US3527384A - Equipment and method for unloading liquids - Google Patents

Description

P 1970 susueu KOYAMA ETAL 3,527,384

EQUIPMENT AND METHOD FOR UNLOADING LIQUIDS Filed May 10, 1968 5 I g l J l I6 t1 T 1 lo I T 8 INVENTORS 5 USUGU Kolnma I TRKEJI KY ATTORNEY$ United States Patent 3,527,384 EQUIPMENT AND METHOD FOR UN LOADING LIQUIDS Susugu Koyama and Takeji Kyogoku, Kobe-shi, Japan, assignors to Mitsubishi Jukogyo Kabushiki Kaisha, Tokyo, Japan Filed May 10, 1968, Ser. No. 728,277 Claims priority, application Japan, May 24, 1967, 42/ 32,934 Int. Cl. B67d /52 US. Cl. 222-1 4 Claims ABSTRACT OF THE DISCLOSURE Equipment for unloading liquids, such as oil from oil tankers, is comprised of an auxiliary tank disposed near the bottom of the tank to be unloaded. A piping system containing a jet pump connects the auxiliary tank and the tank to be unloaded. Liquid flows from the tank into the auxiliary tank and is withdrawn by means of a main pump and discharged to another vessel or point of use. The auxiliary tank is provided with control means for regulating the level of liquid within it which in turn regulates a control valve in the line discharging liquid from the main pump. Liquid can be bypassed from between the main pump and the discharge control valve and is used as the driving fluid for the jet pump. The jet pump is used for completely unloading the liquid from the tank.

SUMMARY OF THE INVENTION The present invention is directed to a method of and equipment for unloading liquid from a tank or a similar vessel and, more particularly, it is directed to an arrange ment for completely unloading the liquid from the tank.

In unloading oil from tankers and in similar liquid unloading operations, in general, the unloading work must be completed in as short a space of time as possible. To accomplish this result centrifugal pumps of large capacity have been used in the past, however, as the oil drops below a certain level the pump can no longer operate because of cavitation within the pump and also because air or gas is drawn into the outlet line from the tank. For completely unloading the oil as the level drops below a certain point reciprocating pumps and the like are used in addition to the main centrifugal pumps. However, the use of separate pumping systems for unloading the tank is uneconomical because of the duplication of equipment and piping systems and also because of the extended time period required for unloading the oil.

To overcome the difliculties experienced in the past, within recent times an auxiliary tank has been provided between the main centrifugal pump and the tank to be unloaded to provide a chamber for the separation of any gas from the liquid. However, the use of such an auxiliary tank has had the following disadvantages:

(1) It requires a vacuum pump or similar equipment for discharging the gas because the separation within the auxiliary tank is accomplished by reducing the pressure within the tank,

(2) The level to which the tank can be unloaded is not sufficiently low because of the restriction imposed on the arrangement by the capacity of the vacuum pump, and

(3) The liquid level in the auxiliary tank must be regulated to prevent any flow of oil into the vacuum pump.

Accordingly, such use of an auxiliary tank is disadvantageous because of its manner of performance and because it is uneconomical. *It has been suggested to avoid the defect mentioned in 2 above by increasing the size ice of the auxiliary tank to include control means for reducing the speed with which the level of the liquid drops in the tank, however, while increasing the size of the auxiliary tank assists in overcoming the disadvantage set forth in 2, it does not aid in overcoming the disadvan tages indicated in 1 and 3.

Accordingly, it is the primary object of the invention to provide arn arrangement of equipment for effectively and economically completely unloading liquid from a tank.

Another object of the invention is to combine the use of a main centrifugal pump which alone performs the majority of the unloading operation with a jet pump which assists in completing the unloading operation when the liquid level drops to the lower part of the tank. In addition, the liquid circulated by the main pump is employed to drive the jet pump.

Therefore, the present invention is intended to overcome the various disadvantages which have been experienced in the past and to accord a method of and equipment for completely unloading liquid from a tank in a fast and efiicient operation.

