Infrared Heated Solid Bed for Contamination-Free Gas Heating
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Solution Overview
Problem
Existing methods for heating gases in fluidized bed deposition processes, such as those used for high-purity polycrystalline silicon production, often result in contamination due to the use of metallic heating elements, especially at high temperatures, which can introduce impurities into the gas being heated.
Innovation Solution
A method and device where high-purity gases pass through a container filled with a non-reactive, immobile solid, such as high-purity silicon, that is heated using infrared radiant heaters with a container wall highly transparent to infrared rays, ensuring minimal contamination and efficient heating of gases to temperatures between 300°C to 1200°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If metallic heating elements are used to heat gases to high temperatures, then the heating efficiency is improved, but the gas becomes contaminated with metal impurities
Solution Approach 1:
The patent introduces an intermediary substance (solid granules such as silicon dioxide, silicon carbide, or aluminum oxide) that absorbs infrared radiation and transfers heat to the gas without directly contacting the gas in a way that causes contamination. This intermediary acts as a heat transfer medium that eliminates the harmful metal-gas contact while maintaining efficient heating.
Solution Approach 2:
The patent replaces the mechanical contact-based heating system (metallic heating elements directly contacting the gas) with a radiation-based heating system where infrared radiation heats the solid granules, which then transfer heat to the gas through convection and conduction without requiring direct mechanical contact between the heat source and the gas.
2Loss of energy
If the gas is preheated before entering the fluidized bed, then the heating requirement of the fluidized bed is reduced, but the risk of contamination from the preheating device increases
Solution Approach 1:
The solid granules serve as an intermediary heat transfer medium in the preheating section, allowing the gas to be heated efficiently through radiation and convection without direct contact with metallic heating elements, thus reducing energy requirements while preventing contamination.
Solution Approach 2:
The patent uses chemically inert solid materials (such as silicon dioxide, silicon carbide, or aluminum oxide) that do not react with or contaminate the process gas, creating a chemically inert heating environment that prevents contamination while enabling efficient preheating.
3Productivity
If the temperature of metallic heating elements is increased to heat the gas more effectively, then the heating efficiency is improved, but the degree of gas contamination increases
Solution Approach 1:
The solid granules act as a thermal intermediary that can be heated to high temperatures by infrared radiation and then transfer this heat to the gas without causing contamination, thus maintaining high heating efficiency while eliminating the contamination problem associated with metallic heating elements at high temperatures.
Solution Approach 2:
The patent changes the physical state and material parameters of the heating medium from metallic solids to inert non-metallic solids, and changes the heating mechanism from direct contact conduction to radiation-based heating, thereby decoupling the relationship between temperature and contamination.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for contamination-free heating of gases to near their decomposition temperature, reducing the risk of impurity introduction and enabling efficient preheating of gases for fluidized bed deposition processes without compromising the purity of the gas or reaction products.
Implementation Method 1
the container is irradiated by infrared rays, thereby heating the solid and heating the gas
Implementation Method 2
the container wall is made of a material which is more than 85% transparent to infrared rays
Implementation Method 3
the solid is heated by the infrared rays
Data Source
Figure 1
AI summary
A highly pure gas is passed at pressure of 0.1-10 bar over a highly pure solid which does not contaminate the gas. The solid is placed in a highly pure container. The wall (3) of the container has transparency of 85% or more. The container is subjected to irradiation using infrared rays to heat the solid, and then to heat the gas to a temperature of 300-1200[deg] C. A highly pure gas is passed at pressure of 0.1-10 bar over a highly pure solid which does not contaminate the gas. The solid is placed in a highly pure container. The wall of the container has transparency of 85% or more. The container is subjected to irradiation using infrared rays to heat the solid, and then to heat the gas to a temperature of 300-1200[deg] C. The solid contains silicon, silicon carbide and/or silicon nitride (Si 3N 4), preferably polycrystalline silicon (2). The container comprises quartz glass. An independent claim is included for apparatus for contamination-free heating of gas.