DK149507B - Overflow safety system for tanker vessels - Google Patents

Description

The invention relates to a tank overflow protection system for a tanker with a number of closed liquid cargo tanks, each cargo tank having a side connection to a main connection which ventilates the cargo tank and carries excess cargo to a collection tank which is ventilated to the atmosphere.

Loading of liquid chemicals and oil products such as bulk cargo oil takes place in tankers by means of transport hoses and loading pipes, which are interconnected with inlet sockets which are connected to the tank sections of the tanker. During loading or transfer of cargo, the liquid or chemical product may continue to flow after the tank in question is filled. As a result, the 20 liquid loaded flows out through overflow openings, vent pipes or other cover openings, vent pipes or other cover openings associated with that cargo tank and flows beyond the tanker's deck and into the water, -25 causes loss and water pollution, air pollution, and often fire and explosion hazards are created.

Overflows can occur in various ways, which include both human errors, such as negligence, and mechanical errors, e.g. may be leaks or malfunctioning valves.

Such cargo overflows can cause significant pollution of coastal waters, especially when the cargo handled is crude oil. For example, depending on the size of the tanker, the pumping speed during loading and the duration of the overflow before being discovered, amounts of between a few barrels to several thousand barrels of oil can be spilled during a single overflow accident.

Previously, overfill control systems have been described to prevent overflow from cargo tanks in tankers during loading. Level alarms and continuously functioning tank contents indicators are used e.g. for registration of cargo tank filling in tankers during loading. Although such devices are of great help, they may be malfunctioning and dependent on human operation and do not prevent automatic contamination. These characteristics make such devices unacceptable for tankers that carry cargoes such as crude oil 20 and which have the potential to create serious environmental pollution in coastal waters and seas if discharges occur during loading of the tanker. Remote-operated quick-closing shut-off valves have been used in such tankers to reduce overflows, but such valves may create unreliable pressure waves in loading tubes and pipelines used to load the ship, and these pressure waves may be sufficiently severe to produce breakage in hoses and pipe joints, thus resulting in 30 discharges of cargo. Furthermore, such valves still rely on human intervention to function effectively.

It is therefore an object of the invention to provide an automatic overflow protection system for tankers, which remedies the aforementioned disadvantages of known tank level indicators and overflow management.

5 systems which automatically prevent the release of liquid chemicals and crude oil products during loading operations or cargo moving operations in tankers without the danger of causing breakage of hoses and wires used for loading the ship or the ship's manifold system.

This is accomplished as the side connection comprises a check valve which opens in the event of overflow from the cargo tank and a pressure vacuum relief valve is arranged parallel to the check valve by means of a gas vent pipe, the side connection having a clearing sufficiently large. to avoid overpressure in the cargo tank during overflow.

20 If the tank is overfilled, overflow load will be passed through the check valve to the main connection and on to the collection tank. Thus, no pollution of the environment will take place.

Normally, the tank is vented through the pressure-vacuum equalization valve in a known manner. However, this valve will not be able to be manufactured with such a large flow opening as is required if the valve is also to lead overflow. It is therefore arranged parallel to the non-return valve in a generally sized vent pipe.

The check valve can easily be manufactured with dimensions corresponding to the illumination of the branch connection forδΙΤ ί 1. This must be so large that there is no undue pressure in the tank during overflow.

This ensures that feed pipes and hoses are not ruptured.

Thus, the combination of the check valve and the pressure-vacuum equalization valve ensures both an effective venting of the tank and an efficient discharge of one. possibly overflow.

It is convenient if the non-return valve as defined in claim 2 is positively maneuvered.

A simple and effective design of the non-return valve is a non-return valve as defined in claim 3.

15

If the equalizing valve as claimed in claim 4 is of a closed type, an effective venting of the tank is achieved.

The invention will now be described in more detail with reference to the drawing, in which 1 is a partial cross-sectional view of a tanker with built-in overflow protection system 25 according to the invention; FIG. 2 shows the overflow protection system of FIG.

1 is a partial sectional view, and at the same time the construction of the main connection, side connections and control valves in system one, and FIG. 3 shows the overflow protection system of FIG. 1 together with the construction of the collection tank.

5 The drawing shows a tanker, which in its entirety is designated by reference numeral 10, comprising a hull consisting of a bottom 11 and sides 12, a main deck 13 and a number of waterproof cargo tanks 14. The cargo tanks are located within the hull between main deck 13 and hull burid 11 10 and can absorb liquid chemicals and oil products, e.g. Crude oil from an onshore storage tank 15 · An expansion well 16 is banned with and open downward against each cargo tank 14. A cargo pipe connection 17 is connected to each of the cargo tanks l1! for filling the dispenser 15 with load from the storage tank 15.

