Patent Application
20220347600
The present invention relates to a coalescer for an oil-water separation device for, for example, wastewater treatment.
A coalescer includes a packed bed formed using, for example, resin fibers. The coalescer is installed on a flow path for a treatment target liquid to capture, in the liquid, oil droplets to accumulate into larger droplets. Such larger oil droplets can float easily, leaving the coalescer. This allows separation of oil from water. The mechanism has long been known, as described in, for example, Patent Literature 1, and remains mainstream.
However, oil droplets captured and accumulating inside the packed bed cause more pressure loss in the flow of the target liquid. The target liquid thus uses more driving energy to flow.
At low flow rates, oil droplets to be captured and accumulate inside the packed bed may flow through voids without hitting the packed material. Such oil droplets may flow out of the system without forming larger droplets, thus disabling the coalescer from working effectively. To achieve accurate separation using known coalescers, the flow rate is to be increased to cause fewer oil droplets to flow without hitting the packed material and instead cause oil droplets to hit the packed material under inertia. This causes more pressure loss in the flow and increases the driving energy to be used.
The coalescer described in Patent Literature 1 may also be clogged with oil droplets accumulating (gathering), thus involving relatively frequent regular replacement.
One or more aspects of the present invention are mainly directed to achieving high separation performance and reducing pressure loss and clogging using an oil film to facilitate the coalescence of oil droplets.
In response to the above issue, a coalescer is installable on a flow path for a target liquid to be treated. The coalescer includes an assembly including a sheet of metal mesh. The metal mesh has a surface extending along a flow of the target liquid.
The coalescer with this structure causes oil droplets in the flowing target liquid to form into an oil film on surfaces of the wires of the metal mesh. This facilitates the coalescence of oil droplets on the surfaces of the metal mesh and between the layers of the metal mesh. The oil film of coalescent oil droplets moves downstream along the layers of the metal mesh extending along the flow of the target liquid, forming larger oil droplets at the downstream ends of the mesh layers. The larger oil droplets that can no longer stay on the mesh leave the downstream end of the assembly along the flow.
The coalescer according to one or more aspects of the present invention causes oil droplets in a treatment target liquid to form into an oil film along metal mesh layers extending along the flow of the target liquid to quickly coalesce into larger droplets without accumulating. This causes less pressure loss and decreases the driving energy to be used for the flow. The oil droplets move as the oil film without accumulating and cause less blockage, thus reducing clogging and largely reducing burdensome maintenance.
The coalescer according to one or more aspects of the present invention causes all oil droplets to hit the oil film to achieve high separation performance at low flow rates unlike known coalescers that may cause some oil droplets at low flow rates to flow without hitting the packed material and without forming larger droplets.
An embodiment of the present invention will now be described with reference to the drawings.
An overview of the oil-water separation device 21 will be described, and then the coalescer 11 will be described.
The feed tank 22 stores a target liquid 26 to be treated. The feed tank 22 stores the target liquid 26 from which unintended fine particles have been removed. The oil-water separation device 21 may further include a filter (not shown) for removing fine particles upstream or downstream from the feed tank 22.
The pump 23 pumps the target liquid 26 downstream from the feed tank 22. The pump 23 has a capacity selected in accordance with the scale of the oil-water separation device 21.
The treatment tank 24 treats the target liquid 26 for oil-water separation. The treatment tank 24 has an inlet 24a at the lower end and an outlet 24b at the upper end. The treatment tank 24 defines a flow path 24c for a flow in one direction, or an upward direction. The flow path 24c includes the coalescer 11. The coalescer 11 allows the target liquid 26 pumped by the pump 23 to flow in one direction. The coalescer 11 thus causes fine oil droplets contained in the target liquid 26 to coalesce and form larger oil-droplet particles for easy separation from water.
The collection tank 25 stores the target liquid 26 passing through the treatment tank 24. The larger oil-droplet particles from the treatment tank 24 float on water. Thus, oil (O) and water (W) are separate from each other in the collection tank 25. The water (W) stored below the oil (O) is discharged downward.
The coalescer 11 will now be described in detail.
