US2008686A - Floating roof - Google Patents

Description

July 23, l1935. c. l.. DAY 2,008,686

FLOATING ROOFl Filed Jan. 10, 1931 5 Sheets-Sheet 1 WWI im HU Ml! WHW l WW HIM Il@ HHM llll | l HIM :im l l Il WHW l III lhllll l HI lhli

Julyzs, 1935. j C. r., DAY 2,008,686 FLOATING RQOF` v I Filed Jan. 1d. 1931 s sheets-sheet 2 l/OJ n l? E: i 7 5 2, /j Y 2 1 3. j/ I 4 .doM No Y 1hJuly 23, 1935. c. L. DAY 2,008,686

"FLOATINQ ROOF Filed Jan.` 10, 1951 5 Sheets-Sheet 3 jzveyzzaw.. u

Patented July 23, 1935 FLOATING ROOF Clayton L. Day, Chicago, Ill., assignor to Chicago Bridge & Iron Company, Chicago, -Ill., a corporation of Illinois Application January 10, 1931, Serial No. 507,977

3 Claims.

This invention relates to improvements in floating roofs and, more especially, such floating roofs as are commonly used on oil storage tanks to eliminate or lessen losses by evaporation, gas

escape, and the like.

Among the features of my invention may be vmentioned the following.

The roof has an annular pontoon giving it sufcient buoyancy so that it is non-sinkable.

l0 The roof has an upstanding rim permitting the retention of water (for example, rain water) on top of the roof, such water acting as an insulator to keep the oil under the roof cool. As here shown, the upstanding rim is formed by the annular pontoon.

The roof is also provided with a depending annular rim forming a downwardly open gasreceiving space under the roof so that gas forming in the liquid or rising therefrom lcan be trapped in this gas-receiving space. As here shown, lthis depending rim is also formed by the annular pontoon.

The central portion of the floating roof may be exible so that the same can flex upwardly some distance to increase the capacity of the gasreceiving space. This central portion, for example, may be made of flexible sheet metal.

The pontoon is high enough so that a substantial portion of it will be above the liquid on which the roof floats when substantially the entire area of the central sheet metal portion is in contact with said liquid. In a roof of this kind, it frequently is desirable tokeep as much of the metal area of the roof in contact with the liquid as possible. This contact will lessen evaporation from the surface of the liquid, and also lessen corrosion. My improved roof is so made that the entire central portion of the roof may be in contact with the liquid, and still a substantial portion of the pontoon will be above the liquid so that the roof will still have considerable buoyancy. In fact, it may be made and is here shown as having sufficient buoyancy in such case so that the central part may be entirely lled with water, and the roof still remain non-sinkable.

The roof is so made that as gas collects in the gas-receiving space, the flexible sheet metal central portion will flex upwardly to its maximum extent before the roof rises sufficiently to "U vent gas under the rim.

Another feature of the invention is the provision of an annular pontoon which is relatively deeper at the outside than the inside, in order s* to give greater buoyancy at the periphery, This additional buoyancy assists in supporting the weight of the sealing means,` for example, the shoes, hangers and other sealing means provided for sealing the space between the roof and the tank shell.

Other features and advantages of my invention will appear more fully as I proceed with my specification. v

In that form of device embodying the features of my invention shown in the accompanying drawings- Figure 1 is a vertical sectional view; Figs. 2, 3 and 4 are similar views showing the different ways of using the roof; and Fig. 5 is a similar view showing a modified form.

Another feature of my invention is the provision of means for causing some circulation of the oil. By uslngan annular pontoon, there is obtained some insulation of the oil near the periphery of the tank from heat above. This insulation is obtained by the confined air in the peripheral pontoon. Consequently, sun beating downon the roof will cause the oil in the center of the tank to heat more rapidly than under the periphery of the roof. This will cause some circulation of oil by convection in the tank, as indicated by the arrows in Fig. 3. That is, the oil under the pontoon will have a tendency to fall, move toward the center of the tank and there rise. This circulation will lessen or prevent undue heating of the oil directly under the central sheet metal portion of the roof and thus lessen losses.

As shown in the drawings, I0 may indicate a cylindrical tank in which is stored oil or other liquid II.

Any means, such as the shoes I4, hangers I4a and flexible fabric seal I5, may be employed for sealing the space between the periphery of the roof and the wall of ythe tank I0. Such sealing means, however, forms no part of the present invention and, consequently, the same need not be described in detail here. The roof may also be provided with a manhole I6 giving access to the interior of the pontoon and a manhole I1 in the central portion of the roof. Numeral I8 may indicate a gage hatch. The central part of the roof may be provided with a sump I9 having a cover 2D, and a drainage system of any desired construction, as indicated by 2| may lead from the sump to the outside of the tank.

The roof itself comprises primarily a peripheral circular pontoon I2 and a centr-a1 sheet metal portion I3. The interior of the pontoon may be braced by suitable truss members 22.

The pontoon is preferably so made as to provide anupstanding rim 23 surrounding the roof permitting the retention of rain water thereon. It is also here shown as formed to provide a dependingrim 24 to form a downwardly open gas-receiving space under the roof. As here shown, therim 24 constitutes the bottom of the pontoon, the rim being formed byslanting this bottom downwardly and outwardly from the 'edge where it is attached to the periphery of the central portion I3. By this construction, it will be seen that a radial cross-section of the pontoon is substantially rectangular but somewhat deeper at the outer edge than the inner edge. 'I'he bottom of the surface of the pontoon, therefore, forms the downwardly projecting rim above referred to.