Where the present invention is employed in unloading oil from a tanker a piping system including an auxiliary tank for effecting liquid-gas separation is located in the bottom of the ship roughly at the level of the bottom of the tanks to be unloaded. A jet pump is positioned in the piping system between the auxiliary tank and the tank to be unloaded. When in use the jet pump is driven by a portion of the liquid discharged from a main pump and a by-pass line is provided from the discharge line from the pump to the jet pump. The by-pass line contains a valve for controlling flow to the jet pump. A control valve is disposed in the discharge line from the main pump and is operated by control means which regulate the level of the oil within the auxiliary tank. When the level within the tank being unloaded reaches a certain point the level within the auxiliary tank starts to drop and the control valve in the discharge line from the pump is regulated to provide a by-pass flow of the liquid to the jet pump, which then commences operation for assisting in completing the unloading of the oil from the tank. Additionally, an air discharge pipe is connected to the upper end of the auxiliary tank and extends upwardly opening to the atmosphere or into the upper end of the oil tank being unloaded.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in 'which there is illustrated and described a preferred embodiment of the invention.

DESCRIPTION OF THE DRAWING The drawing illustrates a schematic arrangement of the equipment embodying the present invention in which the view is taken along the center line of an oil tanker.

DETAILED DESCRIPTION OF THE INVENTION In the drawing an oil tanker is schematically illustrated containing a number of oil tanks 1 extending between an upper deck 2 and the bottom 4 of the ship with partition walls 3 separating the tanks. Within a pump room 5 alongside the tanks 1 a main pipe system .6 extends between the oil tanks to be unloaded and an auxiliary tank 9 wherein any gas mixed with the oil is separated from it. A branch pipe 8 extends from the main pipe system 6 downwardly toward the bottom of the oil tank 1 and has a bell-mouthed inlet 7 located just above the bottom 4 of the ship through which the oil passes into the piping system. The auxiliary tank 9 is connected to the main oil pump and a discharge line 12 extends from the pump 10 to another receiving vessel or point of use of the oil, not shown. Extending upwardly from the top of the auxiliary tank 9 is an air discharge pipe 11, the upper end of which is arranged to discharge into the atmosphere.

A control valve 13 is located in the discharge line 12 from the pump 10. Positioned between the pump 10 and the control valve 13 is the inlet to a by-pass line 14 which extends to a jet pump 16, of a known type, located in the main pipe system 6 between the branch pipe 8 and the auxiliary tank 9. In the by-pass line .14, a valve member is arranged to control flow to the jet pump 16.

Control means 17 are mounted on the auxiliary tank 9 to detect the level of oil within the tank and to adjust the control valve 13 for regulating the amount of oil passing through the discharge line 12, whereby the oil level within the auxiliary tank 9 can be maintained at a selected level.

DESCRIPTION OF THE OPERATION OF THE INVENTION At the outset only the main pump 10 is employed in unloading the oil from the tanks 1, because the oil level within the auxiliary tank 9 is maintained at a suflicient level without utilizing the jet pump 16. The main pump 10 withdraws the oil from the auxiliary tank 9 and discharges it to a point of use or storage through the discharge line 12. During this part of the unloading operation the valve 15 in the by-pass line 14 is closed and the control valve 13 in the discharge line 12 is kept open. Similarly during this period the control means 17 are maintained in the off position and this may be accomplished by a manually operated switch, not shown. While this part of the unloading operation proceeds the jet pump merely acts as a part of the main pipe system 6 supplying the oil from the tanks 1 into the auxiliary tank 9.

As the first part of the unloading operation progresses the oil level within the auxiliary tank 9 is maintained at its predetermined height and the main pump 10 continues to work uninterruptedly because any gas or air in the auxiliary tank is discharged through the line 11. When the level within the auxiliary tank starts to drop below the predetermined level the control means 17 is activated and the control valve 13 regulates the flow through the discharge line 12 so that a portion of the flow from the pump 10 passes into the by-pass line .14 and with the bypass valve member 15 opened, enters and drives the jet pump 16 for assisting in pumping out the bottom of the oil tanks 1.

As soon as the unloading operations in the oil tank is completed air is drawn through the bell-mouthed inlet 7, however, because the control valve 13 is closed at this point by the action of the control means 17, oil continues to circulate through the by-pass line 14 from the main pump 10 to the jet pump 16 and then into the auxiliary tank without causing any discontinuance in the operation of the main pump. Additionally, under ordinary circumstances the pressure in the upper part of the auxiliary tank 9 is equal to the pressure in the oil tank 1 (atmospheric pressure), and when no air or other gas is flowing into the bell-mouthed inlet 7 any gas separated within the auxiliary tank passes outwardly through the discharge pipe 11. However, when gas or air enters the bell-mouthed inlet 7 the control valve .13 operates automatically to increase the pressure to the extent of the pressure loss experienced in the discharge pipe due to the action of the jet pump 16.

