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144 THE CIVIL ENGINEER AND LIQUID FUEL.* * * § By Benjamin H. Paul. One pound of hydrocarbon, containing 14 per cent, of hydrogen, yields about 31 pounds of furnace gas, consisting Relative evaporative efficacy as ) . compared with carbon or coal = 1 j Furnace gas. Quantities of heat in furnace gas Equivalent evaporation of water. at 212® at 60 Q lbs. Heat units. Carbonic acid gas .... 3'16 411 Water vapour 1'20 359 Nitrogen gas . . . 11'45 1,683 Surplus air 14'37 2,124 2'2 30'74 4,577 4-8 Total heat of combustion . . 21,154 Latent heat of water vapour 1,217 1'3 Available heat 19,937 Waste heat of furnace gas 4,577 4'8 Effective heat 15,360 15'8 13'6 Theoretical evaporative power 21'9 One pound of hydrocarbon, containing 25 per cent, of hydrogen, yields about 36 pounds of furnace gas, containing— Relative evaporative efficacy as ) compared with carbon or coal = 1 j Quantities. Quantities of heat in furnace gas. Equivalent evaporation of water. at 212° at 60° lbs. Heat units. lbs. lbs. Carbonic acid gas .... 2'75 358 Water vapour .... 2'25 641 Nitrogen gas 13'39 1,968 Surplus air 17'39 2,483 2'6 35'78 5,450 5'6 Total heat of combustion Latent heat of vapour 26,283 2,174 2'2 Available heat 24,109 Waste heat of furnace gas 5,450 5'6 Effective heat 18,659 19'3 16'6 Theoretical evaporative power 27T The use of this oil as fuel presents great advantages for gas tar distillers, with whom it is a troublesome waste product. If it should come into demand as steam fuel its value would of course rise above that of coal, to an extent proportionate to its greater efficacy and any other advantages resulting from its application as steam fuel. Such an application might there fore be a great advantage to gas companies. Unfortunately the quantity of this oil which is available is very small as compared with the requirements of steam navi gation, probably not amounting to 100,000 tons a year in the whole country, and therefore its application must be very limited. ' Concluded from page 112. ARCHITECT’S JOURNAL. [May j, 1888 . In order now to arrive at some estimate of the advantage to be gained in a steam vessel, either in point of weight to be carried, or space occupied by liquid fuel as compared with coal, it is evident that 100 tons of petroleum, or coal cil, would do the work of about 140 tons of good coal. But as coal is rarely burnt in such a way as to be rendered useful to its full capability, and as there is always a considerable waste in the shape of dust and cinders, which would not be the case with liquid fuel, a further allowance must be made for this. Assum ing that one-fifth of the coal is wasted in this way. then the equivalent of 100 tons of oil would be 175 tons of coal, for taking the density of the oil as ’850, it would occupy about the same space as an equal weight of coals, or at the rate of about 53 pounds per cubic foot. This difference would enable a vessel capable of carrying coal for twelve days’ steaming, to carry oil for twenty-one days. In burning this oil there would be a saving of labour in stoking, and as it would not give any ashes, a great deal of trouble would be saved in that way. These results differ widely from the statements which have been made in reference to the relative efficiency of oil and coal, according to which it has been represented that one ton of oil was equal to from four to five tons of coal,* and that in regard to stowage room the saving was “ more than nine-tenths in bulk ” ! f It is true that those who have propounded these views have not arrived at them by a consideration of the data I have above referred to, and if I may judge from remarks lately made at the meeting of the Institute of Naval Archi tect J they would appear to deny the applicability of those data for determining the question between coal and oil as fuel. Such a denial, however, would be of little account if it be not supported by adequate evidence of results, such as those which have been so much dwelt upon, being really obtainable ; and although this subject has now been some years before the public, I am not aware of any evidence having yet been brought forward, such as would call for, or justify the abandonment of those well-established principles by which the heating power and efficacy of fuel is determined, as above stated. § The results of the experiments made at Woolwich, under the superintendence of Mr. Trickett, the Engineer-in-Chief of the Dockyard, give, as the highest evaporative effect obtained with petroleum, 11'63 pounds of water converted into steam per pound of oil burnt. In this case, however, the combustion was imperfect. But in the most successful trials with coal oil and shale oil, when very little smoke was given off, the evapo rative effect was about 18 pounds of steam produced per pound of oil burnt. In this case some deduction required to be made for the steam applied as a blast to the fire, but the amount was not ascertained. This result was also obtained under pecu liarly favourable circumstances as regards the proportion of heating surface of the boiler to the rate of evaporation. In regard to the supply of material capable of being used as liquid fuel, it is necessary to make a few remarks. First, as regards petroleum, I imagine it is now generally acknowledged that this material in its natural state is not well adapted for the purpose. In that state it contains a large amount of very volatile hydrocarbon, which, even at the ordinary temperature, vaporises by contact with air, and the mixture of this vapour with air is explosive. At the temperature of a steam vessel’s stoke-hole this vaporisation would take place more readily, and if there were any leakage in the supply pipes or tanks, dis astrous consequences might ensue. In order to remove this objection to the use of petroleum as liquid fuel, the more volatile portion of it must be separated by distillation, and that operation, when carried far enough to render the oil fit for use with safety, would reduce the quantity to about one- third. Another objection to petroleum in its natural state is its * See Journal of the Royal United Service Institution, ix. 66. “ Petroleum as Steam Fuel,” by Capt. J. H. Selwyn, R.N. ; also C. J. Richardson, p. 70. t Ibid, p. 69. $ See Engineer, 10th April, 186S, p. 257. § Since writing this paper I have learnt that the same subject was discussed by Professor W. J. M. Rankine, at the United Service Institution, about a year ago, and I have great pleasure in referring to the opinions of such an authority in confirmation of the views I have expressed in regard to “ Liquid Fuel.”—[“On the Economy of Fuel, comprising mineral oils.” Journal of the United Service Institution, xi., 218.] The very lucid and exhaustive exposition, given by Pro fessor Rankine, of the conditions which determine the theoretical evaporative power of fuel ought to have been sufficient to prevent any continuance of mis conceptions as to the possibility that the evaporative effects realized with fuel can exceed or even equal the extreme calculated power it is capable of producing.