The central part of the roof may be provided with avent pipe 25 controlled by avalve 26. When'the roof is first put into use, or at other times, if desired, this vent pipe may beused to permit the escape of air or other gases from under the roof. After the roof has been put into use and air permitted to l escape from underneath, thevalve 26 may then be closed so that gas arising from the liquid by boiling or otherwise will be trapped and retained under the roof. In Fig. 2 the roof is shown in use in this manner. It will be seen that there isa gas space 21 under' the roof. Since the central portion I3 vof the deck is made flexible, it may-flex upwardly and downwardly to vary the capacity of this gas space. For example, as shown in Fig. 2, the central. portion I3 is exed upwardly to a considerable extent, giving a relatively large gas space under the roof. The roof is preferably designed so that this .upward flexing will' be carried to its maximum point before any gas will escape under the rim of the roof. As gas in the space 21 condenses, or goes back into the liquid, or decreases in volume', the central portion I3 of the roof will flex downwardly `to decrease the volume of the gas space. This up- -wardly and downwardly flexing of the central portion of the roof I3 to change the capacity of the gas space under the same, in accordance with changes in pressure of the gas, is sometimes referredto as breathing. That is, the flexible central portion I3 will permit a breathing action of the roof. It is to be particularly noted, however, that the breathing action is not due solely to the flexible central portion of the roof. That is, even if the central portion I3 were not flexible but made rigid, the roof' would breathe somewhat by rising and failing bodily. Reference to Fig. 2 will show that the gas space 21 is not formed entirely by the upward flexing of the central portion I3 but that the whole roof has risen bodily somewhat and that this upward bodily movement has formed a part of the gas space 21. That is, the roof also breathes by its bodily upward and downward movement. For example, as vdiagrammatically shown in Fig. 5, the central portion I3 may be stiifened and prevented from flexing by radially arrangedtrussing 28 and there may still be formed a gas space 21, as shown by the bodily rising of the roof. Also, the capacity of this gas space will vary with changes in pressure of the gas. That is, the roof will rise or fall in accordance with different pressures and quantities of gas formed under the same to vary the capacity of the space 21.

Such a roof, therefore, even though it does not have a flexible central portion I3, will still have a breathing action. Making the central portion flexible will increase the maximum capacity of increased in capacity by lowering the rim or by l making the central portion flexible. Lowering the rim, however, might interfere with the stability of the roof and will also interfere with its minimum capacity because a lower rim will .strike the bottom of the tank sooner than a higher one. Some increase to the maximum capacity of the space 21 may, therefore, be provided by making the central portion I3 flexible without interfering with the stability of the roof or its minimum capacity.

If desired, all the gas under the roof may be. permitted to escape through thevent pipe 25 so that the entire area of the central portion I3 of the-roof will be in contact with the surface of the oil. The roof in use in this manner is shown in Fig. 3. This contact' of the central'metal portion I3 will serve tohlessen or stop evaporation from the surface of the oil. Of course, some gas may collect by boiling but if this occurs, any such gas collected may be vented off through the vent pipe. Ordinarily, when the roof is exposed to the suns rays, boiling will occur first at the top since the upper surf-ace of the oil will become heated by contact with the `metal of the roof; As explained before, however..the pontoon will `provide some insulation at the periphery so that the oil near the wall of the tank will be cooler than in the center and this will cause circulation, as shown by the arrows, which will serve to lessen or prevent boiling of the oil at the surface, as just referred to. In short, it may be stated that the roof may be used, as shown in Fig. 3, with the central portion I3 having its entire area in contact with the surface of the oil. It may be maintained in this position by immediately venting any gas through thepipe 25 as soon as it collects under the roof. If desired, of course, thevalve 26 can be left open all of the time so that no gas can collect. The roof will then operate as shown in Fig. 3.

Theupstanding rim 23 surrounding the central portion I3 permits the retention of water, such asrain water 23, on top of the roof, such layer of rain water serving to insulate the oil against heat. In Fig. 4, the roof is shown as being used with a layer of rain water on top of it for such insulating purposes. In such case, thevalve 26 may be left open so that no gas can collect under the roof or it may be kept closed and some gas permitted to collect. In case more gas than desired collects, the valve may be opened and a. sufficient amount vented.

While I have shown and described certain embodiments of my invention, it is to be understood of said pontoon forming an upstanding rim around the flat sheet; and a downwardly depending con-f tinuous rim surrounding said sheet.

2. A iloating roof, including, a substantially iiat sheet supported by an annular pontoon, a portion 5 of said pontoon forming an upstanding rim around the dat sheet, and a portion of said pontoon forming a depending rim around the flat sheet to form a gas spaced under the flat sheet and inside of said depending rim.

3. A oating roof, including, a. substantialhr dat sheet supported; by an annular pontoon having inner and outer and top and bottom walls, said sheet being attached to the lower edge of said inner wall, and said bottom wall slanted downwardly and outwardly to form a gas space under said sheet.

CLAYTON L. DAY.

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