US2061836A - Process and apparatus for cracking hydrocarbons - Google Patents

Description

Nov. 24, 1936. w. A. s. HARMON 2,061,836

PROCESS AND APPARATUS FOR CRACKING HYDROCARBONS F ile'd Oct. 10, 1952 s Sheets-Sheet 1 m'vEmoR [May a 5. armor BY 59100 ATT RNEY Nov. 24, 1936.

5 Shee'ts-Sheet 3 Filed Oct. 10, 1932 w Y Rm E arm m jf 5 T E. T V A Ne V v 5 Nov. 24, 1936. w. A. s. HARMON PROCESS AND APPARATUS FOR CRACKING HYDROCARBONS Filed Oct. 10, 1932 5 Sheets-Sheet 4 ici. E1

W0 BY lll i Z M 0 N06. 24, 1936. w. A. s. HARMON 2,061,836

PROCESS AND APPARATUS FOR CRACKING HYDROCARBONS Filed Oct. 10, 1932 5Sheets-Sheet 5 \NVENTOR fl ay r .5. r0700 BY {M ATT RN EY Patented Nov. 24, 1936 UNITED PATENT OFFICE PRGCE SS AND APPARATUS FOR CRACKING HYDROCARBONS Wayne A. S. Harmon, Los Angeles, Calif., is-

slgnor, by mesne assignments, to George G.

Peckham This invention relates to a process for reforming hydrocarbon compounds. It is 'now well known that the pyrolytic decomposition of petroleum, with the consequent breaking up of its molecules, results in the production of both lighter and heavier hydrocarbon fractions than were contained in the original charging stock. In the terminology of the-petroleum industry the reforming process is termed cracking. The economic factors involved are to utilize the pyrolytic decomposition process to reform the heavier and cheaper petroleum fractions and convert them into lighter and more valuable hydrocarbon products, such as the conversion of a heavy fuel oil residuum into gasolines and kerosenes.

Such processes are commercially important as the economic value of the light fractions formed (such as gasoline, kerosene, etc.) is greater than that of the original charging stock (such as topped or skimmed crude, heavy residuum, or a very low gravity crude oil). In ordinary refining distillation methods the yield of light hydrocarbon fraction from the charging stock is inadequate and results in a large percentage of heavy fraction residuum. To increase the yield of light fraction, it is necessary to utilize pyrolytic decomposition to reform the heavy fractions. If the yield of light or low boiling point fractions can then be increased to double or treble the yield by ordinary distillation, and if this additional yield be obtained at less cost per gallon, its economic value is important. I

Petroleum hydrocarbons have a characteristic temperature above which reforming of some of the molecules begin. This temperature varies for different fractions from a given crude oil and for similar fractions from different crude oils. This temperature may be termed the temperature of molecular instability and has associated with it the "creative pressure of temperature of molecular instability. The temperature of molecular instability has been defined as the degree of heat at which the bonds of intermolecular attraction between the relative atomic constituents are stretched to a point of inequilibrium. Hydrocarbon fractions of low boiling point have high temperatures of molecular instability and high creative pressures, whereas high boiling point fractions have low temperatures of molecular instability and very low absolute creative pressures. The gasoline fractions have low boiling points, high temperatures of molecular instability, and very high creative pressures. The fuel oil fractions and heavy residuums have high boiling points, low temperatures of molecular instability, and low absolute creative pressures. This is fortunate, as this relatively cheap residuum is the desirable charging stock for my process. To carry on the pyrolytic decomposition process, it is necessary to elevate the temperature of the hydrocarbon molecule above its temperature of molecular instability. A time element is involved and by elevating the temperature above that necessary to start molecular readjustment, the time interval can be shortened, the higher the temperature, the shorter the interval, until a tempera- I ture is finally reached at which the readjustment takes place almost instantaneously, the interval approaching zero as a limit. However, due to economic factors, there is a most economical temperature at which the greatest economic yield of low boiling point fractions can be made, this temperature usually falling within the 850 F. to 900 F. range, the time interval varying with the charging stock. It is readily seen that large quantities of hydrocarbon compounds must be heated uniformly to an upper limitingtemperature to obtain the maximum gasoline yield, molecules heated beyond this temperature receive too much heat energy input and in reforming a portion convert into fixed gases (an economic waste). In my process the limiting temperature approached by the hydrocarbon molecules is that of the molten metal at the point where the molecules leave contact with the metal, and by having definite control of the metal temperature at the aforesaid point, I am able to vary the leaving molecule temperature to whatever is desirable and economical for the charging stock being processed.

The transfer of heat through the wall of a conduit to an interior moving stream falls far short of providing the requisite uniform heating, because of those layers of the charging stock which are nearest the wall are in the most favorable position to be heated. This is true for several reasons, among which are that these layers are nearest the source of heat, and that these layers flow slower than the stock at the center of the conduit, permitting a greater period for heat exchange. Thus the outermost layers of the stock become overheated in endeavoring to heat the inner portions to the desired temperature.

Aside from the immediate reduction in the output of the system below that capable of attainment with more uniform heating, the additional disadvantage often arises that the conduits in which the stock is heated, are soon coated interiorly with a carbon layer, which acts further to hinder the effective transfer of heat. It has been proposed in the past to provide an alternative form of cracking, in which a quicker and more uniform heating ofthe stock can be provided, by passing the stock through -a bath of moltenmetal. At first blush, such a process seems to have advantages of simplicity and inexpensiveness as compared with .other systems. The metal used must be such that is chemically inert. The most practicable metal for this purpose is lead, more particularly because the temperatures at which it stays molten are within the range of useful cracking temperatures. Examples of such proposals are found in the disclosures of Patent No. 1,187,874, issued June 20, 1916, to A. A. Wells; and Patent No. 1,391,568, issued September 20, 1921, to J. Nelson.

However, such molten metal processes have never been commercially feasible. "The reasons for this are numerous. Among them may be mentioned several, which will now be discussed.

It has been found that oil which is to be cracked, carries certain impurities, such as sulphur, water, salt, nitrogen, oxygen, carbon dioxide, and organic matter. At least some of the impurities can combine with the molten metal; and under the temperature and .pressure conditions required for cracking, such chemical union is facilitated. There is accordingly, a large metal loss due to this combination; and in addition the formation of explosive compounds is probable, with attendant danger to life and property.

