US2872298A - Pressure vessel venting device - Google Patents

Description

Feb. 3, 1959 w. F. VAN LOENEN 2,872,298 l PRESSURE VESSELx VENTING DEVICE Filed Aug. 1e, 1954 wilu lillfv. mi

' INVENTOR. WlLMIM E. VBN

JETTORNEY United PRESSURE VESSEL VENTING DEVICE William Fn Van Loenen, Baton Rouge, La., assignor to Kaiser Aluminum & Chemical Corporation, Oakland, Calif., a corporation of Delaware Application August 16, 1954, Serial No. 449,980

2 Claims. (Cl. 23-290) anisms controlling the gas discharge.

The desirability and necessity in some cases for bleeding off or discharging gases from high pressure vessels employed in chemical processes is apparent to those skilled in the art. Thus, for example, in the digestion phase of the Bayer process for recovering alumina from bauxites, non-condensable gases are found to accumulate in the upper regions of the high pressure vessels employed for extracting the alumina content from the bauxites. Not only do these non-condensable gases decrease the residence time of the liquids and solids undergoing treatment in the vessels and in general disrupt the effectiveness of the solubilizing conditions but the non-condensable gases, furthermore, pass through the digestion 'step and become associated with `the high temperature steam evolved during subsequent ashing operations wherein the liquids are depressurized. This steam is thereafter used in heat exchange apparatus wherein the non-condensable gases decrease the overall heat transfer and in general, decrease the efficiency thereof.

Mechanisms for discharging gases from high pressure vessels -are well known. However, such mechanisms usually employ a valve through which the gases are eX- pelled automatically and wherein the valve mechanism is actuated according to the level of the liquid in the vessels by some directly contacting mechanical or electromechanical means. Where the liquids employed for actuating the valve mechanisms are of a highly corrosive nature and/or are susceptible to leaving deposits of scale on the mechanical or other means employed for actuating the valve, it is highly desirable to have a non-mechanical contact between the means for actuating the valve and the corrosive and/or scale forming liquors so as to eliminate the failures of the gaseous discharge mechanism caused by the corrosion and/or scale.

The caustic aluminate liquors found in the digestion step of the Bayer process are an excellent example of liquid having scale forming properties which interfere, as a result of the deposits of scale, with mechanical means employed either directly or indirectly for actuating valve mechanisms utilized for controlling the discharge of non-condensable gases from high pressure vessels. Thus, when attemptsvare made to automatically expel the non-condensable gases from the digesters, as the vessels are known in the alumina art, by means of mechanical mechanisms contacting the caustic aluminate liquors, it is found that desilicaton and aluminate scales 2,872,298 Patented Feb. 3, 1959 form thereon and in a short time completely immobilize the operation thereof. Because of these characteristics of the Bayer liquors, it is customary, in order to expel the non-condensable gases from the digesters, to periodically crack a valve in a conduit leading to the regions wherein the non-condensable gases collect and in general to accomplish the desired result manually. This method of periodically expelling the non-condensable gases is, of course, time consuming. In some cases bleeding noncondensables in this manner is likewise uneconomical in view of the fact that the condensable component associated with the non-condensable gases is often of considerable value.

According to the invention herein described, the noncondensable gases may automatically be removed from the high pressure vessels and such removal can be accomplished independent of direct mechanical contact of valve mechanisms employed with the liquid in the vessel to facilitate maintaining a predetermined level of liquid desired therein. In most instances, the predetermined level of the liquid in the vessel will be such as to maintain the vessel at full capacity and the invention is described with this point in view. However, it will be apparent from the following description that the inventive concept will not be varied if less than full capacity of the vessel is desired as the predetermined level of liquid.

According to the invention as applied to removing or expelling the non-condensable gases from the digesters of the Bayer process or other vessels containing scale forming or corrosive liquids, the non-condensable gases, which have water vapor associated therewith, are withdrawn from the top of the digester and the water vapor condensed and collected in a separate condensate zone. The water, thus collected, is then employed in the separate condensate zone for actuating the valve mechanism which controls the discharge of the non-condensable gases. The separate condensate zone of condensed water vapor employed for actuating the non-condensable gas discharge valve mechanism is maintained either in direct or indirect contact with the scale forming liquid in the vessel depending primarily upon whether sufficient condensate is formed during the periods when gases are not being expelled to provide a continuous return thereof to the mother liquid so as to overcome appreciable diffusion of the scale forming liquids into the separate condensate zone. In any event, the level of water in the separate condensate zone is responsive to the level of the mother liquid in the pressure vessel as hereinafter more particularly described.

