SCR Reactor Control via NOx Rate Estimation
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Solution Overview
Problem
Existing methods for controlling the dosage of reducing agents like ammonia or urea in selective catalytic reduction reactors are slow to respond to variations in NOx load, leading to potential NOx or ammonia emissions above environmental limits.
Innovation Solution
A method that estimates the rate of change in NOx parameters to adjust the dosage of reducing agents, allowing for quick increases or decreases to prepare the SCR catalyst, thereby maintaining high removal efficiency and minimizing slip during varying NOx loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If feedback control is used to measure NOx concentration downstream of the SCR-reactor and control ammonia dosage, then the system is simple to implement, but the response time to load changes is very slow
Solution Approach 1:
The patent applies preliminary action by using feed-forward control that measures NOx concentration upstream of the SCR-reactor and adjusts ammonia dosage in advance before the gases reach the reactor. This anticipatory approach allows the system to respond quickly to load changes without waiting for downstream measurements, thereby improving response time while maintaining implementation simplicity.
2Speed
If feed-forward control is used to control ammonia supply based on upstream NOx concentration, then the response to load changes is faster, but the response is sometimes not quick enough resulting in emissions above limit values
Solution Approach 1:
The patent applies dynamics by implementing a dynamic control strategy that combines feed-forward control with real-time adjustments. The system continuously monitors upstream NOx concentration and dynamically adjusts ammonia dosage based on the rate of change of NOx load, allowing the system to respond quickly to load changes while ensuring emission compliance through adaptive control adjustments.
Solution Approach 2:
The patent applies feedback by incorporating downstream NOx measurements to verify and adjust the feed-forward control. The system uses downstream measurements to detect any deviations from expected performance and makes corrective adjustments to ammonia dosage, ensuring that emissions remain below limit values while maintaining the fast response characteristics of feed-forward control.
3Reliability
If the dosage of reducing agent is increased to prepare the SCR catalyst for higher inlet NOx amount, then the removal efficiency is kept high during increasing NOx load, but the dosage may be excessive when NOx load is constant
Solution Approach 1:
The patent applies dynamics by implementing a dynamic dosage adjustment strategy that responds to the rate of change of NOx load. When NOx load increases, the system proactively increases ammonia dosage to prepare the SCR catalyst, ensuring high removal efficiency. When NOx load stabilizes, the system automatically reduces dosage to the appropriate level, preventing excessive consumption while maintaining effective NOx removal.
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 provides a rapid and effective response to changes in NOx inlet amounts, reducing the risk of NOx emissions and minimizing reducing agent slip, ensuring compliance with emission limits.
Implementation Method 1
a method is frequently used, in which a reducing agent, usually ammonia or urea, is mixed with the flue gases. The flue gases, mixed with said ammonia or urea, are then passed through a catalyst in which the ammonia reacts selectively with the NOx to form nitrogen gas and water vapour. Usually the catalyst is installed in a so called Selective Catalytic Reduction reactor (SCR-reactor).
Implementation Method 2
An SCR catalyst comprises active sites on which elements, such as molecules, of the reducing agent may temporarily bind. Thus the SCR catalyst has a capability of storing reducing agent on active sites thereof.
Data Source
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AI summary
A method of controlling the feeding of a reducing agent, such as urea or ammonia, to a selective catalytic reduction reactor (12), which is operative for removing NOx from a process gas of a process plant (1), comprising the steps of estimating a present value of at least one predetermined parameter which is indicative of the amount of NOx that needs to be removed from said process gas in the selective catalytic reduction reactor. The rate of increase of said at least one predetermined parameter is then estimated. When said estimated rate of increase pf said at least one predetermined parameter is found to be positive, the amount of said reducing agent being supplied is increased to a higher value than would be the case if said at least one predetermined parameter were to be kept constant at the estimated present value thereof.