Pulp Bleaching Dilution Using Recycled Effluent
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Solution Overview
Problem
Chemical pulp mills face challenges in minimizing chlorine-containing effluents and water usage while maintaining pulp quality and chemical consumption levels, especially in areas with strict environmental regulations and limited water resources.
Innovation Solution
A method is introduced where purified effluent from a biological treatment plant is recycled and used in the pulp bleaching process, specifically in the dilution stage after the washing press, to reduce lignin content and optimize chemical consumption, allowing for a more closed-loop system without the need for additional treatment stages or new processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If purified effluent is recycled and used in the pulp bleaching process, then water usage is reduced and the system becomes more closed-loop, but the complexity of effluent purification and recycling infrastructure increases
Solution Approach 1:
The patent applies the discarding and recovering principle by treating and recycling effluent from the biological treatment plant back into the pulp bleaching process. Instead of discarding the effluent as waste, it is purified and reused in the dilution stage after the washing press, thereby reducing water consumption and creating a more closed-loop system.
Solution Approach 2:
The patent implements self-service by using the mill's own effluent treatment capacity to provide purified water for its own processes. The biological treatment plant treats the mill's effluent, and the purified water is then reused within the same mill, reducing external water demands and creating a self-sufficient water management system.
2Object-generated harmful factors
If purified effluent is used in the dilution stage after the washing press, then organic chlorine compounds are reduced, but the requirements for effluent purification quality increase
Solution Approach 1:
The patent applies feedback by monitoring the quality of effluent from the biological treatment plant and using it in a controlled manner in the bleaching process. The effluent is used in the dilution stage where its composition can influence the bleaching chemistry, and the system adjusts to maintain pulp quality while reducing organic chlorine compounds.
Solution Approach 2:
The patent implements parameter changes by modifying the composition and properties of the dilution water used in the bleaching process. Instead of using pure fresh water, purified effluent with different chemical parameters is used, which changes the bleaching chemistry to reduce organic chlorine compound formation while maintaining effective bleaching.
3Object-generated harmful factors
If the mill operates with a more closed process to minimize effluents, then environmental impact is reduced, but the availability of water resources for the mill decreases
Solution Approach 1:
The patent implements continuity of useful action by maintaining a continuous cycle of effluent treatment and reuse. The biological treatment plant continuously treats effluent, and the purified water is continuously fed back into the bleaching process, creating an ongoing closed-loop system that minimizes effluent discharge while ensuring adequate water supply.
Solution Approach 2:
The patent applies universality by using the purified effluent for multiple purposes within the mill. The recycled water is used in the dilution stage of bleaching and can potentially be used in other processes, maximizing the utility of the treated water and reducing the overall water demand of the mill.
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 significantly reduces organic chlorine compounds and water usage, achieving a more closed pulp production process with minimal emissions and maintaining pulp quality, while keeping chemical consumption at acceptable levels.
Implementation Method 1
purified effluent from a biological treatment plant
Implementation Method 2
effluent, which is passed entrained in the pulp from the dilution into the first process stage of the bleaching
Data Source
AI summary
A method in connection with washing of pulp at a chemical pulp mill including at least an alkaline cooking process utilizing cooking liquor for producing pulp, brown stock treatment with essentially closed liquid cycles, in which the last washing device is a washing device based on pressing of pulp, a press or a washing press, a pulp bleaching plant using ECF-bleaching, wherein chloride-containing effluents are formed, a chemical recovery plant and effluent purification. The liquid flows generated at a chemical pulp mill are efficiently circulated without disturbing the main process and minimizing the emissions from the mill. Purified effluent in the amount of at least 1 m3/adt pulp is introduced into the dilution after the press or washing press, whereby the effluent is passed from the dilution into the first process stage of the bleaching.