US2411986A - Liquid-gas-phase control - Google Patents

Description

, Dec. 3, 1946o n. o. cowHERD LIQUID-GAS-PHASB CONTROL 2 Sheets-Sheet 1 Filed lay 21, 1942 Dec. 3, 1946. R. n. cowl-usan Y LIQUImGAs-rms coumor.

Filed lay 2i, 1942 2 Sheets-Sheet 2 TO SOLENOID VALVE 36 FIG. 6

' INVNTOA M QS. GWW .BY

Patented Dec. 3, 1946 mamadas-PHASE coNTnoL Robert' n. cewherd, Metairie, La., assigner to The Bristol Company, Waterbury, Conn., a oorporation of Connecticut Application May 21. 1942, Serial No. 443,895

Claims. (Cl. 137-78) l This invention relates to automatic control in the operation of pulp-digesters or other apparatus wherein under abnormal conditions la liquid may enter a conduit or a pipe line or a reaction vessel Whose content is normally restricted to a gaseous medium. While there is no intention of limiting the utility of the invention to one specific type of apparatus, yet because of its special l adaptability to certain processes in the manufacture o1' paper, the invention will be described in its application to a pulp-digester.

In the manufacture of 'wood pulp it is customary to charge a closed vessel known as a digester with a quantity of wood chips and suitable chemicals and then to set up a reaction by the admission of steam or other heating agent. In the course of this process certain gases are given ofi; and it is usual to vent these from the top of the digester in a manner to main-tain predetermined pressure values within the digester. Due to the chemical device be made responsive to the energy-transcharacteristics of the solution or liquor within the digester there is atendency toward foaming, with the result that under certain conditions some of the solution may be drawn oil' with the gas, thus depleting the chemical content of the digester and interfering with the proper conversion ofthe pulp. Automatic control of the venting of gases is not new; and it is customary to equip digesters with instrumentaiities which will regulate a valve in the vent pipe in accordance with predetermined pressure settings. Such devic'es, however, take no cognizance of the condition of the fluid being vented, Y and will as readily vent the digesting liquor as the gaseous products oi' the reaction. It is recognized, also, that there are available various phase-discriminating devices, lying inthe general category of steam traps, operating for the most part either on a gravimetric' principle or on a basis of relative temperature of a liquid and its vapor;v but, as the former require intricate weighing mechanisms and are inherently slow in their action, and as the factor of actual temperature is not necessarily an element in the vde sired discrimination, such devices are not sui-ted to the objects of the invention.

It is an object oi this invention to provide means whereby an automatic control of the venting of the products of the reaction will discriminate between the gas phase and the liquid phase of saidproducts independently of the temperature of the same.l

It is a further object to provide means whereby said products in their gaseous form will be freely vented, while liquids will be effectively retained in the digester.

.2 V It is a further object to provide means fo automatically clearing the vent pipe of foam or liquid products when such ilnd their way into said pipe, and leaving the pipe free for the exit 'of gaseous products.

In the carrying out of the invention i-t is proposed lto provide in the vent pipe of a digester or similar piece oi.' apparatus a ldevice whichwill respond to characteristics wherein the gas phase of the vented products will diifer from the liquid phase, to eilect control of the venting valve and also of the admission of a medium for flushing out the vent pipe. It is proposed that the sensitive mitting properties', rather than the energy content, of the products being vented from the digester; and for this purpose discrimination between gas and liquidphases is made on a basis of their relative electrical conductivity or .their transparency to light.

In the drawings: v Fig. 1 is a diagrammatic representation of a pulp-digester showing the invention applied to the control oi' relief of internal pressure by regulating the outflow of products of the reaction.

Fig. 2 is a diagraml showing partlyin section the details of the sensitive element as based on electrical conductivity of the efuent. l

Fig. 3 is a diagram showing in section the details of the sensitive element as based on the lighttransmitting properties of the eilluent.

