CA1053780A - Apparatus for controlling operational parameters in a polymerization and related method - Google Patents

Abstract

APPARATUS FOR CONTROLLING OPERATIONAL PARAMETERS
IN A POLYMERIZATION AND RELATED METHOD

ABSTRACT OF THE DISCLOSURE
In apparatus for polymerizing high-pressure ethylene to produce polyethylene, a tubular reactor is connected to a source of high pressure ethylene. A piston-type intensifier pump assem-bly supplies an initiator solution to the tubular reactor. This solution includes one or more catalysts which promote the poly-merization reaction. Within the tubular reactor, a peak tempera-ture occurs in downstream proximity of the point at which the ca-talysts are introduced. If the catalysts are introduced at more than one point, a temperature peak will result downstream of each of such points. For various reasons, these peaks can be displaced along the tubular reactor from time to time as the reaction pro-ceeds. Therefore, a plurality of thermocouples are distributed at spaced positions in the tubular reactor throughout the local-ized zone in which each peak temperature might occur. These ther-mocouples generate signals which are fed into a gating arrange-ment which selects the peak signal which is compared in a compar-ator circuit with a preset reference signal representative of the peak temperature which is desired. A difference signal is gener-ated which relates to the difference between the peak temperature thermocouple signal and the reference signal with which it is com-pared. This difference signal is converted by a transducer into a pressure signal which is fed to a control valve which controls the speed of operation of the intensifier pump feeding the initi-ator into the reactor just upstream of said localized zone. If initiator is fed into the reactor at more than one point, a sepa-rate intensifier pump assembly operated by a separate set of con-trols will be provided for each point.

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Description

BACKGROUND OF THE INVENTION

This invention relates to apparatus and methods for the controlled high pressure polymerization of ethylene into polyethylene and to similar types of processes in which temper-ature control is essential for assuring good quality as wellas efficient and effective production.
While the invention relatesgenerally to the control-ling of processes in accordance with a critical peak temperature which may shift position back and forth in a reactor during the process, the invention will be best understood in terms of a preferred embodiment which is concerned with the polymeriza-tion of high pressure ethylene to produce polyethylene.
As set forth in U.S. Patent 2,852,501 of September 16, 1958 (W.R. Richard, Jr., et al), polyethylene is an excep-tionally important material of commerce suitable for use inmolding and also having substantial use in film form. Poly-ethylene is most effectively produced by subjecting ethylene to the polymerizing action of elevated temperatures while the ethylene is confined within a high pressure tubular reactor or the like. The polymerization reaction is comparatively slow and it is known to employ an initiator solution which is intro-duced into the reactor to speed up the reaction. The solution includes catalysts such as, for example, benzoyl peroxide or other free-radical promoting catalysts. As will be seen, tem-perature peaks occur in reactors downstream of the positions atwhich the initiator solution is introduced.
As further stated in Patent 2,852,501, to obtain practical reaction rates and production yields, the ethylene/
catalyst mixtures can be passed continually through a tubular reactor. Since the polymerization of ethylene is highly exo-i~S3780 thermic, conditions of temperature control are important and particularly peak temperatures which are reached within the reactor are of extreme importance. If too high a peak tempera-ture occurs within the reactor, degradation of the product will result, this ranging in severity from discoloration of the polymer product to substantially complete carbonization of ethylene and polymer. For this reason it was sometimes be-lieved preferable in the past to reduce various operational parameters to a lower value than would achieve an optimum yield in order to achieve a better quality of product. However, op-erating at milder reaction conditions does not necessarily as-sure trouble-free operation and sometimes degradation of the product can occur even at these reduced temperatures.
Pressure fluctuations occurring in reactors employed for the production of polyethylene result in temperature changes which also make the temperature difficult to monitor and :~-control. Some of these pressure changes are incidental to reac-tions taking place during polymerization, but other pressure changes are purposefully employed to prevent the accumulation of polymer on the interior walls, these purposeful changes being known as "bump-cycles" and being effected by the opera-tion of "let-down" valves at the exit end of the reactor. This bump cycle may, for example, cause the reduction of pressure within~arreactor from 40,000 psi to 35,000 psi, this being a drop of 5,000 psi which causes a shifting of the temperature profiles throughout the reactor thus contributing to the diffi-culties experienced in monitoring critical peak temperatures and controlling the associated process in accordance therewith.
Temperature profiles as mentioned hereinafter are discussed by way of example in U.S. Patent 3,299,033 of January ~05;~780 17, 1967 (R.M. Douglas). In this patent is discussed a method for continuously injecting a controlled volume of ini~iator solution through a line into a polymerization zone maintained at operating pressures in excess of 7,500 psi and in which zone the pressure is subjected to periodic variations. The technique disclosed in this patent comprises applying and maintaining a pressure on the initiator solution in the line which is greater than the operating pressure existing in the reaction zone, con-tinuously sensing the periodic pressure variations occurring in this zone, and continuously controlling the volume of initiator solution injected into this zone in response to the periodic pressure variations.
In U.S. Patent 3,079,372 of February 26, 1963 (R.P.
Fulknier et al.) is disc]osed a system in which thermocouples are arranged at spaced intervals within a tubular reactor in temperature sensing contact with the contents of the rea~tor.
Also provided is a product diversion valve which diverts pro-duct from a product collector. A valve actuator is provided which is responsive to the thermocouples to divert product when the temperature at any point in the reactor exceeds a pre-determined level. A collector is disposed to receive the di-verted product.
As will be seen hereinafter, the instant invention detects a peak temperature in a reactor despite the positional shifting of the same and processes the signal to generate a basic signal to control the amount of initiator solution intro-duced into the reactor. This technique is of course wholly different from that disclosed in U.S. Patents 3,079,372 or

