US2347371A - Processing of flowing fluids - Google Patents

Description

PROCESSING oF 'FLowING FLUIDS y Filed sept. so, 193s IllllllflIHPlllluHHHllll.. I l I |l llnlrlllrlhnnun l .Nunnnlf l l L @ca/e Patented Apr. 25, 1944 PROCESSING 0F FLOWING FLUIDS Robert. L. Rude, Toronto, Ontario, Canada, as-

signor to The British American Gil` Company, Ltd., Toronto, Ontario, Canada, a corporation of Canada Application September 30, 1938, Serial No. 232,563

(Cl. ISS- 47) 14 Claims.

The present'invention is a continuation in part oi" my copending United States applications Serial No. 700,485, filed December 1, 1933, and No. 152,860-, led July 9, 1937, (now Patent No. 2,217,- 634) and relates generally to the production of hydrocarbons suitable for motor fuel, either by pyrolitic cracking, catalytic cracking, or thermal polymerization.

More particularly, the present invention relates` to the cracking of petroleum and to a method and apparatus for controlling the same.

As is well known in the art, a preliminary treatment commonly called viscosity breaking of the raw oil charging stock is desirable in order to produce the maximum ultimate yield of motor l fuel. Due to the thermal instability of raw oil charging stocks, diiculty is encountered in carrying out this preliminary operation in conventionally red furnaces. It is therefore proposed,

in accordance with one aspect of the present invention, that the heat necessary to bring about the endothermic reaction involved in viscosity breaking be supplied by the heatV in the synthetic crude produced in a secondary cracking operation. It is furthermore proposed to control this hydrocarbons of wide boiling range in a single cracking coil or unit the time and temperature of treatment is optimum only for a limited portion of the stock charged to that coil. The heavier portions of the stockl are therefore overcracked,Y whereas certain of the lighter ccmponents are undercracked. This results in the production of excessive quantities of residuum, high gas losses, and also in excessive fuel and energy costs due to recycling stocks at inadequate crac-lring conditions.. For these reasons, in accordance with a furtherv aspect of the present invention, it is proposed to treat selected charging stocks in a multi-coil system, the individual coils being regulated at conditions more representative of optimum time-temperature relationships for the selected stocks for the production of motor fuel of a higher octane rating, with the maximum yieldr and with a minimum loss result'mg from excessive productionv of uncondensible gases and heavy cracked residuum. Accordingly, in accordance with the preferred embodiment above mentioned, the primary conversion or viscosity break-` ing of the virgin stock is for the essential purpose of breaking the raw oil down into boiling ranges that are more suitable for higher rates of conversion, particularly where the raw oil charge constitutes highly parainic residue from crude distillation.

In the copending application Serial No. 152,860 (now Patent No. 2,217,634), it is pointed out that the in situ density of a flowing fluid undergoing a condition change may be employed as a means of obtaining an indication of the time of treatment and the degree of conversion or yield per pass eiected during said change. It is also pointed out that when a given cracking coil is operated with a given charging stock at a sub' stantially constant. yield per pass, the in situ density of the synthetic crude at the outlet of said furnace may be used as an indication or reflection of the total heat of the fluid, due to the fact thatr under these conditions the in situ density is responsive not only to sensible heat changes, but. also to latent heat changes in the fluid.

From a study of cracking in coils equipped with the instrumentalities described in the aforesaid applications, it has been found that a given charging stock may be cracked at a substantially constant desired yield per pass over a certain range of time-temperature conditions. Under these circumstances, when the yield per pass is maintained constant, variations in the time and temperature of treatment reflect themselves in a variation in the outlet density. Inasmuch, however, as the outlet in situdensity under these conditions reflects the total heat of the synthetic crude, it will be apparent that a given charging stock may be converted at a given yield per pass andA yet the total heat in the synthetic crude resulting from such treatment may be changed within, a certain range by readjustment of the time-temperature conditions. It is therefore proposed, in accordance with another aspect of the present invention, to maintain the cracking of the selected charging stocks at a substantially constant chosen value; likewise, to maintain the primary conversion or viscosity breaking operation at a substantially constant chosen degree of conversion; to accomplish the maintenance of the chosen per cent conversion in the viscosity breaking operation by regulating the total heat in the fluid during this operation; and to regulate the total heatv in turn by varying the time-temperature conditions in the cracking operation, While at the same time maintaining a substantially constant yield per pass in the cracking step.

