Temperature control of exothermic reactions

In a selective hydrogenation process wherein at least two catalyst beds in series are utilized, the temperature of the feed stream to the first catalyst bed and the temperature of the feed stream from the first catalyst bed to the second catalyst bed are manipulated so as to maintain a desired reaction temperature in both catalyst beds. The desired reaction temperature of the first catalyst bed is manipulated so as to insure that a desired percent of a specific feed component is selectively hydrogenated in the first catalyst bed. The reaction temperature of the second catalyst bed is manipulated so as to maintain a desired concentration of the specific feed component in the product stream from the second catalyst bed.

This invention relates to temperature control of an exothermic reaction. In 
a specific aspect this invention relates to selective hydrogenation of 
unsaturated hydrocarbons in mixed hydrocarbon streams. In another specific 
aspect this invention relates to selective hydrogenation of acetylenic 
compounds in olefin-rich hydrocarbon streams. 
In many exothermic chemical reactions it is necessary to control 
temperature within certain limits in order to maintain satisfactory yields 
and to prevent side reactions. This is particularly true in selective 
hydrogenation processes. For example, ethylene is commonly produced by the 
thermal cracking of hydrocarbon feedstocks. Unfortunately, some acetylene 
(impurity) is also produced which must be removed for many applications. 
This can be accomplished by selective catalytic hydrogenation of the 
acetylene. 
In selective hydrogenation operations of this type, it is very important to 
maintain the operating temperature within narrow limits. If the 
temperature is too low, the hydrogenation reaction is not carried out in a 
sufficiently complete manner to remove the acetylene. If the temperature 
becomes too high, side reactions such as the hydrogenation of ethylene and 
the formation of polymers may result. It is also very important to prevent 
excessive temperatures from being reached because of the danger of 
explosions. 
It is also important, where two catalyst beds in series are utilized as in 
the present invention, to maintain a relationship between the percentage 
of the acetylene hydrogenated in the first catalyst bed and the percentage 
of the acetylene hydrogenated in the second catalyst bed. Preferably the 
first catalyst bed is utilized to hydrogenate most of the acetylene with 
the second catalyst bed being utilized primarily as a cleanup process. 
Close control of the percentage of the acetylene hydrogenated in each 
catalyst bed provides for a more efficient conversion of acetylene and 
reduces the risk of excessive temperature in either catalyst bed. 
It is thus an object of this invention to provide method and apparatus for 
controlling the reaction temperature of an exothermic chemical reaction 
process. Another object of this invention is to provide method and 
apparatus for controlling the selective hydrogenation of unsaturated 
hydrocarbons in mixed hydrocarbon streams. Still another object of this 
invention is to provide method and apparatus for controlling the selective 
hydrogenation of acetylenic compounds in olefin-rich hydrocarbon streams. 
In accordance with the present invention, a selective hydrogenation process 
which utilizes two catalyst beds in series is controlled so as to maintain 
a desired reaction temperature in each catalyst bed. The reaction 
temperature of the first reactor is manipulated so as to insure that a 
desired percentage of the impurity wall be hydrogenated in the first 
reactor. The reaction temperature of the second reactor is manipulated so 
as to insure that the concentration of the impurity in the product flowing 
from the second reactor is maintained below a predetermined level. Two 
separate reactors may be utilized or a single reactor with two catalyst 
beds may be utilized so long as control and analysis of the fluid stream 
flowing between the two catalyst beds is possible. Hereafter, the term 
first reactor and second reactor is utilized to describe the invention but 
the invention is not limited to the use of separate reactor vessels. 
The feed stream to the first reactor and the feed stream from the first 
reactor to the second reactor are split into at least two portions. A 
first portion of the feed stream to the first reactor is heated before 
being passed to the first reactor. A second portion of the feed stream to 
the first reactor is utilized as a quench fluid and is introduced into the 
first portion of the feed stream to the first reactor after the first 
portion of the feed stream to the first reactor has been heated. The first 
portion of the feed stream from the first reactor to the second reactor is 
supplied directly to the second reactor. The second portion of the feed 
stream from the first reactor to the second reactor is cooled and is 
utilized as a quench fluid and is introduced into the first portion of the 
feed stream from the first reactor to the second reactor before the feed 
stream enters the second reactor. 
An analysis of the feed stream flowing to the first reactor is utilized to 
provide an indication of the amount of acetylene in the feed stream. An 
analysis of the feed stream flowing from the first reactor to the second 
reactor is utilized to provide an indication of the amount of acetylene in 
the feed stream flowing from the first reactor to the second reactor. The 
temperature of the feed stream flowing to the first reactor is controlled 
in response to the analysis of the amount of acetylene in the feed stream 
flowing to the first reactor and the analysis of the amount of acetylene 
in the feed stream flowing from the first reactor to thereby maintain a 
desired percent conversion of the acetylene in the first reactor. 
A feed forward model based on an analysis of the acetylene in the feed 
stream flowing to the first reactor, an analysis of the amount of carbon 
monoxide in the feed stream flowing to the first reactor and the flow rate 
of the feed stream flowing to the first reactor is utilized to predict 
temperature changes required for the feed stream flowing to the first 
reactor to maintain the desired percent conversion of acetylene in the 
first reactor. This prediction is utilized to bias the control of the 
temperature of the feed stream based on the analysis of the feed stream 
flowing to the first reactor and the analysis of the feed stream flowing 
from the first reactor to thereby compensate for required temperature 
changes before the analysis of the feed stream flowing from the first 
reactor indicates that a temperature change should have been made to 
compensate for some change in the feed rate or some change in the 
composition of the feed stream. 
An analysis of the product stream flowing from the second reactor provides 
an indication of the concentration of acetylene in the product stream 
flowing from the second reactor. This concentration is compared to a 
predetermined concentration and the comparison is utilized to manipulate 
the temperature of the feed stream flowing from the first reactor to the 
second reactor. A feed forward model based on the analyses of the feed 
stream to the first and second reactor and the flow rate of the feed 
stream to the first reactor is utilized to provide a prediction of 
required changes in the temperature of the feed stream flowing from the 
first reactor to the second reactor necessary to maintain the 
concentration of acetylene in the product stream flowing from the second 
reactor below the predetermined level. This prediction is utilized to bias 
the comparison of the desired concentration of acetylene with the actual 
concentration of acetylene to thereby provide feed forward predictive 
control for the second reactor. 
In this manner, the required reaction temperatures are maintained in each 
reactor. A desired percentage of acetylene is hydrogenated in the first 
reactor and the concentration of acetylene in the product stream from the 
second reactor is maintained below the predetermined level.

The invention is illustrated and described in terms of a selective 
hydrogenation process for the hydrogenation of acetylene in an ethylene 
product. However, it should be understood that this invention can be 
utilized for carrying out other selective hydrogenation processes such as 
the conversion of diolefins to olefins and/or saturated compounds. 
