RESIN DEGASSING

Abstract

Disclosed are processes and systems for degassing liquid resin. Resin is provided at a resin inlet and pumped into a first duct using a resin pump to achieve a first absolute pressure of at least 1.6 bar in the first duct; the resin pump and/or a flow control valve are configured to achieve a first pressure drop across the flow control valve of at least 1.5 bar; a second duct communicates the resin from the flow control valve to a storage tank; a gas evacuation system maintains a pressure in the storage tank below 100 mbar at least partly concurrently with pumping resin into the first duct.

Claims

1. A process for degassing a liquid resin in a degassing system, the degassing system comprising: a first duct (205) having a resin inlet (202) for receiving liquid resin to be degassed, a resin pump (203) for pumping liquid resin into the first duct (205) via the resin inlet (202), a flow control valve (208) arranged at a downstream end of the first duct (205), configured to control a flow rate of resin through the first duct and configured or configurable to provide a pressure drop of at least 1.5 bar across the flow control valve (208), a second duct (211, 311) in fluid communication with the first duct (205) via the flow control valve (208), a resin storage tank (213) having a resin storage tank inlet (212) in fluid communication with an outlet end of the second duct (211, 311), and a gas evacuation system (214) operable to reduce an absolute pressure in the resin storage tank to below 100 mbar, the process comprising: connecting a liquid resin source (201) to the resin inlet (202), pumping liquid resin into the first duct via the resin inlet (202) using the resin pump (203) to achieve a first absolute pressure of at least 1.6 bar in the first duct (205), configuring the resin pump (203) and/or the flow control valve (208) to achieve a first pressure drop across the flow control valve of at least 1.5 bar, maintaining, using the gas evacuation system (214), a pressure in the storage tank (213) below 100 mbar at least partly concurrently with pumping resin into the first duct (205).

2. A process in accordance with claim 1, wherein the flow control valve (208) and/or the resin pump (203) are controlled so that an average resin transit time from the output (209) of the flow control valve (208) to the inlet (212) of the storage tank (213) is in the range 10-120 s, such as in the range 15-75 s, such as in the range 20-60 s, such as in the range 30-50 s, such as in the range 30-40 s.

3. A process in accordance with claim 1, wherein the degassing system (200, 300) further comprises a chamber (330) inline between the flow control valve (208) and the storage tank (213), the chamber having a smallest flow area A.sub.2 which is at least 20 times a largest flow area Ai of a duct portion (310) connecting the flow control valve (208) and the chamber (330).

4. A process in accordance with claim 3, wherein the degassing system (200) further comprises a duct (311) inline between the chamber (330) and the storage tank (213), said duct having a largest flow area A.sub.3 which is at most A.sub.2/20, such as substantially equal to the largest flow area A.sub.1 of the duct portion (310) connecting the flow control valve (208) and the chamber (330).

5. A process in accordance with claim 3, wherein the largest flow area A.sub.1 is in the range 2-6 cm.sup.2 and the smallest flow area A.sub.2 is in the range 130-200 cm.sup.2.

6. A process in accordance with claim 3, wherein a volume of the chamber (330) is in the range 5-50 L, such as in the range 10-40 L, such as in the range 15-25 L.

7. A process in accordance with claim 3, wherein the flow control valve (208) and/or the resin pump (203) are controlled so that an average resin transit time through the chamber (330) is in the range 10-120 s, such as in the range 15-75 s, such as in the range 20-60 s, such as in the range 30-50 s, such as in the range 30-40 s.

8. A process in accordance with claim 1, wherein the first absolute pressure is at least 3 bar.

9. (canceled)

10. A process in accordance with claim 1, wherein the a flow rate of resin into the resin inlet is in the range 20-60 L per minute.

11. (canceled)

12. (canceled)

13. A process in accordance with claim 1, wherein the first absolute pressure is at least 4 bar, the first pressure drop is at least 3.5 bar, the absolute pressure in the storage tank is maintained below 50 mbar, and optionally a flow rate of resin at the resin inlet is in the range 20-60 L per minute.

14. A process in accordance with claim 1, wherein the storage tank has an outlet (220) coupled to an outlet pump (221) for outputting degassed resin during a first time period overlapping with pumping resin into the first duct.

15. A process in accordance with claim 14, wherein the resin pump (203) and/or the flow control valve (208) and/or the outlet pump (221) are controlled to maintain a substantially constant amount of degassed resin in the storage tank during the first time period.

16. A process in accordance with claim 15, wherein the system comprises measuring means for measuring a parameter representing an amount of degassed resin in the storage tank, and the system further comprises control means configured to receive measurements from the measuring means and control the resin pump (203) and/or the flow control valve (208) and/or the outlet pump (221) to maintain a substantially constant amount of degassed resin in the storage tank.

17. A process in accordance claim 14, wherein the outlet (220) is in fluid communication with a manufacturing area where a fibre-reinforced composite part, such as a wind turbine blade part, is being manufactured at least during the first time period.

18. A process in accordance with claim 1, wherein no gas, such as air, is provided into the resin during the degassing process apart from the gas contained in the resin when pumped into the first duct (205).

