Three-Stage Gas Distribution for Oxy-Fuel CFB Combustion
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Solution Overview
Problem
The challenge in oxy-fuel combustion on circulating fluidized beds is safely mixing and transporting high concentration oxygen and recycled flue gas, which can lead to deflagration risks due to fine combustible particles and localized high temperatures.
Innovation Solution
A three-stage gas distribution method is implemented, where the first-stage gas contains oxygen and recycled flue gas blown from the bottom, the second-stage gas is recycled flue gas blown into a transition zone, and the third-stage gas is pure oxygen injected from the side wall, maintaining a stable oxygen concentration and avoiding safety hazards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high concentration oxygen and recycled flue gas are mixed and transported together, then combustion efficiency is improved, but deflagration risk increases due to fine combustible particles
Solution Approach 1:
The gas distribution is divided into three separate stages with distinct functions: first-stage gas (oxygen and recycled flue gas mixture) for reducing zone, second-stage gas (recycled flue gas only) for transition zone, and third-stage gas (pure oxygen) for combustion zone. This segmentation prevents fine combustible particles from encountering high concentration oxygen during transport while ensuring efficient combustion at the appropriate location.
Solution Approach 2:
The first-stage gas is introduced at the bottom of the furnace to create a reducing zone before fuel combustion occurs. This preliminary action establishes a safe environment where oxygen concentration is controlled and combustible particles are prevented from deflagrating during the transport and mixing process.
2Productivity
If high oxygen concentration is used in the furnace, then combustion efficiency is improved, but localized high temperatures occur causing safety hazards
Solution Approach 1:
Different oxygen concentrations are applied to different zones within the furnace: the first-stage gas provides moderate oxygen concentration (21-31% O2) in the reducing zone, while the third-stage gas provides high oxygen concentration (≥50% O2) specifically in the combustion zone where fuel is present. This localized quality control ensures efficient combustion while preventing localized high temperatures in other areas.
Solution Approach 2:
The second-stage gas (recycled flue gas) acts as an intermediary substance introduced into the transition zone between the reducing zone and combustion zone. This intermediary gas helps bridge the temperature and concentration gradients, preventing thermal shock and localized high temperatures while maintaining stable combustion conditions.
3Reliability
If three-stage gas distribution is implemented, then safety and combustion control are improved, but system complexity increases
Solution Approach 1:
The three-stage gas distribution system uses a single furnace structure that performs multiple functions: the bottom inlet serves as both the reducing zone and the first-stage gas injection point, the transition zone serves as both the second-stage gas injection point and temperature buffer, and the side wall serves as both the third-stage gas injection point and combustion zone. This multi-functionality reduces the need for additional separate equipment.
Solution Approach 2:
The recycled flue gas serves dual purposes: it is used as the second-stage gas in the transition zone to prevent localized high temperatures, and it is also mixed with oxygen in the first-stage gas for the reducing zone. This self-service approach reduces the need for separate gas sources and simplifies the overall system architecture.
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 method ensures stable combustion and avoids localized high temperatures, ensuring safe transportation and combustion efficiency in high oxygen concentrations, reducing the risk of deflagration and maintaining combustion control akin to air combustion conditions.
Implementation Method 1
A three-stage gas distribution method is implemented, where the first-stage gas contains oxygen and recycled flue gas blown from the bottom, the second-stage gas is recycled flue gas blown into a transition zone, and the third-stage gas is pure oxygen injected from the side wall
Implementation Method 2
the circulating fluidized bed combustion achieves heat transfer of the furnace by means of turbulent flow and circulating flow of a large number of inert bed materials
Implementation Method 3
the circulating fluidized bed combustion achieves heat transfer of the furnace by means of turbulent flow and circulating flow of a large number of inert bed materials
Implementation Method 4
the circulating fluidized bed combustion achieves heat transfer of the furnace by means of turbulent flow and circulating flow of a large number of inert bed materials
Implementation Method 5
The technique of oxy-fuel combustion on the circulating fluidized bed effectively enables an efficient combustion of low volatile poor quality coal, a biomass combustion and an incineration of waste
Data Source
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AI summary
The present disclosure provides a method for distributing gas for oxy-fuel combustion on a circulating fluidized bed. In the method, the gas is provided by three stages into a furnace of the circulating fluidized bed, the method includes: blowing in a first-stage gas containing oxygen and recycled flue gas from the bottom of the furnace; blowing in a second-stage gas containing recycled flue gas from a transition zone between a dense-phase zone and a dilute-phase zone of the furnace; and blowing in a third-stage gas containing oxygen from a side wall of the furnace. The present disclosure realizes stable combustion inside the furnace of the circulating fluidized bed in high oxygen concentration, thus avoiding the problem of localized high temperature caused by the high oxygen concentration, and solving the safety problem of transporting a mixture of oxygen and recycled flue gas having high oxygen concentration.