Although the invention is illustrated and described in terms of a specific 
hydrogenation process, the applicability of the invention described herein 
extends to other process configurations such as using different heat 
exchanger configurations, more than two reactors or, as has been 
previously stated, two catalysts beds in a single reactor vessel. The 
invention also extends to different types of control system configurations 
which accomplish the purpose of the invention. Lines designated as signal 
lines in the drawings are pneumatic in this preferred embodiment. However, 
this invention is also applicable to electrical, mechanical, hydraulic or 
other signal means for transmitting information. In many control systems 
some combination of these types of signals will be used. However, use of 
any other type of signal transmission, compatible with the process and 
equipment in use, is within the scope of the invention. 
Both the analog and digital controllers shown may utilize the various modes 
of control such as proportional, proportional-integral, 
proportional-derivative, or proportional-integral-derivative. In this 
preferred embodiment, proportional-integral controllers are utilized but 
any controller capable of accepting two input signals and producing a 
scaled output signal, representative of a comparison of the two input 
signals, is within the scope of the invention. The operation of 
proportional-integral controllers is well known in the art. The output 
control signal of a proportional-integral controller may be represented as 
EQU S=K.sub.1 E+K.sub.2 .intg.Edt 
where 
S=output control signals; 
E=difference between two input signals; and 
K.sub.1 and K.sub.2 =constants. 
The scaling of an output signal by a controller is well known in control 
systems art. Essentially, the output of a controller may be scaled to 
represent any desired factor or variable. An example of this is where a 
desired pressure and an actual pressure is compared by a controller. The 
output could be a signal representative of a desired change in the flow 
rate of some gas necessary to make the desired and actual pressures equal. 
On the other hand, the same output signal could be scaled to represent a 
percentage or could be scaled to represent a temperature change required 
to make the desired and actual pressures equal. If the controller output 
can range from 0 to 10 volts, which is typical, then the output signal 
could be scaled so that an output signal having a voltage level of 5.0 
volts corresponds to 50 percent, some specified flow rate, or some 
specified temperature. 
The various transducing means used to measure parameters which characterize 
the process and the various signals generated thereby may take a variety 
of forms or formats. For example, the control elements of the system can 
be implemented using electrical analog, digital electronic, pneumatic, 
hydraulic, mechanical or other types of equipment or combinations of one 
or more of such equipment types. While the presently preferred embodiment 
of the invention preferably utilizes pneumatic control elements in 
conjunction with pneumatic signal handling and translation apparatus, the 
apparatus and method of the invention can be implemented using a variety 
of specific equipment available to and understood by those skilled in the 
process control art. Likewise, the format of the various signals can be 
modified substantially in order to accommodate signal format requirements 
of a particular installation, safety factors, the physical characteristics 
of the measuring or control instruments and other similar factors. For 
example, a measurement of a system parameter may exhibit a generally 
proportional relationship to the square of the actual system parameter. 
Other measuring instruments might produce a signal which is proportional 
to the measured parameter, and still other measuring instruments may 
produce a signal which bears a more complicated, but known, relationship 
to the measured system parameter. In addition all signals could be 
translated into a "suppressed zero" or other similar format in order to 
provide a "live zero" and prevent an equipment failure from being 
erroneously interpreted as a low (or high) measurement or control signal. 
Regardless of the signal format or the exact relationship of the signal to 
the parameter which it represents, each signal representative of a 
measured process parameter or representative of a desired process value 
will bear a relationship to the measure parameter or desired value which 
permits designation of a specific measured or desired value by a specific 
signal value. A signal which is representative of a process measurement or 
desired process value is therefore one from which the information 
regarding the measured or desired value can be readily retrieved 
regardless of the exact mathematical relationship between the signal units 
and the measured or desired process units. 
Referring now to FIG. 1, an ethylene feed stream containing some 
concentration of acetylene and carbon monoxide is introduced through 
conduit means 13 and 14 to the reactor 11 which contains a first catalyst 
bed containing a hydrogenation catalyst. Heat exchanger 15 is operably 
located between conduit means 13 and 14 such that fluid from conduit means 
13 flows through heat exchanger 15. The heat exchanger 15 is utilized to 
provide heat to the feed stream flowing through conduit means 13 and 14 to 
the reactor 11. Steam or another suitable heating fluid is provided 
through conduit means 17 to the heat exchanger 15 and is utilized to 
provide heat to the feed flowing through conduit means 13 and 14. The 
pneumatic control valve 21 is operably located in conduit means 13 and is 
utilized to split the flow of the feed between conduit means 13 and 
conduit means 16. The feed flowing through conduit means 14 and the bypass 
conduit means 16 are preferably mixed before the feed enters the reactor 
11. The feed flowing through the bypass conduit means 16 is utilized as a 
quench fluid to provide further temperature control of the feed flowing to 
the reactor 11. 
The effluent flowing from the reactor 11 is passed through conduit means 23 
and 24 to the reactor 12 which contains a second catalyst bed containing a 
hydrogenation catalyst. Heat exchanger 25, which is operably located 
between conduit means 23 and 24, is utilized to provide a means for 
cooling the effluent flowing through conduit means 23 and 24. A cooling 
fluid, such as water, is provided through conduit means 26 to the heat 
exchanger 25. The pneumatic control valve 28, which is operably located in 
conduit means 23, is utilized to control the relationship between the 
amount of effluent flowing from the reactor 11 which flows to the reactor 
12 through the heat exchanger 25 and through the bypass conduit means 27. 
The effluent flowing through conduit means 27 may be considered the 
primary effluent stream and the effluent flowing through conduit means 23, 
the heat exchanger means 25, and conduit means 24 may be considered the 
quench fluid stream. The two fluid streams flowing through conduit means 
27 and conduit means 24 are preferably mixed before entering the reactor 
12. 
The ethylene product, which will generally have a very low concentration of 
acetylene, is removed from the reactor 12 through conduit means 19. The 
product removed from the reactor 12 through conduit means 19 is generally 
provided to other portions of the ethylene manufacturing process. 
The selective hydrogenation process described to this point is a 
conventional selective hyrogenation process. It is the manner in which the 
selective hydrogenation process, illustrated in FIG. 1, is controlled so 
as to maintain a desired percentage conversion of acetylene in reactor 11 
and to maintain the concentration of acetylene in the product flowing from 
the reactor 12 through conduit means 19 below a predetermined level which 
provides the novel features of the present invention. 
Control of the selective hydrogenation process illustrated in FIG. 1 is 
generally accomplished by measuring a plurality of system parameters and 
supplying the measured parameters to computer means 100. Computer means 
100 is preferably an Optrol 3600 manufactured by Applied Automation, Inc., 
Bartlesville, Okla. Computer means 100 is also supplied with a plurality 
of set point signals which are representative of desired operating 
characteristics for the selective hydrogenation process illustrated in 
FIG. 1. In response to the measured inputs and the set point inputs, 
computer means 100 calculates the temperature of the feed stream flowing 
to the reactor 11 and the temperature of the feed stream flowing to the 
reactor 12 required to maintain a desired percent conversion of acetylene 
in the reactor 11 and to maintain the concentration of acetylene in the 
bottom product flowing from the reactor 12 through conduit means 19 below 
the predetermined level. 
