Apparatus for reintroducing vapor into a volatile liquid

Abstract

The device for reintroducing steam into a volatile liquid comprises a tank (10) for the volatile liquid, a circulation pump (14) and connecting conduits (13, 113, 213) for pumping liquid from said tank (10) through a mixing zone or mixing device (12, 112, 212) for mixing the steam with the liquid, and a conduit (15, 115, 215) for conveying steam from the space above the level of the liquid to said mixing zone or mixing device (12, 112, 212), the mixing zone or mixing device (12, 112, 212) being arranged to ensure a pressure independent of the level of the liquid in the tank (10).

Description

[Technical Field]

[0001] The present invention relates to an apparatus for reintroducing / absorb- ing vapors from volatile liquids, in particular for reintroducing oil vapors into oil in the cargo tanks of tank ships. [Background technology]

[0002] The transportation of volatile and flammable fluids such as oil in large tanks on tank ships can result in cargo losses if vapours released from the oil are not captured and / or reintroduced into the oil, and also pose a risk of fire or explosion as such vapours are highly flammable.

[0003] These vapors establish equilibrium with the corresponding components in the liquid phase under a certain overpressure in the tank. However, the pressure required to reach such equilibrium is higher than the current tank design pressures of oil tankers, making it neither practical nor economically feasible to design a ship capable of meeting this pressure requirement. Generally, vapors emitted from oil cargoes are referred to as "volatile organic compounds" (VOCs).

[0004] Attempts have been made in many different ways to overcome the above mentioned problems. Norwegian Patent No. 316 045, U.S. Patent No. 6,786,063 and U.S. Patent No. 3,003,325 describe systems and devices that use equipment located outside the storage tank, and Norwegian Patents Nos. 315 293 and 315 417 describe systems integrated into the tank. A more recent solution is described in WO 2007086751. Summary of the Invention [Problem to be solved by the invention]

[0005] Lack of efficiency at low or medium oil levels in cargo tanks is a common drawback of conventional systems that do not function optimally unless the tank is nearly full. Improvements are needed in this area of ​​technology to further reduce losses and improve safety associated with transporting oil in oil tankers.

[0006] It is therefore an object of the present invention to provide an apparatus for absorbing vapor from a volatile liquid that is efficient, inexpensive, and eliminates the inherent drawbacks of existing solutions. The apparatus should be easy to manufacture, easy to maintain, easy to operate, and inexpensive.

[0007] In particular, it is an object to provide a method for reintroducing oil vapor evaporated from oil into the oil in the cargo tank of an oil tanker. [Means for solving the problem]

[0008] This object is achieved by the device according to the invention as defined in claim 1.

[0009] Preferred embodiments are disclosed in the dependent claims.

[0010] The main advantage of the present invention resides in the fact that the reintroduction of vapor into the volatile liquid occurs at a pressure exerted by a column of volatile liquid that is maintained independently of the level of liquid in any tank to which the device is connected.

[0011] Some embodiments of the present invention include vertical and horizontal columns that are oriented slightly different from strictly vertical and strictly horizontal, respectively. composition This may be done.

[0012] In the further description, the terms "volatile liquid", "liquid" and "oil" are used interchangeably and, unless otherwise specified, refer to the liquid form of the volatile liquid described in the appended claims.

[0013] The invention will now be explained in more detail in the form of non-limiting embodiments illustrated by the accompanying drawings, in which: FIG. [Brief explanation of the drawings]

[0014] [Figure 1A] FIG. 1A is a diagram of a first embodiment of the present invention in the early stages of cargo tank filling. [Figure 1B] FIG. 1B is a view similar to FIG. 1 at a later stage of cargo tank filling. [Figure 2] FIG. 2 is a diagram of a second embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional side view of one component of FIG. [Figure 4] FIG. 4 is a cross-sectional side view of the assembly of the two components of FIG. [Figure 5] FIG. 5 is a side cross-sectional view of an alternative component to one of the components of FIG. [Figure 6A] FIG. 6A illustrates an embodiment of the present invention that includes variations on the components shown in FIG. [Figure 6B] FIG. 6B illustrates an embodiment of the present invention that includes variations on the components shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention requires a system, such as the apparatus according to WO2007086751, for reintroducing volatile vapors into the liquid used as the absorption medium. Other embodiments of such a reintroduction system may include a fan, pump, or compressor, preferably in combination with a microbubble generator, for the supply of gas, and a pump for circulating the absorption medium liquid through the column. For simplicity, an ejector-type mixing device (similar to that of WO2007086751) will be used as the primary example for all embodiments of the invention described herein. This device will hereinafter be referred to as the "mixing device."

