How should the secondary air position of the circulating fluidized bed boiler be determined?

The position of secondary air in a circulating fluidized bed (CFB) boiler plays a crucial role in ensuring proper combustion, reducing emissions, and optimizing fuel efficiency. Determining the appropriate position for secondary air injection requires understanding the fundamental principles of fluidized bed combustion and addressing specific requirements based on the design and operation of the particular boiler. Here's a guideline on how to determine the secondary air position:

ZOZEN circulating fluidized bed (CFB) boiler

Combustion Requirements: Understand the combustion requirements, such as the type and properties of the fuel used, the temperature of combustion, and the desired combustion efficiency.

Primary Air Flow: Analyze the flow of primary air which directly impacts the bed's fluidization quality. Typically, primary air provides 60-80% of the total air needed for combustion.

Temperature Profile: Monitor the temperature profile of the combustion chamber. The position of secondary air injection should aim to stabilize this profile and prevent hotspots or temperature variations that might cause inefficient combustion or equipment damage.

Bed Material: Consider the properties and size distribution of the bed material. Secondary air can be used to help distribute heat, ensuring a uniform temperature profile throughout the bed.

Emission Control: Proper positioning of secondary air can help in controlling emissions, particularly the reduction of NOx. Introducing secondary air at the right point can promote staged combustion, which lowers peak temperatures and subsequently reduces NOx formation.

Mixing and Turbulence: Secondary air can be used to enhance turbulence and mixing in the freeboard region above the bed. This aids in ensuring the complete combustion of volatiles released from the fuel.

Operational Feedback: Regularly monitor and analyze operational data, such as boiler efficiency, unburnt carbon in ash, and emission levels. Use this feedback to adjust the position and quantity of secondary air if necessary.

Computational Fluid Dynamics (CFD): Employ CFD simulations to model the flow, mixing, and combustion processes inside the boiler. This can provide insights into the best positions for secondary air injection.

Consult Manufacturer Guidelines: Manufacturers usually provide guidelines and best practices based on the specific design and features of their CFB boilers.

Regular Inspections and Adjustments: Regular inspections and operational checks will offer insights into how the system is behaving. Changes in fuel properties, wear and tear, and other factors might necessitate adjustments over time.