2,852,501.

,l.o5:~780 DESCRIPTION t~F TEIIS IN~7ENTION

It is an object of the invention to provide improved high pressure apparatus for the polymerization of ethylene and more generally to provide improved apparatus for controlling critical temperatures which may occur during operation of such polymerization apparatus.
Another object of the invention is to provide im-proved methods for controlling the introduction of catalysts into materials undergoing polymerization in order to control operational parameters such as temperatures in such polymeriz-ing materials.
Yet another object of the invention is to provide im-proved electronic circuits capable of distinguishing between a plurality of electrical signals representing the temperatures at various points within a reactor to select the critical peak signal therefrom and to use such peak signal in controlling the magnitude of the associated critical temperatures.
A further object of the invention is to provide im-proved methods and apparatus for improving the quality and yield of products such as polymers by controlling the introduc-tion of catalysts used in the production thereof.
To achieve the above and other objects of the inven-tion, there is provided an apparatus comprising a source of materials and an elongated reaction system coupled thereto in which a process involving these materials takes place. Where, for example, the polymerization of high pressure ethylene is involved, the high pressure ethylene will be fed into a tubular reactor and at one or more zones of the reactor there will be introduced catalysts which promote the polymerization and affect the quantity and quality of the polyethylene produced.

With reference to the general type of apparatus con-templated in accordance with the invention, peak or other such critical temperatures will occur within the reactor and may for various reasons, shift back and forth positionally along the reactor. In accordance with the invention, there are pro-vided circuits which detect the critical temperature despite the movement of the same within the reactor and which employ this critical temperature to generate a corrective signal to adjust conditions which affect the magnitude of this tempera-ture.
In the case of polymerization of high pressure ethy-lene, the corrective signal is employed to adjust the quantity of catalyst injected into the high pressure reactor. In accor-dance with one embodiment of the invention, this is accomplished by converting the difference signal generated by a comparator, which compares the peak temperature signal with a preset re-ference signal representative of the magnitude of the desired peak temperature, into a pressure signal, which is used to control a catalyst intensifier pump.
Thus, in accordance with the present teachings, an improvement is provided in elongated apparatus for conducting chemical reactions which includes feed means for introducing the reactant materials thereto. The improvement includes a plurality of thermocouples which are spaced along a portion of the apparatus downstream of the point of introduction of a key reactant material.
A plurality of matching electrical amplifiers which are coupled to each of the thermocouples amplifies the temperature responsive electrical signals emitted therefrom. A gating circuit is provided coupled electrically with the amplifiers in such a way that only t~le peak signal from among the amplifiers is transmitted. Means are provided for applying the peak signal to controls on the feed means in order to adjust the rate of introduction of the key ~ _5_ B

