US1985680A - Process and apparatus for treating hydrocarbons - Google Patents

Description

De. 25, 1934; D B MAPE 1,985,680

PROCESS AND APPARATUS FOR TREATING'HYDROCARBONS Filed July 2, 1931 3% A if WM. 7 mn U46 UNITED STATES PATENT OFFICE PROCESS AND APPARATUS FOR TREATING HYDROCARBONS Dwight 1:. Mains, Frankforter Oil Process, Inc.,

Lincoln, Nebr., assignor to Omaha, Nebr., a

corporation of Nebraska Application July 2, 1931, Serial No. 548,453

9 Claims.

The present invention relates to a process and apparatus for treating vapors and gases and more particularly contemplates the cracking of hydrocarbons in vapor A primary object of phase. the invention is to accomplish an efiicient heat transfer without reliance upon the conductivity of the gases, such as is now an objectionable characteristic of conventional vapor phase cracking methods.

.Such an efiicient heat transfer is accomplished by utilizing a heated passageway comprising'a plurality of small diameter tubular portions enabling a tremendous heatingsurface to be presented to the gases or vapors.

An important feature of the invention is the provision of a construction wherein the pressure upon the inner and outer wallsof the tubular portions will be substantially equalized so that the tubular portions may be constructed of relatively thin material without fear of pres sure strain.

An additional object of the invention is to utilize the tubular portions as the resistance in a constantly energized such tubular portions present to a reversely traveling gas stream,

electric circuit, whereby will be heated and will posite wall surfaces having a uniform temperature.

A further object of the invention is to provide for accurate control, whereby the heat input may be automatically controlled to give constant cracking conditions.

An additional object of the invention is to provide means acting automatically to maintain the temperature of the below a predetermined resistance elements at or limit.

A further object of the invention is to provide a construction wherein a battery of heating tubes capable of operating at high temperatures has one end of each tube order to prevent any strain as a result of lack of free for expansion in which might develop uniformity of expansion throughout the battery.

Referring to the drawing: Figure 1 is a longitudinal section. Figure 2 is a transverse section, and Figure 3 is a plan view.

It will be understood paratus of this invention,

that the process and apwhile primarily suitable for the treatment and cracking of hydrocarbon vapors and gases,

may be employed with equal facility in connection with materials in the liquid phase as well of various characters, sired reactions.

as with gases and vapors and to promote the de- The improved cracking unit will preferably be attached to a distillation equipment of the usual character in such manner that the vapors of any desired fractions of the hydrocarbons may be passed through the unit and subjected to the 6 action of the heating elements in ,a manner to produce vapor phase cracking. Where fixed or natural gases are to be treated in .the apparatus, they will be supplied from any suitable source and may or may not be preliminarily 10 heated.

The process and apparatus is very efiicient for cracking hydrocarbon gases to produce aromatics, unsaturateds, or hydrogen gas, as well as for cracking heavy hydrocarbon gases or vapors 15 to produce large yields of gasoline or motor fuels of high anti-knock value". Moreover, the invention can be used for cracking gas oils to produce large yields of fixed gases for increasing the B. t. u. content or illuminating value of artificial gases.

The cracking unit of the invention is indicated as a whole at 10 and comprises a suitable chamber or shell within which is disposed a plurality of longitudinally extending tubes 11. The shell may be constructed of any high heat resisting material, and will preferably have its inner wall highly polished to provide a reflecting surface which .will be substantially non-absorbent to radiant heat.

The tubular portions 11 may be of any suitable construction; while I have indicated these members as tubes, it will be understood that this termis used in its broadest sense.

The tubes 11 will preferably be of very small diameter, substantially one-fourth inch to onehalf inch, and the wall of the tube will be of relatively thin material, a thickness of .025-.05 being preferable.

The material of which the tubes are formed will preferablybe capable of withstanding the high cracking temperatures, and I propose to use a material having this characteristic which will be electrically conductive and which will comprise, when necessary, a material capable of exerting catalytic or other beneficial effect for the particular reaction. v

While I preferably employ nickel chromium or other similar alloy, it will be understood that various conductive materials will be utilized capable of constituting electrical resistance elements, and developing the required heat for the desired operation.

