Vapor transfer assembly and method of use thereof

Abstract

A vapor transfer assembly for a plurality of oil tanks (T1, T2, etc.) connected to a common vent pipe (50) for displacing atmosphere from the tanks while avoiding pressure build-up within the tanks. The tanks are grouped into a cluster (C) of tanks including at least two tanks (T1, T3). A vapor transfer conduit (54, 64a) from a first tank (T1) of such cluster (C) is connected to a second tank (T3) of the same cluster (C) to move atmosphere displaced from the first tank (T1) of the cluster (C) through the second tank (T3) of the cluster (C) of said tanks (T1, T3) before entering the common vent pipe (50). Thereby, a slower concentration build-up of volatile organic compounds (VOCs) is obtained in the common vent pipe (50). A method for filling such tanks is also considered.

Description

[Technical field]

[0001] The present invention relates to a vapour transport assembly and a method for loading oil into a tanker in a manner that reduces the emission of oil vapours (volatile organic compounds, i.e. VOCs) into the atmosphere. More precisely, the present invention relates to a vapour transport assembly as indicated by the preamble of claim 1 and to a method as indicated by the preamble of claim 12. [Background technology]

[0002] During loading of an oil tanker, the atmosphere within the cargo tank is displaced by the incoming oil. Even though the atmosphere in the cargo tank is pure inert gas at the start of loading, during the loading process it becomes mixed with increasing amounts of oil vapours. This atmosphere must be relieved in order to maintain the pressure within the design limits of the cargo tank design criteria.

[0003] In all tankers transporting oil, it is a mandatory feature to maintain a slight overpressure in the cargo tank atmosphere to prevent the ingress of oxygen into the cargo tanks, which could make the gas composition explosive. All cargo tanks are connected to a common venting assembly, and the atmosphere is ultimately vented through a common venting mast. To maintain this slight overpressure during cargo loading, adjustable valves in the venting mast are used to affect the tank atmosphere pressure in the cargo tanks, regardless of which tank is receiving oil at a particular time.

[0004] Increasing pressure in cargo tanks is a simple and well-documented method of reducing vapour emissions from oil, so some ships also use adjustable valves to increase tank pressure above the minimum required.

[0005] An oil tanker typically contains 12 cargo tanks arranged in six pairs along the length of the ship. Other cargo tank arrangements are also common, but for simplicity, the described arrangement shown in FIG. 1 is used as an example herein. During filling, the left and right tanks of a pair are typically filled simultaneously. Also, when a tank pair is filled, the adjacent pair is typically temporarily skipped; that is, every other tank pair is filled simultaneously. A typical sequence could be to fill pairs P1, P3 and P5 simultaneously, followed by pairs P2, P4 and P6 simultaneously. Summary of the Invention [Problem to be solved by the invention]

[0006] It is therefore an object of the present invention to provide a method and / or assembly for loading cargo into an oil tanker which reduces the unwanted release of oil vapours into the environment. [Means for solving the problem]

[0007] This object is achieved by an assembly according to claim 1, which constitutes a first aspect of the invention. According to another aspect, the invention relates to a method according to claim 12.

[0008] Preferred embodiments of the invention are disclosed by the dependent claims.

[0009] As used herein, a "cluster of tanks" refers to two or more tanks fluidly connected in a manner that allows for vapor displacement between the individual tanks in each cluster in a manner that defines an assembly of the present invention. Although a cluster can include more than two tanks, the following detailed description will primarily focus on a cluster of two tanks for simplicity.

[0010] It is most convenient and provides the best effect if all cargo tanks of a ship belong to a cluster in the sense described herein, but this is not a requirement of the invention. For practical purposes it is very convenient if all clusters are the same size, but this is also not a requirement of the invention. For example, a ship with 12 cargo tanks can have the tanks organized as 6 clusters of 2 tanks, 4 clusters of 3 tanks, 3 clusters of 4 tanks or, for example, 2 clusters of 4 tanks + 2 clusters of 2 tanks.

