Title:
Fluid trap for storage tanks
United States Patent 2247566


Abstract:
This invention relates to new and useful improvements in fluid traps for storage tanks. One object of the invention is to provide an improved device generally known as a gas trap and particularly adapted for use with liquid storage tanks, which is arranged to maintain a desired vapor pressure...



Inventors:
Walton, David H.
Application Number:
US23228538A
Publication Date:
07/01/1941
Filing Date:
09/29/1938
Assignee:
Walton, David H.
Primary Class:
Other Classes:
55/446, 96/358, 220/747, 220/748
International Classes:
A62C4/00
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Description:

This invention relates to new and useful improvements in fluid traps for storage tanks.

One object of the invention is to provide an improved device generally known as a gas trap and particularly adapted for use with liquid storage tanks, which is arranged to maintain a desired vapor pressure within the interior of the tank, whereby evaporation of the liquid within the tank is retarded.

An important object of the invention is to provide an improved device which is mounted in the top of a liquid storage tank and which is constructed to permit escape of vapors from the tank when the vapor pressure exceeds a predetermined point; the device also permitting admission of air into the tank in the event the pressure therein falls below a predetermined point, whereby danger of damage to the tank by excessive pressure or by a lack of pressure, is obviated. A particular object of the invention is to provide an improved device, of the character described, wherein a liquid seal is employed to control the escape of vapors from the tank and the admission of air to the tank, said device being simple and inexpensive in construction and relatively short, whereby the usual elongate vent pipe is eliminated; the liquid seal also preventing damage to the tank due to "flash back" caused by lightning, sparks or fire. Still another object of the invention is to provide an improved device for controlling the escape and admission of fluid to a liquid storage tank, wherein a U-tube having liquid therein is employed, said tube having an upwardly extending extension through which the vaporous fluids or gases from the tank pass, the extension being constructed so as to permit expansion of said fluid, whereby the velocity thereof is decreased and separation of said gas from any liquid in solution therewith, is promoted; the extension also having means therein for further promoting separation of the gas and liquid, whereby escape of any liquid is substantially eliminated.

A construction designed to carry out the invention will be hereinafter described, together with other features of the invention.

The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawing, in which an example of the invention is shown, and 5 wherein: Figure 1 is an elevation of the upper portion of a liquid storage tank, having a gas trap, constructed in accordance with the invention, applied thereto, Figure 2 is an enlarged view. partly in elevation and partly in section, of the trap, Figure 3 is a plan view thereof, Figure 4 is a transverse, vertical, sectional view, taken on the line 4-4 of Figure 2, and Figure 5 is a horizontal, cross-sectional view taken on the line 5-5 of Figure 2.

In the drawing, the numeral 10 designates a liquid storage tank of the usual construction, such as is used for storing oil, or other hydrocarbon liquids. The tank has the usual conical top 12 which has a gas or vapor outlet opening 13 disposed axially therein. A vertically extending outlet pipe 14 has its lower end secured in Sthe opening 13 and ordinarily an elongate verticaly vent tube (not shown) is connected to the upper end of said pipe 14.

In carrying out the present invention, a laterally extending line 15 has one end connected to the upper end of the outlet pipe by means of an elbow 16. The opposite end of the line 15 is connected with the inlet of a U-shaped housing or casing .17. As clearly shown in Figure 2, the housing includes a relatively short vertical Sportion 17ai which has the lateral inlet made integral with its upper end. The lower end of the portion is bent at substantially a right angle to provide a connecting duct 18 and is then directed upwardly to provide an elongate extension 1.9. The extension is flared or enlarged outwardly toward its upper end which is open and this open upper end has a cap member or hood 20 mounted thereabove. The hood does not close this upper end but prevents foreign and extraneous matter from falling into the extension. The portion 17a, duct 18 and extension 19 may be of any desired cross-sectional shape but have been shown as cylindrical.

The interior of the vertical portion 17a forms a chamber A, while the interior of the extension 19 forms a chamber B, said chambers being connected at their lower ends by the lateral duct 18, whereby a U-tube effect may be had, as will be explained. Since the housing 17 is connected Swith the outlet pipe 14 in the top of the tank 10, it is obvious that gas or vapors from the tank may pass through the chambers A and B of the housing and escape to atmosphere from the open top of the extension 19, said vapors or gas passing outwardly beneath the hood 29. Similarly, Sair may enter the upper end of the chamber B and pass through the duct 18, chamber A, pipes IS and 14 and into the tank.

For controlling the flow of fluid through the chambers A and B, a suitable liquid is introduced into the chambers A and B, through an opening provided for the purpose in the top of the chamber A. This opening is normally plugged by a plug 21 threaded into said opening. The liquid introduced into the chamber A will flow through Sthe duct 18 into the chamber B and said liquid will find its level in the chambers, whereby said level is the same in both chambers, as indicated by dotted lines in Figure 2. The amount of liquid introduced is dependent upon the amount of vapor pressure to be maintained in the tank 10 and a gage glass 22 is mounted in the side of the chamber A to indicate the liquid level in the chambers.

