CA1070713A - Control of hydrogen/hydrocarbon mole ratio in a hydrogen-consuming process - Google Patents

Abstract

ABSTRACT
A system for controlling the hydrogen/hydrocarbon mole ratio in a continuous hydrocarbon conversion process in which hydrogen is consumed in a catalytic reaction zone.
Applicable to processes in which the reaction zone effluent is separated to provide a liquid product phase and a hydro-gen-rich vaporous phase, a portion of the latter being recy-cled to the catalytic reaction zone, the control system af-fords improved overall operation in addition to increased catalyst activity and stability. Analyzers are utilized to monitor composition characteristics of the charge stock and liquid product, and the hydrogen concentration of the vapor-ous phase introduced into the reaction zone. Representa-tive process output signals are transmitted to comparator/
computer means which compares the rate of change of the com-position characteristics and the hydrogen concentration, and generates additional, comparator output signals which are utilized within the control system for regulating the hydrogen/hydrocarbon mole ratio.

Description

~al7~7~3 The method for controlling -the hydrogen/hydrocar-bon mole ratio and the control system encompassed by the inventive concept herein described, are generally applicable to processes for the catalytic conversion of hydrocarbons in a hydrogen-containing atmosphere, in which processes the consumption of hydrogen occurs. Such processes include hydrocracking to produce lower molecular weight hydrocar-bons, hydrogenation of olefinic hydrocarbons to produce the corresponding paraffins and hydrorefining (desulfurization) for the purpose of contaminant removal, etc. In all these processes, as in most hydrogen-producing processes such as catalytic reforming, a commonly-practiced technique in-volves the utilization of a hydrogen-rich vaporous phase recycled to combine with the fresh hydrocarbon charge to ~ the reaction zone. Practical reasons for employing this technique reside in maintaining both the activity and opera-tional stability of the catalytic composite, employed to effect the desired reactions, and the assurance of achiev-ing the desired product slate. The former is more difficult to attain in hydrogen-consuming processes in view of the operating severity generally required. In hydrogen-pro-ducing processes, such as catalytic reforming, hydrogen in excess of that required for recycle purposes is recovered and utilized in other processes integrated into the overall refinery. For example, excess hydrogen from a catalytic reforming unit is often employed as make-up hydrogen in a hydrocracking process. Regardless of the particular process, the recycled hydrogen is generally obtained by ~7~q~3 condensiny the reaction zone product effluent, most often at a temperature in the range of about 60F. to about 140F., and introducing the thus-cooled effluent into a vapor-liquid separation zone. That portion of the recovered vaporous phase necessary to satisfy the hydrogen require-ment within the reaction zone is recycled to combine with the hydrocarbon charge stock prior to the introduction thereof into the reaction zone.
Prior art abounds with hydrocarbon conversion pro-cesses wherein a relativel~y hot reaction zone effluent is condensed and cooled, and introduced into a high pressure separator from which a hydrogen-rich vaporous phase and a normally liquid product phase are recovered. Generally, at least a portion of the vaporous phase is recycled with-out further treatment, to combine with the charge stock prior to the introduction thereof into the catalytic reac-tion zone. In some situations, however, usually involving sulfur service, that portion of the vaporous phase to be recycled is treated to remove contaminating influences which would have some adverse effect with respect to the reaction zone environment.
Exemplary of the variety of processes employing this basic technique, and to which the present invention is directed, is the pentane isomerization process dis-closed in United States Patent No. 3,131,325 (Cl. 260-683.68).
Similarly, United States Patent No. 3,133,012 (Cl. 208-95) illustrates this technique as applied to a catalytic re~

~L~'7~7~3 forming system. In United States Patent No. 3,71&,575 (Cl. 208-59), which is directed toward a two-stage hydro-cracking process, the reaction product effluent from the second stage is cooled prior to the introduction thereof into a vapor-liquid separation zone; the hydro~en-rich stream therefrom is recycled to the first stage to combine with the charge stock. The present method for regulating the hydrogen/hydrocarbon mole ratio in the combined charge to a catalytic reaction zone, and the control system there-for, are applicable to any hydrocarbon conversion process wherein a hydrocarbon charge stock and hydrogen are reacted in a catalytic reaction zone. Therefore, our invention may be readily integrated, with minor modifications, into processes such as hydrogenation, isomerization, hydrore-fining, hydrocracking, hydrodealkylation, dehydrogenation, and catalytic reforming, etc.
Exemplary of hydrocracking processes, into which the present invention can be integrated, are those schemes and techniques found in United States Patents No. 3,252,018 (Cl. 208-59), 3,502,572 (Cl. 208-111) and 3,472,758 (Cl.
208-59). Hydrocracking reactions are generally effected at elevated pressures of about 500 to about 5,000 psig.
Circulating hydrogen is admixed with the charge stock in an amount of about 3,000 to about 50,000 scf./Bbl., inclu-sive of make-up hydro~en from an external source. The charge stock contacts the catalytic composite, disposed within the hydrocracking reaction zone, at a liquid hourly space velocity of about 0.25 to about 5Ø Since the bulk 7~3 of the reactions being effected are exothermic in nature, an increasing temperature gradient is experienced as the charge stock/hydrogen reactant stream traverses the cata-lyst bed. Catalyst bed temperatures are generally main-tained at a maximum in the range of about 700F. to about 900F., and are conveniently controlled through the use of conventional quench streams, usually vaporous, directly introduced into the catalyst bed at intermediate loci thereof.
The foregoing, briefly described processes are illustrative of those into which the present invention may be advantageously incorporated. In all such processes, the hydrogen/hydrocarbon mole ratio in the combined feed to the reaction zone constitutes an important operating variable. Changes in feed stock composition characteris-tics require changes in the hydrogen/hydrocarbon mole ratio ~ ~
in order to maintain acceptable catalyst activity and ~ -stability. Furthermore, changes in reaction zone severity (principally temperature and pressure) are required as the product quality and/or quantity changes; however, this also affects the hydrogen/hydrocarbon mole ratio.
Also, variations in the hydrogen/hydrocarbon mole ratio will affect somewhat the product quality and/or quantity.
Briefly, in accordance with the present control method, a charge stock composition characteristic is sensed (a product composition characteristic may also be sensed~
and the hydrogen concentration within the vaporous phase introduced into the reaction zone with the feed stock is 1(3 7~7. 3 sensed. Appropriate representative output signals are transmitted to a comparator/computer which in turn gen-erates computer output signals which are transmitted as required to adjust reaction zone severity (temperature and pressure), charge stock flow and recycle gas flow in order to regulate the hydrogen/hydrocarbon mole ratio while simultaneously achieving the desired product quality and/or quantity. With respect to hydrogen-consuming processes -- i.e. hydrocracking to produce lower molecular weight hydrocarbons -- comparator output signals are transmitted, as necessary, to regulate the quantity of make-up hydrogen introduced into the process from an external source and the flow of any required reaction zone temperature quench stream.
A principal object of our invention is to control the hydrogen/hydrocarbon mole ratio in a catalytic hydro-carbon conversion process, and particularly wherein the reactions being effected are hydrogen-consuming. A corol-lary objective is to maintain catalyst activity and stability `
while attaining the desired product slate.
Another object is to provide a control system and accompanying method for controlling the hydrogen/hydrocar-bon mole ratio. In conjunction, it is a specific object to offer a method which compensates rapidly for changes in charge stock characteristics and operating parameter's, which changes necessitate an adjustment of the hydrogen/
hydrocarbon mole ratio within the catalytic reaction æone.