[0011] The invention will now be explained in more detail in the following in the form of exemplary embodiments illustrated by the drawings. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic plan view of a ship with cargo tanks according to the prior art, the tanks not being interconnected except for a common connection to a ventilation system (not shown). [Diagram 2] FIG. 1 is a schematic plan view of a ship having 12 cargo tanks, which for the purposes of the present invention are arranged in six clusters of two tanks each. [Diagram 3] Schematic plan view of a ship with 12 cargo tanks, connected in four clusters of three tanks each. [Figure 4A] FIG. 1 shows a schematic side view of two cargo tanks T1, T3 arranged to be filled in the conventional way, i.e. prior art, at an early stage of filling of tank T1. [Figure 4B] A view similar to FIG. 4A, at a later stage of filling of tank T1. [Figure 4C] 4A and 4B at an early stage of filling of tank T3. [Figure 4D] 4A to 4C at a later stage of filling of tank T3. FIG. [Figure 4E] FIG. 4C is a graphical representation of VOC concentrations in a common vent line during filling according to FIGS. 4A and 4B, etc. [Figure 5A] FIG. 3 is a schematic side view of a cluster of two tanks T1, T3 shown in FIG. 2 arranged to be filled successively according to the invention, during an initial stage of filling. [Figure 5B] FIG. 5B is a view similar to FIG. 5A at a later stage of filling. [Figure 5C] 5A and 5B at a later stage of filling. [Figure 5D] FIG. 5B is a graphical representation showing the contribution to VOC concentration in a common vent pipe during filling according to FIGS. 5A-5C etc., compared with FIG. 4E. [Figure 6A] FIG. 1 is a schematic side view of a cluster of three tanks T1, T3, T5. [Figure 6B] FIG. 6B is a view similar to FIG. 6A at a later stage of filling. [Figure 6C] 6A and 6B at a later stage of filling. [Figure 7A] FIG. 6B is a schematic side view showing details of the tank T3 of FIG. 6A. [Figure 7B] FIG. 6B is a schematic plan view showing details of the tank T3 in FIG. 6A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In the following description, several designations are used. For tanks, the designations T1, T2, etc. are usually used. For the last tank of a cluster of more than two tanks, the designation TL is used. For non-specific tanks (any tank), the designation TA is used. For clusters of tanks, the designations C1, C2 are used for the first and second clusters, etc. For non-specific clusters, the designation CA may be used.

[0014] Figure 1 shows diagrammatically a tanker including 12 cargo tanks arranged to be filled with oil in the conventional manner, with the tank atmosphere being displaced individually from each tank being filled to a common vent system. For simplicity, the piping has been omitted.

[0015] The dotted lines indicate that the tanks are considered to belong to six tank pairs (P1-P6). Tanks that belong to a common pair are usually filled in parallel, i.e. at the same time.

[0016] Figure 2 shows diagrammatically a tanker having 12 tanks arranged in six clusters of two tanks each, each cluster of tanks arranged to be filled according to an embodiment of the invention further described below. Piping has been omitted, except to symbolically show the steam connections between the tanks in each cluster. It is important to note the difference between a pair of tanks and a cluster of tanks. A first pair of tanks consists of tanks T1 and T2, while a first cluster of tanks, if it contains two tanks, consists of tanks T1 and T3.

[0017] 3 shows diagrammatically a tanker having 12 tanks arranged in four clusters of three tanks each, with each cluster of tanks arranged to be filled in accordance with an embodiment of the invention described further below, with piping omitted except to symbolically show the steam connections between the tanks in each cluster.

