Coal-Air Coordinated Control for Stable NOx During Load Changes
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Solution Overview
Problem
Traditional coal-air sequence control logic in coal-fired units leads to a lag in combustion-supporting air volume adjustment relative to coal feed, causing unbalanced combustion atmospheres and significant fluctuations in nitrogen oxide concentrations during rapid load changes, which affects the operation of SCR denitration systems.
Innovation Solution
A coal-air synchronous dynamic coordinated control method that calculates and adjusts coal feed rates and operation wet-basis oxygen content in real-time using regression analysis and functional relationships to maintain balanced combustion, reducing response lag and stabilizing nitrogen oxide concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional serial sequence control logic is used to adjust coal feed first and then combustion air, then the control sequence is simple to implement, but the combustion air volume lags behind coal feed adjustment causing unbalanced combustion atmosphere
Solution Approach 1:
The system performs preliminary calculation of the required combustion air volume based on the coal feed adjustment amount and historical data before the actual control action. This allows the combustion air damper to be adjusted in advance or simultaneously with coal feed changes, eliminating the lag time inherent in traditional sequential control where air adjustment waits for coal adjustment to complete.
2Device complexity
If traditional serial sequence control logic is used, then the control system structure is simple, but nitrogen oxide concentration fluctuates significantly during rapid load changes
Solution Approach 1:
The system incorporates feedback mechanisms where the actual combustion air volume and nitrogen oxide measurements are continuously monitored and fed back to the control system. This feedback is used to dynamically adjust the coal-air coordination control strategy, ensuring nitrogen oxide concentration remains stable during load changes while maintaining a relatively simple control structure through adaptive rather than overly complex fixed logic.
3Stability of the object's composition
If combustion air is adjusted to match rapid coal feed changes, then the combustion atmosphere remains balanced, but the control logic becomes more complex requiring predictive calculations
Solution Approach 1:
The control system performs preliminary calculations using historical data and current operating conditions to predict the required combustion air volume before coal feed adjustments are made. This predictive approach maintains balanced combustion atmosphere during rapid load changes while avoiding the need for overly complex real-time iterative control logic, achieving a balance between combustion stability and control simplicity.
4Reliability
If online CEMS measurement lag time of 1-3 minutes is considered, then the measurement system is reliable, but the denitration ammonia injection adjustment lags behind operating condition changes
Solution Approach 1:
The system performs preliminary adjustment of denitration ammonia injection based on predicted nitrogen oxide trends from the coal-air coordinated control before the CEMS measurement becomes available. By using the predictive control model to anticipate nitrogen oxide changes and adjusting ammonia injection in advance, the system compensates for the 1-3 minute measurement lag while maintaining reliable CEMS operation.
Data Source
AI summary
A coal-air synchronous dynamic coordinated control method for a coal-fired unit is provided, comprising: determining functional relationship between unit loads and designed coal feed rates and functional relationship between unit loads and flue gas operation wet-basis oxygen contents, respectively; obtaining a theoretical wet flue gas volume and a combustion-supporting dry air volume per unit mass of burning coal, and calculating an actual combustion-supporting dry air volume per unit mass of burning coal; calculating an actual low calorific value of feed coal; calculating a combustion-supporting dry air volume and an outlet wet flue gas volume; according to the target value of load instruction at a future time point, calculating a coal feed rate variation and a combustion-supporting dry air volume variation; obtaining an operation wet-basis oxygen content variation; and obtaining target values of the coal feed rate and the operation wet-basis oxygen content to be adjusted.