Fig. 4 shows in section certain elements which may be substituted for corresponding parts in the embodiment shown in Fig. 3.

Fig. 5 is a diagram showing partly in section a form of electrode adapted to utilize the' property of electrical capacitance.

Fig. 6 is a bottom elevation of said electrode.

Referring now to the drawings, the numeral I0 designatesa pulp-digesterinto which mixture of wood chips and suitable chemicals-may be charged through an opening in the top; which is afterwards sealed by a cover plate Il secured to place by means of bolts I2. A conduit I3 provides for the conduit Il and subject to actuation by air admitted to its operating element through a conduitiQ, ,aid valve I5 is of the freverse-act suppressed. A diaphragmvalve I8 of the reverse-- acting type is inserted in the pipe I1 'and has its operating element placed in communication with a conduit I9 whereby air pressure in said conduit will cause said valve to be opened.

A controlling instrument 29 which may expedientiy be cf the type fuuy set forth and disclosed in U'.l S. Letters Patent No. 1,880,247, granted October 4, 1932, to Griggs and Mabey, is adapted to regulate in the conduit I9 the pressure of air derived from the source 2I, in response to 4 ilow in the coil 21. A

' nected between the conduit I9 and the source'of' l and the control valve I9; and when pressure is changes in pressure within the digester III, as"

communicated to said instrument through a conduit 22. The connections and adjustments of thel instrument 29 and associated elements are made such that under normal operating conditions said-instrument, acting through the medium of air in conduit I9. tends to adjust the valve II in a sensev to regulate the rate of escape of vasus--` eous products of the reaction to maintain a predetermined constant pressure within the digester I0.

Inserted in the conduit I4 at a point near its emergence from the digester `Il) is an insulated electrode 23, which may expediently be prof vided by the use of a spark plug 28 of the type commonly used for the ignition of internal combustion engines. An electro-responsive instrul ment is connected in circuit with the electrode 29and the conduit I4 and adapted to control the now of fluids in conduits I4 and II by means which will bemore fully understood by reference to Fig. 2 taken in conjunction with Fig. 1.

'Ihe controlling instrument 29 shown in Fig.' 2 may expediently be of the form fully set 'fo'rth and described in U. S. Letters-Patent No.'

air supply 2I (or an independent source if' desired), and is electrically wired to have its actuating winding energized fromthe conductors II and 32 (or an independent electrical source it desired) in series with the contacts- 29 and 2li in such a manner that when said solenoid is energized bythe closing of said contacts, the valve 36 will be opened, and will be closed when said solenoid is deenergized.

Inserted in the conduit is is a diaphragm valve 39 of the .three-way type, having its operating 'element in communication with the conduit I9,

and being arrangedin such a manner that when no'pressure exists in the conduitv I9 said valve provides a direct connection through the conduit I9 between the regulating instrument 20 applied throughthe conduit I9, communication between said instrument and control valve. is interrupted. and the operating element of the latter -vented to the atmosphere.

The operation of the device as thus far disclosed is-'as follows: Upon the digester being charged and steam admitted through the conduit I9, a reaction is set up in which there are given of! ycertain gaseous products which accumulate- Y in the upper part of the digester. As the pressure due to accumulation oi' these gases attains a predetermined value, the instrument 20, acting in response to said pressure, tends to increase lthe pressure in the conduit Il, and thus adjust .the valve I 5 to allow a certain quantity of said gases to be vented through the conduit Il, whereby said pressure will be relieved. As hereinbefore pointed out, there sometimes develops' a I tendency for liquid' components of the contents. of the digester to be carried over with the vent,-

ed gases and discharged through the conduit I4. The insulated electrode 23 projecting into the interior of the conduit I4 is Surrounded by the 1,979,330, issued November 6, 1934, to G'. W.