- ` 105;~780 reactant material in response to the relative strength of the peak signal.
In accordance wi~h a further teaching, an improvement is provided in the process for carrying out a chemical reaction on a S substained basis wherein at least one key reactant is gradually introduced as the positive flow delivery system into an elongated reaction zone over a considerable period of time. The improvement comprises electrically sensing the temperature at a plurality of stations in the reaction zone spaced apart through a portion of the zone just downstream from the point of introduction of the key reactant. The resultant plurality of separate electrical signals are passed simultaneously through matching amplification circuits and the amplified signals are converged into a gatin~ -circuit which transmits only the peak signal while cutting off all of the rest. The peak signal if transmitted back to control responsively the diriving element of the positive flow delivery stream and thus the rate of introduction of the key reactant.

According to a further feature of the invention, temperatures are measured at positions, spaced along a tubular reactor, by thermocouples which generate signals which are fed into a gating circuit which selectes the critical peak signal therefrom. This peak signal is then fed into a comparator which yields a difference signal which is representative of the extent of departure from the desired peak temperature in the reactor. This difference signal is fed to a transducer which converts the same into a pressure signal controlling a valve which in turn controls the speed of a pump supplying one or more materials to the tubular reactor. According to a -5a-~, lQ53780 further feature of the invention, the peak or critical tem-perature is also fed to a recording and display device so that an operator can monitor trends in the operation.
Materials can be injected into reactor apparatus of the invention at a plurality of positions in which event the critical temperature in each reactor zone relating to each such position can be monitored in accordance with the invention.
Other objects and features of the invention, as well as advantages thereof will appear from the detailed description which follows hereinafter as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS
Figure 1 diagrammatically illustrates a polyethlene reactor including the improvements of the invention;
Figure 2 illustrates a detail of the reactor of Fig.
1 with respect to the mounting of one of the thermocouples in the reactor;
Figure 3 is a chart illustrative of possible tempera-ture profiles in the reactor of Fig. l;
Figure 4 is a partially block, and partially schema-tic, diagram of electrical circuits constituting the tempera-ture measuring and reactor control elements associated with the reactor of Fig. l; and Figure 5 is a diagram of one of the peak temperature picker or selection circuits included in the circuitry of Fig.
4.