Analyzer transducer 31, which is operably connected to the conduit means 
13, provides a pair of output signals 32 and 35. Signal 32, which is 
representative of the concentration of acetylene in the feed stream 
flowing to conduit means 13, is provided from the analyzer transducer 31 
to the analog to digital (A/D) converter 33. Signal 32 is converted from 
analog form to digital form by the A/D converter 33 and is provided a 
signal 34 to computer means 100. Signal 35, which is representative of the 
concentration of carbon monoxide in the feed stream flowing through 
conduit means 13, is provided from the analyzer transducer 31 as an input 
to the A/D converter 36. Signal 35 is converted from analog form to 
digital form by the A/D converter 36 and is provided as signal 37 to 
computer means 100. 
The flow transducer 41 in combination with the flow sensor 42, which is 
operably located in conduit means 13, provides an output signal 43 which 
is representative of the flow rate of the feed stream flowing through 
conduit means 13. Signal 43 is provided from the flow transducer 41 as an 
input to the A/D converter 44. Signal 43 is converted from analog form to 
digital form by the A/D converter 44 and is provided as signal 45 to 
computer means 100. 
Temperature transducers 51, 52 and 53, which are each representative of 
three temperature transducers, provide a plurality of output signals which 
represent a temperature profile across the reactor 11. The three 
temperature transducers, represented by temperature transducer 51, in 
combination with three thermocouple elements, which are operably located 
in reactor 11, provide three output signals which are represented by 
signal 54. The three output signals, represented by signal 54, are 
representative of a temperature profile of the upper portion of the 
reactor 11. The three signals, represented by signal 54, are provided from 
the three temperature transducers, represented by temperature transducer 
51, to three A/D converters represented by A/D converter 55. The three 
temperature signals, represented by signal 54, are converted from analog 
form to digital form by three A/D converters, represented by A/D converter 
55, and are provided as three signals, represented by signal 56, to the 
computer means 100. 
The three temperature transducers, represented by temperature transducer 
52, in combination with three thermocouple elements, which are operably 
located in reactor 11, provide three output signals which are represented 
by signal 58. The three output signals, represented by signal 58, are 
representative of a temperature profile of the middle portion of the 
reactor 11. The three signals, represented by signal 58, are provided from 
the three temperature transducers, represented by temperature transducer 
52, to three A/D converters represented by A/D converter 59. The three 
temperature signals, represented by signal 58, are converted from analog 
form to digital form by the three A/D converters, represented by A/D 
converter 59 and are provided as three signals, signal 56, to the computer 
means 100. 
The three temperature transducers, represented by temperature transducer 
53, in combination with three thermocouple elements which are operably 
located in reactor 11 provide three output signals which are represented 
by signal 63. The three output signals, represented by signal 63 are 
representative of a temperature profile of the lower portion of the 
reactor 11. The three signals, represented by signal 63, are provided from 
the three temperature transducers, represented by temperature transducer 
53, to three A/D converters represented by A/D converter 64. The three 
temperature signals, represented by signal 63, are converted from analog 
form to digital form by the three A/D converters, represented by A/D 
converter 64 and are provided as three signals, represented by signal 65, 
to the computer means 100. 
Temperature transducer 71, 72 and 73, which are each representative of 
three temperature transducers, provide a plurality of output signals which 
represent a temperature profile across the reactor 12. The three 
temperature transducers, represented by temperature transducer 71, in 
combination with three thermocouple elements which are operably located in 
reactor 12 provide three output signals which are represented by signal 
74. The three output signals, represented by signal 74, are representative 
of a temperature profile of the upper portion of the reactor 12. The three 
signals, represented by signal 74, are provided from the three temperature 
transducers, represented by temperature transducer 71, to three A/D 
converters represented by A/D converter 75. The three temperature signals, 
represented by signal 74, are converted from analog form to digital form 
by the three A/D converters, represented by A/D converter 75, and are 
provided as three signals, represented by signal 76 to the computer means 
100. 
The three temperature transducers, represented by temperature transducer 
72, in combination with three thermocouple elements which are operably 
located in reactor 12 provide three output signals which are represented 
by signal 78. The three output signals, represented by signal 78, are 
representative of a temperature profile of the middle portion of the 
reactor 12. The three signals, represented by signal 78, are provided from 
the three temperature transducers, represented by temperature transducer 
72, to three A/D converters represented by A/D converter 79. The three 
temperature signals, represented by signal 78, are converted from analog 
form to digital form by the three A/D converters, represented by A/D 
converter 79, and are provided as three signals, represented by signal 81, 
to the computer means 100. 
The three temperature transducers, represented by temperature transducer 
73, in combination with three thermocouple elements which are operably 
located in reactor 12 provide three output signals which are represented 
by signal 83. The three output signals, represented by signal 83, are 
representative of a temperature profile of the lower portion of the 
reactor 12. The three signals, represented by signal 83, are provided from 
the three temperature transducers, represented by temperature transducer 
73, to three A/D converters represented by A/D converter 84. The three 
temperature signals, represented by signal 83, are converted from analog 
form to digital form by the three A/D converters, represented by A/D 
converter 84, and are provided as three signals, represented by signal 85, 
to the computer means 100. 
Analyzer transducer 91, which is preferably a chromatographic analyzer, is 
operably connected to conduit means 23. The analyzer transducer 91 
provides an output signal 93 which is representative of the concentration 
of acetylene in the effluent flowing through conduit means 23. Signal 93 
is provided from the analyzer transducer 91 as an input to the A/D 
converter 94. Signal 93 is converted from analog form to digital form and 
is provided as signal 95 to computer means 100. 
Analyzer transducer 101, which is preferably a chromatographic analyzer, is 
operably connected to conduit means 19. The analyzer transducer 101 
provides an output signal 103 which is representative of the concentration 
of acetylene in the effluent flowing through conduit means 19. Signal 103 
is provided from the analyzer transducer 101 as an input to the A/D 
converter 104. Signal 103 is converted from analog form to digital form 
and is provided as signal 105 to computer means 100. 
In response to the described inputs, computer means 100 calculates two 
control signals which are utilized in controlling the selective 
hydrogenation process illustrated in FIG. 1. One control signal 111, 
calculated by the computer means 100, is representative of the temperature 
of the feed stream flowing to the reactor 11 required to maintain a 
desired reaction temperature in the reactor 11 which will insure that a 
desired percentage of acetylene is selectively hydrogenated in reactor 11. 
