US2263443A - Apparatus for making acetylene - Google Patents

Description

W 1941- L. A. MATHESON ETAL 2,253,443

APPARATUS FOR MAKING ACETYLENE Filed Dec. 3, 1958 3 Sheets-Sheet 1 Gaseous proof/c755 1 N V EN TORS [0/06 4. Ma/befion ATTORNEYS.

1941- L. A. MATHESON ETAL 2,263,443

APPARATUS FOR MAKING AGETYLENE Filed Dec. 5, 1958 s sheets-Shea 2 INVENTORS lame 4. M/fiesaa Wf/son 11. A601 L A TTORNEYS.

8, 1941- 1.. A. MATHESON ETAL 2,263,443

APPARATUS FOR MAKING ACETYLENE Filed Dec. 3, 1938 3 Sheets-Sheet 5 IN V EN TORS [0/06 14 fife/A2900 t? I BY n mww Mn/ y A TTORNEYS.

' through the increased disc diameter.

Patented New. T18, 119% t me AIPIPARATUS FOR MAKING ACETYLENE Lorne A. Matheson and Wilson W. Hunt, Midland,

Mich, assignors to The lliow Chemical Company, Midland, Mich, a corporation oi? Michigan Application December 3, 1938, Serial No. 243,734

6 Claims.

This invention concerns an improvement in electric arc apparatus for the pyrolysis of liquid hydrocarbons and relates particularly to an ap paratus for the production of acetylene.

It has been suggested that an increase in opermore efficient as the diameter of the disc is in:

creased. However, the increased resistance to the motion of large electrodes by the body of liquid acts to ofi-set the arc efiiciency gained In order to avoid this difiiculty, electrode arms have been i I *cient and-more economical manner than has been attached to small discs, which afiords the advantage of the large disc and longer arc. This type of equipment has the disadvantage of presenting a continuously changing distance between the electrodes. The latter is a serious fault, since variations in the voltage across the electrodes, especially in the case of alternating current, may cause a failure of the arc to strike at the time the electrodes are at their shortest distance of separation. This may result in a failure of the arc to strike at all during a particular cycle or may cause'a delay in the striking of the arc until the alternating current voltage is decreasing, resulting in the. production of a correspondingly short arc. In thelatter event,

full advantage of the possible arclength is 10st,.

and the time the electrodes approach sufficiently near to enable the arc to strike. The life of the arc is cut down thereby since it is in existence over a smaller fraction of the voltage cycle.

On the other hand, when the arc is once struck, it is desirable to draw out the are as far as possible. An increased gap between electrodes increases the resistance in that particular part of the circuit and establishes a greater voltage drop in the arc itself. A large quantityof energy is thereby expended in the arc. The longer are has the incidental but valuable advantage of coming in contact with a larger quantity of hydrocarbon liquid.

It is a principal object of this invention to provide an apparatus adapted to the electric are cracking of liquid hydrocarbons for the production of acetylene, which operates in a more efiipossible with the apparatus used heretofore.

It is a further object to provide for rotating or otherwise moving one ormore of .the electrodes in an electric arc apparatus in such a manner as to insure the striking of the are at the time the anarc to bridge an ordinarily non-conducting gap is approximately proportional to the length;

of the gap. To start the arc, it is therefore desirable to have as small a gap as practically pos-- sible. However, it is also necessary, because of mechanica limitations, to place the electrodes an appreciable distance apart. There are then values of voltage in the alternating voltage cycle which are insufiicient to bridge this minimum gap and there is no certainty that the arc will strike in any one cycle. It is also possible to have a voltage at the time of minimum separation of the electrodes which is in excess of that required. In this case, a period of time elapses between the time the normal breakdown voltage is reached electrodes are at a point of minimum separation, in order that the process maybe carried out with the highest possible power factor.

,It is astill further object to provide an increased length of electric arc in an are cracking apparatus in order that a greater amount of hydrocarbon material may come in contact with each individual arc, and in order that the maximum voltage will be attained in the arc itself. We have now found that the foregoing and related objects can be accomplished in an apparatus for the pyrolysis of liquid hydrocarbons in an alternating current arc in such manner that one to three moving electrodes, synchronized with the alternations of the alternating current voltage, are disposed in relation to one to three fixed electrodes so that at least one movable electrode is at its minimum distance of separation from a fixed electrode when a voltage suflicient for breakdown is reached. "Fixed electrode" means an electrode which is serving merely as a circuit completing means and ls so placed that it is not a variable in the synchronized system under consideration. It may be stationary or even moving-in synchronized motion in accordance with the principles of our invention, but in any event it is not a variable in the present systerm.