As shown in
More specifically, as in the plan view of
As in the perspective view of
The coalescer 11 has an inlet surface 11a and an outlet surface 11b opposite to each other and each having a shape corresponding to the cross-sectional shape of the flow path 24c. The inlet surface 11a faces the inlet 24a of the treatment tank 24. The outlet surface 11b faces the outlet 24b of the treatment tank 24. The warp wires 13 or the weft wires 14 extending along the flow of the target liquid 26 each have an end exposed at the inlet surface 11a and the outlet surface 11b. In this embodiment, the warp wires 13 extend along the flow of the target liquid 26. In addition to the inlet surface 11a and the outlet surface 11b, the coalescer 11 has side surfaces 11c in contact with the inner surface of the flow path 24c.
In the coalescer 11 with this structure, the alternate mesh layers 16 and interlayer portions 15 extend along the same plane and are parallel to each other.
The type of metal mesh 12 included in the coalescer 11 is selected in accordance with the type of target liquid 26, and may be a fine stainless steel mesh or a tungsten mesh. The metal mesh 12 may typically be a fine stainless steel mesh with a plain weave, a twill weave, or a thick weave (3D-mesh, registered trademark) of metal fibers having a wire diameter of about 0.01 to 0.2 mm with an aperture of about 0.02 to 0.3 mm. Any of such different types of mesh may be combined as appropriate.
In the oil-water separation device 21 including the coalescer 11 with the above structure, the pump 23 is driven to pump the target liquid 26 from the feed tank 22 to the treatment tank 24, which then causes oil droplets in the target liquid 26 to form larger oil-droplet particles in the manner described below.
As schematically shown in
As shown in
While the oil droplets 31 coalesce one after another into the oil film 32, the oil film 32 moves downstream along the mesh layers 16 and the interlayer portions 15. The oil film 32 forms into larger droplets at the downstream ends of the mesh layers 16. The larger droplets further grow into larger droplets 33 at the ends of either or both of the warp wires 13 and weft wires 14 at the outlet surface 11b until such droplets 33 can no longer stay against the flow of the target liquid 26 and leave the coalescer 11 as larger droplet particles 34.
The larger droplet particles 34 flowing out of the treatment tank 24 easily float on water in the collection tank 25 to form a layer of oil (O) above a layer of water (W) in the collection tank 25.
The oil droplets 31 in the target liquid 26 thus quickly coalesce into the oil film 32 on the surface of the metal mesh 12 and flow downstream as the oil film 32 along the mesh layers 16 and the interlayer portions 15 without accumulating or gathering while passing through the coalescer 11. The oil droplets 31 are not captured or do not accumulate or gather into a lump. The oil film 32 can freely flow downstream through the interlayer portions 15 with less pressure loss. The pump 23 for pumping the target liquid 26 can thus have a smaller capacity and a smaller size.
The oil droplets 31 quickly coalescing into larger droplets allow oil-water separation for the target liquid 26 in a shorter time. The flow path 24c can be shortened to downsize the coalescer 11.
The oil droplets 31 move as the oil film 32 without accumulating as described above, thus allowing a sufficient clearance and space in the coalescer 11 and causing less blockage. This reduces clogging and thus largely reduces burdensome maintenance.
The larger droplet particles 34 resulting from the growing oil droplets 31 form on the outlet surface 11b of the coalescer 11. This allows easy maintenance with any larger droplet particles 34 remaining on the outlet surface 11b, unlike the larger droplet particles 34 forming in the internal clearance.
The coalescer 11 includes an assembly including sheets of metal mesh 12 with the interlayer portions 15 easily defined by the sheets.
The coalescer 11 is formed by stacking sheets of metal mesh 12 and is thus easy to manufacture.
Another embodiment will now be described. The same components herein are given the same reference numerals and will not be described in detail.
The coalescer 11 with this structure has the effects similar to those of the coalescer 11 described above. In particular, the coalescer 11 is formed by rolling a single sheet of metal mesh 12 and thus is easy to manufacture. The coalescer 11 with this structure may include a stack of multiple sheets of metal mesh 12 rolled into an assembly.
The mixer 27 includes appropriate stirrer blades 28 and is located upstream from the coalescer 11. The mixer 27 may be located outside the treatment tank 24.
The oil-water separation device 21 with this structure stirs the target liquid 26 to break and micronize oil droplets immediately before the oil droplets coalesce into larger droplets in the coalescer 11. This allows quicker coalescence through the formation of an oil film in the coalescer 11.