It was found in experimenting that all of the charging stock was not vaporized on reaching the top surface of the molten metal. The unvaporized portion continued to receive heat from the metal beneath and if not removed promptly, would start the formation of coke. The coke would bridge over the molten metal and the oil vapors leaving the metal surface would blow a portion of the metal above the coke, thereby filling the pores of the coke with said metal. The coke formation would continue until the space above the metal surface was filled with a mixture of coke and metal. In my invention, means are provided to continuously remove this residuum adjacent to the metal surface before it has had sufficient time to start the formation of coke.

In experimenting with metal temperatures of the order of 1200 F., dry carbon dust collected on the metal surface and after sufllcient accumulation was cemented into porous coke. At these temperatures excessive quantities of fixed gases were formed.

It is one of the objects of this invention to provide a molten metal process that obviates these, as well as other disadvantages in a simple manner, thus ensuring a thoroughly commercial and practical system.

With the aid of this invention the heat transfer is so regulated, by a circulation of the molten metal in a. heating chamber, that the temperature of the molten metal remains at all times at relatively moderate levels. Furthermore, the temperature difference between extremes in the molten metal, corresponding respectively to the inlet temperature and outlet temperature of the metal in the heating chamber, need not exceed a few hundred degrees Fahrenheit. In other words, the heat head of the molten metal is moderate. The heat transfer is conducted by this means under the most favorable condition for high yield said metal near the bottom and permitting it to rise upwardly through the molten metal, thus producing a counterflow.

The downward velocity of the molten metal is regulated such thatthe buoyancy of the charging stock permits said stock to rise upwardly; said rate of rise can be made variable by varying the downward velocity of the metal. I

This counterflow is in itself highly advantageous in addition to the factors already given.

, The charging stock is by this means continually brought into intimate heat transfer relation with new, warmer, and different portions of the molten metal. This increases the rate of heat transfer. Furthermore, the molten metal scrubs the charging stock, thereby producing a rapid mixing of the petroleum molecules at the metal-oil interface and consequently continuously brings new metal and oil molecules rapidly into contact for heat transfer.

It is another object of my invention to inject the charging stock into the heating chamber in such manner that it is subdivided into small 3 globules of the stock, subjected to the heat transfer from the molten metal. Atomizing the charging stock greatly increases the area of surface contact at the molten metal-oil interface, thereby accelerating the heat transfer, and makes possible a much higher degree of uniformity in heating the stock.

It is still another object of this invention to make possible the operation of the process without danger of depositing carbon or forming coke in the heating chamber. This is accomplished by so agitating or moving the molten metal such that the hydrocarbon liquid in contact at the oil-metal interface is uniformly and continuously removed before the reforming has progressed to the coke formation stage. All portions of the circumferential periphery of the hydrocarbon liquid adjacent the upper metal surface are passed by the outlet opening and a portion removed at each revolution. Otherwise, portions of the liquid located remotely from the outlet would be placed in unfavorable position for removal and little, if any, be removed, continuing to receive heat from the molten metal beneath would continue reforming and deposit coke.

The process consists in heating the charging stock in direct contact with molten metal to whatever temperature is desirable and then passing the stock into a chamber in which it is held for reaction or reforming and consequent conversion into desirable low boiling point fractions, the heating and conversion process taking place continuously and simultaneously, the charging stock entering continuously and the reformed hydrocarbon products removed continuously. The

heating unit and conversion unit can be combined into a single structure, by superimposing the conversion chamber directly on top of the heating unit, or they may be conveniently sep- 75 begins.

arated into separate units having communicating conduits. The heating unit can be operated continuously and by having two conversion chambers, placing one conversion chamber in operation at a time while the other is being cleaned and inspected, the process can be carried on continuously. Some conversion takes place within the heating unit, for as soon as an oil molecule has had its temperature raised above its temperature of molecular instability readjustment of its atoms The depth of the metal bath could be made such that the desired conversion can be completed within it. From economic considerations, it is usually desirable to heat the hydrocarbon fractions in the molten metal bath and conduct them to a chamber wherein the reaction or reforming is carried onto the desired conversion.

The process can be conveniently carried on either as a liquid phase, vapor phase, or mixed phase process. The .reaction or reforming can be carried forward to the formation of coke in the conversion unit, or it can be stopped short of coke formation by removing the liquid hydrocarbon before the reforming has been carried to that point.

My invention possesses many other advantages, and has other objects which may be made more easily apparent from a consideration of one embodiment of my invention. For this purpose I have shown a form in the drawings accompanying and forming part of the present specification. I shall now proceed to describe this form in detail, which illustrates the general principles of my invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of my invention is best defined by the appended claims.

Referring to the drawings:

Figure ll is a diagram of a plant for cracking and fractionating the stock in which the invention is incorporated; Fig. 2 is an enlarged sectional view partly diagrammatic, of the heating conversion chambers embodying the invention, togethe with various apparatus associated therewith; L

Fig. 3 is an enlarged sectional vie taken along plane 3-3 of Fig. 2; w

Fig. 4 is a detail section, take, along plane 4-4 of Fig. 3; U

Fig. 5 is a detail section, taken along plane 5-5 of Fig. 3;

Fig. 6 is a fragmentary top plan view, partly in section, of the apparatus, taken from plane 6-6 of Fig. 2;

Fig. 7 is a fragmentary sectional view, taken along plane 1-! of Fig, 2;

Fig. 8 is an enlarged detail section, partly broken away. of the injection valve, taken along plane 8-8 of Fig. 2;

Fig. 9 is a detail section taken along plane 99 of Fig. 8; and

Fig. 10 is a detail section, taken along plane Ill-l0 of Fig. 8.

In Fig. 1, the fractionating apparatus as well as the cracking apparatus is disclosed- In cracking of course, the charging stock must be elevated to a desirable temperature, and the resultant reformed products retain a good deal of this heat, although they should be stored in cool condition. In the present instance, the usual practice of providing heat exchangers between the products of cracking and the charging stock is employed. The heat exchangers can be of any suitable or usual construction. Since these heat systems already well-known and in use.

exchangers are located in conduits leading from the conversion or reaction chamber and fractionating apparatus to various units or storage tanks, these units can first be specified.