Although water vapor and water are used herein to describe the condensable component associated with the non-condensable gases, it will be apparent to those skilled in the art that as the concept of the invention is applied to other processes and applications, any condensable component or components associated with the non-condensable gases will serve the purpose so long as they are not scale forming orcorrosive with respect to the materials employed in the mechanical valve mechanisms employed for the control of the gaseous discharge. Thus, even in actual Bayer operations, it has been found that there is often associated with the con'- densate an oily emulsion, which apparently results from volatilization of hydrocarbons, which appears during the digestion step. These hydrocarbons may, furthermore, advantageously be removed from the system through the incidental application of the herein described invention to Bayer operations. Likewise, mercury is sometimes found in bauxites and may become volatilized and associated with the water vapors and likewise removed or employed in the separate condensate zone. In any event, with due regard for the density of the condensed component and t its mode of use, the scope of the invention will be apparent from the following description and diagram.

Likewise, although the invention is primarily directed to expelling non-condensable gases containing a cou-` densable component associated therewith, it will also be apparent that the concept of the invention is; not limited thereto. Thus, where two condensable compo.- nents have sufficiently different condensing temperatures, the apparatus herein described may be employed for separating one from the other in a manner dependent upon the level of the liquid within the vessel yet independent of the corrosive or scale forming properties thereof.

Accordingly, it is an object of the invention to provide a practical apparatus and process for discharging` gases from high pressure vessels.

Still another object is to provide apparatus for discharging gases from high pressure vessels characterized in that the valve mechanisms employed for actuating said discharge are not mechanically in contact with the highly corrosive and/,or scale' forming liquids.

Still another object is to provide apparatus for discharging gases from high pressure vessels and for maintaining a predetermined level of liquid in said vessels.

A further object is to provide apparatus for discharging non-condensable gases from high pressure vessels when said gases contain a condensable component such as water vapor.

lt is a further object to provide apparatus for discharging non-condensable gases from high pressure vessels, wherein said gases contain a condensable component, and for separating the condensable component from the gases prior to discharge of the latter.

It isa further object to provide apparatus for discharging gases,V containing a condensable component from high pressure vessels characterized by the fact that the condensable component is liquiiied prior to the discharge ofv said gases and said liquied' component is separated from or returned to the vessels.

It is a further obiect' to provide apparatus for discharging non-condensable gases having a condensable component associated therewith from high pressure vessels characterized by the fact that the condensable component is separated from the non-condensable gases by liquiiication and said liquified component is employed in a separate condensate zone for actuating the valve for discharging the non-condensable gases prior to returning said component to the vessels.

Another object is to provide apparatus for discharging gases containing a condensable component from high pressure vessels through valve mechanisms actuated according to the level of the liquid in said vessels in a mannerindependent of direct mechanical contact with said liquor in the vessels.

It is another object of the invention to provide apparatus for removal einen-condensable gases from the pressure vessels of the Bayer process without interference with the uniform rate of flow of theV bauxite solvent slurry stream.

lt is another object to provide apparatus for removal i of hydrocarbon vapors and condensed hydrocarbons from Bayer process liquor streams.

It is a further object of the invention to provide an automatic venting system forpressure vessels from which it is desirable to remove non-condensable gases in order to reduce the manual labor necessary in operation of the equipment.

Other objects will become apparent from the following disclosuresand figures associated therewith:

According to one phase of the invention the non-condensable gases and associated condensable component are withdrawn from the vessel and the water vapor condensed. rThereafter, the condensed water vapor is employed in a separate condensate zone, the level of`which is varied according to the level of theV mother liquid in 4 the vessel, and the uctuating level of the liquid in the separate condensate zone is employed for actuating the valve mechanism utilized for controlling the gaseous discharge of non-condensable gas.

