Ships – Building – Freighters
Patent
1995-01-26
1996-02-20
Avila, Stephen
Ships
Building
Freighters
B63B 2508
Patent
active
054920752
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and a vessel for offshore oil loading, wherein the vessel comprises a number of center tanks arranged in the longitudinal direction of the vessel, and a number of wing tanks located in pairs on either side of respective center tanks, a loading line being connected to the center tanks via respective valves, and adjacent center tanks being connected to each other via bulkhead valves.
In connection with offshore oil loading a part of the load will be lost to the atmosphere because of de-gassing from the liquid surface. As an example, in a typical buoy loading in the North Sea, there may be lost approximately 200 tons per loading of tankers of about 120 000 tons. The release of gas mainly is due to splashing and stirring of crude oil in the loading tanks, and occurring pressure drop in the hydrocarbon load during the handling thereof.
Measurements have shown that the extent of the degassing is proportional to the time before the tanks are full, and the period of the condition of standing waves (resonance) in the tanks. In addition, loads on the tank structure will be increasing with the period of standing waves. It is therefore essential to fill the individual tanks as quickly as possible, both to reduce the de-gassing period and therewith the total spill of gases, and to reduce loads on the tank structures during loading.
Thus, the object of the invention is to provide a method and a vessel resulting in a substantial reduction of the degassing during loading, and also in a substantial reduction of loads on the tank structures.
It is also an object of the invention to provide a vessel having a tank arrangement which has technical and economic advantages, especially with direct loading of tankers on the field.
For the achievement of the above-mentioned objects there is provided a method of the introductorily stated type which, according to the invention, is characterized by the steps of being substantially narrower and having a correspondingly smaller volume than the wing tanks, appurtenant wing tank pair and sluicing out oil from the center tanks into the two wing tanks by means of the static pressure from the center tanks, the bulkhead valves between the center tanks being open, so that the wing tank pair is filled as quickly as possible by suitable operation of the bulkhead valves between the center tanks and of the valves of the loading line to the center tanks, appurtenant center tank are filled to a desired level, and successively for additional wing tank pairs after that all center tanks have been filled again.
According to the invention there is also provided a vessel of the introductorily stated type which, according to the invention, is characterized in that the center tanks have a width which is less than half the width of the wing tanks, that all tank triplets consisting of a center tank and an appurtenant wing tank pair are connected to each other via bulkhead valves, and that the loading line extends through the center tanks, all valves with appurtenant drive units being arranged centrally, in connection with the center tank area.
The invention will be further described below in connection with exemplary embodiments with reference to the drawings, wherein
FIGS. 1, 2 and 3 show a side view, a plan view and a cross-section, respectively, of a vessel having a tank arrangement according to the invention;
FIGS. 4 and 5 show a side view and plan view, respectively, of the vessel in FIGS. 1-3, and show the principal set-up of conduits and valves;
FIGS. 6 and 7 show cross-sections of two different bottom arrangements; and
FIGS. 8, 9 and 10 are a side view, a plan view and a cross-section, respectively, showing a separate emergency loading or "stripping" arrangement which is also installed on the vessel.
In the drawings there is shown a vessel 1 in the form of a tanker wherein a pair of longitudinal bulkheads 2 are arranged so that the tank area of the vessel is divided into a narrow center tank section and a pair of relatively wide wing tank sections. In the illustrated e
REFERENCES:
patent: 2321811 (1943-06-01), Harris
patent: 3766875 (1973-10-01), Baki
patent: 3926135 (1975-12-01), De Gregorio
Breivik Kare
Egge Trygve G.
Lerstad Arve
Overli Ole
Smedal Arne
Avila Stephen
Den Norske Stats Oljeselskap A.S.
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