19. A process for degassing liquid resin, comprising: providing liquid resin into a first duct (205) to achieve a first absolute pressure of at least 1.6 bar in the first duct, passing the liquid resin from the first duct (205) to a second duct (211,311) through a flow control valve (208), wherein the first absolute pressure and the flow control valve (208) are configured to cause cavitation on a downstream side (209) of the flow control valve (208) at least when the first absolute pressure is at least 1.6 bar, and transferring the liquid resin to a storage tank in fluid communication with the second duct and maintaining an absolute pressure in the storage tank below 100 mbar.

20. A process in accordance with claim 1, wherein the liquid resin comprises at least one of: epoxy resin, polyurethane resin, polyester resin, unsaturated polyester resin, vinyl ester resin, thermosetting resin, and/or thermoplastic resin, such as thermoplastic infusion resin.

21. A degassing system (200, 300) for degassing liquid resin, the degassing system comprising: a first duct (205) having a resin inlet (202) for receiving liquid resin to be degassed, a resin pump (203) for pumping liquid resin into the first duct (205) via the resin inlet (202), a flow control valve (208) arranged at a downstream end of the first duct (205), configured to control a flow rate of resin through the first duct and configured or configurable to provide a pressure drop of at least 1.5 bar across the flow control valve (208), a second duct (211, 311) in fluid communication with the first duct (205) via the flow control valve (208), a resin storage tank (213) having a resin storage tank inlet (212) in fluid communication with an outlet end of the second duct (211, 311), and a gas evacuation system (214) operable to reduce an absolute pressure in the resin storage tank (213) to below 100 mbar.

22. A degassing system in accordance with claim 21, further comprising a chamber (330) inline between the flow control valve (208) and the storage tank (213), the chamber (330) having a smallest flow area A.sub.2 which is at least 20 times a largest flow area A.sub.1 of a duct portion (310) connecting the flow control valve (208) and the chamber (330).

23. A system in accordance with claim 22, wherein a duct (311) inline between the chamber (330) and the storage tank (213) has a largest flow area A.sub.3 which is at most A.sub.2/20, such as substantially equal to the largest flow area A.sub.1 of the duct portion (310) connecting the flow control valve (208) and the chamber (330).

24. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Embodiments of the invention will be described in more detail in the following with reference to the accompanying figures. The figures show selected ways of implementing the present invention and shall not to be construed as being limiting the scope of the invention.

[0061] FIG. 1 is a schematic diagram illustrating an exemplary wind turbine.

[0062] FIG. 2 is a schematic view of a system for degassing liquid resin in accordance with an embodiment of the invention.

[0063] FIG. 3 is a schematic view of a system for degassing liquid resin in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF SELECTED EMBODIMENTS

[0064] Unless otherwise indicated, the drawings are not necessarily drawn to scale.

[0065] FIG. 1 illustrates a conventional modern upwind wind turbine 2 according to the so-called “Danish concept” with a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub 8 and three blades 10 extending radially from the hub 8, each blade having a blade root 16 nearest the hub and a blade tip 14 furthest from the hub 8. The invention is not limited to use in wind turbines of this type.

[0066] The blades 10 are usually made at least partly of fibre-reinforced composites, such as glass fibres and/or carbon fibres in a resin matrix. The strength of such blades is very dependent on the amount of gases and also water remaining in the resin when the fibres are impregnated with the resin, whatever the method of impregnation. It is therefore important that the resin be degassed as much as possible before use.

[0067] FIG. 2 illustrates a system 200 for degassing liquid resin in accordance with an embodiment of the invention. The system comprises a first duct 205 having a resin inlet 202 for receiving liquid resin to be degassed. In the present example, the resin inlet 202 of the system 200 is connected to a resin source 201 comprising liquid resin to be degassed. A resin pump 203 pumps liquid resin from the resin source 201 farther into the system. The system also comprises a flow control valve 208 arranged at a downstream end of the first duct 205. The first duct 205 is connected to an input port 207 of the flow control valve 208. The flow control valve 208 is configured to control a flow rate of resin through the degassing system 200, particularly to provide a pressure drop of at least 1.5 bar. The resin pump 203 and/or the flow control valve 208 are controlled to allow the absolute pressure in the first duct 205 to reach a desired level and to obtain a desired pressure drop across the flow control valve 208, as will be described below. A second duct 211 is in fluid communication with the first duct 205 via the flow control valve 208. The second duct is connected to an output port 209 of the flow control valve 208. Accordingly, the absolute pressure in the second duct 211 is significantly lower than the absolute pressure in the first duct 205.

[0068] The second duct 211 connects to an inside of a resin storage tank 213 via a storage tank resin inlet 212. The inside of the storage tank 213 is also connected to a gas evacuation system 214 comprising a gas duct 215 connected to the inside of the storage tank 213, to a vacuum pump 217, and to an exhaust 219. The vacuum pump 217 is operable to maintain a low absolute pressure in the resin storage tank 213 by removing gases from the inside of the storage tank 213. The system in FIG. 2 also includes a pump 221 for pumping degassed resin to a part manufacturing area via a storage tank outlet 220. In this way, degassed resin can be provided directly to the manufacturing area. As described previously, the system 200 may even run inline, producing degassed resin while the part manufacturing is taking place.