DETAILED DESCRIPTION
The apparatus illustrated in Fig. 1 represents the essential sections of a polyethylene tubular reactor. Th~rein, ~0537~30 for example, the pressure can vary up to 60,000 psi and greater and the temperatures can vary from about 225F up to 700F
and possibly greater. The usual operating pressure in the pre-ferred embodiment of the invention will, however, generally be in the order of 30,000 + 10,000 psi, whereas the temperature may vary between about 500 and about 650F and preferably within a range of from 550-600F.
More particularly, the apparatus of Fig. 1 comprises a source 10 of high pressure ethylene feeding into a tubular reaator consisting of a plurality of tubular sections 12a to 12z. These tubular sections are connected in series relation by connecting blocks such as the block 42 between sections 12d and 12e.
As is well known, the tubular sections usually have water jackets (not shown) operatively associated therewith.
These tubular jackets are supplied with hot water via a line 16 and cold water via a line 18, there being provisions made for water return via a line 20. The blocks such as 42 consti-tute discontinuities in the water jackets and are bypassed as indicated by line 22. Valves such as indicated at 24 are dis-tributed throughout the water jacket system to provide for varying the flow of hot and cold water, these valves serving to a limited extent to control temperature within the reactor.
According to known techniques, an initiator solution including, for example, a peroxide initiator in a solvent, is introduced into the reactor system to promote polymerization and improve and control the quality and quantity of the poly-ethylene produced therein. This initiator solution in the illustrated reactor is introduced into the block indicated at 26 and at the block indicated at 28. The source of the initia-tor solution is the intensifier pump 30 with respect to the block 26 and the intensifier pump 32 with respect to the block 28. The intensifier construction may be as indicated in U.S.
Patent 3,234,882, which issued February 15, 1966 ~R.M. Douglas et al).
As will be described in greater detail hereunder, the introduction of initiator solution into the system at posi-tions corresponding to the blocks 26 and 28 will result in peak temperatures which may occur at varying positions within two zones downstream of said respective blocks. To measure temperatures within these zones, thermocouples are installed in the blocks in the first zone indicated at 38, 40, 42, 44 and 46 and in the second zone in the blocks indicated at 48, 50, 52, 54 and 56. Additional thermocouples may be installed in the remaining blocks but will not be discussed in connec-tion with th~s embodiment of the invention.
The thermocouples in the first zone are coupled to an automatic control system 58 connected via line 60 to in-tensifier pump 30. The thermocouples in the second zone are coupled to an automatic control 62 connected via line 64 to intensifier pump 32. The details and operation of these two automatic control systems will be described in greater detail hereinafter.
The upstream end of the tubular reactor is consti-tuted by the block 26. The downstream end of the tubularreactor is indicated at 66. The downstream end discharges in-to a separator 68 which functions to separate the ethylene and polyethylene. The functions of the separator are described in U.S. Patent 2,852,501, previously mentioned herein. Valve 70 is a high pressure letdown valve functioning to reduce the pressure in the tubular reactor periodically to cause pres-sure pulses therein for minimizing the accumulation of poly-mer within the reactor. For example, with a pressure of 40,000 psi employed within the reactor, valve 70 will provide for a 5,000 psi reduction every thirty seconds to a pressure of 35,000 psi. This "bump cycle" is a known technique and is not within the scope of the present invention, except for the fact that it contributes to peak temperature displacements within the reactor with which the present invention is con-lm~ cerned. Valve 70 is shown as coupled via line 72 to source lO
sinee it is a back-pressure controller.
As has been indicated above, an essential part of the apparatus illustrated in Fig. 1 is constituted by the thermocouples which are spaced downstream of the positions at which initiator solution is introduced into the reactor system.
These thermocouples are mounted, as shown by way of example in Fig. 2 wherein is seen block 38 connecting tubular sections 12b and 12c. .
Tubular section 12b comprises a flange 74 connected to block 38 by means of bolts 76 and 78. Tubular section 12c comprises flange 80 connected to block 38 by bolts 82 and 84.
Within block 38 is defined recess 85 through which is extended tip 86 of thermocouple elements well known in the art.
A complete thermocouple structure is illustrated with respect to tip 86. This tip is a part of sheathed thermo-couple 87 which at end 88 is connected to braided lead wire 90 terminating in a connect-disconnect type plug 92. Plug 92 leads the signal generated in the thermocouple to a circuit arrangement which will be described hereinafter. Sheathed ~hermoeouple 87is mounted within plug 94. The oombined _g_ thermocouple 87 and plug 94 are mounted within fitting 96 for accommodation within recess 85 by means of threads 98. The thermocouples may be of various types mounted in any suitable manner, the locations rather than the details of the thermo-couples being significant in the invention.
Fig. 3 is a chart illustrating temperature profiles in a typical tubular reactor of the type described hereinabove wherein are included thirty-six blocks within selected of which may be installed one or more thermocouples in the manner indicated, for example, in Fig. 2.
The abscissa 102 in Fig. 3 indicates the block number commencing with the upstream end 104 and terminating with the downstream end 106 of the tubular reactor. The ordinate 108 indicates temperature of increasing degree. Curve 110 indi-cates, by way of example, a peak occurring at block number 4and a second peak occurring at block number 22. These peaks are substantially immediately adjacent and downstream of block numbers 1 and 19 to which intensifier pumps connect. Curve 112 illustrates the profile at a subse~uent time period of the pro-cess. This curve illustrates that the peaks have shifted andnow occur at block numbers 7 and 23.
