IS OIL A PRACTICAL GREENHOUSE FUEL? 



Conditions Must Govern the Choice of a Heat Source — Not Entirely a Matter of Relative Cost 



Editor's Note: The recently published "Greenhouse Heating Problem" question opens up the whole subject of oil burn- 

 ing, so interesting to fuel users at the present time, that we have made an effort to get a concise presentation of the available facts. 

 At its meeting of November last the Horticultural Club of Boston discussed the subject of Oil Burning. Prof. E. F. Miller of 

 the Mechanical Engineering Department of the Massachusetts Institute of Technology; Mr. A. H. Ballard, Oil Engineer; and Mr. 

 J. C. Scorgie, experienced user of oil for fuel, were speakers. Mr. Fred A. Wilson, himself a mechanical engineer, is secretary; 

 and it is from the secretarial notes and his own technical knowledge of the subject that this article is derived. 



ERY little has actually been accomplished in the 

 burning of oil on a scale small enough to judge of it 

 in the greenhouse for the average country home, yet 

 there are definite deductions that can be made from 

 experiences with large scale operations. In the matter of 

 cost alone, the oil to be used is fuel oil, and not kerosene or 

 any other derivative. The large oil companies have made 

 extensive preparations to handle fuel oil. Crude oil once 

 came chiefly from the paraffine base oil fields of the Appala- 

 chian region, but the growing use of gasolene, a derivative, 

 extended the supply to the asphaltum base oil fields of the 

 southwest, and of Mexico. Crude oil at the wells costs little; 

 transportation to the refineries costs four times as much, and 

 the refineries take off about 8 per cent, as gasolene, and mar- 

 ket the remainder as fuel oil. It is certain to supplant soft 

 coal to a very large extent as steam fuel, and increasing de- 

 mands will place it at the disposal of any customer in a 

 convenient manner. 



The consumer's cost of fuel oil varies according to the ex- 

 pense of delivery. But this cost seems not the important 

 feature, for sharpening competition between coal and oil is 

 likely to result in a price accommodation so that the cost of 

 fuel per unit of heat will be about the same with either ma- 

 terial. Just now oil fuel will figure cheaper, except near the 

 coal mines. Broadly speaking, as prices are to-day a plant 

 using 1,500 tons of coal at $10.00 a ton could with good effi- 

 ciencies save $400 to $500 by using oil at the average present 

 cost, but the real savings are in other directions. 



In a large power plant with mechanical stokers, underfed, 

 and with overhead coal pockets, one man can care for twenty 

 thousand horse power. In a small hand-fed plant one man 

 can care for only about five hundred horse power. With oil 

 fuel one man can handle a tremendous capacity. The labor 

 is therefore a serious item in favor of oil burning on a large 

 scale. The freedom from ashes is another, and in some in- 

 stances the storage, for where space is limited oil has the 

 advantage. It may happen that where additions have been 

 made to a greenhouse range heated with coal the original 

 chimney capacity is now inadequate. In such cases a change 

 to oil would be a distinct advantage, for the stack capacity 

 needed for oil is far less than for coal. 



Under ordinary conditions an efficiency of 68 per cent, is 

 good for a coal-fired boiler. With expert supervision the 

 efficiency runs higher, even to 8o.per cent. A pound of coal 

 can only use 12 to i2§ pounds of air for complete combustion. 

 Uneven thickness in the coal bed lets the air draw through 

 thin places in greater quantity than needed, so that with all 

 parts of the fire getting at least enough, a common consump- 



tion of air is 20 pounds per pound of coal. This excess air 

 is heated and goes off up the stack, taking away heat even to 

 the extent of 20 per cent., while radiation and flue gases 

 waste more. The loss reaches 30 per cent, or more. The 

 other extreme of too little air is a worse alternative, for in- 

 complete combustion to carbonic oxide results, instead of 

 complete combustion to carbonic dioxide. With oil con- 

 taining 68 per cent, carbon and a larger amount of hydrogen 

 the heating value is greater. There will be excess air, but 

 not in such great amounts. There is less wastage and a cor- 

 responding greater efficiency, which may easily be around 

 80 per cent. Comparisons of heating values do not mean 

 much in specific instances, but it may be said, taking average 

 efficiencies, that a long ton of coal at 65 per cent, efficiency, 

 has an equal heating value with 168 gallons of oil at 80 per 

 cent, efficiency. 



INSTALLATION costs vary with conditions. Burners 

 are inexpensive, and should have large holes and be 

 easily removable. Oil contains sand and burners must be 

 easily cleaned. The most expensive items of first cost are the 

 pump and the storage tank. The pump delivers oil under 

 pressure, and an auxiliary outfit may furnish steam for 

 atomization. Mechanical atomization may be developed 

 for small hot-water heating plants, but steam is in common 

 use for stationary work. Atomization except under pressure 

 is insufficient and therefore wasteful. The storage tank is 

 commonly a water-proof reinforced concrete underground 

 tank. If one is to carry 3^ barrels of oil for every ton 

 of coal formerly held on hand, this tank would be about 

 half as large as the coal pocket, and far more expensive to, 

 build. 



On the basis of a 60 day supply, for a plant using 6 tons of 

 coal a day, the tank will contain 8,000 cubic feet. A small 

 electrically driven pump is perfectly practicable for a small 

 installation but the whole conditions are more complicated, 

 especially because skilled and continuous attention is not 

 devoted to such a plant. Kerosene may be the fuel for these, 

 even at three to five times the cost of fuel oil, for atomization 

 is easier, and clogging and carbonizing should be less trouble- 

 some. To sum up — an exact appraisal of the value of oil as a 

 greenhouse fuel in any specific case requires engineering 

 service. The general statements made here will serve as 

 guides, however, in the consideration of its possibilities. 



Finally answering the question "are oil fires dangerous?" 

 While perhaps not so completely "fool proof" as coal fires, 

 the best answer is that insurance companies do not change 

 their rates when oil fuel is used. 



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