The thermal energy of the joint preparation method of polysilicon and quartz glass is fully utilized, and the production process does not have the phenomenon of repeated heating and cooling, so it can save energy, and the number of energy saving is considerable.
The polysilicon is produced by the traditional single production method, and the raw materials are sent to the reduction furnace after coming out of the bubbler. In the furnace, the raw material is heated to 1150-1250°C, and a hydrogen reduction reaction occurs to generate polycrystalline silicon. With this production method, only a few (generally considered 10% to 20%) of the raw materials entering the reduction furnace participate in the reaction to generate polysilicon, most of which are discharged as tail gas. Initially, these exhaust gases were discharged as exhaust gas, resulting in great waste. In order to avoid waste, people recover the hydrogen and silicon tetrachloride in the exhaust gas, and then reuse them after purification and purification. In this way, the high-temperature material that comes out enters the recovery system composed of the refrigerated separator and hydrogen recovery for recovery. In the recovery system, the raw materials are frozen and cooled to below the boiling point of silicon tetrachloride (57.6°C), which is generally considered to be at 40-38°C. For example, according to the minimum temperature of 1150 °C in the reduction furnace for the returned raw materials,
The maximum temperature after cooling is 40. C calculation, but also to cool down 1100 ℃. The problem is that after recovery, the raw materials at room temperature of 4()°C should be sent to the bubbler again, then passed into the reduction furnace, and heated to 11501250 again. C high temperature.
It can be seen from the above process that most of the reduced raw materials (accounting for 9()% of the incoming charge) that are heated in the reduction furnace are sent out for cooling without being used, and after cooling, they are sent back to the reduction furnace to participate in a new round of The raw material for the reaction. Obviously, this is a waste, and the raw materials that did not participate in the reaction should not be heated. The problem is that in the reduction furnace, the raw materials that did not participate in the reaction and the raw materials that participated in the reaction are mixed together and cannot be separated at all. If the raw materials that did not participate in the reaction are not heated, the raw materials that participate in the reaction cannot be heated either. . We know that if the temperature of the reducing material participating in the reaction is low, chemical reaction cannot be carried out, and polysilicon cannot be produced. Therefore, if polysilicon is produced by the traditional single-item production method, the above-mentioned waste is unavoidable.
If the joint preparation method of polysilicon and quartz glass is adopted, the raw materials that have not participated in the reaction from the reduction furnace will not enter the recovery system, but will be directly entered into the mass-making machine as the raw materials for the production of quartz glass, so there is no need to cool down. That is to say, using the joint preparation method of polysilicon and quartz glass to produce polysilicon can avoid the above waste and save 80% to 90% of energy. This is only the production of polysilicon, and the production of quartz glass by the joint preparation method of polysilicon and quartz glass also has obvious energy-saving advantages.
The production of quartz glass by the traditional single-item production method also needs to heat the synthetic material fed into the weight machine, and the heating rate is larger. It is generally believed that a high temperature of 1400-1600°C is required in the reaction zone of the pounding machine, and a large amount of energy is required to reach such a high temperature. The traditional single production method to produce quartz glass relies on the combustion of hydrogen and oxygen to obtain high temperature. We know that the synthetic material produced by a single item already contains hydrogen, but in order to achieve this high temperature, fuel hydrogen and combustion-supporting oxygen must be fed into the reaction zone of the pounding machine, and the amount of fuel hydrogen is larger than that of the synthetic material. contained hydrogen.
If the combined preparation method of polysilicon and quartz glass is used, the reducing material that has not participated in the reaction from the reduction furnace is directly entered into the mass making machine as a synthetic material. The temperature of the material is already very high, around 1150-1250 °C. When such material is passed into the mass making machine, there is no need to pass fuel hydrogen to the reaction zone of the mass making machine, because the heat generated by the combustion of the hydrogen contained in the material can fully meet the needs of the chemical reaction. From this it can be seen that
Using the joint preparation method of polysilicon and quartz glass to produce quartz glass can save 50% to 6()% of hydrogen, which shows that these figures are quite considerable.