Signal 111 is provided from computer means 100 as an input to the digital 
to analog (D/A) converter 112. Signal 111 is converted from digital form 
to analog form by the D/A converter 112 and is provided as signal 113 to 
the temperature controller 114. The temperature transducer 115 in 
combination with a temperature measuring device such as a thermocouple, 
which is operably located in conduit means 14, provides an output signal 
116 which is representative of the actual temperature of the effluent 
flowing through conduit means 14. Signal 116 is provided from the 
temperature transducer 115 as a second input to the temperature controller 
114. In response to signals 113 and 116, the temperature controller 114 
provides an output signal 117 which is responsive to the difference 
between signals 113 and 116. Signal 117 is scaled so as to be 
representative of the split of the feedstream between conduit means 13 and 
the bypass conduit means 16 required to maintain a desired temperature for 
the feed stream flowing into reactor 11 and thus maintain a desired 
reaction temperature in reactor 11. Signal 117 is provided from the 
temperature controller 114 as an input to the current to pressure (I/P) 
transducer 118. Signal 117 is converted from electrical form to a 
pneumatic form by the I/P converter 118 and is provided as signal 119 to 
the pneumatic control valve 21. The pneumatic control valve 21 is 
manipulated in response to signal 119 to thereby maintain a desired split 
of the feed stream flowing to reactor 11 between conduit means 13 and the 
bypass conduit means 16. 
A second control signal 131, calculated by the computer means 100, is 
representative of the temperature of the feed stream flowing to the 
reactor 12 required to maintain a desired reaction temperature in the 
reactor 12 which will insure a concentration of acetylene in the product 
flowing through conduit means 19 which is equal to or less than a desired 
concentration. Signal 131 is provided from computer means 100 as an input 
to the digital to analog (D/A) converter 132. Signal 131 is converted from 
digital form to analog form by the D/A converter 132 and is provided as 
signal 133 to the temperature controller 134. The temperature transducer 
135 in combination with a temperature measuring device such as a 
thermocouple, which is operably located in conduit means 24, provides an 
output signal 136 which is representative of the actual temperature of the 
effluent flowing through conduit means 124. Signal 136 is provided from 
the temperature transducer 135 as a second input to the temperature 
controller 134. In response to signals 133 and 136, the temperature 
controller 134 provides an output signal 137 which is responsive to the 
difference between signals 133 and 136. Signal 137 is scaled so as to be 
representative of the split of the feedstream between conduit means 24 and 
the bypass conduit means 27 required to maintain a desired temperature for 
the feed stream flowing into reactor 12 and thus maintain a desired 
reaction temperature in reactor 12. Signal 137 is provided from the 
temperature controller 134 as an input to the current to pressure (I/P) 
transducer 138. Signal 137 is converted from electrical form to a 
pneumatic form by the I/P converter 138 and is provided as signal 139 to 
the pneumatic control valve 28. The pneumatic control valve 28 is 
manipulated in response to signal 139 to thereby maintain a desired split 
of the feed stream flowing to reactor 12 between conduit means 24 and the 
bypass conduit means 27. 
The logic flow diagram utilized to calculate the control signals 111 and 
131 in response to the prevously described input signals to the computer 
means 100 is illustrated in FIG. 2a and FIG. 2b. Referring now to FIGS. 2a 
and 2b as a combination, signal 95, which is representative of the 
concentration of acetylene in the feed stream flowing through conduit 
means 23 from the reactor 11, is provided as a first input to the 
conversion calculation for reactor 11 block 201. Signal 34, which is 
representative of the concentration of acetylene in the feed stream 
flowing to the reactor 11, is provided as a second input to the conversion 
calculation for reactor 11 block 201 and is also provided as a first input 
to the feed forward model for reactor 11 block 202. In response to signals 
95 and 34, the conversion calculation for reactor 11 block 201 provides an 
output signal 203 which is representative of the percentage of acetylene 
in the feed flowing to the reactor 11 which has been converted in reactor 
11. Equation (I) is utilized in the conversion calculation for reactor 11 
block 201 to calculate signal 203 based on signals 95 and 34. 
EQU CONV=[1.0-(A.sub.out /c10000.0.times.A.sub.in)][100.0] (I) 
where 
CONV=the actual percentage of acetylene in the feed stream flowing to the 
reactor 11 which is converted in the reactor 11; 
A.sub.in =the concentration of acetylene in the feed stream flowing to 
reactor 11 (mole percent) (signal 34); 
A.sub.out =concentration of acetylene in the feed stream flowing out of the 
reactor 11 (parts per million) (signal 95). 
Signal 203 is provided from the conversion calculation for reactor 11 block 
201 as an input to the controller block 205. The controller block 205 is a 
digital implementation of a proportional-integral controller. 
The switching logic block 208 is provided with a set point signal 209 which 
is representative of the desired percentage of acetylene being selectively 
hydrogenated in reactor 11 (preferably 70%). The switching logic block 208 
is also provided with the output signal 211 from the controller block 212. 
Either signal 211 or signal 209 is selected by the switching logic block 
208 to be provided as signal 213 to the controller 205. Signal 209 is 
selected only when no high temperature limits have been reached in reactor 
11 and high temperature limits have been reached in reactor 12. Signal 
213, from the switching logic block 208, is representative of the desired 
percentage of acetylene which is to be selectively hydrogenated in reactor 
11. Signal 213 is provided from the switching logic block 208 as a second 
input to the controller block 205. 
In response to signals 203 and 213, the controller block 205 provides an 
output signal 214 which is responsive to the difference between signals 
203 and 213. Signal 214 is representative of the temperature of the feed 
stream flowing to the reactor 11 required to maintain a desired reaction 
temperature in the reactor 11 so as to insure that a desired percentage of 
acetylene is selectively hydrogenated in the reactor 11. Signal 214 is 
provided from a controller block 205 as a first input to the summing block 
215. 
Signal 37, which is representative of the concentration of carbon monoxide 
in the feed stream flowing through conduit means 13, is provided as a 
second input to the feed forward model for reactor 11 block 202. Signal 
45, which is representative of the flow rate of the feed stream flowing to 
the reactor 11, is provided as a third input to the feed forward model for 
reactor 11 block 202. In response to the described input signals, the feed 
forward model for reactor 11 block 202 utilizes Equation (II), Equation 
(VI) and Equation (X) to provide signal 221 which is representative of a 
prediction of the change required in the temperature of the feed stream 
flowing to the reactor 11 to compensate for changes in the composition of 
the feed stream flowing to the reactor 11 or a change in the flow rate of 
the feed stream flowing to the reactor 11. Equation (II) represents the 
feed forward contribution from feed rate changes; Equation (III) 
represents the feed forward contribution for changes of the concentration 
of acetylene in the feed stream; and Equation (IV) is representative of 
the feed forward contribution for changes in the concentration of carbon 
monoxide in the feed stream. Results of equations (II), (VI) and (IX) are 
combined to provide signal 221. 