[0018] Reference is now made to FIG. 4A, which shows diagrammatically the initial filling of tank T1 via oil feed conduit 41, according to the prior art. The oil level 42 in the tank is very low, and a substantial volume 43 above the oil level is available for inert gas and oil vapours. At this initial stage of filling, the concentration of oil vapours in the vent pipe 44 leading to the common vent pipe 50 is low or moderate. However, as filling continues, the available volume 43 decreases, and the concentration of oil vapours in both the available volume 43 and in the vent pipe 44 increases due to evaporation from the oil. The vent pipe 44b between tank T3 and the common vent pipe 50 has the same general function as the vent pipe 44 from tank T1. Still referring to FIG. 1, it should be understood that tank T2 is filled simultaneously with tank T1, and there is the same overall vapour displacement therefrom as described with reference to tank T1. Usually, two tanks laterally adjacent to each other are filled simultaneously.

[0019] The common vent line 50 typically includes a throttle valve 57 near the outlet (ie, the vent mast) to allow for the building and maintaining of a slight overpressure throughout the tank system.

[0020] 4B, when oil level 42' is reached, filling and evaporation has been going on for some time and the volume available for vapor 43' is about 1 / 4 of what it was at the start. At this point, the oil vapor concentration in effective volume 43', vent pipe 44 and common vent pipe 50 has increased, and may have increased significantly depending on the quality of the oil being filled. During the process described here, nothing has happened with tank T3 except that some of the vapor transported through common vent pipe 50 may have lateral flowed into tank T3 through vent pipe 44b.

[0021] There is a fairly rapid increase in VOC concentration from low to high for each pair of cargo tanks that are filled. The term "tank pair" as used herein refers to two tanks located laterally adjacent to each other, and not to a cluster of tanks, which is the focus of this invention.

[0022] In practice, cargo tanks are not filled in the order from bow to stern, taking into account the stability and strength of the ship. For a ship with six tank pairs arranged in six clusters, as shown in Fig. 2, a more common sequence is as follows: First, the odd-numbered tank pairs are usually filled in parallel, i.e. pairs P1, P3 and P5, and then the even-numbered tank pairs are filled in parallel, i.e. pairs P2, P4 and P6. Thus, the filling is performed in a two-stage process, during each process six tanks, i.e. three tank pairs, are filled simultaneously. Six tanks, i.e. three tank pairs, filled in parallel can also be called a "set of tanks". Thus, still within the framework of Fig. 2, tanks T1, T2, T5, T6, T9 and T10 constitute one tank set, and tanks T3, T4, T7, T8, T11 and T12 constitute another tank set.

[0023] 3, where each cluster contains three tanks, the filling sequence can be pair P1 and pair P4 in parallel, then pair P2 and pair P5 in parallel, and finally pair P3 and pair P6 in parallel. Thus, in this case there will be three tank sets, namely tanks T1, T2, T7 and T8 belonging to a first set, tanks T3, T4, T9 and T10 belonging to a second set, and tanks T5, T6, T11 and T12 belonging to a third set.

[0024] For purposes of illustration, we will focus on the filling of tank T3 with respect to vapor displaced from the tank since tank T3 is a clustered tank with tank T1.

[0025] Figure 4C shows the initial filling of tank T3 through oil feed conduit 41b, showing a similar progression to that described with reference to Figure 4A for the initial filling and vapour generation of tank T1. The oil level is indicated with reference numeral 42b and the space available for vapour with reference numeral 43b. At this stage, the vapour concentration transferred to the common vent pipe 50 is low or moderate, but typically slightly higher than in the situation shown by Figure 4A. It is worth noting that evaporation in tank T1 still contributes to VOCs in pipe 50 after the filling of tank T1 has been completed, as indicated by arrow 44 in Figure 4C.

[0026] Figure 4D shows the filling of tank T3 at a later stage, where the oil level has risen, as indicated by 42b', and the space available for steam has decreased, as indicated by 43b'. The situation is similar to that shown in Figure 4B for tank T1. The concentration of steam released into the common vent pipe 50 has increased, and may have increased significantly depending on the quality of the oil filled.

