US3115888A - Water drawoff system for oil tanks - Google Patents

Description

Dec. 31, 1963 F. D. MOYER WATER DRAWOFF SYSTEM FOR OIL TANKS 2 Sheets-Sheet 1 Filed Feb. 25, 1960 :I WMNMWMWMMW- WMWMMWW ffizaerzfor Dec. 31, 1963 F. D. MQYER 3,115,388

WATER DRAWOFF SYSTEM FOR OIL. TANKS Filed Feb. 23, 1960 2 Sheets-Sheet 2 United States Patent 3,115,888 WATER DRAWUFF SYSTEM FOR 01L TANKS Frederick D. Mayer, Chicago, 11]., assignor to Chicago Bridge & Iron Company, Chicago, ill., a corporation of Illinois Filed Feb. 23, 1960, Ser. No. 10,343 1 Claim. (Cl. 137-172) This invention relates to a drainage system for withdrawing water which accumulates in the bottom of liquid hydrocarbon storage tanks. It more specifically is concerned with an automatic Water drawoff system which substantially reduces drawoff fire hazards and also conserves substantial quantities of oil products. In many oil storage tanks there is a tendency for water tdcollect and, being heavier than the stored product, the water generally settles to the lowest portion of the tank. Among the factors which contribute to the accumulation of water are water mixed in the petroleum product when pumped into the tank, condensation of vapors within the tank caused by daily and seasonal variations in temperature and atmospheric conditions, and passage of rain water and other precipitation into the tank through openings of various types in the tank roof.

Most flat bottom oil storage tanks are provided with a sump in the bottom of the tank in which collects all accumulated water. When the water level becomes sufficiently high the water in the sump is drained off through a drain pipe which extends from the sump out through the shell of the tank.

In areas where temperatures go below freezing, it is necessary to provide some means to prevent Water, which may be trapped in the drain line, from freezing in order to avoid rupturing the line. One conventional method of preventing freezing is to provide an expensive anti-freeze valve at the end of the drain line which causes all water which may be trapped in the drain line when the valve is closed to return to the sump.

The valve system generally used in conventional type rawoff lines is manually operated. If the operating personnel fail to draw off water in sufiicient quantity as it accumulates, the water level may reach the height of the product line and water may thereby be drawn oil with the stored product, resulting in production contamination and other undesirable consequences.

In the operation of conventional water drawolf systems the drain line is always filled with the stored petroleum product. When the drawoff valve is first opened the product flows from the line into the sewer or onto the ground before water is discharged. This loss of product not only is wasteful but also presents a major safety hazard because of the danger of fire or explosion. The disadvantages of operating conventional water drawofi systems are recognized when it is realized that a water drawofl line can extend 100 feet or more from the sump to the tank exterior and can be from three to ten inches in diameter. A usual size, for example, is a line 100 feet long constructed from 8 inch steel pipe. In a line of this size about 100 gallons of petroleum product would be normally trapped during use. This amount of flammable petroleum product, when drained from the line into a sewer or other exposed area, provides a serious fire or explosion hazard, as well as waste product.

According to this invention there is provided a water drawoff system which eliminates the withdrawal of product through the drawoif system and therefore eliminates a dangerous fire hazard. This system employs a water drawoff valve located either in or near the sump which can operate automatically, does not depend upon the fallibility of operating personnel, and effectively prevents rupturing of the drawoff pipe due to freezing without requiring expensive, poorly functioning anti-freeze valves.

To aid in the description of this invention reference will hereafter be made to the drawings, in which:

FIGURE 1 is a cross sectional fragmentary view of the bottom portion of a flat bottom oil storage tank utilizing one embodiment of the water drawofr system of this invention;

FiGUFJE 2 is an enlarged partial cross sectional view of the specific embodiment of the pump and automatic valve portion of the drawoff stern shown in FIGURE 1;

FIGURE 3 is an enlarged cross sectional view of the same portion of the storage tank illustrated in FIGURE 2 showing the valve in the open position;

FIGURE 4 is a vertical cross sectional View of the drawoif line showing the positioning of transverse bailles which provide an air space to absorb expansion in case of freezing;

FiGURE 5 is a cross sectional view through line 55 of FIGURE 3 illustrating the valve closure mechanism;

FIGURE 6 is an elevation view of an alternative type of automatic sump valve employed in this invention;

FIGURE 7 is a plan view of the sump valve of FIG- URE 6; and

FIGURE 8 is an illustration of another type of automatic sump valve which can be employed in this invention.