With the liquid within the lower ends of the chambers A and B, gas or vapors from within the tank cannot pass outwardly through the chambers without bubbling through said liquid, and similarly, air cannot enter the tank and thus the liquid in said chambers forms a seal.

Assuming that the vapor pressure in the tank builds up, it will be manifest that such pressure is acting against the top of the liquid column in the chamber A. When this pressure builds up to a point sufficient to overcome the weight of the liquid column in the chamber B, the column in the chamber A is forced downwardly which raises the column in the chamber B. Sufficient gas pressure within the tank will finally force the level of the liquid in the chamber A downwardly below the top of the duct 18 and then the gas will bubble upwardly through the liquid column in the chamber B. As this gas moves upwardly through the column, it is forced to take a circuitous path since it must travel around transverse, inclined baffles 23 which are disposed in staggered relation within the interior of the chamber B. As the gas strikes the baffles, any liquid particles picked up by said gas in its travel through the liquid are knocked out and separated therefrom. Also, since the chamber flares outwardly toward its upper end, the gas is permitted to expand during its upward travel and such expansion decreases the velocity of the gas and further promotes separation of the gas and liquid.

The liquid which is separated from the gas during its upward travel in the chamber B falls downwardly onto the inclined baffles and flows downwardly on the surface thereof by gravity. This liquid escapes back to the lower end of the chamber B through openings 24 provided in the lower ends of the baffles.

The gas escaping from the chamber and passing outwardly from beneath the hood is relatively free from liquid and escapes to atmosphere.

As the gas or vapor escapes from the tank 10, the pressure within the tank is lowered and when such pressure falls below a predetermined point, as determined by the amount of liquid in the chambers, the liquid will automatically seek its own level in the chambers and will thus seal the gas outlet. Further, gas or vapor cannot escape from the tank until the pressure within the tank again builds up beyond the necessary predetermined point.

In the event that liquid is rapidly drawn from the storage tank, the pressure within the tank will drop and a partial vacuum may occur in said tank. When such condition arises, the atmospheric pressure which is acting downwardly on the column of liquid in the chamber B forces said column downwardly until the level in said chamber is below the top of the connecting duct 18. Air may then bubble upwardly through the liquid in the chamber A and then pass into the tank 10 through the pipes 16 and 14. When the pressure within the tank again equals or exceeds atmospheric, the liquid in the chambers A and B again seeks its level and remains so until an unbalanced condition again occurs.

From the above, it will be seen that an efficient control of the escape and admission of fluid to a storage tank is provided. The pressure at which the device operates to permit passage of fluid is dependent upon the amount of liquid within the chambers A and B and, by varying the volume of liquid, operation at different pressures may be had. The construction is simple and inexpensive and its use eliminates the usual tall vent pipe. For draining the liquid from the chambers A and B, a suitable drain cock 25 is mounted in the bottom of the duct 18.

It is noted that the device has been illustrated as applied to a standard storage tank but it may be employed with other units, wherein automatic relief of vapor pressure is necessary. Although the housing is shown as made in one piece, it could be constructed of several sections suitably connected together. The flaring or enlarging of the outlet extension 19 or chamber B is a feature of the invention as it allows the gas or vapor to expand prior to its escape, whereby separation of the gas and any liquid admixed therewith is greatly enhanced.

The foregoing description of the invention is explanatory thereof and various changes in the size, shape and materials, as well as in the details of the illustrated construction may be made, within the scope of the appended claims, without departing from the spirit of the invention.

What I claim and desire to secure by Letters Patent is: 1. A gas trap including, a one piece housing angular in cross-section having an upright chamber connected with a fluid line and having a second upright chamber which has its lower end conmmunicating with the lower end of the first chamber, the chambers being adapted to receive a liquid which finds its level in the chambers to act as a seal to prevent passage of fluid through the housing, the second chamber being of a larger cross-sectional area than the first chamber and being flared toward its upper end which is open to atmosphere, and a plurality of baffles secured to the inner wall of the second chamber and extending inwardly toward the center thereof, said baffles having their inner ends inclined upwardly so as to conduct liquids falling thereon toward the wall of the chamber and away from the center thereof.

2. A gas trap including, a one piece housing, angular in cross-section having an upright chamber connected with a fluid line and having a second upright chamber which has its lower end communicating with the lower end of the first chamber, the chambers being adapted to receive a liquid which finds its level in the chambers to act as a seal to prevent passage of fluid through the housing, the second chamber being of a larger cross-sectional area than the first chamber and being flared toward its upper end which is open to atmosphere, a plurality of baffles secured to the inner wall of the second DO chamber and extending inwardly toward the center thereof, said baffles having their inner ends inclined upwardly so as to conduct liquids falling thereon toward the wall of the chamber and away from the center thereof, each baffle having 5 an opening in its lower portion adjacent the wall of the chamber for permitting any liquid flowing downwardly along the baffle to travel downwardly along the wall of the chamber, the first chamber having a normally closed liquid inlet in its top and a valve controlled discharge at its lower portion.

DAVID H. WALTON.