Arrangement for making removal of by-products more efficient in gas circulation of cable vulcanisation process

Abstract

An arrangement for enhancing the removal of by-products in the gas circuit of a cable vulcanisation process comprising a certain part of a vulcanisation tube between an inlet connection and an outlet connection, and a recirculation tube (7A) and recycling equipment operating thereon between said outlet and inlet connections, is characterised in that the recirculation tube (7A) comprises one or more arrangements (12A), wherein the tube (14) is provided inside it with a tube section (17) with a smaller diameter directed against the gas flow, and fastened (18) at its end to the tube (14) so that the space (CS) between it and the tube (14) is there closed, for collecting into said intermediate space (CS) the waste drifting with the gas flow essentially as a liquid film on the inner surface (15) of the tube (14), and in the area of the intermediate space (CS) a controlled opening and closing arrangement (20, 21, 22, 23) for removing the collected waste. A significant advantage of the arrangement according to the invention is that the purification of the gas inside the circulation tube is intensified without substantially disturbing the gas circulation and its operation. The solution reduces the load on the equipment operating in the gas circuit, such as the pre-filter and the heat exchanger, and reduces the need for cleaning them.

Description

[0001] ARRANGEMENT FOR MAKING REMOVAL OF BY-PRODUCTS MORE EFFICIENT IN GAS CIRCULATION OF CABLE VULCANISATION PROCESS

[0002] FIELD OF THE INVENTION

[0003] The invention is related to the arrangement of the gas circulations of the cable vulcanisation process, and in particular to the intensification of the removal of vulcanisation by-products in the gas circuits. The invention can be applied, for example, to vulcanisation processes in cable production.

[0004] BACKGROUND OF THE INVENTION

[0005] In the production of cables, the vulcanisation line is usually equipped with several gas circuits intended to operate either continuously or when necessary. In addition to the actual vulcanisation zone gas circulation, there may be at the very beginning of the line a so-called EHT (Entry Heat Treatment) circuit for cooling the molten insulation pressed around the cable at high temperature to minimize runoff and support roundness. After the vulcanisation zone, the line is followed by cooling, which can be done with either gas or water. If it is done with gas, then there is a separate gas circuit for it. If it is done with water, then the line may also have gas-cooled pre-cooling, which lowers the surface temperature of the cable and for which there is a separate gas circuit.

[0006] The gas used in the vulcanisation process as a shielding gas and as a mediator of pressure and heating and cooling is usually nitrogen. Especially in cooling cycles, the volumes of gas flows are large, for example in the order of 300 to 400 m3 / h. In nitrogen vulcanisation, the cable runs in a pressurised tube, where the heated gas and the radiant heat of the vulcanisation tube maintain the temperature of the cable at a certain level according to the process. The temperature of the gas circulating in the vulcanisation zone is usually in the range of 200 to 400 °C, but can be also higher. Pressurisation is required, among other things, to prevent bubbling of the decomposition products from vulcanisation, and the normal gas pressure is about 10 bar. The temperature of the nitrogen gas fed to the cooling circuit, on the other hand, is, for example, in the order of 25 °C.

[0007] In addition to heat treatment and pressurisation, vulcanisation is also a chemical process that generates gaseous, liquefiable and solid by-products, i.e. vulcanisation waste, which mixes with the circulating gas and accumulates very quickly in the vulcanisation and cooling tube and gas recirculation equipment unless it cannot be extracted from the gas. The most advantageous in gas cleaning are solutions in which waste is removed from the gas in arrangements belonging to the gas circuit itself. WO 2016189184 Al discloses a solution in which a gas cleaning and waste removal arrangement is added to a central heat exchanger in gas recirculation. The purification of the gas has been further enhanced by adding to the gas circuit a pre-filter, through which the gas enters the heat exchanger and where waste is removed from it.

[0008] Even after pre-filtration and cleaning in a heat exchanger, by-products remain in the gas returning in the circuit, especially in the form of light small droplets, which over time accumulate on the inner surface of the circulating pipeline, and when carried by the strong gas flow finally also on the surface of the produced cable. Therefore, it would be desirable that the removal of by-products in the gas cycles of the vulcanisation process could be further enhanced and improved.

