Feb., 191j
T H E J O U R S A L O P I - V D C S T R I A L A N D E A\TGI,lrE E RI LVG C H E M I S T R Y
THE RENNERFELT ELECTRIC FURNACE A new Swedish invention in the field of electric smelting or refining, LIr. Ivar Rennerfelt’s furnace, differs from all types which up to the present time are in operation [Engineering (London), 98 (1914),6381. I t s practical merits have demonstrated themselves very quickly, and it has met with much attention in Sweden and abroad. The first Rennerielt electric furnace was constructed a t Hallstahammar, in STveden, in the year 1912,and i t worked
so satisfactorily that within a year a steel foundry with four electric furnaces was erected a t the place (and orders have been received also from the neighboring countries), the furnaces in question varying in size from 300 kg. to 3 tons. The manufactures for which the furnaces already in operation are applied comprise steel castings, iron castings, tool steel, electro-steel from pig-iron and ore, refined steel from liquid charges, etc. I n order to put in a few words the special features of this furnace, i t may be described as an economical small furnace for crucible works, steel foundries, copper alloys, and chemical processes requiring a high temperature. The Rennerfelt furnace is preferably built with a horizontal, cylindrical steel shell, with longitudinal axis, and it turns cradlefashion, or is tilted round a horizontal-diametrical axle. It is lined with silica, carbon, or magnesite brick, according to the uses to which i t is to be put. A charging and casting-door, closely fitting, is placed in one side or in each end of the furnace (Figs. 1-41. The electric current is transmitted by means of three electrodes, one descending yertically through the top cii the roof, and two horizontal, one a t each side or end. The positions and arrangement of the electrodes will be seen from the illustrations. n‘hen the furnace is used for melting light scrap, requiring a fair amount oi space below the arcs prior to melting, rerticallyadjustable electrodes are to be preferred. This is a special feature of the Rennerfelt iurnace, and enables the operator to run the furnace with free-burning arcs, independent of the volume of the charge, or with the arcs in contact with the metal, in case he desires to ernploy the method of heating as used in the different types of arc furnaces previously constructed. I n ordinary working, the electrodes do not come in contact with the slag or steel, the arcs being free burning. This ensures unusually smooth working when melting cold scrap, which always has been a difficult operation, especially in cases where the furnace receives the electric energy from a power plant of limited capacity. As to the nature oi the energy, a three-phase current of any voltage or frequency is passed into a transformer arranged for Scott’s method oi phase transformation, transforming the received energy into a balanced two-phase current (or twophase current may be directly generated) delivering a singlephase current to each of the horizontal electrodes. A return cable (Fig. 5 ) connects the common point of the two phases with the central electrode. The currents entering through the horizontal electrodes neutralize one another, but the action of the returning current
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into the central electrode generates a field of force which deflects the arc downwards to the bath, thus forming the arcs into an inverted arrowhead, or $ezir-de-Zys. The heat generated in the arcs is here, more t h a n in any other furnace, concentrated down upon the bath, though the el ctrodes do not touch, or even approach, the slag or the metal. The height of the arcs from the points of the electrodes to the surface of the bath can be adjusted, but i t is usually kept a t about 6 in. to 1 2 in. In operation the charge is rapidly melted and covered by a thin, but unbroken, sheet of slag, which serves as a protection against any oxygen that may be present in the furnace. As a rule, however, the atmosphere is neutral or strongly reducing, being charged with carbon monoxide, for the outside air is not admitted during the melting and ‘refining. n’hen ready the steel is poured into a ladle, and that a t a much higher temperature than is obtainable in an open-hearth furnace. It is therefore often necessary to keep the steel in the ladle while it cools down to a temperature a t which it can be safely cast without burning the moulds or spoiling the castings. Perfect deoxidation is thus easily obtained, ensuring unusually good castings or ingots free from blowholes or piping. One steel-melter and two men or boys per shift can work a furnace of several tons capacity, turning out as much as 20 to 30 tons within 24 hours. The lining is threefold: first a n insulating lining of asbestos board, then silica or first-quality bricks in rings against the former, and this again forms the bedding for the actual inner lining-acid or basic. This is made of special bricks, which do not require any cutting, and are set in rings of different diameters, so as to form an egg-shaped interior melting-chamber. The electrodes enter into the furnace through circular openings, formed by special bricks. To facilitate relining, the cylindrical shell is divided into an upper and a lower half, the two being bolted together, when lined, and the cost of renewal of lining is stated to be exceedingly low. The electrodes are held with what may be called a loose but practically gas-tight fit in