1.Save energy
The heat energy of the joint preparation method of polysilicon and quartz glass is fully utilized, and the production process does not repeatedly raise and lower the temperature, 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 material is sent to the reduction furnace after coming out of the bubbler. In the furnace, the raw materials are heated to 1150 to 1250℃, and a hydrogen reduction reaction occurs to produce polysilicon. With the production method,only a few (generally considered to be 10% to 20%) of the raw materials that enter the reduction furnace participate in the reaction to generate polysilicon, and most of them are discharged as tail gas. Initially, these exhaust gases were discharged as exhaust gases, causing great waste. In order to avoid waste, people recycle the hydrogen and silicon tetrachloride in the tail gas, and reuse them after purification. In this way, the high temperature material that comes out enters the recovery system composed of a 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℃), which is generally considered to be 40～38℃.
For example, the lower limit temperature of the raw material in the reduction furnace is 1150℃, and the upper limit temperature after cooling is 40℃ is calculated, and the temperature should be reduced by 1100℃. The problem is that after recovery, the raw materials at room temperature of 40℃ have to be sent to the bubbler again, then passed into the reduction furnace, and heated to 1150~1250℃’s high temperature again.
It can be seen from the above process that most of the raw materials (accounting for 90% of the incoming charge) that enter the reduction furnace to be heated are sent out to be cooled without being used, and then sent back to the reduction furnace to participate in a new round after cooling. The reaction is also the raw material. Obviously, this is a waste. The raw materials that have not participated in the reaction should not be heated. But 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, then the raw materials that participate in the reaction cannot be heated either. . We know that the low temperature of the raw materials participating in the reaction cannot carry out the chemical reaction, and thus cannot produce polysilicon. Therefore, if the traditional single production method is used to produce polysilicon, the above-mentioned waste is inevitable.
If the combined preparation method of polysilicon and quartz glass is adopted, the raw materials that do not participate in the reaction from the reduction furnace will not enter the recycling system, but will be used as raw materials for the production of quartz glass directly into the mound machine, so there is no need to cool down. That is to say, the production of polysilicon by the combined preparation method of polysilicon and quartz glass can avoid the above-mentioned waste and can save 80% to 90% of energy. This is only the production of polysilicon, and the use of the combined preparation method of polysilicon and quartz glass to produce quartz glass also has obvious energy saving advantages.
In the production of quartz glass by the traditional single production method, it is also necessary to heat the synthetic material sent to the mound machine, and the increase in temperature is greater. It is generally believed that the high temperature of 1400 to 1600 ℃ in the reaction zone of the mound machine is required, and a large amount of energy is required to reach such a high temperature. The traditional single production method produces quartz glass by hydrogen-oxygen combustion to obtain high temperature. We know that the synthetic material produced in a single production already contains hydrogen. In order to achieve this high temperature, it is necessary to pass fuel hydrogen and combustion-supporting oxygen into the reaction zone of the mound machine, and the amount of fuel hydrogen is greater than the synthetic material. The hydrogen contained.
If the combined preparation method of polysilicon and quartz glass is used, the raw materials that do not participate in the reaction from the reduction furnace are treated as synthetic materials and directly enter the mound maker. The temperature of the material is already very high, about 1150 ~ 1250 ℃. This kind of material is passed into the mound making machine and there is no need to pass fuel hydrogen to the reaction zone of the mound making machine, because the heat generated by the combustion of the hydrogen contained in the material can fully meet the needs of chemical reactions. It can be seen that the use of the combined preparation method of polysilicon and quartz glass to produce quartz glass can save 50% to 60% of hydrogen. It can be seen that these figures are considerable.
2.2.Environmental protection
The combined 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 is comprehensively utilized. Therefore, it can not only reduce exhaust emissions, but also reduce environmental pollution.
The production of polysilicon using the traditional single-phase production method requires exhaust gas. Even with a recovery system composed 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 raw materials that have not participated in the reaction and exhaust gas generated after participating in the reaction. The raw materials that did not participate in the reaction were mainly composed of hydrogen and silicon tetrachloride; the waste gas produced after participating in the reaction was 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 and will cause serious pollution to the environment. They cannot be directly discharged into the atmosphere. Silicon tetrachloride is a strong irritant substance and can suffocate people. It is said that the Germans once wanted to use silicon tetrachloride as a chemical weapon during the Second World War, so you can imagine how harmful it is. Hydrogen chloride gas is also very toxic. It will become hydrochloric acid, one of the three strong acids when it meets with water, which is extremely harmful to humans, buildings, equipment, and the environment.
The production of quartz glass using the traditional single-phase production method also emits tail gas. The exhaust gas also contains toxic hydrogen chloride, so it also harms 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 combined preparation method of polysilicon and quartz glass produces polysilicon. The exhaust gas from the reduction furnace is not directly vented, but is directly sent to the mound machine to produce quartz glass. In this way, the exhaust pollution problem of polysilicon production will be greatly reduced.
