Liquid loading assembly for filling holds or tanks

Abstract

A liquid loading assembly for filling a hold or tank (12) with a volatile liquid includes an oil supply conduit (11) fluidly connected to the tank (12), the outlet end (111) of the conduit (11) extending vertically within a drop line (13). The drop line extends from a drop line lower end (131) located below the oil supply conduit outlet end (111) to a drop line upper end (132) located above the oil supply conduit outlet end (111), the drop line lower end (131) being at least partially blocked by a valve (14). The valve (14) is configured to gradually open to a maximum opening in response to either i) an increase in pressure on the valve (14) or ii) the level of liquid above the valve.

Description

[Technical field]

[0001] The present invention relates to an assembly for loading oil into a tanker in a manner that reduces the release of oil vapours by flashing in the cargo transfer piping system. More specifically, the present invention relates to an assembly as defined in the preamble of claim 1. [Background technology]

[0002] background Flashing of light end hydrocarbon components from oil during cargo transfer is a major contributor to Volatile Organic Compounds (VOC) emissions from tankers and typically occurs upstream of vertical drops and downstream of nozzles or other flow disturbances in the cargo transfer piping system. During cargo transfer operations, the oil flows through pumps, piping bends, valves, metering skids, and piping at various heights. All these obstacles contribute to the emission of gases (VOCs) from the oil. Some of the gas is reabsorbed in the oil and some is carried into the cargo transfer system as bubbles in the two-phase flow.

[0003] Gas bubbles from the two-phase flow eventually rise to the surface and are released into the tank atmosphere as VOCs. On their way to the surface, these gas bubbles cause a stripping effect that further increases the release of VOCs from the oil. Once at the surface, the gas bubbles vigorously agitate the oil / tank atmosphere interface, further increasing the release of VOCs from the oil.

[0004] Most of this hydrocarbon vapour is generated by flashing at the top of conventional drop lines, vertical oil supply conduits used to transfer oil directly from deck level to the bottom of the cargo tanks, or to connect the deck level cargo transfer lines to the tanker's bottom distribution system and direct the oil to the individual cargo tanks. Typical heights for such drop lines are 20-30m.

[0005] Oil in the vertical section of the oil supply conduit accelerates due to gravity, creating a siphon effect that results in an undesirable pressure drop at the top of the conduit. This behavior is due to the natural property of fluids to flow according to known principles of fluid dynamics, e.g., Bernoulli's equation. A common problem associated with this is the excessive emission of VOCs due to the pressure drop.

[0006] EP 1 463 683 B1 (patent no. 315417) teaches a method for reducing the evaporation of VOCs during the loading of liquid petroleum products into cargo or storage tanks. The core of this method is the use of a supply pipe terminating in a loading column having a cross-sectional area significantly larger than that of the supply pipe.

[0007] Other publications in this field include EP 1 576 313 B1, EP 1 373 062 B1, and EP 1 509 721 A1. Summary of the Invention

[0008] the purpose It is therefore an object of the present invention to provide a system, apparatus, method, or assembly that significantly reduces VOC evaporation from oil as it is loaded into a tanker.

[0009] The present invention The liquid loading assembly according to the present invention as defined by claim 1 satisfies the above mentioned objectives.

[0010] Preferred embodiments are disclosed by the dependent claims.

[0011] The present invention uses a flow control valve at the outlet to raise the liquid level in a vertical drop line surrounding the oil supply conduit, which extends from the top of the cargo tank to nearly the bottom. The increased liquid level significantly reduces the drop height in the oil supply conduit, thus significantly reducing the siphon effect and VOC emissions from the oil.

[0012] The assembly according to the invention also reduces the formation and splashing of air bubbles due to the fact that the drop line fills up to and above the level of the free end of the oil supply conduit in a very short time and due to the location and function of the flow control valve combined with the outlet piping design at the lower end of the drop line.

[0013] Furthermore, once the supply conduit is submerged in oil, any vapor released at the top of the vertical oil supply conduit must overcome hydrostatic pressure at the conduit exit. As more vapor is released from the oil stream, the gas pressure within the oil supply conduit is expected to increase, thereby further reducing the typical low pressure region at the top of the oil supply conduit.