In the annexed drawings:

Fig. 1 is a side elevation, partly in section, illustrating a preferred embodiment of the invention;

Fig. 2 is a detail of one type of electrode which may be employed in the apparatus of Fig. 1;

Fig. 3 is a wiring diagram of an electrical circuit adapted for use in connection with the apparatus shown in Fig. 1;

Fig. 4 is a diagram showing an alternative electrical circuit adapted for use with the apparatus shown in Fig. 1;

Fig. 5 is a part sectional elevation showing a means for adapting the apparatus shown in Fig. 1 to a modified electrode structure; and

Fig. 6 is a part sectional elevation showing a means for supplying a jet of hydrocarbon liquid to the arc region.

According to one embodiment of our invention, a rotating disc carrying one or several electrode arms is disposed in the space between fixed electrodes or adjacent to a single fixed electrode, the latter being connected to a source of alternating current. The electrode is driven at a speed in relation to the current alternations of the arc circuit such that the arms are closely approaching or are at their shortest distance of separation from the fixed electrodes in the instant break down voltage, which causes the arc to be struck, is reached in the current cycle. Regulation of the rotational speed of the electrodes is secured by synchronizing the motor driving the rotating electrode with the arc current. The latter is accomplished by maintaining a constant phase relationship between the current supplying the motor and the current supplying the arc.

Referring now to the drawing, Fig. 1 shows a reaction chamber 7| provided with an inlet 8 for the hydrocarbon liquid to be cracked, a liquid residue outlet 9, and a gas off-take pipe Ill. The side walls of the reaction chamber I are provided with two wells |5, |5, through each of which is inserted a fixed electrode mechanism which may be either inclined as shown or horizontal. Each of the fixed electrode mechanisms consists of a carbon electrode |6, |6, held in position by a steel supporting rod ill, Ill, to each of which steel supporting members is attached a cable l8, it for supplying alternating current to the electrodes. Each of the steel supporting rods I 1, I1, is insulated from the walls by porcelain members l9, W. A rotating central electrode mechanism is inserted through the top of the reaction chamber 1. This mechanism comprises essentially the electrode proper 20,,a shaft 2| for rotating the electrode 20, and a motor 22 for driving the shaft 2|. The/driving motor 22 is insulated from the shaft by a shaft section 23 of insulating material. The shaft 2| enters the top of the reaction chamber through a suitable stuffing box 24 which is insulated from the walls by a porcelain member 25. The structure of the central electrode is shown in greater detail in Fig. 2.

Fig. 1 also shows a means for supplying hydrocarbon liquid to the reaction chamber 1 and a means for removing the liquid-carbon residue resulting from the cracking process. The liquid supply system consists of an inlet valve II which controls the amount of hydrocarbon liquid :added to the system, a pump l2 for circulating the liquid, and a cooling coil I3, which is immersed in a body of circulating water I4. The residue removing system consists of the liquid residue outlet 9 and a receptacle 26 provided at its lower end with a valve 21 for removing the residue from the system and a valve 28 for returning some of the residue to the. liquid supply system.

Fig. 2 shows in greater detail a plan View of the rotating member 20 shown in Fig. 1. Member 20, as illustrated, is adapted to be rotated in a counter-clockwise direction. It comprises essentially a steel disc 29 provided on its periphery with two oppositely extended L-shaped carbon electrode arms 30, 30 and two follower baiiles 3|, 3|.

The rotor electrode arms were bent through about in order that there be a minimum of wear on the electrodes. When the arms were bent through an angle greater than 90, the arc tended to strike somewhere along the outside surface of the arm and move along said surface during the rotation. When the arms were bent through an angle less than 90, the arc was pulled along the inside surface. This may be caused partly by the liquid turbulence peculiar to each position of the electrode as well as by the relative distance between the electrode surfaces. It was found that electrode wear remained at a minimum only when the arc was not allowed to move away from the point of formation.

The bafiles 3|, 3|, the leading faces of which are preferably concave but may be any convenient shape, are so positioned on the periphery of the disc 29 that they direct a current of hydrocarbon liquid into the path of the are as the latter is being drawn out from the tip of the electrode arms 30, 30'. The bailles add efficiency to the cracking operation by insuring the presence of a high concentration of fuel in the arc region. The movement of the baflles, in addition, adds to the liquid turbulence and thereby aids in the cooling of the gases by their rapid removal from the arc region.

