US3751229A

US3751229A - Control of reaction zone severity by response to octane number of effluent liquid at reaction pressure

Info

Publication number: US3751229A
Application number: US00177801A
Authority: US
Inventors: W Bajek; J Mclaughlin
Original assignee: Universal Oil Products Co
Current assignee: Honeywell UOP LLC; Universal Oil Products Co
Priority date: 1971-09-03
Filing date: 1971-09-03
Publication date: 1973-08-07
Anticipated expiration: 1990-08-07

Abstract

An improved control system for adjusting and controlling reaction zone severity in a continuous flow hydrocarbon conversion process, wherein a hydrocarbon charge stock is passed through a reaction zone at conversion conditions comprising elevated temperature and pressure, and the resulting product effluent is separated into a vapor phase and into a liquid phase comprising gasoline boiling range hydrocarbon constituents. A sample of liquid phase effluent is continuously passed without intervening depressurization into a hydrocarbon analyzer which adjusts the reaction severity, and preferably heat input to the reaction zone, in response to the octane number of the liquid phase of the effluent. The octane measurement is effected by an analyzer comprising a stabilized cool flame generator with a servo-positioned flame front which provides a real time output signal indicative of sample octane number.

Description

United States Patent Bajek et al.

ll :Nap/H/m Charge Slack Inventors: Walter A. Bajek, Lombard; James". McLaughlin, La Grange, both of III.

Universal Oil Products Company, Des Plaines, Ill.

The portion of the term of this patent subsequent to Mar. l4, I989, has been disclaimed.

Filed: Sept.'3, 1971 Appl. No.: 177,801

Related US. Application Data Con tinuation'in-part of Ser. No. 868,460, Oct. 22, I969, abandoned.

Assignee:

Notice:

US. Cl 23/253 A, 23/253 PC, 23/263,

23/288 R, 208/139 208/DIG. 1 Int. C|..... B01] 9/04, Clog 35/04, G011] 33/00 Field of Search 23/253 A, 253 PC, 23/230 A, 230 PC; 208/l39, DIG. 1, I38, 163

References Cited UNITED STATES PATENTS 3/l972 Bajek et al 23/253 A .*Aug. 7, 1973 Primary Examiner- Joseph Scovronek Attorney-James R. Hoatson, Jr. et al.

[57] ABSTRACT An improved control system for adjusting and controlling reaction zone severity in a continuous flow hydrocarbon conversion process, wherein a hydrocarbon charge stock is passed through a reaction zone at conversion conditions comprising elevated temperature and pressure, and the resulting product effluent is separated into a vapor phase and into a liquid phase comprising gasoline boiling range hydrocarbon constituents. A sample of liquid phase effluent is continuously passed without intervening depressurization into a hydrocarbon analyzer which adjusts the reaction severity, and preferably heat input to the reaction zone, in response to the octane number of the liquid phase of the effluent. The octane measurement is effected by an analyzer comprising a stabilized cool flame generator with a servo-positioned flame front which provides a real time output signal indicative of sample octane number.

14 Claims, 3 Drawing Figures Ne! Gas 1' Preh eater Separator Nat LIqU/d 7'0 Fracr/onarian Octane Man/tar FIELD OF THE INVENTION This application is a continuation-in-part ofour copending application Ser. No. 868,460, filed Oct. 22, I969 and now abandoned.

The invention of this application is a process control application of the hydrocarbon analyzer described in U.S. Pat. No. 3,463,613 issued Aug. 26, 1969 to E.R. Fenske and J .l-l. McLaughlin, all the teachings of which, both general and specific, are incorporated by reference herein.

As set forth in U.S. Pat. 3,463,613, the composition ofa hydrocarbon sample can be determined by burning the sample in a combustion tube under conditions to generate therein a stabilized cool flame. The position of the flame front is automatically detected and used to develop a control signal which, in turn, is used to vary a combustion parameter, such as combustion pressure, induction zone temperature or air flow, in a manner to immobilize the flame-front regardless of changes in composition of the sample. The changein such combustion parameter required to immobilize the flame following a change of sample composition is correlatable with such composition change, An appropriate read-out device connecting therewith may be calibrated in terms of the desired identifying characteristic of the hydrocarbon sample, as, for example, octane number.

Such an instrument is conveniently identified as a hydrocarbon analyzer comprising a stabilized cool flame generator with a servo-positioned flame front. The type of analysis effected thereby is not a compound-bycompound analysis of the type'presented by instruments such as mass spectrometers or vapor phase chromatographs. On the contrary, the analysis is represented by a continuous output signal which is responsive to and indicative of hydrocarbon composition and, more specifically, is empirically correlatable with one or more conventional identifications or specifications of petroleum products such as Reid vapor pressure, ASTM or Engler distillations or, for motor fuels, knock characteristics such as research octane number, motor octane number or composite of such octane numbers.

For the purpose of the present application, the hydrocarbon analyzer is further limited to that specific embodiment which is designed to receive a hydrocarbon sample mixture containing predominantly gasoline boiling range components, and the output signal of which analyzer provides a direct measure of octane number, i.e., research octane, motor octane or a predetermined composite of the two octane ratings. For brevity, the hydrocarbon analyzer will be referred to in the following description and accompanying drawings simply as an "octane monitor.

An octane monitor based on a stabilized cool flame generator possesses numerous advantages over conventional octane number instruments such as the CFR engine or automated knock-engine monitoring systems. Among these are: elimination of moving parts with corresponding minimal maintenance and down-time; high accuracy and reproducibility; rapid speed of response providing a continuous, real-time output; compatibility of output signal with computer or controller inputs; ability to receive and rate gasoline samples of high vapor pressure, e.g., up to as high as 500 psig., as well as lower vapor pressure samples (5-250 psig.). These characteristics make the octane monitor eminently suitable not only for an indicating or recording function, but particularly for a process control function wherein the octane monitor is the primary sensing element of a closed loop control system comprising zero, one, two or more subloops connected in cascade.

DESCRIPTION OF The PRIOR ART Typical of such a hydrocarbon conversion process is catalytic hydroreforming, wherein a naphtha fraction is passed into a reaction zone containing a noble metal catalyst, in the presence of a molor excess of hydrogen. The basic processing technique and a preferred catalyst are indicated in U.S.- Pat; Nos.- 2,479,l09 and 2,479,110, issued to Vladimir I-I'aensel, wherein the catalyst comprises alumina, platinum, and halogen. Re forming is undertaken at a temperature in the range of from about 600 F. to about l,l00 F.; at a pressure in the range of from about psig. to about] ,000 psig.,

but more normally in the range of from about 200 to about 500 psig.; at a liquid hourly space velocity in the range of from about 0.5 l/hour to about l0.'0 l/hour; and in the presence of from about 0.5 to about 10.0 moles of hydrogen per mole of hydrocarbon.