water-cooled insulated holders of phosphor-bronze or copper, those for the horizontal electrodes preferably being adjustable in the vertical plane. The cables are attached to the electrode-holders, the current being transmitted to the electrodes themselves through sliding contacts or brushes. The size oi the electrodes varies from ~ l , ’ t in. to 7 in. ior the largest furnace, fitted with several sets coupled in parallel. rlssuming the ingoing current a t each side electrode t o be I amperes, then the current passing the central electrode will equal 14; amperes, provided that the power on the two-side electrodes is perfectly balanced, as is generally the case. In the same way, if we assume the voltage across the central electrode and each side electrode to be E volts, then the voltage volts. between the side electrodes will equal E With regard to efficiency, a small furnace of 600 kg. a t the
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Ljusne Iron Works, in Sweden, illustrated in Figs. 3 and 4,will melt and refine a full charge of cold scrap with not more than 700-kw. hours per ton. The normal rating of a furnace of this capacity is 1 2j kw., but 8 2 kw. to go kw. have been shown to be sufficie?t to complete a goo-kg. heat in five hours, indicating a very satisfactory thermal efficiency even when running with only 75 per cent of full load. White pig-iron has been melted in the same furnace under similar conditions with an average of 405 kw.
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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
hours per ton. With 425 kw. hours per ton, gray pig-iron has been melted and overheated, the melting including 2 2 kg. basic slag per ton of iron. This consumption of energy indicates a furnace efficiency of about 7 0 per cent, but the thermal efficiency has been as much as 85 t o 90 per cent.
QUALITY OF SULFATE OF AMMONIA FOR EXPORT Speaking editorially of the English situation the J . Gas Lighting says [128( 1 9 1 4 ,4041: We cannot afford-either a t the present time with nitrate of soda in active competition, nor in future when Germany resumes her operations in the export market-to spoil our position as exporters of sulfate of ammonia by producing a n article which does not come up t o the standard t h a t is demanded by customers, and which arrives a t its destination in a condition, as regards weight and packing, which is anything but conducive to permanence of business relations. An important letter upon the subject from Mr. D. Milne Watson, the Chairman of the Sulfate of Ammonia Association, and a circular which has been distributed among the members, are published in today’s issue of the Journal. Both are in the nature of a warning; and the one emphasizes the other. It is hoped that they will have due and immediate effect, because appeal and caution in the past appear t o have been in vain. The matter was one to which Mr. Thomas Milne addressed himself a t the Sulfate of Ammonia Conference a year ago. H e then urged sulfate of ammonia makers not to produce the commodity under a standard of 25 per cent of ammonia, about 2 . 5 per cent moisture, and not more than 0.5 per cent acid. In Mr. Milne Watson’s letter, and in the circulated leaflet, we get the appeal repeated, with the difference t h a t “not more than 3 per cent moisture” is mentioned. What is found is, and it is a serious disadvantage t o the sulfate of ammonia export business, t h a t the bulk of the British production is still made and marketed on a basis of 24 per cent of ammonia, without any mention of moisture and free acid. This condition of things will not do. Nearly all distant consumers have raised their standard from 24 t o 25 per cent ammonia; and when they find this standard is not complied with, t h a t there is a loss in weight of I to 3 per cent through excessive moisture content, and t h a t the bags in which the sulfate of ammonia is packed, through excess of free acid and moisture, have en route declined to maintain their integrity, then they become greatly dissatisfied, and do not need further inducement t o turn to sources from which they know their requirements can be fulfilled. The losses fall upon the receiver; and he is indisposed to continue t o bear them when there is no reason why he should do so. British producers know how much they depend upon the export market; and i t will be suicidal on their part not t o recognize what is essential in the matter of quality in order t o ensure the market for themselves, and not be driven out of i t by continued shortsightedness. Directly the war is over Germany will recommence operations for the development of her export trade. The competition of synthetic ammoniathe production from the nitrogen of the atmosphere-will come into the reckoning again with full force. It will not be surprising, too, t o find a t the close of the war t h a t Germany will have a decent accumulation of stock with which i t will be very pleased to part. The absence of German competition is the opportunity for the British producer t o fortify his position abroad; and the best way t o do so is t o give purchasers the standard material they want, and see t h a t it gets into their hands in good condition and with as little loss of weight as possible. The future of the export market very largely depends upon the action taken in the present. Therefore, the necessity for heeding the warning of Mr. Milne Watson, and complying with the enjoinment contained in both letter and circular, is apparent.
