Fluidized Bed Temperature Control in Silicon Granulate Reactors
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Solution Overview
Problem
Existing methods for determining fluidized bed temperature in polycrystalline silicon granulate production are hindered by direct measurement issues, such as contamination and disturbance from dust formation, making precise temperature control impossible.
Innovation Solution
Determine the fluidized bed temperature (TWS) indirectly through the mass and energy balance of an offgas stream from the fluidized bed region, using balance ambits I and/or II, and adjust the heating output to maintain optimal process conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct measurement of fluidized bed temperature is performed using a thermocouple, then temperature data can be obtained, but the thermocouple causes contamination and disturbs process quality
Solution Approach 1:
The patent uses an intermediary substance (tracer gas) to indirectly measure fluidized bed temperature. The tracer gas is introduced into the fluidized bed, and its temperature is measured outside the bed, providing temperature data without direct contact with the process material, thus avoiding contamination and disturbance.
Solution Approach 2:
The patent replaces the mechanical thermocouple measurement system with a gas-phase measurement system. Instead of using a solid thermocouple that physically contacts the fluidized bed, the invention uses a tracer gas that mixes with the fluidized bed atmosphere and carries temperature information to an external sensor.
2Measurement precision
If pyrometer is used to measure fluidized bed temperature, then non-contact measurement is achieved, but dust formation disturbs the beam path and prevents precise control
Solution Approach 1:
The patent introduces a tracer gas as an intermediary that is transparent to the measurement method and not affected by dust formation. The tracer gas molecules carry temperature information from the fluidized bed to external sensors without being scattered or absorbed by dust particles, enabling precise temperature measurement despite dust presence.
3Measurement precision
If thermocouple is placed in the fluidized bed for temperature measurement, then temperature control can be implemented, but reactor running time is limited due to silicon deposition on the thermocouple
Solution Approach 1:
The patent uses tracer gas as an intermediary to transfer temperature information from the fluidized bed to external measurement devices. The tracer gas does not deposit silicon and can continuously carry temperature data without degradation, enabling long-term operation without the thermocouple fouling problems that limit reactor running time.
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
Enables precise and undisturbed temperature control, ensuring consistent product quality and extended reactor operation by maintaining a stable chlorine content and minimizing dust formation.
Implementation Method 1
The fluidized bed region is heated via the reactor wall with a heating apparatus
Implementation Method 2
continuously supplied seed particles are fluidized in a fluidized bed by means of a gas flow
Implementation Method 3
A supply of a feed gas stream comprising hydrogen and silane and/or halosilane causes elemental silicon to be deposited on the seed particles to form the granulate
Data Source
AI summary
Silicon granulate is produced in a fluidized bed reactor having a fluidized bed region fluidized by a gas flow and heated by a heating apparatus. Seed particles and a feed gas including hydrogen and silane and/or halosilane is continuously supplied, and elemental silicon is deposited on the seed particles to form the silicon granulate, which is discharged as a continuous product stream from the reactor. The fluidized bed temperature affects the quality and formation of the product stream, which may be determined as the temperature of an offgas stream from the fluidized bend region. The temperature, as a responding variable may be determined and controlled by means of the mass and energy balance of a defined scheme.