It has also been found, when cracking stocks of low asphaltic residue content (as determined, for example, by the Conradson residue test), that the range of time-temperature conditions which may be used to crack at a chosen yield per pass is considerably wider than the range when cracking stocks of higher asphaltic residue content at a chosen yield per pass. In other words, the total heat in the synthetic crudes resulting from the treatment of stocks of low asphaltic residue content may be varied within considerably wider limits while operating at the same yield per pass, than stocks of higher asphaltic residue content. Accordingly, the former type of stock is more exible and affords a more convenient means for regulating the heat required in the viscosity breaking operation. In the preferred embodiment of the present invention, the viscosity breaking operation or preliminary conversion is therefore maintained at a substantially constant chosen rate, by controlling the back pressure valve on the synthetic crude line from the furnace wherein stocks of greater flexibility are being treated at a substantially constant yield per pass.

It is a further object of the present invention to provide apparatus for carrying out the foregoing processes and for effecting control thereof, either manually or automatically.

One form of apparatus in accordance with the present invention comprises a cracking zone, the transfer line of which leads to a preliminary conversion or viscosity breaking zone. The virgin stock is charged into the system between the outlet of the cracking zone and the inlet of the primary conversion zone, preferably just ahead of the back pressure valve of the cracking unit. The introduction of the virgin raw oil charge at this point brings about a thorough mixing, due to the turbulence and atomization caused by the restriction of the back pressure valve.

'I'he primary conversion Zone is provided with flow-responsive and temperature-responsive elements located therein, as disclosed in my copending applications and/or patent above referred to. From the interrelation of these elements, Variations in the per cent conversion effected in the primary zone may be made manifest. The cracking zone is also provided with flow-responsive and temperature-responsive elements located therein, the manifestations of these instrumentalities likewise affording a basis for the control of the cracking operation therein.

In order to maintain a chosen per cent conversion in the primary conversion Zone, the back pressure valve in the transfer line from the cracking zone is controlled in accordance with the indications of the temperature-responsive and flow-responsive elements which are reflective of the degree of conversion in the primary zone. As the back pressure on the cracking zone is altered, the time of treatment in the cracking zone will likewise be affected. Therefore, to maintain the yield per pass in the cracking zone at the chosen value, the conditions must be altered to give the proper time-temperature relationship necessary to crack to the desired yield per pass. The manifestations of the flow-responsive and temperature-responsive elements in the cracking zone afford a satisfactory basis for the maintenance of an optimum yield per pass.

With a system of the character described, it will be seen that the heat necessary to effect the primary conversion of the virgin raw oil charge is supplied by the heat of the synthetic crude. The percent conversion in the primary zone is controlled or maintained substantially constant by regulating the total heat of the fluid therein. The total heat in turn is controlled, at least in part, by regulating the back pressure valve on the synthetic crude line and at the same time readjusting the conditions in the cracking Zone so that the proper time-temperature relationship obtains therein for maintaining the yield per pass in the cracking operation at a substantially constant value.

In order more clearly to describe the present invention, an illustrative embodiment will now be described with reference to the single gure of the accompanying drawing, which is a schematic new sheet of a commercial cracking system in accordance with my invention. -It should be clearly understood, however, that this is done solely by way of example, and the invention is not to be considered as limited to the preferred embodiment hereinafter described. Many variations in the preferred embodiment will be immediately apparent to those skilled in the art,

and these are included within the scope of the invention.

Referring now particularly to the drawing, the virgin raw oil charging stock, designated by the letter A, is accumulated in storage tank I. This virgin charging stock is impelled by constant pressure regulated pump 2 through conduit 3, and selectively introduced through the branched charging lines 3a, 3b, and 3c, into synthetic Crude transfer lines 4, 5, and 6, the rate of charge into each transfer line being regulated by ow control instrumentalities, l, 8, and 9, which actuate valves I, I I, and I2. The setting of ow control instrumentalities l, 8, and 9 may be dictated by the temperatures prevailing in the transfer lines just ahead of the back pressure valves 24, 36, and 48.

Charging stock B, comprising relatively heavy hydrocarbon fractions, as hereinafter more fully explained, is accumulated in tank I3, and is forced by pump I4 through conduit 55 to furnace X. The rate of charge is controlled by iiow control mechanism I 5, the fluid entering the furnace through convection section I 'I and passing thence to radiant or sensible heat section I8, wherein sufficient heat is imparted to bring the charging stock to substantially cracking conditions. The charging stock at cracking temperature then leaves the sensible heat section I8 through conduit I9, flows through density-responsive element 2! and enters the conversion section 2l. In this section, the time-temperature relationship is controlled, as hereinafter explained, in order to effect conversion of the particular charging stock B at the empirically determined optimum yield per pass. The synthetic crude resulting from this conversion is conducted through transfer line 22, and the density responsive element 23 located therein, to back pressure control valve 24.