As understanding of the reaction mechanisms occurring within the reforming zone has increased, it has become possible to adjust operating techniques and catalyst compositions to enhance the specific reaction desired. Thus, it is a primary purpose of catalytic reforming to subject a substantially sulfur, nitrogen, oxygen, olefin, and metal free gasoline boiling range or naphtha boiling range charge stock to high temperature and pressure in the presence of hydrogen in 'order to enhance the anti-knock properties of the hydrocarbons contained therein. It has been determined that such enhancement, resulting in a high octane gasoline product, is derived from four specific chemical reactions; (1) the dehydrogenation of naphthenic hydrocarbons to produce the corresponding aromatic derivative, (2) the dehydrocyclization of paraffinic hydrocarbons to produce corresponding aromatic hydrocarbons, (3) the hydrocracking of high molecular weight hydrocarbons to produce lower molecular weight hydrocarbons, and (4) the isomerization of normal paraffinic hydrocarbons to produce branched chain isomers of equal molecular weight.

Each of these four reaction mechanisms upgrade low octane hydrocarbons to high octane hydrocarbons, but as the automotive manufacturers haveincreased engine compression ratios it has become necessary to adjust operating techniques in order to control the reaction mechanisms selectively to maximize octane with minimum loss of liquid product yield and minimum production of paraffinic gas (methane, ethane, and propane). It has thus been determined that the dehydrogenation of naphthenes to aromatics is promoted by operating at lower pressure levels; that dehydrocyclization of paraffins to aromatics is promoted by low pressure and high temperature; that. hydrocracking of paraffins is promoted by high pressure, high temperature, and high residence time of the charge stock on the catalyst; and that isomerization of paraffins is promoted by intermediate temperature, and a catalyst comprising a much higher halogen content than normally employed. Since aromatic hydrocarbons have higher octane ratings than other hydrocarbonsof equivalent molecular weight, catalytic reforming has showed a current tendency to operate at higher temperatures and lower pressures in order to enhance the resulting gasoline octane rating by increasing the aromatic hydrocarbon content of the gasoline. Therefore, the catalyticreforming unit producing high octane motor fuel, typically is maintained at operating conditions sufficient to enhance the dehydrogenation of naphthenes and the dehydrocyclization of paraffins in order to maximize the production of both aromatics and hydrogen, maximum hydrogen being desired since it is normally consumed elsehere in the typical petroleum refinery. The production of aromatic hydrocarbons is enhanced by catalytic reforming at a temperature in the range of from about 850 F. to about l,050 F. and at a pressure in the range of from about 100 psig. to about 400 psig. when the end boiling point of the charge stock is about 350 F., but when the end point of the charge stock is about 400 F. or more, the preferred pressure is about 500 psig. in order to maintain catalyst stability.

The operator of the catalytic reforming unit judi ciously selects the operating conditions which he believes will most economically produce the desired high octane gasoline. The naphtha charge stock is passed into the reaction zone under conditions of temperature, pressure, catalyst composition, hydrogen to hydrocarbon ratio, etc., which will produce a reactor effluent having the composition necessary to result in the desired high octane product. When analysis indicates that the product does not meet octane specification, it is normal in the art for the operator to manually change conditions within the reaction zone to compensate for any deviation from specification.

The resulting hot vaporous reactor effluent containing hydrogen, normally gaseous hydrocarbons and gasoline boiling range hydrocarbons is withdrawn from the reaction zone, cooled, condensed, and passed to a separation zone which is normally a single stage gravitytype phase separator maintained at reforming pressure of, say, 50-500 psig. The liquid hydrocarbon or unstabilized reformate phase is in equilibrium therein with the gas phase containing a major proportion of hydrogen. The hydrogen-rich vapor phase is withdrawn and a portion thereof is recycled to the inlet of the catalytic reforming zone for circulation across the catalyst together with the naphtha charge. The liquid hydrocarbon phase from the separator is then ultimately fed to a distillation zone which normally comprises a stabilizer column. The liquid phase contains a substantial portion of dissolved hydrogen and C -C hydrocarbons which must be removed in order that the stabilized reformate will meet vapor pressure and octane number specifications. A typical sample of catalyticreformate from a separator operating at 250 psig. consists of:

Component Mol 2.5 i 0.5

The overhead from the stabilizer column is predominently C and lighter hydrocarbonsand the column bottoms is stabilized gasoline typically'comprising predominantly C to about 400 F. endpoint material.

By and large it has been the practice to operate the catalytic reforming unit mostly in the dark so far as octane number of the stabilized gasoline product is concerned. That is to say, the stabilizer column bottoms is manually sampled perhaps once every 8-hour shift or perhaps even only once a day. The samples are picked up and taken to the laboratory where each sample is run and the result is then transmitted back to the unit operator who, untilthen, has not been able to ascertain what change, if any, should have'been 'made at the time the sample was taken. K

Therefore, to be on the safe side, the unit operator will usually run the reforming reaction zone with excessive heat input in order to guarantee that the octane quality of the reformate gasoline will meet specification. The net result is that the resulting stabilized reformate will actually exceedxproduct specifications with respect to octane a good part of the time. This mode of operation increases the refiners costs since, as those skilled in the art know, decrease in product yield accompanies increase in product octane number.

The control problem is further complicated by the not uncommon practice of using'a single stabilizer column to process more than onegasoline stream. For example, a single stabilizer column will often receive plural or combined feeds which may comprise unstabilized reformates from two or more independently operated catalytic reforming units. An upset in the operation of a single such reformer will carry through to the stabilizer and be reflected in off-specification product so that the stabilizer bottoms product is no longer indicative of only the operation of a single reformer.

Continuously meeting octane number specification is, thus, an exceedingly difficult and haphazard task when employing a single stabilizer column to handle a plurality of gasoline streams. When the octane number of the stabilizer bottoms falls below the specification level, it often is not possible to determine which of the plural unstabilized reformate feeds to the column is the source of the low octane number gasoline boiling range hydrocarbon components in the final stabilized gasoline product, If product. reaction severity is increased at the wrong reforming unit, there is the danger that the resulting yield loss will far outstrip the resulting value of octane enhancement for the combined stabilized gasoline.