Reasons for the shifting of the peaks include the bump cycle referred to hereinabove as well as changing condi-tions within the reactor such as, for example, adherence to the interior wall of the reactor of polymer which is generated and so forth. Experience has shown, however, that the peaks will move to a limited exten~ only and that the temperature peaks can be monitored by thermocouples arranged in two groups of about five blocks each, defining first and second zones lo-cated respectively downstream of the two blocks through which 105;~780 initiator solution is introduced into the reactor. For thenormal velocities of material through the reactor, i.e. about 5 to 100 feet per second, the peak temperature will occur some-where within less than five blocks. The distance between blocks can be varied from about 5 to 60 feet depending on the diameter of the reactor and the v~locity of material through the reactor. The distance is chosen such that once the peak temperature has been determined as disclosed herein, the tem-perature in the adjacentdownstreamthermocouple will usually be a few degrees lower than the peak temperature and no more than about 10F lower.
In Fig. 4 are illustrated thermocouple groups 114 and 116 associated with each of the two zones indicated above.
Thermocouple group 114 is connected to peak picker 118, where-as thermocouple group 116 is coupled to peak picker 120. The details of these peak pickers will be described in more detail hereinafter in conjunction with Fig. 5. It is sufficient at this point merely to understand that each peak picker operates to pass through one of the five thermocouple signals received, said one signal being the peak temperature in the associated zone. Power for peak picker 118 is controlled by switch 122, whereas power for peak picker 120 is controlled by switch 124.
Power sources are indicated generally at 126 and 128.
Two comparators 130 and 132 are included in the cir-cuit of Fig. 4. Comparator 130 receives power from source 126 whereas comparator 132 receives power from source 128.
Comparator 130 is connected to peak picker 118 via line 134 and comparator 132 is connected to peak picker 120 via line 136.
A recorder and display unit 138 is also included in the circuit of Fig. 4. It is connected to peak picker 118 via line 140 and with peak picker 120 via line 142. Recorder 138 is connected with comparator 130 via line 144 and with comparator 132 via line 146. Recorder 139 and comparators 130 and 132 are connected in a loop circuit with peak pickers 118 and 120 and form load circuits therefor.
The function of recorder 138 is to record the peak voltages or temperatures for each of the two zones in the reac-tor downstream of the positons at which the initiator solu-tions are introduced and to display the same so that an opera-tor can follow and analyze trends in the process if so desired.
For this purpose there may be employed a two-pen recorder which traces temperature and/or voltage recordings on a paper strip.
The purpose and function of comparators 130 and 132 are to receive peak indicating signals from peak pickers 118 and 120 and to compare these signals with operator-selected reference signals indicative of the peak temperatures which are desired in the respective zones in the reactor of Fig. 1.
Comparators 130 and 132 generate difference signals which re-present the -differences between the magnitudes of the peak temperatures in said zones and the respective values desired therefor. These difference signals are transmitted onto lines 148 and 150.
The signals on lines 148 and 150 are transmitted to transducers 152 and 154. In these transducers, the electri-cal signals received from comparators 130 and 132 are converted into pneumatic signals which are transmitted onto lines 156 and 158. Transducers 152 and 154 may be any type of trans-ducer suitable for converting a signal of, for example, 10-50 105;~780 milliamps to a pneumatic pressure signal of, for example, 3 to 15 psig. One such transducer which has been satisfactorily employed is the ~ype 546 Electropneumatic Transducer manufac-tured by the Fisher Governor Company of Marshalltown, Iowa.
Intensifier pumps which are adapted to be controlled by the signals on lines 156 and 158 have associated therewith control valves 160, 162, 164 and 166 indicative of the provi-sion of four such pumps. While only two pumps are actually necessary (i.e., one for each of the aforesaid æones) four pumps are provided which may be selectively coupled to the in-dicated blocks by the use of switches 168, 170, 172 and 174.
This permits holding one or more pumps in reserve to accomo-date possible breakdowns. More particularly, lines 156 and 1~8 are connected to solenoids 176, 178, 180, 182, 184, 186, 188 and 190 which selectively feed valves 160, 162, 164 and 166, selection being controlled by selector switches 168, 170, 172 and 174.
Connected between solenoids 176 and 178 and valve 160 is a booster 192. Connected between solenoids 180 and 182 and valve 162 is a booster 194. A booster 196 is connected between solenoids 184 and 186, on the one hand, and valve 164 on the other hand. A booster 198 is connected between valve 166 and solenoids 188 and 190.
The function of the boosters 192, 194, 196 and 198 is to improve the stroking speed and frequency response of the intensifier pumps coupled to valves 160, 162, 164 and 166.
Such boosters are well known and commercially available.
Fig. 5 illustrates schematically how a peak picker circuit (118 or 120 in Fig. 4) operates to select and pass only the strongest signal rQm the five thermocouples in a ~053780 given zone of the tubular reactor shown in Fig. 1. Thus, thermocouples 202, 204, 206, 208 and 210 from the given zone are each connected to identical power driven D.C. amplifiers 212, 214, 216, 218 and 220. In these D.C. amplifiers, the very low voltage level thermocouple signals are magnified and then fed to separate but identical isolation circuits 222, 224, 226, 228 and 230. In these isolation circuits each signal is first chopped by an oscillator input into 60 cycle per second A.C. and then transformed to a higher power level.