[0016] 1A shows a portion of a tank 10 having a bottom wall 101 and a top wall 102. Within the tank is a vertical liquid-tight tube or column 11. composition The mixing device 12 is located adjacent to the bottom of the vertical column 11. composition The mixing device 12 is adapted to be filled with oil supplied by a pump 14 from a location adjacent the tank bottom 101. composition The oil flow 13 is used to extract vapor 15 from the space above the liquid. The flow of vapor 15 may be assisted by an optional pump, fan or compressor 16.

[0017] The space above the liquid from which the volatile vapor is extracted is typically the space within the tank, but may also be the space from any space or conduit to which the vapor is directed after evaporation.

[0018] The combined flow 17 of liquid and entrained vapor bubbles leaves the mixer 12 adjacent the bottom of the column 11, where the pressure of the liquid above causes the vapor bubbles to condense into liquid. This mixer unit (assuming an ejector-type device) is configured to direct a jet of liquid vertically downward from its outlet toward the bottom of the column 11. composition The maximum distance to the bottom should be small enough so that the jet can carry the entrained air bubbles to the bottom.

[0019] The recommended distance from the outlet of the mixing unit to the bottom plate is typically in the range of 2-5 m, depending on the flow rate. Other types of mixing units, e.g., microbubble generators, are often located at or close to the bottom of the column 11 to ensure maximum hydrostatic pressure available for efficient condensation of the bubbles. composition It should be.

[0020] The function of the vertical column 11 is to quickly achieve a pressure in the mixer 12 at least similar to that of a full cargo tank, even if the tank is less than full or nearly empty. The conduit 18 is designed to conduct oil from the top of the column to the surrounding cargo tanks without splashing, even if the tank is nearly empty. compositionIn Figure 1A, the cargo tank is filled to less than 10% but still achieves the desired pressure conditions within the mixing device.

[0021] For operational purposes, column 11 has an outlet 19 near the bottom of the column. An isolation valve 20 at outlet 19 is closed when pump 14 is on and the system is running, but may be opened to gravity drain column 11 when tank 10 is emptying. To avoid a lack of pressure in column 11 during gravity drain, conduit 21 connects the top of the column to the top of tank 10 when valve 22 is open. Gas from tank 10 can then flow into the column and displace liquid. Valve 22 is closed when pump 14 is on and the system is running.

[0022] Figure 1B shows the same configuration when the cargo tank is filled to a higher level of about 75%. The conditions regarding the pressure in the mixer remain the same, and the level of oil in the cargo tank is not a condition, only the level of oil in the vertical column is a condition.

[0023] The vertical column 11 is physically located within the tank 10. composition Although shown as a column outside the tank, but fluidly connected to the tank, in the manner generally taught by the above description, composition You may do so.

[0024] Generally speaking, the mixing device 12 is placed in a liquid-tight vertical column 11 that is filled with liquid to a level independent of the level in the tank 10. composition This ensures a desired pressure in the mixing device independent of the level of liquid in the tank 10.

[0025] Assuming an ejector type mixing unit similar to that of WO 2007086751, the outlet of the mixing device 12 is typically located 2 to 5 m above the bottom of the liquid-tight vertical column 11. compositionIn this case, the outlet of the mixing device 12 also typically has a central axis aligned with the central axis of the column 11, and this outlet faces vertically downward toward the bottom of the column 11. For other methods of reintroducing volatile vapors into a liquid used as an absorption medium, the mixing / gas introduction unit is preferably located close to the bottom of the vertical column 11 to optimize the effective absorption pressure. composition It may be more advantageous to do so.

