US 3775622 A
A device for the suppression of reactions involving undue pressure rise in large-size containers having an explosive or thermo-chemically reacting contents, comprising a pressure sensor exposed to the internal pressure of the container controlling a pressure relieving device via two parallel-connected contact assemblies, one of the contact assemblies responding to the transgression of a predetermined value of the internal pressure of the container and the second contact assembly responding to the transgression of a predetermined pressure rise per unit of time.
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Description (OCR text may contain errors)
United states Patent [191 Fredericks et a1.
DEVICE FOR THE SUPPRESSION or- REACTIONS INVOLVING UNDUE PRESSURE RISE IN LARGE-SIZE CONTAINERS Inventors: George Fredericks; Rudolf Zeiringer; Kurt Wiederwohl, all of Graz, Austria Assignee: Hans List, Graz, Austria Filed: Oct. 20, 1972 Appl. No.: 299,405
Foreign Application Priority Data Nov. 4, I971 Int. Cl. H01h 35/24 Field of Search 307/118; 137/487.5, 13.7/488; 340/236; 73/4; 169/26, 27, 28
References Cited UNITED STATES PATENTS Austria 9537 Cooper et a1 l37/487.5 X g [451' Nov. 27, 1973 3,628,563 12/1971 Tomital 137/460 X 3,665,945 5/1972 Ottenstein... 137/487.5 X 3,726,307 4/1973 Carmen eta 137/487.5 3,732,887 5/1973 l-layner '137/486 Primary Examiner-David Smith, Jr. Assistant Examiner-William J. Smith Att0rney-Watson, Cole, Grindle & Watson A device for the suppression of reactions involving undue pressure rise in large-size containers having an explosive or thermo-chemically reacting contents, comprising a pressure sensor exposed to the internal pressure of the container controlling a pressure reliev- ABSTRACT ing device via two parallel-connected contact assemblies, one of the contact assemblies responding to the transgression of a predetermined value of the internal pressure of the container and the second contact assembly responding to the transgression of a predetermined pressure rise per unit of time.
7 Claims, 4 Drawing Figures I DEVlCEiFORi-THE'SUPPRESSIONOF REAGTIONSr INVOLVING UNDUEi-PRESSUREiRISEaLIN.
This invention'relatesto-a device forithe suppression of reactionsinvolving: undue pressureriser-in large-size. containers carrying. explosivev or thermo-chemical charges, comprising a pressure sensor and a'pressurerelief-unit controlled by thev latter.
designating. a predetermined pressure value has been. exceeded; and the other whenan input voltage denot ing. transgression of a predetermined rise of pressure.- perrunit of time releases an'output signal, the outputs of the contact assembly eachbeing-connected with an input of an AND-gate through which thepressure relief device can be released. The criterium forthe evaluation of pressure rises inside thecontainer not'only takes In the'field' of research technique, it is inevitable'for" l0 explosive fuel-and-air mixtures to be 'producedtinrlarge.. size containers' where the presence oftsources' of' igni tion cannot besafely excluded. The term f fiiel'-andair" v mixture! also includes dust-and-air mixturesandgas or? vapour-and-airmixtures; Unlessthe containers used for 15.
these-mixtures offer adequate'resistance to 'such-zpres sures, thisrtype ofexplosion may undercertainicircum= stances cause substantial personal :injuries and material damage' and; similar. effects may. resultfrom thermopressure proper, but also the rise of pressure by unit ofz time into account. Therefore, the fire-extinguishing system-and other equipment for'the relief of pressure inside the-container can be operated only. if and when pressure and rise of pressure per unit oftime simulta-: neously exceed certain'limits. It isrthus possible to eliminatethe'influence of operations accompanied-bypressure-"fluctuations upon the releasingsystem of the device imsuch cases where the=pressure patternof these.