The respective signals, now in 60 cycle A.C. current, are further amplified by means of A.C. amplifiers 232, 234, 236, 238 and 240. The initial outputs from said A.C. ampli-fiers are taken off to low temperature selector circuit 244 which is biased to respond to an excessively low signal to pass a signal to alarm circuit 252 which can activate a warning light 256 and/or ring a bell (not shown), Just beyond the low temperature selection point, each output signal from said A.C. amplifiers is connected to the anode of identical recti-fier diodes 231, 233, 235, 237 and 239. Since the cathodes of each of said diodes are connected to a common junction or terminal 241, a gating circuit is formed which cuts off all diode outputs except the strongest and thus passes only the peak signal into high selector circuit 242. This high tempera-ture signal from circuit 242 can be used for several purposes, e.g., to trigger alarm and/or safety shutdown devices 246 and/
or 248 and to operate record~r 138 of Fig. 4.
In accordance with the present invention, however, the most vital feedback contro~ function performed by the high temperature signal is indicated by current output branch cir-cuit 250 which leads to comparator 130 from which a difference signal can be obtained as previously explained. This differ-ence output 254 would then be sent through line 148 of Fig.
4 to control the speed of the intensifier pump feeding the initiator solution to the reaction zone in question.
With reference to the circuits and apparatus described above, polymerization of high pressure ethylene takes place as follows:
High pressure ethylene is introduced into the reactor from source 10. Initiator solution is introduced into the reactor from intensifier pumps 30 and 32. Temperature peaks occur in respective zones downstream of the positions at which the initiator solution is introduced. During the polymeriza-tion of the high pressure ethylene, pressure in the reactor is periodically reduced by operation of valve 70. This, as stated above, assists in preventing accumulation of polyethylene on interior walls within the system. Due to this bump cycle and for other reasons, the peak temperatures occurring in the zones referred to above do not have fixed positions, but instead are displaced within their respective zones. These zones are, how-ever, limited and by no means constitute the entire extent of the reactor. In each of the zones, the associated groups of thermocouples bracket the distance through which peak tempera-tures can be displaced during normal operation. The tempera-tures sensed by these two groups of thermocouples are converted into voltages which are fed to peak pickers 118 and 120 respec-tively. In these peak pickers, the voltages are amplified by D.C. amplifiers 212-220, chopped by circuits 222-230 and fed to A.C. power amplifiers 232-240 to provide stronger output signals.
The gating circuit formed by connection of diodes 231-239 to the common terminal 241 of high selector circuit 242 permits only the peak signal to be passed. The peak sig-nal for each of the two zones is fed to comparator 130 or 132 respectively. The peak signals are also fed to recorder 138 whereat they are traced, according to known procedures, on paper strips for display purposes so that an operator can follow the trends of the peaks in each zone, irrespective of the positional shifting thereof.
Preset reference signals having a strength represen-tative of the peak temperatures desired in the respective zones are entered by an operator into comparators 130 and 132 which compare same with respective peak signals coming from peak pickers 118 and 120. Difference signals of the order of 10-50 milliamps are transmitted to transducers 152 and 154 which pro-duce corresponding pneumatic signals which are transmitting via lines 156 and 158 and selected of solenoids 176-190 to valves 160-166. Selection is made by switches 168-174.
Boosters 192-198 minimize the delay in responding to the sig-nals produced on lines 156 and 158.
The pumps selected by switches 168-174 correspond to intensifiers 30 and 32 (Fig. 1). The valves 160-166 cor-respond to the valves which control the speed of operation of these pumps in the manner set forth in U.S. Patent 3,234,882 (see for example valve 14 in said patent). The outputs of the intensifiers are fed through valves 34 and 36 into the reactor system.
From what has been stated hereinabove, it is seen that the peak voltage in each of the two zones in the reactor system is used to control the rate of introduction of initiator solution at positions ~pstream of such zones. Despite the fact that the peak temperature may shift position somewhat from time to time due to a variety of reasons, the peak tempera-ture is always maintained under close control. It is to be understood that some slight deviation is permissible such as, for example, might occur due to the presence of a peak inter-mediate the thermocouples. This, however, has not been foundto be of significance in view of the speed of flow of materials through the reactor system. In such processes, where the possibility of peaks occurring intermediate adjacent thermo-couples might be of importance, it would of course be possible to position additional thermocouples between the blocks thereby to minimize the importance of this problem.
From what has been stated hereinabove, it will be seen that the invention relates generally to an apparatus ~
wherein an elongated reaction system receives raw materials in such a manner that a critical or peak temperature occurs in the system and is displaceable therein, the invention providing for monitoring the critical peak temperature despite displace-ment of the same and for controlling the supply of at least one of the aforesaid materials to the reaction system based on said critical or peak temperature.
Generally, the method of the invention involves con-trolling a reaction which is taking place in an elongated reaction system in which there is a shifting temperature pro-file. From what has been stated herein, it will now be under-stood that the method involves establishing a temperature cri-terion such as, for example, a desired peak temperature, and sensing temperatures at a plurality of stations spaced along the aforenoted system whereafter the reaction is controlled accordingly to maintain a peak temperature which corresponds most closely to the temperature criterion.