Thus a conduit l carries the hot vapor or gaseous products of the cracking process to a fractionating tower 2. In this conduit is located a heat exchanger 3. Fractionating tower 2 can be of any usual or suitable type, having various conduit discharges, leading off the products in ac- 10 cordance with their fractionation. Thus at the top, a conduit 4 leads ofi? gasoline, and a gas trap 5 is provided for extracting fixedgases therefrom. The fixed gases proceed by way of conduit 6 to a receiver. A refluxing conduit 1 returns from a conduit '4 near the top of tower 2, in the usual manner. A conduit 8 removes another product, such as kerosene distillate; a lower conduit 9 removes a still heavier product, such as gas oil. From the bottom of the tower 2, heavy fuel oil that collects therein is discharged through conduit l0.

These conduits for the removal of the fractionating products are merely shown as examples, and their arrangement and number can be varied to comply with the character of the desired end products. Any of these conduits can be provided with heat exchangers to transfer heat to the incoming charging stock.

The hot liquid products of the cracking process are conducted through a conduit H through various instrumentalities to separate out the various desired fractions. Thus use can be made of an evaporator .l2, in which the lighter constituents are permitted to evaporate off into the conduit I. The evaporator residuum is passed, by

way of conduit l3, to a flash evaporator l4, operof this tank through conduit l5 and is finally cooled and stored. The residual liquid in tank H4 is heavy, such as pressure tar, and is passed by way of conduit ii to a pressure tarreceiver,

although a portion thereof can be used, via conduit l1. as fuel for the heating system. I

The disposition of the products of the cracking process has been rather summarily described for the purpose of more logically tracing the course of the charging stock through various heat exchangers associated with the outlet conduits mentioned. However, a more thorough discussion of this part of the plant is not considered essential, as it is in all material portions. quite similar to We are now prepared to trace the course of the charging stock through the apparatus. 1

The charging stock can be any fraction cut from fractional distillation of petroleum hydrocarbon oil or any crude oil as removed from the ground. Any fiuid hydrocarbon that can be charged can be cracked or reformed. The most economical charging stock for this process is a heavy residuum or low gravity crude oil having little if any gasoline fractions. The quantity of water or other impurities in the charging stock is immaterial, as it in no wise interferes with the process. other than the added expense in evaporating a product that is an economic waste. L kewise, should the charging stock be a crude oil containing an appreciable quantity of low boiling point fractions, no special provision need be made other than to heatand separate them from the main stream at the stripper. This will be explained more fully further on, The only requirethe start. As shown in Fig. 1, the stock is fed through conduit l8; .It is heated by passing through heat exchangers I3, 20, and 2| in conduits 3, 3 and I respectively. Thence a pump 22 is used to pass the stock successively through various other heat exchangers and apparatus until it reaches the molten metal chamber 23.

By the aid of a T connection 24, and valves 23 and 26 in conduits l8 and 21 respectively, any desired portion or all of the stock can be caused toflow through heat exchangers 23, 29 in conduits i and I6 respectively. In this manner the vapors and liquids leaving thru conduits i3 and i6 can be condensed and cooled by'heat exchangers 23 and 29 to the desired temperature. The stock passing via conduit 21 units with that portion passing-via conduit l3 at connection 30. Thence the stock passes by way of conduit 3| through the heat exchanger 3, and into a heater coil 32. This heater serves to further elevate the temperature of the charging stock. The temperature of the stock, leaving heater coil 32, is maintained such that all low boiling point fractions, water, and dissolved gases may be readily stripped from the stock in stripper 33. Ordinarily this temperature is of the order of 600 F.

It is to be noted that the various heat exchangers are so located that the stock is subjected in succession to higher and higher absolute temperatures. This is accomplished by providing that the heat exchangers, such as 3, 28 and 29, which are the later ones to be contacted by the stock, occur in conduits nearer the heating and conversion chambers.

The heater coil 32 can be heated in any desired manner. In this instance, it is shown as includ ing a gas burner 38 in the base of a furnace cham-- ber 34, provided with a stack 35. The chamber 34 can also be heated by the hot products of combustion from'furnace 36 for heating the molten metal used in the process. For this purpose, a passageway 31 for conducting these gases is provided in one side of the chamber 34. A more detailed drawing of this arrangement is shown in F'g. 2. The burner 38 can be supplied through conduit 39 from the fixed gas outlet conduit 6 leading from the tower 2 to an appropriate gas receiver.

The stripper 33 is an important part of the process, as by its use, the loss of molten metal is held to an inconsequential quantity. All dissolved gases, water, and low boiling point fractions, as well as an appreciable amount of sulphur, a e removed from the charging stock within this apparatus. As an illustration, take the dissolved gas oxygen. Under the temperature and pressure conditions existing in the molten metal 59, Fig. 3, this gas will readily combine with lead, if it be the molten medium, and form lead oxide, PbQ. In forming lead oxide the combining ratios are as their atomic weights, or 16 pounds of oxygen will combine with 207.20 pounds of lead, thereby forming 223.20 pounds'of lead oxide. Now the usual commercial size cracking unit will have several million pounds of oil charged into it for reforming during a month's timeand if the quantity of dissolved oxygen were one tenth of one percent (0.1%), the metal loss would run into thousands of pounds per month. Under proper conditions even nitrogen can be combined with lead to form an explosive and dangerous compound. Danger of forming any lead chlorides or chlorates is eliminated for the water (H2O) containing salt (NaCl) is evaporated and the molten metal temperature of the process is not suiiiciently high enough to melt the salt (melting point 1482" F., boiling point 3012 F.).

The stripping action can be accomplished,

for example, by subdividing the downward flow of the charging stock, within stripper 33, to form thin sheets or small diameter streams, and filling the ambient space with a moving atmosphere of superheated steam. The steam acts as a carrier and sweeps out the removed constituents. As illustrated, the stripper 33 contains several perforated plates 40, the stock being fed onto the top of the series, where it flows through the perforations to the plate below. Successive plates are likewise perforated and permit the liquid to flow through from plate to plate in small streams. A counter or cross-current of superheated steam is conducted past or through or over the liquid sheets or streams. as by feeding the steam in at the bottom through a conduit 4i leading to a source of steam supply.