In addition, it is often found that the stabilizer bottoms fraction does not meet the octane number specification despite the fact that the catalytic reforming unit is operating properly. When such a condition is not recognized, remedial steps may be taken at the reaction zone with no corresponding remedial result being obtained in the octane number of the stabilized gasoline product. The result may later be found to be caused by misoperation of the stabilizer column. Or the result may later be found to be caused by the introduction of extraneous material into the stabilized gasoline product, as when it is found that the stabilizer reboiler is leaking hot oil heating medium into the gasoline product. I

Various schemes have been experimented with to control the reaction severity of a continuous hydrocarbon conversion process to obtain a more efficient operation. Typical of such schemes is set out in Uj.S Pat. 3,497,449 issued to RJ. Urban on Feb. 24, 1970. In that particular patent an octane number monitor of a CFR engine type is shown to be incorporated in a reforming process stream. The use of a CFR engine type monitor is not a practical means to control a continuous hydrocarbon conversion process. Such a device cannot operate at elevated pressures, and the samples to be monitored must be degassed or otherwise stabilized before injection into the monitor. This adds to the analytical lap time that is inherently long to begin with. lt is extremely difficult to achieve and maintain any control stability with such a device. it appears from the general context of the Urban patent that the use of the CFR octane monitor is not so much in the direct controlling of a process, but, on the contrary, for use in long term analysis of a particular process so that empirical data may be obtained for use in controlling that process.

Another prior art scheme is set out in US. Pat. 3,000,812 issued to D.M. Boyd, Jr. on Sept. 19, 1961. In this particular scheme an octane measuring device is used to analyze the product issuing from the fractionator which as set forth above is located downstream of theseparation zone in the reforming process scheme. The data obtained from this octane monitor was contemplated to have a transport lap time and response time of a significant amount. This was the basic reason for using the particular cascade system described in the Boyd patent.

The language of the Fe-nske patent described above indicates that the monitor of that invention may be used as means for detecting composition changes, and for supplying information as to the required direction and magnitude of corrective action to be applied to a control process condition in order to restore the sample composition to specifications. Nowhere in the teachings of the Fenske patent does there appear language to the effect of continually controlling a hydrocarbon conversion process by utilizing a control signal derived from a liquid sample of a vapor-liquid phase separation zone without intervening depressurization of the liquid to control such a process. The Urban patent appears to disclose this feature; however, as mentioned above the octane monitor of the Urban patent must be supplied with a stabilized product which inherently means that the liquid product from the separation zone of the Urban scheme must be stabilized and depressured.

SUMMARY OF THE INVENTION for use in adjusting and controlling conversion severity in a manner sufficient to provide a hydrocarbon product having a constant predetermined level of quality.

It is a particular object of the present invention to provide such an improved continuous monitoring and control system for use in varying heat input to a reaction zone, responsive to the octane number of the effluent liquid hydrocarbon discharged from the reaction zone, whereby the octane number'of the ultimate gasoline product is maintained at a constant predetermined level.

These and other objects of the present invention, as well as the advantages thereof, will be more clearly understood as the invention is more particularly disclosed hereinafter.

In accordance with the present invention, the octane monitor comprising a stabilized cool flame generator with servo-positioned flame front is connected to receive a continuous sample of the liquid phase of the reactor effluent, directly from the vapor-liquid separator of the reforming reaction zone without intervening depressurization below the separator pressure. Since the liquid phase sample which is sent to the combustion chamber of the octane monitor-thusremains at substantially the reaction zone pressure, the samplecontains not only the normally liquid hydrocarbon constituents comprising the final gasoline p'roduct, but also a substantial amount of dissolved high vapor pressure constituents, normally comprising dissolved hydrogen and normally vaporous hydrocarbons such as methane, ethane, and propane. However, the output signal of the octane monitor can be, and preferably is, calibrated directly in terms of octane number, notwithstanding the presence of a substantial portion of high'vapor pressure constituents within the sample. The output signal from the octane monitor is then utilized to reset or adjust heat input to the reaction zone so that the octane number of the liquid phase of the reactor effluent is maintained at a substantially constant predetermined level.

The inventive control system thus assures that the liquid phase of the reactor effluent (the unstabilized reformate gasoline being fed to the stabilizer column) will always remain on specification, relative to octane number, regardless of external upsets or disturbances. The control system thus effects a savings in utility cost in that since the octane number is continuously monitored, the reaction zone is thereby continuously operated at a minimum heat input. Raw material cost is also minimized since minimum heat input minimizes the conversion severity and thereby results in a minimum loss of product yield to obtain a gasoline product of substantially constant octane number.

Because there is a direct measurement and control of the octane rating of the unstabilized refonnate gasoline, this control system is to bedistinguished from those prior art control systems wherein some composition property such as percent aromatics, or conductivity, or dielectric constant, is measured and controlled. All of these latter physical properties are merely an indirect indication of octane rating which is only narrowly correlatable therewith. Such indirect correlation becomes invalid for any significant deviation from the design control point.

i The control system of this invention is also to be distinguished from those prior art systems employing automated knock-engines as the octane measuring device, such as shown in the Urban patent referred to above. Since the octane monitor utilized within the inventive control system comprises a stabilized cool flame generator, it is normal to introduce the sample directly into the octane monitor substantially at the separator or reaction zone pressure (separator pressure equals reaction zone pressure less the pressure drop through heat exchange equipment and piping). The sample therefor contains a substantial amount of dissolved hydrogen and normally gaseous hydrocarbon vapors within the liquid phase, and such a sample obviously cannot be sent directly to an automated knockengine type of octane measuring device. The knockcngines cannot operate at elevated pressures, and the samples thereto must be degassed or otherwise stabilized before injection into the knock-engine since a high vapor pressure sample may vapor lock a knockengine type of octane measuring device.

The control system of this invention is further to be distinguished from the prior art systems employing automated knock-engines as the octane measuring device in that the instant octane monitor is compact in size, can be totally enclosed by an explosion proof housing, and therefore can be used in hazardous locations. As a matter of fact, the octane monitor of the present invention is typically field installed immediately adjacent to the reaction zone vapor-liquid separator in order to minimize the run of high pressure tubing conducting the sample of liquid hydrocarbon phase to the combustion chamber of the octane monitor. A knock-engine in contrast cannot be employed in hazardouslocations and must therefore be situated remote from the sample point. I

The sample transport lag ordead time of a close coupled octane monitor as employed within the scope of the present invention is typically of the order to 2 minutes or less, and its 90 response time is another 2 minutes. This provides a very good approach to an essentially instantaneous or real time output. By way of contrast, the transport and response lags alone of a knock-engine as disclosed in the Urban patent may be of the order of 30 minutes or more, which those skilled in the control system art will recognize to be a substantial departure from real time output. With that much dead time built into a closed loop it is extremely difficult to achieve and maintain control stability, and undampened cycling may result. Particularly is this true in the system of the present invention since the sample being sent directly to the octane monitor would have to first be degassed before such liquid could be injected into the knock-engine. Any nonequilibrium or inconsistent degassing will introduce an additional uncontrollable disturbance into the control system since the degassed sample will not be truly indicative of the reactor effluent composition or octane number.

