Why is air introduced at the bottom of the reduction furnace?
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In principle, feeding air from the top of a reduction furnace should increase the conversion rate, so why is air fed from the bottom in many cases?
Personal understanding: Intaking air from below and exhausting it from below can increase the residence time of the mixture inside the furnace, thereby improving the conversion rate
Air enters from below, exerting less impact on the stacked silicon core. Air intake from the sides and top may blow against the silicon core bridge structure. Gas is released from below, and the residence time of the gas in the reduction furnace is controlled based on pressure to increase the conversion rate. I would like to ask everyone a question: for a well-designed reduction furnace, how can we improve the distribution of the gas mixture inside the furnace? Solve the problem of the silicon rod being larger at the top and smaller at the bottom!
Could this be considered for the inlet nozzle? Since the feed material tends to concentrate at the bottom of the reactor, it might be advisable to design the nozzle to be wider
Hydrogen has an extremely low density and serves as a current carrier; entering from below helps to achieve a more uniform distribution of the mixture.
I agree with everyone’s view: entering and exiting from the bottom can **increase** the time that the material stays inside the furnace. Moreover, since the material enters from the bottom at a much faster speed, this ensures that the air flow reaches the top of the furnace and then settles down gradually, in a very uniform manner. If the residence time of the material inside the furnace is very short when it enters from above, the distribution of the material within the furnace will be uneven, unless the speed is very low and the gas distribution is extremely uniform. Entering from the side is even less ideal; firstly, it’s impossible to ensure uniform distribution of the material, and secondly, the airflow blows directly toward the silicon core, which can easily cause the rod to topple over.
I asked many people about this issue, and after reading their responses, I found them all to be quite reasonable. However, when considering this problem, it’s necessary to start with the principle of accuracy; this is also one of the main reasons. Intake from below facilitates easier installation and removal, as well as helps maintain cleanliness
Replying to floor 3: To address the issue of uneven distribution above and below the silicon rod under the current conditions, one approach is to reduce the feed rate, thereby lowering the gas velocity； Second is applying pressure; this also reduces the gas velocity, thereby preventing too much heat from being carried away from the root area, and helping to ensure uniformity across the silicon rod.
The design below makes sense; I have carried out simulated fluid dynamics analyses. These are all the most crucial steps in designing a furnace
We used computer simulations to model the gas flow pattern when air is introduced into the reduction furnace, and found that introducing air from the bottom is most beneficial for the uniform deposition of the entire silicon rod.