~L~7~7~3 Therefore, in one embodiment, our invention in-volves a control system for utilization i.n a continuous hydrocarbon conversion process in which hydrogen is con-sumed, and wherein (1) a hydrocarbonaceous charge stock and hydrogen are introduced into preheating means having external heat-supplying means operatively associated therewith; (2) the resulting heated charge stock-hydrogen mixture is reacted in a catalytic reaction zone; (3) the resulting reaction zone effluent stream is cond~nsed and separated to provide a liquid phase and a first hydrogen-containing vaporous phase~ (4) at least a portion of said ~ :
first vaporous phase is recycled to said preheatiny means, in admixture with said charge stock; and, (5) a second hydrogen-containing vaporous phase, from an external source,~
is introduced into said process, at least a portion thereof -:
is admixed with said first hydrogen-containing vaporous ~:
phase and introduced therewith into said preheating means; ;~
which control system, ~for regulating the hydrogen/hydro-carbon mole ratio within said reaction zone, comprises, in cooperative combination: (a) first flow-varying means, operatively associated with said preheating means, for adjusting the quantity of heat supplied thereto; (b) first flow-sensing means for measuring the rate o~ flow of said charge stock to said reaction zone and developing a first process output signal representative thereof, and second flow-varying means for adjusting the rate of flow of said charge stock; (c) a first analyzer receiving a sample of said charge stock and developing a second 7~L3 process output signal representative of a composition characteris-tic thereof; (d) second flow sensing means for measuring the rate of flow of said second hydrogen-contain-ing vaporous phase, introduced into said process, and de-veloping a third process output signa:L representative thereof, and third flow-varying means for adjusting the rate of flow of said second vaporous phase; (e) a second analyæer receiving a sample of the hydrogen-containi~g vaporous phase introduced into said preheating means and developing a fourth process output signal representative of the hydrogen concentration thereof; (f) third flow-sensing means for measuring the rate of flow of the hydrogen-con-taining vaporous phase .~ntroduced into said preheating means, in admixture with said charge stock, and developing a fifth process output signal representative of the rate of flow thereof; (g) means for sensing the pressure of the separated first hydrogén-containing vaporous phase and developing a sixth process output signal representative thereof; and, (h) comparator means (i) receiving said six process output signals and, operatively responsive thereto, .
(ii) generating first, second and third comparator output signals as functions thereof; said control system further characterized in that said comparator means is in communi~
cation with said first, second and third flow-varying means, .
via signal-transmitting means which transmit at least one of said comparator output signals to at least one of said flow-varying means, whereby at least one of (i) the flow of said charge stock, (ii) the heat supplied to said pre-~'711 17~3 :~ ' heating means and (iii) the flow of said second hydrogen-containing vaporous phase into said process is adjusked in response thereto, and said hydrogen/hydrocarbon mole ratio is regulated.
In another embodiment, the present invention af-fords a method for regulating the hydrogen/hydrocarbon ' .
mole ratio within the catalytic reaction zone of a con-tinuous hydrocarbon conversion process in which hydrogen is consumed, and wherein: (1) a hydrocarbonaceous charge stock and hydrogen are introduced into a preheating means having external heat-supplying means operatively asso~ :.
ciated therewith; (2) the resulting heated charge stock~
hydrogen mixture is reacted in said catalytic reaction zone; (3) the resulting reaction zone effluent stream is condensed and separated to provide a liquld phase and a first hydrogen-containing vaporous phase; (4) at least a .
portion of said first vaporous phase is recycled to said preheating means, in admixture with said charge stocki and (5) a second hydrogen-containing vaporous phase, from a source external of said process, is introduced therein and at least a portion thereof is admixed with said first hydrogen-cohtaining vaporous phase, and introduced there-with into said preheating means, which method comprises the steps of: (a) régulating the quantity of heat supplied to said preheating means by adjusting a first flow-vary-ing means operatively associa~ed therewith; (b) regulat-ing the flow of said charge stock by adjusting a second flow-varying means, sensing the rate of flow of said charge _9_ ~C~7~713 stock and developing a first process output signal repre-sentative o:E a composi-tion characteristic theréof; (c) introducing a sample of said charge stock into a fi.rst analyzer and developing therein a second process output signal representative of a composition characteristic thereof; (d) regulating the flow of said second hydrogen-containing vaporous phase, introduced into said process, by adjusting a third flow-varying meansl sensing the rate of flow of said second hydrogen-containing vaporous phase and developing a third process output signal representa-tive thereof; ~e) introducing a sample of the hydrogen-containing vaporous phase, passing into said preheating means, into a second analyzer and developing therein a fourth process output signal representative of the hydro-gen concentration thereof; (f) sensing the rate of flow of the hydrogen-containing vaporous phase passing into said preheating means and developing a fifth process output signal representative thereof'! ~g) monitoring the pressure of said separated hydrogen-containing vaporous phase and developing a sixth process output signal representative thereof; (h) introd~cing a sample of said separated liquid phase into a third analyzèr and developing therein a seventh process output signal representative of a composition characteristic thereof; (i) transmitting said seven process output signals to comparator means and generating therein first, second and third comparator output signals as func-tions of said seven process output signals; and, (j) trans-mitting at least one of said three comparator output signals ~Q7~37~3 to at least one of said first,second and third flow-vary- ~ .
ing means and regulating the quantity of heat supplied to :
said preheating means, the flow of said charge stock and/or the flow of said second h~drogen-containi.ng vaporous phase .
to control the hydrogen/hydrocarbon mole ratio within said .:
catalytic reaction zone. :: :
In another embodiment, directed toward processes in which a quench stream is directly introduced into the catalytic reaction zone for temperature control, the con-trol system is additionally characterized in that (i) fourth flow-sensing means measures the rate of flow of a third hydrogen-containing vaporous phase, having fourth flow-varying means operatively associated therewith, intro-duced directly into said catalytic reaction zone, develops a seventh process output signal representative thereof and ~:
transmits said seventh output signal to said comparator means, and (ii) sa.id compa~ator means generates said first, second and third comparator output signals and a fourth comparator output signal as functions of said seven process output signals.
These, as well as other objects and embodlments of our invehtion, will become evident to those possessing the requisite expertise in the appropriate art from the following, more detailed aescription thereof.
The utiliæation and integration of sophisticated control systems into a petroleum refining process are generally considered to be among the more recent techno-logical innovations. However, candor compels recognition 7~3 of the fact that the published litera-ture is steadily developing its own field of art. For example, United States Patent No. 3,759,820 (Cl. 208-64) discusses the systematlzed control of a muitiple reaction zone process in response to two different quality characteristlcs of the ultimately desired product. In a specific illustration involving the catalytic reforming of a naphtha charge stock, the two product qualities are the octane rating and the measured liquid yield. Output signals, representative of the two product qualities are utilized to regulate the reaction zone severities in response thereto. In United States Patent No. 3,751,229 (Cl. 23-253A) the reaction zone severity in a catalytic reforming unit is controlled in response to the octane rating of the effluent liquid at the reaction zone pressure.
United States Patent No. 3,756,921 (Cl. 196-132) discloses a control system for a gasoline splitter column utilizing an octane monitor in combination with flow-measuring means on both the overhead stream and the bottom stream. Override means are utilized to prevent the splitter column from emptying should excessive quantities of bottoms material be produced. Similarly, United States Patent No.
3,755,Q87 (Cl. 196-100) discl~oses the control of a frac-tional distillation column operating as a gasoline splitter, by measuring the octane rating of the overhead fraction and adjusting the reflux to the column in response thereto.
Another illustration of the control of reaction zone severity in response to the octane rating of the .
.

