Oxygen-Fired Boiler Combustion Control via Exhaust Gas Recirculation
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Solution Overview
Problem
Existing methods for oxygen-fired boilers face challenges in controlling combustion stability and oxygen concentration due to high flame temperatures and inefficient energy use, particularly in recovering low oxygen concentrations from combustion exhaust gas, leading to operational instability.
Innovation Solution
A method and apparatus that control oxygen supply and recirculation flow rates in an oxygen-fired boiler based on boiler load demand and heat absorption measurements, using an air separation unit to separate oxygen and nitrogen, and recirculating treated combustion exhaust gas to maintain targeted heat absorption and oxygen concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If oxygen combustion is used to separate carbon dioxide and suppress thermal NOx production, then carbon dioxide separation efficiency is improved and thermal NOx production is suppressed, but flame temperature increases causing heat resistance and lifespan issues with combustion furnace materials
Solution Approach 1:
The patent introduces combustion exhaust gas as an intermediary substance to mix with the oxygen-fuel combustion gas. This dilutes the high-temperature oxygen combustion products, reducing the flame temperature to protect furnace materials while maintaining the core benefit of CO2-rich exhaust for efficient carbon dioxide separation and thermal NOx suppression.
2Temperature
If combustion exhaust gas is recirculated to reduce flame temperature, then flame temperature is reduced protecting furnace materials, but combustion stability deteriorates due to complex control requirements
Solution Approach 1:
The patent implements a feedback control system where the recirculation flow rate of combustion exhaust gas is automatically adjusted based on measured flame temperature. The controller continuously monitors temperature and modulates the recirculation rate to maintain optimal combustion conditions, ensuring both flame temperature control and combustion stability without complex manual intervention.
3Productivity
If existing air fired boiler is converted to oxygen fired boiler, then carbon dioxide separation efficiency is improved, but device complexity increases requiring air separation unit and modified combustion control system
Solution Approach 1:
The patent designs the oxygen-fired boiler system to maintain compatibility with existing air-fired boiler infrastructure. The combustion chamber, heat exchangers, and basic control systems can be reused, while only the air separation unit and combustion control system need modification. This multi-functional approach allows the same boiler structure to operate with both air and oxygen fuels, reducing overall device complexity despite the conversion.
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 simplifies and stabilizes combustion control, making it easily applicable to existing air-fired boilers by adjusting oxygen supply and recirculation flow rates to match heat absorption and oxygen concentration, thereby enhancing operational stability and efficiency.
Implementation Method 1
air is separated into oxygen and other nitrogen-prevailing gas by an air separation unit
Implementation Method 2
the oxygen obtained by the air separation unit and fuel being burned in a boiler body to heat feedwater to produce steam
Implementation Method 3
measuring a heat absorption amount of the boiler using an inlet temperature of the feedwater supplied to the boiler body and an outlet temperature of steam
Data Source
AI summary
Provided are a method and an apparatus for controlling combustion in an oxygen fired boiler which are easily applicable to an existing air fired boiler for easy and stable control of the combustion.Oxygen with a setting amount in accordance with a boiler load demand 35 is supplied to a boiler body 4. Heat absorption amount of the boiler is measured from inlet temperature of feedwater supplied to the boiler body 4 and outlet temperature of steam. Recirculation flow rate of combustion exhaust gas 14a is controlled such that heat absorption amount 41 of the boiler body 4 becomes equal to a targeted heat absorption amount 42 to thereby control oxygen concentration in all gas guided to the boiler body 4.