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Title:
DEVICE FOR TREATMENT OF DECOCTION FROM LIQUEFIED NATURAL GAS AND USE OF AN INCINERATION PLANT FOR BURNING SUCH DECOCTION
Document Type and Number:
WIPO Patent Application WO/2000/047463
Kind Code:
A1
Abstract:
A device for treatment of boil-off form liquefied natural gas, LNG, which is stored in a tank (4) of a vessel (1), comprising a first and a second plant (14 and 30 respectively) for treatment of the boil-off (6). According to the invention the second plant (30) is an incinerator with a combustion chamber (32) for incineration of the boil-off (6). The combustion chamber's (34) outlet (36) communicates with the open atmosphere.

Inventors:
CHRISTIANSEN PER ERIK (NO)
Application Number:
PCT/NO2000/000049
Publication Date:
August 17, 2000
Filing Date:
February 09, 2000
Export Citation:
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Assignee:
MOSS MARITIME AS (NO)
CHRISTIANSEN PER ERIK (NO)
International Classes:
B63B25/14; B63J99/00; F17C9/02; F23G7/08; (IPC1-7): B63B25/14; B63B25/16; F23G7/08
Domestic Patent References:
WO1998043029A11998-10-01
Foreign References:
US3021809A1962-02-20
US4493638A1985-01-15
US3110156A1963-11-12
US3114344A1963-12-17
Attorney, Agent or Firm:
Onsagers AS. (P.O. Box 265 Sentrum Oslo, NO)
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Claims:
PATENT CLAIMS
1. A device for treatment of boiloff from liquefied natural gas, LNG, in order to prevent the discharge of untreated boiloff (6) to the open atmosphere, wherein the liquefied natural gas is stored in a tank (4) of a vessel (1), and the device comprises a first and a second plant (14 and 30 respectively), the first plant (14) being arranged for liquefaction of the boil off (6) and returning it to the tank (4), and the second plant (30) being an emergency plant for use in the event of the failure of the first plant (14), characterized in that the second plant (30) is an incinerator, which comprises a combustion chamber (32) with a burner (34) for incineration of the boiloff (6), and an outlet opening (36) through which incinerated boiloff (6) can flow from the burner (34) into the open atmosphere.
2. A device according to claim 1, characterized in that the combustion chamber's (32) walls are heatinsulated.
3. A device according to claim 1 or 2, characterized in that the combustion chamber (32) is installed near a funnel (38) of the vessel.
4. A device according to claim 1 or 2, characterized in that the combustion chamber (32) is installed inside a funnel (38) of the vessel (1).
5. The application of an incinerator (30) comprising a combustion chamber (32) with a burner (34) and an outlet opening (36) which communicates with the open atmosphere, for incineration of boiloff (6) from liquefied natural gas, which is stored in a tank (4) of a vessel (1), where the incinerator (30) acts as an emergency plant for use in the event of the failure of a main plant (14) which is arranged for liquefaction of the boiloff (6).
Description:
DEVICE FOR TREATMENT OF DECOCTION FROM LIQUEFIED NATURAL GAS AND USE OF AN INCINERATION PLANT FOR BURNING SUCH DECOCTION The invention relates to a device for treatment of boil-off from liquefied natural gas, LNG, which is stored in a tank of a vessel, comprising a first and a second plant for treatment of the boil-off.

It is a requirement for vessels transporting LNG that untreated boil-off from the vessel's LNG tank or tanks should not be released into the open atmosphere, thereby polluting it. The vessel therefore has a first plant or main plant for treatment of all the boil-off which may be produced. Since the amount of boil-off can be considerable, the main plant is usually of the type which permits recycling of the boil-off, whereby it is liquefied and returned to the tank.

In order to ensure that this requirement is also fulfilled in the event of failure of the main plant, it is required that a further, second plant or emergency plant with the same treatment capacity should be provided.

In the applicant's patent application no. PT/NO98/00088 there is disclosed a plant whereby boil-off can be liquefied and transported back to the LNG tank. Such a plant is complicated and very expensive.

The use is also known of a plant of the same type as an emergency plant. The complete device is therefore very expensive and complicated.

The object of the invention is to provide a cheaper and simpler device of the type mentioned in the introduction.

The characteristic of the device according to the invention is presented in the characterising features indicated in the claims.

The invention will now be described in more detail with reference to the drawing whose single figure is a schematic side view of a vessel with a device according to the invention.

In the upper portion of a tank 2 which contains LNG 4 and is provided in a vessel 1, on account of a heat flow through the tank wall, LNG boil-off 6 is formed which is collected in the upper portion of the tank 2. This boil-off is passed via a pipe 8 and a pipe 10, wherein there is provided a first shut-off

valve 12, to a main plant 14 for liquefaction of the boil-off 6, thus producing LNG, whereupon this LNG is transported back to the tank 2 via a pipe 16.

From the pipe 8 there branches off a pipe 20, wherein there is provided a second shut-off valve 22 which is connected to a second plant or emergency plant 30 for treatment of the boil-off. This emergency plant 30 has the same capacity, i. e. it can treat the same amount of boil-off per time unit as the main plant 14.

The emergency plant 30 is an incinerator, comprising a combustion chamber 32, wherein there is provided a burner 34 for boil-off which is supplied to the burner 34 via the pipe 20.

The combustion chamber 32 may be in the form of a substantially vertically extending steel pipe, at the upper end of which is an outlet opening 36 which communicates with the open atmosphere. On the lower portion of the combustion chamber there are openings (not illustrated) for admitting combustion air to the burner 34. On the inside of the combustion chamber a heat insulation means may be provided, and inside the heat insulation there may be provided a heat-resistant coating, thereby preventing heat conduction and radiation to the combustion chamber's surroundings and injuries to personnel. The combustion chamber 32 is preferably long enough to prevent the flame which is formed at the burner 34 when the emergency plant is in operation and the supply of boil-off is at a maximum from reaching the outlet opening 36. The emergency plant 30 can thus be described as an enclosed flare, through which incinerated boil-off can flow out into the open atmosphere.

During operation of the device by means of the main plant 14, the first valve 12 is open, while the second valve 22 is closed.

In the event of failure of the main plant 14, the first valve 12 can be closed and the second valve 22 opened, whereupon boil-off flowing out of the burner 34 can be ignited.

The emergency plant 30 is preferably installed at a distance from personnel on board the vessel. Thus the combustion chamber 32, e. g., can be located beside the vessel's normal funnel 38 which surrounds the exhaust pipes, through which exhaust gas from the vessel's main and auxiliary engines is

passed into the free atmosphere. Alternatively, the combustion chamber 32 may be installed inside the funnel 38, beside the exhaust pipes from the main and auxiliary engines, thereby further securing the safety of the personnel.

Furthermore, the heat insulation may be reduced, thus giving the vessel a more aesthetic appearance.

Even though the emergency plant 30 does not provide a recirculation of boil- off 6 to the tank 4 for recycling of the boil-off, a loss of boil-off may be acceptable since a main plant of the above-mentioned type is reliable and therefore the emergency plant will only rarely be used, and because the emergency plant according to the invention is relatively inexpensive.

According to the invention, moreover, an emergency plant is obtained which is exceptionally reliable due to its simplicity.

It will be understood that the above-described plant may comprise additional components, such as extra valves, pumps, etc. which have not been included, the arrangement of such components being obvious to a person skilled in the art.

Also the main plant may of course be an incinerator of this kind.