In a broad embodiment it may, therefore, be summarized that the present invention comprises a control system for use and in combination with a continuous flow hydrocarbon conversion process wherein a hydrocarbon charge stock is passed through a conversion zone at conversion conditions comprising elevated temperature, and the resulting conversion product effluent is separated into a vapor phase and into a liquid phase comprising gasoline boiling range hydrocarbon components, said conversion process having charge stock preheating means, said conversion zone, a vaporliquid phase separation zone, first conduit means for passing charge stock to said preheating means, second conduit means for passing charge stock from said preheating means to said conversion zone, third conduit means for passing conversion product effluent from said conversion zone to said separation zone, and means for supplying heat to said preheating means from an external source, the improved control system for said conversion process comprising in combination; (a) operatively associated with said heat supplying means, means to vary the heat input to said preheating means; (b) a hydrocarbon analyzer comprising a stabilized cool flame generator with a servo-positioned flame front, continuously receiving a sample of said liquid phase from said separation zone, and developing an output signal which in turn provides a measure of sample octane number; and, (0) means transmitting said analyzer output signal to said heat input varying means whereby the heat input to said preheating means is regulated responsive to octane number of said liquid phase and said octane number is thereby maintained at a constant predetermined level.

Preferred specific embodiments of the present invention will incorporate one or more cascaded subloops which more immediately control the heat input to the reation zone. For example, where the reaction zone is indirectly heated by a fluid heating medium such as combusition gas, steam, reactoreffluent, or hot oil, there may be a flow control loop on the heating medium to the reactor preheater, the octane monitor output then being cascaded to the flow controller setpoint. Alternatively, a reactor inlet temperature control in strument may reset the flow controller and the octane monitor output may reset the temperature controller setpoint. Other embodiments will become apparent in light of the detailed description of the invention which follows.

The invention may now be more clearly understood by reference to the accompanying figures which set forth a simplifiedschematic flow diagram of a typical catalytic reforming reactor system in which particular embodiments of the inventive control system are utilized.

FIG. 1 illustrates a catalytic reforming unit wherein the heat input to the reaction zone preheater is controlled by cascading the octane monitor output signal to a temperature controller which then sends a signal to reset a flow controller on the heating medium.

FIG. 2 illustrates a triple cascade system for regulating the heat input to the reaction zone by sending the octane monitor output signal to a differential temperature controller which in turn resets the reactor inlet temperature controller which in turn resets the flow controller on the heating medium.

FIG. 3 illustrates a further embodiment wherein the octane monitor reset a differential temperature controller which in turn resets the flow controller on the heating medium.

DESCRIPTION OF THE FIGURES With reference now to FIG. 1 there is shown a simplified schematic flow diagram for a typical catalytic reforming unit. A low octane number charge stock comprising naphtha or gasoline boiling range, hydrocarbon constituents having an end boiling point of about 350 F. enters the reforming process via line I. A recycle gas stream is injected into line 1 via line 2. This gas stream comprises predominantly hydrogen, with a minor portion of normally gaseous hydrocarbon vapor comprising methane, ethane, and propane, with traces of heavier hydrocarbons. The resulting mixture of hydrogen and hydrocarbon passes into a reactor preheater 3 via line 1. Preheater 3 may be any type of heat exchanger employing any type of heating medium such as steam, hot oil, hot vapor, flue gas, etc. Normally, however, in order to achieve the high temperature required, preheater 3 will be a direct fired furnace as illustrated. The reaction mixture of hydrogen and hydrocarbon is heated within coil 4 in preheater 3. Coil 4 is typically placed in the radiation section and the convection section of the preheating furnace 3.

The heated reaction mixture leaves preheater 3 via line 5, typically at a temperature of from about 900 F. to l,000 F. depending upon the composition of the hydrocarbon feed stock.'The hot mixture passes into a reaction zone comprising at least one reactor vessel 6 at a pressure of about 300 psig. The reaction zone contains a noble metal reforming catalyst and the reaction mixture undergoes a conversion to lower boiling hydrocarbon constituents having a higher octane number. The reaction primarily comprises dehydrogenation of naphthenes which is an endothermic reaction. Consequently, the reaction mixture leaves the reaction zone via line 7 at a temperature typically from 20 to 150 F. below the reactor inlet temperature, depending upon the naphthene content of the charge stock.

The reactor effluent passes via line 7 into a heat exchanger 8 wherein the mixture is cooled and normally liquid constituents are condensed. The condensed and cooled mixture leaves the heat exchanger 8 at a temperature of about 60 -l 20 F., and passes into a separator 10 via line 9. Separator 10 will be at a pressure which is substantially the same pressure as the reaction zone, but it will be at a slightly lower level due to pressure drop through the reactor catalyst bed, line 7, heat exchanger 8, and line 9. Thus, whereas reactor 6 will typically be at an inlet pressure of about 300 psig., separator 10 will typically be at a pressure of about 250 psig.

The condensed and cooled effluent entering separator 10 via line 9 is separated therein into a vapor phase and a liquid phase. The vapor phase is withdrawn via line 2 for recycle to the reaction zone inlet. Compressor means, not shown, sends the hydrogen-rich vapor phase via line 2 into line 1 for mixture with the charge stock, as was previously set forth hereinabove. The catalytic reforming raction not only upgrades the hydrocarbon constituents to higher octane number components but it also produces hydrogen as a byproduct of the process. Consequently, a net hydrogen-rich gas is withdrawn via line 11 by conventional pressure control means, not shown, as a net gas product which is typically sent to further processing units for consumption elsewhere in the refinery.

The liquid phase of the reactor effluent will have a component analysis similar to that presented hereinabove. The liquid phase containing dissolved gaseous components is withdrawn from separator 10 via line 12, and is passed through a control valve 13 and line 14, usually into a fractionation zone, not shown. The liquid phase withdrawal rate typically is adjusted by a liquid level contr'ller 15 which may be operated by a level sensing means 16, such as a float mechanism, dielectric probe, DP cell, or other similar level sensing means. The level controller 15 adjusts valve 13 by transmitting a pneumatic, electrical, or hydraulic output signal thereto via line 17.

Heat input to the raaction zone is provided by introducing a fuel via line 18 into a bank of combustion nozzles 19 within the furnace 3. The fuel,- which may be liquid or gas, is burned within the combustion zone and the hot combustion gas passes through the furnace and out the stack. As the fuel is burned and the combustion gas passes through the furnace, it imparts the necessary heat input into the reaction mixture contained within the coil 4 by means of radiation and convection. The heat input into the reaction mixture is controlled and adjusted by varying the flow of fuel to the bank of combustion nozzles 19. The control of the flow of fuel is achieved by means of a flow control loop contained in line 18. The flow control loop comprises a control valve 20 and a flow sensing means 24, which for illustrative purposes is shown as an orifice. A flow signal line 23 transmit the flow signal from orifice 24 to flow controller 22. Flow controller 22 then transmits an output signal to the control valve 20 via line 21. The setpoint of flow controller 22 is automatically adjustable.

