Solid Fuel Burner Cavity Design for Rapid Ignition
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Solution Overview
Problem
Existing combustion systems face challenges in achieving complete and stable combustion of solid fuels, particularly at high speeds and in applications where the rate of mixing of oxygen and fuel is limited, leading to inefficiencies and high costs due to excessive transport gas pressures and rapid erosion of equipment.
Innovation Solution
A burner design that incorporates a strategic cavity placement in the flow passage to enhance reactant mixing rates, using a high-speed oxy-gaseous fuel pilot flame to rapidly entrain and combust solid fuels, with the solid fuel introduced at a moderate velocity through an annulus outside the flame, ensuring rapid heating and ignition within a short distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high speed solid fuel flows are used to achieve rapid combustion, then combustion speed is improved, but transport gas pressure requirements increase excessively and equipment erosion increases
Solution Approach 1:
A pilot flame is introduced as an intermediary medium to transfer energy to the solid fuel particles. The pilot flame, consisting of gaseous fuel and oxygen, acts as a mediator that rapidly heats the solid fuel without requiring high transport gas pressures, thus achieving fast combustion while avoiding excessive pressure requirements and equipment erosion
Solution Approach 2:
The patent replaces the mechanical approach of using high pressure transport gas to accelerate solid fuel combustion with a thermal approach using a pilot flame. Instead of relying on mechanical pressure to drive the combustion process, the system uses thermal energy from the pilot flame to ignite and sustain combustion, thereby eliminating the need for excessive transport gas pressures
2Speed
If high speed solid fuel flows are used to achieve rapid combustion, then combustion speed is improved, but equipment erosion increases
Solution Approach 1:
The pilot flame serves as a protective intermediary between the solid fuel injection system and the combustion zone. By using the pilot flame to initiate and sustain combustion, the system avoids the need for high velocity solid fuel jets that would cause severe erosion of injection nozzles and combustion chamber walls
Solution Approach 2:
The patent substitutes the mechanical kinetic energy approach (high velocity solid fuel flow) with a thermal energy approach (pilot flame). This replacement eliminates the erosive mechanical impact of high speed solid fuel particles on equipment while maintaining rapid combustion through thermal ignition
3Speed
If solid fuel is introduced at high velocity to achieve rapid combustion, then combustion speed is improved, but entrainment into the flame is reduced
Solution Approach 1:
Instead of attempting to entrain high velocity solid fuel into a stationary or low velocity flame, the patent inverts the approach by using a high velocity pilot flame to intercept and ignite the solid fuel particles. The flame actively seeks out the fuel particles rather than the fuel particles being forced into the flame, thereby improving entrainment effectiveness
Solution Approach 2:
The pilot flame acts as an intermediary that bridges the velocity mismatch between solid fuel injection and combustion. The high velocity pilot flame can effectively capture and ignite solid fuel particles even when they are injected at high speeds, solving the entrainment problem by using the flame as a mobile ignition source
4Productivity
If cavity-actuated mixing is used downstream from initial mixing to enhance combustion rates, then mixing enhancement is achieved, but temperatures exceed maximum service temperature of commercially-available steel
Solution Approach 1:
The combustion process is segmented into distinct zones: a pilot flame zone for initial combustion and a separate solid fuel injection zone. The pilot flame is positioned upstream or adjacent to the solid fuel injection point, allowing combustion to occur in stages rather than all at once in a single high-temperature zone, thereby distributing thermal loads and avoiding excessive temperatures
Solution Approach 2:
The pilot flame serves as a thermal intermediary that provides controlled heating to the solid fuel particles before they enter the main combustion zone. This staged thermal processing prevents sudden temperature spikes that would exceed steel service temperatures, while still achieving rapid combustion through the combined effect of pilot flame heating and subsequent fuel oxidation
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 enables stable and complete combustion of solid fuels at high speeds, reducing the need for excessive transport gas pressures and minimizing equipment erosion, while maintaining operational within acceptable temperature limits, thus improving combustion efficiency and reducing costs.
Implementation Method 1
a cavity formed in a cavity-containing wall, the cavity having a downstream wall positioned proximal to and a non-zero distance upstream from the outlet plane
Implementation Method 2
using a high-speed oxy-gaseous fuel pilot flame to rapidly entrain and combust solid fuels
Implementation Method 3
the solid fuel would resist entrainment into even a high speed oxy-gas flame, and would thus fail to adequately heat-up, ignite, and combust as needed
Implementation Method 4
using a high-speed oxy-gaseous fuel pilot flame to rapidly entrain and combust solid fuels
Data Source
Figure 1~2A
Figure 2B~2C
Figure 3~4
AI summary
An oxy-gaseous fuel burner (400, 500) or a solid fuel burner (700) having an annular cavity (404, 504, 704) upstream from and proximate to an outlet plane (416, 516, 716) and a converging (434, 734) or converging-diverging nozzle (537) located upstream from and proximal to the cavity (404, 504, 704). The solid fuel burner (700) also is preferably operated so that the velocity of gas exiting a second annulus (730) is less than the velocity of gas exiting a central conduit (710).