In the preferred embodiment disclosed herein, the charging stock B is composed of heavy hydrocarbon fractions that usually decompose to form coke and uncondensible gases unless moderately treated. Accordingly, this stock is treated at time-temperature conditions adapted to crack them into fractions of lower boiling range for the purpose of forming charging stocks suitable for higher conversion rates. To take advantage of the inhibiting effect of pressure on the formation of gas and coke, this particular cycle is operated at a predetermined controlled substantially constant back pressure, which results in a long-time, low-temperature relationship that has been empirically arrived at as the optimum for conversion of this particular stock.

Charging stock C, comprising a somewhat lower boiling fraction than stock B, is accumulated in the base of bubble tower 25, and pumped by pump 26 through conduit 21 and flow-controlling mechanism 2B into the convection heating section 29 of furnace Y, and thence to sensible heat section 30, wherein the stock is raised to substantially cracking temperatures. The stock is then conducted through conduit 3l, wherein density-responsive element 32 is installed, into conversion section 33. In conversion section 33, the heat required to effect conversion at the desired rate is supplied. The synthetic crude resulting from this conversion is conducted through transfer line 35 in which density-responsive element 34 is installed at the outlet of the furnace, to back pressure valve 36.

Due to the preliminary fractionation of the vapors evolved from synthetic crudes discharged into vapor separator 59, the condensates C accumulating in the base of bubble tower 25 are of such a character that they may be treated at a higher conversion rate than the stock previouslyv referred to herein as charging stock B. The primary purpose of the cracking cycle performed in furnace Y is for the purpose of manufacturing gasoline boiling hydrocarbons at the optimum time-temperature relationship which` may be empirically arrived at for the particular stock treated. In general, the time of treatment in furnace 'Y is somewhat shorter and the temperature somewhat higher than the corresponding conditions existing in furnace X.

Charging stock D, comprising a fraction of still lower boiling range, is accumulated in the base of side stripper 31 and is pumped by pump 38; into conduit S9, the rate of charge being: governed by valve 92 which is regulated by flowcontrol mechanism lill installed on the input vside of furnace Z. (Similar means may be employed to control the charging rates of stocks B and C if desired.) The stock then enters the convection section of furnace Z, whence it is con-- ducted to sensible heat section 42. In this section the hydrocarbon is brought to substantially cracking temperature, before passing through conduit 43, in which density-responsive element M is installed, into the conversion section 45, where heat is absorbed necessary to effect the desired rate or degree of conversion at the particular time-temperature relationship which may be empirically arrived at as optimum for this charging stock. The synthetic crude resulting from this conversion is conducted through transfer line 46, in which density-responsive element 4.1' is installed, to back pressure control valve 48.

Charging stock D has not only been subjected to the preliminary stages of fractionation in vapor separator 5:1, but has been further fractionated through bubble trays in tower 25, and has characteristics which make it suitablev for treatment at a considerable range of varying time-temperature relationships, at a predetermined` optimum yield per pass. It is therefore a flexible stock and, together with the syntheticA crude from furnace Y, serves as a suitable means of controlling the heating required in later parts of the system, as hereinafter explained.

The synthetic crudes produced in furnaces X, Y, and Z, are mixed with the virgin raw oil charge, which enters the system ahead of the back pressure control valves 24, 36, and 48, through the branched raw oil charge lines 3a., 3b, and 3c, which discharge into the transfer lines 4., 5, and 6, respectively, from the individual furnaces. These mixtures of raw oil and the individual synthetic crudes flow into the single conduit 49 and the composite mixture is then conducted through density-responsive element 50 into conversion section W.

In the preferred embodiment of the present invention, as shown in the drawing, the primary conversion zone W comprises a heat insulated coil which serves the function of a conversion section for the virgin raw oil in the presence of the combined synthetic crudes. In the drawing, no other source of heat is indicated for effecting this primary conversion step other than the heat contained in the synthetic crudes leaving coils X, Y, and Z. It is, however, within the comprehension of this invention to provide separate heating means for the coil W, if desired. It is to be understood that such heating means may be a separately fired furnace; or the conversion section W may be located in a waste heat section of one or a combination of several furnaces; or any other suitable means may be used to impart additional heat.

From conversion section W the resulting uid is conducted by conduit 52, through densityresponsive element 5|, and thence through back pressure regulating means 53, into vapor separator 59.

The composite synthetic crudes entering vapor separator 59 are separated into vapor and liquid, the proportions of each depending upon the temperature and pressure to which they are subjected in this portion of the apparatus. The vapors ascend through suitable fractionating and heat exchange means, and the lighter portions, after being subjected to primary distillation in the vapor separator, are conducted to bubble tower 25 through conduit 59. The condensate resulting from the iirst stage of fractionation is conducted as a side cut through conduit 6| into accumulator I3, and serves as charging stock B for furnace X.

