Ilmenite Oxygen Carrier Residence Time in Fluidized Bed Boilers
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Solution Overview
Problem
Fluidized bed boilers face challenges with the rapid deterioration of ilmenite particles' oxygen-carrying capacity and mechanical strength due to chemical aging and mechanical wear, requiring frequent replenishment and leading to increased resource consumption and mechanical wear on boiler structures.
Innovation Solution
Ilmenite particles are used in fluidized bed boilers with an extended average residence time of at least 75 hours, which surprisingly maintains good oxygen-carrying properties and mechanical strength, reducing attrition rates and the need for frequent replenishment, and are recycled from ash streams for further use, enhancing boiler operation efficiency and longevity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ilmenite particles are used as oxygen carrier in fluidized bed boiler, then combustion efficiency is improved, but oxygen-carrying capacity and mechanical strength deteriorate rapidly due to chemical aging and mechanical wear
Solution Approach 1:
The patent changes the operational parameters by extending the residence time of ilmenite particles to at least 75 hours, which transforms the degradation pattern from rapid deterioration to stable performance. This parameter change allows the system to operate in a regime where the ilmenite maintains its oxygen-carrying capacity despite extended exposure to combustion conditions.
Solution Approach 2:
The patent implements continuous recirculation of ilmenite particles from ash streams back to the fluidized bed, ensuring the oxygen carrier remains continuously engaged in the combustion process. This continuous action maximizes combustion efficiency while the extended residence time allows the material to stabilize and maintain its functional properties.
2Productivity
If ilmenite particles are used as oxygen carrier in fluidized bed boiler, then combustion efficiency is improved, but mechanical wear on boiler structures increases
Solution Approach 1:
By extending the residence time to at least 75 hours, the patent transforms the mechanical properties of ilmenite particles. The prolonged exposure to combustion conditions causes the particles to stabilize and reduce their attrition rate, thereby minimizing mechanical wear on boiler structures while maintaining combustion efficiency.
Solution Approach 2:
The patent converts the initially harmful effect of mechanical wear into a beneficial outcome. The extended residence time causes the ilmenite particles to undergo surface stabilization, where the harmful abrasiveness decreases over time, transforming the wear-prone fresh particles into stable, low-wear seasoned particles that protect boiler structures.
3Reliability
If ilmenite particles are frequently replenished to maintain oxygen-carrying capacity, then oxygen transport is maintained, but resource consumption increases
Solution Approach 1:
The patent implements a recovery system where ilmenite particles are separated from ash streams and recirculated back to the fluidized bed. This discarding and recovering approach allows the oxygen carrier to be reused multiple times, significantly reducing ilmenite consumption while maintaining adequate oxygen-carrying capacity through the extended residence time of at least 75 hours.
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 extends the residence time of ilmenite particles, reducing overall ilmenite consumption, improving environmental and economic efficiency, and minimizing mechanical wear on boiler structures, while maintaining effective oxygen-carrying capacity and mechanical strength even after extended use.
Implementation Method 1
Ilmenite can be repeatedly oxidized and reduced and has been used as a redox material in chemical looping combustion (CLC). Due to the reducing/oxidizing feature of ilmenite, the material can be used as oxygen carrier in fluidized bed combustion.
Implementation Method 2
Once the velocity of the fluidization gas rises above the minimum 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 similarly to a fluid and the bed is said to be fluidized.
Implementation Method 3
Usually oxygen containing gas, typically air or a mixture of air and recirculated flue gas, is used as the fluidizing gas (so called primary oxygen containing gas or primary air) and passed from below the bed, or from a lower part of the bed, through the bed material, thereby acting as a source of oxygen required for combustion.
Data Source
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AI summary
The invention relates to a method for operating a fluidized bed boiler, comprising carrying out the combustion process with a fluidized bed comprising ilmenite particles, wherein the average residence time of the ilmenite particles in the boiler is at least 75 hours. The invention further relates to ilmenite particles obtainable by a corresponding method and the use of said ilmenite particles as oxygen-carrying material.