In other words, the structure further facilitates the coalescence of oil droplets, forming larger droplet particles with a shorter flow path 24c. The coalescer 11 can thus be downsized further, in addition to having the same effects as described above.
To verify the separation performance for oil droplets, the experiment below was conducted.
In the experiment, a sample containing oil droplets was pumped by a tube pump, passed through the coalescer, and then collected. The absorbance of the sample before being pumped by the tube pump, or in other words, a feed liquid, was measured. The absorbance of the collected sample, or in other words, a collected liquid, was also measured. The measurement results were used to calculate the degree of separation measured with visible light.
The degree of separation measured with visible light was calculated using Formula 1 below.
The absorbance of the feed liquid and the absorbance of the collected liquid were used to calculate an exponential approximation curve, which was then used to examine the degree of separation measured with visible light (degree of separation).
A pressure transducer was used to measure the pressure (inlet voltage) of the liquid before entering the coalescer and the pressure (outlet voltage) of the liquid after exiting the coalescer. The measurement results were used to calculate the inlet pressure and the outlet pressure. The outlet pressure was then subtracted from the inlet pressure to calculate the pressure loss.
The sample was prepared by adding 3 milliliters of tetradecane to 1.5 liters of deionized water and emulsified using an ultrasonic irradiator with a horn.
The sample was pumped by the pump continuously and measured in the manner described above in multiple stages over time from immediately after the emulsification. The multiple stages are the 11 stages shown in Table 1. The tube pump has a capacity of 80 mL/min and 173 kPa.
The coalescer includes 158 sheets of plain weave stainless steel mesh (380 mesh, 20-mm square) stacked flat to be substantially rectangular. The coalescer was packed in a rectangular flow path with a length of 20 mm, a width of 20 mm, and a height of 3 mm.
In experiments of comparative examples, coalescers described below were each packed in the same flow path. The coalescer in comparative example 1 was packed with fibers of Teflon (registered trademark) or polytetrafluoroethylene (PTFE) with a wire diameter of 10 to 50 μm at a packing factor of 0.4. The coalescer in comparative example 2 was packed with fibers of polypropylene (PP) with an average wire diameter of 16 μm at a packing factor of 0.4. The coalescer in comparative example 3 was packed with polyurethane (PU) foam.
Table 1 shows the results of the experiment using the coalescer according to the embodiment of the present invention.
In Table 1, Run indicates the 11 stages described above, Cin indicates the absorbance of the feed liquid, Cin.fitting indicates the exponent, Cout indicates the absorbance of the collected liquid, Vp1 indicates the inlet voltage, Vp2 indicates the outlet voltage, Pin indicates the inlet pressure, Pout indicates the outlet pressure, and ΔP indicates the pressure loss.
For all of Run 1 to Run 11, the degree of separation was higher than 0.9, which was very high, with any pressure loss.
The exponential approximation curve for the absorbance of the feed liquid indicated by the dashed line in
The device in the embodiment of the present invention achieves high separation performance at low pressure losses. The device thus allows oil droplets to form larger droplets effectively at low flow rates, unlike the known technique that may cause oil droplets to flow without hitting the packed material at low flow rates and fail to form larger droplets and cause a low degree of separation.
The coalescers in the comparative examples yielded results largely different from the results for the coalescer according to the embodiment of the present invention.
In each of comparative examples 1 and 2, the pressure loss is between 10 kPa and 20 kPa, revealing the separation performance achieved for a specific operating range.
In comparative example 3, the degree of separation is about 0.2, which is much lower than in comparative examples 1 and 2.
The above experiments reveal that the coalescer according to the embodiment of the present invention allows a high degree of oil-water separation for a wide operating range.
The structure described above is an embodiment of the present invention. The present invention is not limited to the structure but may be modified.
For example, the assembly of the metal mesh 12 may include multiple sheets of metal mesh 12 stacked in multiple directions. In some embodiments, the assembly may include a bundle of multiple rolls of sheets of metal mesh 12.
The metal mesh 12 may undergo any treatment that increases lipophilicity, such as silica coating.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-115271 | Jun 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/019940 | 5/20/2020 | WO |
