RU2637959C1 - Device for oxidating polyacrylonitrile fibres by producing carbon fibres - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: device for oxidating polyacrylonitrile fibres by the production of carbon fibres contains a body 1 with removable end walls 5 having a through window 6 for input and output of the processed fibres 4, guide shafts 20 located outside the body 1. Inside the body 1 there is an oxidation chamber 2 with channels 3 for moving the fibres, which are combined into several temperature zones 8. Each temperature zone 8 is associated with at least one heater 15 and a fan 12. The temperature zones 8 are made insulated from each other, each of which is provided with a receiver cavity 9 and an aspirating cavity 10. Each receiver cavity 9 is connected to the pumping channel 11 of the fan 12 through the perforated walls 13 and channels 3 to move the fibres from one side of the chamber 2, and each of the aspiring cavity 10 is connected to the channels 3 to move the fibres from the other opposite side of the chamber 2, and the suction channel 14 of the heater 15. The device comprises means for removing exhaust gases from the oxidation chamber 2 that are connected to the pumping channel 11 of the fan 12 and means for enriching the oxidizing medium connected to the suction channel 14 of the heater 15. The means for removing exhaust gases and means for enriching the oxidizing medium are made in the form of nozzles 16, 18 with chokes 17, 19.

EFFECT: increasing the efficiency of heat treatment of PAN-fibres due to the equivalence of temperatures and velocities of gas flows, streamlined fibres in the channels of each temperature zone of the oxidation chamber.

2 cl, 3 dwg

Description

The invention relates to equipment for the production of chemical fibers, in particular to a furnace for continuous low-temperature processing of polyacrylonitrile fibers in the production of carbon fibers.

The prior art camera for continuous temperature processing of long material (PAN fibers), comprising a through-type housing with holes at the ends for material input and output, guide shafts located outside the housing, perforated media for supplying the processing medium located in the housing between the axes openings for supplying material in which the means of supplying the processing medium are made in the form of cone-shaped boxes installed towards each other in the direction of decreasing the cross section, and the axis openings for supplying material, between which the pipe is placed, outside the housing are made intersecting. The chamber is equipped with sealing partitions located in the housing between the holes for supplying material (patent RU 2017867, IPC D01F 9/12, B29B 13/02, 08/15/1994).

The presence of sealing partitions in the design of the chamber allows, as stated in this patent, to use different processing media in different parts of the chamber, which improves the quality of the output material. However, in the suction system, various media will mix, since a cone-shaped suction box takes gas from both sides of the partition, and the secondary use of these media is eliminated, they will be disposed of. Consequently, the possibility of using an energy-efficient gas recirculation system is excluded.

In the known design of the chamber, it is claimed that it is possible to carry out effective gas filtration in a selected fiber section to suppress the exothermic effect. However, this function is possible only without the use of a gas recirculation system, since each pumping cone-shaped box must have an individual adjustment of the flow rate and temperature of the gas medium. Such a constructive solution of the chamber for continuous heat treatment excludes the possibility of creating equal temperatures and velocities of gas flows in different parts of the chamber. The considered chamber is energy inefficient and will lead to a rise in the cost of the finished material.

A device for the oxidation of polyacrylonitrile fibers containing prechambers with conveying rollers, nozzles for suctioning gaseous products of pyrolysis and fittings for suctioning fresh air, an oxidation chamber connected through pipelines to a fan and an electric heater. The oxidation chamber is equipped with slotted channels for moving filaments and localizing gas emissions. Each slotted channel is formed by two flat plates that can be paired with one or both ends (patent RU 2042753, IPC D01F 9/14, 08/27/1995) - prototype.

In the known device during the oxidation process in the slotted channels are transported strands isolated from the direct influence of the circulating oxidizing medium. At the same time, both heating of the filaments to ensure the occurrence of the oxidative reaction, and the entrainment of exothermic heat from the filaments is carried out along the chain: fan → electroheater → flow of the heated oxidizing medium → walls of the slotted channels → oxidizing medium in the slotted channels → processed threads. This heat transfer system, due to the long heat transfer chain, has a high inertia. When exothermic heat is removed, such a temperature chain is inefficient. So, upon receipt of a signal on the overheating of the filaments in the control system, the electroheater will receive a command to lower the temperature, then the temperature of the oxidizing medium will begin to decrease, then the temperature of the walls of the slotted channels will begin to decrease, then the temperature of the oxidizing medium in the slotted channels will begin to decrease, and finally, the lowered temperature will reach processed threads. In practice, in oxidation furnaces having a high inertia of the heat transfer system, there are cases when the threads do not cool in time and self-ignite, fires occur in the working chambers. The device’s design does not provide means for the organized supply of an oxidizing medium - air - into slotted channels. Air with a normal temperature of + 20 ° C enters the prechambers and this air is entrained in moving filaments in slotted channels. But the filaments, as they oxidize, change their geometrical dimensions, therefore, the amount of cold air entering the slotted channels will change with each passage, there is no stable oxidizing environment. The oxidation process will be unstable. The considered device for applying the method of oxidation of polyacrylonitrile threads is technically unsafe and will not provide a stable and effective oxidation reaction.

The technical result when using the claimed invention is to increase the efficiency of heat treatment of polyacrylonyl fibers (PAN fibers) by providing a stable oxidizing environment, namely the equivalence of temperatures and velocities of gas flows flowing around the threads in the channels of each temperature zone of the oxidation chamber.

