In order to ensure the good practicability of continuous high temperature mode graphite purification equipment and process, it is necessary to recognize the importance of continuous high temperature mode graphite purification process, combination with the difficulties in graphite purification and the characteristics of the purification equipment and process, scientifically use continuous high temperature mode graphite purification equipment and process to purify graphite materials.
In the development of modern society, the requirement for the properties of various materials is increasing. Graphite materials has not only excellent structural characteristics, but also good electrical conductivity, high temperature resistance and other characteristics, which makes it widely used in metallurgy, electronic parts manufacturing and new energy sources’ development and so on. Therefore, it is more necessary for graphite manufacturer to use advanced production equipment and processes such as continuous type high temperature reaction to promote graphite production.
Development in the field of graphite production.
1 purification equipment and process analysis of graphite production
Graphite materials is used in many fields of modern development, which makes the demand for graphite increasing. The actual storage of graphite resources in China is huge, but the graphite purification process needs further development, especially some high-purity graphite needs to rely on imports. Natural graphite raw materials contain many kinds of impurities, such as silica, magnesium oxide, ferric oxide, carbon dioxide, ammonia and so on, which lead to the low content of carbon elements in graphite raw materials and difficult to use directly. Therefore, during the production of graphite materials, purification operation is an important content. With the continuous research and development of graphite production and purification, there have been a variety of purification processes, various purification measures have their own characteristics. Chemical type purification method has the advantages of low production and processing cost, strong adaptability of treatment process, and high efficiency of impurity treatment. However, this kind of chemical purification method also has the shortcomings of serious loss of graphite raw materials, a large number of wastewater and waste gas produced in the production process, and serious impact on the natural environment. For example, in the use of chemical acid-base treatment of graphite raw material purification, need to use sodium hydroxide, sulfuric acid, hydrochloric acid and hydrofluoric acid, and these substances have strong corrosiveness. At present, there are also physical type purification methods in the field of graphite raw material purification. This physical type of purification method emits less pollutants, but the results of various purification methods are quite different, and the actual process adaptability is poor. For example, in the use of high-temperature purification method, although a higher purity of graphite materials can be obtained, but the raw materials need to process natural graphite with higher original purity. When the original purity of natural graphite is low, it will not only consume a lot of energy, but also the actual production cost will be high, coupled with the production efficiency is also low, so it is difficult to achieve large-scale production of graphite materials. In order to enhance the quality of graphite raw material purification, it is necessary to combine physical type purification process with chemical type purification process, such as mixing non-polluting reactive gases into high temperature purification environment, and finally realizing high efficiency, non-polluting and high stability of graphite material purification process. High-performance equipment is an indispensable basic condition for high-level graphite raw material purification production. In the development of equipment hardware, Acheson furnace equipment, intermediate frequency induction graphite raw material purification furnace equipment, continuous type pusher boat graphite raw material purification furnace equipment appeared. The development of these equipment is closely related to the development of graphite raw material purification process. In order to purify graphite raw material by continuous high temperature reaction mode, advanced continuous type hot working equipment is needed, and high purity graphite materials with stable output can be obtained by reaction treatment with chemical high temperature type. This will also push forward the continuous development of graphite processing industry.
2 Analysis of operation process and test mode of graphite purification equipment
2.1 equipment operation process analysis
At present, the advanced continuous type of resistance heating purification equipment in the process of graphite purification will mainly go through four steps, namely automatic feeding link, equipment heating purification link, automatic discharging link and tail gas treatment link.
First, in the automatic feeding process, the graphite raw material enters the silo from the feeding port of the equipment feeding structure and closes the feeding valve at the same time; the argon needed for purification treatment is injected into the silo through the gas displacement pipeline, thus completing the gas displacement in the silo and making the oxygen content continues to decrease in the silo until the oxygen content is reduced to the standard conditions, then the feed valve is opened and the powder is fed into the heating system through a spiral feeding device. At the same time, in order to ensure a stable material supply in the purification stage, it is necessary to adjust the powder feeding rate of feeding equipment and the purification rate of graphite powder in the heating region.
Secondly, in the heating and purification process, the graphite powder material will enter the heating system directly from the feeding pipe, and transmit forward by means of the high-temperature type conveyor, keeping this state through the heating region, thus achieving continuous purification at high temperature. In the process of heating and purification, some impurities in the raw materials of graphite powder will also volatilize, and the carrier gas will be eventually sent to the tail gas treatment system through the exhaust pipe structure. The purified graphite powder needs to move forward after leaving the high temperature heating area. It falls into the discharge tube structure under the influence of its own gravity, and then enters the cooling silo and the discharge system in turn. In operation, this equipment will use frequency conversion type motor to control the time of processing material passing through the processing area and the discharging speed.