[0027] FIG. 4E is an idealized graphical representation of the concentration of VOCs in the common vent pipe 50 caused by evaporation in tanks T1 and T3 during the filling of tanks T1 and T3 with oil in a conventional manner. In this example, for illustrative purposes, the concentration of VOCs at time zero is shown as zero. In reality, this is rarely the case because tanks contain different amounts of residual VOCs from the previous cargo. However, the general principle remains the same. As shown, the concentration level does not usually drop to a level of zero during the transition period before the start of tank T3 filling. This is because some oil vapor from the filling of T1 is usually lateral flowing into tank T3 via the common vent pipe 50.

[0028] Reference is now made to Fig. 5A, which illustrates the principle of filling tank T1 when arranged as the first tank of a cluster of two tanks T1, T3 according to the invention. First, oil is filled into tank T1 via oil supply pipe 51. The atmosphere in tank T1 is displaced into tank T3 via steam transfer conduit 54, and then leaves tank T3 via vent pipe 55b to the common vent pipe 50. When tank T1 is nearly empty, as shown in Fig. 5A, the volume available for steam 53a+53b is twice as large as the volume available in the conventional method. As the filling continues, the relative difference between the available volumes of the two methods increases.

[0029] It is worth noting that the vapor transfer conduit 54 is equipped with a throttle valve 56 which allows throttling of the vent line to increase the pressure in the available volume 53a of tank T1 during filling to reduce evaporation from the oil in tank T1. By increasing the pressure only in the tanks receiving the cargo, the pressure increase occurs more quickly in these tanks and the full effect of the pressure increase is achieved sooner.

[0030] Referring to FIG. 5B, for example, when tank T1 is 3 / 4 full of oil, according to the illustrated embodiment of the present invention, the volume 53a'+53b available for VOCs is 5 / 4 of the tank volume, whereas according to the prior art method shown by FIG. 4B, the available volume 43' is 1 / 4 of the tank volume.

[0031] 5A-5C according to the invention, at the stage shown by Fig. 5B, 5 / 4 of the tank volume is still available for VOCs, so the highest concentration is near the bottom of tank T3 due to the relatively high density of VOCs compared to the inert gases constituting the rest of the tank atmosphere. Thus, the concentration of VOCs passing through vent pipe 55b to common vent pipe 50 at this stage is correspondingly low, much lower than the concentration of VOCs passing through vent pipe 44 at the stage shown by Fig. 4B.

[0032] 5C, filling of Tank T1 has been completed and filling of Tank T3 has just begun. Now, the increased concentration of VOCs in Tank T3 caused by the transfer of tank atmosphere from Tank T1 (with the highest concentration near the bottom of Tank T3 due to the high density of VOCs) significantly reduces evaporation from the oil and thus the total evaporation from the oil filled in Tank T3 compared to the oil filled in Tank T1.

[0033] As filling of tank T3 continues, the evolution of VOC concentration above oil level 52b is slower than that experienced during the filling shown in Figures 4C and 4D due to the higher initial concentration of VOCs. In other words, the VOC concentration in vent pipe 55b continues to increase slowly and steadily, as it did when tank T1 was being filled. It is noteworthy that evaporation in tank T1 still contributes to the VOCs in pipe 50 after filling of tank T1 is completed, as shown by arrow 55 in Figure 5C.

[0034] FIG. 5D is an idealized graphical representation showing the contribution to VOC concentration evolution in the common vent pipe 50 displaced from tanks T1 and T3 during the filling of tanks T1 and T3 with oil according to the embodiment shown in FIGS. 5A-5C, compared to the VOC concentration evolution during filling according to FIGS. 4A-4D (prior art), shown as a dashed line. In this example, for illustrative purposes, the concentration of VOC at time zero is shown as zero. In reality, this is rarely the case, since tanks contain residual VOC from the previous cargo to different degrees. However, the general principle remains the same.

[0035] Although only the filling of tanks T1 and T3 in Figures 5A-5C has been described, it should be understood that the filling of all clusters of tanks achieves the same general effect.

