US-12617518-B2 - Vapour transfer assembly and method for use thereof

US12617518B2US 12617518 B2US12617518 B2US 12617518B2US-12617518-B2

Abstract

Vapour transfer assembly for a plurality of oil tanks being connected to a common ventilation pipe to allow the atmosphere to be displaced from the tanks to avoid excessive pressure build-up in the tanks. The tanks are grouped into clusters of tanks comprising at least two tanks. A vapour transfer conduit from at least a first tank of such cluster of tanks is connected to a second tank of same cluster causing the atmosphere displaced from the first tank of the cluster of tanks to move through at least the second tank of said cluster of tanks before entering a common ventilation pipe. Thereby, a slower concentration build-up of volatile organic compounds in the atmosphere entering the common ventilation pipe is obtained. A method for loading such tanks is also contemplated.

Inventors

Rune Bø
Helge K. Aasen

Assignees

GBA MARINE AS

Dates

Publication Date: 20260505
Application Date: 20220916
Priority Date: 20210921

Claims (13)

1 . A vapour transfer assembly for a plurality of tanks connected to a common ventilation pipe, wherein the tanks are oil tanks, comprising: at least some of the plurality of tanks being grouped into a cluster of tanks that comprises at least two tanks; a vapour transfer conduit from at least a first tank of said cluster of tanks to a second tank of the said cluster being configured for causing an atmosphere displaced from the first tank of the cluster of tanks to move through at least the second tank of said cluster of tanks prior to entering the common ventilation pipe, thereby slowing a build-up of concentration of volatile organic compounds (VOC) in the atmosphere entering the common ventilation pipe, wherein the vapour transfer conduit enters the second tank of said cluster at a height that is within a range of 20-50% of a height of the second tank.
2 . The vapour transfer assembly of claim 1 , wherein all of the tanks connected to the common ventilation pipe are grouped into clusters of tanks with each cluster having at least two tanks.
3 . The vapour transfer assembly of claim 1 , wherein the cluster of tanks has three or four tanks.
4 . The vapour transfer assembly of claim 1 , wherein the vapour transfer conduit includes a throttle valve configured to allow a predetermined pressure build-up in the first tank, whereby a vaporization of oil is counteracted.
5 . The vapour transfer assembly of claim 1 , wherein the cluster comprises plural clusters each utilizing a vapour transfer conduit that includes a throttle valve.
6 . The vapour transfer assembly of claim 1 , wherein the vapour transfer conduit enters the second tank horizontally or at a slight upwards inclination of up to 10 degrees.
7 . The vapour transfer assembly of claim 1 , wherein the vapour transfer conduit includes a diffusor element at an outlet end and the diffusor element is arranged symmetrically in relation to a vertical center axis of the second tank.
8 . The vapour transfer assembly of claim 1 , wherein the plurality of oil tanks are arranged on an oil tanker.
9 . The vapour transfer assembly of claim 1 , wherein the vapour transfer conduit includes a diffusor element at an outlet end configured to spread a flow of vapour into a substantially horizontal fan-shaped flow.
10 . The vapour transfer assembly of claim 9 , wherein the diffusor element is arranged to spread the flow about a spread angle of at least 75 degrees.
11 . The vapour transfer assembly of claim 9 , wherein the diffusor element is arranged to spread the flow about a spread angle of at least 90 degrees.
12 . A vapour transfer assembly for a plurality of oil tanks connected to a common ventilation pipe, comprising: at least some of the plurality of oil tanks being grouped into a cluster of tanks that comprises at least two tanks; a vapour transfer conduit from at least a first tank of said cluster of tanks to a second tank of the said cluster being configured for causing an atmosphere displaced from the first tank of the cluster of tanks to move through at least the second tank of said cluster of tanks prior to entering the common ventilation pipe, thereby slowing a build-up of concentration of volatile organic compounds (VOC) in the atmosphere entering the common ventilation pipe, wherein the vapour transfer conduit includes one of: a throttle valve configured to allow a predetermined pressure build-up in the first tank, whereby a vaporization of oil is counteracted; or a diffusor element at an outlet end configured to spread a flow of vapour into a substantially horizontal fan-shaped flow.
13 . A method for filing a plurality of oil tanks connected to a common ventilation pipe and allow atmosphere to be displaced from the plurality of the oil tanks and avoid excessive pressure build-up, comprising: grouping at least some the oil tanks into a cluster of tanks having at least two tanks; and connecting a vapour transfer conduit from a first tank of the cluster to a second tank of the cluster, said vapour transfer conduit allowing the atmosphere displaced from the first tank to move through at least the second tank prior to entering the common ventilation pipe and slowing a build-up of concentration volatile organic compounds (VOC) in the atmosphere entering the common ventilation pipe, wherein the vapour transfer conduit enters the second tank at a height that is within a range of 20-50% of a height of the second tank.

