Urea Bead Injection for NOx Reduction in Waste Incineration
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Solution Overview
Problem
Existing methods for reducing NOx emissions from combustion processes, such as those from household waste, often require thermal converters, electric heaters, or the use of ammonia, which can be costly and produce secondary pollutants.
Innovation Solution
A non-catalytic process using urea beads injected into specific temperature zones within the combustion chamber, with temperature measurement and nozzle adjustment to optimize urea injection, ensuring efficient NOx reduction without generating harmful secondary species.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermal converters or electric heaters are used to adjust gas temperature for NOx reduction, then the temperature control precision is improved, but the device complexity and energy consumption increase
Solution Approach 1:
The patent extracts and eliminates the thermal converters and electric heaters from the system by injecting urea beads directly into the combustion chamber where they naturally decompose at appropriate temperatures, removing the need for separate temperature adjustment devices while maintaining effective NOx reduction
Solution Approach 2:
The urea beads serve multiple functions simultaneously: they act as the reducing agent for NOx and their decomposition temperature provides the necessary temperature indication for optimal injection timing, making the system self-regulating without external temperature control devices
2Productivity
If ammonia is used as the reducing agent for NOx, then the NOx reduction efficiency is improved, but harmful secondary pollutants are generated
Solution Approach 1:
The patent changes the chemical parameter by substituting ammonia with urea beads as the reducing agent. Urea decomposes to form isocyanic acid which then reacts with NOx, providing effective NOx reduction while minimizing the formation of harmful secondary pollutants like ammonia slip
Solution Approach 2:
The patent converts the potential harm of urea decomposition into a benefit by utilizing the decomposition products (isocyanic acid) as the active reducing species that effectively reduces NOx while the controlled decomposition process prevents harmful secondary pollutant formation
3Device complexity
If urea beads are injected without temperature optimization, then the device complexity is reduced, but the NOx reduction efficiency decreases
Solution Approach 1:
The patent implements a feedback mechanism where temperature sensors monitor the combustion chamber temperature and this information is used to control the injection timing and rate of urea beads, ensuring optimal reduction efficiency while maintaining simple device architecture
Solution Approach 2:
The patent makes the urea bead injection system dynamic by adjusting the injection rate and timing based on real-time temperature conditions in the combustion chamber, allowing the system to adapt to varying operating conditions and maintain high NOx reduction 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
Significantly reduces NOx emissions to below 200 mg of NO2 equivalent per N.m³ while minimizing ammonia production to less than 10 mg/N.m³, ensuring an environmentally friendly and cost-effective solution.
Implementation Method 1
injecting urea beads into a zone of the combustion chamber whose temperature is between 850° C. and 1000° C.
Implementation Method 2
This non-catalytic reduction process makes it possible to considerably reduce the NOx present in a gas
Implementation Method 3
Provision can be made for the measurement of the temperature of the gas to consist in measuring the energy emitted by the gases to generate a temperature signal
Data Source
Figure 1
Figure 2~4
AI summary
The procedure for reducing the nitrogen oxide (NOx) content of discharged gases, e.g the fumes from the incineration of household waste, consists of injecting urea pellets into a predetermined gas zone at a temperature of 850 - 1000 degrees C. After measuring the temperature of the gases from their emitted energy and a comparison of vapour rates, the pellets are injected in a flow of gas, e.g. pressurized air, through nozzles (21, 22, 23, 24) that have flat lower and upper walls converging towards their outlet ends.