[0009] SUMMARY OF THE INVENTION

[0010] An object of the present invention is to provide an arrangement for enhancing the removal of by-products in the gas cycles of the cable vulcanisation process.

[0011] In order to achieve the above object, the arrangement according to the invention for enhancing the removal of by-products in the gas circuit of a cable vulcanisation process comprising a certain part of a vulcanisation tube between an inlet and an outlet, and a recirculation tube and recycling equipment operating thereon between said outlet and inlet, is characterised in that which is defined in the characterising part of the independent claim 1 of the attached claims. Other claims define various embodiments of the invention.

[0012] A significant advantage of the arrangement according to the invention is that the purification of the gas inside the circulation tube is intensified without substantially disturbing the gas circulation and its operation. The solution reduces the load on the equipment operating in the gas circuit, such as the pre-filter and the heat exchanger, and reduces the need for cleaning them. When the gas circulation equipment and tubes also have to be decommissioned at certain intervals for a special purification process, the need for purifications can be reduced and the intervals extended by using the solutions according to the invention.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS implementation

[0014] The invention is described in more detail below with reference to the accompanying drawings, in which:

[0015] Fig. 1 schematically shows the use of a solution according to the invention in cooling carried out by gas circulation,

[0016] Fig. 2 shows a corresponding use of the solution in pre-cooling realised by gas circulation when cooling is carried out by means of water circulation, and Figs. 3 to 7 present examples of implementations of the solution according to the invention in a gas recirculation tube.

[0017] DETAILED DESCRIPTION OF THE INVENTION

[0018] Figs. 1 and 2 present schematically two possible gas circuits at the end of the vulcanisation process. The cable 2 to be vulcanised comes, as indicated by the arrow C, from the vulcanisation zone 1 A of the production tube to the end part IB of it, where the cable is cooled and from where it passes through the line termination end 3 for finishing and storage. Nitrogen gas is fed to the vulcanisation gas circuits from the tank 4 via the tube 5 provided with the valve arrangement 6. The equipment 8 required to control the gas recirculation system need not be described in more detail here, as well as the water circuit WC in which the actual cooling is carried out in the example of Fig. 2.

[0019] In the gas circuit of Fig. 1, the cable is cooled with gas in the tube section IB into which it comes from the connection Al and flows around the incoming cable as indicated by the arrow G, cooling it. The gas, which is considerably heated and has collected the vulcanisation waste, is directed from the connection A2 to the recirculation tube 7A for treatment for a new cooling cycle. In the recycle, the pre-filter 9, which cleans and removes the vulcanisation byproducts from the gas, can be, for example, as described in WO 2016189184 Al. The recirculation is then followed by a heat exchanger 10 in which the gas is cooled back to a certain temperature, for example 25 °C. The heat exchanger is also combined with gas purification and waste removal, for example as described in the above-mentioned publication. After the heat exchanger, the blower 11 feeds the gas forward with the desired flow rate and through the connection Al back to the tube IB to cool the cable.

[0020] However, the pre-filter 9 and the cleaning arrangement operating in the heat exchanger 10 are not able to completely purify the gas from the vulcanisation by-products. In particular, small light droplets remain in the gas and are efficiently transported forward, especially by the very strong gas flow in the cooling circuit. Droplets gradually accumulate on the inner surface of the tube, and a liquid film begins to form, and when it is thickening, the gas stream begins to carry it forward. The purpose of the solutions according to the invention is to provide the recirculation tubes with arrangements by which the resulting wet film and waste liquid can be removed from the tube efficiently while the disturbance of the gas circulation itself is kept to a minimum. The arrangements are also combined with solutions that at the same time enhance conversion into droplets of the by-products drifted by the gas and condensation in the liquid film to be collected off.

[0021] In the gas circuit of Fig. 1, the arrangement 12A according to the invention is in the recirculation tube 7A shortly before the connection Al and gas entry into the cooling tube IB, and the second arrangement 12B according to the invention after reentry of the gas via the connection A2 to the recirculation tube 7A and close to the pre-filter 9.