The liquid or nonvaporized portions accumulating in the base of vapor separator 59 are conducted through conduit 52, liquidlevel control means 53 regulating their discharge, into a suitable atmospheric or vacuum distillation apparatus 54. The residuum resulting from the flashing operation is accumulated in the base of the tower t, and is conducted through conduit 69 to pump lil, the pump being regulated by suitable liquid level means l, and the product is discharged to storage through suitable cooling means (not shown), if desired. From the flashing tower S4, the overhead vapors are conducted through heat exchange means 55, thence through conduit $5 to condenser 6l, into accumulator (i8,A

which accumulator is connected to suitable venting or vacuum-creating equipment (not shown), as the case may be. The condensed overhead vapors accumulated in vessel 98 are designated as stock E. This stock is conducted through conduct 'i2 to pump 13, which is regulated to discharge at a constant pressure by regulator lll, and passes through valve l5, which is actuated by liquid level means 16. Stock E then enters vapor separator 59 above the liquid level draw-off of stock B, thus providing means for returning a portion of the unvaporized liquid that had previously accumulated in the base of vapor separator 59. It may also be found desirable to introduce a portion of stock E into condut 52 through valve 11, in case it is found that the combined synthetic crudes conducted from the primary conversion section W are entering vapor separator 53 at too high a temperature. rIhe lighter vapors and uncondensible gas entering fractionating tower 25 from the vapor separator 56 through conduit 60 are subjected to suitable fractionating means, the heavier condensates resulting from this fractionation (indicated as stock C) being accumulated in the base of tower 25. The lighter condensates are drawn off as a side cut through conduit 18, into side stripper 3l, and are designated as stock D.

The uncondensible gas and gasoline boiling fractions are taken overhead through conduit 'P9 and are condensed and cooled in suitable means 80 before entering gas separator 6i, in which the noncondensible gas and liquid are separated. The noncondensible gas is conducted from the system through conduit 82 and back pressure regulating means 83, and may be passed, if desired, to an absorption or treating system (not shown) The liquids accumulating in the base of gas separator 3l, designated as stock F, may be conducted through conduit 64, through suitable liquid level control means S5, to storage or any desired apparatus for treating or stabilization (not shown). F may be used for the purpose of controlling the temperature at the top of fractionating tower 25, entering the tower through conduit 86, and pumped by pump 81, the rate of reflux being controlled by any suitable temperature control means (not shown) 'Ihe control of the system described generally above is preferably accomplished automatically by means of instrumentalities which correlate the manifestations of the various low-responsive instrumentalities. One forni of correlating means suitable for this purpose is more particularly described and claimed in my copending United States application Serial No. 152,860 (now Patent No. 2,217,634), to which reference may be had for a more detailed description. Manual control of the system, however, is within contemplation of the present invention, such manual control being effected in a manner similar to that also set forth in my copending United States application Serial No. 152,860 (now Patent No. 2,217,634). Moreover, in lieu of the automatic control system herein diagrammatically illustrated, other automatic regulating means may be used, such for example as those described and claimed in the copending United States application of Junkins, Serial No. 152,858, led July 9, 1937 (now Patent No. 2,217,637), and in the copending United States applications of Luhrs, Serial Nos. 152,855, 152,856 (now Patent No. 2,217,638), and 152,857 (now Patent No. 2,217,- 639), led July 9, 1937, and Serial No. 193,333, led March 1, 1933 (now Patent No. 2,217,642). Other instrumentalities which may be used are described in the copending United States application of Rude, Serial No. 152,859 (now Patent No. 2,217,643), filed July 9, 1937.

In general, the control system diagrammatically illustrated in the drawing is based upon the correlation of the flow-responsive instru- 1f desired, a portion of stock mentalities to obtain a value reflective of the in situ density of the flowing huid while it is undergoing a condition change.

conversion zones, a representation of the time of detention therein is obtained by correlation with the input weight-rate and the total volume The mean temperatureI the yield per pass or per cent conversion effectedy inthe treating zone in question.

In describing the control of the preferred em bodiment of the present invention as representedin the drawing, it will be convenient to consider` first the regulating means for the primary conversion section W and thereafter to describe the control means for the individual furnaces X, Y, and Z;

Referring now to the primary conversion zone W, the object to be accomplished in regulating this section is to maintain the yield per pass or per cent conversion therein at a substantially constant optimum value which may be empirically determined. To this end, the total weightrate of input of iiuid into the primary conversion zone is determined. The total input weight-rate into this section is, of course, the sum of input Weight-rates into the furnaces X, Y, and Z, plus the input weight-rates of the virgin raw oil charging stock through the branched raw oil charging lines 3a, 3b, and 3c, which join the synthetic crude transfer lines 4, 5, and 6, respectively. The manifestations of each flow-responsive instrumentality, I6, 28, 40, 1, 6, and 9 (which may, if desired, be charge meters of the xed orifice type) are transmitted to the receiving and con' trolling center 56 where they are totalized through any suitable totalizing means as will be understood by those skilled in the art.