[0026] FIG. 2 shows a significantly different embodiment from that of FIGS. 1A and 1B, but with a tank wall 101 adjacent to it. composition The pressure advantage at the outlet of the mixer 112 is approximately the same. The mixer 112 is filled with oil 113 supplied by a pump 114 from a location close to the tank bottom 101. composition The oil flow 113 is used to extract vapor 115 from the space above the liquid.

[0027] The combined stream of liquid and entrained vapor bubbles from mixer 112 enters horizontal column 116, which extends substantially horizontally along bottom wall 101. The column outlet is attached to conduit 117, which extends to a position near or preferably above top wall 102 of the tank. During operation, conduit 117 is filled with oil, so that the pressure within the horizontal column is determined by the vertical extent of conduit 117. An optional gas separation unit 119 may be installed at or near the top of conduit 117 to remove any remaining air bubbles if, for some reason, not all of the air bubbles are absorbed by the oil. composition The conduit 117 then continues to a lower level in the tank 10 through an optional drop line 111, which will not be described in detail here.

[0028] This proposed configuration allows the vapor bubbles to intimately mix with the liquid at elevated pressure for a longer period of time compared to the first embodiment, thereby also enhancing mass transfer (condensation) from the vapor to the liquid. In general, the parameters for the efficiency of this second embodiment of the invention are the pressure emerging from conduit 117, the diameter and length of horizontal column 116 following the mixer, the volumetric flow rate per cross-sectional area, and the residence time occurring at elevated pressure downstream of mixer 112.

[0029] The arrangement described above with reference to FIG. 2 ensures a desired pressure in the mixing device 112, which is independent of the level of liquid in the tank 10 and which is typically at least equal to the pressure of a tank filled with oil.

[0030] The mixer 112 is separate from the horizontal column 116. composition or may be combined with column 116 to form an integral unit.

[0031] For the configuration depicted in FIG. 1, it is recommended that both the outlet near the bottom of column 116 and the gas supply conduit from the top of tank 10 be equipped with isolation valves for gravity drain of the system.

[0032] FIG. 3 is a cross-sectional side view of a mixing device 112 in the form of an ejector useful in the present system. This mixing device is similar to that described in WO2007086751. The mixing device 112 has an inlet on the left side in the form of a through-opening 31 through which liquid oil 113 is filled, providing the driving force for the ejector as it moves from left to right at a significant velocity. Steam enters the mixing device laterally as a stream 115 into an annular space 32 surrounding the through-opening 31, where it is drawn into the liquid stream by the suction force created by the moving liquid. The annular opening between the space 32 and the tube section 33 can optionally contain static vane blades to create a helical flow. The advantage of such a helical flow is improved dispersion of steam bubbles in the liquid stream.

[0033] A drawback of the second embodiment is that due to the density difference between the liquid and the vapor, vapor bubbles tend to accumulate at the top of the horizontal absorption column 116, causing many fine bubbles to coalesce into fewer larger bubbles, reducing the contact area between the vapor and the liquid.

[0034] This potentially negative effect can be counteracted by introducing one or more sections containing curved or angled vane blades 41, 42, as shown in Figure 4. When multiple sections are introduced, the horizontal column 116 is divided into multiple segments 1161, 1162, as shown in Figure 4. The vane blades according to Figure 4 are only at the inlet end of each segment 1161, 1162, respectively. composition However, there are composition It may also have an extension over the entire section.

[0035] The configuration according to Figure 4 converts the linear flow motion into a spiral flow motion, providing a velocity component transverse to the axis of the column that is greater than the effect of the upward force on the bubbles caused by the density difference between the liquid and vapor. An additional feature of such rotational flow is the outward gravitational effect, which brings the heavier liquid to the outside and the lighter vapor to the inside of the center of the column within the horizontal column 116. Note that the reference numeral 116 is used to refer commonly to a single horizontal column 116 and to a column consisting of multiple horizontal column sections, such as column sections 1161 and 1162. The horizontal column 116 shown in Figure 4 has a longitudinal axis z.