[0022] In the example of Fig. 2, where the actual cooling is performed with a water circuit, the recirculation tube 7B brings the precooling gas via the connection Bl to the end of the vulcanisation tube 1 A and via the connection B2 before water cooling circulation back to the recirculation tube 7B and onwards to be processed in the same way for a new cooling circulation as in the example of Fig. 1. Also the arrangements according to the invention are placed in the recirculation tube, respectively. The arrangement 12A is in the recirculation tube 7B shortly before the connection Bl and the entry of the gas to the vulcanisation tube 1A, and the second arrangement 12B after the gas has returned via the connection B2 to the recirculation tube 7B and close to the pre-filter 9.

[0023] The gas circuit to which the solution according to the invention is applied can equally well be, for example, the EHT cycle mentioned above in the background consideration or some other gas cycle developed for the cable vulcanisation process, in which the use of the solution works and is useful.

[0024] Figs. 3 and 4 show an example of the implementation of the arrangement according to the invention in a tube section 14, which is at both ends (only one end shown here) connected by respective flanges 16A and 16B to the recycle tube 7 A to form a part of it. The diameter of the tube section is, for example, 125 mm. The gas flows in the direction of the arrow G. Between the flanges 16A and 16B is by means of a flange ring 18 attached an into the tube section 14 and against the gas flow extending tube section 17, referred herein also as an inner tube, having a length of 200 to 250 mm and a diameter of about 100 mm, for example. The waste moving ahead with the flow as the liquid film on the inner surface 15 of the tube, is now accumulated in the space CS between the tubes, from where it is removed via the connection 20, the tube 21 and the valve 22 to a waste container or the like 23.

[0025] In addition to the fastening, the function of the flange ring 18 or the like is to close the intermediate space CS and the flow of gas through it at this end of the inner tube 17. The inner tube is dimensioned according to its purpose so that the length and volume of the intermediate space CS are sufficient and suitable for the collection of liquid waste. The diameter of the inner tube can be, for example, 70 to 90 % of the diameter of the tube itself and the length, for example, 2 to 3 times the diameter of the tube.

[0026] The accumulated liquid is removed through the waste disposal arrangement 13 either by continuous small leakage or by periodic blowing. Similar waste disposal arrangements are found in gas recycling not only in the arrangements according to the invention but also in the prefilter 9 and the heat exchanger 10, and are in Figs. 1 and 2 shown schematically by the same drawing symbols and indicated by reference number 13. In the arrangement according to the invention, the gas flow is tapered when it meets the tube section 17 as shown by the arrows G1 in Fig. 3, and if the flow is, for example, 350 m3 / h, the gas flow rate increases from about 7 m / min to about 10 m / min. In particular, a very sudden change in velocity can cause flow disturbances or suction that releases droplets from the fluid membrane to join the flow. To prevent this, it is advantageous that the inner surfaces 15 of the tube are smooth. A rough inner surface makes it easier for the liquid film to disperse into droplets and drift with the gas.

[0027] The arrangement according to Fig. 3 is preferably placed on a vertical portion of the recycle tube. The downward flow of gas facilitates the passage of liquid into the intermediate space CS of the tubes. The arrangement can also be placed in a horisontal portion of the tube, in which case it is advantageous to bevel the end 19 of the inner tube 17A at an angle of, for example, 15 to 30 degrees as shown in Fig. 5. In this way, the steepness of the change in gas flow rate is decreased and its potential effect on the dispersion into droplets and drift of the liquid film with the gas is reduced. The inner tube 17A may also exit from the outlet end flange plate 18 as a tapering portion 24 for narrowing the intermediate space CS of the tubes in the flow direction.

[0028] Fig. 6 presents another solution to decrease the steepness of the change in gas flow rate and its possible effect on liquid dispersion into droplets and drift with the gas flow. The inner tube 17 is extended by a perforated plate tube 25 which fits over and overlaps in part it increasing the length of the inner tube, for example, to about 400 millimeters. The solution attenuates, on the one hand, the increase in the gas flow rate so that it occurs gradually in the inner tube in the region of the perforated plate tube, and, on the other hand, the slowing of the movement of the liquid film as it enters the intermediate space. This additional solution is especially useful when the tube and gas flow are directed downwards.