Description

BACKGROUND The disclosed embodiments concern a vapour transfer assembly and a method for loading oil to tank ships in a manner which reduces emittance of oil vapour (Volatile Organic Compounds, or VOC) to the atmosphere. During loading of oil tankers, existing atmosphere in the cargo tanks is displaced by the inflowing oil. Even if the atmosphere in the cargo tanks may be pure inert gas at the start-up of loading, it will over the course of loading be combined with an increasing amount of oil vapour. This atmosphere must be released to maintain a pressure within design limits of the cargo tank design criteria. Maintaining a slight overpressure in the cargo tank atmosphere is a mandatory feature in all tank ships transporting oil to prevent intrusion of oxygen into the cargo tanks, which could make the gas composition explosive. All cargo tanks are connected to a common ventilation assembly, and the atmosphere is eventually released though a common ventilation mast. An adjustable valve in the ventilation mast is used to affect tank atmosphere pressure in the cargo tanks irrespective of which tank receives oil at a certain point in time to keep this slight overpressure throughout the cargo loading. Increasing pressure in the cargo tanks is a simple and well documented way of reducing vapor release from the oil, and some vessels are therefore also using this adjustable valve to increase tank pressure beyond the minimum requirement. An oil tanker typically contains 12 cargo tanks arranged as six pairs in the length direction of the ship. Other cargo tank configurations are also common, but for simplicity the described arrangement as shown in FIG. 1 is used as example in this document. During loading, the left and the right tank of a pair will typically be filled simultaneously. Also typically, when a pair of tanks is filled, the adjacent pair is temporarily omitted, i.e., every second tank pair is filled at the same time. A typical sequence could be to fill pair P1, pair P3 and pair P5 simultaneously, then filling pair P2, pair P4 and pair P6 simultaneously. SUMMARY It would thus be useful to have a method and/or an assembly for loading cargo to oil tankers that reduces the inconvenience of oil vapour release to the environment. As used herein, a “cluster of tanks” refers to two or more tanks fluidly connected in a manner allowing displacement of vapour between the individual tanks in each cluster in a manner defined as the assembly. The cluster or clusters may comprise two or more tanks, and for simplicity in the following detailed explanation, we mostly concentrate on clusters of two tanks. While it is most convenient and provides the best effect that all the cargo tanks of a ship belong to a cluster in the sense described herein, it is not a requirement of the disclosed embodiments. While it for practical purposes is most convenient that all clusters are of the same size, this is neither a requirement of the disclosed embodiments. Thus, a ship of 12 cargo tanks may have the tanks organized as six clusters of two tanks, four clusters of three tanks, three clusters of four tanks, or even, for instance, two clusters of four tanks, and two clusters of two tanks. BRIEF DESCRIPTION OF THE DRAWINGS The invention is described in further detail in the following in the form of exemplary embodiments illustrated by drawings, where FIG. 1 is a schematic top view of a ship with 12 cargo tanks according to prior art, in which the tanks are not interconnected except for their common connection to a ventilation system (not shown); FIG. 2 is a schematic top view of a ship with 12 cargo tanks in which the tanks are arranged in six clusters of two tanks each; FIG. 3 is a schematic top view of a ship with 12 cargo tanks in which the tanks are connected in four clusters of three tanks each; FIG. 4A is a schematic side view of two cargo tanks T1, T3 arranged to be loaded in the traditional manner, i.e., prior art, at an early stage of loading of tank T1; FIG. 4B is a view according to FIG. 4A at a later stage of loading of tank T1; FIG. 4C is a view according to FIGS. 4A and 4B at an early stage of loading of tank T3; FIG. 4D is a view according to FIGS. 4A-4C at a later stage of loading of tank T3; FIG. 4E is a schematic illustration of the VOC concentration in the common ventilation pipe during loading according to FIGS. 4A and 4B and more; FIG. 5A is a schematic side view of a cluster of two tanks T1, T3 as illustrated by FIG. 2, arranged to be filled in succession at an early stage of loading; FIG. 5B is a view according to FIG. 5A at a later stage of loading; FIG. 5C is a view according to FIGS. 5A and 5B at an even later stage of loading; FIG. 5D is a schematic illustration of the contribution to the VOC concentration in the common ventilation pipe during loading according to FIGS. 5A to 5C and more, compared with FIG. 4E; FIG. 6A is a side schematic view of a cluster of three tanks T1, T3, T5; FIG. 6B is a view according to