The volatile constituentsendeavor to establish their respective vapor pressure in the ambient vapor space and by dividing the stock into numerous sheets or streams a large surface for their escape is presented. As rapidly as they emerge into the ambient space, the steam carries them away, thereby preventing their establishing their respective vapor pressures. The larger the surface exposure, the faster the stripping action is carried forward. Bubbling steam through the liquid charging stock will also strip it as the volatile constituents escape into the steam bubble and endeavor to establish their respective vapor pressures therein. Stripping steam enters continuously at the bottom and continuously leaves the top of stripper 33.

The rate of flow of charging stock into stripper 33 is regulated, as for example, by a valve 42, controlled by a float mechanism 43. The resultant stripped gases and vapors are passed through back-pressure valve 44 into conduit I that connects with fractionating tower 2.

The stripped hydrocarbons are collected in the bottom of stripper 33, whence they are conducted through a conduit 45 to the molten metal chamber 23. If desired or advantageous, a pump 46' can be included in conduit 45, to supplement the pressure of pump 22, and to make it possible to inject the stock into the chamber 23. This injection is accomplished by the aid of a special valve 41, which will later be described in connection with Figs. 8, 9 and 10. The stock at this point has a temperature of about 500 degrees Fahrenheit and is fed in near the bottom of the chamber 23, in which molten metal is circulated. The pressure in this chamber can be of any suitable value; it usually is of the order of 100 to 125 pounds per square inch.

Heat to elevate the temperature of the hydrocarbon charging stock to the desired temperature is transferred from the molten metal 59 to said stock, by direct contact, within heating chamber 23. Conversion chamber 48 could be superimposed directly on 23, the side wall 10, of 23, Fig. 3, could be extended to form the side wall of 43. However, such an arrangement would not be suitable, were it desired to permit the conversion to carry forward to the formation of coke; this was discussed previously. Hence a more suitable commercial apparatus is had by separating the heating chamber 23 and conversion chamber 43, Fig. 2, into separate units having a communicating conduit 30, Figs. 1 and 6.

With the arrangement of the heating chamber 23, and conversion chamber 48 into separate communicating units, it is possible to confine the heating of the charging stock to 23, thence transferit into 48, wherein the desired reaction or reforming is completed. A valve 48 is located in conduit 50. As shown in the illustration, all the products of combustion from furnace 36 pass around conversion chamber 48. On some installations this may not be desirable and consequently the gases would be by-passed around chamber 48 and enter directly into furnace 34, below the heating tubes, only such portion of the gases as is desired passing around chamber 48. Heat may or may not be added to the hydrocarbon stock within conversion chamber 48, as

desired, the main object being to provide an insulating blanket of hot gases around 48 to prevent loss of heat therefrom while the hydrocarbons within are undergoing the desired conversion. Work is done in reforming the hydrocarbons with consequent loss of temperature in the liquid-stockremaining within 48.

The fixed gases and vaporized fractions coming off the charging stock undergoing reforming within chamber 23 and 48 are passed to the fractionating tower 2, through conduits 52 leading from the top of the respective chambers. Usually conduit 5l is closed and all gases and vapors from both chambers 23 and 48 pass through the back-pressure valve 53 in conduit 52. This is desirable, as it will be apparent further on in the description of chamber 23.

That portion of the liquid collected in chamber 48, and not vaporized, is passed through a valve 54 and conduit H to theevaporator l2. Valve 54 can be either manually controlled or controlled by a float mechanism 55. The liquid level held in chamber 48 depends on the charging stock and the time interval required to give the desired conversion.

In evaporator l2, the lighter hydrocarbons, such as gasolene, kerosene, and gas oil are flashed on? in the form of vapor into conduit l, to tower 2. The remaining hydrocarbons are passed through valve 56 and conduit l3 to the flash chamber l4. Valve 56 is controlled by a float mechanism 51 located in chamber l2.

In flash chamber I4, the absolute pressure may be atmospheric or less, the residual desired fractions are flashed off as a vapor through conduit 15, are condensed, and run to storage. The vapor is usually a low gravity gas oil. The hydrocarbons collecting in the bottom of i4 is a residual pressure tar and is discharged to conduit l6 and i1 byway of float controlled valve 58.

Variations in the cycle of operation are of course permitted to meet the requirements of the refiner. In liquid phase operationhigh enough absolute pressures are maintained within chambers 23 and 48 to prevent the vaporization of normally liquid hydrocarbons. Mixed phase is normally conducted with a pressure range lower than liquid phase, the pressure depending on the temperature of the hydrocarbon undergoing reforming and the conversion desired.

In vapor phase operation the charging stock is preliminarily heated to high enough temperature, that on entry into chamber 23 only the heat of vaporization is added by the molten metal to substantially vaporize all of it. However, in some cases it is desirable to elevate the temperature of the liquid hydrocarbon charging stock after charging it into chamber 23, before vaporizing it. In vapor phase operation, the heating and reforming is performed substantially with the charging stock in the vapor state. Egress of vapor to conduit 5| is prevented by closing valves therein, and valve 53 is pressure controlled.

Since the essential features of this invention reside in the heating chamber 23 and conversion chamber 48, and in the manner of heat transfer utilized therein, a complete description thereof will now be set forth. The molten metal 59 (Fig. 3) is conveniently lead, but other metals may be used, singly or in combination. The metal temperature at ingress to 23 is preferably about 850 to 950 F.

The lead is kept molten by the aid of a coil of metal pipes 68 (Figs. 1 and 2) through which it is circulated. This coil is located inv furnace chamber 36, so as to be heated by a flame generated by burner 6|, fed with fuel through con duit I1, and pump 62. The products of combustion circulate not only through furnace 36, but also via passage 63, through flue 64 in which chamber 23 is located; thence through flue 65 to top. of flue 66 in which chamber 48 is located; thence through passage 31 into furnace 34 and finally out through stack 35.

The flame generated by burner 6| can be controlled manually or automatically. If automatically controlled, the control apparatus is actuated by the temperature of the lead leaving the heating coils 68 within furnace 36, or by the temperature of the oil and vapor passing through transfer pipe 58. Several such control apparatus are now in commercial production, and need only be adapted for use in this invention.