A temperature controller 26, also with an automatically adjustable setpoint, senses the reactor inlet temperature as detected by a thermocouple or other sensing means 27 located in the reactor inlet line 5or in any other suitable inlet portion of the reaction zone. The resultingtemperature output signal is transmitted from temperature controller 26 to flow controller 22 via line 25 to adjust or reset the setpoint of flow controller 22. Octane monitor 28 utilizing a stabilized cool flame generator with servo-positioned flame front is field installed immediately adjacent to separator 10. In a preferred embodiment, the flows of oxidizer (air) and fuel (effluent liquid phase sample) are fixed, as in the induction zone temperature. Combustion pressure is the parameter which is varied in a manner to immobilize the stabilized cool flame front. Upon a change in sample octane number, the change in pressure required to immobilize the flame front within the octane monitor provides a direct indication of the change of octane number in the sample delivered to the combustion chamber. Typical operating conditions for the octane monitor are:

Air Flow Fuel Flow Induction Zone Temperature 3500 cc/min. (STP) l cc/min.

700F. (Research Octane) 800F. (Motor Octane) Combustion Pressure 4-20 psig.

Octane Range (Max.) -102 The actual calibrated span of the octane monitor as here utilized will, in general, be considerably narrower. For example, if the target octane is clear (research method), a suitable span may be 92-98 research octane. When a relatively narrow span is employed, the octane number change is essentially directly proportional to the change in combustion pressure.

Dashed line 29 represents a suitable sampling system to provide a continuous sample of the liquid phase of the reactor effluent to the octane monitor. The sample is withdrawn from separator 10 or from line 12 upstream of control valve 13 and passed into the octane monitor without intervening depressurization. The sample system may comprise a sample loop taking a liquid sample at a rate of cc. per minute from a point The octane monitor output signal is transmitted via line 30 to the setpoint of the temperature controller 26. This may be a direct field connection but preferably the octane monitor output will first be sent to an octane controller recorder located in the refinery control house and the control signal therefrom is then sent to reset the setpoint of temperature controller 26 which may also be a temperature recording controller located in the control house.

Upon a decrease in the measured octane number of the liquid phase sample, the octane monitor will call for an increase in the reaction zone temperature in order to dehydrogenate a greater proportion of the naphthanes in the charge stock, to produce a greater amount of high octane aromatic hydrocarbon in the effluent. Temperature controller 26 then will call for an increase in the flow of fuel to the preheater 3 in order to increase the heat imput into the reactants in coil 4, and thereby increase the temperature of the reaction mixture entering the reaction zone.

If the octane number of the effluent sample is higher than the required specification, the octane monitor will call for a decrease in the reaction zone temperature and the overall corrective action will be the reverse of that previously described. In either event the octane number of the liquid phase of the reactor effluent is continuously monitored and the reaction zone is controlled, under conversion conditions sufficient to provide a substantially constant octane number on the liquid phase of the effluent at a constant predetermined level.

It is well known to those skilled in the art that the overall heat of reaction for catalytic reforming is endothermic. That is to say, the temperature of the effluent leaving the reaction zone will be a substantial number of degrees below the temperature of the reactant mixture entering the reaction zone. The difference in temperature between inlet and outlet of the reaction zone is typically utilized as an indication of the reaction severity or as an indication of the degree and type of reaction occurring within the reaction zone. While the indicated temperature difference is an indication of the reaction severity it is not a direct indication of the resulting octane number of the liquid hydrocarbon components being produced within the zone. However, it is often desirable to monitor this temperature difference across the reactor with a differential temperature indicator.

Accordingly, there is indicated in FIG. 2 a further preferred embodiment of the present invention wherein the control system employing the octane monitor, comprising a stabilized cool flame generator with servo-positioned flame front, also incorporates a differential temperature control instrument. FIG. 2 illustrates the typical schematic flow diagram of a catalytic reforming unit which is identical to the unit illustrated in FIG. I and described hereinabove.

Referring now to FIG. No. 2 there is again shown the flow control loop on the fuel line 18 feeding the reaction zone preheater 3. The flow control loop comprises the flow control valve 20 receiving an output signal via line 21 from flow controller 22. Flow controller 22 receives the flow rate signal from sensing means 24 via the flow signal line 23. Flow controller 22 has an adjustable setpoint which again is reset by the output signal of temperature controller 26, said output signal being transmitted via line 25. Temperature controller 26 receives a temperature signal from the inlet of the reactor 6 by means of a temperature sensing device such as thermocouple 27. Temperature controller 26 also has an adjustable setpoint.

On the inlet to the reactor 6 there is shown another temperature sensing means such as thermocouple 31, which may be located in line 5 or in an inlet section of reactor vessel 6 or of the catalyst bed contained therein. On the outlet of the reactor 6 there is additionally shown a temperature sensing means such as thermocouple 32, which may be located in line 7 or in an outlet section of reactor vessel 6 or of the catalyst bed contained therein. Temperature sensing means 31 and 32 send the temperature singals to a differential temperature controller 33 having an automatically adjustable setpoint. The difference temperature controller 33 senses the temperature difference across the reaction zone. Temperature controller 33 develops an output signal which resets the automatically adjustable setpoint of temperature controller 26 by means of a transmitting line 34.

As the liquid portion of the hydrocarbon effluent from the reaction zone is sampled by octane monitor 28 by means of sampling loop 29, octane monitor 28 develops an output signal which is transmitted via line 30 to the automatically adjustable setpoint of the differential controller 33. As the octane monitor 28 receives a sample which is below the required octane number for the liquid phase of the reactor effluent, the monitor resets the automatically adjustable setpoint of differential controller 33 in order to increase the temperature difference between inlet and outlet of the reactor. The increase in temperature difference is a direct indication of an increase in the degree of dehydrogenation of naphthenes, and thereby indicates that high octane number aromatic constituents are being produced in greater amount. In order to increase this temperature difference across the reaction zone, differential temperature controller 33 sends a signal via controller output line 34 to temperature controller 26, and resets the automatically adjustable setpoint thereto in order to increase the inlet temperature to reactor 6. Temperature controller 26 in turn develops a controller output signal which is sent via line 25 to the automatically adjustable setpoint of flow controller 22. The output signal from temperature controller 26 readjusts the setpoint of flow controller 22 in order to open control valve 20 and thereby introduce more fuel into the bank of nozzles 19 for added combustion and a greater heat input into the reaction mixture.