The employment of the term separate condensate zone, as herein used, is not to be construed as meaning no direct liquid contact between the condensed water K vapor and the mother liquid. As will be apparent from the following disclosure, the zone of condensed water vapor may be maintained substantially free of the corrosive and/or scale forming mother liquid providing the return of the condensable component to the vessel is substantially maintained so as to overcome the tendency of the mother liquid to diiuse into the separate condensate zone. In another embodiment the condensate may essentially be maintained separate from the mother liquid by means of an intervening gaseous zone.

The figure shows schematically one embodiment of the herein described invention wherein a ball float valve is employed for actuating a gaseous discharge valve mechanism in a gas trap defining a zone for separating condensed water vapor from non-condensable gases, and also partially defining the separate condensate zone.

The figure also shows the concept of maintaining a separate condensate zone wherein, under normal operation, the separate condensate zone contacts the mother liquid in the vessel.

With reference to the gure and the embodimentof the herein described invention shown therein, 1 schematically represents a gas trap employed for separating non-condensable gases from condensed liquid and for confining the gases. 2 indicates a condensing unit, 3

a" digester, such as employed in the extraction phase of the Bayer process, and 4 is a standpipe connected therewith for facilitating accumulation of the gases as, for example, in zone 30.

With regard to the gas trap 1, there is shown a sliell 5 having upper flange portions 6, which are connected in a suitable manner (not shown) to flange portions 'l of shell cover 8. An inlet 9 is provided in shell 5 for feeding the condensed water vapor and non-condensable gas to gas trap 1, a gas outlet l@ being provided in shell cover 8. A liquid discharge 11 is provided in the bottom of shell 5 which also, in this case, delines a portion of the separate condensate zone as in reservoir 3l. Av

valve seat 14 is provided in gas outlet 10 ofshell cover 8. Needle valve 13 connected to ball lioat 12 by means of the member i5 is directed to open and close gas outlet 10 by co-acting with valve seat 14. The needle valve 13 is maintained in position by means of guide rnernbers 16 and 17, respectively, which. include bearing surfaces 18 and 19, respectively.

Standpipe 4 is provided on digester 3 to facilitate collection of the non-condensable gases in an appropriateplace. Pipe 2@ is connected to standpipe 4 and passes to condenser 2 by means of plug cock 20' and is utilized.

to afford passage for the non-condensable gases and condensable components associated therewith to the con as for providing a portion of the return passage to thev digester for the condensate. In normal operation, the plug valve 23 is closed but may be employed forcleaning purposes and for periodically withdrawing undesirable products which collect in the' liquid trap 22, aathe occasion arises. Plug valve 23 may be employed' for-removing the oily emulsion heretofore referred to. The upper portion of the liquid trap 22 is shown connected to T 24 having nipple 25 with a pipe cap 25v attached thereto to facilitate cleaning as well as for priming the apparatus initially. Pipe 26 attached to T 24 leads by means of plug valve 27 into standpipe 4 wherein it is directed generally downward therein by means of elbow 28 to the discharge 34. The "separate condensate zone, herern referred to, is shown in the embodiment as including the condensate in reservoir 31, liquid trap 22 and pipe 26.

The non-condensable gases which find their way into the digester 3 when the process is in operation collect in zone 30 above the level of the liquid 29 in the standpipe 4. From zone 30, the gases, when the apparatus of the herein described invention is functioning to expel same from digester 3 together withthe associated water vapor, are delivered to the condenser 2 by means of pipe 20 through open plug cock 20' wherein the water vapor is condensed and forwarded to gas trap 1 together with the non-condensable gases by means of pipe 21. In gas trap 1 the condensate separates from the gases in gas pocket V33 and is collected in the reservoir 31 which is defined by the bottom portion of shell 5. On the liquid level 32 of the condensate in lreservoir 31 rides ball float 12 which co-acts with valve 13 to open and close gas outlet 10. The upper regions of the gas trap 1 define a zone 33 in which the non-condensable gases are collected and from which they are discharged through gas outlet according to the actuation of valve 13 which, in turn, is responsive to the ball float 12 on the liquid level 32 in the reservoir 31.

