employed gave out its full measure of heat in other words, its combustion was complete. Another thing was also equally certain, that we had not the means of absorbing and usefully applying that heat. The question then remains, What quantity of heat was lost? What was its evaporative value? And how can it be turned to evaporative purposes? These shall be considered in a future communication. Time. 18 28 .... |