Kuntny. This instrument includes .an electrosensitive device 29, which may be the conventional permanent-magnet moving-coil class of galvanometer. in which a movable coil 21 placed between opposite magnetic poles N, B, is caused to deilect through a limited angle when electric current is passed through said coil. The deflection of the coil 21 causes a movablevcontact 29 to be brought rinto electrical engagement with a stationary ctmtact 30. Electrical connection whereby the instrument 25 is made'responsive to current passing between the insulated electrode 22 and the conduit I4 is provided by the following means: A conductor 3l forming one side of a source of A.C. supply is connected to the electrode 29. A conductor 32 forming the Aother side of said source is connected to one terminal of the primary winding of a transformer 93.' the other terminal of said winding being connected by means of a conductor 34 to the conduit Il. The

- secondary winding of transformer 39 is connected to two opposite terminals of a 4-terminal recftifying bridge Il. 4'I'he other two terminals of reaction products which are being vented through said conduit. So long as normal conditions exist and these products are gaseous in their nature, the electrical resistance from the electrode 22 to the conduit I4 is extremely high, so that no appreciable current passes through the circuit of 'which said electrode and conduit form a part.

Under this condition no current will pass through the coil 21 in the instrument 25, and the contacts 29 and 30 will remain separated, leaving the actuating winding of the solenoid valve 39 in a de-energized condition and said valve closed. Thus there will be no air pressure applied to either of the diaphragm valves vI9 and 28, with the result that the valve I9 will remain'closed,

' preventing the admission of steam through the conduit I1, and the v'alve 3.9 will remain in' a position to allow free operative 'communication between the regulating instrument 2II'andA the diaphragm v alve I9. 4

In the event of a portion ofthe liquid contents of the digester III being carried into the'conduit I4, the relatively high electricalv conductivity ofsaid liquidwill provide a path between the elecing of the transformer 33, the secondary current ofthe transformer will be rectied by the bridge Il. causing a representative directcurrent t0 trode 23 and the walls of the conduitI Il, thus permitting current to ilowbetween the conductors 3| f and 32 through the primary winding of the transformer 33. 'I'his in turn will set up a current in` the secondary winding oi' said transformer. which. passing through the rectifyingv bridge Il, will cause a unidirectional current to pass through the galvanometer coil 21 in the instrument 29defiecting the contact 29 into enggement-with the solenoid valve I9 is con-j, f.,

l contact 30 and thereby completing the circuit of which said contacts form a part. Current will struct the now of light. causing the cell then pass between the wires 3I and 32 through said contacts and associated conductors and the winding -of valve 38, causing said valve to be opened, admitting air from' the source 2I to the conduit I8. Air pressure in the conduit I3 being applied to the operating element of the valve 38 will cause said` valve to interrupt communication through the conduit I6 between the controller 20 and the valve I5 and vent the latter to the atmosphere, causing said valve I8 to be closed. At the same time air pressure in the conduit I9'acting upon the valve I8 will cause the same to be opened, admitting steam through the pipe I'I to the conduit Ill` and blowing back into the digester I0 any liquid or semi-liquid material which may be present in said conduit, thereby flushing said conduit for further operation, and suppressing the reaction. Upon the clearing of the electrode between said electrode and the walls of conduit I4 will be interrupted, thus terminating the flow of current through the transformer 33, the rectierbridge 35 and the eoil'2'l, whereupon the contact 29 will be separated from the contact 30, the solenoid of the valve 38 de-energized, the valve 38 closed. and the control system caused to revert to its normal operatingcondition.

