Rectangular After-Air Nozzle Swirl Flow Design
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Solution Overview
Problem
The existing after-air nozzles in pulverized coal boilers, particularly those with a circular outlet shape, face difficulties in forming a swirl flow along the inner wall of the furnace, leading to inefficient reduction of unburned components and CO near the inner wall.
Innovation Solution
The after-air nozzle is designed with a rectangular outlet shape and incorporates a cylindrical section with a circular swirl blade to generate a strong swirl flow, ensuring effective injection of combustion air along the inner wall of the furnace, reducing unburned components and CO by optimizing the flow rate distribution and swirl number.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a circular outlet shape is used for the after-air nozzle, then the structure is simple and easy to manufacture, but it is difficult to form a swirl flow along the inner wall of the furnace
Solution Approach 1:
The patent changes the outlet shape from circular to rectangular, creating an asymmetric geometry that naturally promotes swirl flow formation. The rectangular shape with specific aspect ratio (width/height between 0.5-2.0) generates asymmetric flow patterns that enhance the swirling motion along the furnace inner wall, resolving the contradiction between structural simplicity and swirl flow formation capability.
Solution Approach 2:
The patent introduces a cylindrical section with a specific length-to-diameter ratio (L/D between 0.5-2.0) upstream of the rectangular outlet. This curved geometry element generates rotational flow and enhances the swirl effect as the air passes through and exits the rectangular opening, enabling effective swirl flow formation without complex manufacturing.
2Device complexity
If the injection flow is not fed to the vicinity of the inner wall, then the nozzle structure is simple, but unburned components and CO cannot be effectively reduced
Solution Approach 1:
The rectangular outlet shape creates asymmetric flow distribution that naturally directs the injection flow toward the furnace inner wall. This asymmetric geometry ensures that the high-velocity jet adheres to the wall surface, effectively reaching the region where unburned components and CO accumulate, thereby improving combustion efficiency without adding structural complexity.
Solution Approach 2:
The cylindrical section with curved surfaces generates swirl flow that causes the injection stream to follow a helical path toward the inner wall. This curvature-induced swirl ensures the combustion air reaches the wall vicinity region, enhancing the burning of unburned components and CO while maintaining a relatively simple nozzle structure.
3Loss of energy
If swirl flow is not generated, then the pressure loss is low, but the mixture of combustible gas and after-air is insufficient
Solution Approach 1:
The rectangular outlet shape with optimized width-to-height ratio creates asymmetric flow patterns that generate moderate swirl without excessive energy loss. The asymmetric geometry promotes mixing between combustible gas and after-air through natural flow instabilities and shear layers, achieving adequate mixture performance with minimal pressure loss.
Solution Approach 2:
The cylindrical section with specific L/D ratio generates a controlled swirl flow that enhances mixing through rotational motion and centrifugal effects. The curvature-induced swirl creates favorable flow patterns for mixing combustible gas with after-air while maintaining reasonable pressure loss levels, optimizing the trade-off between mixing performance and energy consumption.
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 design allows for uniform distribution of the injection flow along the inner wall, effectively reducing unburned components and CO, while maintaining a controlled pressure loss, thus enhancing the combustion efficiency and suppressing NOx generation.
Implementation Method 1
incorporates a cylindrical section with a circular swirl blade to generate a strong swirl flow
Implementation Method 2
permitting an injection flow of combustion air injecting from the after-air nozzle into the furnace to be fed in the vicinity of the inner wall of the furnace
Implementation Method 3
to perfectly burn the unburned components and CO which are generated in the reductive atmosphere
Data Source
AI summary
A pulverized coal boiler of the present invention is structured so as to form, among upper and lower after-air nozzles, an opening serving as an outlet of the lower after-air nozzle positioned on the upstream side is formed in a rectangular shape, a cylindrical section for defining a minimum flow path area of combustion air flowing through a flow path of the after-air nozzle is installed inside of the lower after-air nozzles along the flow path of the lower after-air nozzle, and a swirl blade for giving a swirl force to the combustion air flowing through the flow path of the after-air nozzles is installed inside of the cylindrical section, and the flow path of the lower after-air nozzles is formed so that a flow path area of the flow path of the after-air nozzles through which the combustion air flows from a position where the cylindrical section is installed toward the opening of each of the lower after-air nozzles is expanded.