The molten metal is heated in the coils 60, located in furnace 36, to the desired temperature and conducted by way of conduit 61 to an inlet 68 (Figs. 2, 3, and 6) near top of chamber 23. This chamber has an elongated lower body 69 to which is joined a top portion 10 of larger diameter, or by conical walls II. The temperature of the molten metal entering chamber 23 can be automatically controlled to any desired temperature by means of automatically controlling the flame generated by burner 6|, as previously disclosed.

' One of the important features of the invention resides in the provision of a helical-like movement of the molten lead 59 downwardly in body 68,

to the outlet conduits 12 (Figs. 2 and '7) For this purpose, a center conical top I3 (Figs. 3 and 5) is disposed over member 68, and is extended as a small cylinder 14 into the upper por tion 10. The lead is fed to portion Ill in a nonradial direction; or in a substantially tangential manner adjacent the outer wall of portion. 10. This is clearly shown in Fig. 6. The molten metal is thus given a rotation (in this instance counterclockwise), and in the course of its rotation, it is guided into the top of elongated body 69 through tangential inlets 15 (Fig. 5). These inlets are formed by guide walls 16, substantially tangential tothe conical top 13. They act to maintain the helical path downward to the outlets 12.

The rate at which this rotation takes place, is dependent upon the rate of circulation of the metal. Ordinarily this rate of rotation is of the order of one or two hundred revolutions per minute, and is controlled by adjusting the speed of a variable speed pump 16 (Fig. 2), for the molten metal. This pump has an inlet l1 connecting directly to the pair of pipes 12 leading by way of connection I8 into the bottom of chamber 23. The outlet connects to the heating coil 60. It is apparent that pump 16 is a pressure pump, constantly forcing the molten metal through a closed cycle, including coil 88 and chamber 28.

It is apparent that the rate of heat transfer in coils 88 can be varied by'increasing or diminishing the flame generated by burner 8| and also by varying the rate of flow of the molten metal within tubes 88. For a given tube temperature the higher the rate of flow of .moltenmetal therein, the higher the rate of heat transfer from tube to molten metal. It is thereby seen that by varying eitherthe flame generated \by burner 8| or varying the rate of flow of molten metal within tubes 88, or varying both simultaneously, complete control may be had of the heat transfer rate between tubes 88 and the molten metal within as well as control of the desired maximum molten metal temperature. Usually the desired maximum molten metal temperature is controlled automatically and the. rate of flow within tubes 88 by manual control of variable speed pump 18.

The pump 18 can be of the centrifugal type, and driven by a variable speed motor 88 supported above the furnace 88. Since the pump must operate effectively at the temperature of the molten metal, it must be designed to comply with these-requirements, For example, to protect the upper bearings and the packing for the pump shaft, a conduit 8| (Fig. 2) is connected between the shaft housing 82 and the chamber 28. This conduit is located above the molten metal level and hydrocarbon liquid level within chamber 28. This conduit 8| serves to return the moltenmetal leakage around the lower pump bearing to chamber 28, also serves as an oil vapor communicating conduit to equalize the pressure in shaft housing 82 and chamber 28. It also permits the upper water-cooled packing gland of the pump to be sealed against condensed oil vapors instead of molten metal. Any condensed oil vapor, or its residuum, is continuously returned to chamber 28 by the molten metal flowing from shaft housing through conduit 82, the molten metal occupying only a small portion of the available space within said conduit.

The level of the molten metal in chamber 28 is maintained at the port opening l2l of valves 88, for the egress of the heated hydrocarbon. Two suchvalves are shown diametricallyoppositely arranged, but only one is used at a time. The duplex arrangement is provided for the purpose of alternating the operation of the supplemental conversion chamber 88 with a relief conversion chamber 88', shown in Fig. 6. Thus one chamber can be cleaned from coke or other deposits,

while the other is active, by appropriate manipulation of the valves 48 and the dampers in flue 85 and passage 81. One damper is shown at 88, Fig. 2, and the control handles therefor at 88, 88, Fig. 6 and damper 1| is shown in passage 81.

It is apparent as thus far described, that the molten metal 58 descends in a helical-like path from the top to the bottom of the body 88, where it leaves through pipes 12. Adjacent the bottom of this column, either one of a pair of injection valves 81, 81' (Fig. 7) is used to pass the charging stock into the column of molten metal. These valves are provided to enable one to be kept continually in service whenever any repairs are necessary. They are constructed as shown most clearly in Figs. 8, 9, and 10. Each of them is so arranged that the emitting liquid stock is impelled in a circular path, in the same direction as the circular motion of the molten metal, and in subdivided condition. Since the oil is lighter, it ascends to the top of the molten metal in a h lical-like path generally counter-current to the helical-like path of the metal.

The downward vertical velocity of the molten metal is maintained such that the buoyancy of the lighter charging stock is not overcome. However, the vertical velocity of the hydrocarbon stock can be diminished by increasing the downward velocity of the molten metal. By being able to) vary the downward vertical velocity of the molten metal, the time of contact between said metal and the charging stock can be made whatever is desirable. I

This is important as the time of contact for heat transfer between the molten metal and the charging stock is not dependent on the vertical depth of the metal bath. As an illustration, suppose the vertical traverse of the charging stock thru the molten metal be only flve feet, but, due to the method of control of the downward velocity of the molten metal, the time-of contact can be made the equivalent of a stationary molten metal column several times this height.

This opposed flow of charging stock and molten metal is of considerable importance. There are continually, different exposures to new and hotter metal as the stock ascends. There is thus a much greater opportunity for rapid heat transfer' so that by the time the stock reaches the metal surface, it has been elevated to the desired temperature. The height of the metal column in chamber 28 may be of the order of flve feet for an installation capable of handling about 500 barrels of charging stock a day, but of course particular conditions may require a variation of this height.

Furthermore, the counterflow is advantageous as heretofore explained, because the' stock is introduced at a point in the metal having a lower temperature than where the stock emerged from the bath. Accordingly, a lower heat head of the column o metal fromthe top to bottom is required, as the maximum temperature of the metal need be only a little higher than the requisite maximum temperature of the stock where it leaves the bath.