The tanker 10 comprises a longitudinal main connection 18 which may be disposed either above or below the main deck 13 and a plurality of side joints 19 which 20 are connected at one end to the main connection 18 and at the other end are connected to the expansion well 16. A number of check valves 20 , which may be of the flap type, are inserted into the side joints 19 immediately at their ends for the purpose of allowing free passage of liquid chemicals and petroleum products, i. the liquid load, from the expansion wells 16 to the main connection 18 through branch connection 19. If the valve type check valves are used, the valves only allow free flow. of fluid load from the expansion wells 16 to the main connection 18 through the branch connections 19. A cargo collection tank 21, which may comprise either a side tank or a number of interconnected tanks in the ship, is connected to the main connection 18 for collecting cargo therefrom. An overflow pipe 22 is mounted within the collection tank 21 and has an enlarged opening 23 at the end located below the end of the main connecting line 18. The latter is bent downwards and opens into the collection tank 21 just 5 below the main deck 13. The enlarged opening 21 of the tube 22 receives load overflow from the main line 18 and is spatially spaced apart from the outlet of the main connection in the tank 21 to allow gases e.g. hydrocarbons and the like to escape from the main connection into the collection tank 21. Further openings are arranged around the periphery of the opening 23 to enable gases to escape into collection tank 21. The collection tank is provided with a vent valve 24 which comprises a flame retardant network 25 and a pressure-vacuum relief valve 26 for venting gases between the collection tank and the atmosphere.

Gases are vented from the cargo tanks through the main connecting ice 18 and the side joints 19 to the collection tank 21. A plurality of gas vent pipes 27 are connected to the side joints 19 immediately at their ends and parallel thereto, each comprising a pressure-vacuum equalization valve 28 which is preferably of closed type 25. and inserted into the gas vent tube immediately at its ends for venting gases from the cargo tanks 14 to the collection tank 21 through the main connection 18 and the side connections 19. This occurs when the valves 20 are closed, i. during all operations of the ship except during filling of a cargo tank or during transhipment between the cargo tanks. When the valves 20 are flap type check valves, the gas vent pipes 27 and the valves 28 allow for vacuum relief in the cargo tanks 14.

The side connections 19 are dimensioned, ie. have a sufficient diameter to prevent overpressure in the cargo tanks even during an overflow situation 'during loading or transhipment of cargo. The terminology "overpressure situation" means a build-up of pressure in the cargo tanks due to the pumping of cargo into the tanks at such a high pressure that it can cause damage to the ship.

Such pressure build-up is prevented by dimensioning the side joints 19 in such a way that these joints have a diameter greater than the diameter of the pumping joints or tubes used for filling the cargo tanks, and that the oversize is so large that the pressure in the cargo tanks 15 is reduced to a level below the maximum pressure that the hull can withstand before sustained damage. It should be noted that both the main connection 18 and the side connections 19 can be connections with either rectangular or square cross section, or also partially 20 circular tubes, as well as they can be circular.

As a general rule, the diameter of the main connection 18 will always be considerably larger than that of the side connections 19 and will, for this reason, usually not be a factor 25 to be taken into account in the considerations of overpressure of the cargo tanks 14. However, for some reason the main connection can produce a backpressure, e.g. if the main connection has a diameter smaller than the side connections, this back pressure must be taken into account together with the back pressure, which can result from the side connections when the dimensions of the connections are determined, the total back pressure having to keep the pressure in the cargo tanks 14 below the maximum permissible overpressure. .

A flow flow alarm 29 is connected in series with the main connection 18 to the load flow alarm in the main connection. Furthermore, it is preferred that the collection tank 21 is a side tank in the tanker 10 to give 5 an additional indication of cargo flow through the main connection and of overflow thereby providing the ship with a slight impact side. This will mean an additional level of security in the event that the pipe flow alarm does not work and / or that crew members working on the ship are not aware or not present and therefore do not detect an overload from the cargo section through the main connection.

If the volume of cargo pumped into one or 15 more cargo tanks in the ship exceeds the capacity of these cargo tanks and overflow is produced, the excess cargo is passed through the expansion well 16 and the branch connection 19 to the main connection 18 and flows through the main connection into the collection tank 21. If the valves 20 are actively operated shut-off valves, the valves are opened prior to the commencement of the loading operation. If the valve type check valves are used, the valves will open automatically when overflow occurs. The plow through the main line 18 is controlled by the flow alarm 29, which triggers an audible and / or visible alarm. Cargo inflow into the collection tank flows into the enlarged opening 23 of the overflow pipe 22 and is led down the tank to the tank bottom by the pipe inside the tank.

Gases found in cargo tanks 14, e.g. Hydrocarbons, which are separated from petroleum products, are discharged into the cargo tanks and flow through the side connections 19 to the main connection 18 and escape from the end of the main connection in the collection tank 21. The gases are vented under pressure to the atmosphere through the venting 24. designed so as to result in an open upper end at level above the deck of the ship, clearly clear of areas of passenger traffic and other ignition risk on the ship. It should be noted that a closed tank loading system is required during loading and transhipment and transhipment operations on the tanker.

The system can be either an automatic or manually closed system or a simple inspection pane with an internal scrubber. The overflow protection system of the present invention can also be used in conjunction with bunker tanks, chemical tanks, etc., to prevent overflow losses and risks in the same way as with cargo tanks.