. operations differs from the-pressure pattern characterchemical: reactions" going: on. in these containers al-- though ithese 1 reactions require alonger' period of time for theifibuild-up; V j
lt qis known that in the past', nascent explosions were.
occasionally suppressed by means of a 'device asihereaboveadescribed so :as tolreduce the effective range cithe explosion and attenuatethe expected blast pressure r orthe external pressure ofJthethermochemical reaction'; The pressure feelers detect nascent-reactions= in. time before they attain 'a:- really: destructive "force Randi".
will automatically release-:- the pressureireliefii devices which'may eitherabea-a fire extinguisher, cooler orrair e'scape device asrequired. For example; in-response to the-pressuresensorssuitable:extinguishing-fluids stored in, appropriate tanks accommodatedtinside. the large siz'e: container under adequatepressure "are introduced inthe; large-size container either by: actuating; quickactionopeningvalves or blowingtoff burstingzplates, at" a high; dischargervelocity The: success of the fire.- extinguishing action is dependentfnot only -on 1the type ofextin'guishingagentused,its'storage pressureiandithe 4 arrangement and. numberqof 'fi'reextinguisher contain? .ers, but primarily; on the behaviour and--sensitivityf:of
repons of the pressure detectors who start the fire fighting; effort. With know devices for the suppression of explosions', thefire-fi'gh'ting action starts when awpredetermined minimum; pressure 'ofresponse; very'low. in
- the abovereasonsthe knownx'equipmentappeared'ito be i in need .of improvement in several important} re,- spects.
60 Itisthe'purpose'of the p'resent'invention to improve upon adevice'of thetypehereabove mentionedinsuch a manner as tomake sure. that fire extinguishingsson other pressure 'relievingactions willbe started only following the actual occurence. of: dangerous reactions. F 'or that purpose, the pressure sensure is followed by two'contact' assemblies in parallel connectiom'ofwhichi thefirst releases an output signal whenaninputxvoltage 1.
istictfor explosive or thermo-chemical: reactions. Thus erroneousreleases as areliable to occour dueto operaq tional pressurel variations, but'also to external. influa ences, such as concussion, lightning: discharge: and the like; can besafelyprecluded;
Theselection of the limit values forcontainer press a sure and pressure rises per unit of time, whose simultaa neoustransgression would provoke a response from-the pressure. relief 7 device, depends both on the composition andquality of the contents'of the container. and on the size 'of the. container, as. these data are. of a: decisive w influence upon the determination'ofthe pressure pat-' ternin-the event of an explosion; This pressure'pattern'r is already known for various dust-and-air mixtures'andu. certain'container sizes and can be determined by-trialv and:error if .and when required. Since the time available for the suppression of nascent explosions isextraordinarily short, it is absolutely necessary to make sure that the response 'of 'the'contact" assemblies will be practically instaneous. Accordingtto another feature of the invention, the first'contact assembly is an analog to-digital converter and the-second" contact assembly'is a differentiating circuit followedby ananalogvto-digitalconverter by means ofan-amplifier;
eachof the two. analog-to-digitalconverters consisting of'a differential amplifier whose negative-output. is connectedby means of a resistor 'to a'voltage regulator'fed 1 by areference voltage. By means ofthe voltage regulator-:the'threshold of operation 'of theanalog-to-digital converters can be altered and adapted togiven'requirementszwhen necessary. In normal conditions, the-out-z puts of thetwo analog-to-digital converters are. set to;
the logical 1. voltage; The first analogto-dig'ital. con verter switches to logical 1 when thecontainerpressure has exceeded the predetermined limit. The secondianalog+to-digital converter switches to logical 1 only when the output voltage of the differentiating circuit which isproportionate to the riseper unit of time of the con tainer'pressure, has exceeded thepredeterminedvalue;
Only when logical '1. voltage is available atthe. outputs of'both analog-to-digital converters, does the-'AND gate transmita signal for the release of the pressure'reliefdevice. At the same time, the output signalof'the AND-gate can be used for the triggeringof'a monosta, ble switch step followed by a pulse shaper releasing-a.
rectangular pulse to be used after adequate -amplifica+ tion; for'the release of a fire-extinguishing deviceor the: like: For example, it'may be that-thereleasepulsefusesa filament as a result of which'azvalveopensthrough- 1 I According to another feature of the invention, the
output and the negative input ofeach of the two differ- .ential amplifiers are fed back by means of a resistor;
The purpose of this circuitry operation is to produce a hysteresis on the threshold of operation of the analogto-digital converter, which means that although the analog-to-digital converter may be switched on as soon 4 tainers are shown'in FIG. 1. The ordinate shows 'the container pressure Pex on a logarithmic scale and the abscissa the time t'also on a logarithmic scale. The diagram area is subdivided into monitoring areas I,v II, and
as the pressure has attained a certain level, the pressure then will have to fall slightly below this threshold, so as to make the analog-to-digital reverse again. This produces a clearly positive change-over precluding swinging about the conversion point at minor pressure variations.