The combined preparation method of polysilicon and quartz glass is used to produce quartz glass, and the tail gas from the mound machine is sent to the tail gas treatment system. The tail gas treatment system can convert the tail gas from the mound machine into dilute hydrochloric acid and silica. Silica is harmless, its particles are small and the purity is extremely high, it is an advanced nano-level material, and its use is relatively wide. It can not only be used as an additive in pharmaceuticals and paint, but also as a raw material for many chemical production. Dilute hydrochloric acid is harmful, but it can be recycled and concentrated into finished acid. The finished hydrochloric acid is also an important chemical product with a wide range of uses. Dilute hydrochloric acid does not need to be recycled, as long as some alkali is added to neutralize it, there will be no harm, and it can be discharged. From this point of view, the use of a joint preparation method of polysilicon and quartz glass to produce polysilicon and quartz glass can not only reduce exhaust gas emissions, but also reduce environmental pollution.
3.3.Less equipment cost
The combined production method of polysilicon and quartz glass can save some equipment, which can save investment and reduce the labor intensity of operators.
To produce polysilicon using the traditional single production method requires a silicon tetrachloride synthesis furnace and a silicon tetrachloride purification system. The production of quartz glass using the traditional single production method also requires a silicon tetrachloride synthesis furnace and a silicon tetrachloride purification system. If the joint preparation method of polycrystalline silicon and quartz glass is used to produce silicon tetrachloride and polycrystalline silicon, the above-mentioned equipment is integrated. In terms of the number of equipment, the joint preparation method of polycrystalline silicon 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 equipment will not increase too much. For example, if the diameter of a silicon tetrachloride synthesis furnace is doubled, its output can be increased four times. The equipment in the silicon tetrachloride purification system is also the same. A little increase in size will increase the output a lot.
The production of polysilicon by the traditional single production method and the production of quartz glass by the traditional single production method also require a hydrogen purification system composed of freezing dehumidification, deoxidation, and drying, and a bubbler. If the joint production method of polysilicon and quartz glass is used, these equipments are also integrated.
This is not the place where the joint production method of polysilicon and quartz glass saves the most compared to the single production method.
This is not the place where the joint production method of polysilicon and quartz glass saves the most compared to the single production method.
The production of polysilicon using the traditional single production method requires a recovery system composed of a refrigerated separator and a hydrogen recovery system. However, the production of polysilicon and quartz glass by the combined preparation method does not require this recovery system. This system is composed of a complete set of equipment with high technological content and high cost. We know that the minimum temperature of a household refrigerator is only minus ten degrees Celsius, and the minimum temperature of a general cold storage is only minus thirty degrees Celsius, but the freezing temperature used in this system must reach minus 80 degrees Celsius, or even more Low; domestic refrigerators only have single-stage compression, and cold storage that requires deep cooling also only have two-stage compression, and the refrigerator used in this system is a cascade type, which is a two-stage compression, and The combination method is also special. According to estimates, the cost of this system should account for about one-third of the total equipment cost. In this regard, the use of a combined production method of polysilicon and quartz glass can save about one-third of equipment costs.
Obviously, less equipment not only saves investment, but also reduces the labor intensity of operators.
4.Low infrastructure investment
Using the combined production method of polysilicon and quartz glass can save some equipment and workshops, reduce capital investment, and reduce total investment (Table 3), and the cost is small, thereby promoting the production of these products.
5.5.Cooperate with the chlor-alkali industry to solve the balance problem and pollution problem
In recent years, my country’s chlor-alkali industry has developed rapidly, and its output has now ranked second in the world. Even so, my country’s chlorine and alkali products still cannot meet the needs of the domestic market.
Can my country’s chlor-alkali industry be further developed? It depends on whether the balance between chlorine and alkali can be solved.
At present, the production methods of caustic soda almost all adopt the method of electrolysis of salt water, so that for every 0.88t of chlorine produced, 1t of caustic soda is co-produced. This ratio cannot be changed at present. But the problem is that the market demand for chlor-alkali is not 0.88:1, but a variable, that is, the market demand for chlorine and alkali is not balanced. Sometimes chlorine is surplus, and sometimes alkali is surplus. Regardless of the excess of chlorine and alkali, there will be an imbalance between chlorine and alkali. The imbalance between chlorine and alkali also affects the environment. Regardless of which excess of chlorine and alkali accumulate, it may cause environmental pollution. Therefore, the balance between chlorine and alkali is the key to the development of the chlor-alkali industry. If the problem of the balance between chlorine and alkali is not solved, it will be difficult for my country’s chlor-alkali industry to develop further.
Chlorine is an important raw material for the combined preparation method of polysilicon and quartz glass, which consumes chlorine. If there is an excess of chlorine, the preparation method can be combined with the chlor-alkali industry with excess chlorine to help solve the problem of the balance between chlorine and alkali. When the balance between chlorine and alkali is solved, the accumulation of chlorine will be reduced, or even zero, and the pollution problem will be solved.
6.6.Electronic industry materials-the solution to the bottleneck problem of polysilicon
As we said earlier, polysilicon is the basic material of the electronics industry. Due to the use of traditional single-phase production methods to produce polysilicon, a great price for resources and the environment is required. The excessive price has restricted the production and development of polysilicon. At present, due to the shortage of polysilicon, some electronics industry manufacturers are forced to reduce production or even shut down. Obviously, polysilicon has become a bottleneck in the current development of the electronics industry, hindering the development of the electronics industry.
The production of polysilicon by the joint preparation method of polysilicon and quartz glass will reduce the cost, which will promote the development of polysilicon, and the bottleneck problem of electronic industry materials (polysilicon) will therefore be solved.