Cement Mill Control via Predictive Choking Detection
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Solution Overview
Problem
Cement finish mill control systems face challenges in maintaining stable operation and maximizing production rate due to nonlinear interactions and sluggish responsiveness, exacerbated by variations in feed quality and equipment conditions, leading to oscillations and sub-optimal control.
Innovation Solution
Implementing a Model Predictive Control (MPC) system that measures fresh and rejected feed, predicts rejected feed errors, and adjusts fresh feed input based on real-time mill power and sound measurements to prevent choking and optimize operating conditions, using a choking model to incrementally adjust feed rates and maintain optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If automated control systems adjust fresh feed based on reject flow rate changes, then the system responds automatically to feed hardness and separator operation changes, but this causes moderate to severe oscillations in the finish mill response
Solution Approach 1:
The control system predicts future reject flow rates based on current mill charge conditions and feed rate changes before they actually occur. By anticipating the reject flow response to feed rate adjustments, the system can make preliminary corrections that prevent oscillations rather than reacting to them after they start
Solution Approach 2:
The system uses feedback from mill power, mill sound, and separator performance to continuously monitor mill charge conditions and adjust fresh feed rates. This closed-loop feedback enables automatic adaptation to changing feed hardness and separator operation while maintaining stable mill operation through predictive rather than reactive control
2Productivity
If the mill operates at maximum production rate, then productivity increases, but stable operation becomes difficult to achieve due to nonlinear interactions and sluggish responsiveness
Solution Approach 1:
The control system dynamically adjusts operating parameters including fresh feed rate, separator fan speed, and mill power based on real-time mill charge conditions. This dynamic control allows the mill to operate stably at maximum production rates by continuously adapting to changing conditions rather than relying on fixed setpoints
Solution Approach 2:
The predictive control model anticipates future mill charge conditions and reject flow rates, allowing the system to preemptively adjust feed rates and separator operation to maintain stable operation at high production rates before instability can develop
3Productivity
If fresh feed rate is increased to maximize profitability, then productivity improves, but this may cause mill choking and require reduction in feed rate
Solution Approach 1:
The system uses feedback from mill power measurements and mill sound measurements to continuously monitor mill charge level and detect early signs of choking. This enables automatic reduction of fresh feed rate before choking occurs, maintaining reliable operation at maximum sustainable feed rates
Solution Approach 2:
The predictive control model forecasts future mill charge conditions based on current feed rate and grinding performance. By predicting when the mill charge will become excessive, the system can preemptively reduce feed rate to prevent choking rather than reacting after it occurs
Data Source
AI summary
Methods and systems for controlling a cement finishing mill, and operating the mill at an optimal point, are disclosed. To determine an optimal point of operation, values of mill power and sound are collected and compared to values predicted by a model to determine if the mill is choking. This choking determination is used in one of two processes to determine an optimal point of operation for the mill. In the first process, as long as the mill is not choking, the amount of fresh feed input to the mill is incrementally increased; when choking occurs, the amount of fresh feed is decreased until choking ceases. In the second process, the amount of fresh feed input to the mill is increased and decreased in an oscillating manner over time, to find the amount of feed that results in the mill approaching, but never reaching, a choking state.