According to another embodiment of the invention, the pressure sensor is made to follow apreamplifier preferably combined ,with it so as to produce a structural unit. This provides a possibility for producing a long cable connection between the measuring element and the rest of the electronic circuit. v
According to the invention, other advantages can be obtained by, introducing a low-pass filter between the pressure sensor and the two connecting assemblies,
The low-pass filter serves to filter out undesirable frequencies and the area of operations of the device further narrowed 'asrequired.
Anothterembodirnent of the invention comprises an additional circuit for ,the suppression of I thermochemical reactions, comprising a monostable switchstep followed by a pulse sharper connected to the output of the first connecting assembly, a reversing stage connected to theoutput of the second connecting assembly and a bistable switch-step followed by a power amplifier, with the block input of the bistable switchstep being connected with the output of the pulse sharper, the preparatory input of the bistableswitchstep with the output of the reversing stage, and the bistable switch-step being reset, if required, by means of aswitch' into the initial position. This additional circuitry makes it possible to detect and suppress also thermo-chemical reactions for which a relatively slow rise of pressure is characteristic and whichare, therefore, located below the response limit of the second contact assembly. The output voltage of the additional circuitry can, for example, be used to actuate a relay controlling the aperture of air evacuation valves. In this way the container where in the thermo-chemical process takes place and which is unable to withstand the pressure to be expected, can be protected from damage and even destruction.
Further details of the invention will become apparent from the following description of the invention with reference to the accompanying drawings wherein.
FIG. '1 shows a diagram of the monitoring borders of a device according to the invention,
FIG. 2 the schematic diagram of the electronic sector of the device, v
FIG. 3 a pressure sensor as part of the device according to the invention, and FIG. 4 a variant of this pressure sensor. Knowledge of the pattern of pressure developments inherent in explosions and other reactions involving rise of pressure is above all necessary for their suppression. These pressure developments per unit of time as may arise in view of different parameters in closed con- III defined by the releasing pressures adjustable within sure rise values P and P As a rule, pressure patterns coming within the monitoring area I should not produce and releasing functions in the device. The monitoring area I is subdivided into two sectors a and b, the sector a being limited against diminishing pressure gradients by grad P with 0.1 at/us. This limitation results from the knowledge that larger gradients than 0.1 at/us are safely precluded from occurring during explosions. However, if voltage patterns with gradients of that size occur at the input of the electronic circuit hereafter described in greater detail, they may be safely presumed to be caused by lightning strokes, atmospheric conditions or by mains interference.
In all of these cases, the release of any security measures in the device is undesirable. Curve A inthe diagram stems'from such an electronic interference signal the limits of 0.05 to 0.5 atmospheres and'the' two pressimulating a pressure .pattem in the diagram which is actually non-existant in the container.
The second sector 17 of the monitoring area -I is that pressure range inside which operational pressure variations caused by example, by the opening and closing of for exemple, should not release fire-extinguishing or other pressure-relieving measures either. v
On the other hand, the monitoring area Il comprises all pressure patterns that are characteristic for dustand-gas explosions. The monitoring area II is defined by two constant pressure gradients P and P on the one hand, and by the releasing pressure adjustable within the range from 0,05 to 0,5. Curve C shows a typical pressure pattern for dust-and-gas explosions. Any pressure pattern arising inside area Ilmust positively release the fire-extinguisher. I
The monitoring area III covers the field wherein thermo-chemical reactions, such as for example, selfignition of the contents of the container, occur. For these processes an initially slow and flat pressure rise is a characteristic feature. 0nly then will an explosion actually occur and the blast pressure valve proper superposes itself on the flat pressure rise. A curve pattern 7 which is typical for thermo chemical reactions of this kind is reproduced in curve D.
If the flat pressure rise exceeds the releasing pressure previously set, fire-extinguishers are actuated via a special channel or other measures are released to inhibit the nascent explosion. These combating measures depend on the type ofplant to be protected. For example,
'monitoring'of the container pressure, classification of pressure variations if any, and also for releasing fireextinguishing and other protective devices if required. The input of this circuit is a pressure transducer 1 which responds not only to pressure variationsbut also to the absolute value of pressure. It can be of the active orpassive transducer variety, that is, capable of producing a voltage itself, such as for example, a quartztype transducer or it canbe fed by means of a-source of power of its own, such as for example, a slide-wire bridge. The pressure transducerl gis attached to the pressure container (not shown in the drawings) requiring monitoring and directly exposed to '.the pressure prevailinginside the container. Depending on the type and size of container used, one or more pressure trans- .ducers 1 will be provided. t
The .pressure transducer 1 is followed by a preamplifier-2either attached to the pressure transducer 1 so as to form a single structuralelement, or located in the immediate vicinity of the pressure transducerv 1 so as to provide a long cable connection, if necessary, for the following members of the circuit.