I propose to employ a plurality of tubes 11 and these may be arranged in segmental batteries or gible, but I have -tially the same end section is detachable 2 groups, as indicated in Figure 2, although such an expedient is not essential. I

The tubes are preferably supported at the outlet end of the shell by a header 12 which acts to seal the shell at that end. The tubes, it will be observed, extend through the header, and intermediate their ends the said tubes are supported by suitable spacing and supporting means connected to the rings 13. The supporting and spacing means will preferably be insulated and will be constructed in a manner not to obstruct the longitudinal passageway between the tubes. The rings 13 are of insulating material, and the spacing and supporting means are connected thereto, the said rings, it will be observed, forming a slight obstruction in the space between the wall of the chamber and adjacent tubes which will have abeneficial effect in that the tendency of any gases to hug the wall will be interrupted,

since such gases upon meeting the ring will be directed into contact with the walls of the tubu- The effect of this space is neglifound that the rings exert the function just described.

The header 12 is bolted to the chamber as shown at 14. There is also bolted to the header so as to communicate with the tubes 12' projecting therethrough, a suitable outlet 15 for the cracked or heated product.

At this point it should be stated, that this outlet 15 may have means for maintaining the temperature of the gas discharged from the tubular members at -a constant temperature, or the cracked product upon discharge from the tubes may be immediately cooled. The gases from a vaporizer or other source, are supplied to the chamber throughthe inlet 16, preferably under a suitable'pressure. I propose, wherever necessary to preheat such gases by passing them in heat exchange relationship with the gases discharged through the outlet 15 in a suitable heat exchanger not shown. 7

The inlets 16, for convenience, have been shown spaced from the header, but in the practical operation of the apparatus and process, the inlet 16 will be disposed as close to the header as mechanically possible. It will be understood that a single inlet 16 may be employed, or any number thereof may be disposed radially about the periphery of the chamber.

At this-point, it should also be noted that the inlet and outlet of the chamber are at substanthereof. At the opposite end, there is bolted to the chamber and forming a part thereof, a convenience section 17. This from the body of the chamberby reason of the bolted connection 18', and while it has been shown as somewhat enlarged, in the practical embodiment ofthe process and apparatus, it will be of just sufflcient size to accommodate the necessary electrical connections for the respective tubes.

As stated, the tubular portions may be disposed simply in individual spaced'relation, or comprise segmental groups of spaced tubes with the segments spaced apart as shown in Figure 2.

As many tubes or as many segments as desired may be employed, but I preferably employ three segmental groups since I can conveniently operate the apparatus with such an arrangement as a three phase electrical system.

The electrical input can be conducted to the tubes either as a single phase system or a three phase system, or in any other manner desired.

I have shown a-three phase system which I lar portions.

the open ends of have found convenient for large scale cracking operations, wherein a three phase transformer 18 is connected to the service line 19 through a switch 20 and an automatically controlled rheostat or voltage control 21 on the primary of the transformer 18. 1

The three leads 22 are passed into the chamber through suitable insulated terminals 23'. Each terminal 23 is connected to a single segmental group of tubes by means of flexible leads 24 each leading from the terminal to the adjacent end of a tube 11 of the group. Thus, the three groups of tubes complete the three legs of the'three phase system, the current passing through the tubes to the header which affords a common connection.

I prefer to use low voltage, high amperage current stepped down as described, from a power service line. The transformer 18 will preferably be one which will be suitable to step down the current as required, from any power line to ten to fifty volts, and of capacity suflicient to supply the amperage necessary for heating.

I preferably employ a thermocouple connected to one or more of the tubes 11 and leading to a suitable control and recording instrument 25 which is associated with an electrical circuit, whereby should the temperature of any tube pass above a maximum limit, controlling mechanism 25 through its associated circuit will act upon the primary voltage control to reduce the heat input to the desired point.

I also employ either in the outlet chamber 15 adjacent the outlet ends of the tubes 11, or within the cracking zone in the chamber adjacent the header, a suitable thermocouple connected to arecording and controlling instrument 26, which likewise has an associated electric circuit acting on the primary voltage control 21. The purpose of this is to provide accurate control of the electric input to give a constant and accurately controlled cracking condition, thereby obtaining maximum yield of the desired product. In other words, by having a thermo-couple sensitive to minute changes in cracking conditions, the electrical input will be automatically increased or decreased during an operation or run to give the desired optimum cracking conditions and maintain these conditions constant throughout the run. 1

It will be observed upon reference to the drawing, that the preheated vapors or gases supplied to the inlet 16 will pass through a passageway defined by the space between the respective tubes, and the tubes and the wall of the chamber. The pressure will be suflicient to move these gases along at the desired speed toward the ends of the tubes while the stream will be uniformly increased in temperature. At the end of the passageway the gas will small chamber defined by the convenience section, in a reverse direction to the header and outlet. Thus, a continuous passageway is provided which is reversely directed and wherein the gas or vapor contacts both externally and internally with the wall of the electrically heated resistance element or tube.