Though the discharge pipe .11, as shown in the drawing, opens to the atmosphere, it is more advantageous to locate the outlet from the discharge pipe in the upper end of the oil tank 1 since no problems will develop if the oil flows into the discharge pipe caused by any fluctuation in the oil level within the auxiliary tank.

In the past equipment has been proposed which appears, under superficial observation, to be analogous to the equipment of the present invention just described. However, in the previously proposed equipment the main pump and the auxiliary tank were positioned on the deck of the tanker instead of the bottom of the ship. Moreover, the level control of the auxiliary tank in the prior equipment was accomplished by means of a control valve for the fluid driving the jet pump instead of the arrangement in the present invention. In the present arrangement the control valve for the fluid driving the jet pump is located in a by-pass line which extends from the discharge line from the main pump. While the previous equipment obviates the requirement for a complicated valve arrangement and an extended piping system by positioning the main pump and the auxiliary tank on the deck of a vessel it is incapable of performing in the manner of the present invention wherein the complete removal or stripping of the oil from within the tanks is accomplished quickly, simply and safely in a shortened period of time. In the previously known equipment the continuous operation of the jet pump is required for unloading and conveying the oil from its tank to the auxiliary tank on the deck. The jet pump must be utilized because during unloading operations the height between the bottom of the tank and the deck is too great and would cause cavitation if the main pump was employed by itself.

When the jet pump is utilized the flow of oil in the unloading operation is decreased greatly in comparison to the amount which is removed when only the main pump is used. Further, in the previously known arrangement, when the level in the auxiliary tank Was maintained by regulating the control valve in the line supplying the driving fluid to the jet pump, the quantity of oil flowing from the discharge pipe could not be increased. Accordingly, in that arrangement it is impossible to maintain the level of the oil in the auxiliary tank in the event it drops below the predetermined level or drops to zero because the inflow to the auxiliary tank becomes smaller than the outflow even though the control valve is opened to its maximum extent. As a result of such a drop in the level, the main pump draws air and it cannot continue to operate. Therefore, in the previous equipment it can only operate when the level of the oil in the auxiliary tank can be maintained by the jet pump. It will be apparent from this explanation that stripping operations, that is, completely unloading all of the oil from the tank, cannot be achieved with the previously known equipment. On the contrary, however, with the present invention, it is possible to achieve the stripping operation in a quick, simple and safe manner and at the same time to shorten the time required to complete the unloading operations.

In view of the foregoing, it can be appreciated that while surface appearances of the equipment of the present invention and that previously proposed may appear to be similar, the previous equipment is completely incapable of operating in the manner of the present invention.

As set .forth above, when the jet pump is being used the flow of oil being unloaded is greatly reduced as compared to that when only the main pump is operated. However, if the main pump is positioned on the deck of the tanker then it is necessary to use the jet pump at all times which is contrary to the manner of operation by the present invention. Accordingly, in the present invention the main pump is provided in the bottom of the ship and it is arranged to continue to operate for as long as possible during the unloading operations before the jet pump is placed in operation.

Since the efliciency of the jet pump is inferior to that of the main pump, the longer the jet pump is used, the more will the efliciency of the overall unloading equipment decrease. Accordingly, though the jet pump is indispensable for completing the stripping operations within the individual tanks in the oil tanker, it is preferable to limit the extent to which it is required. If the auxiliary tank is positioned on the deck of the tanker the discharge pressure for the jet pump is increased and the operating load on it is increased. On the contrary if the auxiliary tank is positioned in the bottom of the tanker the discharge pressure on the jet pump is maintained at a low value and similarly its operating load is kept at a low value. Therefore, the efliciency of the overall equipment is reduced by only a small amount when the jet pump is operated.