Such totalization will involve the addition 0f the indicated values and may be accomplished' through the use of straight line cams situated like those illustrated in my Patent No. 2,217,634; a general discussion of totalizing through the use of Selsyns appeared in the General Electric Review, September, 1930 issue, pages 500-504, inclusive. Moreover, reference may be had to Fig.

17 of my Patent No. 2,217,634 in which is illus-4 trated a similar receiving and controlling element indicated as a totalizer and which is used rial No. 152,860, now Patent No. 2,217,634, and in' the above mentioned patents of Junkins Iandl The indications of the inlet and outlet- Luhrs. now-responsive instrumentalities and 5| (which may be ow meters connected to adjustable orifices as indicated) are likewise transmit-'-y ted by similar means to the receiving and controlling center, wherein these indications are correlated with the mean temperature of the uid Within the conversion zone to obtain a continuous indication reiiective of the yield per pass or per cent conversion within the primary convex- From an indi--v cation of the mean in-situ density in the variousl sion zone, this being indicated by the position of the arm l, With reference to a scale 57a. The relative position of the indicator arm 51 shifts the pilot stem 53 to reset back pressure control mechanism 58a and 58h, which selectively controls back pressure control valve 36, and after the latter valve has reached a predetermined maximum position, further control, if necessary, is effected by readjustment of back pressure control valve 48. It Will thus be seen that any variation from a predetermined optimum yield per pass or per cent conversion in the primary conversion Zone W Will cause a selective readjustment of the back pressure valves in the transfer lines from furnaces Y and Z.

The resetting of the back pressure valves of the furnaces Y and Z will necessitate the readjustment of the conditions in these furnaces, if the optimum yield per pass therethrough is to be maintained substantially constant at the ernpirically determined optimum value. Without such readjustment, as the back pressure on the furnace is varied, the outlet density, the time of treatment, and the yield per pass will all be altered. Accordingly, to prevent variation in yield per pass, the control valves of the fuel supply lines in the respective conversion sections are reset as hereinafter more fully described.

In the case of furnace Z, the manifestations of the flow-responsive elements 46, 44, and il4 (which may be any of the type described in my copending United States application Serial No. 152,860 (now Patent No. 2,217,634 are transmitted to the receiving and controlling center.

In the receiving and controlling center the indications of flow-responsive elements fl and 44 are interrelated by suitable means (not shown) to obtain a continuous indication of the in situ density of the fluid at the outlet of the sensible heat section 42, from the relative position Yof the arm 88a, with reference to scale 88h. The transmitting elements and the receiving and controlling center 8B may comprise, for example, the instrumentality described more particularly in the various views (for instance, Figs. 6, 7 and 17) of my Patent No. 2,217,634, it being understood that the values transmitted to the controlling center are combined in the manner indicated in said figures to eventuate the density and yield per pass values, which latter are utilized as described to 'control the heat input into sections 42 and 45.

Such instrumentality `is `also described in Junkins, et al. Patent No. 2,315,527.

Due to the fact that the in situ density yof the -uid serves asa measure of the total heat of the fluid at any given point, the continuous indication of the in situ density at this point may be used, if desired, to control the supply of fuel to the sensible heat section 42 by regulating burner control valve 89 through the agency of a suitable pilot Valve 33C, the stem of Which is positioned by the arm 88a which continuously reflects the density of the fluid at the outlet of the sensible heat section. However, inasmuch as substantially all the heat imparted to the fluid in sensible heat section 42 reflects itself as a temperature rise, temperature-responsive means 9B .may Ibe employed if desired in lieu of the in situ density-responsive instrument, as a Lmeans for controlling fuel supply valve 86. The control of the heat supplied to sensible heat section (i2 may therefore be accomplished optionally `either through the use of the in situ densityor l:temperature-responsive means .located iat the foirtlet from this section.

The control of the heat supply in the conversion section 45 is accomplished by utilizing the manifestations of the flow-responsive instrumentalities. The indications of the flow-responsive instrumentalities 4D, 44 and 41 are transmitted to the receiving and controlling center 88. The indications of temperature-responsive means and 96a at the inlet and outlet of the conversion section 5, are also transmitted to the receiving and controlling center. At this center, `the indications of the flow-responsive and temperatureresponsive instrumentalities are interrelated by suitable means as described in the above-identified applications, patents and publications to refleet the time-temperature relationship or the yield per pass through furnace Z, or both. The indication of the yield per pass provided by the relative position of arm 88d with reference to scale 86e is employed as a means for controlling the heat supply in the conversion section 4.5, this being accomplished by the positioning of the stem of a suitable pilot valve 86j from the yield-,perpass indicating arm 88d, the pilot valve regulating the burner supply control valve 9 I.