[0036] During the filling of tank T1 as shown in Figures 5A and 5B, the concentration buildup and general levels of VOCs in the tank atmosphere passing through vent line 55b to the common vent line 50 is much lower in accordance with an embodiment of the present invention compared to the prior art method in which the tank atmosphere passes through vent line 44 to the common vent line 50. During the filling of tank T3, the VOC concentration buildup continues through vent line 55b, but due to the previous transfer of the VOC-saturated tank atmosphere during the filling of T1, there is less evaporation from the raw material caused by the initial concentration buildup of VOCs in T3. Overall, a significant overall reduction in VOC emissions is obtained as shown by the different areas under the two curves in Figure 5D.

[0037] Simulations have shown that the method according to the invention can reduce the amount of oil vapor released by approximately 10-35% compared to conventional methods when displacing the vapor through an adjacent empty tank, depending on the oil quality and the level of tank atmosphere mixing.

[0038] Following the same principle, it is possible to combine three or more tanks to obtain two or more intermediate tanks instead of one where VOCs can accumulate before entering a common ventilation system.

[0039] FIG. 6A is a schematic side view of a cluster CA of three tanks T1, T3, T5 arranged as a cluster of three tanks according to FIG. 3, using the same general principle as shown for the two tanks in FIGS. 5A-5C. According to this embodiment, when oil is filled into tank T1 via oil supply pipe 61, steam is displaced via steam transfer conduit 64a to tank 3, and further from tank T3 to tank T5 via steam transfer conduit 64b, and then via vent pipe 65c to the common vent pipe 50. The throttle valves 66a and 66b arranged in the steam transfer conduits 64a, 64b respectively, have the same function as the throttle valve 56 shown in FIGS. 5A and 5B. When tank T1 is full, the oil supply conduit 61 switches to tank T3. From this point on, the development of this embodiment can be compared to the embodiment described with reference to FIGS. 5A-5C. It should be noted that the connection of the three tanks T1-T3 to the cluster CA does not require the tanks to be arranged in a straight line, it only requires that the piping between the tanks be appropriately arranged.

[0040] 6B shows the situation when tank T1 is filled completely, or to the desired extent, and filling of tank T3 has begun via oil supply conduit 61b. At this stage, throttle valve 66A would be closed and a direct connection 65a from T1 to 50 would again be established.

[0041] While the embodiment shown in Figures 5A-5C obtains a significant reduction in VOC concentration during filling of the first tank, the embodiment of Figure 6A obtains a similar reduction while filling not only tank T1 but also tank T3 (i.e., 2 / 3 of the tanks encountered). Overall, a more substantial reduction in VOC emissions can be obtained by increasing the number of tanks in the cluster from 2 to 3.

[0042] In combination with all the embodiments of the present invention, the throttle valves 66a and 66b shown in FIG. 6A and the throttle valve 56 shown in FIG. 5A, 5B allow for individual pressure regulation limited to the tank receiving oil only, to increase the static pressure of the available volumes in the tank during filling. With reference to FIG. 6A, the throttle valve 66a would be used to increase the pressure in T1 (volume 63a) with the throttle valve 66b fully open. With reference to FIG. 6B, the throttle valve 66b would be used to increase the pressure in T3 (volume 63a) with the throttle valve 66a fully closed in order to separate the full tank T1 from the cluster. Also with reference to FIG. 6B, the throttle valve (57) in the common vent mast 50 could be used to increase the pressure in T5 and generally in the entire tank and piping system connected to this vent mast during filling of T5.

[0043] Referring to FIG. 6B, throttle valve 57 is typically used to set a general overpressure for the entire tank system, while local valves such as throttle valve 66b may be set differently to apply higher pressure in a particular tank, if desired.

[0044] 6C shows the situation when tanks T1 and T3 are filled completely or to the desired extent and filling of tank T5 begins via oil supply line 61c. At this stage, throttle valve 66b (not shown) is closed and a direct connection 65b from T3 to 50 is again established. As T5 is the last tank in the cluster and generated VOCs are directly transported via conduit 65c, the VOC concentration in 65c is generally higher in this stage than in the previous two stages.

