US3024617A - Reduction of tank corrosion - Google Patents

Description

March 13, 1962 w. 1.. MILLER REDUCTION OF TANK CORROSION Filed June 16, 1959 IN V EN TOR. M44 727? L Mauve arena thee 3,fi24,6l7 Patented Mar. 13, 1962 3,024,617 REDUCTION OF TANK CORROSION Walter L. Miller, 160 Hendrickson Ave, Lynbrook, FLY. Filed June 16, 1959, Ser. No. 820,831 17 Claims. (Ci. 6254) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to the reduction in the corrosion of walls of large tanks that are used to store or convey vaporizable cargo liquids which are immiscible with water.

Various procedures have been used heretofore to reduce corrosion of the walls of large tanks, particularly in tanker ships, by drying air or gas and then circulating it through the air spaces of the cargo tanks. This requires means for cleaning and drying the air or gas, and elaborate circulating equipment. Very large volumes of air or gas must be circulated in order to remove moisture from initially wet walls, bottoms and seepage. Another attempt to solve this problem was to place drying agents in closed spaces, but such agents must, at frequent intervals, either be replaced or regenerated. Drying agents are impractical in large spaces which must be used in carrying liquid cargos.

Objects of the invention are to provide an improved means and method for reducing the corrosion of walls of large tanks, which require no moving parts or equipment except to compress, cool and circulate the cooling medium or refrigerant, which employs small diameter piping, which causes no contamination of cargo and no loss of volatile portions of the cargo liquid, which employs no chemical desiccants, which has a minimum of loss of volatiles through conventional breather valves on tanks, which reduces corrosion of tank walls beyond that caused by a reduction in humidity by virtue of lowered tank temperatures, which is independent of the nature of the air or gas in the tank and reduces the corrosion through lowered humidity and temperature, and which is simple, and practical, uses compact and relatively inexpensive apparatus, and requires little servicing attention.

Other objects and advantages will be apparent from the following description of one example of the invention and the novel features will be particularly pointed out hereinafter in connection with the appended claims.

In the accompanying schematic drawing a sectional elevation of the upper part of a cargo tank is illustrated, having applied thereto apparatus for reducing the corrosion of the tank walls in accordance with this invention.

In the illustrated embodiment of apparatus useful for reducing corrosion in accordance with this invention, the cargo tank includes side walls 1 and a top wall 2. This tank, in this example, is used to store and transport a liquid lighter than water, such as a petroleum product and such tanks are seldom, if ever fully filled with the cargo liquid, and have an air or vapor space at the top to allow for expansion of the liquid during temperature changes in the cargo liquid. In this air space at the top of each such cargo tank, and above the maximum expected liquid level therein, a heat exchange element or unit 3 is disposed and mounted in any suitable manner. A refrigeration unit 4 operated by a motor 5 or other source of power is disposed exteriorly of the tank and connected by pipes 6 to the ends of the heat exchange unit 3 so as to pass through the unit 3 a suitable cooling medium. One of the pipes 6 may have a motor operated pump or circulator 7 therein to circulate the cooling medium through element 3. It is not necessary that this cooling medium be cooled below the freezing temperature of water, but it should be cooled by the unit 4 to a temperature which will cause the heat exchange element 3 to cool the adjacent air or ambient vapors to about 50 F. or lower. Frosting of the element 3 may be prevented by using large cooling surfaces of element 3 at temperatures above freezing temperatures, or by periodic defrosting of the element 3 whenever it is necessary to use temperatures below freezin for eflicient cooling.

A tray 8 is disposed in the tank 1 beneath the heat exchange element 3 to catch ambient vapors condensed by the element 3 and dropping therefrom. The element 3 is exposed for contact by ambient vapors in the upper part of the tank, and the condensation of some of the ambient vapors will set up convection currents that cause more ambient vapors to come in contact with the element 3 and be condensed thereby. A sump 0r casing 9 is disposed in the tank and supported in the upper air space thereof in any suitable manner such as by suspending it from the top wall 2 of the tank.

A pipe 10 connects the tray 8 to the sump 9' and drains into the sump by gravity the condensation from element 3 that is collected in tray 8. The sump has an overflow passage or pipe 11 in its side wall intermediate of its top and bottom edges, and no higher than the opening of pipe 10 at the tray. The condensed vapors of water and of the cargo liquid stored in the tank, when deposited in the sump will stratify into layers, according to the specific gravities of the water and stored cargo liquid. Th liquid of higher specific gravity will settle to the bottom, and the lighter liquid will float on the lower layer of liquid. In the case of petroleum products the products will float as a layer on the water layer.