[0014] Close proximity as used herein is usually understood to mean a (distance) of less than 2 m, more preferably less than 1 m, even more preferably less than 0.5 m.

[0015] By combining the present invention with a gas / liquid separation device (commercially available technology, not part of this invention), the majority of the gas bubbles generated in the oil supply conduit before the drop line, which typically includes the portion of the oil supply conduit outside of an oil tanker from an oil terminal, floating storage vessel, or production platform, can be removed from the oil in the supply conduit, further reducing this source of VOC emissions.

[0016] In the following, the invention will be explained in more detail in the form of non-limiting exemplary embodiments illustrated by the drawings. [Brief description of the drawings]

[0017] [Figure 1] FIG. 2 is a cross-sectional view of one embodiment of a drop line having a first fluid according to the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of one embodiment of a drop line using a second fluid according to the present invention. [Diagram 3] FIG. 2 is a cross-sectional view of one embodiment of a drop line with a bypass conduit and a sensor-based control system in accordance with the present invention. [Figure 4] FIG. 4 is a cross-sectional view showing a modification of the embodiment shown in FIG. [Diagram 5] FIG. 1 is a cross-sectional view of a series of tanks with drop lines in accordance with the present invention in combination with a cargo distribution system for filling the individual cargo tanks. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] 1 is a cross-sectional view of one embodiment of a liquid loading assembly according to the present invention. The oil-filled assembly 10 mainly comprises a lower portion of an oil supply conduit 11 having an outlet end 111, surrounded by a drop line 13, the latter being terminated by a valve 14, the function of which will be explained below. The apparatus is disposed within an oil tank 12 having a bottom wall 121 and a top wall 122.

[0019] One problem of the present invention is to regulate the flow rate through the valve 14. A typical configuration is to use an actuated valve together with a control system and sensor based level monitoring of the drop line 13. This can also be solved mechanically with the valve opened by hydraulic pressure acting on a pressure spring assisted closure member, which is the preferred valve design for this invention.

[0020] If the valve 14 includes a pressure spring, the spring is designed to hold the closure member in the closed position when the drop line is empty, but is unable to hold the closure member in the closed position when the drop line is filled to a level above the outlet end 111 of the oil supply conduit 11 with a volatile fluid, typically with a density greater than 0.6 kg / l.

[0021] As shown in FIG. 1, the liquid level 15 in the drop line is very high, at a height H above the outlet end 111 of the oil supply conduit 11. T1 , indicating that the liquid has a relatively low density and requires a significant height of liquid to fully open the valve 14.

[0022] As also shown in FIG. 1, the oil supply conduit 11 only extends a significant distance OSCv, at least 4 m, preferably 6-8 m above the lower end of the drop line, to a position 111, to limit disturbances around the outlet valve 14 caused by the incoming oil flow.

[0023] In order to avoid local pressure drops or siphon effects at the outlet of the drop line, the outlet of the valve 14 is located at a small distance D from the bottom wall 121 of the tank. v , typically 1-2 m, and not exceeding 3 m. To the outlet end of the valve 14 is shown connected a non-essential conduit 18. Depending on the vessel configuration, the conduit 18 may be routed to a common load distribution system, as shown in Figure 5, or may be used directly as a horizontal outlet with a vertical distance of 0.25-0.5 m from the tank bottom, thereby reducing splashing of oil being loaded into the tank 12.

[0024] As a precaution, valve 14 includes a closure member configured to ensure a limited open fluid passageway even in the normally designated closed position.

[0025] As indicated above, it is also an option or alternative in the general aspect of the invention to control the opening of the valve terminating the drop line 13 by means other than the liquid pressure acting thereon, for example a level sensor that continuously monitors the liquid level in the drop line 13 and in combination with a control system causes the valve to open more and more as the liquid level in the drop line 13 rises. In that way, a sensor-based system attempts to keep the liquid level approximately constant, as in the case of a pressure-determined valve. The advantage of a sensor-based system is that the liquid level is independent of the density of the liquid, but the disadvantage is that it is more complex and there is a higher risk of failure in the sensor itself or in the control system and connections to the valve.

