NOx Controller Optimizes SCR Efficiency via Exhaust Temperature
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Solution Overview
Problem
Gas turbine engines face challenges in controlling nitrogen oxides (NOx) emissions, particularly in minimizing nitrogen dioxide (NO2) production, due to varying NO2-to-NO ratios influenced by temperature, carbon monoxide, and unburned hydrocarbons, which can decrease the efficiency of selective catalyst reduction (SCR) systems.
Innovation Solution
A NOx emissions controller is implemented to regulate the gas turbine engine system by adjusting exhaust temperature and fuel flow, using a NOx emissions controller that monitors NO2 and NO levels, calculates a ratio signal, and adjusts the exhaust temperature offset to maintain an optimal NO2-to-NO ratio, thereby reducing NO-to-NO2 conversion upstream of the CO catalyst and ensuring efficient NOx reduction in the SCR system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the SCR system is used to reduce NOx emissions, then NOx reduction efficiency is improved, but the system performance becomes dependent on the NO2-to-NO ratio which varies with operating conditions
Solution Approach 1:
The patent adjusts operating parameters (exhaust gas temperature, fuel flow rate, air-to-fuel ratio) to control the NO2-to-NO ratio in the exhaust stream, transforming it into a controllable variable that optimizes SCR system performance under different operating conditions
Solution Approach 2:
The system employs sensors to monitor NO2 and NO levels in real-time, feeds this information back to the controller, and dynamically adjusts fuel flow and temperature to maintain the optimal NO2-to-NO ratio for SCR efficiency
2Reliability
If exhaust gas temperature is increased to improve SCR performance, then NOx reduction efficiency is improved, but NO-to-NO2 conversion increases which is undesirable
Solution Approach 1:
The patent precisely controls exhaust gas temperature within an optimal range (not excessively high) while adjusting other parameters like oxygen concentration and residence time to achieve the desired balance between SCR performance and minimizing unwanted NO-to-NO2 conversion
Solution Approach 2:
The system dynamically adjusts temperature control based on real-time monitoring of NO2-to-NO ratio and operating conditions, adapting the heating rate and temperature setpoint to maintain optimal SCR performance while preventing excessive NO-to-NO2 conversion
3Object-generated harmful factors
If CO catalysts are used to convert CO to CO2, then CO emissions are reduced, but NO-to-NO2 conversion is promoted which decreases NOx reduction efficiency
Solution Approach 1:
The patent implements preliminary control measures upstream of the CO catalyst by optimizing combustion conditions and exhaust gas composition to minimize the formation of conditions that promote NO-to-NO2 conversion, thereby protecting downstream NOx reduction equipment
Solution Approach 2:
The system uses an intermediate control mechanism (adjusting exhaust gas temperature and composition before the CO catalyst) to decouple the CO conversion function from the unwanted side effect of excessive NO-to-NO2 conversion, maintaining both CO and NOx reduction efficiencies
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 reduces NOx emissions and maximizes the efficiency of the SCR system by maintaining a favorable NO2-to-NO ratio, promoting increased NOx reduction efficiency without sacrificing overall gas turbine output or efficiency.
Implementation Method 1
The SCR system adds a reductant, typically ammonia or urea, to the exhaust gas stream before passing the stream through a catalytic bed so as to absorb selectively the nitrogen oxides and the reducing agent. The absorbed components undergo a chemical reaction on the catalyst surface and the reaction products are desorbed.
Implementation Method 2
CO catalysts may be utilized downstream of the gas turbine yet upstream of the NOx reduction equipment to convert CO to CO2 so as to reduce CO emissions. For example, a commercially-available CO catalyst can oxidize about 95% of CO to CO2
Implementation Method 3
The conversion of NO to NO2 in combustion gases can be quite sensitive to temperature, the presence of carbon monoxide (CO), and the presence of unburned hydrocarbons (UHC's) due to uncombusted gas turbine fuels.
Data Source
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AI summary
The present application thus provides a gas turbine engine system (100). The gas turbine engine system (100) may include a gas turbine engine (110), a nitrogen oxides reduction system (200) in communication with a flow of combustion gases (160) downstream from the gas turbine engine (110), and a nitrogen oxides controller (300) to control the ratio of nitrogen dioxide to nitrogen oxides in the flow of combustion gases (160) entering the nitrogen oxides reduction system (200).