The manner of injecting the stock into the column of molten metal can be best described in connection with Figs. 8, 9 and 10. A valve seat 88 is provided, whereby a radial valve opening 81 is formed. Cooperating with this opening is a valve closure 88, fastened to the end of a long valve stem 88. This valve stem is guided in a cylinder 88 that carries the seat 88, as by the aid of one or more spiders 8| fastened to the stem. A screw 82 and handle 88 are arranged to move the stem '88 longitudinally. The screw 82 ,is threaded in a socket 88 which is made part of a gland housing 88. The charging stock is supplied to cylinder 88 through the pipe 88.

The arrangement is such that the valve parts, including cylinder 88 and stem 88 can be removed. For this purpose, a cylindrical housing 881s disposed around cylinder 88, and spaced therefrom. It is fastened, as by welding, at the edge of an aperture in the body member 88. This housing 88 has a flange 81 at its free end, cooperating with flange 88 fastened to cylinder 88. Bolts 88 hold the flanges together, to position the cylinder 88 and the valve 81-88 near the inner periphery of the chamber in body member 88. Guides I88 in the form of rings can be fastened to the outside of cylinder-88 to maintain the concentric alinement during operation and during withdrawal of cylinder 88 and its associated parts.

are made for cooling the molten metal to solidify it, in the cylinder 98, whenever this withdrawal is desired. As cylinder 90 is withdrawn, valve 88 being closed and the flow of charging stock diverted to the other injection valve, the molten metal follows the end surface of member 88 toward the right, but is ultimately solidified, and

1 before it reaches the end of housing 98. This solidification can be secured by circulating cooling water through jacket IOI formed around the outer portion of housing 96. This jacket is provided by a supplemental cylinder I02 fastened as by welding, both to the exterior of body 89 and the flange 91.

An intermediate wall I03 limits the extent of the water jacket, so that only the'outer portion of cylinder 96 is cooled. The cooling water is circulated in through pipe I04 and out through pipe I05. In order to move the cylinder 90 slow- 1y from housing 98, bolts 99 can be made long so that they can serve as a restraint. One or more long bolts I06 can also be provided for forcing the flanges 91, 98 apart, if such a force is found necessary. Furthermore, the inner surface of housing 96 can be made slightly converging toward the right, whereby the solidified plug of metal will act as a stopper therein and will be able to withstand the internal pressures without being blown out of housing 96.

During the period that the valve is thus removed, water is continually circulated through the jacket It", to maintain the plug solid. When the valve structure is to be replaced, the cylinder 90 is pressed inwardly on the exposed solidifiedv metal, and is drawn inwardly by bolts 99, long bolt I06 being gradually eased off. This act pushes the solid plug into the molten metal, and when bolts 99 are tightened, the water circulation can be stopped.

During operation, the molten metal mayextend around cylinder 90 as far as flange or guide I00. To reinforce the body member 89 at the valve aperture, a ring I01 can be provided at the edge thereof. I In order to subdivide and atomize the charging stock issuing through opening 81, and also to initiate a helical motion thereof, a stream of molten metal is'directed across the opening 81 transverse to the radial direction of the liquid stock.

For-this purpose, a part of the metal passing through outlet 19 of Dump 18 (Fig. 2) is passed through a conduit I08 (Figs. 2, '7, and 8) that leads to a passage I09 (Figs. 7 and 8) arranged transverse to the nozzle opening 81. This passage is formed by a plate IIO with the outer wallof body member 69, and directs the stream of molten metal in a counterclockwise direction across opening 81, being in the same direction as the rotation of the molten metal 59.

The charging stock is thereby subdivided into small globules, and is therefore in a favorable condition for heat transfer from the molten metal. .The globules rise in helical-like path toward the top of the metal 59. Some or all of the globules may be vaporized, depending upon the rate of heat transference, as determined by temperatures, pressure, and speed of movement. These factors can be governed as previously explained. When the stock ultimately reaches the top of metal 59, it rises through the relatively narrow cylinder 14 (Figs. 3 and 4) joined to the conical body 13. The top of this cylinder is capped, and the material is instead forced out through tangential openings IIZ near the top. The arrangement of these openings is such that (Fig. 3). The molten metal injected into chamber 23 through opening 88 flows inwardly into body 89 through the inlet ports 15. This prevents the escape of the hydrocarbons through these. ports and forces them to leave contact with the molten metal within cylinder 14. The disengaging surface I II, within 14, is p rposely made small so that the leaving velocity of the hydrocarbon stock will be high. The hydrocarbon vapor and liquid. together with any entrained molten metal, blows out of cylinder 14 through openings II2, the liquid falling onto that accumulated above the molten metal, and the entrained molten metal falling onto the hydrocarbon. liquid continues on through to rejoin the metal bath beneath.

The molten metal is injected into chamber 23 non-radially or tangentially, as at 68, and maintains a high rate of rotation in the metal bath on which the liquid hydrocarbon rests. Due to friction at the metal-hydrocarbon liquid interface, the hydrocarbon liquid rotates with the metal. Thus at each revolution all portions of the outer periphery of the hydrocarbon liquid pass the active outlet port, as at I2I. As all other valves are closed, except 49, the fixed gases and hydrocarbon vapors generated in the heating process pass out of chamber 23 through valve 49 into conduit 50 communicating with conversion chamber 48. Thus these fixed gases and vapors continuously blow a portion of .the liquid hydrocarbon outwardly through port I2I and thence through conduit 50 'to chamber 48. It is seen that all portions of the hydrocarbon liquid outer periphery, in chamber 23, are being removed at each revolutiomand by this manner the accumulated liquid above the molten metal is removed before it has received sufllcient heat input to carry the conversion too far and deposit coke within chamber 23. By this manner of circulation and removal, the inner-most particle of hydrocarbon liquid ultimately reaches the outlet port III. The depth of the hydrocarbon liquid above the molten metal can'be diminished by adding additional metal to the bath. The liquid surface II3 will remain fairly constant, for should it tend to rise, the generated gases and vapors would blow more liquid hydrocarbon out through port I2I, thereby lowering it. The leaving conduit 50 is inclined and due to the high specific gravity of the molten metal, the leaving gases and vapors do not attain sufficient velocity to carry any of it over into chamber 48.

As previously explained. none of the charging stock flows downwardly in the molten metal 59,

tion with the coils '80, and being connected as shown, the molten metal passing therein is at higher absolute pressure than at its point of egress adjacent valves 41 and the molten metal 88 at said point.