In Fig. 3 is shown an alternative form of the invention in which discrimination between normal operating conditions and abnormal conditions is based on the light transmitting characteristicsof the effluent. A .body part or iitting 40- is inserted in the conduit I4 at a point near its emergence from the digester I0. The part; 4I!v provides a passage for the contents of the digester I0, and is iitted with opposed laterally located windows 4|, 42 formed of glass or other suitable'transparent materialclamped in place by suitable bolts 43, 44, and having gaskets 45 and 48 whereby a tight seal is effected.' Outside the window 4I. in a, suitable housing 41, is placed a light source 48, which may expediently be a small incandescent bulb energized from an electric power supply not shown in the drawings. Outside the window 42 is placed a photosensitive cell v49,- which may be of the block- 23 from conducting matter, the electrical path 43 to reduce the potential of its output', de-energizing the galvanometer of the instrument 80, and allowing the contacts of that instrument to be closed, energizing and opening the solenoid valve 38, and thus applying air pressure to the operating elements oi.' the valves I8 and 38 to introduce influences to meet the abnormal situation as hereinbefore set forth. Upon cessation of ilow of black liquor in the body part the cell 49 will again become active, the' contacts in the instrument 58 will be opened.- the valve 38 closed, and the system will revert to its normal operating condition,

The operation o f the device in response to light conducting properties of the eilluent, as thusfar described, is based on the fact that the black liquor in a digester is opaque to light. In the event of it being desired to utilize the principles of the invention in connection with a control process wherein the liquid effluent is transparent, and in which the interposition of a body of such liquid between the windows 4I and 42- might not materially obstruct the passage of light, the windows may be given a curved conformation as shown at 82 and 53 in Fig. 4. With'this construction, so long as there is a body of clear gas between the windows, the passage of a light beam through the iltting '48 will not be materially disturbed by the curvature of the windows. If, however, a, body of clear liquid replaces the gaseous content within the fitting 40, the curved surface of said liquid as defined by its contact with the curved windows, will cause said body of liquid photocell'will no longer lreceive illumination to ing-layer or so-called Photronic type, adapted to become a source of electromotive force when exposed to radiant energy projected from the light source 48 through the Windows 4I and 42 and the intervening space within the body part 48. 1A controlling instrument 50, mechanically similar in all strument 58, will tend to maintain the controlling contacts of said instrument in an open condition, allowing the solenoid valve to be de-energized.

Under normal operating conditions the gaseous effluent from the digester will offer no obstruction to the passage of light from the source 48 to the cell 49, with the result that the galvanometer element of the controller 50 will be energized, and the solenoid valve 38 will remain closed. In the and the electrolyte.

event of anl abnormal condition developing and cause it to develop sufncientpower to open the contacts in the controlling instrument 50. It is possible, however,. to replace the inwardly convex Windows by outwardly convex windows, in which case the relative disposition of the photocell and the light source so that the refractiveacl tion of the body of liquid will bring the light rays to a focus at a point where the photocell will not bestrongly excited, becomes a matter of longitudinal adjustment.

In the form of the invention shown in Figs. 5 and 6, use is made of the principle of the electrolytic capacitor in which the property of capacitance is due to thev presence of an insulating illm of molecular thickness formed by the action of certain electrolytes upon the surface of certain nlm-forming materials. It is a unique property possessed by some metals, such for example, as tantalum, that when immersed in certain electrolytes and subjected to a difference of potential, there will be formed on the surface of one of said plates a iilm of insulating oxide which manifests the property of uni-lateral conduction, and which by virtue oi its molecular thickness serves to provide the dielectric layer for a capacitance of relatively high value between the plate When two such plates are used, and an alternating potentialapplied, the layers on the respective plates function as dielectrics toward the respective half-waves of the potential, so that a complete bilateral capacitor is formed. i

In applying this property to the purposes 4of the invention, lan electrode 80, adapted to be threadedly inserted into a conduit I4 in the 'same manner as the spari; plug 24 shown in Fig. 2, in-

