Staged Lean Premix Radiant Wall Burner for Flashback and NOx Control
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Solution Overview
Problem
Pre-mix radiant wall burners face issues such as flashback due to high hydrogen content fuels, require significant spacing to avoid flame interference, and produce high NOx emissions, especially in ethylene cracking processes.
Innovation Solution
A low NOx, staged fuel, pre-mix radiant wall burner design with a primary fuel tip assembly, venturi, radial discharge tip, and staged fuel discharge tip, featuring a flow diverter and strategically positioned staged fuel discharge, which eliminates low velocity areas and equalizes discharge velocity, allowing high hydrogen fuels and reduced flame diameter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the longitudinal length of the discharge slots is increased to increase the flow area, then the flow area is improved, but the relative flow velocity of the pre-mix discharged from the rearward end portions decreases creating low velocity areas which increase the danger of flashbacks
Solution Approach 1:
The discharge slots are segmented into multiple sections along the longitudinal axis, with each section having optimized dimensions. The slots are divided into a first section with a first longitudinal length and a second section with a second longitudinal length, allowing different flow characteristics in different regions to prevent low velocity areas while maintaining adequate flow area
Solution Approach 2:
Different sections of the discharge slots have different local properties - the first section has a longer longitudinal length to provide adequate flow area, while the second section has a shorter longitudinal length to maintain higher flow velocity and prevent flashback. This local differentiation allows each section to perform its specific function optimally
2Productivity
If the hydrogen content of the pre-mix fuel is increased to meet ethylene cracking process requirements, then the fuel efficiency is improved, but flashback generally has a greater tendency to occur
Solution Approach 1:
The discharge slots are differentiated into sections with different longitudinal lengths to create local variations in flow characteristics. The second section with shorter length maintains higher velocity at the rearward end to prevent flashback, while the overall design accommodates high hydrogen content fuel for efficient ethylene cracking operation
Solution Approach 2:
The longitudinal length parameter of the discharge slots is changed and optimized to prevent flashback. By reducing the longitudinal length of the second section, the flow velocity parameter is increased in that region, creating conditions that prevent flashback while allowing high hydrogen fuel usage
3Reliability
If the burners are spaced five feet or more apart to avoid flame interference, then the flame interference is eliminated, but the required spacing increases reducing space utilization
Solution Approach 1:
The burner flame diameter parameter is reduced through the staged fuel discharge design and flow velocity optimization. This parameter change allows burners to be spaced closer together (less than five feet apart) while still preventing flame interference, improving space utilization in the furnace
4Object-generated harmful factors
If staged fuel operation is used to reduce NOx emissions, then the NOx emissions are reduced, but the diameter of the burner flame increases requiring increased burner spacing
Solution Approach 1:
The fuel discharge is segmented into staged sections with different timing and locations. The first staged fuel discharge occurs at a first location, and the second staged fuel discharge occurs at a second location, creating a more compact flame structure that reduces diameter while maintaining NOx reduction benefits
Solution Approach 2:
The staged fuel discharge utilizes different spatial dimensions and timing sequences. By discharging fuel at different locations and times rather than simultaneously, the flame development is controlled to achieve lower NOx emissions without the excessive diameter increase that would require greater burner spacing
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
The burner operates with over 90% hydrogen without flashback, reduces NOx emissions to 22 ppmv at 1221°C, and allows burner spacing of less than five feet, providing a more even flame profile for efficient heating.
Implementation Method 1
a venturi (8) and a radial discharge tip (10) positioned on or forwardly of the discharge end of the venturi (8)... The primary fuel ejector (22) ejects a primary gas fuel stream forwardly into the venturi (8) and draws an air stream into the venturi (8) which mixes with the primary gas fuel stream to form a pre-mix stream
Implementation Method 2
Radiant wall burners form and radially discharge a mixture of gas fuel and air to produce a flat flame which surrounds the burner tip and lies against or close to the surface of the firebox wall
Implementation Method 3
multiple radiant wall burners are typically installed in one, two, or more walls of the furnace firebox in order to heat the entire wall and to radiate heat to the process tubes
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A staged, lean pre-mix radiant wall burner having an internal staged fuel discharge tip and an internal flow diverter, and a method of using the radiant, wall burner, which, allow the combustion of a high hydrogen content fuel without the occurrence of flashbacks and which also provide reduced NOx emissions and allow a closer spacing of the burners when installed in a wall, floor, or ceiling of a fired heater in a multiple burner arrangement.