Feed-Forward Pulping Control via Wood Material Indicator
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Solution Overview
Problem
Conventional chemical pulping processes face challenges in accurately controlling the supply of chemicals and process parameters due to variations in wood chip properties, leading to inefficient use of resources and environmental concerns, as existing methods are costly, time-consuming, and lack precision in real-time feedback control.
Innovation Solution
A method that calculates a Wood Material Indicator (WMI) ratio by measuring actual mass flow of moisture wood chips and estimating dry wood chip flow, allowing for on-line feed-forward control of chemical supply and pulping process parameters such as liquor-to-wood ratio and temperature, improving process stability and pulp quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional feedback control methods are used to control pulping process based on pulp properties or residual alkali content measurements, then process control is achieved, but the response to short-term or sudden variations in chip properties is delayed and inaccurate
Solution Approach 1:
The invention measures chip properties (bulk density, moisture content) before the chips enter the digester, allowing the control system to predict and prepare for upcoming variations in raw material quality. This preliminary measurement approach enables feed-forward control that responds to chip property variations before they affect the pulping process, eliminating the time delay inherent in feedback control methods that measure pulp properties after cooking.
Solution Approach 2:
The invention combines feed-forward control based on preliminary chip property measurements with feedback control using pulp quality measurements. The system uses the measured chip properties to predict required chemical dosing adjustments, then verifies and fine-tunes these predictions using actual pulp quality feedback, creating a hybrid control system that achieves both rapid response and high accuracy.
2Measurement precision
If commercial measurement systems are used to measure raw material properties, then measurement capability is provided, but investment costs are high and analysis time is long
Solution Approach 1:
The invention extracts only the essential measurement parameters (bulk density and moisture content) that most significantly affect pulping process control, rather than implementing comprehensive commercial measurement systems that analyze numerous chip properties. This selective measurement approach provides sufficient control capability while minimizing investment costs and system complexity.
Solution Approach 2:
The invention uses simple, inexpensive measurement devices for bulk density and moisture content that can be easily implemented in the chip feed line, replacing or supplementing expensive commercial measurement systems. These simpler instruments provide adequate measurement accuracy for control purposes at a fraction of the cost of comprehensive commercial systems.
3Reliability
If more chemicals are used to account for raw material variations, then pulp quality consistency is maintained, but chemical consumption increases and environmental impact worsens
Solution Approach 1:
The system predicts the required chemical dosing adjustments based on preliminary measurements of chip bulk density and moisture content before the chips enter the digester. This allows the control system to precisely dose chemicals in advance according to the specific properties of the incoming charge, avoiding both under-dosing (which would compromise quality) and over-dosing (which wastes chemicals and increases environmental impact).
Solution Approach 2:
The invention dynamically adjusts chemical dosing parameters (alkali charge, liquor-to-wood ratio) based on measured chip properties. When chips have higher moisture content or different bulk density, the system automatically modifies the chemical dosing parameters to maintain optimal pulping conditions, ensuring consistent pulp quality while minimizing chemical consumption by dosing only what is needed for each specific charge.
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 method enables precise control of chemical dosing and pulping conditions, reducing variations in kappa number and improving pulp quality while minimizing investment costs, as demonstrated by a trial run at the Oulu mill, achieving a 41.7% reduction in kappa variation and 22.1% change in residual alkali extraction.
Implementation Method 1
measuring the actual mass flow of moisture wood chips conveyed to the impregnation vessel or the digester, by use of a chip conveyor scale
Implementation Method 2
measuring the actual mass flow of moisture wood chips conveyed to the impregnation vessel or the digester, by use of a radiating wood flow meter
Data Source
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AI summary
The invention discloses a method of controlling a pulping process wherein wood chips are conveyed to an impregnation vessel and/or to a digester where said wood chips are treated with a liquor comprising chemicals. According to the method of the invention a ratio between a measured, actual mass flow of moisture wood chips to an impregnation vessel or to a digester and an estimated mass flow of dry wood chips conveyed to the impregnation vessel or to the digester is calculated. Said ratio is used to control the pulping process. The method makes it possible to control e.g. the supply of chemicals, the liquor to wood ratio and the pulping temperature on-line, in a feed-forward manner.