[0036] Figure 5 is a cross-sectional side view of a mixer 212 that uses a different principle than mixer 112 of Figure 3. Liquid stream 113 enters the mixer from the left, and vapor stream 115 enters the mixer through pipe 51 with perforated section 52 within the mixer, causing the vapor to entrain as small bubbles into the liquid stream. Although not shown in Figure 5, horizontal column section 116 is downstream of mixer 212 in a manner similar to that shown in Figure 4. composition FIG. 6A shows a vertical column 11 of the type shown in FIGS. composition5. In this case, no housing such as 212 in FIG. 5 is required, and the conduit 15 conveying the vapor from the top of the tank has a perforated end or perforated box 62 which serves the same purpose as the perforated section 52 shown in FIG. 5. composition The pump 14 pumps the oil toward the perforated section or box 62, which increases the efficiency of the steam entrainment and condensation.

[0037] Figure 6B is an enlarged view of the lower part of the vertical column 11 and the surrounding area of ​​Figure 5, showing the mixing zone 63 as a circle, where the steam bubbles from the perforated box 62 come into contact with the oil entrained therein. Of course, this zone has no clear boundary.

[0038] All embodiments of the present invention may be advantageously combined with other devices that are not part of the present invention, such as drop line devices configured to reduce evaporation from volatile liquids during tank filling, or gas-liquid separators to remove any remaining gas bubbles in the liquid before it is reintroduced into the cargo tank.

Claims

1. 1. An apparatus for reintroducing vapor into a volatile liquid, comprising: a tank (10) for a volatile liquid; a circulation pump (14) and connected conduits (13, 113, 213) for pumping the liquid from the tank (10) through a mixing zone or device (12, 112, 212) for mixing the vapor with the liquid; a conduit (15, 115, 215) for conveying vapor from the space above the liquid level to the mixing zone or mixer (12, 112, 212); Including, The apparatus, wherein the mixing zone or mixing device (12, 112, 212) is configured to ensure an internal pressure independent of the level of the liquid in the tank (10).

2. 2. The apparatus according to claim 1, wherein the mixing device (12) is configured to be in a liquid-tight vertical column (11) filled with the liquid to a level independent of the level in the tank (10), thereby ensuring the desired pressure.

3. 3. The apparatus of claim 2, wherein the mixing device (12) is configured to be less than 5 meters and preferably more than 2 meters from the bottom of the vertical column (11), the column being configured to be within the tank (10), the column having an upper end in fluid communication (18) with the body of the tank (10).

4. 4. The apparatus according to claim 1, wherein the central axis of the outlet of the mixing device (12) is aligned with the central axis of the column, and the outlet faces vertically downwards towards the bottom of the vertical column (11).

5. 2. The apparatus according to claim 1, wherein the mixing device (112, 212) is configured adjacent to the bottom (101) of the tank (10), the outlet of the mixing device (112, 212) is connected to a horizontal column (116) configured adjacent to the bottom (101) of the tank (10), the horizontal column (116) extending upward to a vertical height higher than the vertical height of the mixing device (112, 212) and the vertical height is independent of the level of the liquid in the tank (10), thereby ensuring the desired pressure.

6. The apparatus of claim 5, wherein the mixing device (112, 212) is configured to be separate from the horizontal column (116).

7. 6. The apparatus of claim 5, wherein the mixing device (112, 212) is combined with the horizontal column (116) to form an integral unit.

8. 8. The apparatus of claim 5, wherein the horizontal column (116) comprises one or more sections including static vane blades (41, 42) configured to induce vortices in a flow entering the horizontal column (116).

9. 9. The device according to claim 8, wherein the vane blades (41, 42) are inclined with respect to the longitudinal axis (z) of the horizontal column (116) and / or curved to extend in the longitudinal direction thereof.

10. The apparatus according to any one of claims 5 to 7, wherein a gas separation unit (119) is arranged on the conduit (117) from the horizontal column (116).

11. Apparatus according to any one of claims 5 to 7, wherein the conduits (117) from the horizontal columns (116) terminate in drop lines (111).

12. 8. Apparatus according to any one of claims 5 to 7, wherein the conduit (15) is configured to convey the vapor to a perforated end or box (62) arranged at the bottom of the vertical column (11), and the conduit (13) is configured to pump the liquid to a zone (63) surrounding the end or box (62).

13. 8. Apparatus according to any one of claims 1 to 3 or 5 to 7, configured to maintain an overpressure of at least 1 bar, more preferably at least 1.5 bar, most preferably at least 5 bar compared to ambient pressure.

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