In the drawing, a possible upper level of a layer of the water in the sump is shown by dot and dash line A, and a possible upper level of a layer of gasoline floating on the water layer in the sump is shown by the dot and dash line B. When the level B rises to or beyond the overflow 11, the gasoline or condensed cargo liquid forming the upper layer will pass out of the sump through the overflow 11 and be returned to the body of cargo liquid in the tank.

Before the level A of water reaches the overflow 11, it should be withdrawn and isolated as necessary to prevent level A from reaching the overflow. For this purpose, a pipe 12 may depend into the sump to near the bottom thereof, and at its upper end have means to withdraw the water from the sump. For example a pump 13, operated by a motor 14 may be disposed outside of tank 1, such as above the tank top 2, and connected at its intake side to the upper end of pipe 12, The motor is operated, as needed, through operation of switch 15, to keep the water level below the overflow.

The sump is preferably placed within the top zone of the tank interior, but it can, if desired, be placed at the bottom of or even outside of the tank. The sump may advantageously have an aperture 9a near its top. This will permit any cargo liquid which enters the sump through condensation or splashing to be returned to the cargo space by overflow 11. In order that one may know when water level A closely approaches the overflow, making advisable the removal of some of the water from the sump, a tube 16 extends from near the bottom of the sump upwardly through the top 2 of the tank. Within this tube 16 is confined a float 17 which floats in water but sinks in the lighter cargo liquid such as gasoline. This float has a rod-like stem 18 extending upwardly in the tube 16 and above its top, which stem by its position or extent of projection above the upper end of tube 16, indicates the level of water in the sump.

It is important that the element 3 and tray 8 be located within and at the top of the vapor space inside the tank and above the maximum expected liquid level therein. This makes it possible to have a continuous condensing action on the mixed vapors of water and the cargo liquid, accompanied by separation in the sump of the condensed vapors of the water and the cargo liquid with isolation and removal of the condensed water. This action is independent of the vapor pressure within the vapor space of the tank, and there is a continuous cycling of the ambient vapors within the vapor space past and under the condensing influence of the cooling element. The cooled dry air and vapor at the element 3 is heavier than the warmer humid air and vapor at the liquid surface, and this causes a continuous movement downwardly of the air and vapor past the element 3, during which the water and cargo liquid vapors are condensed and other air and vapor replaces the downwardly moving air and vapor. The convection currents thus established are fortified, when the ship having the cargo tanks, is moving, through movement of the cargo liquid in the tank.

While this method and apparatus are particularly useful in tanks carrying a vaporizable cargo liquid, they are also very useful in tanks carrying non-vaporizable cargo liquids, in which latter case the coil 3 will condense water vapors in the air that is present above the stored liquid and thus reduce possible corrosion of the tank walls that might be caused by the presence of water vapors in the tank above the liquid cargo. While it is advantageous to have the sump 9 within the upper part of the tank, it can be placed elsewhere in the tank or even outside of it. The sump is also useful in separating the condensed water vapors from any of the cargo liquid whether condensed vapors of the cargo liquid or just spray from the cargo liquid, that may get into the tray 8 along with condensed water and other vapors.

It will be understood that various changes in the details, materials and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

I claim:

1. Apparatus for reducing corrosion in a closed ships cargo storage tank under atmospheric pressure and containing a stored liquid immiscible with, and of different specific gravity from, water, which comprises the combination with said tank of a heat exchange element supported in the full open space in the main body of said tank above the maximum expected liquid level therein, means connected to said element and supplying thereto a cooling medium and forming therewith a complete refrigerating unit independent of and separate from said tank and said storage liquid, a collector member in said tank disposed beneath said element, also above said maximum expected liquid level, and having an upwardly open face at least coextensive in area with the overall horizontal area occupied by said element, for collecting condensations by said element of ambient vapors in the atmosphere above said maximum level, said element being unenclosed and fully exposed for continuous contact therewith of said ambient vapors, a sump disposed with a portion below the level of said collector member, means for draining condensed vapors and any spray of the stored liquid created by motion of the tank and collected by said member into said sump where they may stratify and separate the condensed water from said tored liquid, means for returning the condensed said stored liquid from said sump to said stored liquid in said tank, and means for removing excess water from said sump.