The pre-amplifier 2 is followed by a low-pass filter 3 by means of which electric interfering signals of the typeof curve A in FIG. 1 liable to produce an errone- .ous.release of the device, are suppressed.
verter 8. i I I The differentiating circuit 5 designated by symbols only comprises a condenser 9 followed by an operation amplifier 10 whose output and inp'utare .fed back via a resistor l l. The voltage at the output of the differentiatingcircuit 5 is proportional to the rise of the container pressure. measured by meansof the pressure transducer 1 with time,- that is the value dp/dt. The output signal of the differenting circuit 5 amplified in the amplifier 6 passes via aninput resistor 12 to the positive input of a differential amplifier 13 whose output is connected with the positive amplifier input via a reaction resistor l4. The negative input of the differential explosive character comprised in the monitoringarea ll and for the release of adequate suppression measures. The area [I is delimited by the appropriate adjustment of the threshold of operation of the analog-todigital converters 7 and 8 by means of the voltage regulators l6 and 21. If the pressure-proportionate released v 27 of the circuit.
by the amplifier 4 rises above the response value setting of the analog-to-digital converter 8, the analog-todigital converter 8 whose output is normally at logical 0 voltage, is set to logical 1. In conformity with the above, the analog-to-digital con-verter 7, whose output is normally at logical 0voltage, switches over to logical I time, that is, if. in the container both the predetermined limits for pressure and pressure rise are exceeded at the same time, so that the criterium of the presence of an explosive action prevails.
The output signal of the AND-gate 22 triggers the monostable switch step 23 whose output pulse is transformed into a rectangular pulse in the following pulse shaper stage 24. The width of the rectangular pulse can be set as required in a manner'known per se by means of the pulse shaper 24. Therectangular pulse amplified in the amplifiers 25 and -26is of sufficient capacity to actuate the fire-extinguisher connected to the output For the control of dangerous thermo-chemical reactions inside the monitoring area lll an additional circuit amplifier 13 is via an input resistor 15 connected to the .voltage regulator 16 fed by a reference voltage Um. The differential amplifier 13 in conjunction with the resistors l2, l4 and 15 provides the aforesaid analogto-digital converter 7. i
The second analog-to-digital converter 8 is of the same design as the converter 7 and the pressuredependent voltage released by the amplifier 4 passes via the input resistor 17 to the positive input of the differential amplifier l8 belonging to the analog-to-digital converter 8 whose output is feedback-coupled with the positive input vi'a'a resistor" 19. The negative input of the differential amplifier 18 also is connected via an input resistor 20 to a voltage regulator 21 which likewise lies at the reference voltage U Each of the outputs of the two analog-to-digital converters 7 and 8 is connected to an input of an AND- converter 7 and a bistable switch step 31. followed by a power amplifier 32 whose output is designated by ref-v erence number 33. The output'of the pulse shaper 29 is connected with the clock input of the bistable switch step 31 and the output of the reversing stage 30 with the preparatory input of the bistable'switch step 31. The bistable switch step 31 is moreover, reversible into its initial position by means of a switch 34.
The operation of this additional section of the circuit is as follows. When the reponse pressure setting (lower limit of the monitoring area III) has been exceeded, the logical signal arising at the output of the analog-todigital converter 8 heads for themonostable switch step 28. The rectangular pulse then released" by the pulse shaper 29 arrives at the bistable switch step 31.
This islocked, however, when a logical 1 signal prevails time has been exceeded. However, if the pressurerise in the container is only slow, that is of the type of pressure pattern of thermo-chemical reactions shown by curve D of FIG. .1, then a logical-O signal prevails at the output of the analog-to-digital converter 7, so that the rectangular pulse arriving from the pulse shaper 29 reverses the bistable switch step 31.The output signalof the bistable switch step 31 adequately amplified by means of the power amplifier 32 will then release the I safety device connected to the output 33. This may be a relay controlling the opening of air-evacuation valves on the container. The container is thus also protected from damage or destruction by thermo-chernical reactions.