EQU FF1(n)=[ARR(6)][FF1(n-1)]+[ARR(7)][DF(n-.theta..sub.F)]+[ARR(8)](II) 
where 
FF1(n)=Feed forward contribution from feed rate changes to first reactor; 
FF1(n-1)=FF1(n) from last program pass; 
DF(n-.theta..sub.F)=Change in feed rate delayed by .theta..sub.F intervals; 
DF(n-.theta..sub.F -1)=DF(n-.theta..sub.F) from last program pass; 
ARR(6)=Tuning constant; 
ARR(7)=Tuning constant; 
ARR(8)=Tuning constant; and 
.theta..sub.F =Time required for a change in the feed rate to cause a 
change in output of analyzer transducer 91. 
The tuning constants ARR(6), ARR(7) and ARR(8) are defined as follows: 
EQU ARR(6)=e-(T/.tau..sub.1) (III) 
where 
T=cycle time for the computer means 100; and 
.tau..sub.1 =time required for 63% of the process response for reactor 11 
to occur in response to a step change in the feed rate to reactor 11. 
EQU ARR(7)=(-K.sub.1 /K.sub.2) (.tau..sub.2 /.tau..sub.1) (IV) 
where 
.tau..sub.2 =time required for 63% of the process response for reactor 11 
to occur in response to a step change in the temperature set point for 
temperature controller 114; 
K.sub.1 =the change in the reaction temperature for reactor 11 caused by a 
change in the flow rate of the feed stream to reactor 11 divided by the 
change in the flow rate of the feed stream to reactor 11; 
K.sub.2 =the change in the reaction temperature for reactor 11 caused by a 
change in the set point to temperature controller 114 divided by the 
change in the set point; and 
.tau..sub.1 is as previously defined. 
##EQU1## 
where K.sub.1, K.sub.2, T, .tau..sub.1 and .tau..sub.2 are as previously 
defined. 
EQU FF2(n)=[ARR(36)][FF2(n-1)]+[ARR(37)][DA(n-.theta..sub.A)]+[ARR(38)][DA(n-.t 
heta..sub.A -1)] (VI) 
where 
FF2(n)=Feed forward for change in the concentration of acetylene in feed to 
first reactor; 
FF2(n-1)=FF2(n) from last program pass; 
DA(n-.theta..sub.A)=Change in the concentration of acetylene delayed by 
.theta..sub.A intervals; 
DA(n-.theta..sub.A -1)=DA(n-.theta..sub.A) from last program pass; 
ARR(36)=Tuning constant; 
ARR(37)=Tuning constant; 
ARR(38)=Tuning constant; and 
.theta..sub.A =Time required for a change in the concentration of acetylene 
to cause a change in the output of analyzer transducer 91. 
The tuning constants ARR(36), ARR(37) and ARR(38) are defined as follows: 
EQU ARR(36)=e.sup.-(T/.tau..sbsp.3.sup.) (VII) 
where 
T=cycle time for the computer means 100; and 
.tau.=.sub.3 =time required for 63% of the process response for reactor 11 
to occur in response to a step change in the concentration of acetylene in 
the feed flowing to reactor 11. 
EQU ARR(37)=(-K.sub.3 /K.sub.2) (.tau..sub.4 /.tau..sub.1) (VIII) 
where 
.tau..sub.4 =time required for 63% of the process response for reactor 11 
to occur in response to a step change in the temperature set point for 
temperature controller 114; 
K.sub.3 =the change in the reaction temperature for reactor 11 caused by a 
change in the acetylene concentration in the feed stream to reactor 11 
divided by the change in the acetylene concentration in the feed stream to 
reactor 11; 
K.sub.4 =the change in the reaction temperature for reactor 11 caused by a 
change in the set point to temperature controller 114 divided by the 
change in the set point; and 
.tau..sub.3 is as previously defined. 
##EQU2## 
where K.sub.3, K.sub.4, T, .tau..sub.3 and .tau..sub.4 are as previously 
defined. 
EQU FF3(n)=[ARR(66)][FF3(n-1)]+[ARR(67)][DC(n-.theta..sub.C)]+[ARR(68)][DC(n-.t 
heta..sub.C- 1)] (X) 
where 
FF3(n)=Feed forward for change in the concentration of carbon monoxide in 
feed to first reactor; 
FF3(n-1)=FF3(n) from last program pass; 
DC(n-.theta..sub.C)=Change in the concentration of carbon monoxide delayed 
by .theta..sub.C intervals; 
DC(n-.theta..sub.C -1)=DC(n-.theta..sub.C) from last program pass; 
ARR(66)=Tuning constant; 
ARR(67)=Tuning constant; 
ARR(68)=Tuning constant; and 
.theta..sub.C =Time required for a change in the concentration of carbon 
monoxide to cause a change in the output of analyzer transducer 91. 
The tuning constants ARR(66), ARR(67) and ARR(68) are defined as follows: 
EQU ARR(66)=e.sup.-(T/.tau..sbsp.5.sup.) (XI) 
where 
T=cycle time for the computer means 100; and 
.tau..sub.5 =time required for 63% of the process response for reactor 11 
to occur in response to a step change in the concentration of carbon 
monoxide flowing to reactor 11. 
EQU ARR(67)=(-K.sub.5 /K.sub.6)(.tau..sub.6 /.tau..sub.5) (XII) 
where 
.tau..sub.6 =time required for 63% of the process response for reactor 11 
to occur in response to a step change in the temperature set point for 
temperature controller 114; 
K.sub.5 =the change in the reaction temperature for reactor 11 caused by a 
change in the carbon monoxide in the feed stream to reactor 11 divided by 
the change in the carbon monoxide in the feed stream to reactor 11; 
K.sub.6 =the change in the reaction temperature for reactor 11 caused by a 
change in the set point to temperature controller 114 divided by the 
change in the set point; and 
.tau..sub.5 is as previously defined. 
##EQU3## 
where K.sub.5, K.sub.6, T, .tau..sub.5 and .tau..sub.6 are as previously 
defined. 
Signal 221 is provided from the feed forward model for reactor 11 block 202 
as a second input to the summing block 215. 
Signals 56a-c which are representative of a temperature profile of an upper 
portion of the reactor 11 are provided as inputs to the high select block 
261. The highest temperature is selected by the high select block 261 and 
is provided as signal 262 as a first input to the controller block 263 and 
as a first input to the subtracting block 264. Signal 265, which is 
representative of the temperature limit for the upper portion of the 
reactor 11, is provided as a second input to the subtracting block 264 and 
is also supplied as a first input to the subtracting block 266. Signal 
267, which is representative of the difference between the highest 
temperature in the upper portion of the reactor 11 and the highest 
allowable temperature in the upper portion of the reactor 11, is provided 
from the subtracting block 264 as a first input to the high select block 
268. The set point signal 269, which is representative of a dead band, is 
provided as a second input to subtracting block 266. The dead band signal 
269 is utilized to prevent switching transients and is preferably 
representative of 5.degree. C. Signal 270 from the subtracting block 266 
is thus representative of the result of subtracting the dead band 
represented by signal 269 from the temperature limit represented by signal 
265. Signal 270 is provided from the subtracting block 266 as a second 
input to the controller 263. In response to signals 262 and 270, the 
controller 263, which is a digital implementation of a 
proportional-integral controller, provides an output signal 272 which is 
responsive to the difference between signals 262 and 270. Signal 272 is 
representative of the temperature of the feed stream flowing to the 
reactor 11 which is required to maintain the reaction temperature in the 
upper portion of the reactor 11 below the temperature limit represented by 
signal 265. Signal 272 is provided from the controller 263 as a second 
input to the switching logic 232. 