Fig. 7 of my Patent No. 2,217,634 illustrates one system of operating heat control devices in response to the in situ density at certain orifices While Fig. 6 illustrates the manner in Which elements optionally responsive to either density .or yield per pass are moved to actua-te certain heat controls. In the latter figure it will be noted that the heat control of the right-hand heating section is capable of optional actuation from either density or yield per pass land accordingly reference to this figure will indicate to those skilled in the art the manner in which the heat input -to the various furnace sections described in the instant application may be controlled from either of the aforesaid values. With this prior showing in mind, the control of heat input at 91 from yield per pass and the control o-f the heat input at 8% from density may `be clearly understood.

Thus the instrumentalities for effecting complete control of furnace Z may take the form .of those described with greater particularity `in connection with the above enumerated figures of Ymy copending Patent No. 2,217,634. The latter ,is therefore made a part hereof :by reference for a more detailed description vof operations outlined herein.

Furnaces X and Y are likewise lpro-vided with the control mechanisms similar to those -briey described above With reference to .furnaceZ vIn the drawing, however, the various control instr-umentalities for furnaces X and Y are not indicated, in order to facilitate an understanding of the process as a Whole. n'

As previously mentioned, the selective readjustment of the back pressure valves 36 and 48 on the synthetic crude transfer lines from furnaces Y and Z aifects the .density at the `outlet of the respective furnaces. At the same time, the-con.- trol devices for the individual furnaces readjusts the time-temperature conditions .in the Vtwo furnaces to maintain the yield per pass vtherethrough at the optimum. The result of this readjustment fof, the time-temperature conditions prevailing -inffurnaoes Y and Z when the back pressure valves are selectively readjusted is that the heat Vin :thesyntheticcrudes iis changed, Without, however, `a material` deviation 5in the yield per pass through `the individual -furnaces from a pre-established; optimum value.. Since, however, the total .heat ofthe synthetic `crueles is changed, the total heat in the primary conversion section W is likewise changed. It will therefore be seen that the control system contemplated by the present invention utilizes the heat in the synthetic crudes coming from the various furnaces to perform useful work-namely, the heat -of reaction required for primary conversion of In a similar manner, the back pressure valve 53 `may be reset to maintain a different selected constant pressure at the outlet of the primary conversion zone W. At the same time, the control :center S will reset the back pressure valves on furnaces, to maintain a substantially constant lper cent conversion in the conversion zone W.

The controls on the furnaces in turn readjust the fuel supply thereto. Hence it will be seen that by resetting the valve 53, the total heat in the combined synthetic crudes entering the vapor separator may be controlled or regulated, and this e`in turn provides a convenient means for controlling the degree of distillation in the vapor separator and the reduction of residuum therein.

In the preferred embodiment of the invention the system is completely automatic; but, as hereyinbefore mentioned, the control may be effected manually. Thus, the flow-responsive elements illustrated in the single figure of the drawing -may be correlated or interrelated, either by sim- -ple computations or by means of mathematical devices such as graphs and the like, to arrive at the desired value or values which serve as a basis for regulating the various factors affecting yield per-pass. The automatic controlling system di- Vagrammatically illustrated, however, affords a much more uniform regulation of the system and constitutes the preferred embodiment of the present invention.

It will furthermore be apparent that many variations in detail may be made without departing from the spiritand scope of the invention. Thus,

`for example, while furnaces having separately fired sensible heat and conversion sections have been diagrammatically represented in the single fl'gure of the drawing, any other type of fur- `naces may be substituted if desired, such as the type illustrated in the aforementioned copending -'United States application Serial No. 152,860 (now Patent No. 2,217,634), for example. While the -invention has been illustrated with three furnaces, any number may be employed as desired, from one up. Y

It will moreover be apparent that other types of How-responsive elements other than those diagrammatically illustrated may be substituted without departing from the spirit and scope of the invention. Thus, volumetric flow meters,

Pitot tubes, Thomas meters, and the like may be 'employed if desired.

- Again, in the preferred embodiment illustrated in the drawing, the back pressure in furnace X is maintained substantially constant, the control of the available heat in the primary conversion zone being preferably effected by selectively regulating the back pressure valves on furnaces Z and Y,-wherein the more flexible stocks are being v"treated, But, while it is preferred to use the more flexible stock as the primary heatcontrol medium, and thereafter if necessary to use the somewhat less eXible stock as a reserve or secondary control medium, the order in which the valves are regulated may be changed as desired. Thus, in certain installations the operator may prefer to operate the valves'on all the furnaces either conjointly or in any desired order. Such modifications are included within the contemplation of the present invention.