lOS3780 According to the method of the invention, control of the reaction is preferably effected by controlling one of the materials introduced into the reactor. From the preferred embodiment described above, it is seen that, where the reaction is the polymerization of high pressure ethylene in which ethylene and initiator solution are supplied to the reaction syst~m, control is best effected by adjusting the rate at which the initiator solution is supplied.
Finally, it has been seen that the method of the in-vention preferably involves continuously displaying the peak temperature, this being effected, for example, by a recorder tracing one or more lines indicative of peak temperat~res in the reactor system.

Claims (14)

WHAT IS CLAIMED IS:

1. In an elongated apparatus for conducting chemical reactions including feed means for introducing reactant materials thereto, the improvement comprising a plurality of thermocouples spaced al-ong a portion of said apparatus downstream of the point of intro-duction of a key reactant material; a plurality of matching elec-trical amplifiers coupled to each of said thermocouples to amplify the temperature responsive electrical signals emitted therefrom;
a gating circuit coupled electrically with said amplifiers in such a way that only the peak signal from among same is transmitted thereby; and means for applying said peak signal to controls on said feed means in order to adjust the rate of introduction of said key reactant material in response to the relative strength of said peak signal.

2. The improved apparatus of claim 1 wherein said means for ap-plying said peak signal to said feed means includes an electrical comparator in which said peak signal is compared with a preset reference signal to obtain a difference signal which is transmit-ted to the controls for said feed means.

3. The improved apparatus of claim 2 wherein a transducer is interposed between said electrical comparator and said controls for said feed means in order to convert said difference signal into a proportionate pneumatic signal to operate said controls.