The specified technical result is achieved in that the device for the oxidation of polyacrylonitrile fibers in the production of carbon fibers comprises a housing with removable end walls having passage windows for entering and exiting the processed fibers, guide shafts located outside the housing, inside which an oxidation chamber with channels for moving fibers combined in several temperature zones, each of which is associated with at least one air heater and fan, as well as means for removal of exhaust gases from the oxidation chamber and means for enriching the oxidizing medium, while the temperature zones are made isolated from each other, each of which is equipped with a receiver cavity and an aspiration cavity, each receiver cavity connected to the blower channel of the fan through a perforated wall and with channels for moving fibers on one side of the chamber, and each suction cavity is connected to channels for moving fibers on the other, opposite side of the chamber, and on the suction m channel of the heater, while the means for removing exhaust gases from the oxidation chamber are connected to the blower channel of the fan, and the means for enriching the oxidizing medium are connected to the suction channel of the heater.

In addition, the above technical result is achieved in that the means for removing exhaust gases and means for enriching the oxidizing medium are made in the form of nozzles with chokes.

The claimed invention is illustrated by drawings, where:

in FIG. 1 shows a longitudinal section of a four-zone device for the oxidation of PAN fibers in the production of carbon fibers, general view;

in FIG. 2 shows the same, section AA in FIG. one;

in FIG. Figure 3 shows the same section AA with two-sided injection of an oxidizing medium.

The device for the oxidation of PAN fibers (Fig. 1-3) contains a housing 1. Inside the housing 1 there is an oxidation chamber 2 with channels 3 for moving the processed fibers 4. The housing 1 has removable end walls 5 in which slotted passage windows 6 for entry are made and the exit of the processed fibers 4. Slotted passage windows 6 are equipped with gates 7 that prevent the passage of exhaust gases into the space of the workshop and vice versa, the workshop atmosphere into the oxidation chamber 2. Channels 3 for moving fibers 4 are made isolated from each other with the formation of temperature zones 8. Each temperature zone 8 is equipped with a receiver cavity 9 on one side of the chamber and an aspiration cavity 10 on the other side of the chamber.

Each receiver cavity 9 is connected to the discharge channel 11 of the fan 12 through a perforated wall of aerodynamic resistance 13 and with channels 3 for moving fibers 4 of the corresponding temperature zone 8 on one side of the chamber 2.

Each suction cavity 10 is connected to the channels 3 of the corresponding temperature zone 8 on the other, opposite side of the chamber 2, and to the suction channel 14 of the air heater 15.

Each injection channel 11 of the fan 12 is connected to a gas outlet pipe 16 equipped with a gas concentration choke 17. Each suction channel 14 is connected to a discharge supply pipe 18 equipped with a vacuum choke 19. There are guide shafts 20 outside the casing 1 for transporting the processed fibers 4 to the oxidation chamber 2.

A device for the oxidation of PAN fibers in the production of carbon fibers works as follows.

PAN fibers 4 are pulled through the channels 3 of oxidation chamber 2, entering and leaving the casing 1 through slit-like passage windows 6. Outside the casing 1, the fibers change their direction of movement around the guide shafts 20. When moving through the channels 3, PAN fibers 4 are blown through an oxidizing medium coming from the receiver cavity 9. In this case, the temperature and velocity of the gas flows in all channels 3 of the temperature zone 8 will be equivalent. This is due to the fact that in the receiver cavity 9 an oxidizing medium of a higher pressure is created, uniform in temperature and density, with respect to the space in the channels 3. The creation of such a medium is achieved by an equal-density flow of gases passing through the perforated wall of the aerodynamic resistance 13 from the discharge channel 11 of the fan 12. Gas pressure in receiver cavity 9 will be higher than the pressure in the channels 3, due to the increased velocity of gas flows in the channels 3 relative to the speed of gases in the receiver cavity 9 With an increase in the flow rate in the pipeline, the pressure in it decreases. This phenomenon of aerodynamics is used in the claimed invention to create gas flows of equal velocity in the channels 3 of the oxidation chamber 2.

To remove the exhaust gases from the oxidation chamber 2, a discharge pipe 16 is attached to the discharge channel 11 of the fan 12, equipped with a gas concentration throttle 17. To enrich the oxidizing medium with oxygen, the suction channel 14 of the air heater 15 is connected to the discharge supply pipe 18. The discharge pipe 18 is equipped with a vacuum choke 19. A decrease in the supply of fresh air provides a decrease in pressure in the gas supply system of the oxidation chamber 2. This increases the efficiency of the valves 7.

The claimed device may have two designs depending on the required performance. One design is made with one-sided injection of the oxidizing medium into the temperature zones and the second with two-sided injection of the oxidizing medium.

The proposed design of the device provides an effective stable process for processing polyacrylonitrile threads. This is achieved by creating equal conditions for the composition, speed and temperature of gas flows in the channels of each temperature zone for the oxidation reaction to occur.

Claims (2)

1. A device for the oxidation of polyacrylonitrile fibers in the production of carbon fibers, comprising a housing with removable end walls having a through hole for entry and exit of the processed fibers, guide shafts located outside the housing, inside which is placed an oxidation chamber with channels for moving fibers combined in several temperature zones, each of which is associated with at least one heater and fan, as well as means for removing exhaust gases from the oxidation chamber and means for enriching the oxidizing medium, while the temperature zones are isolated from each other, each of which is equipped with a receiver cavity and an aspiration cavity, each receiver cavity being connected to the blower channel of the fan through a perforated wall and with channels for moving fibers on one side of the chamber, and each aspiration cavity is connected to channels for moving fibers from the other, opposite side of the chamber, and to the suction channel of the air heater, while Ia exhaust gas from the oxidation chamber connected with blowing fan channel, and means for enriching an oxidizing environment connected to a suction conduit heater. 2. The device according to claim 1, characterized in that the means for removing exhaust gases and means for enriching the oxidizing medium are made in the form of nozzles with chokes.

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