~ ~7~7~3 :

liquid phase effluent from a catalytic reforming process is disclosed in United States Patent No. 3,~49,202 (Cl.
23-253A). In this illustration, the reaction zone sever-ity in each of three reaction vessels is individually regulated in response to the octane rating and the tem-perature differential across each of the reaction zones.
The control system of the present invention like-wise regulates operating severity in one or more reaction zones of a hydrocarbon conversion process. However, a significant improvement is afforded in that extended utilization of the catalytic composite disposed within the reaction zone, at its optimum activity, is achieved, and maximum volumetric yield of the target product slate is realized throughout the overall economically effective catalyst life. Our technique involves controlling the hydrogen/hydrocarbon mole ratio in response to changes in feed stock and product compositions, reaction zone effluent composition and the then current life of the cata-lyst, in order to attain target product quality over an extended period of effective catalyst activity.
Briefly, our preferred method involves analyzing the product for a composition characteristic, the charge stock for a composition characteristic and the recycled vaporous phase for hydrogen concentration, and sensing operating variables including reaction zone temperatures~
pressure, flow rates, etc. Output signals representative of these items are transmitted to computer/comparator ~07~7~L3 means which generates additional output signals employed to regulate reaction zone severities, flow rates, etc.
A complete refinery within the petroleum lndustry comprises a multiplicity of hydrocarbon conversion pro-cesses integrated together for the principal purpose of attaining a particularly desired product slate. Such pro~
cesses include the catalytic reforming of naphtha fractions to produce a relatively high octane liquid product, hydro-cracking to produce lower molecular weight hydrocarbons, a portion of which can be utilized as the feed to the cata-lytic reforming unit, paraf~inic dehydrogenation to produce olefins, hydrocarbon isomerization and hydrorefining for the purpose of contaminant removal, etc. Additionally, many refineries will include processes designed for the production of specific compounds finding utilization as petrochemicals. For example, aromatic isomerization to produce paraxylene, alkylat~on to produce alkyl-substituted aromatic hydrocarbons, etc. These processes involve hy-drogen-consuming reactions, hydrogen-producing reactions, or both, and are generally effected by contacting the hydrocarbonaceous charge stock with a catalytic composite in a hydrogen-containing atmosphere at elevated tempera-ture and pressure. In the interest of brevity, further discussion of our inventive concept, its function and the method for effecting the same, will be directed toward hydrogen-consuming processes, and specifically to the well known and thoroughly documented hydrocracking process.

7~1L;3 It is understood that such a specific discussion is not intended to limit the present invention beyond the scope and spirit of the appended claims.
In catalytic hydrocarbon conversion processes exemplified by the foregoing, the recycle o~ a hydrogen-rich vaporous phase, to combine with the fresh feed charge stock, is a common practice. Experience has indicated that this technique maintains a "clean" catalytic composite which promotes acceptable catalyst activity and the sta-bility required to function effectively over an extended period of time. Whether considering a single-stage pro-cess, or a multiple-stage process, the recycled hydrogen- ~
containing vaporous phase is obtained from the reaction zone eEfluent via high-pressure separation at a temperature in the range of about 60F. to about 140F. In a hydrogen-consuming process, such as hydrocracking, that portion o~
the separated reaction zone effluent, containing hydrogen is insufficient, and must be supplemented by make~up hy-drogen from a suitable source external of the process --i.e. catalytic reforming which produces an abundance of hydrogen.
In addition to reaction zone temperatures, pres-sures and space velocities, it is generally conceded that the hydrogen/hydrocarbon mole ratio of the combined feed to the reaction zone constitutes an extremely important operating variable. Constantly changing feed stock com-position characteristics necessitate corresponding changes in the hydrogen/hydrocarbon mole ratio in order to maintain ~7~713 : ~

acceptable catalyst activity and stability. As the product quality and/or quantity changes, the reaction zone severity, principally temperature and pressure, must necessarily be adjusted. This, however, further affects the hydrogen/hydrocarbon mole ratio.
In accordance with the present control method and system, a charge stock composition characteristic is sensed and the hydrogen concentration within the vaporous phase being introduced into the reaction zone is sensed. The latter is, in a hydrogen-consuming proce~s, partially sepa-rated hydrogen and partially make-up hydrogen from an external source. In a preferred system, a composition characteristic oE the separated liquid product-containing stream is also sensed. Appropriate output signals are transmitted to a comparator/computer which in turn gener-ates computer output signals which are transmitted to ad-just reaction zone severity (temperature and pressure), charge stock flow and the flow of the make-up hydrogen-containing vaporous phase, as required, in order to regu-late the hydrogen/hydrocarbon mole ratio. As ~reviously stated, in many hydrogen-consuming processes, the exother-micity of the reactions, which causes a significant tem-perature increase as the reactants traverse the catalyst, is controlled within specified limits through the use of a hydrogen quench stream. An additional process output signal, representative of the rate of flow of the quench stream, is transmitted to the comparator mean's. An output ~7~7~3 signal is developed therein, as a function thereof, in conjunction with the other process output signals, and is transmitted to flow-varying means by which the rate of flow of the quench stream is adjusted. ~dditionally, -output signals which are representative of reaction zone inlet and outlet temperatures and the pressure of the vaporous phase separated from the reaction zone product effluent are transmitted to the comparator/computer means.
In one embodiment, the signal responsive to the pressure of the separated liquid phase may be directly transmitted to adjust the flow rate of the make--up hydrogen introduced from the external source. In this manner, the comparator output signals are representative of all the operating variables which afect the hydrogen/hydrocarbon mole ratio, or partial pressure of hydrogen within the reaction zone, as well as the product quality and/or quantity.
Prior to the start-up of a hydrocracking process unit, or other hydrocarbon conversion process, the various operating variables are initially determined by preparing a yield estimate directed to a predictable product quality and/or quantity, based upon a relatively de-tailed analysis of the hydrocarbonaceous charge stock. Charge stock analyses will generally include molecular weight, gravity, boiling range and the relative concentrations of various types of hydrocarbons. The estimated required hydrogen/
hydrocarbon mole ratio is calculated and the computer/
comparator means is appropriately programmed to maintain )7~3 the indicated mole ratio. Changes ln feed stock composi-tion characteristics are transmitted to the computer/
comparator, as is the flow rate thereof, The pressure and flow rate of the recycled vaporous phase, as well as the hydrogen concentration thereof, is also transmitted to the computer/comparator. The latter back-calculates the required hydrogen/hydrocarbon mole ratio and transmits appropriate output signals to achieve the values so indi-cated. A later change in the product quality and/or quan-tlty is sensed and the computer/comparator means appro-priately adjusts the furnace ~iring to regulate reaction zone temperatures and/or to adjust the operating pressure within the reaction zone, in order to reatta:in the target product characteristics. The computer/comparator means then compares the resulting hydrogen/hydrocarbon mole ratio and again transmits appropriate output signals to achieve the optimum.
The control system of the present invention uti-lizes at least three analyzers, two of which serve to determine composition characteristics of principally liquid streams, and the third of which determines the hydrogen cohcentration in that portion of the hydrogen-containing vaporous phase being introduced into the reaction zone in admixture with the charge stock,. One of the hydrocarbon analyzers develops an output signal which is correlatable with, and representative of a composition characteristic of the hydrocarbonaceous charge stock. Complete details of one such hydrocarbon analyzer ~7~7~3 may be obtained upon reference to United States Patent No. 3,463,613 (Cl. 23-230). As stated therein, a compo-sition characteristic of a hydrocarbon sample can be determined by burnlng the same in a combustion tube under conditions which generate a stabilized cool flame. The position of the flame front is automatically detected and employed to develop a signal which, in turn, is employed to vary a combustion parameter, such as combustion pres-sure, induction zone temperature or air flow, in a manner which immobilizes the flame front regardless of changes in the composition characteristic of the hydrocarbon sample.
The change in the combustion parameter, required to immo-bilize the flame front, following a change of sample com-position, is correlatable with the composition character-istic change. An appropriate r~ad-out device, connecting therewith, may be calibrated in terms of the desired identifying characteristic, such as molecular weight, boiling point, vapor/liquid ratio, etc.
The hydrocarbon analyzer is identified as com-prising a stabilized cool flame generator having a servo-positioned flame front. The type of analysis afforded thereby is not a compound-by-compound analysis such as presented by lnstruments including 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 correlatable wi-th one or more 3L~7~7~L3 conventional identifications or specifications of petro-leum products.
Other examples of cool flame generators, having servo-positioned flame fronts, and their use in analyzing hydrocarbon compositions and monitoring the same, are illustrated in United States Patents 3,533,745 (Cl. 23- -~
230), 3,533,746 (Cl. 23-230) and 3,533,747 (Cl. 23-230).
It is this type of hydrocarbon analyzer which is also preferred for monitoring one or more composition charac- ~;
teristics of the liquid stream separated from the reaction zone product-containing effluent.
With respect to the hydrogen concentration in the vaporous phase introduced into the reaction zone, chro-matographic monitors of the gas-solid type, utilizing a bed of zeolitic molecular sieves, are suitable. Addi-tionally, a density monitor, calibrated to mole percent hydrogen, is suitable for utilization as the analyzer.
Still another suitable analyzer constitutes a differen-tial pressure monitor which determines the partial pres-sure of hydrogen diffused through a hot palladium dia-phragm. In any event, the two hydrocarbon analyzers and the hydrogeh analyzer develop output signals representa-tive of the composition characteristics and hydrogen con-centration, which output signals are transmitted to the computer/comparator means.
The present control system and method for regu-lating the hydrogen/hydrocarbon mole ratio utilizes com-puter/comparator means which receives various output ~L~7~73L3 signals from the stream analyzers and operating variable indicators, or transmitters, generates computer output signals and transmits the same to various controls and/or control loops within the overall procéss Signals re-ceived by the computer are compared with previously received signals to determine the actual value of!the stream composition characteristics and hydrogen concen-tration. Preferably, the computer also determines the rate of change thereof. Additional output signals, received by the computer, represent temperatures asso-ciated with the conversion zone, or zones, the flow rate of the fresh charge stock, the flow rate of the vaporous phase introduced into the reaction zone with the charge stock, the temperature of the charge stock following heat exchange with a hot reaction zone effluent stream, the flow of total vaporous phase from the high-pressure separator and the pressure of the vaporous phase from the separator. Still other process output signals, which are transmitted to the comparator/computer means, represent the quantity of the make-up, hydrogen-containing vaporous phase introduced into the process from an external source, the quantity thereof which is combined with the reaction zone effluent vaporous phase and the quantity of the hydro-gen-containing vaporous phase employed as reaction zone quench.
As herein~fter more thoroughly described with reference to the accompanying drawing, the computer/