[0026] The drop line 13 extends to its upper end 132 above the top 122 of the tank 12. Near the upper end 132 of the drop line 13, an assembly including piping 16 and a check valve 17 is disposed to allow vapor from the top of the tank 12 to enter the drop line 13. The check valve 17 ensures that vapor cannot pass in the opposite direction. This ensures that the gas pressure above the liquid level 15 in the drop line 13 is always higher than or equal to the gas pressure in the surrounding tank 12, which is usually useful to avoid pressure starvation during gravity drain of the drop line 13.

[0027] FIG. 2 is in most respects the same as FIG. 1, with one exception: for the type in which the valve is opened by hydraulic pressure acting on it, the liquid level 15 in the tube is lower and there is a height H above the outlet end 111 of the oil supply conduit 11. T2 2, showing the denser liquid. Another exception is the different embodiment of the tubing 16 and check valve 17 assembly, which in FIG. 2 further includes a conduit 19 with a closeable valve 20. This arrangement allows the atmosphere inside the drop line 13 to be replaced with an inert gas or breathable air for inspection or maintenance.

[0028] The main feature of both alternatives is that the loading of a volatile liquid, typically oil, can be carried out in a controlled and tolerant manner already when the tank is empty or nearly empty. The liquid level 15 above the free end 111 of the oil supply conduit 11 ensures that the liquid is added under slight pressure, while the valve 14 placed low in the tank 12 ensures that there is little or no splashing of liquid from the drop line 13 or conduit 18 which would cause excessive evaporation.

[0029] FIG. 3 shows an embodiment of the invention in which the oil-filled assembly 10' is configured slightly differently. It is similar in most respects to FIG. 1 and FIG. 2, with one exception being a sensor 31 that continuously monitors the liquid level in the drop line 13 and, in combination with a control unit 32, causes the valve 14 to open more and more as the liquid level in the tube rises, and vice versa. In that way, the sensor-based system attempts to keep the liquid level approximately constant, as does a pressure-determined valve. Another exception is a bypass conduit 30 that has an inlet from the top of the drop line 13 just below the top wall 122 of the tank 12, and an outlet close to the bottom wall 121 of the tank 12. In FIG. 3, the bypass conduit 30 is shown connected to conduit 18. This is a possibility, not a requirement. If for any reason, such as a sensor failure, the liquid level in the drop line 13 rises above the bypass conduit inlet, the oil will simply flow through the bypass conduit 30 to the cargo tank, or to the cargo distribution system, depending on the piping arrangement. The bypass conduit has no restrictions, valves, or monitoring of any kind and is therefore free of failure possibilities. Although the bypass conduit 30 may be used in any embodiment of the invention, it is generally more useful in a sensor-based system such as that described in FIG. 3, as it is expected to be at higher risk of failure than gravity-actuated flow control devices.

[0030] Although the embodiment illustrated in Figures 1-3 shows valve 14 connected to conduit 18, valve 14 may in other embodiments comprise the terminus of a drop line that is not connected to a conduit or other piping.

[0031] Figure 4 is a cross-sectional view of an embodiment of the invention in which an oil filling assembly 10' is located outside the cargo tank. An outlet conduit 41 from the valve 14 is connected to the tank 12 adjacent to its bottom wall. The oil filling assembly 10' of Figure 4 is similar to that of Figure 3, but can also be located outside the tank 12 in the embodiment shown in Figures 1 and 2. The embodiment of Figure 4 can be combined with assemblies 16, 17, 19, 20 as shown in Figures 2 and 3 and / or with the bypass conduit 30 of Figure 3.