As is apparent, the liquid level 32 in reservoir 31, which determined the actuation of valve 13, is responsive to the liquid level 29 in standpipe 4. For example, the -valve 13 of gas trap 1 is shown in open relationship, .suchthat non-condensable gases are being discharged through gas outlet 10. It is'apparent that this removal of the non-condensable gases will decrease the volume of gases in zone 30 defined in standpipe 4. Accordingly, the liquid level 29 in standpipe 4 will increase to a point shown for example as 29. Under these circumstances, the increased head caused by the increase in liquid level 29 to level 29 causes a greater quantity of condensate to remain in reservoir 31 to balance this increased head caused vindirectly by the discharge of gases through gas outlet 10. The greater quantity of condensate which is retained in the reservoir raises the liquid level 32 thereof to a point such as 32. This corresponding increase in ,liquid level 32 to 32 in the gas trapv 1 will, of course, raise the ball float 12 to the point where n-eedle Valve 13 contacts valve seat 14, thereby closing gas outlet 10 and preventing further discharge of the non-condensable gases.

The reverse of the operation is also apparent as more non-condensable gases accumulate in zone 30, the level 29 will recede to level 29 and the needle valve 13 will once again be in open relationship with respect to the valve seat 14 because of the lower level 32 of the condensate in reservoir 31.

When valve 13 is in closed relationship under normal operation, suflicient condensation of the water vapor in condensing unit 2 should take place to provide a continuous supply of condensate to reservoir 31 so as to maintain a reasonably constant volume of ow of condensate from liquid discharge 11 through liquid trap 22 and pipe 26 to digester 3. Thus, in order to be assured of a separate condensate zone uncontaminated with corrosive liquors, the condenser 2 should provide sufficient cooling capacity to maintain a reasonable diffusion rate of water vapor from zone 30 thereto. In this manner, sufficient condensate is provided continuously to reservoir 31 to maintain a continuous flow of liquid in pipe 26 such as to overcome any tendency of the mother liquid .to diffuse back into the reservoir 31v From the descrip- 'tion of the invention and the objects thereof, this is, of course, apparent to those skilled in the art.

Where it is undesirable to reux large quantities of condensate in comparison to the quantity of gases removed, e. g. where because of the relatively small amount of non-condensable gases present, it becomes undesirable to maintain continuous reuxing in large amounts during the periods when gases are not being expelled from the gas trap, the capacity of the condensing unit may be reduced to the point where substantially little or no condensate is formed except when excessive amounts of non-condensable gases require expulsion thereof. In such a situation, diffusion of the corrosive Wise independent condensate zone may take place. Under such circumstances it is advisable to operate with pipe 26 substantially filled with air thereby providing a gaseous zone between the liquid in vessel 3 and the condensate in liquid trap 22. Under these circumstances pipe 26 can be made of suflicient size to accomplish4 maintaining the gaseous zone as well as providing a pas sage for the condensate which is returned to vessel 3 from the independent condensate zone which in such a` case is maintained only in the liquid trap 22 and reservoir 31.

Where circumstances are such that reuxing of the= condensate is undesirable, a separate condensate zone may be employed which is separated from the mother liquid by a gaseous zone and the condensate removed, as for example, through plug cock 23 in amounts corresponding to the amount of condensate formed. Similarly, where the condensable component can be bled olf together with the non-condensable gases, utilization of a condensing unit is unnecessary and the separate condensate zone, heretofore referred to, may be filled with immiscible liquid, which will co-act through the means of a gaseous zone to actuate the valve mechanism. Other adaptations of the separate zone concept are, of course,-

apparent to those skilled in the art.

