JPS61216716A - Treatment of exhaust gas in manufacturing of carbon fiber - Google Patents

Abstract

PURPOSE:To efficiently remove a tar component and to reduce the viscosity of washing water, by removing the tar component of the exhaust gas formed in a baking furnace by washing and holding the used washing water to specific temp. or less in a water treatment tank to separate the tar component by flotation. CONSTITUTION:The exhaust gas formed in a process, wherein a flame resistant fiber or carbon fiber is prepared by heating a stock fiber M such as a polyacrilonitrile fiber at 300 deg.C or more in a baking furnace 1 under an inert atmosphere, is sucked from an exhaust pipe 4 and washed by washing water from spray nozzles 9 in the gas-liquid contact chamber 7 of a scrubbing dust collector 5 while the used washing water is treated in a pyrolytic apparatus 10 packed with a platinum catalyst. The washing water from a drain pipe 13 is cooled to 40 deg.C or less by a heat exchanger 18 to be sent to a treatment tank 12 where the tar component in washing water is separated by flotation. The water purified in the treatment tank 12 is supplied to the spray nozzles 9 through a water feed pump 16 and a water feed pipe 17 and recirculated for reuse.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for treating exhaust gas in carbon fiber production, which is suitable for use in a carbon fiber production process, particularly in a sintering process.

[Prior art] Carbon fibers are generally produced by heating raw material fibers (brecasa) such as polyacrylonitrile fibers and pitch fibers at 200°C to 300°C.
It is produced by carbonizing or graphitizing it by heating in the air to make it flame resistant (flame-proofing treatment, infusibility treatment), and then heating it in an inert atmosphere such as nitrogen to 1000°C to 1500°C (firing process).

The above firing step is carried out, for example, in a continuous firing furnace I as shown in the attached drawing, but at that time, when polyacrylonitrile fiber is used as the precursor, 35 to 50 wt% of the brecaser is decomposed as a decomposition product. Occur. This decomposition product consists of substances that are gaseous at room temperature (including toxic CN) and tar that contains organic polymer substances. However, this tar content is an essential condition for hygiene control of the working environment, product quality control, and even for continued operation, but this tar tends to condense, adhere, and accumulate at the outlet of the kiln or in the piping after that, and is especially This tendency becomes more noticeable as the temperature decreases, so it is necessary to remove it as soon as possible near the firing furnace.

Conventional methods for this purpose include treatment with an electrostatic precipitator, filtration treatment with a filter, cooling condensation treatment, wet treatment with a scrubber dust collector, and combustion treatment. Because of this, methods other than wet processing tend to cause clogging and clogging of pipes, malfunctions due to adhesion to equipment, etc., and stable operations cannot be maintained.

[Problems to be solved by the invention] On the other hand, in wet processing using a scrubber dust collector, problems such as clogging and adhesion as described above are eliminated.
It is necessary to treat the wash water. Particularly, when water containing toxic components such as those mentioned above must be treated, it is desirable to use a so-called closed circuit system in which the treated water is circulated and reused in order to reduce the amount of treatment.

However, when performing such circulation treatment, the viscosity of the water increases as the tar content of the cleaning water increases.
This increases the load on the water pump and reduces the efficiency of liquid-gas contact in the scrubber dust collector.On the other hand, increasing the amount of washing water to prevent this increases the amount of water that needs to be treated. .

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention heats a fibrous material to 300°C or higher in a firing furnace in an inert atmosphere to form flame-resistant fibers or carbon. In the method for producing fibers, the exhaust gas generated in the above-mentioned firing furnace is washed with water to remove tar from the exhaust gas, and the cleaning water containing the tar is maintained at a temperature of 40°C or less in a water treatment tank. This process involves flotation and separation of tar.

Hereinafter, the method of the present invention will be explained in more detail with reference to the drawings.

In the drawing, the symbol l is a vertical continuous firing furnace,
The raw material fiber M is continuously passed through the roll 2.2 and fired. The inside of the furnace is maintained in an inert atmosphere by gas such as nitrogen supplied from the air supply pipe 3.3, and the generated exhaust gas is discharged from the exhaust pipe 4.

Reference numeral 5 denotes a scrubber dust collector, which is separated by a partition wall 6 into a gas-liquid contact chamber 7 and an air chamber 8 which communicate at the bottom. The exhaust gas introduced from the exhaust pipe 4 is washed in the gas-liquid separation chamber 7 with washing water dispersed from the spray nozzle 9, then led out from the upper part of the air chamber 8, and further introduced into the pyrolysis device IO. After harmful components are removed, it is released into the atmosphere. Note that the code 1. t is a water ring pump that sucks exhaust gas.

Reference numeral 12 denotes a treatment tank that stores the cleaning water discharged from the scrubber dust collector 5 through the drain pipe 13 and floats and separates tar in the cleaning water. Between 14 and 50 μl:! H store light 19 times 70 minutes, 1q^Oht÷mu base. The water purified in the treatment tank 12 is supplied to the spray nozzle 9 of the scrubber dust collector 5 through a water supply pipe 17 by a water supply pump 16, and is circulated and reused.

Reference numeral I8 is a heat exchanger for cooling the circulating washing water, and is provided in the middle of the drain pipe 13. This heat exchanger 18 has a structure in which fins 19 are provided on a straight inner tube to prevent pipe clogging.