~L~7~7~L3 comparator, having previously been programmed to select -the optimum hydrogen/hydrocarbon mole ratio, in response to all the signals received thereby, generates additional compara-tor output signals which are transmitted to a con-trol loop which effects adjustment of the fuel supplied to heating means into which the reaction zone charge stream is introduced, to charge stock flow control means, to control means which adjusts the flow of the make-up, hydrogen-containing vaporous phase introduced into the process, and to control means which regulates the quan-tity of vaporous phase quench directly introduced into the reaction zone. Where a portion of the separated vaporous phase is removed from the process, a comparator output signal may be transmitted to control means to adjust the quantity thereof. It may be that any one, or more of the additional computer output signals will indicate that no change is then required in any of the above-described variable controls. The computer/comparator means can include the appurtenances necessary for comparing the actual values of the signals received with previously determined deviation limits and for generating adjustment signals responsive to this comparison. For example, the practical maximum catalyst bed temperature in any given process may be critical as concerns catalyst activity and product quality. Should the comparator means indicate a trend to exceed the particularly specified limit, the appropriate adjustment signal is transmitted. This is especially of import in a hydrogen-consuming process : ' 7~)7~3 where an increasing temperature gradient is experienced as -the reactants traverse the catalyst bed. In a hydro-cracking process, the maximum catalyst temperature might be set at 950F., such that an appropriate adjustment slgnal is transmitted should other computer output sig-nals tend to indicate an ultimate dev:iation.
The accompanying drawing illustrates several embodiments of the present control system integrated into a single-stage hydrocracking process. It is not intended, however, that our invention be unduly limited thereby be-yond the scope and spirit of the appended claims., Modifi-cations to the diagrammatic flow diagram will become evident to those having the requisite skill in the appro-priate art.
The illustrated hydrocracking process is shown as a single-stage unit comprising reaction zone, or reactor 7, heat exchanger 3, charge heater 5, high-pressure separa-tor 13, compressor bank 18, surge drum 15 and computer/
comparator 95. The latter recei~es one or more various process output signals via instrument lines 40, 44, 98, 49, 52, 57, 62j 66, 69, 73, 80, 85, 90 and 94, generates additional computer output signals and transmits the same via instrument lines 36, 46,,58, 81 and 86. Hydrocarbon analyzer 37 receives a sample of the charge stock from line 1, develops an output signal representative of a composi-tion characteristic thereof and transmits said output signal via instrument line 40 to computer/comparator 95.
Analyzer 78 receives a sample of the recycled hydrogen-rich ~7~7~3 vaporous phase in line 2, develops an output signal repre-sentative of the hydrogen content and transmits said signal via instrument line 80.' The composition characteristics oE the charge stock (line 1) and the separated liquid phase (line 16), being monitored by analyzc-!rs 37 and 91, will be determined primarily by the particular hydrogen-consuming process in which they are being used. Similarly, in a hydrocrac~in~ process, these composition characteris-tics will be selected on the basis of the particular type of charge stock and the product slate intended to be pro-duced therefrom. As a result, the analyzers may, or may not be identical Hydrocarbon analyzers 37 and 91, which receive samples of the hydrocarbonaceous Eeed stock and the separ-ated liquid phase, respectively, may utilize stabilized cool flame generators having a servo-positioned flame front~ The flow of oxidizer (air) and fuel (the sample being received) are fixed, as is the induction zone tem-peratwre. Combustion pressure is the parameter which is varied in order to immobilize the cool flame front. When a change in the selected composition characteristic is experienced, the change in combustion pressure required to immobilize the flame front provides a signal which is a i direct, corollatable indication of the change. Common operating conditions for these hydrocarbon analyzers are:
air flow, 3,500 cc./min. (STP);~fuel flow, 1.0 cc./min.;
an induction zone temperature in the range of about 650F.

., 7~713 to about 825F.; and a varying combustion pressure of about 4.0 to about 20.0 psig.
Where, for example, the hydrogen-consuming pro-cess is hydrocracking, wherein the desired result is maxi-mum production of gasoline boiling range hydrocarbons from heavier material, the analyzer may take the form of a vapor/
liquid ratio analyzer similar to that described in United States Patent No. 3,491,585 (Cl. 73-53). In situations where the charge stock is intended for LPG (liquefied petroleum gas) predominating in propane and butane,\a boiling point monitor, or chromatographic analyzers might be utilized. The sample is flashed into the carrier stream, generally helium, and conveyed thereby into the chromato-graphic column. The column impedes the passage of the materials in the sample as a function of their boiling points and carbon chain lengths. As the carrier gas leaves the column and is introduced into the detector, it carries with it components in sequential order according to their respective boiling points.
In order to effect control of the hydrogen/hydro-carbon mole ratio, the concentration of hydrogen in the vaporous phase being admixed with the fresh feed charge stock must be known. Thus, analyzer 78 develops a process output signal which is~representative of the hydrogen content of the vaporous phase in line 2. The sample is introduced by way of line 7g, and the representative out-put signal transmitted via line 80. As hereinbefore stated, analyzer 78 is only required to produce a process ~L~7~7~3 - ~

