US2601317A - Vapor vent for floating roof tanks - Google Patents

Description

June 24, 1952 F. D. MOYER 2,501,317

VAPOR VENT FOR FLOATING ROOF TANKS Filed June 26, 1946 j zza Patented June 24, 1952 VAPUR VENT FOR FLOATING ROOF TANKS Frederick D. Meyer, Chicago, 111., assignor to Chicago Bridge & Iron Company, a corporation of Illinois Application June 26, 1946, Serial No. 679 382 Claims. 1

This invention relates to a vapor venting means for a floating roof tank.

Floating roof tanks include a shell 'for holding the storedliquid and a roof that floats on top of the liquid. Sealing means are provided between the roof and the shell of the tank to prevent contamination of the stored liquid and to reduce evaporation'losses. When the tanks are used for storing volatile liquids, vapor forms under the roof. When this vaporhas accumulated in relatively large quantities it is necessary that it be vented to the atmosphere. The present invention relates to an improved venting means permitting the escape of the vapor whether as formed or when a, predetermined pressure has been reached in the vapor space.

The invention includes broadly a vapor venting means comprising a primary vapor space located above the surface of the stored liquid, a secondary vapor space separate from the primary vapor space, communicating means connecting the two vapor spaces, vent means in the secondary vapor space at a, point remote from the communicating means, means for maintaining a higher pressure in the primary vapor space than in the secondary vapor space during venting, and means for returning condensed liquid from the vapor to the stored liquid. In a preferred form there is provided a downwardly extending barrier around the roof adjacent the edge thereof and extending down into the liquid, so that the primary vapor space-will be located within the confines of the barrier and beneath the floating roof. The secondary vapor space is then between the barrierand the edge of the roof-and the shell of the tank. A passageway is provided through the barrier so that vapor may escape from the primary vapor space into the secondary vaporspace. A vent open to the atmosphere is provided in the secondary vapor space at a point remote from-the passageway. If :lt is desired to vent the vapor only when a predetermined vapor pressure has been reached in the primary vapor space, the inner end of the passageway may be arranged so as to be immersed in the liquid until this predetermined pressure has been reached.

JIn-the ordinary floatingroofs where the shsell is'substantially cylindrical and the roof is substantially circular the vent openin tothe atmospherecan be located 180 from the passageway. Vapor flowing through thepassageway intofthe:secondary vapor space-will then flow in opposite 'directions'around the' tank to the vent. During this travel liquid :will. condense from the vapor andiall into the stored liquid between the barrier and the shell of the tank. When the vapor flows from the relatively high. pressure primary vapor space into the low pressure secondary vapor'space a refrigerating action will'be caused by the expansion of the gas. This-refrigcrating action aids in condensing some of the vapor, and this condensed liquid will fall by gravity into the stored liquid.

The invention may be used oneither a single deck roof or a double deck roof, and the venting means may be caused to operate either at a predetermined vapor pressure or asvsoon as any vapor is formed. When the inventionis used on a single deck roof the barrier separating the primary and the secondary vapor spaces may be an annular pontoon around the edge of the roof. When the invention is used on a-double deck roof wherein the roof itself acts as a pontoon the barrier may be a depending cylindrical plate, either arranged adjacent to the roof or spaced inwardly from the edge of the roof.

The invention will be described as related to the embodiment shown in the accompanying drawings. Of the drawings Fig. 1 is a plan view of a floating roof tank embodying the'invention, and Fig. 2 is a verticalsection taken along line 2-2 of Fig. 1.

In the embodiment shown in the drawingsthe floating roof tank comprises a shell ill and a single deck floating roof H therein. Thereof is lower at the center than at its edge and isprovided with a depending annular pontoon l2. In the center the roof there is provided acylindrical pontoon i3 arrangedon top of the roof so that it will be immersed in; any rain water that collects on top of the roof. This centralpontcon gives added buoyancyto theroof when under a load of water. ;In contact-withthe inner surface of the shellof thetanktherevis located-theordirn ry flat sealingm mber iflw upp ted-from th roof inany desiredymanner. ,A flexible sealing member extends; fromgthe edge of thereof to the top of the flat sealing member 14 and is usually afabricimpregnated witha flexibleirnpervious material.