[0032] FIG. 5 is a cross-sectional view of a series of tanks T1, T2, T3, with one oil-filled assembly according to the invention, more specifically with that shown in FIG. 3. It should be noted that the dimensions of the tanks T1-T3 in FIG. 5 are not to scale with respect to the dimensions of the oil-filled assembly. A special feature of this design is the distribution pipe 51 between the tanks, allowing distribution to several tanks from a common drop line. The distribution pipe 51 typically comprises a valve 52 in each tank to determine which tank is to be loaded. A person skilled in the art will understand that such a distribution pipe does not have to be connected to the outlet valve of the oil-filled assembly. On the other hand, the same distribution pipe may be connected to several drop lines / oil-filled assemblies. Moreover, such a distribution pipe can also be applied in combination with one or more oil-filled assemblies arranged outside the tank, as shown in FIG. 4.

[0033] While the advantages commented above are common to all embodiments of the present invention, the specific features illustrated in the drawings are merely embodiments of the present invention, the scope of which is defined solely by the appended claims.

Claims

1. A liquid loading assembly for filling a ship's hold or tank (12) with a volatile liquid, the apparatus comprising:

1. A liquid loading assembly comprising: an oil supply conduit (11) fluidly connected to a tank (12), the conduit (11) having an outlet end (111) extending vertically within a drop line (13), the drop line (13) extending from a drop line lower end (131) located below the outlet end (111) of the oil supply conduit to an upper end (132) located above the outlet end (111) of the oil supply conduit, the drop line lower end (131) being at least partially blocked by a valve (14), the valve being arranged to gradually open to a maximum opening in response to one of: i) an increase in liquid pressure on the valve (14); and ii) a liquid level above the valve.

2. The outlet end (111) of the oil supply conduit (11) is at a vertical distance (OSC) of at least 4 m above the lower end of the drop line (13). Ｖ 10. The liquid loading assembly of claim 1, wherein the liquid loading assembly is disposed on a

3. 3. A liquid loading assembly according to claim 1 or 2, wherein the outlet of the valve (14) at the lower end of the drop line is located in a range of 3 m or less, preferably 1 to 3 m above the bottom wall (121) of the tank (12).

4. 2. The liquid loading assembly of claim 1, wherein the valve (14) is arranged with the closure member arranged to open in accordance with at least one of the following mechanisms: i) a pressure spring acting against the pressure of the liquid in the drop line (13); and ii) a level sensor in communication with a control system arranged to open the closure member sufficiently to maintain the liquid level in the drop line (13) at a substantially constant level.

5. 5. A liquid loading assembly according to claim 4, wherein if the mechanism includes a pressure spring, the spring is designed to hold the closure member in a closed position when the drop line is empty, but is unable to hold the closure member in a closed position when the drop line is filled with a volatile fluid having a density higher than 0.6 kg / l up to a level above the outlet end (111) of the oil supply conduit (11).

6. 2. The liquid loading assembly of claim 1, wherein the valve (14) comprises a closure member arranged to ensure a limited open fluid passageway even in the designated closed position.

7. 2. The liquid loading assembly of claim 1, wherein the valve (14) is designed to have maximum opening and closing forces adapted to maintain the fluid to be filled in the drop line (13) at a constant level during filling, the level being dependent on the density of the fluid.

8. 2. The liquid loading assembly of claim 1, wherein the bypass conduit (30) has an inlet adjacent to the top wall (122) of the tank (12) from the drop line (13) and an outlet adjacent to the bottom wall (121) of the tank (12) or an inlet to a common distribution pipe (51).

9. 2. The liquid loading assembly of claim 1, wherein an assembly (16) having a check valve (17) is disposed between the top of the drop line (13) and the tank (12) to allow vapor to flow from the tank to the drop line but not from the drop line to the tank.

10. 2. The liquid loading assembly of claim 1, wherein the valve (14) is connected to a conduit (18) having an outlet end adjacent the bottom (121) of the tank (12).

11. 11. A liquid loading assembly according to claim 10, wherein the conduit (18) is connected to a distribution pipe (51) extending through a plurality of tanks.

12. The outlet end (111) of the conduit (11) is disposed within the tank (12). The liquid loading assembly of claim 1 .

13. 3. A liquid loading assembly as claimed in claim 1 or 2, wherein the outlet end (111) of the conduit (11) and the drop line (13) are located outside the tank, while an outlet conduit (41) from the valve (14) is connected to the tank (12) adjacent to the bottom wall (121) of the tank (12).

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