In the construction described, wherein the gas moves in a continuous reversely directed passageway, in contact internally and externally with the walls of the multiplicity of small tubes, a tremendous heating surface is provided. This distinguishes from externally fired constructions enter what is in effect a or expedients where gas contact is made only with one surface of a heated tube.

Furthermore, by providing spaced tubes which are arranged in close relation, and are of small diameter substantially all of the gas is subjected to direct contact with the tube walls. Thus, a greater portion of the gas is directly heated by the tubes than has ever heretofore been accomplished by conventional means, and therefore, a greater quantity of the desired product will be obtained with a minimum amount of undesirables.

It will be observed that the thin wall construction of the tubes is made possible by the continuous reversely directed circuit, whereby no uneven pressures result in the system. Thus the pressure on the tubes is equalized on both surfaces relieving the thin walls of any pressure strain.

The electric resistance element constituting the tubes will have a substantially uniform temperature on both surfaces throughout its length, and can be accurately controlled to any predetermined limit.

In the process,-the rate of heat absorption by the gas is progressively decreased as the gas approaches the temperature of the heated sur; face. Thus, with the counter-current stream,

1 the sIoW. rate of heat absorption, near the end of the path, compensates for the rapid initial heat absorption on theopposite side of the tube wall. Therefore, with constant heat input throughout the length of the tubes and compensated rates of heat absorption from the two surfaces of the tube, the tube is maintained at substantially uniform temperature throughout its length. v

Where desired, steam may be periodically or continuously admitted to combine with any carbon which may be formed. In this connection, the invention has been found to operate with a minimum of deposited carbon or other undesirable products.

I have found that by this process of passing the hydrocarbon vapors counter-currently through and over a multiplicity of small diameter tubes, that the vapors are heated much more rapidly and uniformly to the desired cracking conditions, and that with a suitable control mechanism it is possible to maintain the necessary conditions for cracking various hydrocarbon vapors or gases and tosecure ,all of the products obtainable by such processes and obtain them more quickly and also more efijciently, in that the formation of undesirable products is substantially decreased. It will, moreover, be observed, that by reason of the construction employed, not only .will a greater portion of the vapors or gases be subjected to direct contact with the resistance element, but since the resistance element is maintained at a uniform temperature, it will be observed that the gases will be uniformly heated throughout their reversely directed path, permittingagreater proportion of the desired end product to be obtained. r

In order that the operation of the-construction and process of this invention may be understood, I shall describe one embodiment in connection with a cracking process, but it will be, of course, understood, that various reactions may be accomplished, and I do not wish to be limited to the specific material described as being treated.

An ordinary conventional type pipe still consisting of the necessary tube banks and furnace and a suitable vaporizing chamber maybe operated on a topped crude or crude residium. The pipe still outlet should be operated at as high a temperature as is possible without producing cracking in the tubes. The oil is then passed into the vaporizing chamber, which will give heavy hydrocarbon vapors at a temperature of 800 F. or higher. The vapors leaving this chamber continuously, .at a uniform rate will then enter a vapor heat exchanger in heat exchange relationship with the cracked vapors coming from the outlet 18 of the cracking unit. This will raise the temperature of the vapors another 50 to 100, bringing them to the inlet of the cracking unit-at a temperature of 850 to 900. Here the vapors pass through the cracking chamber, pas

ing in counter-current flow over the outer surface of, and back through a multiplicity of small diameter tubes which are electrically heated to the proper temperature, for-example, 1200 F. The vapors passing in contact with the large amount of heated surface will be heated to the desired temperature, for example 1050 or 1100 F. at which temperature cracking takes place to produce motor fuel of high anti-knock value. 1

The thermocouple recording the temperature of the vapors leaving thetubes, operates a control mechanism to automatically control the electrical heat input to the tubes and thereby maintain a constant outlet temperature.

The cracked vapors are then rapidly cooled .by passing through heat exchangers and thence to a fractionating tower from which gasoline passes to storage and the heavy fractions are returned to the system for further treatment.