When the liquid hydrocarbon effluent which is sampled via sample loop 29 indicates that the octane of the effluent being produced is too high, the octane monitor 28 will send an output signal via line 30 to the automatically adjustable setpoint of differential temperature controller 33 calling for a reduction in the-temperature drop across the reaction zone. The reduction in temperature drop is an indication of a reduction of dehydrogenation of naphthenes and thereby indicates that the octane number of the resulting effluent will be reduced. In order to accomplish this temperature reduction, differential temperature controller 33 will call for a reduction of inlet temperature by sending an output signal vialine 34 to readjust the setpoint of the temperature controller 26 to a lower temperature level. Temperature controller 26 in turn sends a controller output signal via line 25 to the automatically adjustable setpoint of flow controller 22 to reset the flow of fuel via line 18 into combustion nozzles 19. The lower fuel flow rate reduces the rate of the heat input into the reaction mixture and the inlet temperature to the reactor is thereby reduced.

While the triple cascade system illustrated in FIG. 2 represents a preferred embodiment, it is within the scope of this invention to omit the temperature controller 26 and to reset flow controller 22 directly by the output signal of the differential temperature controller. This modified embodiment is illustrated in FIG. 3.

Referring now to FIG. 3 there is again shown the differential temperature controller 33 receiving an inlet temperature signal by means of thermocouple 31 and an outlet temperature signal by means of thermocouple 32. The controller output signal is transmitted via line 34 to the automatically adjustable setpoint of the flow controller 22.

When the sample of the liquid phase of the hydrocarbon effluent passing via line 29 into octane monitor 28 indicates that the octane is too low, the octane monitor will send an output signal via line 30 to the automatically. adjustable setpoint of differential temperature controller 33 calling for an increase in the temperature difference across the reaction zone. In order to achieve this increase in temperature difference the inlet temperature of the reaction zone 6 must be increased, as evidenced by .a temperature indicator 41 receiving a signal from a temperature sensing means such as a thermocouple 40. Those skilled in the art realize, of course, that indicator 41 is not essential to effect control, but is typically provided for convenience in monitoring temperature. Differential temperature controller 33 sends an output signal via line 34 to flow controller 22 toopen control valve 20 and thereby increase the flow of fuel via line 18 into the bank of combustion nozzles 19. A greater heat input is thereby imparted to the reaction mixture in coil 4 and the temperature of the incoming feed to the reaction zone is thereby increased. The increased temperature level on the inlet of reactor 6 will precipitate a greater temperature difference since the increased inlet temperature creates a greater rate of reaction for the dehydrogenation of naphthenes and the other octane enhancing reactions occurring within the catalyst bed.

When the octane of the liquid sample passing into octane monitor 28 via line 29 is greater than is required, the octane monitor 28 will transmit an output signal via line 30 which adjusts the automatically adjustable setpoint of differential temperature controller 33 to reduce the temperature difference across the reaction zone. The differential temperature controller 33 then sends an output signal via line 34 to the automatically adjustable setpoint of flow controller 22 in order to reduce the flow of fuel into the preheater combustion nozzles 19. The reduction of preheat input into the reaction mixture will produce a decrease in the inlet temperature as shown by temperature indicator 41 which indicates the temperature as sensed by the thermocouple 40. The reduction of the inlet temperature produces a decrease in the rate of reaction ,within the reac tion zone as evidenced by a decrease in the temperature drop across the catalyst bed. The resulting effluent leaving. separator 10 via line 12 will then have a decreased octane number.

PREFERRED EMBODIMENTS While the multiple cascade arrangements illustrated in FIGS. 1 through 3 represent preferred embodiments, it is within the scope of this invention to omit the temperature controller 26 and the differential temperature controller 33 and to reset flow controller 22 directly by the octane monitor output signal transmitted via line 30. Similarly, flow controller 22 could be eliminated, in which case temperature controller 26 and/or differential temperature controller 33 would send their respective output signals directly to valve 20. Alternatively, the flow controller 22, temperature controller 26, and differential controller 33 could be eliminated, in which case octane monitor output signal line 30 would connect directly with valve 20. It may be expected, however, that elimination of either or both of the temperature control subloops will obviously result in a poorer overall control system. Since the octane number of the hydrocarbon effluent is not correlatable with the flow of fuel to the preheater, but is correlatable with the inlet temperature of the reaction zone and with the temperature drop across the reaction zorie, it is obvious to those skilled in the art that the temperature controller 26 and/or the differential temperature controller 33 should be included in the'control system for optimum control.

The method of operation of the invention control system is readily apparent to those skilledin the art from the foregoing discussion relative to the figures. In addition, the advantages of the present invention are equally apparent. f

The primary advantage is that the present invention provides an improved continuous monitoring and control system for use in varying heat input to a reaction zone, responsive to the octane number of the effluent liquid hydrocarbon discharged from the reaction zone, whereby the octane number of the ultimate gasoline product is maintained at a constant predetermined level. In particular, reaction severity is controlled to produce a hydrocarbon product having a constant predetermined level of quality despite operational upsets and control system deviations which may occur external or internal to the catalytic reforming unit. For example, the inventive control system allows the petroleum refiner to produce a reformate gasoline product of constant octane despite variations in charge stock composition or changes in catalyst activity.

An additional advantage is that since the control system is proximate to the reaction zone the response time between a change in reaction severity and a change in sample octane number is a matter of minutes. On the other hand, if the sample sent to the octane monitor is a stabilized gasoline sample from the fractionation zone, the intervening fractional distillation equipment introduces a substantial time lag between a change in reaction zone conversion conditions and the corresponding change in octane number of the finished product.

As used herein, the terms reaction zone and conversion zone are held to be equivalent terms. Similarly, the terms reaction conditions" and conversion conditions are used interchangeably. However, the terms separator and separation zone have a limited definition in accordance with the teachings presented hereinabove. In the instant invention the liquid sample is withdrawn from a vapor-liquid phase separator which those skilled in the art know to be readily distinguishable from any component separator or separation zone such as a distillation column or zone.

In the foregoing disclosure the use and application of the improved control system has been disclosed with reference to a catalytic reforming system. Those skilled in the art realize, however, that the inventive control system is not so limited. The inventive control system which has been disclosed hereinabove may be utilized in any hydrocarbon conversion process wherein a resulting product effluent is separated into a vapor phase and a liquid phase comprising gasoline boiling range hydrocarbon constituents such as thermal cracking, catalytic cracking, thermal hydrocracking, catalytic hydrocracking, isomerization, alkylation, polymerization, etc., which have such a separation zone.

Similarly, the simplified process flow drawings of the figures disclose a single preheater and a single reactor vessel. Those skilled in the art realize that many conversion processes employ plural reactor vessels with a preheater at each individual reaction vessel. Thus it is within the scope of the present invention to apply an embodiment of the inventive control system at more than one of a plurality of preheater-reactor combinations. For example, catalytic reforming typically employs three or more reactor vessels and corresponding preheaters. For a three reactor catalytic reforming unit then, a preferred application would be to monitor the separator liquid as taught hereinabove, and transmit the octane monitor output signal via three individual output signal lines to an independent cascaded control system of the type disclosed herein at each of the three preheater-reactor combinations. The method of adapting the present invention to provide multiple applications of the inventive control system, will be readily apparent to those skilled in the art utilizing the teachings which have been presented hereinabove.