Vol. 7 , No.
2
DANISH ENGINEERS AND THE UNITED STATES For a considerable number of years Danish engineers, with diplomas from the State Polytechnic College in Copenhagen, have gone to the United States or other parts of the world. According to Engineering, 98 (1914),753, the Danish Society of Engineers has recently looked into this matter, and it has transpired t h a t out of 933 engineers who, during the years 1900-1912 (both included), passed the final examination of the above college, I O per cent, or, to be accurate, 92 engineers, have gone to Korth America, and out of these 2 8 have subsequently returned t o Denmark. The largest proportion is among “constructive engineers,” of whom about 12 per cent have gone to the United States, while the figure for “factory engineers” is only 4 per cent. All the electrical engineers have remained in .imerica, while two-thirds of the mechanical engineers have returned. Out of six factory engineers, only one has returned; and of 64 constructive engineers, 47 have remained in America. CONSUMPTION OF GAS IN ITALY A recent issue of the Journal f u r Gasbeleuchtung quoted from a n Italian paper on acetylene some figures as to the consumption of gas, electricity, petroleum, and calcium carbide in Italy for three years past. The English equivalents of the figures are as follows: COALGAS 1910-11 1911-12 1912-13
....... ....... .......
Cubic feet 9,182,056,000 9,358,634,000 9,888,368,000
ELECTRICITYPETROLEUMCARBIDE Board of Trade units 1,460,000 1,649,000 1,826,000
Tons 83,392 117,337 111,420
Tons 23,156 24,913 20,816
Though all four classes of illuminants exhibit a n increase in t h e second year over the first, in the last year only coal gas and electricity continue to show a n advancing consumption. Evidently the figures given for coal gas refer only to gas used for lighting and heating, since, according t o a table given in W. J. A. Butterfield’s lectures on “Chemistry in Gas-Works,’’ the total consumption of gas in Italy in rgro was I 1,985 million cubic feet. But excluding from this total the gas used for industrial purposes, t h a t used for lighting and heating only was in 1910, 9024 million cubic feet. Peat gas is also used and now t h a t the regions of hlantua and Ferrara have been drained, it has become possible t o work the peat bogs below sea-level. A company has accordingly been formed, and works erected, for the production of gas and the recovery of residuals by the Mond process. According t o a description in the Monilbre Tecnico, two bogs, one 1730 and the other 1235 acres in extent, are being worked. The thickness of the bed of peat varies from I f t . 8 in. to 3 f t . 3 in. After being dried, the peat is carbonized in six retorts, the capacity of each being 30 metric tons per 24 hours, with a daily production of about a million cubic feet of gas having a heating value of 155 B. T. U. per cu. f t . At the same time I Z O quintals of sulfate of ammonia are obtained. There are also adjoining works for the manufacture of the sulfuric acid required for making the sulfate. Large quantities of t a r are also produced. The works cover a n area of 2 2 acres. The results are stated to have been satisfactory, from both the technical and the financial point of view.
PATENTS IN WAR TIME There have now been heard in England in what have been named the Patents Court quite a number of applications t o “avoid or suspend” enemy patents, under the Act which was recently passed for the purpose of regulating this important industrial question. At the outset, naturally, there was doubt as t o what would be the attitude adopted in official quarters on particular points; and this, of course, was an uncertainty which could be set a t rest only by seeking decision on individual ap-