output signal representative of the hydrogen concentra-tion; therefore, it may be selected from a variety of suitable devices described in the appropriate art.
As previously set forth, hydrocracking is effected in one or more fi~ed-bed catalytic reaction zones, depend-ing upon the product slate desired from a given Eeed stock. For example, United States Patent No. 3,718,575 (Cl. 208-59) describes a multiple-stage hydrocracking process for LPG production. The charge stock boils above the gasoline boiling range, for example, a full boiling range ~as oil having an initial boiling point of about 500F. and an end boiling point above 1,000F. In its virgin state, such a feed stock will contain contaminants in the form of nitrogenous and sulfurous compounds, and will, therefore, be subjected initially to hydrorefining whereby these deleterious contaminating influences are converted into ammonia, hydrogen sulfide and hydrocarbons. ~ -Hydrorefining is one of the hydrogen-consuming processes into which the control system of our invention can be advantageously integrated. ;
Hydrocracking reactions are effectad at catalyst bed temperatures in the range of about 650F. to about 950F., and preferably from about 700F. to about 900F., The reaction zones are maintained under an imposed pres-sure of about 500 to about 5,000 psig., generally with an upper limit of about 2,500 psig. The ra~e of hydrocarbon charge stock flow will be from 0.25 to about 5.0 liquid hourly space velocityl and the hydrogen concentration will range from 3,000 to about 50,000 scE./Bbl. Of all the hydrogen-consuming processes, hydrocracking exhibits the greater degree of exothermicity. I'herefore, in order to control the increasing temperature gradient, as the reactants traverse the catalyst bed, a quench stream, generally hydrogen-containing, will be introduced directly into the catalyst bed at one or more intermediate loci thereof.
The selection of the catalytic composite, for utilization in the hydrocracking reaction zones,is prin-cipally determined following a detailed analysis of the fresh feed charge stock and desired product yield esti-mate founded thereon, and is directed toward the product quality and quantity. Generally, although the catalytic composite is "tailored" for its intended use, it will comprise at least one metallic component selected from Groups VI-B and VIII of the Periodic Table, rhenium, tin and germanium, which are combined with a siliceous refrac~
tory material c~ntaining from about 12.0~ to about 30.0%
by weight of alumina. Appropriate prior art indicates an apparent preference for a catalyst where the metallic components are impregnated, or ion-exchanged onto a crys-talline aluminosilicate molecular sieve, a variety of which are cammonly referred to by the broad term "zeolites".
One such catalyst, which exhibits the desired character-istics of activity and stability, is a composite, for example, of about 5.3% by weight of nickel and a synthe-tically-prepared faujasite which is distributed throughout :~L07Q7~3 a silica matrix. Other suitable zeolitlc materials in-clude mordenite, Type X or Type ~ molecular sieves, as well as zeolitic material which is dispersed within an amorphous matrix of alumina, silica or alumina-silica.
It is understood that the precise composition of the catalytic composite employed in hydrocracking, or in any of the previously delineated conversion processes, wherein hydrogen is consumed, does not constitute a feature essen-tial to our invention. Furthermore, it is not intencled to limit our invention to a process having a specific number of individual reaction zones. Thus, although our invention is illustrated as a single-stage process, in ~' the accompanying drawing, it is readily adaptable to a two-stage, or three-stage process.
As comprehension and understanding of the cata-lytic reaction mechanisms involved in hydrogen-consuming processes, and particularly hydrocracking, increased, it became possible to correlate operating techniques and con~
ditions with specific catalyst compositions, consistent with charge stock properties, to enhance the attainment of the target product quality and quantity. While the intended hydrocracking function is the same in all situa-tions, to "crack" higher molecular weight hydrocarbon into lower molecular weight hydrocarbons, it is necessary to select operating conditions and techniques which will prolong the acceptable, effective period during which the selected catalyst performs its intended function. Problems ~L~7~

and difficulties attendant the control of a hydrocracking process, in order to judlciously promote the effective catalyst life -- generally defined as barrels of fresh charge stock per pound of catalyst wi.thin the reaction zone -- are considerably more perple~ing than in many other hydrocarbon conversion processes, particularly those which are categorized as hydrogen-producing. Some of these problems have been at least partially alleviated by the incorporation of various process techniques. For example, where the increasing -temperature gradient is excessive, direct quench streams are employed; also, charge stock diluents, generally of lower boiling range are somewhat effective.
Significant problems and difficulties remain, and stem from a myriad of aspects including a constantly changing fresh charge stock composition, with its accom-panying effect upon the desired product slate and the re-quired changes in reaction zone severity. This is com-pounded by the fact that a common technique involves recycling that portion of the product effluent which boils at temperatures above the desired product -~ i.e. when producing naphtha boiling range liquid product, that portion of the effluent boiling above about 390F~ is recycled. Varying compositions of the total reaction zone .
; 25 effluent further affect product quality and quantity, and the severity of operation within the reaction zone as a result of the varying compositions of the vaporous and liquid phases separated within the high-pressure ~29-~t7~7~3 separator. Additionally, the introduction of the quench stream, or streams directly into the catalyst disposed within the reaction zone becomes a contributing factor respecting process control. Also to he considered is the normal deterioration of the active components within the catalytic composites, the rate of which is partially decelerated through the use of recycled hydrogen in amounts based upon the flow of fresh charge stock.
In view of the foregoing, continuously meeting target product quality and quantity, while simultaneously extending the effective life of the selected catalytic composite remains a dilemma which plagues the refiner.
Controlling the hydrogen/hydrocarbon mole ratio in ac-cordance with the present invention effectively solves the problems and thus avoids the attendant difficulties. ;~
Our method for controlling the hydrogen/hydrocar-bon mole ratio in a catalytic hydrocarbon conversion pro-cess wherein hydrogen is consumed, and the control system therefor, will be more clearly understood with reference to the accompanying diagrammatic sketch. Although the drawing is directed toward a single-stage, fixed-bed catalytic p~ocess, it is equally well suited for multiple-stage hydrogen-consuming processes hereinbefore delineated.
Furthermore, while the descriptive illustration is directed toward the production of LPG from naphtha boiling range hydrocarbons, it is obviously not the intention to limit our invention thereto. In the drawing, process flow lines, including sample taps, and major items of equipment are 7~3 therein illustrated by solid lines, while the dashed lines represent signal-transmitting means to and from the computer/comparator and in the indicated cascade control loops. The drawing will be described in conjunc-S tion with a commercially-scaled unit designed to produce maximum quantities of a propane/butane concentrate from 10,200 Bbl./day of a comparatively light naphtha fraction having a gravity of 64.0'API, an initial boiling point of about 175F. and an end boiling point of about 248F.
With specific reference now to the drawing, 1016.0 moles/hr. of the fresh naphtha charge stock is introduced into the process by way of line 1, in admixture with 548.7 moles/hr. of a recycled pentane-plus liquid stream, the source of which is hereinafter described. A hydrogen-rich, principally vaporous phase in line 2, in the amount of 9,981.5 moles/hr. (79.3% hydrogen) is admixed therewith, the mixture continuing through line 1 into heat-exchanger 3. Heat-exchanger,3~is an indirect heat exchanger generally of the tube and shell type; the hydrogen/hydrocarbon mixture is introduced thereto at a temperature of about 161F.
and a pressure of about 1155 psig. The heating medium is relatively hot reaction zone effluent introduced into the heat exchanger via line 9. The thus-preheated mixture is introduced, via line 4, at a temperature of about 610F.
and a pressure of about 1125 psig., into a direct-fired furnace heater 5. Although heater 5 may be any type of heat exchanger employing various heating media such as f~t7~D7~L3 steam, hot oil, hot vapor, flue gas, etc. in order to achieve the high temperature required, the heater will generally be a direct-fired furnace as lllustrated.
The heated reaction mixture i.s withdrawn from direct-fired heater 5 by way of line 6, and introduced ~ ~.
thereby into a fixed-bed reaction zone 7, at a temperature of about 650F. and a pressure of about 1090 psig. In this illustration, the catalytic composite disposed within reaction zone 7 contains about 5.0~ by weight of a nickel component (calculated as the elemental metal~ combined with a carrier material of synthetic faujasite interspersed throughout a silica matrix. As hereinbefore stated, since the principal reaction is hydrocracking which exhibits a relatively high degree of exothermicity, an increasing temperature gradient will be experienced as the reactant .
stream traverses the catalyst bed. In this particular .
instance, operating techniques dictate a maximum temperature increase of about 100F. Therefore, a hydrogen-rich stream is introduced, via line 8, intermediate the reaction zone at a temperature of about 120F. The effl/uent from reactor I :
7 passes through line 9 into heat exchanger 3 wherein it is utilized~as the heating medium to preheat the fresh feed charge stock and recycled hydrogen prior to the intro- -duction thereof and to direct-fired heater 5. Following heat-exchange the reaction zone effluent in line 10 is introduced into cooler 11 at a temperature of about 223F.
and a pressure of about 1015 psig. The thus-cooled reaction zone effluent is introduced via line 12 into high-pressure -~7~713 separator 13 a-t a temperature of about 100F. and a pres-sure of about 1000 psig.
A principally vaporous phase :is withdrawn from separator 13 by way of line 14, and introduced therethrough into surge drum 15. The LPG-rich principally liquid phase is withdrawn by way of line 16 and introduced thereby into suitable separation facilities for the removal therefrom of vaporous material, principally hydrogen, methane and ethane, and hydrocarbons containing more than about four carbon atoms per molecule. The latter, in an amount of about 54B.7 moles/hour, is recycled to combine with the charge stock in line 1, prior to the sample thereo being introduced into analyzer 37. The final product, in an amount of about 12,800 Bbl./day (1942 moles/hr.~ contains about 99.1~ propane and mixed butanes. Surge drum 15 serves to remove entrained normally liquld material from the separated vaporous phase in line 14, which material is periodically withdrawn by way of line 19 containing valve 20. The remaining vaporous phase is withdrawn by way of line 17 and introduced thereby into compressor bank 18 for recycle through line 2 to line 1 wherein it is admixed with the hydrocarbon charge stock and intro-duced into heat exchanger 3. At least a portion of the recycle vaporous phase in line 2 is diverted by way of line 8, being introduced thereby directly into reaction zone 7 as the quench stream.