Third, the automatic discharging link, high-temperature state graphite powder after cooling treatment in the cooling silo, from the discharging valve structure into the discharging silo, and then through the discharging valve structure discharged. Argon is used to replace the gas in the whole discharge bin before the next batch of graphite powder enters the discharge bin, so that the air entering the part of the discharge bin is exhausted.
Finally, the tail gas treatment process produces a certain amount of by-products, such as tar, metal chloride, carbon black and other excess gases, when using this method to purify raw graphite materials. These substances often pose certain environmental hazards and need to use a four-stage collection device to collect these by-products together to avoid environmental pollution caused by these by-products.
2.2 Purification of raw materials of cryptic graphite
When graphite raw materials are purified using a continuous type of high-temperature reaction equipment, the highest reaction temperature of the equipment is 2600 degrees Celsius. After vacuum is pumped into the equipment of the purifying furnace, high purity argon is injected into it, argon is used as protective gas, and the pressure condition in the furnace is kept stable by adjusting the actual opening of the tail gas electric valve components, and the flow rate of argon is maintained at 200 litres per hour. The raw graphite powder to be processed is put into the feeding device and heated at a rate of 6 degrees Celsius per minute until the temperature rises to 2600 degrees Celsius. The graphite powder is continuously added to the feeding device, and the freon gas is injected into the feeding device. The gas flow rate is set at 80 liters per hour to maintain the continuous purification mode type. After the purification operation was completed, the flow of argon gas was stabilized and the temperature of the reaction chamber was gradually lowered.
3 Analysis of the advantages of new high temperature graphite material purification furnace
3.1 high temperature heating and insulation technology analysis
In the current high temperature heating operation, there are mainly two types of induction heating mode and resistance heating. The resistance heating mode needs to distribute the heating power of the high-temperature elements in the furnace according to the specific heating power, so that the distribution of the heating field in the furnace can reach the optimal state. In the ultra-high temperature type of heating equipment, the actual temperature of the heating element must be able to exceed the maximum operating temperature of the equipment, so as to ensure that the heating element and other workpieces in the same furnace will not be polluted and corroded each other. When the furnace is running, if the reaction temperature is set to 2600 degrees Celsius, then the furnace with different heating areas will generally be between 2995 and 2604 degrees Celsius, to ensure that the temperature difference is within 5 degrees Celsius, so that the furnace temperature distribution has good uniformity.
3.2 high temperature insulation and energy saving technology
In order to satisfy the requirements of water, electricity, gas and heat in the process of purification, high temperature materials must have strong refractory temperature in use, high load softening temperature, small variation of reburning line and thermal shock resistance. The more common refractory insulation materials mainly include high-purity silicic acid, high-alumina fiber felt, high-temperature furnace design will also have an impact on the insulation effect, in most cases, many technicians in order to make the structure design simpler, will use a single insulation layer, although this has certain advantages, but the existence of shortcomings can not be ignored.
3.3 high temperature measurement and control technology
High temperature will be produced in the actual operation of the equipment, so the technical staff in the selection of high temperature measurement and control components, to select carefully, not only have enough heat resistance, but also have a strong temperature measurement accuracy, in the actual application process of chemical stability, and the furnace for joint use will not be due to For high temperature environment change. There are two types of measuring operation in high temperature environment, contact and indirect measurement. The quality of contact measurement mainly depends on the temperature resistance of components such as measuring filament and insulating sleeve. At present, the maximum temperature of thermocouple side is 1800℃, the material of couple wire can choose platinum rhodium or platinum.
3.4 exhaust treatment technology
The tail gas treatment system is mainly composed of condenser, physical collision absorber, and other four-stage collection devices. In general, the copper fin structure is used as a condensation converter, which works by solidifying the gaseous tar of graphite particles and collecting it. Physical collision adsorber for large particles of solid dust can play a complementary role in the adsorption capacity is more prominent, can be directly ultrafine particles of dust filtration treatment, this bag filter structure has many advantages, can filter the turbid gas in the mechanical pump, and then discharge. After the acid mist purification system is set up with multi-stage spraying structure, water-soluble gases such as chlorine can be dissolved by high efficiency spraying, and the relevant indexes of tail gas can not meet the discharge standards.
From the above discussion on the purification process of natural graphite powder, it can be concluded that the new industrial scale continuous graphite purification process and equipment have a good use effect, the actual operation of this equipment is relatively simple, and can be used for feeding, heating purification, discharging and other processes one-stop. The development ensures the efficiency of the whole purification process and saves a lot of manpower and material resources.
Author: Zhao Jianmin
