Horizontal Overfire Air Windboxes for Boiler Emission Control
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Solution Overview
Problem
Tangentially fired boilers face challenges in achieving ultra-low nitrogen oxide emissions and maintaining uniform water tube outlet temperatures, leading to thermal stresses and inefficient combustion due to the orientation of overfire air windboxes and spiral to vertical water tube transitions.
Innovation Solution
The implementation of a tangentially fired boiler with a horizontal overfire air system, where overfire air windboxes are positioned in a substantially horizontal orientation, allowing for improved mixing of combustion gases and reducing the height of the combustion chamber, thus optimizing the spiral to vertical transition and minimizing thermal stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If overfire air windboxes are positioned in vertical orientation, then mixing of combustion gases may be achieved, but nitrogen oxide emissions are not reduced to ultra-low levels
Solution Approach 1:
The patent inverts the conventional vertical orientation of overfire air windboxes to a horizontal orientation. This inversion changes the flow dynamics of combustion air injection, allowing tangential injection that enhances mixing with fireball gases while controlling nitrogen oxide formation through optimized air distribution patterns.
Solution Approach 2:
The patent changes the orientation parameter of overfire air windboxes from vertical to horizontal, and adjusts the number of windboxes and their positioning parameters to achieve optimal performance. These parameter changes enable ultra-low nitrogen oxide emissions while maintaining combustion efficiency.
2Temperature
If the number of spiral turns is increased, then uniform water tube outlet temperatures are achieved, but pressure drop increases
Solution Approach 1:
The patent applies partial action by implementing a limited number of spiral turns (typically 2-4 turns) rather than excessive spiraling. This partial spiraling is sufficient to achieve uniform temperature distribution across water tube outlets while avoiding the excessive pressure drop that would result from too many turns.
Solution Approach 2:
The patent optimizes the spiral configuration parameters including the number of turns, spiral diameter, and pitch to achieve the right balance between temperature uniformity and pressure drop. By carefully adjusting these parameters, the system achieves uniform water tube outlet temperatures with acceptable pressure loss.
3Ease of operation
If the height of combustion chamber is increased to accommodate vertical windboxes, then overfire air injection is achieved, but thermal performance is reduced
Solution Approach 1:
The patent inverts the windbox orientation from vertical to horizontal, which fundamentally changes the spatial requirements. This inversion allows overfire air injection to be achieved with a more compact combustion chamber height, reducing the overall chamber dimensions and improving thermal performance by minimizing heat loss through additional chamber walls.
Solution Approach 2:
The patent transitions the windbox orientation from the vertical dimension to the horizontal dimension. This dimensional change allows the overfire air system to function effectively without increasing combustion chamber height, thereby reducing the volume of the combustion chamber and improving thermal efficiency.
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 configuration achieves reduced nitrogen oxide emissions, improved combustion efficiency, and uniform water tube outlet temperatures, enhancing overall thermal performance and reducing operational complexity.
Implementation Method 1
Overfire air is combustion air that may be tangentially injected into the combustion chamber between the primary firing zone and a furnace outlet. Thorough mixing of the overfire air with the gases in the fireball may achieve low levels of nitrogen oxides, carbon monoxide, and other types of emissions with an overall increase in combustion efficiency.
Implementation Method 2
Such boilers may use a combination of spiral and vertical water tubes positioned about the walls of the combustion chamber. The spiral tubes may benefit from the averaging of the lateral heat absorption variation in each water tube.
Data Source
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AI summary
The present application provides a tangentially fired boiler (300). The tangentially fired boiler (300) may include a combustion chamber (310) and an overfire air system (320) positioned about the combustion chamber (310). The overfire air system (320) may include a number of overfire air windboxes (330) positioned in a horizontal orientation (340).