~07~7~3 i5ake-up hydrogen, to supplement that consumed within reaction zone 7, is introduced :into the process via line 21; the hydrogen concentration approxi~ates 85.0% (on a mole basis). This supplemental hydrogen-rich stream is discharged via compressor k~ank 18 through line 22, from which it is admixed with the cooled reaction zone product effluent in line 12 for introduction thereby into high-pressure separator 13. Situations will arise where judicious operating techniques dictate the removal of a portion of the recycle vaporous phase in line 17 through line 23 containing control valve 24. Although control valve 24 may function in response to a computer output signal being transmitted thereto via instrument line 81 (as illustrated), it may be adjusted by transmitting the signal from pressure transmitter 68 directly (not illus-trated). Similarly, control valve 25, in make-up hydrogen line 21, can either be adjusted via a computer output signal from instrument line 86, or directly in response to the signal transmitted via line 26 from pressure indica-tor 68. Those possessing the requisite skill in the appro-priate art will, obviously, recognize that both control valve 24 and control valve 2S might receive output signals in a given situation.
Withdrawal of the principally liquid phase, from high pressure separator 13 via line 16, is adjusted and controlled through the use of a liquid-level control system consisting of level-sensing means transmitting a level output signal via instrument line 74 to level controller ~7iD~3 75 which, in turn, regulates the operation of control valve 77 by transmitting an appropriate signal through instrument line 76. The level-sensing means may be a floating lever mechanism, a dielectric probe, a DP cell, or any similar device capable of maintaining a preset liquid level seal in the lower portion of high-pressure separator 13.
In the illustrated hydrocracking embodiment, hydrocarbon analyzer 91 is adapted to function as a boiling point monitor. A sample loop connects analyzer 91 with the normally liquid separat~r bottoms material in line 16, and consists of line 92 which removes a sample at a rate of about 100 cc~min.,and line 93 which returns ex-cess sample at a rate of about 99 cc/min. The sample itself is drawn off the analyzer from some intermediate portion of the sample loop and injected at full line pressure and a carefully controlled rate of 1.0 cc./min.
The output signal can be, and preferably is calibrated in terms of boiling points, and transmitted via line 94 to computer/comparator 95 which is operatively respon-sive to the boiling point output signal, and which, in turn develops a comparator output signal as a function thereof.
In order to effect optimum control of the hydro-gen/hydrocarbon ratio within the reaction zone, computer/
comparator 95 receives a number of other output signals, ir. addition to that representative of the composition characteristic of the separated liquid phase in line 16, -35~

~37~7~

which other process output signals are indicative of oper-ating conditions within the process and other composition characteristics. Process output signals, or input signals to computer/comparator 95, include one which is repre-sentative of at least one composition characteristic of the hydrocarbonaceous charge stock in line 1. A 100 cc./
min. sample of the feed stock is withdrawn through line 38 and introduced into hydrocarbon analyzer 37, the excess being returned via line 39. Suitable composition charac-teristics, with which the process output signal is cor-relatable, include boiling point, molecular weight, den-sity, etc. Of these, the molecular weight of the feed stock is preferred since changes therein will have the greatest bearing upon the desired product slate and the hydrogen/hydrocarbon mole ratio. It is, of course, within the scope of our inventive control system to utiliæe a plurality of analyzers in order to monitor several charge stock characteristics. Thus, instrument line 40 will transmit one or more output signals representative of one or more charge stoc~ composition characteristics. Of course, the more processing output signals transmitted to computer/co~parator 95, the closer the control of the hydrogen/hydrocarbon mole ratio.
As hereinbefore set ~orth, the concentration of hydrogen within the vaporous phase being recycled to direct-fired heater 5, in admixture with the charge stock in line 1, must be known. Thus, analyzer 78 develops a process output signal representative of, and correlatable with ~7~7~3 the hydrogen content in the vaporous phase in line 2.
The sample is introduced by way of line 79, and the repre-sentative output signal transmitted to computer/compara-tor 95 by way of line 80. Since analyzer 78 is only required, in this illustration, to p:roduce a process out-put signal representative of the hydrogen concentration, it may be selected from a variety of suitable devices described in the appropriate prior art.
` Other process output signals, developed and transmitted to computer/comparator 95, involve operating variables, and are utilized to further refine the present control system and thus enhance the overall operation of the hydrogen-consuming process. One princ.ipal operating variable is the pressure at which the vaporous phase is separated from the reaction zone effluent in high-pressure separator 13. The output signal representative thereof is sensed, via line 67, by pressure indicator 68, and trans-mitted to computer/comparator 95 through instrument line 69. Additionally, flow indicator 43 senses the rate of flow of charge stock through line 1, by way of line 42, as metered by a .~low-determining means ~1, the latter being a venturi, orifice, turbine meter, or other suitable device. The output signal representative of the rate of flow of charge stock is transmitted via instrument line 44. Likewise, the rate of flow of the hydrogen-rich vapor-ous phase, being recycled via line 2, is measured and sensed by flow-determining means 59, line 60 and flow ~7~7~3 indicator 61; the output signal is transmitted by way of line 62.
Although not essential to the present hydrogen/
hydrocarbon mole ratio control system" but preferred from the viewpoint of overall process operation, are the flow rates of the liquid and vapor phases separated in high-pressure separator 13. The former is measured by flow-determining means 70, transmitted via line 71 to flow indicator 72, the output signal from which is trans-mitted via line 73 to computer/comparator 95. The flow rate of the vaporous phase, separated and withdrawn through line 14, is measured by flow-determining means 63 which transmits a signal via line 64 to flow indicator 65, the output signal from which is, in turn, transmitted to computer/comparator 95 by way of instrument line 66.
Other output signals, indicative of processing conditions employed within the illustrated conversion process, are representative of various temperatures therein. One such temperature is that of the combined feed stream which is preheated in heat exchanger 3, and introduced into direct-fired heater 5 through line 4.
The temperature of the preheated stream is sensed via line 96 and temperature indicator 97. The latter trans-mits a representative output signal to computer/comparator 95 via~instrument line 98. The inlet and outlet tempera-ture across the reaction zone is sensed, and appropriate signals transmitted to the computer/comparator. As previously stated, the temperature differential (delta-T) ~t7~713 across the catalyst bed is an important variable, in a hydrogen-consuming process, with respect to product spe-cifications and catalyst activity and stability. The delta-T across the catalyst bed in reactor 7 is!deter-mined by the inlet temperature sensed by temperature-sensing means 51 and temperature indicator 50, and the outlet temperature sensed by temperature-sensing means 48 and temperature indicator 47; the representative output signals are transmitted through instrument lines 52 and 49, respectively It is understood that pressure indi-cator 68 and temperature indicators 50, 47 and 97 may operate "blind". That is, they may simply transmit their respective output signals, and not simultaneously register the measurement on some control panel.
Still other process output signals, which further enhance the operation of the illustrated control system and thus the overall operation of the process, include that which is representative of the rate of flow of make-up hydrogen being introduced by way of line 21; this is metered by flow-de~ermining means 82 which transmits the appropriate signal to flow indicator 84, by way of line 83, the latter in turn transmitting the output signal by way of line 85. Similarly, the flow rate of that portion of the make-up hydrogen stream through line 22, to be admixed thereby with the reaction product effluent in line 12, is metered by way of flow-determining means 87, line 88 and flow indicator 89; the appropriate output signal representative thereof being transmitted to computer/