Plug cocks 20 and 27 are normally open during operations; whereas, plug cock 23 is normally closed. During starting up operations, according to the preferred embodiment shown in the ligure, plug cocks 20 and 27 and 23 are closed, cap 25' is removed and liquid trap 22 and reservoir 31 filled with water. Cap 25 is then replaced and plug cock 20 opened. In this manner diffusion of the water vapor from zone 30 to condensing unit 2 takes place and condenses therein. The condensate is permitted to build up in the condenser and line 20 to the extent possible prior to opening plug cock 27. The head presented by the condensate in the condenser causes the lines 26 to become filled and the mechanism begins operation. it is appaernt, of course, that manual venting from a cock, not shown, is normally required to fill the digester initially above the discharge 34 prior to opening plug cock 27. This may be accomplished by means of a manual vent (not shown in standpipe 4). Other suitablemethods for start-ing the functioning of the equipment are, of course, apparent, and the scope of the invention is in no way to be construed as limited accordingly. Of course, when it is desirable to operate with a gaseous zone in pipe 26, care in filling the liquid trap and reservoir must be exercised to prevent filling of pipe 26.

lt is apparent from a consideration of the embodiment shown in the figure that by utilizing a condenser to provide a liquid which is non-scale forming in all practical respects in a separate condensate zone that the mechanical means employed for actuating the gaseous discharge valve is maintained separate from the scale forming mother liquid and accordingly, is not susceptible to the crystalline deposits of scale and/or corrosive nature thereof.

Still further, although the embodiment described in the drawing shows a standpipe as being utilized for c0l lecting the gases in the vessel, it is apparent that this is not critical to the scope of the invention. Still further, it is also apparent that the liquid trap, as shown in the form of a U-shaped conduit, is not critical but that various Aother means for providing and maintaining a sufficient amount of condensate in the reservoir 31 may be employed.

On the other hand, it is apparent that the particular level at which it is desired to maintain the mother liquid in the vessel is determined by the respective differences between the desired level (for example 29) in the vessel and the level of the liquid (for example 32) in the sepl arate condensate zone such as shown as being maintained in the gas trap Regard for the differences in specic gravities of the condensate and the mother liquid, of course, must be considered in determining the particular level ofV operation of the liquid in the separate condensate zone as well as the particular desired liquid level of operation in the vessel. For example, it is apparent to those skilled in the art with regard to the embodiment shown that lby physically moving the gas trap 1 downward, the level of the liquid in the vessel may be maintained at any position within the vessel as is deemed appropriate. The change in position which determines the level of liquid in the vessel, of course, must be made with regard to the densities of the liquids and the pressure differences between the trap and Vessel, a factor which is normally not of great consequence. lt goes without saying, of course, that lit is essential in this embodiment to maintain the discharge end 34 of pipe 26 submerged in the mother 'liquid during operation in order to provide the diierences in head lwhich cause the fluctuations of the condensate lever in the separate zone.

Although the embodiment shown in the drawing employs a ball loat type valve System, it is apparent that other mechanisms may be employed which are responsive to the level of the liquid in the separate zone. Thus, an electro-mechanical mechanism may be employed which operates a solenoid valve type mechanism according to the level of the liquid. Still further, a diaphragm type valve mechanism may also be employed with equal facility especially where the refluxing ot the condensate is undesirable and a diilerent liquid is employed in the separate zone. Thus, the liquid level in the separate Zone may act on a diaphragm which in turn may actuate a valve mechanism. Other and further variations are likewise apparent to those skilled in the art.

As previously indicated, wherein it is undesirable to reux the water vapor or other condensable component, condensing unit 2 may be eliminated and the non-com densaole gases with condensable component led directly to the gas trap from which both are bled through the gas outlet pipes and the valve actuating mechanism controlled by means of a separate liquid zone and a gaseous zone as indicated heretofore. However, in this case an immiscible liquid of greater density than the condensable components is preferably employed in the Ltil liquid trap and liquid reservoir to facilitate actuation of the valves. Under normal operations in such a case, the velocity of the gases and associated components through the inlet and from the gaseous discharge may be adjusted to sweep along any liquitied condensable componentswhich have condensed on the surface of the immiscible liquid. It is, of course, apparent that under such an operation that the liquid trap would be so positioned as to retain the immiscible liquid employed for actuation of the valve Within the reservoir and the trap.

Although pipes have been described for retaining the liquid and/ or gas in the separate zone and gaseous zones respectively, it is also apparent that the invention is not limited thereto as other and well known apparatus may be employed for accomplishing the desired separate zone and gaseous zone result. `The invention, nevertheless, in its most advantageous aspect is directed to employing a condensing -unit to facilitate the maintenance of the liquid in the separate zone.