4 eludes-two plates vIl and l2.the forme-r being at-v tached to the'metallic part-of the body electrode Il and thereby grounded to the conduit Il and the latter-attached to the insulated phrt or said electrode, wherebyfelectricsl"connection may be independently made toan outside circuit. The plates ci and Ilare'mutually juxtaposed anct so positioned that when theeiiluent carried bly/the conduit Il is in a liquid'state it will immerse both of said plates. so that upon application of la suitable`electrical potential between them they will acquire the properties of capacitor pla.tes. 'By virtue of the extremely high capacitance in pro-v portion to the physical dimensions of the plates,

it is found thatthe charging current which passes through such `a capacitor is, for most values of l alternating current, comparable with, or higher the plates Il and i2 will causesaid coil to be.

energized. Tests have shown that the performance of thistype oi electrode is extremelysensitive, and that as s nas an actual connection between the plat is made by a suitable electrolyte, of which the black liquor formed -in a pulp digester is an excellent example, there is a definite threshold action, whereby the relay 8l is operated to close the contacts 65 and brins the protective lapparatus into action immediately upon the appernce of the liquid phase of the eiliuent of the pulp digester in the conduit Il. l

The term liquid" as employed in the foregoing speciiicationanddn the ensuing claims includes material of-Isemi-liquid character, i. e., mixtur of liquiand solid material.-

The terms and expressions which I have employed are used as terms o f description and not of limitation. andI have no intention, in theuse of such terms and expressions. of excluding any equivalents of the features shown and described or portions thereof, but recognize that various modincations are possible within the scope of f the invention claimed.-

I claim:

l.- In apparatus for regulating the venting of,

'55 means for discriminating between eilluent through a conduit extending from a processing container evolving a normally gaseous emuent, Q gaseous and liquid phases of said emuent in said conduit, .control means sensitive to said discriminatory means in response to the presence of aliquidphase' in said eiiluent, ,and means brought into action by said control means in re,

sponse to the presence of said liquidl phase for controllingl the admission of a flushing iiuid to saidconduit to ilush the contents thereof back against the normal now direction.

. 2. vIn apparatus for regulating the venting of eilluent through a conduit extending from a proceasing container evolving a normally gaseous efl fluent, means for discriminating between gaseous and liquid phases of said eiiluent in said conduit. control means sensitive to said discriminatory means in response-to the presence of a liquid 'an ipse conduit to terminate said venting and for eonphase in said eiiluent, and means brought action by said control meansin response to the presence of said liquid vphase for blocking said trolling the admission of a flushing nui'd to said conduit to flush the contents thereof back against w the normal-now direction. v

3. In combination, a processing container adapted to contain an electrically conducting liquid and vapor from the same. a venting conduit adapted -to carry otl eiliuent from said container,

means comprising an electrode `in said conduit for impressing an electromotive -force across a portion of said emuent, normally open valve means, in saidjconduit, means for directing a flushing-duid into said conduit, said electrode being positioned in the path of said ushing duid, normally closed valve means n'sald directing means, and control means brought into action in .valve means in said directing means, and control means brought intoaction in -response to the vflow of electric.current through said electrode flushing nuid'to said conduit, said electrode being positioned betweensaid directing means and said container.

6.' Apparatus for preventing the iiow of liquid throughl a conduit inwhich either a liquid or a gas may ilow, said apparatus comprising means tor impressing upon the iiowing fluid in said conduit 'a force tending lto' cause a diierent amount oi'l energy to pass-from an external source through said fluid when the owing iiuid is a liquid` than when it is gas, means sensitive to the now of energy through said fluid. and means controlled by said sensitive means in respon to e of said energy through a liquid for controlling the admission of .ay flushing iiuid to said conduit to flush the contents thereof back against the normal now direction.

6. Apparatus for preventing the iiow oi' liquid through'a conduitA in which either a liquid or a gas may ilow, said apparatus comprising means Vfor impressing upon the flowing fluid in said conduit a force tending to cause a difierent amount of energy to pass from an external source through said fluid when the ii'owing nuid is a liquid than when it is gas, means sensitive to the now of energy through 'said nuid, means responsive to tion.

ROBERT D. COWHERD.

Va processing container

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