~707~3 comparator 95 by way of instrument line 90. One of the functions of computer/comparator 95 is to determine the quantity of hydrogen quench being diverted from line 2 by way of line 8 directly into the cataLyst bed disposed within reactor 7. The flow rate thereof is determined by flow-metering means 54, line 55 and flow indicator 56, the latter transmitting the appropriate process output signal by way of instrument line 57.
Computer/comparator 95 is internally programmed to be responsive to the various process output signals thus developed, and to develop and generate computer out-put signals which are utilized to make the necessary adjustments within the process in order to control the hydrogen/hydrocarbon mole ratio consistent with liquid product quality and quantity, and thus maintain an extended period of acceptable catalyst activity. The computer output signal transmitted by way of instrument line 36 is generated in a manner sufficient to adjust the tempera-ture level within reaction zone 7. Heat input to reaction zone 7 is provided by introducing a suitable combustible fuel into direct-fired heater 5. The fuel, which may be liquid, gas, or a mixture thereof, is burned within the combustion zone, and the hot combustion gases pass through the furnace and out the refinery stack. Heat input to the ; 25 reactant mixture is controlled by ad~usting the rate of fuel flow to heater 5, wherein the fuel is introduced via line 27 and combustion nozzle 29. The control thereof l~t7~7~3 is achieved by a flow-control. loop comprising flow sensing means 30 -- i.e. a turbine meter --, control valve 28, flow controller 32 and Elow signal line 31 whic~h transmits the flow signal from sensing means 30 to co:ntroller 34. Flow controller 32, which is equipped with a:n automatically adjustable setpoint, then transmits an appropriate adjust-ment signal to control valve 28.
In addition to the flow-control loop provlded in the fuel introduction system of direct-fired heater 5, there is preferably associated therewith, in cascade fash-ion, a temperature recorder-controller also having an auto-matically adjustable setpoint, and which senses the tempera-ture of the reactant mixture as it emanates ~rom the direct-fired heater. There is shown thermocouple means 35, con-tained in reactor inlet line 6, transmitting a temperature signal to temperature controller 34. Controller 34 produ-ces an output signal which is transmitted by way of line 33 to flow controller 32 to adjust, or reset the automatically adjustable setpoint thereof. Temperature controller 34, al-so having an adjustable setpoint, receives the appropriate computer output signal via line 35. Computer/comparator 95 thus adjusts the ternperature associated with reactor 7 by resetting the setpoint of temperature controller 34 which, in turn, resets the automatically adjustable setpoint of flow controller 32.
In addition to the comparator output signals above described, provision is made within the computer pro-gram to regulate the fresh feed charge stock flow rate, the flow rate of the hydrogen-rich recycled vaporous phase, the ~at7~7~3 flow rate o~ the quench stream introduced directly into the reaction zone and the quantity of make-up hydrogen removed from the process through line 25. Flow indicator 43 trans-mits a process output signal, represen1:ative of the charge stock flow rate, to computer/comparator 95 by way of instru-ment line 44. This signal is cons.idered in determining the required adjustments to achieve the then best hydrogen/hy-drocarhon mole ratio, and an appropriate computer output signal is transmitted by way of instrument line 46 -to ad-just flow control valve 45, thereby either increasing, or decreasing the flow of charge stock through line l. Simi-larly, the flow rate of the recycled gaseous phase admixed with the charge stock in line l is sensed by flow indicator 59, and a representative signal is developed and transmit-ted to the computer/comparator via line 62. This signal is considered in conjunction with that representative of t~
separator pressure, being sensed by pressure indicator 68, and is conjunctively employed to develop a computer output signal in line 86. These process output signals are also conjunctively considered by computer/comparator 95, and may simultaneously regulate the operation of control valve 24 by way o~ instrument line 81. A comparator output signal is also transmitted by way of instrument line 58 to regu-late control valve 53 which in turn increases, or decreases the quantity o~ the quench stream introduced by way of line 8. With respect to the quantity of make-up hydrogen intro-duced via line 22 and control valve 25, the principal out-put signals to which the computer~comparator responds are those transmitted thereto by way of instrument lines 57, 66, 1~7~

62, 85 and 90.
From the foregoing discussion, the method by which the present control system is effeeted is readily ap-parent to those having the requisite e~pertise in the appro-priate art. Also, the benefits and numerous advantages will be easily recognized. Prineipal among the advantages is the eontinuous monitoring whieh enhanees catalyst stabil-ity and maintains catalyst activity by eontrolling reaction zone hydrogen/hydroearbon mole ratio at that current opti-mum eonsistent with produet quality and quantity. Prior art control systems whieh monitor only a composition ehar-acteristie of the separated, produet-eontaining liquid phase, and adjust only the reaetion zone severity (prinei-pally temperature) in response thereto, must necessarily accept whatever effective eatalyst aetivity and stability results. To the contrary, the present control system focus-es upon hydrogan/hydrocarbon mole ratio to enhance catalyst stability, or extend the period of time that the catalyst functions acceptably, while simultaneously attaining the de-

2~ sired produet slate. Our invention reeognizes the neeessity of additionally monitoring eharaeteristies of the eharge stoek and its rate of flow, as well as the flow and hydro-gen eontent of the various vaporous phases within the over-all proeess.

Claims (15)

WE CLAIM AS OUR INVENTION:

