Low NOx Fuel Injection for Indurating Furnace
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Solution Overview
Problem
Indurating furnaces produce high levels of nitrogen oxides (NOx) due to the unmixed or poorly mixed combustion of fuel and air, which leads to inefficient heating processes and environmental concerns.
Innovation Solution
The implementation of premix burners that inject fuel and combustion air in a lean fuel-to-oxidant ratio, combined with preheated recirculation air, to form a combustible mixture that ignites within the downcomer, reducing interaction NOx production. This is achieved through a burner structure with mixer tubes and a reactant supply and control system that ensures uniform mixing and controlled combustion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If fuel and air are injected in a fuel-rich ratio without pre-mixing, then high temperatures are achieved for the indurating process, but high levels of NOx are produced due to poor mixing and interaction between fuel and air
Solution Approach 1:
The patent applies preliminary action by pre-mixing the fuel and air in a lean ratio before injection into the combustion zone. This pre-mixing occurs in the downcomer passage where fuel is injected into the downdraft of preheated air, allowing the combustible mixture to form and ignite before reaching the heating station. This preliminary mixing prevents the formation of fuel-rich zones that would otherwise produce high NOx levels.
Solution Approach 2:
The patent changes the fuel-to-oxidant ratio parameter from a conventional fuel-rich ratio to a lean fuel-to-oxidant ratio. This parameter change is implemented through the pre-mixing mechanism where fuel is injected into preheated air in controlled amounts, ensuring complete combustion and reducing peak temperatures that lead to thermal NOx formation.
2Object-generated harmful factors
If preheated recirculation air is used to reduce NOx production, then combustion efficiency may be reduced, but the patent maintains high temperatures through controlled lean combustion
Solution Approach 1:
The patent applies self-service by recirculating the hot exhaust gases back through the downcomer passage to preheat the incoming air-fuel mixture. This self-recirculation system uses the waste heat from combustion to preheat the reactants, reducing the energy required for combustion and maintaining high combustion efficiency while simultaneously reducing NOx production through the lean pre-mixed combustion process.
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 effectively suppresses NOx production while maintaining high temperatures necessary for the indurating process, achieving lean combustion conditions with reduced efficiency penalties and lower peak flame temperatures, thereby improving the environmental impact and operational efficiency of the furnace.
Implementation Method 1
A draft of preheated recirculation air is driven through the passage toward the heating station and is mixed with fuel gas to form a combustible mixture that ignites in the passage
Implementation Method 2
A draft of preheated recirculation air is driven through the passage toward the heating station and is mixed with fuel gas to form a combustible mixture that ignites in the passage
Data Source
AI summary
An indurating furnace has a heating station and an air passage leading to the heating station. A draft of preheated recirculation air is driven through the passage toward the heating station, and is mixed with fuel gas to form a combustible mixture of preheated recirculation air and fuel gas that ignites in the passage. This is accomplished by injecting the fuel gas into the passage in a stream that does not form a combustible mixture with the preheated recirculation air before entering the passage.