Signals 61a-c, which are representative of a temperature profile of a 
middle portion of the reactor 11, are provided as inputs to the high 
select block 281. The highest temperature is selected by the high select 
block 281 and is provided as signal 282 as a first input to the controller 
block 283 and as a first input to the subtracting block 284. Signal 285 
which is representative of the temperature limit for the middle portion of 
the reactor 11, is provided as a second input to the subtracting block 284 
and is also supplied as a first input to the subtracting block 286. Signal 
287, which is representative of the difference between the highest 
temperature in the middle portion of the reactor 11 and the highest 
allowed temperature in the middle portion of the reactor 11, is provided 
from the subtracting block 284 as a second input to the high select block 
268. The set point signal 289, which is representative of a dead band, is 
provided as a second input to subtracting block 286. The dead band signal 
289 is utilized to prevent switching transients and is preferably 
representative of 5.degree. C. Signal 290 from the subtracting block 286 
is thus representative of the result of subtracting the dead band 
represented by signal 289 from the temperature limit represented by signal 
285. Signal 290 is provided from the subtracting block 286 as a second 
input to the controller 283. In response to signals 282 and 290, the 
controller 283, which is a digital implementation of a 
proportional-integral controller, provides an output signal 292 which is 
responsive to the difference between signals 282 and 290. Signal 292 is 
representative of the temperature of the feed stream flowing to the 
reactor 11 which is required to maintain the reaction temperature in the 
middle portion of the reactor 11 below the temperature limit represented 
by signal 285. Signal 292 is provided from the controller 283 as a third 
input to the switching logic 232. 
Signals 65a-c, which are representative of a temperature profile of a lower 
portion of the reactor 11, are provided as inputs to the high select block 
301. The highest temperature is selected by the high select block 301 and 
is provided as signal 302 as a first input to the controller block 303 and 
as a first input to the subtracting block 304. Signal 305, which is 
representative of the temperature limit for the lower portion of the 
reactor 11, is provided as a second input to the subtracting block 304 and 
is also supplied as a first input to the subtracting block 306. Signal 
307, which is representative of the difference between the highest 
temperature in the lower portion of the reactor 11 and the highest 
allowable temperature in the lower portion of the reactor 11, is provided 
from the subtracting block 304 as a third input to the high select block 
268. The set point signal 309, which is representative of a dead band, is 
provided as a second input to subtracting block 306. The dead band signal 
309 is utilized to prevent switching transients and is preferably 
representative of 5.degree. C. Signal 310 from the subtracting block 306 
is thus representative of the result of subtracting the dead band 
represented by signal 309 from the temperature limit represented by signal 
305. Signal 310 is provided from the subtracting block 306 as a second 
input to the controller 303. In response to signals 302 and 310, the 
controller 303, which is a digital implementation of a 
proportional-integral controller, provides an output signal 312 which is 
responsive to the difference between signals 302 and 310. Signal 312 is 
representative of the temperature of the feed stream flowing to the 
reactor 11 which is required to maintain the reaction temperature in the 
lower portion of the reactor 11 below the temperature limit represented by 
signal 305. Signal 312 is provided from the controller 303 as a fourth 
input to the switching logic 232. 
Signal 274 from the high select 268 is representative of the zone of the 
reactor 11 which has the greatest positive temperature difference between 
the highest temperature in that particular zone and the highest allowable 
temperature for that particular zone. If the largest difference between 
the actual temperatures in the reactor 11 and the limiting temperature for 
the reactor 11 are negative, then signal 231 is selected by the switching 
logic 232 to be provided as signal 111. If the largest difference between 
the temperatures in the reactor 11 and the temperature limits for the 
reactor 11 is positive, the temperature controller associated with this 
temperature difference is selected by the switching logic 232 to be 
provided as signal 111. Temperature control will remain in effect until 
all temperatures in reactor 11 are below their respective limit 
temperatures and the last temperature being controlled is below its limit 
temperature minus the dead band temperature represented by signals 269, 
289 and 309. 
Signal 105, which is representative of the concentration of acetylene in 
the product flowing from the reactor 12 through conduit means 19, is 
provided as a first input to the controller block 212. The controller 
block 212 is also provided with a second input signal 241 which is 
representative of the desired concentration of acetylene in the product 
flowing from the reactor 12 through conduit means 19. In response to 
signals 105 and 241, the controller block 212, which is a digital 
implementation of a proportional-integral controller, provides an output 
signal 211 which is responsive to the difference between signals 105 and 
241. Signal 211 is representative of the temperature of the feed stream 
flowing to the reactor 12 required to maintain the concentration of the 
acetylene in the product stream flowing through conduit means 19 equal to 
or less than the concentration represented by signal 241. Signal 211 is 
provided from the controller 212 as a first input to the summing block 242 
and is also provided as an input to the switching logic 208 as has been 
previously described. 
The feed forward model for reactor 12 block 251 is provided with signals 
34, 95 and 45 which are respectively representative of the concentration 
of acetylene in the feed stream flowing to the reactor 12, the 
concentration of carbon monoxide in the feed stream flowing to the reactor 
11 and the flow rate of the feed stream flowing to the reactor 11. In 
response to signals 34, 95 and 45 the feed forward model for reactor 12 
block 251 utilizes Equation (XIV), Equation (XVIII) and Equation (XXII) to 
calculate signal 252 which is representative of a prediction of any 
changes in the temperature of the feed stream flowing to the reactor 12 
required to maintain a desired reaction temperature in the reactor 12. The 
prediction is based on changes in the concentration of carbon monoxide in 
the feed stream flowing to reactor 11 and/or a change in the flow rate of 
the feed stream flowing to the reactor 11 and/or a change in acetylene to 
reactor 12. The results of Equations (XIV), (XVIII) and (XXII) are 
combined to provide signal 252. 
EQU FF4(n)=[ARR(96)][FF4(n-1)]+[ARR(97)][DF(n-.theta..sub.x)]+[ARR(98)][DF(n-.t 
heta..sub.x -1)] (XIV) 
where 
FF4(n)=Feed forward contribution from feed rate changes to first reactor; 
FF4(n-1)=FF4(n) from last program pass; 
DF(n-.theta..sub.x)=change in feed rate delayed by .theta..sub.x intervals; 
DF(n-.theta..sub.x -1)=DF(n-.theta..sub.x) from last program pass; 
ARR(96)=Tuning constant; 
ARR(97)=Tuning constant; 
ARR(98)=Tuning constant; and 
.theta..sub.x =Time required for a change in the feed rate to cause a 
change in the output of analyzer transducer 101. 
