Staged Fuel Injector Burner for Low NOx Emissions
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Solution Overview
Problem
Current methods for reducing NOx emissions in industrial combustion processes, such as those in once-through steam generators, often require significant retrofits and do not effectively achieve NOx levels below 5 ppm, especially in existing burners like ultra-low-NOx burners.
Innovation Solution
A burner system and method that utilize a premix burner with staged fuel injectors and a pre-mixer to inject an unignited mixture of secondary fuel and recirculated flue gas into the combustion chamber, reducing NOx emissions by lowering combustion temperatures through controlled fuel and air mixing and flue gas recirculation, without the need for extensive retrofits or changes to existing equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If flue gas recirculation is implemented to reduce NOx emissions, then NOx emission levels decrease, but system complexity and retrofit requirements increase
Solution Approach 1:
The fuel injection system is segmented into multiple staged injectors arranged circumferentially around the premix burner port. This segmentation allows different zones of the combustion chamber to receive different fuel/air mixtures, enabling localized temperature control and NOx suppression without requiring complex system-wide retrofits
Solution Approach 2:
Flue gas is recirculated and mixed with secondary fuel in a pre-mixer before injection into the combustion chamber. This preliminary mixing occurs outside the combustion zone, allowing the recirculated flue gas to be prepared in advance without interfering with the primary combustion process or requiring complex in-chamber modifications
2Object-generated harmful factors
If flue gas recirculation is implemented to reduce NOx emissions, then NOx emission levels decrease, but the need for larger combustion air blowers and additional instrumentation increases
Solution Approach 1:
The staged fuel injectors serve multiple functions: they introduce secondary fuel, mix it with recirculated flue gas in the pre-mixer, and deliver the mixture to the combustion chamber. This multi-functionality reduces the need for separate dedicated FGR injection systems and additional blowers, simplifying retrofits
Solution Approach 2:
The system uses the existing flue gas stream and combustion air supply to provide the recirculated flue gas for mixing with secondary fuel. The pre-mixer utilizes available pressure differentials and the existing fuel delivery infrastructure, minimizing the need for additional powered equipment or complex instrumentation
3Reliability
If conventional burners are used, then existing equipment can be maintained, but NOx emissions cannot be reduced to below 5 ppm
Solution Approach 1:
The combustion chamber is divided into distinct zones with different fuel/air equivalence ratios. The premix burner port receives a fuel-lean mixture for stable combustion, while the circumferentially arranged staged injectors deliver fuel-rich mixtures that suppress NOx formation in specific radial zones, achieving low emissions without compromising overall combustion stability
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 solution achieves NOx emissions of less than 5 ppm on a dry gas volumetric basis corrected to 3% O2, with minimal impact on existing burner systems and flame detection, by creating a diffuse combustion zone that suppresses NOx formation.
Implementation Method 1
feeding a fuel stream and an air stream to a pre-mixer, wherein the fuel and air streams are mixed to form a first fuel air mixture
Implementation Method 2
injecting the first fuel air mixture via at least a primary port into a primary combustion zone of a combustion chamber, wherein the first fuel air mixture is substantially combusted forming primary products of combustion
Implementation Method 3
introducing the primary POC into a secondary combustion zone of the combustion chamber
Implementation Method 4
recirculating a portion of the combined primary POC and secondary POC for use as the RFG for mixing with the second fuel stream
Implementation Method 5
creating a diffuse combustion zone that suppresses NOx formation
Data Source
AI summary
A steam generator system employing a fired burner with a flue gas recirculation system with low NOx emission is disclosed. A method to retrofit fired burners for low NOx emission is also disclosed. In the system, the flue gas recirculation system is configured to include a pre-mixer, and the recirculated flue gas (RFG) is routed to the stage of the pre-mixer for mixing with a portion of the fuel stream, forming a secondary RFG fuel mixture. The secondary RFG fuel mixture is routed to the secondary stage of the burner via a plurality of injector ports. The injection of the second RFG fuel mixture results in a reduction of temperature for the NOx emission to be less than 5 ppm at 3% O2, dry basis.