In the present invention, by means of the control valve in the discharge line from the main pump, the oil is circulated continuously through the main pump, the jet pump and the auxiliary tank, and though a considerable amount of air is drawn through the bell-mouthed inlet into the line supplying oil to the auxiliary tank the flow of oil continues until the stripping of the tank is completed and during this period the main pump does not receive any air from the auxiliary tank. Further, as soon as the unloading operation within one tank is completed the equipment can be switched to another tank without stopping. As has been mentioned previously, though the equipment of the present invention may appear somewhat similar to that used previously, when its arrangement relative to the tank to be unloaded is considered, and its manner of operation reviewed, it will be readily apparent that a completely different and improved result is achieved in the simplicity of the operation, in its efficiency, and in the time required to unload the individual tanks.

In view of the placement of the auxiliary tank for gasliquid separation in the bottom of the oil cargo vessel and the use of the jet pump for supplying the oil to the auxiliary tank in the final stages of unloading the oil tanks the present invention has the following advantages:

(1) Since this arrangement of equipment utilizes the pumping capacity of the main pump even during the final stripping operation, a comparatively large flow of oil can be unloaded.

(2) Since the jet pump continues to operate even when air is drawn into it from the oil tank, it is possible to remove all of the remaining oil from the tank. As a result, the reciprocating pumps and suction pipes Which had been used previously for such stripping operations are no longer required and a considerable savings in equipment is eifected.

(3) Because of the compact arrangement of the main pump, the auxiliary tank, the jet pump and the various control means and valves, one assembly of this equipment in combination with a pipe line system is suflicient for unloading a number of tanks.

(4) Since the air space in the auxiliary tank can maintain a positive pressure due to the action of the jet pump it is not necessary to employ a vacuum pump for removing air or the like. Further, since the separation of any gases from the oil being unloaded is accomplished under atmospheric pressure the evaporation of the oil remains small and the quantity of gas discharged can be large.

(5) If the gas discharge pipe from the auxiliary tank is connected to one of the oil tanks and the level Within the auxiliary tank fluctuates causing the liquid to flow into the discharge pipe, this arrangement will not aifect the operation of the equipment or of the controls and there is little likelihood of other damage.

(6) Since the opening of the control valve in the discharge line from the main pump is operated by a signal generated from the control means detecting the liquid level within the auxiliary tank, during the final stage of the unloading operations there is no danger of drawing air into the main pump or of causing cavitation. This is due to the fact that in the final stages of unloading the control valve is completely closed and the oil circulates in a closed loop through the main pump, the jet pump and the auxiliary tank. When the amount of liquid being drawn into the auxiliary tank drops to zero during this period, the piping system can be switched to another tank to continue the unloading operations without any interruption in its operation. Consequently, the equipment can be operated safely while the oil is completely removed from the tanks.

(7) Since the efliciency of the jet pump is considerably less than that of the main pump if the amount of use of the jet pump is limited, the overall efficiency of the unloading equipment will be greater. Therefore, by positioning the main pump, the jet pump, and the auxiliary tank at approximately the level of the bottom of the oil tanks in the tanker, the use of the jet pump can be limited to the greatest extent possible and the eificiency of the unloading equipment maintained at a maximum. Moreover, since the jet pump is only placed in operation when the level of the tank drops to a certain point during most of the unloading operation the capacity of the main pump is maintained at a high level.

