Note: Descriptions are shown in the official language in which they were submitted.
~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
--2--
~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~
--3--
~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
--4--
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
--5--
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
--10--
~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
--11--
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
-12-
.
.
~ ~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
-13-
~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.
-14-
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
-15-
~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
-16-
~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
-17-
)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
-18-
~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
--19--
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
-20-
~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
: '
-22-
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
-23-
~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.
-24-
.,
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
-25-
~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
-26-
713
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
-27-
:~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
-28-
~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
-30-
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
-32-
-
~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.
-33-
~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
-34-
~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
-36-
~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
-37-
~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)
-38-
~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/
-39-
~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
-40-
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,
-42-
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.
-43-
