Method and an installation for obtaining carbon bodies from carbon-precursor bodies
View Patent ↗The method comprises a first stage of transforming carbon precursor material into carbon by heating, with the resulting gaseous effluent being extracted continuously, and a second stage of high temperature heat treatment under low pressure with the resulting gaseous effluent being extracted continuously. The first and second stages are performed one after the other in the same oven by proceeding, after the end of the first stage, with the steps of switching the gaseous effluent outlet from the oven to interrupt a connection with a first extractor device and to establish a connection with a second extractor device, of adjusting the pressure inside the oven to the value required for the second stage, and of adjusting the heating temperature of the oven starting from the temperature reached at the end of the first stage. It is also possible to switch temperature measurement from at least one first sensor to at least one second sensor different from the first. During the second stage, any alkali metal such as sodium contained in sublimed form in the gaseous effluent coming from the oven can be neutralized, e.g. by injecting CO 2 into an effluent exhaust pipe.
1. An industrial method for obtaining a carbon fiber body from a carbon-precursor fiber body made of fibers in a carbon-precursor material, the method comprising:
placing the carbon-precursor fiber body in an oven;
performing in the oven a first stage heating of the carbon-precursor fiber body under a first pressure and up to a first temperature in the range from 750 to 1,100° C. to transform the carbon-precursor material to carbon and obtain the carbon fiber body, wherein a first gaseous effluent containing gaseous carbonization by-products is continuously extracted via a first extractor device;
performing in the oven a second stage healing of the carbon fiber body under a second pressure lower than the first pressure and up to a second temperature to sublime sodium contained in the carbon fiber body, and
introducing an inert gas into the oven and continuously extracting a second gaseous effluent containing the inert gas and sublimed sodium via a second extractor device, wherein the second extractor device comprises a shaft having baffle plates to trap solids contained in the second gaseous effluent, the first stage heating and the second stage heating performed sequentially with the carbon fiber body in the oven, wherein transitions between the first stage heating and the second stage heating include switching between extraction of the first gaseous effluent and the second gaseous effluent by switching between the first extractor device and the second extractor device.
2. The method of claim 1 , further comprising measuring temperatures via sensors during the first stage heating and the second stage heating, wherein measurement is switched after the first stage heating from at least one first sensor to at least one second sensor.
3. The method of claim 2 , wherein the at least one first sensor is a thermocouple type sensor housed in the oven close to a wall thereof and sacrificed during the second stage heating.
4. The method of claim 3 , wherein the at least one first sensor is disposed in a confined space to avoid polluting the atmosphere inside the oven as the at least one first sensor is sacrificed.
5. The method of claim 1 , wherein transitions between the first stage heating and the second stage heating is automated.
6. The method of claim 1 , wherein the oven is leak-tested prior to the first stage heating.
7. The method of claim 6 , wherein leak-testing comprises sweeping an inside volume of the oven with a gas and measuring a quantity of gaseous oxygen contained in a gas outlet from the oven after the oven is loaded.
8. The method of claim 1 , wherein during the second stage heating, sublimed sodium contained in the second gaseous effluent extracted from the oven is neutralized.
9. The method of claim 8 , wherein neutralizing sublimed sodium is performed at least in part via passivation by injecting carbon dioxide into the second gaseous effluent extracted from the oven by the second extractor device.
10. The method of claim 8 , wherein neutralizing sublimed sodium is performed at least in part via hydration by injecting steam.
11. The method of claim 1 , wherein the fibers in the carbon-precursor material are preoxidized polyacylonitrile fibers.