2. Apparatus for resisting corrosion in a closed tank containing a vaporizable liquid lighter than and immiscible with Water, which comprises the combination with said tank of a heat exchange element supported in the full open space in the main body of said tank above the maximum expected level therein of said liquid, means outside of said tank connected to said element and sup- ,4 plying thereto a cooling medium and forming therewith a complete refrigerating unit independent of and separate from said tank and said storage liquid, a collector tray in said tank and disposed beneath said element and also above said maximum expected level, and opening upwardly beneath all of the overall horizontal area occupied by said element for receiving condensations by said element of ambient vapors in the space of said tank above said maximum level, said element being unenclosed and fully exposed for continuous contact therewith of said ambient vapors, a sump, means for conducting into said sump any condensed vapors collecting in said tray, said sump having an outlet for removal of said vaporizable liquid which separates by stratification from the water in said sump, and means for removing condensed water vapors from the lower part of said sump.

3. Apparatus for application to a closed tank containing a liquid immiscible with water, for reducing corrosion of interior tank walls by ambient water vapor in the tank, which comprises a heat exchange element to be supported in the interior of the full open space in the main body of said tank above the maximum expected level of said liquid therein and fully exposed for contact therewith continuously by ambient vapors in the tank to condense them, means forming with said element a complete refrigeration system independent of and separate from said tank and its contents, and delivering a cooling medium to said element, means having a fully open upper face for collecting condensations by said element of ambient vapors in the space of said tank above said maximum liquid level a sump disposed to receive said condensations and in which the condensations may stratify into separate layers of water and said liquid, said sump having an outlet through which any of said stored liquid therein may be removed and returned back into said tank, and means connected to the interior of said sump for removing therefrom condensed waters vapors from the layer of water as necessary.

4. Apparatus for reducing corrosion in a relatively large closed storage tank containing liquids lighter than and immisicible with water, which comprises the combination with such tank of a heat interchange unit supported in the top space in the main body of said tank above the maximum expected liquid level therein, means outside of said tank for supplying a cooling medium continuously to said unit and forming therewith a complete refrigerating unit independent of and separate from said tank and said storage liquid, a tray with an open upper face disposed within said tank beneath said unit, also disposed above the maximum expected liquid level in the tank, for receiving and collecting vapors condensed by said unit, said unit being unenclosed and fully exposed for continuous, direct contact therewith of ambient vapors in the top portion of said tank, a sump having a chamber separate from said tank, means connecting said tray with said sump for conducting condensed vapors from said tray to said sump, means connected to the lower part of said sump for removing water therefrom, means for discharging into said tank liquids from a selected zone of said sump, whereby when the Water and condensed vapors from said stored liquid and splash from the liquid separate into separate layers, the water may be removed before it reaches said discharging means and the other condensed vapors and liquid can return to the unvaporized liquid in said tank.

5. The apparatus according to claim 1, wherein said means for supplying said cooling medium to said exchange element is disposed outside of the liquid storage space of said tank.

6. The apparatus according to claim 1, wherein said sump is disposed at a level above said maximum expected level, and has a gravity drain from the part thereof occupied by the stratified condensed vapors of the stored liquid into said tank below said sump.

7. The apparatus according to claim 2, wherein said sump is located within said tank and above said maximum level.

8. The apparatus according to claim 1, and means connected to said sump and operable to indicate the level of water in said sump.

9. The apparatus according to claim 3, and means connected to said sump and operable to indicate exteriorly of the tank and sump the position of the stratified division between the water and said liquid in the sump.

10. Apparatus for reducing corrosion in a closed tank containing a stored liquid which i immiscible with water and incompletely filling said tank which comprises the combination with such tank of means disposed in the open space in the upper part of the main body of said tank and unenclosed and fully exposed for continuous contact with all ambient vapors in the upper part of the tank, for condensing out the condensible part of ambient vapors from the air in the space between the maximum liquid level in said tank and the top of the tank, means having an upwardly opening collector also in said space in the upper part of said tank and immediately below said condensing means disposed to receive the condensed vapors, means connected to said receiving means and operable to separate from the col lected condensation the condensed water, means by which the separated water may be removed and discarded, and means by which the balance of the condensed vapors may be returned to the tank.

