US1499615A - Electrical heat treatment of material - Google Patents

Description

m HI6|| 5 7 m 5 aw T 9 .T T Q: E; T j L T. A. F. ELECTRICAL HEAT TREATMENT OF MATERIAL Filed 00%;.

July 1 W24.

. more reaction duly" l, 1924.

eras STATES PATENT @FFECE.

ELECTRICAL HEAT TREATMENT {3F MATEEIAL. V

Application filed October 19, 1921. Serial ltc. 588,815.

c resistance of which at a low temperature he heated, or for the performance of reactions in electric-reslstance furd by an electric current supplied to the he heated by means of one or more lite by means of electrodes the contact e of which towards the charged mass a same or, nearly the same breadth as t ce chamber, so as to create one or zones approximately at right glee to the direction of movement of the through which zone or zones no apihie part of the charge can pass witheing heated to the desired temperature. :-y this arrangement unequal heating is olo- 'yiated, or in other Words, the rise of temperature is confmed within a certain limit, so that no appreciable part ofthe; mass is I ated to temperature so high as to be in jurious to the working of the Process,

E perience, however, has'shown that in cases the cold charge which has been re. for example, into a shaft furnace, W- ing the had conductivity-ofthe material in the cold state has a. tendency, so to speak, to press down'or in the case of horizontal aces to push forward out or its proper position-the heating zone in the direction in which the charge movesthroughthe furnace and in consequence hereof :the rapidity with which the charge moves through the furnace must be limited to the spedconditio'ned hy the amount of heat transmitted to the originally cold charge either by conductivand radiation in the mass or by its transion with the gases generated in the fur- ;e object of the present invention is to cess for the heating of material theelem' greater than at the temperature to which eliminate the ahove-mentioned drawback by introducing a gas suitable for the purpose into the furnace and causing to pass or circulate through the furnace in the opposite direction to the charge, the gas being first heated by the hot charge, which has passed the heating zone whereupon it gives off heat in its turn to the charge just fed into the furnace, so that the charge enters the heat mg zone, previously heated to a high degree of-temperatureand consequently 1s electrically conductive, whereby the a'foresaid drawback is entirely or least partially obviated.

In order to make plain theinvention, three forms of shaft furnace suitable for the performance of the process in question are shown on the appended drawing.

Fig. 1 shows a vertical section of the fur nace along the'line A-A in Fig. 2, which latter shows a horizontal section along the lineB ld in Fig. 1. Figs. 3 and 4 illustrate in a similar manner another form of the furnace. Figs. 5 and 6 similarly show still an other form of the furnace. Corresponding parts are designated 111 the diiferent figures with the same numbers. The invention will he described first, with reference to Figs. 1 and 2.

1 designates the furnace shaft through whose walls :2 pass the electrodes 3 and 4 serving for the supply or discharge of the electric current. in accordance with the present invention, the breadth of the electrodes is equal to, or nearly equal to, the breadth of the shaft, as is shown in Fig. 2, whereby, as indicated above, a more uniform heating of the charge is attained in the zone corresponding to the electrodes, or in the layer of the charge or mass to be treated, which must pass through the aforesaid zone. According to the form illustrated in the drawing, which is intended for the use of single-phase alternating current (although three-phase alternating current may also he used), the current is supplied or discharged through two electrodm 3, 4, situated at some distance above one another. As it often happens that the mass which is to he treated in furnaces of i the kind in question has a greater electric resistance at lower temperature, it may be advisable, as indicated in Fig. 1, to arrange the electrodes so thaijhe distance between theopposite electrod (belonging to the same roup of electo'des) is chosen with regard to this fact/, i. e., to arrange the electrodes in such a way that practically an equal amount of energy is consumed at the two-pairs of electrodes. For this purpose the furnace shaft, in the form illustrated in Fig. 1, is somewhat narrower at the part where the upper electrode pair 4is situated than in that part of the furnace where the lower electrodes 3 are .located, so that the distance between 0 posite ends (or contact surfaces) of the e ectrodes 4 will be less than the distance between opposite ends (or contact surfaces) of the lower electrodes 3, which the mass reaches in a heated condition owing to the action of the current supplied through the electrodes 4. In order to obtain a preheating of the material introduced into the furnace chamber so that it will reach the heating zone or zones in a highly heated condition, a gas suitable for thepurpose is according to the present inventlon introduced into the furnace in such a way, that this gas passes the charge in the direction opposite to the movement of the charge through the furnace, so that, before it reaches the heating zone, the charge meets gases which have passed through one or'more heating zon'ss,