Referring to FIGURE 1, the bottom 10 of the petroleum storage tank has a sump 11 located in the center thereof. A recessed drain well 12 is provided in the bottom of the sump. A water drawotf pipe 13 extends from sump 11 through the tank shell 14. A valve 15 can be attached to pipe 13 at a point outside the shell 14. Baffle plates 16 are spaced along pipe 13 in slots extending generally from the top of the pipe to a point not deeper than half of the pipe diameter, and the plates are welded in place. An automatic fioat control valve 17 is located near the intake end of pipe 13.

FIGURE 2 shows the general construction of one embodiment of the automatic float control valve 17. A float 24? mounted on a lever 21 is pivotally attached to valve housing 22;. A butterfly diaphragm 23 inside the pipe is fixed to the axle 24 which is journaled in the sidewall of the valve housing 22 so as to rotate as the lever 21 is angularly displaced in its movement by float 20. A stop 25 in the form of an outwardly depending stud is connected to the exterior surface of housing 22, and cutout disc 26 is fixed to axle 24 so that the shoulders 27 and 28 limit the amount of rotation of the axle and the valve elements connected thereto.

The operation of float 20 to actuate the butterfly diaphragm valve 23 is made possible by the diiference in specific gravities of Water and the stored product. The size and weight of the float 20* and the length of the lever 21 is preferably selected so that the approximate center of gravity of the float is maintained at the interface I between the Water and the stored product. To accomplish this, the specific gravity of the float must be less 3 than that of water and greater than that of the stored hydrocarbon. In normal operation, therefore, the float will be constantly submersed in liquid but will rise and fall as the level of water in the sump rises and falls. The limit of movement of the float 2b and lever is controlled by the shoulders 27 and 28 of disc 26 coming to bear against stop 25. Thus, if the level of water in the sump falls below the level 1 shown in FEGURE 3, the float neverthless does not fall below the level shown in FIGURE 3, which maintains the valve closure in the closed position and prevent loss of product through the drawofl line even though the interface falls below the Valve inlet. Similarly, the lever never rises beyond the position shown in FIGURE 2 no matter how much higher the water level may become.

FIGURES 6 and 7 show a diflferent embodiment of the invention in which a float id having a specific gravity of less than water and greater than the stored hydrocarbon serves also as a valve closure when seated in the mouth 41 of pipe 13. As the water level i nises above the rim of the sump llll as shown in phantom view in FlGURE 6, the float 4d rises as well until restrained by the upper portion of the float cage which is clamped on the terminal end of pipe 12. As soon as the float rises above the seated position, water in sump it is free to flow through pipe 13 and will continue to flow until float 4e reseats itself in the mouth 41 of pipe 13.

Still another embodiment of the invention is shown in FIGURE 8 in which lever 61 supported by support 62 is connected to flo a-t 53 having a specific gravity such that the non-buoyant ball-shaped closure as which seats at the mouth of pipe 13 and as the level of Water rises in the sump, the float 63 rises, thereby unseating ball-shaped valve closure 64 to permit the water to flow through the pipe.

Other valve designs can be used such that the lever 61 does not have to be horizontal in order to close the valve. The level of water required to close the valve can be varied by the size, Weight and shape of the float or the ball, or by change in lever arms, tilting the axis of th lever or any combination of any of the foregoing.

It is desirable that the automatic valve, whether of the type shown in FIGURES 2, 6 and 8, or another type of the same principle, shall accomplish a tight seal which permits no leakage and if that is the case no valve need be furnished at the end of the pipe outside the tank shell. in order to provide an automatic valve which maintains such a tight seal, however, it may be necessary to obtain a much more complex and expensive device than is otherwise required. It may be desired, therefore, to use such a less complex valve and to provide an auxiliary hand operated valve 15 at the end of pipe 13 outside the tank shell 34, all as shown in FIGURE 1. Where such a valve is provided, however, leakage of water past the automatic valve into pipe 13 might cause relatively large accumulations of water therein, and in areas of extreme cold it is possible that such Water might freeze in pipe 13. A plurality of spaced baflles i6 is therefore provided whenever an external valve 1-5 is provided. These baflles lie usually extend from the top of pipe 13 to approximately the horizontal midline or diameter. When such bellies are inserted in the pipe, the spaces between adjacent baflles become compartments to contain entrapped air when the water level in pipe 13 rises above the bottom edge of the bafiles. Such entrapped air builds up pressure which prevents the water from entirely filling the spaces between baffles, and each unfilled space serves as a cushion to absorb expansion of water as it freezes into ice within the pipe. The bafiles therefore eiiectively prevent damage to the pipe from freezing of water which may have accumulated therein. It is not necessary, however, to provide these baflles where no external valve 15 is used in connection with the Water dl'awoff system.

