Green Liquor Alkali Control via Multi-Sensor Segmentation
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Solution Overview
Problem
Current methods for controlling the chemical cycle in pulp mills, particularly in regulating sodium carbonate concentration in green liquor, are inaccurate due to reliance on conductivity measurements, fail to account for other compounds that can solidify at high concentrations, and do not effectively maximize sodium sulphide recovery.
Innovation Solution
Measuring the contents of sodium sulphate, sodium hydroxide, sodium sulphide, and sodium carbonate in green liquor to optimize total titratable alkali (TTA) and control the flow of weak white liquor, while also monitoring temperature to prevent pirssonite formation, thereby maximizing recovery boiler reduction and maintaining process efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If only electrical conductivity is measured to control sodium carbonate concentration, then the control system is simple, but the measurement precision is insufficient and other compounds affecting dissolution are not detected
Solution Approach 1:
The patent segments the measurement task by measuring different chemical compounds (sodium carbonate, sodium sulphide, sodium sulphate, sodium hydroxide) separately using multiple sensors instead of relying on a single conductivity measurement. This allows precise detection of each compound's concentration while maintaining manageable system complexity through modular sensor deployment.
Solution Approach 2:
The measurement system is designed to perform multiple functions by detecting various compounds (carbonate, sulphide, sulphate, hydroxide) that all affect the dissolution process. This multi-functional approach enables comprehensive monitoring of all relevant compounds simultaneously, improving measurement precision without proportionally increasing complexity.
2Productivity
If the concentration of chemicals in green liquor is increased to efficiently recover chemical, then the recovery efficiency improves, but compounds may solidify and cause process disruptions
Solution Approach 1:
The patent implements feedback control by continuously measuring the concentrations of multiple compounds and using this information to adjust the weak white liquor flow rate. This feedback mechanism allows the system to maintain high chemical concentrations for efficient recovery while preventing solidification by detecting approaching saturation limits and adjusting dilution accordingly.
Solution Approach 2:
The system dynamically changes the concentration parameters of green liquor by adjusting the weak white liquor flow rate based on real-time measurements. This allows optimization of chemical recovery efficiency while staying within safe concentration limits that prevent solidification of compounds like pirssonite.
3Ease of operation
If only the flow of weak white liquor is controlled to maintain sodium carbonate concentration, then the control is simple, but the reduction of the recovery boiler cannot be maximized
Solution Approach 1:
The control system is designed to perform multiple functions simultaneously: it controls sodium carbonate concentration through weak white liquor flow adjustment while also monitoring sodium sulphide, sodium sulphate, and sodium hydroxide concentrations. This multi-functional control enables both simple operation and maximized sodium sulphide recovery by providing comprehensive data for optimization.
Solution Approach 2:
The patent uses feedback from multiple compound measurements to guide control decisions. By monitoring sodium sulphide concentration alongside carbonate, the system can adjust operations to maximize reduction efficiency while maintaining proper carbonate levels, thereby improving productivity without significantly complicating operation.
4Productivity
If the concentration of sodium carbonate is optimized for chemical recovery, then the efficiency improves, but the formation of pirssonite solid may occur reducing process reliability
Solution Approach 1:
The patent implements feedback control that monitors sodium carbonate concentration and adjusts the weak white liquor flow rate to maintain optimal levels for chemical recovery while preventing pirssonite solid formation. The system continuously compares measured concentrations against saturation thresholds and makes real-time adjustments to maintain process reliability.
Solution Approach 2:
The system takes preliminary anti-action by detecting approaching saturation conditions before pirssonite solid actually forms. By monitoring multiple compound concentrations and predicting when saturation will occur, the system adjusts the weak white liquor flow in advance to prevent solidification, thereby maintaining both productivity and reliability.
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 accurate control over green liquor composition, prevents solidification of compounds like pirssonite, and maximizes sodium sulphide recovery, enhancing energy balance and pulp mill capacity.
Implementation Method 1
In the dissolving tank, the smelt is dissolved in weak white liquor to produce green liquor
Implementation Method 2
Process chemicals are recovered to a char bed of a recovery boiler by burning concentrated black liquor therein
Implementation Method 3
the sodium carbonate concentration of green liquor is regulated by measuring the conductivity of the green liquor
Data Source
AI summary
A method for optimizing reduction and content of total titratable alkali of green liquor of a recovery boiler. The method comprises producing green liquor in a dissolving tank by conveying smelt and weak white liquor into the dissolving tank and measuring at least the contents of sodium sulphate, sodium hydroxide, sodium sulphide, and sodium carbonate of the green liquor. The method comprises controlling at least a process parameter of a recovery boiler to maximize the reduction of the recovery boiler and controlling the flow of the weak white liquor into the dissolving tank to optimize the content of total titratable alkali of the green liquor. In addition, a system for producing green liquor with optimized reduction and content of total titratable alkali. The system comprises a first sensor arrangement, a first and a second regulator, and a processing unit arrangement configured to perform the method.