It should furthermore'be understood that although the present invention Vhas been illustrated with particular reference to the treatment of hydrocarbons, certain aspects of the process may be utilized with advantage in processing other fluids wherein similar problems are encountered. The application of the principles herein described to flowing fluids other than petroleum is therefore within the purview of the present invention.

The term in situ density includes not only the absolute value of the density, but any function of density or any manifestation which changes uniformly with the density. For control purposes, it is not essential to ascertain the absolute value of density and the term is employed solely as a matter of convenience. The instrumentalities which maybe employed include those which are responsive to density changes, regardless of whether or not such instrumentalities indicate or record the absolute value of the in situ density.

In addition to the foregoing variations in detail, many others will be readily apparent to any one skilled in the art. I therefore intend to be restricted only in accordance with the following patent claims.

I claim:

l. A process for the preliminary conversion or viscosity breaking of a selected virgin raw oil charging stock which comprises passing said raw oil into a viscosity breaking zone, obtaining an indication of the weight-rate of input thereof, obtaining an indication of the mean in situ density and the temperature of the iiuid at a selected point within said zone, correlating the input rate and said temperature and density indications to provide an indication 0f the per cent conversion effected in said zone, and regulating the total heat of the fluid in said zone in accordance with the per cent conversion effected therein whereby to maintain said per cent conversion at a substantially constant selected value.

2. A process for the preliminary conversion or viscosity breaking of a selected virgin raw oil charging stock which comprises passing said raw oil into a viscosity breaking zone, maintaining a flow-responsive element at the inlet and outlet of said zone, determining the temperature of the fluid at a selected point within said zone, correlating the manifestations of said flow-responsive elements to provide an indication of the mean in situ density of the uid in said zone, utilizing said mean density indication and said temperature indication to obtain an indication of the per cent conversion effected in said zone.

and regulating the total heat of the fluidin' said zone in accordance with said per cent conversion indication, whereby to maintain said per cent conversion at a substantially constant selected value.

3. A system for the preliminary conversion or viscosity breaking of a selected virgin raw oil charging stock, which comprises in combination a viscosity breaking reaction zone, means for passing a selected virgin raw oil into said zone and for conducting the treated oil therefrom, means including flow-responsive and temperature-responsive elements located within said zone for continuously indicating variations'inthe per cent conversion of the virgin stock therein, and means associated with said per cent conversion-indicating means for regulating the total heat of the :fluid in said zone, whereby to maintain the per cent conversion at a substantially constant selected value.

4. A system for the preliminary conversion or viscosity breaking of a selected virgin raw cil charging stock which comprises in combination a reaction zone for effecting viscosity breaking, means for passing a selected Virgin charging stock into said Zone and for conducting the conversion product therefrom, now-responsive means located at the inlet and outlet of said Zone, temperatureresponsive means for determining the temperature of the fluid at a selected point within said Zone, means for correlating the 'manifestations of said flow-responsive element and said temperature-responsive element to continuously indicate variations in the per cent conversion effected in said zone, and means associated with said per cent conversion-indicating means for regulating the total heat of the uid in said Zone, whereby to maintain the per cent conversion at a substantially constant selected value.

5. A system for cracking petroleum hydrocarbons which comprises a primary conversion zone, a plurality of cracking zones, means for conducting the synthetic crudes from the cracking zones to the primary conversion zone, means for introducing the virgin charging stock into the system at a point between the outlet of the cracking zones and the inlet of the primary conversion Zone, means for fractionating the eilluent of the primary conversion Zone into a plurality of individual fractions, means responsive to the per cent con- Version in the primary zone controlling the back pressure of at least one of said cracking zones for maintaining the per Cent conversion in the primary Zone at a substantially constant chosen value, and means responsive to the yield per pass through one of said cracking zones controlling the heat input thereinto for maintaining the yield per pass therethrough at a substantially constant chosen value.

6. A system for cracking petroleum hydrocarbons which comprises in combination a primary conversion Zone, a cracking zone, means for condusting the synthetic crude from the cracking zone to said primary zone, means for introducing the virgin charging stock into the system between the outlet of the cracking zone and the inletI of the primary zone, means including ow-responsive and temperature-responsive elements located in said primary conversion zone for continuously indicating variations in the per cent conversion therein, means associated with said per cent conversion-indicating means for regulating the total heat of the fluid in said primary zone, whereby to maintain the per cent conversion therein ai; a substantially constant selected value, means including flow-responsive and temperature-responsive elements located in said cracking zone for continuously indicating variations in yield per pass, means associated with said yieid-per-passindicating means for regulating the heat absorbed by the fluid in said cracking zone, whereby to maintain the yield per pass therethrough at a substantially constant selected value.

'7. The system of claim 6 wherein said means for controlling the total heat oi the fluid in said primary conversion Zone includes means for controlling the back pressure in said cracking zone in accordance with variations in said per cent conversion-indicating means of said primary conversion zone.