Fig. 3 shows diagrammatically the conducting elements shown in Figs. 1 and 2 and a wiring diagram of the external power source of alternating current for these elements. High voltage alternating current, supplied from. a suitable source (not shown) through the lead wires 32, provides singlephase current to the fixed electrodes l6, I6 and three phase current to the motor 22. The current flows through the lead wires l8, l8 to the fixed electrodes l6, l6 and acros the electrode gaps between the fixed electrodes l6, l6 and the central rotating electrode arms 30, 30'. The single-phase circuit contains inductances 33, 33' for controlling the arc. The motor 22, driving the central electrode disc 29, is inserted in the three phase current circuit by means of a three phase step-down transformer 34.

Fig. 4 shows, in addition to the details Shown in Fig. 3, an excitation circuit 35 between one of the fixed electrodes I6 and the central rotating disc 29, said circuit containing an inductance elements, placing the entire available line potential across the other electrode pair, the electrode arm 30 and the fixed electrode l6. In this manner, the entire voltage drop will be across the fixed electrode I6 and the electrode arm 30' when these electrodes have reached their minimum distance of separation and an arc will strik between these electrodes. At this time,

the major voltage drop will be across the inductance 36 because of the relatively low resistance of the newly formed arc, and practically all the line voltage will be across the gap between the fixed electrode It and the electrode arm 30. The are then strikes in this gap. During the interval between the striking of the arc in the first gap and the striking of the arc in the second gap, further rotation of the central rotor brings the electrode arm 30 to its shortest distance of separation from the fixed electrode I6. However, the striking of the arcs in the two electrode gaps will be sufiiciently close together as to be practically simultaneous. The excitation circuit 35 is especially valuable where electrode wear has caused an increase in the size of the gap to a point where a voltage sufiicient to bridge the gap is appreciably larger than the normal breakdown voltage.

Fig. shows a modification necessary to adapt the apparatus shown in Fig. 1 to the use of either one fixed electrode 16 or one movable electrode arm 30. In this case, the conducting rotor shaft 2| is provided with a brush 3! which is in turn connected to the external power source illustrated in Fig. 3. The rotor shaft Zl is used, therefore, as a circuit completing means in place of a second fixed electrode.

Fig. 6 shows an alternative method of supplying hydrocarbon liquid to the arc region. A hollow truncated cone-shaped member 38, provided withaspiral blade 39 secured to the inside wall of said member, is attached to the central rotor disc 29 by means of webs 60. The rotation of the truncated cone-shaped member 38, with the aid of the spiral blade 39 draws the hydrocarbon liquid into said member 38 and discharges it by centrifugal force over the top rim into the electrode gaps between the synchronously moving electrode arms 30, SI and the fixed electrodes 56, it.

In accordance with the preferred embodiment of our invention, hydrocarbon liquid enters the system through a valve 1 I and is joined with the recycled liquid residue resulting from the cracking operation. The combined liquid streams are then forced by means of the pump I 2 through the cooling coil E3 to the reaction chamber inlet 8. The liquid is maintained at about the level shown in Fig. l but may be varied considerably; it being merely necessary that the are be totally submerged. In the method of supplying liquid to the arc region, as illustrated in Fig. 6, the liquid level is maintained somewhat below the electrode level. In both cases, however, the liquid comes in contact with the arc where it is decomposed to form a mixture of acetylene with other gases, residual hydrocarbon liquid, and free carbon. The gaseous products escape through the gas oiltake pipe l0 and the residual liquid, holding the free carbon in suspension, leaves the reaction chamber through the residual liquid outlet 9. The residual liquid is caught in the chamber 26 from which some can be returned to the original liquid stream through the valve 28. The remainder is removed from the system through the valve 21.

Single phase alternating current is carriedto the reaction chamber by means of a cable l8. During the first half of its cycle, the current enters the reaction chamber through the steel supporting rod l1 and the fixed carbon electrode Hi. The current then bridges the gap between the moving electrode arm 30 and the fixed electrode I6 is bridged-and the current proceeds through the fixed electrode Hi, the steel supporting rod l1, and the cable l8. In the second half of its cycle, the alternating current reverses its path through these same conducting elements.

The central rotor 20 is driven by the motor 22 at a speed such that each electrode arm makes half a revolution while the current is going through one-half its cycle. The position of the central rotor, at any one time, is constant relative to a particular value of voltage in the alternating voltage cycle. This relative position is held constant by maintaining a constant phase relationship between the current supplying the arc and the current supplying the motor. As described above, the particular relative position desired is that each moving electrode be at its minimum distance of separation from a fixed electrode when a voltage sufiicient to bridge this minimum gap is attained in the alternating voltage cycle. In this manner, an arc is struck in each electrode gap at the time that the electrodes are at their minimum distance of separation and at a time that breakdown voltage is first reached.