Ar pe it extends throu h one porti n o th annular pontoon l2, and this pipe hasitsinner end lower than its outer end so that the inner end will ordinarily be'imrnersed in the-stored iquid ii. A ventl8 openin t the a mospher is located substantially around the roof from the pipe 1'6.

When vapor is formed in the tank it Will -col,- lect intheprimary vapor space H) under the deck of the floating roof and within the confines of the annular pontoon l2. The secondary vapor 7 space 20 is located between the annular pontoon I2 and the shell IE! of the tank. As the flat sealing member I4 contacts the shell of the tank the secondary vapor space is actually between the annularpontoon I2, the flat sealing member I4, and the flexible sealing member I5.

When suflicient vapor has accumulated in the primary vapor space I9 to raise the roof so that the inner end of the pipe I6 is exposed, vapor will escape from the primary vapor space I9 through the pipe I5 into the secondary vapor space 28, and will then flow in opposite directions around the roof and escape through the vent It. A baffle plate 2| is provided opposite the outer end of the pipe I6, and this plate will aid in condensing liquid from the vapors.

As the pressure within the primary vapor space I9 is greater than that within the secondary vapor space 20, the vapor flowing through the pipe I6 and into the secondary vapor space will expand, and this expansion produces a cooling efiect on the vapors. While the vapor is flowing through the secondary vapor space to the vent [8, much of the vapor will condense, and the resulting liquid will fall by gravity into the stored liquid that is between the annular pontoon I2 and the flat sealing member I4. When suflicient vapor has escaped from the primary vapor space I9 to materially lower the pressure within the primary vapor space, the annular pontoon I2 will sink back into the liquid until the inner end of the pipe is i immersed in the liquid. No more vapor will flow until the pressure has been again increased to a predetermined value.

Having described my invention as related to the embodiment set out in the accompanying drawings, it is my intention that the invention be not limited by the details of description unless otherwise specified, but i rather be construed broadly within its spirit and scope as set out in the accompanying claims.

I claim:

1. In a floating roof tank comprising a shell adapted to store liquid and a floating roof there in having its peripheral edge spaced from the shell, an annular barrier extendin downwardly from the roof forming a primary confined vapor space located above the surface of the stored liquid inside the barrier, and a secondary confined vapor space located above the surface of the stored liquid and outside the barrier separate from the primary vapor space, communicating means connecting the two vapor spaces and being normally closed by the stored liquid, a vent pipe means in the secondary vapor space at a point remote from the communicating means, said communicating means being so arranged that a higher pressure is required in theprimary vapor space than in the secondary vapor space during venting.

2. The vapor venting means of claim 1 wherein the communicating means remains closed by the stored liquid until a predetermined pressure has been reached in the primary vapor space.

3. The Vapor venting means of claim 1 wherein the secondary vapor space is above the liquid surface between the edge of the roof and the shell.

4; The vapor venting means of claim 1 wherein the Primary vapor space is beneath the roof and the secondary vapor space is above the liquid surface and between the edge of the roof and the shell.

5. In a floating roof tank comprising a substantially cylindrical shell adapted to store liquid, a substantially circular floating roof thereon and a flexible seal between the roof and the shell, said roof having a downwardly extending annular barrier forming a primary confined vapor space located beneath the roof and above the surface of the stored liquid and a secondary confined vapor space located above the liquid and beneath the flexible seal between the floating roof and the shell, communicating means normally closed by the stored liquid and connecting the two vapor spaces, and a vent pipe means in the secondary vapor space at a point substantially from the communicating means.

6. The vapor venting means of claim 5 wherein the barrier extends around the edge of the roof and downwardly into the stored liquid with the primary vapor space being within the confines of said barrier.

7. The vapor venting means of claim 5 wherein the barrier extend around the edge of the roof and downwardly into the stored liquid with the primary vapor space being within the confines of said barrier, and the secondary vapor space being between the barrier and the shell of the tank.

8. The vapor venting means of claim 5 wherein the barrier extends around the edge of the roof and downwardly into the stored liquid with the primary vapor space being within the confines of said barrier, and with the communicating means extending through said barrier.