11. The method of reducing corrosion in a closed liquid storage tank containing a liquid immiscible with water, and having a maximum level below the top of said tank, which comprises continuously condensing within the tank, in the space thereof above the liquid level therein, the ambient vapors in the space between said maximum liquid level and the top of said tank, continuously collecting the condensed vapors within the tank and causing them to stratify into separate layers of water and said liquid, removing said layer of said liquid and returning it to the body of said liquid in said tank, and removing said water of said water layer sufficiently to prevent its return to said body of liquid in said tank with said removed layer of said liquid.

12. The method of reducing corrosion in a closed ships cargo storage tank containing a liquid lighter than and immiscible with water, and having a maximum level below the top of said tank, which comprises continuously condensing within the tank in the space above the liquid level therein, the ambient condensible vapors in the space between said maximum liquid level and the top of said tank, causing the condensed vapors and any splash of the said liquid that may be caused by the motion of the ship, and becoming mixed with the condensed vapors to stratify into separate layers of water and said liquid, draining off and isolating the stratified layer of condensed water, and returning the layer of condensed liquid to said tank.

13. The method of reducing corrosion in a closed tank under variable atmospheric pressure containing a stored liquid immiscible with water, and having a maximum level below the top of the tank, comprising continuously condensing out within the tank in the space above the liquid level therein, the condensible part of ambient vapors from the air in the tank space between said maximum level and the top of said tank, separating out and discarding the water from said condensed vapors, and returning the balance of the condensed vapors to the tank interior.

14. Apparatus for reducing corrosion in closed, ships cargo tank under atmospheric pressure that is used to store a liquid that is immiscible with and of different specific gravity from water, and vapon'zes to some extent under atmospheric pressure, which comprises the combination with said tank of a heat exchange element supported in the top portion of the main body of said tank above the maximum expected level of stored liquid therein and exposed to continuous direct contact with ambient vapors in said top portion for heat exchange therewith, means for supplying a cooling fluid located exteriorly of said tank and connected to said element for circulating said cooling fluid through said element and forming with the latter a complete refrigeration unit independent of and separate from said tank and said stored liquid, an upwardly opening tray disposed in said tank immediately below said element and also above the said maximum expected level of stored liquid in said tank, and of a size to collect substantially all of the ambient air and vapors condensed by said element and any spray and splash therein of the stored liquid due to motion of the tank, -a sump connected to said tray to receive from the tray any liquid collecting in said tray and in which sump the condensed vapors of said stored liquid and water vapor may stratify and separate into superposed layers, a level indicator connected to said sump for indicating the upper level of one of the said stratified layers, means connected to said sump by which a desired part of the layer of condensed vapors of the stored liquid in said sump may be progressively removed from the sump and returned to said tank, and means also connected to said sump for removing to the exterior of said tank and discarding any part of the condensed water layer.

15. The apparatus according to claim 14, wherein said sump is located in the upper part of said tank also above said maximum expected level of stored liquid, and the means connected to said sump enabling removal of condensed vapors of the stored liquid includes a gravity drain into said tank for such condensed vapors of the stored liquid.

16. The apparatus according to claim 14, wherein said heat exchange element has a closed passage therethrough for the passage of a cooling fluid therethrough, and an outer exposed surface in the space of said tank above said maximum expected level of stored liquid, whereby the condensation of ambient vapors in the tank is continuous.

17. The method of reducing corrosion in a storage tank for volatile liquids that are immiscible with water and which has a vapor space in the upper part thereof above the maximum expected liquid level therein, which comprises continuously exposing all ambient vapors in said space while confined in said space to an exposed and uncovered cooled surface at a temperature that condenses from such ambient vapors the vapors of said stored liquid and water vapors, continuously collecting all of said condensed vapors in said space, and separating the water condensation from the condensation of the stored liquid, continuously returning the condensation of the stored liquid to said tank, and discarding the water condensation.

References Cited in the file of this patent UNITED STATES PATENTS 2,059,942 Gibson Nov. 3, 1936 2,321,964 Zieber June 15, 1943 2,344,765 Dana et al Mar. 21, 1944 2,379,215 Brinkmann June 26, 1945 2,449,688 Brinkoeter Sept. 21, 1948 2,577,598 Zwickl Dec. 4, 1951

Images