Pulp Mill Sodium Sulphate Make-Up for Sodium and Sulphur Balance
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Solution Overview
Problem
Existing pulp mills face challenges in controlling sodium and sulphur balance, leading to significant sodium losses and the need for excessive make-up chemicals, while also facing difficulties in efficiently utilizing sulphuric acid plants and managing fly ash disposal.
Innovation Solution
Implement a method in pulp mills using sodium sulphate as the main make-up chemical, with a portion of its sulphur content used to produce sulphuric acid, and oxidized white liquor used in bleaching stages to reduce sodium hydroxide consumption, coupled with efficient removal of non-process elements like chlorine and potassium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If sulphur is removed from the chemical cycle by dumping fly ash, then sulphur content is reduced, but sodium losses increase
Solution Approach 1:
The patent extracts and removes only the sulphur-containing compounds (such as calcium sulphate) from the fly ash through selective leaching processes, while leaving the sodium-containing compounds intact. This allows sulphur removal without proportional sodium loss, resolving the contradiction between reducing sulphur content and minimizing sodium losses.
Solution Approach 2:
The patent applies selective leaching to create local differentiation in the fly ash treatment process. Different components of the fly ash are treated differently: sulphur compounds are removed through chemical leaching, while sodium compounds are preserved. This local quality approach allows targeted sulphur removal without blanket sodium loss.
2Quantity of substance
If make-up chemicals are added to compensate for sodium losses, then sodium balance is maintained, but operational costs increase
Solution Approach 1:
The patent recovers sodium from what would otherwise be waste fly ash through selective leaching processes. The sodium-containing residues from fly ash treatment are recovered and returned to the chemical cycle, eliminating the need for expensive external sodium make-up chemicals while maintaining sodium balance.
Solution Approach 2:
The system makes the fly ash treatment process self-service by using the fly ash itself as the source of sodium recovery. The leaching process extracts sulphur while preserving and recovering sodium, allowing the system to compensate for its own sodium losses without external chemical inputs, thereby reducing operational costs.
3Quantity of substance
If fly ash is dumped to control sulphidity, then sulphur management is improved, but environmental impact increases
Solution Approach 1:
The patent converts the harmful waste product (fly ash containing sulphur and sodium) into a beneficial resource. Through selective leaching, the fly ash is transformed from a disposal problem into a source of recovered sodium that can be returned to the chemical cycle. This eliminates the need for dumping while achieving sulphur management goals, converting environmental harm into benefit.
4Quantity of substance
If sodium hydroxide is used as make-up chemical, then sodium losses are compensated, but sulphuric acid plant capacity is underutilized
Solution Approach 1:
The patent creates a multi-functional system where the sulphuric acid plant serves dual purposes: producing sulphuric acid for the pulping process and generating sodium sulphate through controlled reactions with recovered sodium. This increases the utilization of sulphuric acid plant capacity while still compensating for sodium losses, eliminating the underutilization problem.
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
Reduces the need for sodium hydroxide, optimizes sulphuric acid plant capacity, minimizes fly ash dumping, and enhances the chemical cycle closure, thereby lowering operational costs and environmental impact.
Implementation Method 1
a portion of its sulphur content being used for producing sulphuric acid
Implementation Method 2
oxidized white liquor used in bleaching stages
Data Source
Figure 1
AI summary
According to an example aspect of the present invention, there is provided a method of replacing with sodium make-up chemicals sodium losses caused by outflows in a pulp mill which employs a kraft process for producing cellulosic pulp, wherein the pulp mill includes a unit for conversion of sulphurous compounds, which is fed with sulphurous substances of the kraft process to convert said sulphurous substances into oxidized sulphurous compounds, said method comprising using sodium sulphate possibly together with other sodium salts as the main make-up chemical, to achieve an essentially sodium hydroxide free feed of sodium make-up chemicals, and at least a part of the sulphur contained in the sodium sulphate make-up chemical being used for producing oxidized sulphurous coumpounds in said unit for conversion of sulphurous compounds.