4. In an elongated tubular reactor for continuously converting ethylene at high pressures to polyethylene including means for supplying ethylene to the upstream end, means for releasing the polyethylene containing product stream at the downstream end and intensifier pumping means for introducing a polymerization initi-ator stream into said tubular reactor at one or more points there-in, the improvement comprising a plurality of thermocouples spaced apart in said reactor along the portion of the length thereof immediately downstream of the introduction point of said ini-tiator stream; a plurality of electrical amplifiers coupled respectively in matching circuitry with said thermocouples to amplify the temperature-responsive electrical signals emitted therefrom; a gating circuit coupled electrically with said plurality of amplifiers so that only the peak signal from among the resulting amplified signals is transmitted through same;
an electrical comparator coupled to said gating circuit to accept said peak signal and compare same with a preset refer-ence signal to yield a difference signal; and means for apply-ing said difference signal to responsive controls on said in-tensifier pumping means to provide proportionate adjustment in the rate of introduction of said polymerization initiator.

5. The improved reactor of claim 4 wherein a transducer is interposed between said electrical comparator and said controls on said intensifier to convert said difference signal to pneu-matic form.

6. The improved reactor of claim 4 having bump-cycle means attached near the downstream end thereof for partially re-lieving the pressure in the reactor momentarily and timer means to activate said bump-cycle means at periodic intervals.

7. The improved reactor of claim 4 comprising recording means coupled in a loop circuit with said electrical comparator for continuously monitoring said peak signals passed by said gating circuit.

8. The improved reactor of claim 4 wherein the matching cir-cuitry coupled to each thermocouple to amplify its electrical signal comprises a D.C. amplifier, an isolation chopping cir-cuit containing an oscillator for converting to A.C. and an A.C. amplifier.

9. The improved reactor of claim 8 wherein said gating cir-cuit comprises a plurality of rectifier diodes, the anodes of which are connected to the respective A.C. amplifiers and the cathodes of which are connected to a common terminal.

10. In a process for carrying out a chemical reaction on a sustained basis wherein at least one key reactant is gradually introduced as a positive flow delivery stream into an elon-gated reaction zone over a considerable period of time, the improvement which comprises (a) electrically sensing the temperatures at a plurality of stations in said reaction zone spaced apart through a portion of same just downstream from a point of introduction of said key reactant, (b) passing the resultant plurality of separate electri-cal signals simultaneously through matching amplifi-cation circuits and converging said amplified signals into a gating circuit which transmits only the peak signal while cutting off all of the rest, and (c) transmitting said peak signal back to control respon-sively the driving element of said positive flow deli-very stream and hence the rate of introduction of said key reactant.

11. The improved process of claim 10 wherein step (c) includes comparing said peak signal electrically with a reference signal having a strength directly representative of the peak tempera-ture desired in said reaction zone to yield a difference signal and applying said difference signal to effect direct control of said driving element.

12. In a continuous process for polymerizing ethylene at high pressures in an elongated reaction zone wherein a polymeriza-tion initiator is continuously introduced as an intensifier pumped positive flow stream, the improvement which comprises (a) simultaneously obtaining directly temperature-related electrical signals from a plurality of com-parable thermoelectric devices located in said reac-tion zone at spaced intervals just downstream of where said initiator is introduced, (b) passing the resultant plurality of separate electri-cal signals continuously through matching amplifica-tion circuits and converging the amplified signals into a common gating circuit which cuts off complete-ly all said signals except the strongest or peak one, (c) transmitting said peak signal from (b) to a compara-tor circuit in which it is compared with a reference signal representing a desired peak temperature stan-dard, to yield a difference signal, and (d) transmitting said difference signal back to regulate special feed-back responsive, adjustable drive ele-ments provided on the intensifier pump which propels said initiator into said reaction zone.

13. The improved process of claim 12 wherein step (d) involves converting said difference signal to pneumatic form before ap-plying same to regulate said adjustable drive elements.

14. The improved process of claim 12 wherein, over and above the normal random variations usually inherent in such a pro-cess, periodic, substantial sharp reductions in pressure are superimposed upon the process by the timed cyclical, bump-type, partial discharge or release of reaction zone contents during the process.