In order to ensure smooth operation of the whole device it is necessary to carefully calibrate its sensors'and 8 contactassemblies responding to an inputvoltage designating the transgression of a predetermined pressure value and releasing an outputsignahthe second conefficiency of the unit can be checked any time. The
pressure transducer 1 is connected with the large-size container'37 to be checked by means of a stop cock 39 located inside a connector 36. Between the stop cock 39 and the pressure transducer 1, a tubulure 40'terminates in the connector 36 by means of which the pressure transducer 1 can, after closing the cock 39, be impinged upon by a reference pressure. The reference pressure emanates from a device not shown consisting of a pressure flask and a pressure-reducing valve. The reducing nozzles of this reference-pressure producer are so adjustable that both typical pressure patterns of dust or gas explosions and thermo-chemical reactions can be simulated. Upon completion of the checking operation, the tubulure 40 for the reference pressure con- ,nection are closed and the stop cock is opened, so that the pressure transducer 1 again communicateswith the large-size co'ntainer 37 to be kept under surveillance.
Another possibility of checking the efficiency of the monitoring device as shown in FIG. 4 consists in the impingement of the inside of the transducer membrane by means of reduced pressure.
in that case it is possible for the transducer 1, whose housing also includes the pre-amplifier 35, to stay connected with the container 37 under control also during the checking operation. No stop cock is therefore necessary. The transducerl is provided with a tubulure 41 by means of which the transducer membrane 38 can be impinged upon with underpressure. This underpressure is again supplied by an operation testing unit connected to the transducer to be checked by means of a hose. The size or time slope of the underpressure will be set in such a manner that it will produce at the transducer output designed as a connecting plug 42 the same signal as a gas explosion or a thermo-chemical reaction would. The transducer 1 is preferably attached to the wall of the large-size container by means of a clamp bolt 43 engaging a taphole of the container wall and pressing a front-face flange 44 of the transducer housing against a gasket 45 inserted in the receiving bore of the large-size container'37.
I claim t l. A device for the suppression of reactions involving undue pressure rise in large-size containers with an explosive or thermo-chemically reacting contents, comprising at least one pressure sensor exposed to the internal pressure of the container and having an output delivering an electric signal corresponding to the internal pressure, two contact assemblies each having an input and an output, the inputs of the two contact assemblies being connected in parallel and connected with the output of the pressure sensor, the first'of the tact assembly responding to an input voltage designating the transgression of a predetermined pressure increase per unit time and releasing an output signal, an
AND-gate having two inputs and an output, the first of said inputs being connectedtto the output of the first contact assembly and the secondinput of the AND- gate connected with the output of the second contact assembly, a pressure-relieving device connected to the output of the AND-gate and releasable by means of the output pulses of the AND-gate.
2. A device according toclaim 1, providing a first analog-to-digital converter forming the first contact assembly, a differentiating circuit having an-output, an amplifier with an input and an output, the input of the amplifier beingconnected with the output of the differentiating circuit, a second analog-to-digital converter connected to the output of the amplifier, the differentiating circuit, the amplifier and the second analogtodigital converter forming the second contact assembly, each of the two analog-to-digital converters comprising a differential amplifier having a positiveinput, a negative input and an output, a resistor preceding the negative input of the differential amplifier, a voltage regulator fed by means of a reference voltage, the negative inputs of both differential amplifiers being, connected via the resistors to the voltage regulator.
3.'A device according to claim 2, providing one reaction resistor each inserted between the positive input and the output of each of the differential amplifiers.
4. A device according to claim 1, providing a preamplifier inserted between the output of the pressure sensor and-the parallel-connected inputs of the two contact assemblies.
5. A device according to claim 4, wherein the pressure sensor and the pre-amplifier are combined so as to constitute a common structural unit.
6. A device according to claim 4, providing a lowv pass filter connected between theoutput of the said pre-amplifier and the parallel-connected inputs of the two contact assemblies.
7. A device according to claim 1, comprising an additional circuit for the suppression of thermo-chemical reactions, comprising a monostable switch step with an input and an output, the input of the monostable switch step being connected with the output of the first contact assembly, a pulse shaper with-an input and an output, the input of the pulse shaper being connected with the output of the monostable switch step, a reversing stage with an input and an output, the input of the reversing stage being connected with the output of the second contact assembly, a bistable switch step having a clock input, a preparatory input, a resetting input and an output, the clock input of the bistable switch step being connected with the output of the pulse shaper, the preparatory input being connected to the output of the reversing stage and the resetting input connected with a switch for the resetting of the bistable switch step into the initial position.