Additionally, while the inventive control system has been disclosed with reference to the control of conversion or reaction severity by the adjustment and control of heat input, those skilled in the art realize that the inventive control system may be utilized to control severity by the adjustment of any other operating variable. For example, in fluid catalytic cracking the inventive control system may be utilized to control the rate of catalyst circulation. In HF Alkylation the inventive control system may adjust reaction severity by adjustments to the rate of circulation of isobutane reactant. ln polymerization over solid phosphoric acid catalyst, the inventive control system may adjust reaction severity by adjusting the rate of flow of olefin reactant to the reaction zone. In each instance, the adjustments to the conversion or reaction severity made by the inventive control system, will result in the production of an ultimate gasoline product having an octane rating more easily maintained at a constant specification value.

We claim:

1. ln a continuous flow hydrocarbon conversion process wherein a hydrocarbon charge stock is passed through a conversion zone at conversion conditions comprising elevated temperature, and the resulting conversion product effluent is separated into a vapor phase and into a liquid phase comprising gasoline boiling range hydrocarbon components, said conversion process having charge stock preheating means, said conversion zone, a vapor-liquid phase separation zone, means for passing charge stock to said preheating means, means for passing charge stock from said preheating means, to said conversion zone, means for passing conversion product effluent from said conversion zone to said separation zone, and means for supplying heat to said preheating means from an external source, the improved control system for said conversion process which comprises in combination:

a. operatively associated with said heat, supplying means, means to vary the heat input to said preheating means;

b. a hydrocarbon analyzer comprising a stabilized cool flame generator with a servo-positioned flame front, continuously receiving a sample of said liquid phase from said separation zone without intervening depressurization, and developing an output signal which in turn provides a measure of sample octane number; and,

c. means transmitting said analyzer output signal to said heat input varying means whereby the heat input to said preheating means is regulated responsive to octane number of said liquid phase and said octane number is thereby maintained at a constant predetermined level.

2. The system of claim 1 wherein said heat input varying means comprises a flow control loop including a flow controller having an adjustable setpoint regulating the flow of heating medium through said preheating means, whereby said setpoint is adjusted in response to said analyzer output signal.

3. The system of claim 2 further characterized in the provision of means to sense conversion zone temperature, temperature control means connecting with said temperature sensing means with such control means having an adjustable setpoint and developing a temperature output signal, and means transmitting said temperature output signal to the setpoint of said flow controller, with said means (c) transmitting said analyzer output signal to said temperature control means setpoint whereby the latter is adjusted responsive to liquid phase octane number.

4. The system of claim 3 wherein said temperature sensing means comprises first means sensing the temperature of an inlet section of said conversion zone and second means sensing the temperature of an outlet section of said conversion zone, whereby said temperature output signal provides a measure of temperature difference between said inlet and outlet sections.

5. The system of claim 2 further characterized in the provision of first means to sense a first temperature of said conversion zone, first temperature control means connecting with said first temperature sensing means with such control means having an adjustable setpoint and developing a first temperature output signal, means transmitting said first temperature output signal to the setpoint of said flow controller, second means to sense a second temperature of an inlet section of said conversion zone, third means to sense a third temperature of an outlet section of said conversion zone, second temperature control means connecting with said second and third temperature sensing means with such control means having an adjustable setpoint and developing a second temperature output signal which provides a measure of temperature difference between said inlet and outlet sections, and means transmitting said second temperature output signal to the setpoint of said first temperature control means, with said means (c) transmitting said analyzer output signal to said second temperature control means setpoint whereby the latter is adjusted responsive to liquid phase octane number.

6. In a continuous flow hydrocarbon conversion process wherein a hydrocarbon charge stock is passed through a conversion zone at conversion conditions comprising elevated temperature and a first elevated pressure, and the resulting conversion product effluent is separated into a vapor phase and into a liquid phase comprising gasoline boiling range hydrocarbon components, said conversion process having charge stock preheating means, said conversion zone, a vapor-liquid phase separation zone maintained at a second elevated pressure, means for passing charge stock to said preheating means, means for passing charge stock from said preheating means to said conversion zone, means for passing conversion product effluent from said conversion zone to said separation zone, and means for supplying heat to said preheating means from an external source, the improved control system for said conversion process which comprises in combination:

a. operatively associated with said heat supplying means, means to vary the heat input to said preheating means:

b. a hydrocarbon analyzer comprising a stabilized cool flame generator with a servo-positioned flame front, continuously receiving a sample of said liquid phase from said separation zone substantially at said second elevated pressure, and developing an output signal which in turn provides a measure of sample octane number; and,

. means transmitting said analyzer output signal to said heat input varying means whereby the heat input to said preheating means is regulated responsive to octane number of said liquid phase and said octane number is thereby maintained at a constant predetermined level.

7. The system of claim 6 wherein said heat input varying means comprises a flow control loop including a flow controller having an adjustable setpoint regulating the flow of heating medium through said preheating means, whereby said setpoint is adjusted in response to said analyzer output signal.

8. The system of claim 7 further characterized in the provision of means to sense conversion zone temperature, temperature control means connecting with said temperature sensing means with such control means having an adjustable setpoint and developing a temperature output signal, and means transmitting said temperature output signal to the setpoint of said flow controller, with said means (c) transmitting said analyzer output signal to said temperature control means setpoint whereby the latter is adjusted responsive to liquid phase octane number.

9. The system of claim 8 wherein said temperature sensing means comprises first means sensing the temperature of an inlet section of said conversion zone and second means sensing the temperature of an outlet section of said conversion zone, whereby said temperature output signal provides a measure of temperature difference between said inlet and outlet sections.

10. The system of claim 7 further characterized in the provision of first means to sense a first temperature of said conversion zone, first temperature control means connecting with said first temperature sensing means with such control means having an adjustable setpoint and developing a first temperature output signal, means transmitting said first temperature output signal to the setpoint of said flow controller, second means to sense a second temperature of an inlet section of said conversion zone, third means to sense a third temperature of an outlet section of said conversion zone, second temperature control means connecting with said second and third temperature sensing means with such control means having an adjustable setpoint and developing a second temperature output signal which provides a measure of temperature difference between said inlet and outlet sections, and means transmitting said second temperature output signal to the setpoint of said flrst temperature control means, with said means (c) transmitting said analyzer output signal to said second temperature control means setpoint whereby the latter is adjusted responsive to liquid phase octane number.