To protect the inactive valve 48 and its downwardly directed intake from plugging up with an accumulation of carbon, cold high boiling point petroleum can be passed in small amounts through this inactive passage, as by a conduit 4 or II! (Fig. 3), which is valve controlled. This injectedoil reduces the temperature of the accumulated oil in the valve inlet below the desired conversion temperature and tends to scavenge said accumulation. It also materially reduces the temperature .of valve 43 parts and thereby permits a tighter valve closure.

In order to complete the disclosure, a brief statement regarding the manner in which the apparatus can be started and charged with lead, will be set forth.

First, prior to charging with lead, the furnace fire at burner 8| is started. The flame is generated slowly at first and the temperature of the metal parts,,.located in the various gas passages is'slo wiy elevated. After the metal parts of chamber 23, and associated parts. have been heated in excess of 212 -F. superheated steam, from conduit I28, is admitted to top of chamber 23 by manipulation of suitable valves.

Valves 48, 83, and 84 have been previously opened,

all other valves being closed. The admitted steam scavenges chambers 23 and 48 of air. Heating is continued and the metal parts elevated above the melting point of lead (about 617 F.). The metal to be charged into chamber 23 is melted in a separate container, not shown in the illustration, and is pumped in, as through the sloping intake H8 (Fig. 3), which has a pair of valves II! and 8. After charging the desired quantity of molten metal into chamber 23, valve III is closed. The pump I8 is then gradually accelerated, the metal being circulated by this means through tubes 60. The desired rate of metal circulation is gradually attained and at the same time the furnacefire generated by burner 8| is increased until the desired temperatures are reached. In the meanwhile superheated steam has continuously been admitted to chamber 23 as described.

Cold oil from a supply is pumped through conduit I23 into chamber 23 on top of the molten metal contained therein, steam admission being continued. When the charged oil covers outlet port I2I (Fig. 3) the steam blows the oil over into chamber 48, through valves 48 and conduit 58, as rapidly as it is pumped into chamber 23. By this means oil is accumulated in chamber 48 until the desired liquid level is obtained therein. If desired, chamber 48 can be charged separately with the desired quantity of oil by pumping it in directly without waiting for it to accumulate from chamber 23; time can be saved in this manner.

We now have the molten metal to the desired temperature, have the required depth of oil on top of the molten metal, and have chamber 48 filled to desired level. No conversion has taken place, and no carbon is depositing within the apparatus. The flow of steam is continued and the pressure "in chambers 23 and 48 is built up to about 100 pounds gauge. We are now ready to start charging oil into the bottom of chamber 23, the oil charging stock pump having been previously started and oil delivered through conduit 45 to valve 41. By this time, the flame generated by burner 8| has been placed under automatic temperature control, the method of controlling having been previously described.

The oil injection valve 41 is slowly opened,

the required heat release to elevate the charging stock to the desired temperature, the stock absorbing heatfrom the molten metal. When the injection" valve 41 is opened to the desired charging rate, the steam admission valve admit ting steam into top of chamber 23 is closed, the pumping of cold oil into top of 23 is stopped, and valve II8 (Fig. 3) is closed. The cracking unit is now in full operation, and any further manipulation required from this point on has been previously described.

During the interim the charging stock pump has circulated the stock through the heater 32 into stripper 33, and thence back through heater 32 until the accumulated oil in stripper 33 is at the desired temperature and is stripped. It is then admitted to conduit 48 through which it flows to valve 41. The flame generated by burner 38 is usually manually controlled and is adjusted to give the charging stock the desired temperature before its admission into stripper 33. All refinery apparatus, of course, is steamed out to scavenge it of oxygen before the admission' of any oil or oil vapor into said apparatus 8 being closed, steam valve in conduit I20 is opened, valve H9 in conduit 5| being closed, and valve III cracked open, the steam and residual vapors or gases escaping to the air. Next, valve II! is fully opened and the steam valve closed. The lead is charged into conduit H8 between valves Ill and H8, and valve I" almost closed. Steam is turned on again to scavenge the air, the steam air mixture escaping through the partly closed valve III. Valve H1 is closed and the steam valve closed. Valve I I8 is opened and the lead charge dropped into chamber 23. Valve H8 is closed again, steam turned in again between valves Ill and H8. Valve H3 is opened and the oil vapors blown into conduit 5|, whence they flow via conduit I' to tower 2. Valve H8 is closed and the steam hot oil, above the molten metal surface, via' valve 49 and conduit 50 into chamber 48 or 48', whichever is in service at the time. The fire generated by burner Si is put out. After the cold oil has scavenged the hot oil from chamber 34, its flow is stopped and instead a low boiling point oil, such as kerosene, is pumped into chamber 23. This scavenges the previous high boiling point cold oil, its flow is continued until all traces of the cold oil have been removed from from chamber 23, the flow of gasoline is stopped and steam admitted to said chamber. The steam scavenges the gasoline from chamber 23.

The valve 53 has the meanwhile been opened gradually to reduce the vapor pressure existing in chamber 48 and 23.

Thus the cold oil scavenged the hot oil from chamber 23, it in turn was scavenged by the kerosene, the gasoline scavenged the kerosene, and the steam scavenged the gasoline. All the hydrocarbons accumulated in chamber 48 from which they flow to the evaporator l2 through conduit I l. The flow of steam into chamber 23 is continued until all traces of the gasoline have been removed therefrom, and then the rate of steam flow is diminished if desired, while the apparatus cools down. The circulating pump 16 is now stopped.

The molten metal 59 is drawn off at the bottom of chamber 23 through the opening I22 (Fig. l) by removing a plug from the blind flange. The molten metal is conducted by means of a trough to the tank from which it was originally removed and permitted to cool, if desired. This tank is the one in which it was heated to molten condition and then pumped into chamber 23. The molten metal, if lead, should preferably be cooled below 800 F. before its removal from chamber 23, as above that temperature it oxidizes readily on contact with oxygen. The opening I22 is the low point of the molten metal circuit and all apparatus or parts containing said metal drain to said opening. The cracking apparatus "is now out of service and it is only necessary to drain and steam out the balance of the apparatus to shut down the entire refinery.