What is claimed is:

1. Apparatus for automatically discharging non-condensible gas from a pressure vessel containing a liquor which deposits scale upon lcontacted surfaces, wherein said gas collects in the upper regions of said vessel and has associated therewith a condensible vapor, comprising in combination with `said pressure Vessel and adjacent thereto a gas discharge means, which includes: a closed chamber comprising a float Valve mechanism and a gas outlet positioned above the oat of said float valve mechanism, wherebysaid gas outlet is opened and closed by said oat valve mechanism, a rst conduit means which includes condensing means extending from the upper regions of said vessel and terminating above the float of said float valve mechanism in said chamber, whereby said gas and condensible vapor are delivered from the upper regions of said vessel to said chamber and become separated therein and whereby a liquid reservoir of condensed vapor is formed in said chamber and said non-condensible gas is discharged through said gas outlet, a second conduit means positioned below the oat of said float valve mechanism and below said rst conduit means which includes a liquid trap and extending between said chamber and said vessel, whereby said condensed liquid is returned to said vessel through said second conduit means, and whereby the level of said liquid in said reservoir will fluctuate responsive to the level of said liquor in said pressure vessel.

2. An apparatus according to claim l wherein said liquid trap is a 1-shaped tube.

References Cited in the tile of this patent UNITED STATES PATENTS 1,344,292 Dawley June 22, 1920 2,104,759 Randel vlan 11, 1938 2,263,409 Moreland Nov. 18, 1941 2,518,845 Williams Aug. 15, 1950

Claims (1)

1. APPARATUS FOR AUTOMATICALLY DISCHARGING NON-CONDENSIBLE GAS FROM A PRESSURE VESSEL CONTAINING A LIQUID WHICH DEPOSITS SCALE UPON CONTRACTED SURFACES, WHEREIN SAID GAS COLLECTS IN THE UPPER REGIONS OF SAID VESSEL AND HAS ASSOCIATED THEREWITH A CONDENSIBLE VAPOR, COMPRISING IN COMBINATION WITH SAID PRESSURE VESSEL AND ADJACENT THERETO A GAS DISCHARGE MEANS, WHICH INCLUDES: A CLOSED CHAMBER COMPRISING A FLOAT VALVE MECHANISM AND A GAS OUTLET POSITIONED ABOVE THE FLOAT OF SAID FLOAT VALVE MECHAANISM, WHEREBY SAID GAS OUTLET IS OPENED AND CLOSED BY SAID FLOAT VALVE MECHANISM, A FIRST CONDUIT MEANS WHICH INCLUDES CONDENSING MEANS EXTENDING FROM THE UPPER REGIONS OF SAID VESSEL AND TERMINATING ABOVE THE FLOAT OF SAID FLOAT VALVE MECHANISM IN SAID CHAMBER, WHEREBY SAID GAS AND CONDENSIBLE VAPOR ARE DELIVERED FROM THE UPPER REGIONS OF SAID VESSEL TO SAID CHAMBER AND BECOME SEPARATE THEREIN AND WHEREBY A LIQUID RESERVOIR OF CONDENSED VAPOR IS FORMED IN SAID CHAMBER AND SAID NON-CONDENSIBLE GAS IS DISCHARGE THROUGH SAID GAS OUTLET, A SECOND CONDUIT MEANS POSITIONED BELOW THE FLOAT OF SAID FLOAT VALVE MECHANISM AND BELOW SAID FIRST CONDUIT MEANS WHICH INCLUDES A LIQUID TRAP AND EXTENDING BETWEEN SAID CHAMBER AND SAID VESSEL, WHEREBY SAID CONDENSED LIGUID IS RETURNED TO SAID VESSEL THROUGH SAID SECOND CONDUIT MEANS, AND WHEREBY THE LEVEL OF SAID LIQUID IN SAID RESERVIOR WILL FLUCTUATE RESPONSIVE TO THE LEVEL OF SAID LIQUID IN SAID PRESSURE VESSEL.

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