11. In a continuous flow hydrocarbon conversion process wherein a hydrocarboncharge stock is passed through a conversion zone at conversion conditions comprising elevated temperature, andthe resulting conversion product effluent is separated into a vapor phase and into a liquid phase comprising gasoline boiling range hydrocarbon components, said conversion process having charge stock preheating means, said conversion zone, a vapor-liquid phase separation zone, means for passing charge stock to said preheating means, means for passing charge stock from said preheating means to said conversion zone, and means for passing conversion product effluent from said conversion zone to said separation zone, the improved control system for said conversion process which comprises in combination:

a. operatively associated with said conversion zone, means to vary the severity of conversion conditions therein;

means transmitting said analyzer output signal to said means (a) whereby the severity of said conversion conditions is regulated responsive to octane number of said liquid phase and said octane number is thereby maintained at a.constant predetermined level.

12. The system of claim 11 wherein said means (a) varies temperature within said conversion zone.

13. The system of claim 11 wherein said means (a) varies the flow of at least one reactant within said conversion zone. i

14. The system of claim 11 wherein said conversion process comprises a fluidized catalytic cracking process, and said means (a) varies the flow of fluidized catalyst within said conversion zone.

Claims

2. The system of claim 1 wherein said heat input varying means comprises a flow control loop including a flow controller having an adjustable setpoint regulating the flow of heating medium through said preheating means, whereby said setpoint is adjusted in response to said analyzer output signal.
3. The system of claim 2 further characterized in the provision of means to sense conversion zone temperature, temperature control means connecting with said temperature sensing means with such control means having an adjustable setpoint and developing a temperature output signal, and means transmitting said temperature output signal to the setpoint of said flow controller, with said means (c) transmitting said analyzer output signal to said temperature control means setpoint whereby the latter is adjusted responsive to liquid phase octane number.
4. The system of claim 3 wherein said temperature sensing means comprises first means sensing the temperature of an inlet sEction of said conversion zone and second means sensing the temperature of an outlet section of said conversion zone, whereby said temperature output signal provides a measure of temperature difference between said inlet and outlet sections.
5. The system of claim 2 further characterized in the provision of first means to sense a first temperature of said conversion zone, first temperature control means connecting with said first temperature sensing means with such control means having an adjustable setpoint and developing a first temperature output signal, means transmitting said first temperature output signal to the setpoint of said flow controller, second means to sense a second temperature of an inlet section of said conversion zone, third means to sense a third temperature of an outlet section of said conversion zone, second temperature control means connecting with said second and third temperature sensing means with such control means having an adjustable setpoint and developing a second temperature output signal which provides a measure of temperature difference between said inlet and outlet sections, and means transmitting said second temperature output signal to the setpoint of said first temperature control means, with said means (c) transmitting said analyzer output signal to said second temperature control means setpoint whereby the latter is adjusted responsive to liquid phase octane number.
6. In a continuous flow hydrocarbon conversion process wherein a hydrocarbon charge stock is passed through a conversion zone at conversion conditions comprising elevated temperature and a first elevated pressure, and the resulting conversion product effluent is separated into a vapor phase and into a liquid phase comprising gasoline boiling range hydrocarbon components, said conversion process having charge stock preheating means, said conversion zone, a vapor-liquid phase separation zone maintained at a second elevated pressure, means for passing charge stock to said preheating means, means for passing charge stock from said preheating means to said conversion zone, means for passing conversion product effluent from said conversion zone to said separation zone, and means for supplying heat to said preheating means from an external source, the improved control system for said conversion process which comprises in combination: a. operatively associated with said heat supplying means, means to vary the heat input to said preheating means: b. a hydrocarbon analyzer comprising a stabilized cool flame generator with a servo-positioned flame front, continuously receiving a sample of said liquid phase from said separation zone substantially at said second elevated pressure, and developing an output signal which in turn provides a measure of sample octane number; and, c. means transmitting said analyzer output signal to said heat input varying means whereby the heat input to said preheating means is regulated responsive to octane number of said liquid phase and said octane number is thereby maintained at a constant predetermined level.
7. The system of claim 6 wherein said heat input varying means comprises a flow control loop including a flow controller having an adjustable setpoint regulating the flow of heating medium through said preheating means, whereby said setpoint is adjusted in response to said analyzer output signal.
8. The system of claim 7 further characterized in the provision of means to sense conversion zone temperature, temperature control means connecting with said temperature sensing means with such control means having an adjustable setpoint and developing a temperature output signal, and means transmitting said temperature output signal to the setpoint of said flow controller, with said means (c) transmitting said analyzer output signal to said temperature control means setpoint whereby the latter is adjusted responsive to liquid phase octane number.
9. The system of claim 8 wherein said temperature sensing means comprises first Means sensing the temperature of an inlet section of said conversion zone and second means sensing the temperature of an outlet section of said conversion zone, whereby said temperature output signal provides a measure of temperature difference between said inlet and outlet sections.
10. The system of claim 7 further characterized in the provision of first means to sense a first temperature of said conversion zone, first temperature control means connecting with said first temperature sensing means with such control means having an adjustable setpoint and developing a first temperature output signal, means transmitting said first temperature output signal to the setpoint of said flow controller, second means to sense a second temperature of an inlet section of said conversion zone, third means to sense a third temperature of an outlet section of said conversion zone, second temperature control means connecting with said second and third temperature sensing means with such control means having an adjustable setpoint and developing a second temperature output signal which provides a measure of temperature difference between said inlet and outlet sections, and means transmitting said second temperature output signal to the setpoint of said first temperature control means, with said means (c) transmitting said analyzer output signal to said second temperature control means setpoint whereby the latter is adjusted responsive to liquid phase octane number.
11. In a continuous flow hydrocarbon conversion process wherein a hydrocarbon charge stock is passed through a conversion zone at conversion conditions comprising elevated temperature, and the resulting conversion product effluent is separated into a vapor phase and into a liquid phase comprising gasoline boiling range hydrocarbon components, said conversion process having charge stock preheating means, said conversion zone, a vapor-liquid phase separation zone, means for passing charge stock to said preheating means, means for passing charge stock from said preheating means to said conversion zone, and means for passing conversion product effluent from said conversion zone to said separation zone, the improved control system for said conversion process which comprises in combination: a. operatively associated with said conversion zone, means to vary the severity of conversion conditions therein; b. a hydrocarbon analyzer comprising a stabilized cool flame generator with a servo-positioned flame front, continuously receiving a sample of said liquid phase from said separation zone without intervening depressurization, and developing an output signal which in turn provides a measure of sample octane number; and, c. means transmitting said analyzer output signal to said means (a) whereby the severity of said conversion conditions is regulated responsive to octane number of said liquid phase and said octane number is thereby maintained at a constant predetermined level.
12. The system of claim 11 wherein said means (a) varies temperature within said conversion zone.
13. The system of claim 11 wherein said means (a) varies the flow of at least one reactant within said conversion zone.
14. The system of claim 11 wherein said conversion process comprises a fluidized catalytic cracking process, and said means (a) varies the flow of fluidized catalyst within said conversion zone.