The arcs are then drawn out along the periphery of the path of the rotating electrode arms. While the arcs are being drawn out, the line voltage increases from the breakdown voltage to the maximum voltage and then decreases from the maximum toward the zero value. During this decrease or within a short time after zero line voltage has been reached, the arc quenches. The are currents may lag behind the line voltage be cause of the presence of the inductances 33, 33'.

When the voltage again reaches the breakdown value, each electrode arm is at its minimum distance of separation from the other fixed elecfixed electrode 16 and the moving electrode arm trode. Again the arcs strike and are drawn out while the voltage is approaching its maximum value and while it goes from the maximum to zero value. Again the presence of the inductances 33, 33 may cause the voltage across the electrode to lag behind the voltage in the line so that the arcs may exist a short while after zero voltage has been attained in the line. The above sequence of events again repeats itself, the electrode arms maintaining their constant relative position with respect to the alternating voltage.

The best results were obtained by using a rotor with two electrode arms and two baiiies, the rotor being rotated between two stationary electrodes, but all possible combinations of one, two, or three electrode arms and one, two, or three fixed electrodes can be used. For example, the combination of two electrode arms and one stationary electrode proved quite eflicient. Carbon is the preferred electrode material but tungsten, copper, and other suitable electrode materials have been used.

The apparatus is adapted .to a wide range of voltages, Voltages less than 500 are not desirable because of the small electrode separation necessary to start the arc. Higher voltages allow for greater electrode separation which incidently reduces the possibility of the electrodes striking each other, as well as providing the possibility of supplying greater quantities of energy to the arc. Up to 10,000 volts can be used conveniently but the limit is merely a matter of the size of the apparatus.

The hydrocarbon fuel supplied to the arc may be kerosene, crude oil, fuel oils, benzene, etc., there being relatively little difference in the mode of operation or in the nature of the products obtained from any of the hydrocarbon liquids; Compounds of the benzene type have a more favorable carbon-hydrogen ratio for the production of acetylene and we have obtained'arc gases v 1 containing more than 40 per, cent by volume of acetylene with maximum efiiciency.

The composition of the arc gases produced from the cracked hydrocarbon liquids is to a certain extent a function of the are power.

and are power caused a decrease in the acetylene.v

percentage butcaused an increase in the arc efficiency. the latter being defined in terms of kilowatt hours per pound of acetylene produced.

1 'The'maximum efficiency was obtained when the iacety lenecontentin' the gas'was between 33and I 35 per cent by volume, but thear'c' efficiency did l not deviate far from the maximum value with acetyleneipercentages aslow as per cent.

Some of the particular operating:conditions;:v

EmampZe 'Ihe apparatus'as shown in Fig. '1 was conand the results obtained can be seen from the following examples:

hydrocarbons in an alternating current arc, in

nected to a source of 60' cyclealternating cur+z In this manner, the

the negative maximum. The are current amounted to '76 amperes and 141 kilowatts were expended, the resulting power factor being 80.6 per cent. The hydrocarbon pyrolyzed was crude oil which produced under the above operating conditions a gas containing 34.0 per cent by volume ofacetylene with an expenditure of 3.80 kilowatt hours per pound of acetylene produced.

Example 2 The apparatus consisted of a central rotor with two L-shaped carbon electrode arms and two scoop-shaped baffles attached thereto. A single carbon side electrode was used. It was necessary to modify the apparatus in this case to the extent of attaching a brush to the rotor shaft to provide a current outlet capable of transmitting the total are current. The brush attachment is illustrated in Fig. 5. A 60 cycle current providing 2300 volts was used and the motor was rotated at 60 revolutions per second. The are current amounted to 27 amperes and 37 kilowatts were expended, the resulting power factor being 60.3 per cent. The hydrocarbon pyrolyzed was a light oil which produced under the above operating conditions a gas containing 33.4 per cent by volume of acetylene with an expenditure of 4.05 kilowatt hours per pound of acetylene produced.

