Carbonization furnace/kiln/oven structural framework:
The carbon fiber carbonization furnace is mainly composed of the furnace body, heating system, air control system, traction device and temperature control system.
Basic structure of carbonization furnace/kiln/oven body:
The furnace body is the outer shell of the carbonization furnace, which is generally made of high-temperature resistant stainless steel and can withstand high temperatures and certain pressures. A heat insulation layer will also be set inside the furnace body. Common heat insulation materials include ceramic fiber wool, which can effectively reduce heat loss. It is like putting a warm coat on the furnace, which can not only ensure the temperature inside the furnace is stable, but also avoid safety problems caused by excessive external temperature. Some small-scale carbonization furnaces used for experiments have relatively small furnace bodies and the thickness of the heat insulation layer may be 5-10 cm; while the carbonization furnaces used for large-scale industrial production have large furnace bodies and the thickness of the heat insulation layer can reach more than 20 cm.
Heating system composition of carbonization furnace/kiln/oven:
The heating system is the "heart" of the carbonization furnace, providing heat for the carbonization process. Common heating methods are electric heating and gas heating. Electric heating generally uses resistance wire heating, and the resistance wire is evenly arranged inside the furnace. In small carbonization furnaces in laboratories, resistance wire heating is very common because it has more precise temperature control. Gas heating generates heat by burning natural gas or coal gas. Large industrial carbonization furnaces mostly use this method, which can quickly provide a lot of heat. For example, in a large factory producing carbon fiber, a gas-heated carbonization furnace can consume dozens of cubic meters of natural gas per hour, quickly raising the temperature in the furnace to the high temperature required for carbonization.
Gas control system of carbonization furnace/kiln/oven:
The gas control system is responsible for introducing protective gas into the furnace and exhausting waste gas. The protective gas is usually nitrogen or argon, which can prevent the fiber from being oxidized during the carbonization process. Before the carbonization furnace is started, a large amount of nitrogen will be introduced into the furnace to exhaust the air and form an inert gas environment. The waste gas exhaust system must promptly exhaust the harmful gases generated during the carbonization process, such as carbon monoxide and carbon dioxide. In some areas with high environmental protection requirements, the waste gas exhaust system of the carbonization furnace will also be equipped with a purification device to treat the waste gas before discharging it.
Traction device of carbonization furnace/kiln/oven:
The traction device is to allow the fiber material to move at a uniform speed in the furnace to ensure uniform carbonization. It consists of a motor, a transmission belt and a guide roller. The motor drives the transmission belt to rotate, and the transmission belt drives the guide roller to rotate, and the fiber material is sandwiched between the transmission belt and the guide roller and moves forward. In actual production, the traction speed needs to be adjusted according to the type of fiber and the carbonization process. For example, when producing high-performance carbon fiber, the traction speed may be controlled at a few meters per minute; while when producing ordinary carbon fiber, the speed may be faster, reaching more than ten meters per minute.
Temperature control system of carbonization furnace/kiln/oven:
The temperature control system is the key to ensure the quality of carbonization. It includes temperature sensors, controllers and heating adjustment devices. Temperature sensors are distributed in different positions of the furnace body to monitor the temperature in the furnace in real time. The controller compares the actual temperature fed back by the sensor according to the set temperature curve, and then controls the heating adjustment device to adjust the heating power. For example, when the sensor detects that the temperature in the furnace is lower than the set value, the controller will instruct the heating system to increase the power; when the temperature is too high, the power will be reduced. During the carbonization process, the temperature curve is determined through repeated tests. The temperature requirements at different stages are different. The temperature should be raised quickly in the early stage, the temperature should be stable in the middle insulation stage, and the speed of cooling should also be controlled in the later stage.
Door structure of carbonization furnace/kiln/oven:
The furnace door must be well sealed to prevent heat loss and air from entering. The furnace door generally adopts a double-layer structure, the inner layer is a high-temperature resistant refractory material, and the outer layer is made of stainless steel. There are many ways to seal the furnace door. The most common one is rubber sealing ring sealing. A high-temperature resistant rubber sealing ring is installed on the edge of the furnace door, which can fit tightly to the furnace body when the door is closed. Some large carbonization furnaces also use hydraulic sealing devices to press the furnace door tightly through the hydraulic system, which has a better sealing effect. After opening the furnace door to take in and put in materials each time, check whether the sealing ring is intact and whether it is damaged or aged.
Cooling system configuration of carbonization furnace/kiln/oven:
The temperature of carbon fiber after carbonization is very high, and a cooling system is required to cool it down. There are two cooling systems: air cooling and water cooling. Air cooling is to blow air to the outlet of the furnace through a fan to take away the heat of the carbon fiber. This method is relatively simple, but the cooling speed is relatively slow. Water cooling is to set a water cooling tank at the outlet of the furnace, and the carbon fiber will quickly cool down when passing through the water cooling tank. In large-scale production, water cooling is more commonly used, which can quickly reduce the temperature of the carbon fiber from hundreds of degrees Celsius to room temperature. For example, in a carbon fiber production company, the water temperature of the water cooling tank will be maintained at 20-30℃, and the heat will be continuously taken away by circulating water.
Support structure of carbonization furnace/kiln/oven:
The support structure of the carbonization furnace must be stable and able to bear the weight of the furnace body and internal materials. The support structure is generally welded with steel sections, such as large H-shaped steel sections, which have the characteristics of high strength and good stability. When installing the carbonization furnace/kiln/oven, the support structure should be installed on a flat ground and horizontal calibration should be performed to ensure that the furnace body is level. If the support structure is not stable and the furnace body is tilted, it will affect the movement of the fiber in the furnace and the carbonization effect.
Key points for insulation layer construction:
The construction quality of the insulation layer directly affects the energy consumption of the carbonization furnace. When laying insulation materials such as ceramic fiber wool, pay attention to filling them tightly without gaps. For some corners and joints, special high-temperature resistant glue should be used for sealing. In actual construction, workers will first lay a layer of reflective aluminum foil inside the furnace body, and then fill it with insulation materials, which can further improve the insulation effect. Some factories will also wrap a layer of wire mesh outside the insulation layer to prevent the insulation material from falling off.
Safety protection devices:
The carbonization furnace/kiln/oven is equipped with a variety of safety protection devices. The over-temperature alarm device will sound an alarm and automatically cut off the heating power supply when the temperature in the furnace exceeds the set safety value. The pressure protection device can monitor the pressure in the furnace and automatically open the pressure relief valve when the pressure is too high. There is also a gas leak detection device. Once the protective gas or exhaust gas leak is detected, it will immediately alarm and start the ventilation system. In the production workshop, these safety protection devices are like loyal "guards", always ensuring the safety of equipment and personnel.
Connection with other equipment:
The carbon fiber carbonization furnace/kiln/oven does not work independently, but needs to be connected with the fiber pretreatment equipment in front and the carbon fiber post-treatment equipment in the back. Before the fiber enters the carbonization furnace, it needs to go through pre-treatment processes such as drafting and pre-oxidation; after carbonization, it needs to undergo post-treatment processes such as surface treatment and sizing. Therefore, when designing the carbonization furnace, the interface and process matching with these equipment should be considered. For example, the traction speed of the carbonization furnace must be consistent with the discharge speed of the pre-treatment equipment to ensure a smooth production process.
