Fluidized Bed Boiler Oxygen Mixing via Ilmenite Redox
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Solution Overview
Problem
Fluidized bed boilers face challenges in achieving good mixing of fuel and oxygen, leading to localized high temperatures, fouling, corrosion, and increased maintenance costs due to poor mixing of secondary oxygen containing gas with hot gases, resulting in inefficient combustion and high emissions.
Innovation Solution
Operating a fluidized bed boiler with a ratio of secondary oxygen containing gas to primary oxygen containing fluidizing gas set between 0.0 and 0.8, using ilmenite particles as bed material to enhance oxygen and fuel mixing, reducing the need for secondary oxygen, and adjusting oxygen concentration in flue gas to maintain efficient combustion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If secondary oxygen containing gas is fed into the furnace to improve fuel and oxygen mixing, then combustion efficiency is improved, but local hot zones are created causing fouling and corrosion
Solution Approach 1:
The patent introduces a fluidized bed material as an intermediary substance that facilitates oxygen transfer from the primary gas stream to the fuel particles. This mediator enables effective mixing without directly injecting secondary oxygen-containing gas, thereby avoiding the formation of local hot zones that cause fouling and corrosion while still achieving improved combustion efficiency.
Solution Approach 2:
The patent utilizes fluidized bed technology where a fluidizing gas creates a suspension of bed material particles that behave like a fluid. This pneumatic system enables intimate contact between oxygen carriers and fuel particles, achieving homogeneous mixing and efficient combustion without the harmful effects of direct secondary gas injection.
2Productivity
If secondary oxygen containing gas is injected to achieve adequate mixing, then fuel conversion is improved, but complex boiler design is required
Solution Approach 1:
The fluidized bed material serves multiple functions simultaneously: it acts as a heat transfer medium, an oxygen carrier, and a fluidizing agent. This multi-functionality eliminates the need for separate secondary oxygen injection systems and their associated complex feeding ports and distribution networks, simplifying the overall boiler design while maintaining improved fuel conversion.
3Quantity of substance
If cold oxygen containing gas is fed as secondary gas, then oxygen supply is improved, but streaking occurs due to poor mixing
Solution Approach 1:
The patent changes the physical state and temperature parameters of the oxygen delivery system. Instead of injecting cold secondary gas that creates streaking, the system uses bed material particles that are heated to furnace temperature and circulate through the fuel bed, delivering oxygen at appropriate temperatures and achieving homogeneous mixing without composition instability.
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 significantly reduces the need for secondary oxygen, lowers maintenance costs, improves combustion efficiency, and decreases emissions by ensuring homogeneous mixing and stable operation across varying fuel loads.
Implementation Method 1
The natural occurring mineral ilmenite consists mainly of iron titanium oxide (FeTiO3) which can be repeatedly oxidized and reduced and thus acts as a redox material. Due to this reducing-oxidizing feature of ilmenite, the material can be utilized as an oxygen carrier to improve the mixing of oxygen and fuel
Implementation Method 2
Once the velocity of the fluidization gas rises above the minimum fluidization velocity at which the force of the fluidization gas balances the gravity force acting on the particles, the solid bed material behaves in many ways similar to a fluid and the bed is said to be fluidized
Implementation Method 3
The bed material serves as a heat carrier to promote rapid heat transfer
Data Source
AI summary
The invention relates to a method for operating a fluidized bed boiler, comprising: a) setting the ratio of secondary oxygen containing gas to primary oxygen containing fluidizing gas to a value ranging from 0.0 to 0.8; b) carrying out the combustion of fuel with a fluidized bed comprising ilmenite particle; and to a fluidized bed boiler.