(8) The equipment in the present invention is simple in construction, it is low in manufacturing cost, it is easy to maintain, it is simple and safe in operation, and it requires little in the way of maintenance and repair. While the invention has been described with reference to an oil tanker it will be appreciated that it may be applied to unloading various types of liquids whether from a floating vessel or on land and can be used advantageously in a number of industries.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. Liquid unloading equipment for pumping liquid, such as oil and the like, in a two-stage pumping operation from tanks wherein the tanks can be filled to a considerable height and the location of the tanks requires the liquid being unloaded to be lifted for approximately the height of the tanks in the unloading operation, comprising a conduit system for removing liquid from the tank to be unloaded and for supplying the liquid to an unloading station, an auxiliary tank is arranged in said conduct system exteriorly of the tank containing the liquid to be unloaded for separating gas from the liquid to be unloaded, said auxiliary tank having an inlet thereto and an outlet therefrom spaced above and in the vicinity of the bottom of the tank to be unloaded so that at least a major portion of the liquid to be unloaded when the tank is filled can fiow by gravity feed into said auxiliary tank, said conduit system comprising a first conduit and a second conduit, and first conduit connected to be the inlet to said auxiliary tank and extending into the tank to be unloaded for conveying the liquid into said auxiliary tank and having its opposite end arranged to discharge the liquid at the unloading station; pump means for unloading the liquid from the tank in a two-stage operation in the first stage of which the liquid is pumped from said auxiliary tank into which it has flowed under gravity feed and when gravity feed is insufiicient to maintain a predetermined level in the tank the second stage is actuated for pumping the liquid from the tank into said auxiliary tank from where the liquid is pumped to an unloading station, control means for sensing the level of the liquid in said auxiliary tank for actuating and operating the second stage of the pumping operation when the level of the liquid falls below a predetermined level, said pump means comprising a main pump disposed in said second conduit for withdrawing liquid from said auxiliary tank and discharging the liquid from the opposite end of said second conduit and a normally inoperative jet pump positioned in said first conduit between said auxiliary tank and the inlet to said first conduit from the tank to be unloaded; said control means comprising a control valve located in said conduit on the discharge side of said main pump, a by-pass conduit having one end connected to said second conduit between said main pump and said control valve and its other end connected to said jet pump, a valve member situated in said by-pass conduit for controlling flow therethrough, and selectively operable means arranged for detecting the level of liquid within said auxiliary tank and for controlling said control valve in said second conduit, whereby from the outset of the unloading operation during the first stage of the pumping operation the level of liquid within said auxiliary tank remains at or above a predetermined level and only said main pump is required for the unloading operation, and when the level of the liquid within said auxiliary tank begins to drop as the liquid level within the tank being unloaded approaches the bottom of the tank, said selectively operable means activates said control valve in response to the drop of the liquid level within said auxiliary tank and said control valve is opened to divert flow through said by-pass conduit to said jet pump for actuating and operating the second stage of the pumping operation during which stage the flow through said by-pass conduit operates said jet pump for completing the unloading of the liquid from the bottom of the tank and pumping the liquid into said auxiliary from where it is pumped and by said main pump.

2. Liquid unloading equipment, as set forth in claim 1, wherein a gas discharge pipe is connected to the upper end of said auxiliary gas tank and extends upwardly therefrom for discharging gas separated from the liquid flowing through said auxiliary tank.

3. Liquid unloading equipment, as set forth in claim 1, wherein said first conduit comprises a branch conduit secured to said first conduit and extending downwardly therefrom Within the tank to be unloaded, and a bellmouth inlet member secured to the lower end of said branch conduit and being arranged to be positioned at the bottom of the tank to be unloaded.

4. A method of unloading liquid from a tank in a twostage unloading operation, such as unloading oil from the tanks in an oil tanker and the like, where the liquid is lifted for the height of the tank in the unloading operation,

8 comprising the steps of positioning a container relative to the tank to be unloaded so that from the outset of the unloading operation until the liquid level within the tank to be unloaded drops to a certain level the liquid flows by gravity feed into the container, separating gas from the liquid being unloaded within the container, pumping the liquid from the container through a vertical distance at least approximately equal to the height of the tank being unloaded to an unloading station, detecting the level of the liquid within the container for determining when the level of the liquid within the tank to be unloaded is approaching the bottom of the tank whereby the flow from the tank into the container can no longer be maintained at the certain level without pumping the liquid from tank .into the container, in response to the level of the liquid within the container regulating the flow of the liquid being discharged to the unloading station, when the flow of liquid into the container is insufiicient to maintain the certain level therein by-passing at least a portion of the flow to the unloading station to a jet pump member disposed between the tank to be unloaded and the container for driving the jet pump and pumping liquid from the tank into the container, and withdrawing the final portions of the liquid from within the tank into the container by means of the jet pump member whereby the pumping continues as a supply of liquid is circulated through the container by the jet pump member so that shutdown of the pumping is not'necessitated when the tank is completely emptied.

References Cited UNITED STATES PATENTS 2,651,259 8/1953 Brush 103-5 3,253,746 5/1966 Vreedenburg 114-74 X 3,128,709 4/1964 Arkless et al. 103-113 ROBERT B. REEVES, Primary Examiner H. S. LANE, Assistant Examiner US. Cl. X.R.

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