Since it is definitely known that a diflerent cracking temperature will produce a different character of cracked product, it will be seen that cracking conditions. may be varied at will to produce any desired product which can be produced by such processes.

Each segmental battery or group of tubes will tially continuous fluid passageway therein, said passageway comprising a multiplicity of closely spaced thin walled tubes longitudinally disposed with respect to and substantially filling said cham- ,ber providing one leg of said passageway, said tubes being spaced from the wall of the chamber and from each other to provide another, leg of the passageway communicatingwith the first leg at one end to form a reversely directed continuous fluid path, an inlet and an outlet communicating with the passageway, and means for heating the tubes comprising an electrical cir cuit in which said tubes constitute a resistance element, whereby fluid propelled through said passageway will traverse a continuous reversely directed path in contact with both heated surfaces of the tubes.

preferably comprise thirty-two individual tubes,

2. An apparatus of the class described comprising a chamber, a reversely directed substantially continuous fluid passageway therein, said passageway comprising a multiplicity of closely spaced small diameter tubes longitudinally disposed with respect to and substantially filling said chamber providing one leg of said passageway, said tubes being spaced fro the wall of the chamber and from each other to provide another leg of the passageway communicating with the first leg at one end to form a reversely directed continuous fluid path, an inlet and an outlet communicating with the passageway, and means vfor heating the tubes comprising an electrical said tubes being spaced from the wall of the chamber and from each other to provide another leg of the passageway communicating with the first leg at one end to form a reversely directed continuous fluid path, an inlet and an outlet communicating with the passageway, and means for heating the tubes comprising an electrical circuit in which said tubes constitute a resistance element, whereby fluid propelled through said passageway will traverse a continuous reversely directed path in contact with both heated surfaces of the tube, and means for automatically controlling the electrical heat input to maintain a sunstantially constant fluid temperature at said outlet.

- 4. An apparatus of the class described comprising'a chamber, a reversely directed substantially .continuous fluid passageway therein, said passageway comprising a multiplicity of closely spaced small diameter thin walled tubes longi-L tudinally disposed with respect to and substantially filling said chamber providing one leg of said passageway, said tubes being spaced from the wall of the chamber and from each other to provide another leg of the passageway communicating with the first leg at one end to form a reversely directed continuous fluid path, an inlet and an outlet communicating with the passageway, .and means for heating the tubes comprising an electrical circuit in which said tubes constitute a resistance element, whereby fluid propelled through said passageway will traverse a continuous reversely directed path in contact with both heated surfaces of the tubes, and means for automatically limiting the temperature of the tube to a predetermined maximum temperature.

5. The process of cracking hydrocarbon gases and vapors which comprises passing the vapors or gas to an electrically heated resistance "element in a closed chamber, simultaneously passing the vapors or gases in a continuous stream by a multiplicity of spaced paths, first in one direction over a uniformly heated surface of said element and then in a reverse direction over the opposite uniformly heated surface of said element while maintaining substantially equal pressure on both surfaces of said element.

.6. The process of cracking hydrocarbon gases or vapors which comprises simultaneously passing the gases counter-currently over the outer surface of andthrough a multiplicity of spaced small diameter electrically heated tubes, and maintaining the outlet temperature of the gases constant by controlling the electric heat input to the tubes.

7. The process of treating hydrocarbon gases or vapors which comprises simultaneously passing the gas by a multiplicity of spaced paths over opposed surfaces of a constantly heated electrical resistance element in a continuous counter-current flow, progressively increasing the temperature of the fluid to a predetermined limit by contact with-the said element, and maintaining the temperature of the heating element substantially uniform throughout its length.

8. An apparatus of the class described comprising a chamber, a reversely directed substantially continuous fluid passageway therein, said passageway comprising a plurality .of closely spaced small diameter tubular portions therein extending longitudinally of and substantially filling the chamber, means for passing fluid through said tubular portions and the spaces therebetween, an inlet and an outlet for the chamber, and means for heatingthe tubular portions comprising an electrical circuit in which said portions constitute a resistance element, whereby fluid will be propelled through said portions and the spaces therebetween in a counter-current path and will be heated by contact with the inner and outer surfaces of the tubular portions.

9. An apparatus of the class described comprising a chamber, a reversely directed substantially continuous fluid passageway therein, said passageway comprising a pluralityof closely spaced smalldiameter tubular portions therein e ctending longitudinally of and substantially filling the chamber, means for passing fluid through said material thereof under high temperature.

DWIGHT B. MAPES.

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