9. The vapor venting means of claim 5 wherein the communicating means comprises a passageway with the end of the passageway adjacent the primary vapor space being immersed in the stored liquid until a predetermined pressure has been reached in said primary vapor space.

10. In a floating roof tank comprising a substantially cylindrical shell adapted to store liquid, a substantially circular floating roof therein and a flexible seal between the roof and the shell, a barrier around the edge of the roof and extending downwardly into the stored liquid forming a primary vapor space under the roof located within the confines of said barrier and above the surface of the stored liquid and a secondary vapor space at the edge of the roof beneath the flexible seal between the barrier and the shell of the tank and above the surface of the stored liquid, a pipe connecting the two vapor spaces, and a vent opening from the secondary vapor space and located substantially 180 from the passageway.

11. The vapor venting means of claim 10 wherein the barrier is an annular pontoon located beneath the roof.

12. The vapor venting means of claim 10 wherein the barrier is an annular pontoon located beneath the roof and the pipe extends through the pontoon, the inner end of the pipe being under the liquid surface until a predetermined pressure has been reached in the primary vapor space.

13. In a floating roof for a liquid storage tank including flexible sealing means between the roof and the side walls of the tank and said roof having an outer annular pontoon adapted to be immersed in the stored liquid, said pontoon defining an inner vapor space above the stored liquid and beneath the roof and said pontoon defining an outer vapor space above the stored liquid and beneath the sealing means, means for permitting escape of air from the inner vapor space when liquid is being introduced into said tank and for permitting entrance of air into the inner vapor space when said tank is being drained, during that period of filling or draining when the roof is resting on the bottom of the tank, comprising a first vent extending diagonally upwardly and outwardly through the pontoon and communicating with said vapor spaces, a second vent communicating with the outer vapor space and the atmosphere, the inner end of said first vent being so positioned as to be immersed in the stored liquid when the roof is floating therein.

14. Vent means for a floating roof tank having a floating roof having a deck and an outer annular pontoon defining a vapor space inside the pontoon beneath the deck and a separate confined space outside the pontoon comprising a vent extending through the pontoon and having an inner end opening to the space inside the pontoon and normally immersed in the liqannular pontoon defining a vapor space inside the pontoon beneath the deck and a separate confined space outside the pontoon comprising a vent extending downwardly through the pontoon and having one end opening through the inner side wall of the pontoon at a point below the normal liquid level whereby said end is normally immersed in the liquid in the tank and adapted to be relatively raised above the level of the liquid with relative upward movement of the pontoon in response to increasing pressure in said vapor space, the other end of said vent opening through the outer side wall of the pontoon, and means connecting the space outside the pontoon with the atmosphere.

FREDERICK D. MOYER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,545,352 Rodriguez July 7, 1925 1,653,387 Brown Dec. 20, 1927 1,904,339 Wiggins Apr. 18, 1933 FOREIGN PATENTS Number Country Date 38,851 Netherlands July 17, 1936

Claims (1)

1. IN A FLOATING ROOF TANK COMPRISING A SHELL ADAPTED TO STORE LIQUID AND A FLOATING ROOF THEREIN HAVING ITS PERIPHERAL EDGE SPACED FROM THE SHELL, AN ANNULAR BARRIER EXTENDING DOWNWARDLY FROM THE ROOF FORMING A PRIMARY CONFINED VAPOR SPACE LOCATED ABOVE THE SURFACE OF THE STORED LIQUID INSIDE THE BARRIER, AND A SECONDARY CONFINED VAPOR SPACE LOCATED ABOVE THE SURFACE OF THE STORED LIQUID AND OUTSIDE THE BARRIER SEPARATE FROM THE PRIMARY VAPOR SPACE, COMMUNICATING MEANS CONNECTING THE TWO VAPOR SPACES AND BEING NORMALLY CLOSED BY THE STORED LIQUID, A VENT PIPE MEANS IN THE SECONDARY VAPOR SPACE AT A POINT REMOTE FROM THE COMMUNICATING MEANS, SAID COMMUNICATING MEANS BEING SO ARRANGED THAT A HIGHER PRESSURE IS REQUIRED IN THE PRIMARY VAPOR SPACE THAN IN THE SECONDARY VAPOR SPACE DURING VENTING.

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