Pulp Mill Effluent Treatment for Chloride Control

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Solution Overview

Problem

Chemical pulp mills face challenges in minimizing effluent emissions and chloride accumulation, particularly with the use of chlorine dioxide in bleaching processes, which complicates water recycling and environmental compliance due to high organic chlorine compound levels.

Innovation Solution

Implementing a closed-loop system where purified bleaching effluent, treated to reduce organic matter and chlorides, is recycled back into the pulp mill process, with a focus on utilizing the recovery boiler to manage chloride levels and integrate recycled water into various stages, including brown stock treatment and white liquor production, to minimize environmental impact.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If chlorine dioxide is used in bleaching processes, then bleaching efficiency is improved, but organic chlorine compound levels increase causing environmental harm

Engineering Contradiction:

Improvebleaching efficiencyVSAvoidorganic chlorine compound levels

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent extracts and removes organic chlorine compounds (AOX) from the bleaching effluent through dedicated treatment processes before water recycling, separating the harmful substance from the recyclable water stream

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent converts the harmful organic chlorine compounds into removable target substances through oxidation processes, transforming the polluted effluent into treatable streams that can be purified and recycled

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Loss of substance

If effluent is recycled back into the pulp mill process, then water consumption is reduced, but chloride accumulation occurs in the chemical cycle

Engineering Contradiction:

Improvewater consumptionVSAvoidchloride level in chemical cycle

Core Design Contradiction:

Loss of substanceVSStability of the object's composition

Solution Approach 1:

The patent implements feedback control by continuously monitoring chloride levels in the chemical cycle and adjusting the recycling rate of effluent accordingly, reducing or stopping recycling when chloride thresholds are approached

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent applies partial recycling rather than full recycling of effluent, selectively recycling only portions of the treated water to avoid excessive chloride accumulation while still achieving water conservation benefits

Inventive Principle:

Principle #16Partial or excessive action

3Manufacturing precision

If organic matter content in effluent is decreased through treatment, then water quality for recycling is improved, but treatment process complexity increases

Engineering Contradiction:

Improvewater quality for recyclingVSAvoidtreatment process complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent segments the effluent treatment process into distinct stages (oxidation, clarification, filtration) that can be independently optimized and operated, making the overall complex process more manageable and controllable

Inventive Principle:

Principle #1Segmentation

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 effluent emissions, maintains pulp quality, and allows for a more closed chemical cycle, addressing environmental concerns while keeping chemical consumption and water usage at acceptable levels.

Implementation Method 1

The chloride-containing effluents from the bleaching plant are led to effluent treatment, where they are treated in order to decrease the organic matter content

Methodology Applied

Scientific EffectBiological treatment: Aerobic Digestion

Data Source

PatentUS8632656B2Method for treating liquid flows at a chemical pulp mill

Publication Date: 2014.01.21 ANDRITZ OY

AI summary

A method for treating liquid flows at a chemical pulp mill including at least an alkaline cooking process for producing pulp, brown stock treatment with essentially closed liquid cycles, a pulp bleaching plant using ECF-bleaching, a chemical recovery plant comprising a chemical recovery boiler, and effluent purification. Chloride-containing bleaching plant effluents are led to the effluent purification, where they are treated in order to decrease the organic matter content thereof. At least 20% of the purified effluent is returned to a pulp mill process and purified effluent is used in a last washing stage included in brown stock treatment. In the brown stock treatment the liquid flow is passed counter-currently to evaporation, wherefrom it is led for treatment to a recovery boiler process, wherein a separation process for chlorides is arranged for controlling the chloride level of the liquor cycle.