oil? valve, as described in the immediately preceding paragraph, the operation of the float operated valve serves the added purpose of informing the operator of the manual valve as to the time at which the water level has reached the minimum and the manual valve is to be closed. With out the automatic valve disclosed above, an operator opening a manual valve must, in order to be certain that all possible water has been drained from the tank, permit the valve to stay open until stored product commences flowing out of the open valve. Where the automatic valve disclosed in this invention is used, on the other hand, that valve closes when the Water level is drawn down to its minimum, and when this occurs the amount of flow through the water drawofi line will be reduced to a mere trickle, even though the float operated valve may not afford a perfectly tight seal. The closing of the float operated valve thus prevents any appreciable quantities of stored product from entering the water draw-oil line when the Water level has been lowered to the minimum, and the reduction of flow from the drawoi'l line to a mere trickle is therefore a signal to the operator to close the manual valve. Valuable stored product is conserved and the fire hazard which normally results from permitting appreciable quantities of inflammable liquids to escape is also greatly reduced.

Various materials of construction can be used to fabricate the elements of the valve assembly employed in ttds invention. in the event that this invention is used in the storage of crude oils or distillate stocks which may be corrosive, stainless steel, Monel metal, or other corrosion resistant materials can be used. The construction of the float element will depend upon the type of valve assembly. Solid or hollow floats can be employed as well as hollow shapes having the internal cavity filled with a second material. The float configuration can be sphe roidal, as shown, or any other convenient for l The selected buoyancy of the float will depend upon the design of the sump valve used in accordance with this invention. In most designs using spherical floats, the float, when in equilibrium at the interface, will have its center of gravity coincident with the interface. it may be necessary, however, in other designs to employ floats which barely float in the water phase or even floa completely on the top or" the interface. In all instances, however, the relationship of the valve closure and the rim of the sump with the valve inlet is such that the valve closes when the oil-water interface falls below the rim of the sump and remains closed by virtue of the stop mecha nism thereby preventing product withdrawal even when the interface continues to fall below the valve inlet.

Although shown for use with flat bottom storage tanks, the invention has application in other types of storage tanks having water drawotf sumps located at the lowest level in the tank.

it should be clearly understood from the foregoing disclosure that persons skilled in the art may design alternate types of float operated valves in accordance with this invention to accomplish the same purpose in essentially the same way, and no undue limitations should be implied in the claim which follows on account of the specific disclosures made in this specification.

What is claimed is:

in a liquid hydrocarbon storage tank having a floor, a system for drawing oil accumulations of water, said system comprising:

a sump at the bottom of said tank, the bottom of said sump being below said tank floor, the top of said sump being level with the tank floor and in communication with the tank, and said sump having a relatively insubstantial volume compared to the volume of the tank;

a draw-ofl pipe extending from said sump through the tank to an outlet outside the tank;

said pipe having an inlet located in said sump below the tank floor and including a substantially horizontal 5 run portion extending from the sump to the pipe outlet;

a plurality of spaced, clowniwardly depending baffle plates located within the upper portion of said horizontal run portion and terminating substantially 5 above the bottom of said horizontal run portion to form upper chambers for the entrapment of gases within said horizontal run portion;

valve means at the pipe outlet;

float closure means for said inlet; 10

said closure means comprising a float having a specific gravity less than that of water and greater than that of the hydrocarbon stored in said tank, whereby said float is in equilibrium at the interface between the water and the hydrocarbon and rises and falls as the 15 interface rises and falls;

and means mounting said float for movement from a lower inlet-closing position, in which the interface is at the tank floor level and at least a portion of the float extends above the tank floor level into said tank, to an upper inlet-opening position in response to a rise of the interface above the level of the tank floor.

References Cited in the file of this patent UNITED STATES PATENTS 787,367 French Apr. 18, 1905 1,147,702 Bower July '27, 1915 1,201,558 Cobb Oct. 17, 1916 1,626,245 Little et a1. Apr. 26, 1927 2,413,430 Boone Dec. 31, 1946 2,597,475 Gr-ise May 2 1952 2,845,947 Griswold Aug. 5, 1958

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