. Centain advantages are derived from'the'improved'type of electric are produced according to our invention. This are decomposes liquid hydrocarbons with the formation of acetylene :without the hindrance ofv any quenching action 1 I caused by the near approach of other conducting 7 elements. It is long also because the synchronization of the electrode movement with the alter--v i v nations of the'voltage allows the arc to be struck 1 1 I at the'time breakdown voltage is first reached andat the time that the electrodes are at their j 7 minimum distance of separation. -In the case of i I the former. thearc is certain to be extinguished over only: a small portion of each; voltage. cycle I v and in the latter case thearc is certain to strike 1 with no delay. The method of synchronization .also allows thev efficient use of electrode arms Y which in turn offers the advantage of increased I I 'liquidturbulence. The latter aids in keeping the I are supplied with fresh quantities of fuel and in I the rapid removal ofgases produced. Other modes of applying the principle ,Wetherefore, particularly point out and distinctly claim as our invention: I I I, 1. man apparatus forthe pyrolysis. of liquid rotate in synchronism with'the alternating voltage; two electrode arms mountedoppositelyon v i i said rotor; baffies mounted on the rotor behind with a high efiiciency chiefly because the longer.

,each electrode arm inthe direction of rotation Q and; adapted to direct the: hydrocarbon liquid into the zone of the are formed at said electrode arm; two fixed electrodes of polarity opposite to one another mounted in said chamber in such position as to be brought into arcing relationship with the electrode arms by the movement of the rotor, one of said electrodes being in a position displaced slightly in the direction of rotation from that diametrically opposite the other fixed electrode; and an impedance electrically connected between the rotor and the displaced fixed electrode. e

2. In an apparatus for the pyrolysis of liquid hydrocarbons in an alternating current arc, in combination: a chamber for the hydrocarbon liquid; an electrically conducting rotor centrally mounted within said chamber and adapted to rotate in synchronism with the alternating voltage; two electrode arms mounted oppositely on said rotor; two fixed electrodes of polarity opposite to one another mounted in the chamber in such position as to be brought into arcing relationship with the electrode arms by the movement of the rotor, one of said electrodes being in a position displaced slightly in the direction of rotation from that diametrically opposite the other fixed electrode; and an impedance-elem trically connected between the rotor and the displaced fixed electrode.

3; In an apparatus for the pyrolysis of liquid hydrocarbons in an alternating current arc, in combination: a chamber for the hydrocarbon liquid; two fixed electrodes of polarity opposite to one another oppositely positioned within the said chamber; a rotor electrode mounted within the chamber and adapted to be rotated in synchronism with the alternating voltage; two electrode arms oppositely mounted on said rotor in such position as to be brought into arcing relationship with the fixed electrodes by the movement of the rotor; and a baflle mounted on the rotor behind of our invention maybe employed instead of those exv plained. change being made asregards themech- I anism herein. disclosed. provided the means stated'by any of the; following claims or the 7 equivalent of such stated means be employed; y

each electrode arm in the direction of rotation and adapted to direct the hydrocarbon liquid into the zone of the are formed at said electrode arm.

4. In an apparatus for the pyrolysis of liquid hydrocarbons in an alternating current arc, in combination: a chamber for hydrocarbon liquid; at least one fixed electrode positioned within said chamber; a rotor electrode mounted within said chamber and adapted to be rotated in synchronism with the alternating voltage; at least one electrode arm mounted on said rotor in such position as to be brought into arcing relationship with the fixed electrode by the movement of the rotor; and a baflie mounted on the rotor behind each electrode arm in the direction of rotation and adapted to direct the hydrocarbon liquid into the zone of the are formed at said electrode arm.

5. In an apparatus for the pyrolysis of liquid hydrocarbons in an alternating current are, in combination: a chamber for the hydrocarbon liquid; two fixed electrodes oppositely positioned within the said chamber; a rotor electrode mounted within the chamber and adapted to be rotated in synchronism with the alternating voltage; two electrode arms oppositely mounted on said rotor in such position as to be brought into arcing relationship with the fixed electrodes by the movement of the rotor; and a baflie mounted on the rotor behind each electrode arm in the direction of rotation and adapted to direct the hydrocarbon liquid into the zone of the arc formed at said electrode arm.

6. In an apparatus for the pyrolysis of liquid hydrocarbons in an alternating current arc, in combination with a source of alternating current: a chamber for hydrocarbon liquid; two

fixed electrodes mounted in said chamber and connected to opposite poles of said current source; an electrically conducting rotor mounted in said chamber between the fixed electrodes, electrically insulated from the walls of the chamber and from the ground, and adapted to rotate in synchronism with the alternating voltage; and two electrode arms in series with each other mounted on said rotor in such positions as to be brought into substantially simultaneous arcing relationship with the two fixed electrodes by the movement of the rotor. I

LORNE A. MATHESON. WILSON W. HUNT.

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