8. A system for cracking petroleum hydrocarbons which comprises in combination a primary conversion zone, a plurality of separate cracking zones, means for conducting the synthetic crudes from the individual cracking zones to said primary Zone, means for introducing the virgin charging stock into at least one of the transfer lines from said cracking zones to said primary conversion zone, means including temperatureresponsive and flow-responsive elements located in each of said separate cracking zones for continuously indicating variations in yield per pass, means comprising now-responsive and temperature -responsive elements located within said primary conversion zone for continuously indicating Variations in per cent conversion therethrough, means associated with said per cent conversionindicating means of the primary conversion Zone for controlling the back pressure in at least one of said individual cracking zones whereby to maintain the per cent conversion in the primary zone at a substantially constant selected value, and separate means associated with each of said yield-per-pass-indicating means on the individual cracking zones for individually regulating the heat input into the separate cracking Zone and for maintaining the yield per pass therethrough at substantially constant selected values.

9. A process for converting higher boiling hydrocarbons into lower boiling hydrocarbons which comprises subjecting a charging stock to cracking conditions in a cracking coil, mixing the hot synthetic crude from the cracking zone with virgin raw oil charging stock, passing the mixed synthetic crude and virgin stock into a preliminary raw oil conversion Zone wherein at least part of the endothermic heat of reaction necessary to effect primary conversion of the virgin stock is supplied by the heat contained in the synthetic crude, controlling the per cent conversion in the preliminary conversion Zone by regulating the total heat in the mixture therein, regulating the total heat of the mixture at least in part by controlling the back pressure on said cracking zone, and regulating the total heat absorbed in said cracking zone While maintaining a substantially constant yield per pass therethrough, despite any Variation in the back pressure of said cracking zone.

10. rEhe process of claim 9 wherein the overall synthetic crude from the preliminary conversion zone is fractionated and at least one fraction thereof is used as the charging stock for said cracking zone.

11. A process for converting higher boiling hydrocarbons into lower boiling hydrocarbons, which comprises subjecting a plurality of charging stocks to cracking conditions in separate individually controlled cracking zones, mixing the hot synthetic crudes from the individual cracking zones with virgin raw oil charging stock, passing the mixed synthetic crudes and virgin stock into a common primary raw oil conversion zone Wherein at least part of the endothermic heat of reaction necessary to effect primary conversion of the virgin stock is supplied by the heat contained in said synthetic crudes, controlling the per cent conversion in the primary conversion section by regulating the total heat of the mixture therein, regulating the total heat of the mixture in said primary conversion zone by controlling the back pressure in at least one of the individual cracking zones, and regulating the total heat absorbed in each of the individual cracking zones while adjusting the time-temperature relationship to maintain the yield per pass through each individual cracking zone at a chosen value, despite any variation in the back pressure of the individual cracking zones.

12. A process for converting higher boiling hydrocarbons into lower boiling hydrocarbons which comprises charging a hydrocarbon stock into a cracking zone and therein subjecting said stock to cracking conditions, determining the mean temperature of the fluid within said zone, maintaining a flow-responsive element Within said zone, mixing the hot synthetic crude from the cracking zone with virgin raw oil stock, passing the mixed synthetic crude and the virgin stock at a known input rate into a primary raw oil conversion zone wherein at least part of the endothermic heat of reaction necessary to eiect primary conversion of the virgin stock is supplied by the heat contained in the synthetic crude, maintaining temperature-responsive and owresponsive elements within said primary conversion zone to provide control bases, controlling the per cent conversion in the primary section in accordance with the indications of said iiowand temperature-responsive elements by regulating the total heat of the mixture therein, regulating the total heat of the mixture at least in part by controlling the back pressure on said cracking zone,

and regulating the total heat absorbed in said cracking zone in order to maintain a substantially constant yield per pass therethrough, despite any variation in the back pressure of said cracking zone.

13. In the process of treating a iiowing uid in a thermal treating zone, the method of controlling the total heat in the ifluid leaving said zone by regulating the in situ density of the uid leaving said zone.

14. A system for cracking hydrocarbons which comprises a primary conversion zone, a cracking zone, means for conducting the synthetic crude from the cracking zone to the primary conversion zone, means for introducing charging stock into the system at a point between the outlet of the cracking zone and the inlet of the primary zone, regulatory means responsive to the degree of conversion in the primary zone for controlling the back pressure on said cracking zone whereby to maintain the degree of con- Version in said primary zone at a substantially constant selected Value, and regulatory means responsive to the degree of conversion in said cracking zone for controlling the heat input to said cracking zone, whereby to maintain the degree of conversion therein at a substantially constant selected value despite any variations in the back pressure on said cracking Zone produced by said regulatory means for said lprimary zone.

ROBERT L. RUDE.

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