The tuning constants ARR(96), ARR(97) and ARR(98) are defined as follows: 
EQU ARR(96)=e.sup.-(T/.tau..sbsp.7.sup.) (XV) 
where 
T=cycle time for the computer means 100; and 
.tau..sub.7 =time required for 63% of the process response for reactor 12 
to occur in response to a step change in the feed rate to reactor 11. 
EQU ARR(97)=(-K.sub.7 /K.sub.8)(.tau..sub.8 /.tau..sub.7) (XVI) 
where 
.tau..sub.8 =time required for 63% of the process response for reactor 12 
to occur in response to a step change in the temperature set point for 
temperature controller 134; 
K.sub.7 =the change in the reaction temperature for reactor 12 caused by a 
change in the flow rate of the feed stream to reactor 11 divided by the 
change in the flow rate of the feed stream to reactor 11; 
K.sub.8 =the change in the reaction temperature for reactor 12 caused by a 
change in the set point to temperature controller 134 divided by the 
change in the set point; and 
.tau..sub.7 is as previously defined. 
##EQU4## 
where K.sub.7, K.sub.8, T, .tau..sub.7 and .tau..sub.8 are as previously 
defined. 
EQU FF5(n)=[ARR(126)][FF5(n-1)]+[ARR(127)][DA(n-.theta..sub.y)]+[ARR(128)][DA(n 
-.theta..sub.y -1)] (XVIII) 
where 
FF5(n)=Feed forward for change in the concentration of acetylene in feed to 
second reactor; 
FF5(n-1)=FF5(n) from last program pass; 
DA(n-.theta..sub.y)=Change in the concentration of acetylene delayed by 
.theta..sub.y intervals; 
DA(n-.theta..sub.y -1)=DA(n-.theta..sub.y) from last program pass; 
ARR(126)=Tuning constant; 
ARR(127)=Tuning constant; 
ARR(128)=Tuning constant; and 
.theta..sub.y =Time required for a change in the concentration of acetylene 
to cause a change in the output of analyzer transducer 101. 
The tuning constants ARR(126), ARR(127) and ARR(128) are defined as 
follows: 
EQU ARR(126)=e.sup.-(T/.tau..sbsp.9.sup.) 
where 
T=cycle time for the computer means 100; and 
.tau..sub.9 =time required for 63% of the process response for reactor 12 
to occur in response to a step change in the concentration of acetylene in 
the feed to reactor 11. 
EQU ARR(127)=(-K.sub.9 /K.sub.10)(.tau..sub.10 /.tau..sub.9) (XX) 
where 
.tau..sub.10 =time required for 63% of the process response for reactor 12 
to occur in response to a step change in the temperature set point for 
temperature controller 134; 
K.sub.9 =the change in the reaction temperature for reactor 12 caused by a 
change in the acetylene concentration in the feed stream to reactor 11 
divided by the change in the acetylene concentration in the feed stream to 
reactor 11; 
K.sub.10 =the change in the reaction temperature for reactor 12 caused by a 
change in the set point to temperature controller 134 divided by the 
change in the set point; and 
.tau..sub.9 is as previously defined. 
##EQU5## 
where K.sub.9, K.sub.10, T, .tau..sub.9 and .tau..sub.10 are as previously 
defined. 
EQU FF6(n)=[ARR(156)][FF6(n-1)]+[ARR(157)][DC(n-.theta..sub.z)]+[ARR(158)][DC(n 
-.theta..sub.z -1)] (XXII) 
where 
FF6(n)=Feed forward for change in the concentration of carbon monoxide in 
feed to the first reactor; 
FF6(n-1)=FF6(n) from last program pass; 
DC(n-.theta..sub.z)=Change in the concentration of carbon monoxide delayed 
by by .theta..sub.z intervals; 
DC(n-.theta..sub.z -1)=DC(n-.theta..sub.z) from last program pass; 
ARR(156)=Tuning constant; 
ARR(157)=Tuning constant; 
ARR(158)=Tuning constant; and 
.theta..sub.z =Time required for a change in the concentration of carbon 
monoxide to cause a change in the output of analyzer transducer 101. 
The tuning constants ARR(156), ARR(157) and ARR(158) are defined as 
follows: 
EQU ARR(156)=e.sup.-(T/.tau..sbsp.11.sup.) (XXIII) 
where 
T=cycle time for the computer means 100; and 
.tau..sub.11 =time required for 63% of the process response for reactor 11 
to occur in response to a step change in the concentration of carbon 
monoxide in the feed to reactor 11. 
EQU ARR(157)=(-K.sub.11 /K.sub.12)(.tau..sub.12 /.tau..sub.11) (XXIV) 
where 
.tau..sub.12 =time required for 63% of the process response for reactor 12 
to occur in response to a step change in the temperature set point for 
temperature controller 134; 
K.sub.11 =the change in the reaction temperature for reactor 12 caused by a 
change in the concentration of carbon monoxide in the feed stream to 
reactor 11 divided by the change in the concentration of carbon monoxide 
in the feed stream to reactor 11; 
K.sub.12 =the change in the reaction temperature for reactor 12 caused by a 
change in the set point to temperature controller 134 divided by the 
change in the set point; and 
.tau..sub.11 is as previously defined. 
##EQU6## 
where K.sub.11, K.sub.12, T, .tau..sub.11 and .tau..sub.12 are as 
previously defined. 
Signal 252 is provided from the feed forward model for reactor 12 block 251 
as a second input to the summing block 242. 
Signals 76a-c, which are representative of a temperature profile of an 
upper portion of the reactor 12, are provided as inputs to the high select 
block 321. The highest temperature is selected by the high select block 
321 and is provided as signal 322 as a first input to the controller block 
323 and as a first input to the subtracting block 324. Signal 325, which 
is representative of the temperature limit for the upper portion of the 
reactor 12, is provided as a second input to the subtracting block 324 and 
is also supplied as a first input to the subtracting block 326. Signal 
327, which is representative of the difference between the highest 
temperature in the upper portion of the reactor 12, and the highest 
allowable temperature in the upper portion of the reactor 12, is provided 
from the subtracting block 324 as a first input to the high select block 
328. The set point signal 329, which is representative of a dead band, is 
provided as a second input to subtracting block 326. The dead band signal 
329 is utilized to prevent switching transients and is preferably 
representative of 5.degree. C. Signal 330 from the subtracting block 326 
is thus representative of the result of subtracting the dead band 
represented by signal 329 from the temperature limit represented by signal 
325. Signal 330 is provided from the subtracting block 326 as a second 
input to the controller 323. In response to signals 322 and 330, the 
controller 323, which is a digital implementation of a 
proportional-integral controller, provides an output signal 332 which is 
responsive to the difference between signals 322 and 330. Signal 322 is 
representative of the temperature of the feed stream flowing to the 
reactor 12 which is required to maintain the reaction temperature in the 
upper portion of the reactor 12 below the temperature limit represented by 
signal 325. Signal 332 is provided from the controller 323 as a second 
input to the switching logic 245. 