- ed with two pairs of electro above one another, so that two heating zones are formed, though it is obvious that merely and thereby has been heated, which gas in its turn gives off-heat to the charge before the latter has arrived at the heating zone. The said gas may, for example in the manufacture of cement consist of air, or in the manufacture of graphite consist of carbon monoxide. According to the form of the furnace shown in Figs. 1 and 2 it is providdes arranged cording to this-formshown by way of ex ample in ,the drawing, the gas is supplied between the fltuto heatmgzones or electrode pairs throughai pipe 6, which communicates with a pipei 8. issuing from the upper part of the shaft, in which latter pipe are 1nserted a purifier 9 in order toolean the gas from dust and the like and a pump 10,

by. means of which the gascan be caused to circulate through the furnace chamber.

The pipe 6 is connected-suitably through v a, pipe 11 passing round the number of nozzles 6 debouchin g into the furnace. chamber (and suitably arranged straight under the electrodes), whereby a better distribution of the attained. It is also possihie, as indicated in the drawing, to suppiy the gas in the lower part of the furnace chamber, i. e., under the lowest heating zone, through a pipe 7 and one or more nozzles 7 (which may be arranged in the same manner as above described with reference to the nozzlcs 6 which pipe 7 may also bya pipe 12 shown by the dot-and-dash' lines beconnected to' the pump 10. Through'the pipe rnace'to a.

gas supplied is 7 and the nozzles 7 either gas taken out 7 from the upper part of the furnace, orelse other gas, may be introduced into the lower part of .the furnace andbe caused to pass through the charge and the heating zones in the manner indicated above, with the object of preheating the charge before it has reached the heating zone, whilst at the same time effecting the coolin of the finished product which may be ischarged throu h some suitable discharging device 13. Xccor'ding to; the form illustrated in the drawing, the pipe 8 issues from a free space 15 formed in the upper part of the furnace between the masonry and-the lower part of the feeding funnel 14, which space is closed at the top by a cover; 16 or simi-liar device.

In the above the invention has been described with reference toa shaft furnace,

but it is obvious that it can also be applied to leaning or horizontal furnaces in which the electric heatin is effected in the man-1 ner above describe It should be observed that the present in- I vention is based onthe idea that the gas blown in will serve to transmit heat from the charge which has passed,or. is in the actual heating zones to the charge which is on the way to the heating zone or zones, so that this latter'part of the charge, beforev it reaches the heating zone, has sufiiciently high temperature for ;the normal course of the process and a corresponding electric con-- ductivity. 1

The invention may naturally also be per formed with, for example, two current circuits, which may be arranged so as to pass at right angles to one another, in which case the electric currents may suitably have a.

mutualphase displacement of and thus together form a so called two-phase current system. H

According to the form'illustrated in Figs. 1 and 2, it is the and surfaces of the electrodes that form contact surfaces-with the charge.- According to the form shown In use has not reached the heating zone, the electric In testimony whereof I- have signed my current servin for generating of the heat name to'this specification.

being supplie in the form of two-phase 7 alternating current through two 'or more TORSTEN ANDREAS FRITHlOFSSQN C N- I single-phase circuits arranged above one Witnesses:

another, which may have a mutual phase E. NILON,

displacement 0%90" or approximately90. AUG. HAzELm.

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