Field of Search:
73/29R,34C,1R 141/7,65,95,98,84,1 114/74 222/192 166/102,105,250 137/269,271
Claims:
What is claimed is
1. A liquid cargo storage tank unit having a liquid level gauging system located therein comprising a housing mounted in said tank between near the bottom and extending through the top of said tank; a removable cover for said housing; removable level gauging means mounted within said housing; first valve means at the bottom of said housing for draining liquid from said housing; second valve means at the top of said housing for internally venting said housing; and conduit means operably connected with said housing forming a passageway for the introduction and exhaust of inert gas into and from said housing respectively; wherein the improvement comprises said unit being convertible between said liquid level gauging system and a cargo discharge system in the event of the loss of normal cargo discharge facilities where upon when said cargo discharge system is operable there is provided in lieu of said level gauging means a pump means removably mounted in said housing near the bottom thereof.
2. The tank of claim 1 including control means located external of said tank for operating said first and second valve means.
3. The system of claim 1 including means for permitting removal of a sample to check the inert condition of said housing.
4. A method for converting a liquid level gauging system in a cargo tank to a cargo discharge system wherein a housing mounted in said tank and having a liquid level gauging device comprising the steps of introducing through a valve conduit an inert gas under pressure into said housing, exhausting through a valved conduit the inert gas to the atmosphere, determining the inert condition of the housing and removing the gauging device from the housing and inserting pump means into said housing for removal of cargo from said tank.
5. The method of claim 4 wherein the liquid within the housing is first removed prior to introduction of the inert gas into the housing.
Description:
BACKGROUND OF THE INVENTION
The present invention relates to tankers designed for carrying liquid cargo, such as LPG and LNG, and more particularly relates to a novel tank gauging system which permits repair of such system without the need to remove the cargo-carrying tank in which it is mounted from service and simultaneously may serve as a housing for a pump which can be used to pump out the tank in the event of loss of the cargo pumps.
Heretofore in order to repair a tank gauging system it has been necessary to remove the entire tank containing the system from service. In the case of LPG and LNG cargoes the inerting and aeration that is required in order to remove the tank from service is a very costly and time-consuming procedure. In the event of loss of the cargo pumps which are normally employed to empty a tank, the prior art provides an eductor system which functions to discharge the tank. Typical of the prior art which may be considered pertinent to the present invention are the U.S. Pat. Nos. 2,990,482, Kenny; 3,208,281, Kalmus et al.; and 3,222,920, Kalmus et al. Each of these prior art patents discloses a liquid level gauge of the ultrasonic type which is enclosed in a tube or protective housing. However, none of the prior art provides a tank gauging system which allows for repair to the gauging system without the necessity for removal of the tank from service and simultaneously serving as a housing for installation of a temporary cargo discharge pump if the occasion requires.
SUMMARY OF THE INVENTION
The present invention relates to a novel tank gauging and temporary pump housing which is mounted in a cargo-carrying tank of a ship and which functions as a stillwell. While the tube is intended primarily as a housing for a liquid level gauge, if the occasion arises, it can be utilized for installation of a temporary pump in order to discharge cargo from the tank in the event that the cargo pumps fail. At the bottom of the tube there is provided a drain valve and spaced from the top end of the tube there is provided a laterally extended venting valve. The housing extends through and beyond the top of the cargo-carrying tank and is provided with a removable cover. In operation the tubular housing can be evacuated by opening the bottom drain valve and then introducing an inert gas, such as nitrogen under pressure, into the housing with the top venting valve being closed. Once this is done, the bottom drain valve is closed and the housing is inerted with nitrogen which is exhausted to the atmosphere through the venting valve. Means are provided for checking the inert condition of the housing, after which the cover may be removed and the gauging device removed for repair or inspection. In the event that the cargo pumps fail, the foregoing procedure is followed and a temporary pump may be installed in the housing in order to pump the cargo from the tank. Thus, it is seen that the present invention provides a very desirable and practical dual-purpose system, which eliminates the costly and time-consuming prior art procedures while obtaining the same results.
Accordingly, it is a primary object of the present invention to provide a novel and improved tank gauging system for the cargo-carrying tank of a ship.
Another object of this invention is to provide a novel and improved tank gauging system which allows for repairs thereto without the necessity for removing the tank in which it is mounted from service.
A further object of this invention is to provide a novel and improved tank gauging system which facilitates repair to the system without having to remove the tank from service and also serves for installation of a pump therein in the event of loss of the cargo discharge pumps.
Still yet a further object of the present invention is to provide a novel method of inerting a tank gauging system for purposes of repair or inspection of the gauging device contained therein.