Environmental protection
The joint production of polysilicon and quartz glass is continuous, and the equipment is connected in series. The tail gas or tail liquid of the previous product is used as the raw material of the next product, so that the tail gas that should be discharged as waste gas has been comprehensively utilized. Therefore, it can not only reduce the emission of exhaust gas, but also reduce the pollution to the environment.
Using the traditional single-production method to produce polysilicon requires exhaust gas to be released. Even with a recovery system consisting of a refrigerated separator and hydrogen recovery, exhaust gas is still emitted, but the amount of exhaust gas is much smaller. The above-mentioned tail gas is composed of the reducing material that does not participate in the reaction and the waste gas generated after participating in the reaction. The raw materials that do not participate in the reaction are mainly composed of hydrogen and silicon tetrachloride; the waste gas produced after participating in the reaction is mainly hydrogen chloride. The discharge of hydrogen will not pollute the environment, but silicon tetrachloride and hydrogen chloride are different. They are both toxic substances, which will cause serious pollution to the environment and cannot be directly discharged into the atmosphere. Silicon tetrachloride is a strong irritant that can suffocate people. It is said that during World War II, the Germans once wanted to use silicon tetrachloride as a chemical weapon, so you can imagine how harmful it is. The toxicity of hydrogen chloride gas is also quite large. When it encounters water, it will become hydrochloric acid, one of the three major acids, which is extremely harmful to human body, buildings, equipment and the environment.
Using the traditional single production method to produce quartz glass also emits exhaust gas. The exhaust gas also contains toxic hydrogen chloride, which is also harmful to the environment.
If the joint preparation method of polysilicon and quartz glass is used to produce polysilicon and quartz glass, the exhaust gas problem will be solved. The joint preparation method of polysilicon and quartz glass The exhaust gas released from the reduction furnace for polysilicon production is not directly vented, but is directly sent to the mass making machine to produce quartz glass. In this way, the problem of exhaust gas pollution in the production of polysilicon will be greatly reduced.
Quartz glass is produced by the joint preparation method of polysilicon and quartz glass, and the exhaust gas from the mass-making machine is sent to the exhaust gas treatment system. The tail gas treatment system can convert the tail gas released by the mass making machine into dilute hydrochloric acid and silicon dioxide. Silica is harmless, its particles are small and its purity is very high, it is an advanced nano-scale material, and its use is relatively wide. It can not only become a pharmaceutical and paint additive, but also a raw material for many chemical production. Dilute hydrochloric acid is harmful, but it can be recovered and concentrated into the finished acid. The finished hydrochloric acid is also an important chemical product with a wide range of uses. Dilute hydrochloric acid can also not be recovered, as long as some alkali is added to neutralize it, the harm will be gone, and it can be discharged. From this point of view, using the joint preparation method of polysilicon and quartz glass to produce polysilicon and quartz glass can not only reduce the emission of exhaust gas, but also reduce the pollution to the environment.
Low equipment cost
The joint production of polysilicon and quartz glass can save some equipment, thereby saving investment and reducing the labor intensity of operators.
The production of polysilicon by the traditional single production method requires a silicon tetrachloride synthesis furnace and a silicon tetrachloride purification system. Using the traditional single production method to produce quartz glass also requires a silicon tetrachloride synthesis furnace and a silicon tetrachloride purification system. If the joint preparation method of polysilicon and quartz glass is used to produce silicon tetrachloride and polysilicon, the above equipments are integrated. In terms of the number of equipment, the joint preparation method of polysilicon and quartz glass is reduced by half compared with the traditional single production method. It’s just that the equipment is larger, but the investment in a single device will not increase too much. Such as silicon tetrachloride synthesis furnace, its diameter is doubled, its output can be increased four times. The same is true for the equipment in the silicon tetrachloride purification system. If the size increases a little, the output will increase a lot.
The production of polysilicon by the traditional single-item production method and the production of quartz glass with the traditional single-item production method also require a set of hydrogen purification systems composed of freezing dehumidification, deoxidation, and drying, and a bubbler. These devices are also integrated if the production is carried out using the combined production method of polysilicon and quartz glass.
Less investment in infrastructure
Using the joint preparation method of polysilicon and quartz glass can save some equipment and workshops, reduce capital investment, reduce total investment (see attached table 3), and pay less price, thus promoting the production of these products.