Biocide Dosing Control for Paper Making Storage Towers
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Solution Overview
Problem
In paper making using recycled fibers, slow-moving zones in storage towers create microbiological habitats that are difficult for biocides to reach, leading to unstable wet-end and runnability problems, and potential explosive gas emissions.
Innovation Solution
A method involving monitoring the surface level of a fibrous suspension in a storage tower, identifying when emptying and refilling criteria are met, and responsive biocide dosing into the incoming suspension to target slow-moving zones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If biocide is continuously dosed into the storage tower inlet, then microbial growth is suppressed in the main flow, but the biocide cannot reach the slow-moving zones and the main flow becomes overly chemicalised
Solution Approach 1:
The system uses periodic dosing of biocide based on monitored parameters (pH, conductivity, dissolved oxygen) rather than continuous dosing. When parameters indicate microbial activity, biocide is dosed; when parameters are normal, dosing is reduced or stopped. This periodic approach targets microbial outbreaks without continuously over-chemicalising the main flow.
Solution Approach 2:
The system implements feedback control by monitoring pH, conductivity, and dissolved oxygen levels in real-time. These measurements feed back to the dosing system, which adjusts biocide application rates accordingly. This closed-loop feedback ensures biocide is only dosed when actually needed to suppress microbial growth, avoiding unnecessary chemicalisation.
2Stability of the object's composition
If storage tower volume is increased to improve process stability, then retention time increases and microbial activity accelerates, but increasing volume also creates larger slow-moving zones that are harder to treat
Solution Approach 1:
The system uses the natural parameters of the fibrous suspension (pH, conductivity, dissolved oxygen levels) as indicators of microbial activity. These self-generated signals serve as feedback to trigger biocide dosing, eliminating the need for external complex monitoring systems while effectively treating even large storage towers.
Solution Approach 2:
The patent replaces mechanical mixing systems with chemical sensing and dosing. Instead of relying on mechanical agitation to prevent slow-moving zones, the system uses chemical sensors to detect microbial activity and applies biocide chemically to treat the problem wherever it occurs in the tower.
3Stability of the object's composition
If bottom mixers are used to circulate fibrous suspension, then mixing is improved, but the mixer influence only reaches a small portion of the tower volume and slow-moving zones persist
Solution Approach 1:
The system uses dissolved oxygen as an intermediary indicator of microbial activity. Since aerobic bacteria consume dissolved oxygen, monitoring this parameter provides indirect information about microbial populations in slow-moving zones without requiring direct physical access to those zones. This intermediary signal triggers biocide dosing to treat the affected areas.
Data Source
AI summary
A method for controlling paper making includes monitoring (302) a surface level of a fibrous suspension in a storage, and identifying (303) that the surface level has decreased so that at least one emptying criterion is met and thereafter identifying that the surface level has increased so that at least one refilling criterion is met, and responsively to the identifying that the surface level has increased so that the at least one refilling criterion is met, starting to dose a biocide agent into the fibrous suspension entering the storage. A corresponding apparatus and computer program are disclosed.