[0045] Figure 7A is a slightly enlarged view of tank T3 of Figure 6, showing the outlet end of a vapor transfer conduit 64a for vapor entering tank T3 from tank T1 when tank T1 is filled with oil. Vapor transfer conduit 64a enters tank T3 horizontally or at a slight upward incline of up to 10°. The outlet end of vapor transfer conduit 64a is preferably at a height H in the range of 20% to 50% of the height of tank T3.

[0046] FIG. 7B is a plan view of tank T3 of FIG. 7A and shows that vapor transport conduit 64a includes a diffuser element 71 that diffuses the vapor into a fan-shaped flow horizontally and with little vertical diffusion, thereby slowing the flow and allowing the heavier components to travel downward through the tank with minimal agitation or turbulence and the lighter components to travel upward through the tank to the vapor outlet.

[0047] The flow divergence angle is preferably at least 75° horizontally, more preferably greater than 90° and can be up to about 170°, with negligible or preferably less than 10° vertical divergence. The diffuser element 71 is preferably disposed symmetrically with respect to the vertical central axis of the receiving tank.

[0048] The vapor transfer conduit 64a should preferably be located on or near the longitudinal centerline of the cargo tank in which it is installed (e.g., between T1 and T2) to allow symmetrical diffusion of the incoming vapor. This arrangement also reduces the risk of unintended cargo movement due to vessel motion or damaging list angles, and for the same reason, the highest point of the conduit should also be elevated at least one meter above the cargo deck.

[0049] Although the details of Figures 7A and 7B are shown in relation to the three tank cluster shown in Figure 6, the features of Figures 7A, 7B are beneficial with respect to all structural embodiments of the present invention.

[0050] The general nature and characteristics of the present invention are summarized below.

[0051] All of the cargo tanks of the vapor transfer assembly are fluidly connected to a common vent line.

[0052] Preferably all or at least some of the cargo tanks are grouped into clusters as described and illustrated above, the clusters preferably representing a number of tanks between 2 and 4. Preferably, but not necessarily, each cluster represents the same number of tanks.

[0053] The vapor transfer assembly typically encounters a throttle valve on the conduits that transfer vapor between the tanks of the cluster to allow for a constant individual pressure build-up in each tank during filling, thereby combating oil evaporation.

[0054] The advantages of the present invention are due to at least three factors. The first factor is the advantage of the relatively large volume into which the VOCs are initially dispersed, resulting in a slower concentration increase than in smaller volumes. This significantly reduces the amount of VOCs released into the atmosphere when filling the first set of cargo tanks (T1) see Figures 5A, 5B and the first set of two cargo tanks (T1, T3) see Figures 6A, 6B.

[0055] The second factor is the significantly reduced vapor emissions from oil filled into the cargo tanks of the second tank set (to which T3 belongs) see FIG. 5C and the second and third tank sets (T3, T5) see FIG. 6C, caused by increased VOC concentration in the second (and, if applicable, third) tank set due to transfer of tank atmosphere from the most recently filled tank in the first (and, if applicable, second) tank set.

[0056] The third factor is the effect of settling of the relatively heavy VOC vapors at the bottom of the second tank (and, optionally, further tanks) causing the atmosphere leaving the last tank of the cluster to contain reduced amounts of VOCs compared to the average concentration based on evaporation.

[0057] Additionally, the present invention allows for a significantly faster static pressure increase of the tank atmosphere within the cargo tank receiving the oil. Increasing the cargo tank pressure has a well-documented effect in reducing evaporation from the oil, contributing to reducing overall emissions. Although the principles of the present invention have been described in detail with respect to cargo tanks arranged in pairs, it should be generally understood that the general principles of the present invention are applicable to any tank configuration.