Signals 81a-c, which are representative of a temperature profile of a 
middle portion of the reactor 12, are provided as inputs to the high 
select block 341. The highest temperature is selected by the high select 
block 341 and is provided as signal 342 as a first input to the controller 
block 343 and as a first input to the subtracting block 394. Signal 345, 
which is representative of the temperature limit for the middle portion of 
the reactor 12, is provided as a second input to the subtracting block 344 
and is also supplied as a first input to the subtracting block 346. Signal 
347, which is representative of the difference between the highest 
temperature in the middle portion of the reactor 12 and the highest 
allowed temperature in the middle portion of the reactor 12, is provided 
from the subtracting block 344 as a second input to the high select block 
328. The set point signal 349, which is representative of a dead band, is 
provided as a second input to subtracting block 346. The dead band signal 
349 is utilized to prevent switching transients and is preferably 
representative of 5.degree. C. Signal 350 from the subtracting block 346 
is thus representative of the result of subtracting the dead band 
represented by signal 349 from the temperature limit represented by signal 
345. Signal 350 is provided from the subtracting block 346 as a second 
input to the controller 343. In response to signals 342 and 350, the 
controller 343, which is a digital implementation of a 
proportional-integral controller, provides an output signal 352 which is 
responsive to the difference between signals 342 and 350. Signal 352 is 
representative of the temperature of the feed stream flowing to the 
reactor 12 which is required to maintain the reaction temperature in the 
middle portion of the reactor 12 below the temperature limit represented 
by signal 345. Signal 352 is provided from the controller 343 as a third 
input to the switching logic 245. 
Signals 85a-c, which are representative of a temperature profile of a lower 
portion of the reactor 12, are provided as inputs to the high select block 
361. The highest temperature is selected by the high select block 361 and 
is provided as signal 362 as a first input to the controller block 363 and 
as a first input to the subtracting block 364. Signal 365, which is 
representative of the temperature limit for the lower portion of the 
reactor 12, is provided as a second input to the subtracting block 364 and 
is also supplied as a first input to the subtracting block 366. Signal 
377, which is representative of the difference between the highest 
temperature in the lower portion of the reactor 12 and the highest 
allowable temperature in the lower portion of the reactor 12, is provided 
from the subtracting block 364 as a third input to the high select block 
328. The set point signal 369, which is representative of a dead band, is 
provided as a second input to subtracting block 366. The dead band signal 
369 is utilized to prevent switching transients and is preferably 
representative of 5.degree. C. Signal 370 from the subtracting block 366 
is thus representative of the result of subtracting the dead band 
represented by signal 369 from the temperature limit represented by signal 
365. Signal 370 is provided from the subtractng block 366 as a second 
input to the controller 363. In response to signals 362 and 370, the 
controller 363, which is a digital implementation of a 
proportional-integral controller, provides an output signal 372 which is 
responsive to the difference between signals 362 and 370. Signal 372 is 
representative of the temperature of the feed stream flowing to the 
reactor 12 which is required to maintain the reaction temperature in the 
lower portion of the reactor 12 below the temperature limit represented by 
signal 365. Signal 372 is provided from the controller 363 as a fourth 
input to the switching logic 245. 
Signal 334 from the high select 328 is representative of the zone of the 
reactor 12 which has the greatest positive temperature difference between 
the highest temperature in that particular zone and the highest allowable 
temperature for that particular zone. If the largest difference between 
the actual temperatures in the reactor 12 and the limiting temperature for 
the reactor 12 are negative, then signal 244 is selected by the switching 
logic 245 to be provided as signal 131. If the largest difference between 
the temperatures in the reactor 12 and the temperature limits for the 
reactor 12 is positive, the temperature controller associated with this 
temperature difference is selected by the switching logic 245 to be 
provided as signal 131. Temperature control will remain in effect until 
all temperatures in reactor 12 are below their respective limit 
temperatures and the last temperature being controlled is below its limit 
temperature minus the dead band temperature represented by signals 329, 
349 and 369. 
The control system illustrated in FIGS. 1 and 2 provides both feed forward 
and feed back control of the temperature of the feed stream flowing to the 
reactor 11 and the temperature of the feed stream flowing to the reactor 
12. Feed forward control is provided by the feed forward model for reactor 
11 block 202 and the feed forward model for reactor 12 block 251. These 
models provide predictions of temperature changes needed to compensate for 
changes in either the concentration of acetylene or carbon monoxide in the 
feed stream flowing to reactor 11 or changes in the flow rate of the feed 
stream flowing to the reactor 11. Feed back control for the reactor 11 is 
provided by the comparison of the actual percent conversion of acetylene 
in the reactor 11 to the desired percent conversion of acetylene in 
reactor 11. Feed back control for the reactor 12 is provided by a 
comparison of the actual concentration of acetylene in the product stream 
flowing through conduit means 19 with the desired concentration of 
acetylene in the product stream flowing through conduit means 19. This 
combination of feed forward and feed back control allows close control of 
the acetylene concentration specification for the product stream and also 
allows close control of the temperatures of reactors 11 and 12 which 
avoids dangerous conditions. 
The invention has been described in terms of a preferred embodiment as 
illustrated in FIGS. 1, 2a and 2b. Specific components used in the 
practice of the invention as illustrated in FIG. 1 such as flow sensor 42; 
flow transducer 41; temperature transducers 51, 52, 53, 71, 72, 73, 115 
and 135; temperature controllers 134 and 114; pneumatic control valves 21 
and 28; and current to pressure transducers 118 and 138 are each well 
known, commercially available control components such as are described at 
length in Perry's Chemical Engineers' Handbook, 4th Edition, Chapter 22, 
McGraw-Hill. 
Other components not previously specified are as follows: 
______________________________________ 
A/D converters 33,36,44,55,59,64, 
MM5357 
94,75,79,84 and 104 
8 bit A/D converter 
National Semiconductor 
D/A converters 112 and 132 
AD 559 
8 bit D/A converter 
Analog Devices 
Analyzer transducers 91 and 101 
102 Process Chromatograph 
System, Applied Automation, 
Bartlesville, Oklahoma 
______________________________________ 
For reasons of brevity, conventional auxiliary equipment commonly used in 
selective hydrogenation processes such as pumps, heat exchangers, 
additional measurement-control devices, etc., have not been included in 
the above description as they play no part in the explanation of the 
invention. 
While the invention has been described in terms of the presently preferred 
embodiments, reasonable variations and modifications within the scope of 
the described invention and the appended claims are possible by those 
skilled in the art. Variations such as using an analog computer to perform 
the required calculations are within the scope of the invention. Other 
variations, such as having two catalyst beds in a single reactor, are 
within the scope of the invention as long as an analysis can be performed 
of the feed stream flowing between the two catalyst beds and control can 
be exerted over the temperature of the feed stream flowing between the two 
catalyst beds.