1. In a continuous hydrocarbon conversion process in which hydrogen is consumed, and wherein (1) a hydrocarbona-ceous charge stock and hydrogen are introduced into preheat-ing means having external heat-supplying means operatively associated therewith; (2) the resulting heated charge stock-hydrogen mixture is reacted in a catalytic reaction zone;
(3) the resulting reaction zone effluent stream is condensed and separated to provide a liquid phase and a first hydro-gen-containing vaporous phase; (4) at least a portion of said first vaporous phase is recycled to said preheating means, in admixture with said charge stock; and, (5) a sec ond hydrogen-containing vaporous phase, from an external source, is introduced into said process, at least a portion thereof is admixed with said first hydrogen-containing va-porous phase and introduced therewith into said preheating means; the control system for regulating the hydrogen/hydro-carbon mole ratio within said reaction zone which comprises, in cooperative combination:
(a) first flow-varying means, operatively associa-ted with said preheating means, for adjusting the quan-tity of heat supplied thereto;
(b) first flow-sensing means for measuring the rate of flow of said charge stock to said reaction zone and developing a first process output signal rep-resentative thereof, and second flow-varying means for adjusting the rate of flow of said charge stock;
(c) a first analyzer receiving a sample of said charge stock and developing a second process output signal representative of a composition characteristic thereof;
(d) second flow-sensing means for measuring the rate of flow of said second hydrogen-containing vapor-ous phase, introduced into said process, and develop-ing a third process output signal representative there-of, and third flow-varying means for adjusting the rate of flow of said second vaporous phase;
(e) a second analyzer receiving a sample of the hydrogen-containing vaporous phase introduced into said preheating means and developing a fourth process output signal representative of the hydrogen concentra-tion thereof;
(f) third flow-sensing means for measuring the rate of flow of the hydrogen-containing vaporous phase introduced into said preheating means, in admixture with said charge stock, and developing a fifth process output signal representative of the rate of flow there-of;
(g) means for sensing the pressure of the separa-ted first hydrogen-containing vaporous phase and devel-oping a sixth process output signal representative thereof; and, (h) comparator means (i) receiving said six pro-cess output signals and, operatively responsive there-to, (ii) generating first, second and third comparator output signals as functions thereof;
said control system further characterized in that said com-parator means is in communication with said first, second and third flow-varying means, via signal transmitting means which transmit at least one of said comparator output sig-nals to at least one of said flow-varying means, whereby at least one of (i) the flow of said charge stock, (ii) the heat supplied to said preheating means and (iii) the flow of said second hydrogen-containing vaporous phase into said process is adjusted in response thereto, and said hydrogen/
hydrocarbon mole ratio is regulated.

2. The control system of Claim 1 further character-ized in that (i) fourth flow-sensing means measures the rate of flow of a third hydrogen-containing vaporous phase, having a fourth flow-varying means operatively associated therewith, introduced directly into said catalytic reaction zone, develops a seventh process output signal representa-tive thereof and transmits said seventh output signal to said comparator means, and (ii) said comparator means gen-erates said first, second and third comparator output sig-nals, and a fourth comparator output signal as functions of said seven process output signals.

3. The control system of Claim 2 further character-ized in that at least one of said four comparator output signals are transmitted to at least one of said four flow-varying means, whereby at least one of (i) the flow of said charge stock, (ii) the heat supplied to said preheating means, (iii) the flow of said second hydrogen-containing vaporous phase into said process and (iv) the flow of said third hydrogen-containing vaporous phase directly into said catalytic reaction zone is adjusted in response thereto.

4. The control system of Claim 2 further character-ized in that a third analyzer receives a sample of said separated liquid phase and develops an eighth process out-put signal representative thereof, said eighth output sig-nal is transmitted to said comparator means which generates said four comparator output signals as functions of said eighth process output signals.

5. The control system of Claim 4 further character-ized in that said first and third analyzers comprise stabil-ized cool flame generators having servo-positioned flame fronts.

6. The control system of Claim 4 further character-ized in that first temperature-sensing means senses a first temperature within said reaction zone, develops a ninth pro-cess output signal representative thereof and transmits said ninth output signal to said comparator means.

7. The control system of Claim 6 further character-ized in that said comparator means generates an output sig-nal as a function of said first reaction zone temperature and the composition characteristic of said separated liquid phase, and transmits said output signal to said first flow-varying means whereby the heat supplied to said preheating means is adjusted in response thereto.

8. The control system of Claim 6 further character-ized in that second temperature-sensing means senses a sec-ond temperature within said reaction zone, develops a tenth process output signal representative thereof and transmits said tenth output signal to said comparator means.

9. The control system of Claim 8 further character-ized in that said comparator means generates a comparator output signal as a function of said first and second reac-tion zone temperatures, and the composition characteristic of said separated liquid phase, and transmits said compara-tor output signal to said first flow-varying means whereby the heat supplied to said preheating means is adjusted in response thereto.

10. The control system of Claim 8 further character-ized in that said first temperature-sensing means senses a first temperature in the outlet section of said reaction zone, said second temperature-sensing means senses a second temperature in the inlet section of said reaction zone, the developed ninth and tenth output signals are transmitted to said comparator means and said comparator means generates a comparator output signal as a function of the difference be-tween said first and second temperatures, and the composi-tion characteristic of said separated liquid phase, and said comparator output signal is transmitted to said first flow-varying means.

11. The control system of Claim 9 further character-ized in that said first flow-varying means comprises a flow control loop having a flow controller with an adjustable setpoint regulating the supply to heat to said preheating means, said setpoint being adjusted in response to said com-parator output signal.

12. The control system of Claim 11 further character-ized in that (i) temperature-controlling means, having an adjustable setpoint, develops a controller output signal representative of the heated charge stock-hydrogen mixture from said preheating means, and transmits said controller output signal to said flow controller, whereby the setpoint thereof is adjusted in response thereto, and (ii) said com-parator output signal is transmitted to said temperature-controlling means, whereby the setpoint thereof is adjusted in response thereto.

13. The control system of Claim 2 further character-ized in that said comparator means generates a fifth com-parator output signal as a function of said sixth process output signal and transmits said fifth comparator output signal to fifth flow-varying means operatively associated with said first hydrogen-containing vaporous phase whereby a portion thereof is withdrawn from said process.

14. A method for regulating the hydrogen/hydrocarbon mole ratio within the catalytic reaction zone of a continu-ous hydrocarbon conversion process in which hydrogen is con-sumed, and wherein: (1) a hydrocarbonaceous charge stock and hydrogen are introduced into preheating means having ex-ternal heat-supplying means operatively associated there-with; (2) the resulting heated charge stock-hydrogen mix-ture is reacted in said catalytic reaction zone; (3) the re-sulting reaction zone effluent stream is condensed and sepa-rated to provide a liquid phase and a first hydrogen-con-taining vaporous phase; (4) at least a portion of said first vaporous phase is recycled to said preheating means, in admixture with said charge stock; and, (5) a second hy-drogen-containing vaporous phase, from a source external of said process, is introduced therein and at least a portion thereof is admixed with said first hydrogen-containing va-porous phase, and introduced therewith into said preheating means, which method comprises the steps of:
(a) regulating the quantity of heat supplied to said preheating means by adjusting a first flow-varying means operatively associated therewith;
(b) regulating the flow of said charge stock by adjusting a second flow-varying means, sensing the rate of flow of said charge stock and developing a first process output signal representative of a composition characteris-tic thereof;
(c) introducing a sample of said charge stock in-to a first analyzer and developing therein a second process output signal representative of a composition characteris-tic thereof;
(d) regulating the flow of said second hydrogen-containing vaporous phase, introduced into said process, by adjusting a third flow-varying means, sensing the rate of flow of said second hydrogen-containing vaporous phase and developing a third process output signal representative thereof;
(e) introducing a sample of the hydrogen-contain-ing vaporous phase, passing into said preheating means, in-to a second analyzer and developing therein a fourth pro-cess output signal representative of the hydrogen concentra-tion thereof;
(f) sensing the rate of flow of the hydrogen-con-taining vaporous phase passing into said preheating means and developing a fifth process output signal representative thereof;
(g) monitoring the pressure of said separated hy-drogen-containing vaporous phase and developing a sixth process output signal representative thereof;

(h) introducing a sample of said separated liquid phase into a third analyzer and developing therein a sev-enth process output signal representative of a composition characteristic thereof;
(i) transmitting said seven process output sig-nals to comparator means and generating therein first, sec-ond and third comparator output signals as functions of said seven process output signals; and, (j) transmitting at least one of said three com-parator output signals to at least one of said first, sec-ond and third flow-varying means and regulating the quan-tity of heat supplied to said preheating means, the flow of said charge stock and/or the flow of said second hydrogen-containing vaporous phase to control the hydrogen/hydrocar-bon mole ratio within said catalytic reaction zone.

15. The method of Claim 14 further characterized in that said hydrocarbon conversion process is hydrocracking and said first analyzer develops a process output signal representative of the molecular weight of said charge stock.