Claims

1. 1. A vapor transfer assembly for a plurality of oil tanks (T1, T2, etc.) connected to a common vent pipe (50), which allows atmosphere to be displaced from the tanks (T1, T2, etc.) to avoid excessive pressure buildup within the tanks, comprising:

1. A vapor transfer assembly characterized in that at least some of the tanks (T1, T2, etc.) are grouped into a cluster (C1) of tanks comprising at least two tanks (T1, T3), and a vapor transfer conduit (54, 64a) from at least a first tank (T1) of said cluster (C1) of tanks is connected to a second tank (T3) of the same cluster (C1) so that atmosphere displaced from the first tank (T1) of the cluster (C1) of tanks (C1) travels through the at least second tank (T3) of said cluster (C1) of tanks (T1, T3) before entering a common vent pipe (50), thereby obtaining a slower concentration build-up of volatile organic compounds (VOCs) in the atmosphere entering the common vent pipe (50).

2. The vapor transfer assembly of claim 1, wherein all tanks (T1, T2, etc.) connected to a common vent pipe (50) are grouped into clusters (C1, C2, etc.) of tanks.

3. A vapour transport assembly according to claim 1 or 2, wherein a cluster (C1) or cluster (C1, C2 etc.) of tanks (T1, T2 etc.) represents a number of tanks between 2 and 4.

4. The vapor transport assembly of claim 3 , wherein each cluster (C1, C2, etc.) of tanks (T1, T2, etc.) counts the same number of tanks.

5. 2. The vapor transport assembly of claim 1, wherein a vapor transport conduit (54) from one tank (T1, T3) of a cluster enters a downstream tank (T3, T5) of said cluster at a height in the range of 20% to 50% of the height of said tank (T3).

6. 2. The vapor transfer assembly of claim 1, wherein the vapor transfer conduits (54, 64, 64b) between the tanks (T1, T3, T5) of any cluster (CA) of tanks are provided with throttle valves (56, 66a, 66b) for separately allowing a constant pressure increase in each tank (T1, T3) during filling, thereby counteracting oil evaporation.

7. 7. The vapor transfer assembly of claim 6, wherein the vapor transfer conduit (54, 64a, 64b) enters the next tank (T3, T5) in the cluster horizontally or at a slight upward incline of 10 degrees or less.

8. 2. The vapor transport assembly of claim 1, wherein the vapor transport conduit (54, 64a, 64b) includes a diffuser element (71) at its outlet end arranged to diffuse the vapor flow into a horizontal fan-shaped flow.

9. 9. The vapor transport assembly of claim 8, wherein the diffuser element (71) is arranged to diffuse the flow horizontally at an angle of at least 75 degrees, more preferably at least 90 degrees.

10. 10. A vapor transport assembly according to claim 8 or 9, wherein the diffuser element (71) is arranged symmetrically with respect to the vertical central axis of the receiving tank (T3, T5).

11. 2. The vapor transport assembly of claim 1, wherein the tanks (T1, T2, etc.) are tanks on an oil tanker.

12. 1. A method for filling oil into a plurality of oil tanks (T1, T2, etc.) connected to a common vent pipe (50), wherein the atmosphere above the oil during filling exhibits a gradually increasing amount of oil vapors (VOCs), making it possible to displace atmosphere from the tanks (T1, T2, etc.) in order to avoid excessive pressure buildup in the tanks (T1, T2, etc.), comprising: Grouping at least some of the tanks (T1, T3, etc.) into clusters (C1) of tanks (T1, T3, etc.) comprising at least two tanks (T1, T3), and connecting a vapor transfer conduit (54) from a first tank (T1) of said cluster of tanks (C1) to a second tank (T3) of said cluster of tanks (C1), thereby causing atmosphere displaced from the first tank (T1) to travel through at least the second tank (T3) before entering a common vent line (50), thereby obtaining a slower concentration increase of volatile organic compounds (VOCs) in the atmosphere entering the common vent line (50) from the last tank (TL) of said cluster of tanks (C1).

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