The amount of cooling water supplied to the heat exchanger 18 is controlled so as to maintain the water temperature in the treatment tank 12 at 40°C or lower, preferably at 30°C or lower. This is because if the water temperature is above 40°C, the scum will dissolve, but if it is below 40°C, the scum will float to the surface and be separated.

In addition, as a specific means for controlling the water temperature, it is possible to provide, for example, a flow control valve (not shown) that is interlocked with a water temperature detection means in the processing tank 12. Further, the mounting position and structure of the heat exchanger 18 are not limited to those described above, and for example, the washing water in the processing tank 12 may be directly cooled.

The tar component floated and separated in the form of scum in the treatment tank 12 can be removed by scooping with a wire mesh or the like, and can be easily disposed of separately by incineration or other methods.

On the other hand, the cleaning water contains exhaust gas components HCN and NHs.
etc. are dissolved and the ion concentration gradually increases, but this does not affect operation and can be extracted and processed after an appropriate period of time.

[Operations] According to the present invention, the cleaning water that has been used to clean the exhaust gas is cooled and
By maintaining the temperature at 0° C. or lower, the tar content dissolved or suspended in the washing water is precipitated or condensed and separated by flotation, thereby reducing the viscosity of the washing water.

[Example] Next, examples of the method of the present invention and their results will be shown.

(Example 1) In a firing furnace 1 maintained at a temperature of 900° C., material fiber M obtained by flame-retardant treatment of 12,000 filament tows made of polyacrylonitrile fibers in air was supplied at a rate of 35 m per hour and heat-treated. . Nitrogen gas is supplied to the firing furnace l from the air supply pipe 3.3 at a rate of 400 Q/min to maintain the furnace internal pressure 0.5 to 10 mm higher than atmospheric pressure in terms of water column. Inhaled exhaust gas. This exhaust gas is transferred to the gas-liquid contact chamber 7 of the scrubber dust collector 5.
(diameter: 1 m, height: 2 m), was washed by washing water at a rate of 50 ρ per minute dispersed from the spray nozzle 9, and was discharged from the air chamber 8. This exhaust gas was further mixed with air, introduced into a cylindrical thermal decomposition device IO with a diameter of 500n+a+ filled with a platinum-based catalyst, and treated, and then discharged by a water ring pump 11. The processing tank 12 has a height of in.
The weir 15 is 1.5 m wide and 15 m long, and the weir 15 is connected from the drainage hole 14 to 0.
．． It is located at a distance of 5m. The total amount of washing water is 1.
The cleaning water in the treatment tank 12 contained 3,800 to 4,300 ppm of CN- after two weeks of operation after the water cutoff.
ions and about 5000 ppm of NH,+ ions. Under these conditions, the heat exchanger 18
~121! The temperature of the washing water was maintained at about 20° C. in the processing tank 12 by supplying cooling water of 20°C.

Approximately 40 kg of tar was recovered after two weeks of operation. There was almost no increase in the viscosity of the wash water, and the amount of water sent by the water pump 16 did not change (it was operated normally).

(Example 2) The conditions were the same as in Example 1 except for the amount of cooling water, and the amount of cooling water for heat exchange 4/summer 8 was set at 51/min. The temperature of the washing water in the treatment tank 12 at this time was 33°C.

Approximately 28 kg of tar was recovered after two weeks of operation.
The viscosity of the cleaning water increased only slightly, and the water pump 16 also operated normally.

(Comparative Example) As a result of operating the heat exchanger 18 at a cooling water rate of 30σ per minute under the same conditions as in Examples 1 and 2 except for the amount of cooling water, scale adhered to the heat exchanger 18 due to increased viscosity. The capacity of the heat exchanger 18 was reduced, and the temperature of the washing water in the treatment tank 12 was about 60°C. Even after one week of operation, the amount of tar recovered was 1 kg.When the system was not restarted, the water pump 16 could not be started due to overload, and the washing water had to be replaced.

[Effects of the Invention] The present invention provides fibrous materials in a firing furnace with an inert atmosphere.
In the method of producing flame-resistant fibers or carbon fibers by heating to temperatures above ℃, there is a step of washing the exhaust gas generated in the above-mentioned firing furnace with water to remove tar from the exhaust gas, and washing the cleaning water containing the tar with water. Since the step of flotation-separating the tar content by maintaining the temperature within the treatment tank at 40° C. or lower is performed, the tar content of the washing water can be efficiently removed. Therefore, the viscosity of the washing water can be lowered, and the system of circulation and reuse can be carried out with a relatively small amount of washing water, making it easy to post-process the washing water.

In addition, by increasing the effectiveness of the wet cleaning method, the excellent effect of stably producing carbon fibers is achieved.

The accompanying drawings schematically depict one embodiment of the method of the invention.

1...Calcination furnace, 5...Scrubber dust collector, 10...Pyrolysis device, 11...Water ring vacuum pump,! 2...processing tank, 16...
...Water pump, 18...Heat exchanger.

Claims (2)

[Claims] (1) Fibrous material is heated to 300°C in a firing furnace in an inert atmosphere.
In the method of manufacturing flame-resistant fibers or carbon fibers by heating to the above temperature, the exhaust gas generated in the above-mentioned firing furnace is washed with water to remove tar from the exhaust gas, and the cleaning water containing the tar is washed with water. 1. A method for treating exhaust gas in the production of carbon fibers, comprising a step of floating and separating tar by maintaining the temperature at 40° C. or lower in a treatment tank. (2) The method according to claim 1, characterized in that the washing water is recycled.