Other changes in the construction, arrangement and operation of the parts may be made without departing from the spirit of the present invention or the scope of my broader claims.

I claim:

1. The process of reforming hydrocarbons, which comprises conducting molten metal to a zone and circulating said metal in a helical-like path from a region of higher temperature downwardly to a region of lower temperature, passing charging stock into the metal at the region of lower temperature, and circulating said stock in a reverse helical-like path in contact with the metal.

2. The process of reforming hydrocarbons, which comprises conducting molten metal to a zone and circulating said metal in a helical-like path from a region of higher temperature downwardly to a region of lower temperature, passing charging stock into the metal at the region of lower temperature, circulating said stock in a reverse helical-like path in contact with the metal, and depositing the liquid resulting from the stock, on the upper surface of the molten metal.

3. The process of reforming hydrocarbons which comprises moving molten metal in a helical-like path, downwardly from a region of higher temperature to a region of lower temperature, and injecting charging stock substantially tangentially into the helical-like path at the region of lower temperature.

4. The process of reforming hydrocarbons, which comprises passing liquid stock through molten metal, some of the liquid being thereby deposited as a layer over the metal, moving the top layer of the molten metal-in a circular course, thereby imparting a similar motion to the layer of liquid, and passing at least a part of the liquid from adjacent the outer periphery of the layer, through a discharge aperture below the level of the liquid.

5. The process of reforming hydrocarbons by passing them through a bath of molten metal, which comprises introducing molten metal into the bath adjacent the top level thereof and in a substantially tangential direction to cause the top portion of the metal to move in a circular motion, passing liquid stock into the bath, to cause some-of the liquid resulting from the stock to be deposited over the metal, and to be moved in a circular path thereby, and passing at least some of the liquid through a conduit opening below the level of the liquid.

6. In a system of the character described, a container, molten metal in the container, means for circulating said metal in the container in a helical-like current from a region of higher temperature to a region of lower temperature, means for introducing charging stock into the metal at a region of lower temperature of the metal, and means for circulating said stock in a helical-like current reverse to the current in the metal.

'7. In a system of the character described, a container, molten metal in the container, means forming one or more substantially tangential openingsinto the container for conducting molten metal thereto in a helical-like current, means forming a discharge path for the metal from the container, means forming an inlet for charging stock remote from said openings, and means for creating a current in the charging stock reverse to the current in the metal.

8. In a system'of the character described, a container, means forming an annular space around the top portion of the container, molten metal in the space and in the container, and means forming substantially tangential passageways from the annular space into the top portion of the container.

9. In a system of the character described, a container, means forming an annular space around the top portion of the container, molten metal in the space and in the container, means forming substantially tangential passageways from the annular space into the top portion of the container, and an injection nozzle for charging stock, adjacent the lower end of the container.

10. The method of cracking hydrocarbons that includes, passing a stream of molten metal in a circuitous path of flow through a heating zone and then through a vertically extending cracking zone, moving the metal stream continuously by a pump operating to project the molten metal through the cracking zone in a continuous, rapidly moving stream, passing a stream of hydrocarbons through a preheating zone and thence into and in direct contact with the molten metal circuitous path of flow through a heating zone" and then through a vertically extending cracking zone, moving the metal stream continuously by a pump operating to project the molten metal through the cracking zone in a continuous, rapidly moving stream, passing a stream of hydrocarbons into and in direct contact with the molten metal stream in said cracking zone, removing from the latter the vaporized hydrocarbons, continuously removing unvaporized liquid residuum in a stream flowing laterally from the top surface of the metal stream in said cracking zone to a conversion zone in vapor communication with the cracking zone, maintaining the residuum within said conversion chamber in an accumulated body for a predetermined period of time and under a pressure substantially above atmospheric, and continuously removing the residuum from said conversion zone.

12. The method of cracking hydrocarbons that includes, passing a continuously flowing stream of molten metal in a vertical path through a cracking zone, passing a stream of hydrocarbons into said zone and in direct contact with the molten metal stream, a portion of said hydrocarbons being vaporized and all the hydrocarbons passing upwardly through the metal in the cracking zone, there being a liquid residue left on the top surface of said metal stream, continuously removing said liquid residue from the cracking zone to a conversion zone and maintaining the residue in an accumulated body within the last mentioned zone for a predetermined period of time, continuously removing residue from the conver-- sion zone and the vapors from said cracking zone, vaporizing the residue and combining the vapors with those removed from the cracking zone, and fractionating the combined vapors.

13. The method of cracking hydrocarbons that includes, passing a stream of molten metal in a circuitous path of flow through a heating zone and then downwardly through an elongated cracking zone, continuously injecting into and passing upwardly through said cracking zone a stream of hydrocarbons so that the hydrocarbons remain in contact with the molten metal only a short interval of time, cracking the hydrocarbons in said cracking zone to form cracked vapors and carbon residue, continuously removing the vapors and carbon from the surface of the metal in the cracking zone, and regulating'the downward velocity of the molten metal in said cracking zone to regulate the upward velocity of the hydrocarbons and accordingly their time of contact with the molten metal independently of the rate at which hydrocarbons are injected into the metal stantially vaporizing temperature, cracking the hydrocarbons in said cracking zone to form cracked vapors and carbon residue, continuously removing the vapors and carbon from the surface of the metal in the cracking zone, and regulating the downward velocity of the molten metal in said cracking zone to regulate the upward velocity or the hydrocarbons and accordingly their time of contact with the molten metal, independently of the rate at which hydrocarbons are injected into the metal stream, and independently of temperature diiferences in said metal stream.

15. The method of cracking hydrocarbons that includes, passing a continuously flowing stream of molten metal in a vertical path through a cracking zone, passing a stream of hydrocarbons through a preheating zone and thence into said cracking zone in direct contact with the molten metal stream, a portion of said hydrocarbons being vaporized in the cracking zone and all the hydrocarbons introduced thereto passing upwardly through the metal stream, there being a liquid residue left on the top surface of said metal stream, continuously removing said liquid residue from the cracking zone to a conversion zone in vapor communication therewith, maintaining the residue in an accumulated body within the last mentioned zone for a predetermined period of time, and continuously and separately removing the residue and vapors from the conversion zone.

WAYNE A. S. HARMON.

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