[0029] Referring to Figs. 3 to 6, various embodiments of the arrangement 12A of Figs. 1 and 2 according to the invention are shown. Fig. 7 presents a simplified embodiment 12B of an arrangement according to the invention. A water cooling jacket 26 is added to the recirculation tube section 14 provided with the inner tube 17 according to the invention. When the tube 14 has a diameter of 125 mm, the jacket is formed by a surrounding tube section 26 with a diameter of 150 mm, for example, which covers a large part of the length of the tube portion 14 the ends thereof being, for example, welded to the outer surface of the tube 14 to close the jacket. Water enters the jacket via the connection 28 A and leaves via the connection 28B. The connection 29 is intended, for example, for emptying and rinsing the jacket when necessary.

[0030] Inside the jacket in the vicinity of the ends and water connections, for example, there are flow control arrangements, for example rings, which guide the flow of water to be more even

[0031] RECTIFIED SHEET (RULE 91) throughout the jacket. The cooling jacket 26 operates in the region of the gas flow to the inner tube 17 of the arrangement and certain part of it also in the region of the inner tube, and is intended to enhance progression of droplets, condensation and integration of the waste into the liquid flow of the inner surface of the tube just before the arrangement meant to stop, collect and remove the waste from the tube.

[0032] When the use of a cooling jacket in the arrangement according to the invention is substantially useful, for example in the treatment of gas heated in cooling, the arrangements 12B provided with it are in the examples of Figs. 1 and 2 arranged to act also as gas precoolers before the pre-filters 9. The implementation of the arrangement according to the invention is not limited to the above examples. The design, placement, and dimensions of the inner tube, as well as the other arrangements associated with it, can vary in many ways in practice.

[0033] The invention may vary within the scope of the accompanying claims.

Claims

7CLAIMS1. An arrangement for enhancing the removal of by-products in the gas circuit of a cable vulcanisation process comprising a certain part of a vulcanisation tube (IB, 1 A; 1 A) between an inlet connection (Al, Bl) and an outlet connection (A2, B2), and a recirculation tube (7 A, 7B) and recycling equipment (9, 10, 11) operating thereon between said outlet and inlet connections, characterised in that the recirculation tube (7 A) comprises one or more arrangements (12A, 12B), wherein: at a certain portion (14) of the tube (7 A), a relatively short tube section (17, 17A) with a smaller diameter is placed inside the tube and fastened (18, 24) at its other end to the tube (14) so that the space (CS) between the tube (14) and the tube section (17, 17A) at said end is closed, and directed against the gas flow, for collecting into said intermediate space (CS) the waste drifting with the gas flow as a liquid film on the inner surface (15) of the tube (14), and a controlled opening and closing arrangement (20, 21, 22, 23) is arranged in the area of the intermediate space (CS) for removing the collected waste.

2. The arrangement according to claim 1, characterised in that the diameter of said tube section (17, 17A) is 70 to 90 percent of the diameter of the tube (14).

3. The arrangement according to claim 1 , characterised in that the legth of said tube section (17, 17A) is 2 to 3 times the diameter of the tube (14).

4. The arrangement according to claim 1, characterised in that said tube section (17A) is modified so that the open end (19) thereof is bevelled in relation to the direction of the tube section for attenuating the change of the gas flow rate.

5. The arrangement according to claim 1, characterised in that said tube section (17) is lengthened by a perforated plate tube (25) which fits over and overlaps in part it, for attenuating, on the one hand, the increase of the gas flow rate and, on the other hand, the slowing of the movement of the liquid film.

6. The arrangement according to claim 1, characterised in that the tube (14) is provided with a water cooling jacket (26, 27, 28A, 28B, 29) thereon in the gas coming direction before and partly in the area of the tube section (17), the meaning being that the vulcanisation waste accumulated in the heated gas is more efficiently converted to droplets, condensed andRECTIFIED SHEET (RULE 91)8 collected into the surface flow just before the arrangement meant to stop, collect and remove the waste from the tube.

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