Polysilicon Fluidized Bed Reactor Temperature Gradient Control

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Solution Overview

Problem

Polysilicon fluidized bed reactors face challenges in controlling axial temperature gradients, leading to inefficient reaction kinetics and reduced reactor lifespan due to unmonitored temperature variations and the impact of evolving particle size distributions on temperature profiles.

Innovation Solution

By measuring and controlling the width of the particle size distribution of granules in the reactor bed through adjusting seed addition frequency and pre-determined particle size distribution, the method optimizes axial temperature gradients, ensuring better reactor performance and prolonging reactor lifespan.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If temperature set-points are based on a thermocouple strategically placed along the reactor wall, then temperature monitoring is simplified, but the temperature reading is not a good predictor of temperatures in other (axial) regions

Engineering Contradiction:

Improvetemperature monitoringVSAvoidtemperature prediction accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent uses particle size distribution as an intermediary parameter to indirectly control and predict temperature profiles. By measuring and controlling the particle size distribution of granules in the bed, the system can predict and control axial temperature gradients without requiring multiple thermocouples throughout the reactor, thus maintaining ease of operation while improving temperature prediction accuracy.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If gas flow rates, freeboard pressures and power supply are controlled, then reactor operation is stabilized, but the actual temperature gradient within the bed remains unmonitored

Engineering Contradiction:

Improvereactor operation stabilityVSAvoidtemperature gradient monitoring

Core Design Contradiction:

ReliabilityVSDifficulty of detecting and measuring

Solution Approach 1:

The patent implements a feedback control system where the particle size distribution of granules is continuously measured and used to adjust operating parameters. This feedback loop allows the system to maintain stable operation while actively monitoring and controlling temperature gradients, as particle size distribution serves as a reliable indicator of the thermal state within the fluidized bed.

Inventive Principle:

Principle #23Feedback

3Temperature

If the width of the particle size distribution is controlled by adjusting seed addition frequency, then temperature gradient control is improved, but the complexity of process control increases

Engineering Contradiction:

Improveaxial temperature gradient controlVSAvoidprocess control complexity

Core Design Contradiction:

TemperatureVSDevice complexity

Solution Approach 1:

The patent controls temperature gradients by changing the particle size distribution parameter through adjusted seed addition frequency. Instead of directly controlling temperature with multiple sensors and actuators, the system modifies the particle size distribution (a different parameter) that naturally influences temperature profiles, thereby simplifying the control mechanism while achieving the desired temperature control.

Inventive Principle:

Principle #35Parameter changes

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 precise control of temperature profiles within the reactor, reducing hot spots and improving overall reactor operation by maintaining uniform axial temperature profiles, thereby increasing reactor efficiency and lifespan.

Implementation Method 1

Polycrystalline silicon is typically produced by a chemical vapor deposition mechanism in which silicon is deposited from a thermally decomposable silicon compound onto silicon seed particles in a fluidized bed reactor.

Methodology Applied

Scientific EffectChemical vapor deposition: Chemical Vapour Deposition

Implementation Method 2

silicon is deposited from a thermally decomposable silicon compound onto silicon seed particles

Methodology Applied

Scientific EffectThermal decomposition: Pyrolysis

Implementation Method 3

In gas-solid fluidized bed reactors, temperature is a critical parameter that contributes toward reactor performance

Methodology Applied

Scientific EffectFluidization: Fluidisation

Data Source

PatentUS10189714B2Operation of fluidized bed reactors by optimizing temperature gradients via particle size distribution control

Publication Date: 2019.01.29 CORNER STAR LTD

AI summary

A method of improving the operation of polysilicon fluidized bed reactors is disclosed. The present disclosure is directed to the optimization of axial temperature gradients in gas-solid fluidized bed systems. Varying the width of the particle size distribution in the reactor alters the temperature gradient within the reactor, thereby providing a means of a better control of internal temperature profiles and hence better reactor performance.