[0069] The process of degassing resin from the resin source 201 includes pumping resin into the first duct 205 via the resin inlet 202 using the resin pump 203. The resin pump may itself comprise the inlet 202. This is a matter of design.

[0070] In the present example, the pump maintains an absolute pressure in the first duct 205 around 3 bar, at least during a substantial part of the degassing process when resin is fed through the system. The vacuum pump 217 of the gas evacuation system 214 is at the same time operated to maintain a reduced absolute pressure below 50 mbar.

[0071] This process results in a very efficient degassing of the resin, and as described previously, this is not just by traditional bubble formation. The process conditions described herein cause creation of bubbles that have a size that allows gas and water to very efficiently diffuse out of the resin. In known systems, the primary mechanism behind removal of gases and water is the formation of bubbles due to a reduced absolute pressure. The gas from such bubbles is eventually removed by a gas evacuation system. However, dissolved resin is not efficiently removed in known systems, including systems that add gas as part of the degassing process.

[0072] Embodiments of the present invention treats the resin just long enough and under pressure conditions that result in a more thorough removal of gasses and water from the resin before it reaches the storage tank 213, while maintaining a high flow rate.

[0073] The fact that the processes described herein are different from known processes is also, surprisingly, observable by evaluating the degassing system equipment after degassing liquid resin. For reasons that are not well-understood, known systems and corresponding processes cause significant build-up of residues in various parts of those systems. The build-up rate itself is rather unpredictable, and monitoring the state of the degassing system is therefore a rather time-consuming task. Removing the residue and replacing damaged parts is even more time-consuming and contributes to downtime.

[0074] The process conditions described in the present specification result in much less build-up of residues, possibly due to the foamy state of the resin and the motion of the resin through the system under the process conditions described herein. The present invention therefore makes the degassing more efficient not only with respect to the amount of residual gasses, but also with respect to the maintenance load and associated downtime.

[0075] In another exemplary process, performed in the system shown in FIG. 3, a chamber 330 modifies the flow of the resin by providing a change, in some cases a relatively large change, in the flow area between the control valve 208 and the storage tank 213. As shown in FIG. 3, the chamber 330 between the flow control valve 208 and the storage tank 213 provides a larger surface area A.sub.2 for the resin compared to a largest flow area A.sub.1 in the duct 310 between the control valve 208 and the chamber 330. This further contributes to removal of gasses, not just by allowing bubbles to more easily form, but also by increasing removal of gas from the resin by diffusion.

[0076] A ratio between the flow area A.sub.2 and the flow area A.sub.1 in the range 20-60 results in a very efficient diffusion of gasses out of the resin, including single gas molecules otherwise trapped and unable to form gas bubbles by which they can escape. The large flow area allows the resin to be in the particularly advantageous foamy state that characterizes embodiments of the present invention for a longer time.

[0077] This is further enhanced by providing that the resin after the chamber 330 flows in a relatively narrow duct 311 as illustrated in FIG. 3. It turned out that such a narrowing gives an even foamier resin in the chamber and also leads to smaller and more uniform bubbles in the chamber, which increases the rate at which small gas pockets and individual molecules diffuse out of the resin. Gasses and water trapped in very small amounts, down single molecules, as described above, can diffuse out of the resin, which allows them to be removed together with larger pockets of gas. Without the narrower duct after the chamber, bubbles tend to be somewhat larger and vary more in size, and the diffusion component of the degassing process is lower. As a consequence, more gas remains suspended in the resin especially on a molecular level.

[0078] The invention has been described with reference to selected embodiments. However, the scope of the invention is not limited to the illustrated embodiments, and alterations and modifications can be carried out without deviating from the scope of the claims.

LIST OF REFERENCES

[0079] 2 wind turbine

[0080] 4 tower

[0081] 6 nacelle

[0082] 8 hub

[0083] 10 blade

[0084] 14 blade tip

[0085] 16 blade root

[0086] 200, 300 degassing system

[0087] 201 resin source

[0088] 202 resin inlet

[0089] 205 first duct

[0090] 203 resin pump

[0091] 207 flow control valve input port

[0092] 208 flow control valve

[0093] 209 flow control valve output port

[0094] 211 second duct

[0095] 212 storage tank resin inlet

[0096] 213 resin storage tank after degassing

[0097] 214 gas evacuation system

[0098] 215 gas duct

[0099] 217 vacuum pump

[0100] 219 gas exhaust

[0101] 220 resin outlet

[0102] 221 pump to part manufacturing area

[0103] 230 part manufacturing area

[0104] 310 duct between control valve and chamber

[0105] 311 duct between chamber and storage tank

[0106] 330 chamber

[0107] A.sub.1 largest flow area of first duct

[0108] A.sub.2 smallest flow area of chamber

[0109] A.sub.3 largest flow area of duct between chamber and storage tank