Having in mind the above and other objects and advantages that will be apparent from an understanding of this disclosure, the present invention comprises the combinations and arrangements as illustrated in the presently preferred embodiment of this invention, which is hereinafter set forth in such detail as to enable those skilled in the art readily to understand the function, operation, construction and advantages of it when read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a vertical cross-section of a cargo-carrying tank in a ship having mounted therein a tank gauging system constructed and arranged in accordance with the present invention;
FIG. 2 illustrates an enlarged cross-sectional view of the tank gauging system shown in FIG. 1; and
FIG. 3 illustrates a pump temporarily installed in the housing with the level gauge removed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Having reference to the drawings wherein like parts are designated by the same reference numerals throughout the several views, the present invention is illustrated in FIG. 1 in connection with a conventional prismatic cargo-carrying tank 10 which is mounted in the cargo hold of a ship such as an LPG or LNG tanker. Such a tanker may be of the conventional type and typically may include a double hull generally designated 11, which comprises a pair of spaced walls 12, 13. The space between the walls 12 and 13 defines a ballast tank 14. The tank is mounted on a pair of conventional tank supports, such as the schematically illustrated key/keyway systems designated 15. The sides 16 of the tank 10 are suitably spaced from the inner hull wall 13 to provide a suitable access space 17 which may be employed for inspection of the cargo tank or inner hull for leaks and the like. It should be understood that while the invention is disclosed in connection with one type of tank, it may readily be employed in any type of tank, whether it be mounted in a ship or on land, as long as there exists the need for a gauging system. The novel system constructed and arranged according to this invention includes a tank gauging tube or housing 18 extending vertically in between the top and bottom 9 of the tank 10 and removably mounted therein by means of suitable sliding supports 19. These supports facilitate removal of the entire tube if necessary, while also functioning to hold the tube in place within the tank. The tube extends through the top of the tank and is provided with a removable cover 20. Within the gauging tube 18 there is shown in dotted lines a gauging device 21, which may be of the ultrasonic type or any other suitable variety. As shown in FIG. 1 the gauging device is sectioned to facilitate its removal and repair in the event of any damage thereto. At the bottom of the gauging tube 18 there is provided a laterally extending drain valve schematically shown as 22. Spaced from the upper end of the tube 18 within the cargo tank is venting valve 23, which also extends laterally from the housing. The valves 22 and 23 are connected through conduits to the interior of tube 18.
In operation tube 18 can be evacuated, that is the liquid normally used to determine the level of cargo in the tank may be forced out by inerting the tube whereupon the gauging device can be removed and repaired while the tank remains in service. The liquid is forced out of the tube by first closing the top internal venting valve 23. This is accomplished by means of an external control mechanism schematically illustrated at 24. Then nitrogen can be admitted into the tube by means of an inlet conduit 25 (see FIG. 2) located within the gauging tube 18. After the liquid is forced out through the open bottom drain valve 22, which is controlled by means of an externally accessible valve control mechanism 26, the drain valve is closed and the tube may be inerted with nitrogen. The nitrogen is vented to the atmosphere through the venting tube 27 also contained within the gauging tube. The inert condition of the tube may be checked by means of the sample upper and bottom taps 28 and 29. When inerting is complete, the tube cover 20 may be removed and the gauging device 21 taken out for repair of inspection. In the case of using the ultrasonic gauging device shown in the preferred embodiment, the stillwell sections may be dismantled and removed from the tube.
If the cargo pumps normally employed for discharging cargo from the tank are ineffective for that purpose, the gauging device 21 described above may be removed from the tube and a conventional pump generally designated 30 (see FIG. 3) can be installed in the gauging tube 18 for pumping out the tank. The pump 30 is connected through pipe sections 31 or flexible hose to a suitable receptacle or piping (not shown) located on board the ship. The use of the gauging tube 18 for installation of a pump for discharge of the tank cargo eliminates the need for the eductor system normally employed for discharging the tank cargo in the case of loss of the cargo pumps. The foregoing construction and arrangement provides for improved reliability of the gauging system and also reduces the costs of the backup tank discharge systems which are now necessary.
It will be appreciated from the foregoing description that there has been provided a novel and improved tank gauging system which serves the dual function of determining the level of liquid cargo in a tank and providing a backup tank discharge system. It should be understood, however, that the construction and arrangement herein illustrated and described are intended to be representative only of a preferred embodiment and that certain changes readily may be made therein without departing from the clear teachings and true scope of the present invention. Accordingly, reference should be made to the following appended claims in determining the full scope of this invention.