Membrane Distillation for Sodium Sulfate Recovery

Solution Overview

Problem

The recovery of sodium sulfate (Na2SO4) from wastewater generated in the precipitated silica manufacturing process is not economically viable due to high energy requirements and waste heat disposal in existing methods.

Innovation Solution

A membrane distillation process utilizing the residual heat from the drying step of precipitated silica manufacturing to create a thermal gradient for Na2SO4 recovery, where hot gas from the drying apparatus is used to heat the wastewater stream, increasing its temperature and concentrating Na2SO4 through a membrane distillation unit.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional evaporation methods are used to recover Na2SO4 from wastewater, then high purity Na2SO4 can be obtained, but energy consumption is excessively high

Engineering Contradiction:

Improvepurity of Na2SO4VSAvoidenergy consumption

Core Design Contradiction:

Manufacturing precisionVSUse of energy by moving object

Solution Approach 1:

The invention converts the harmful waste heat discharged from the drying apparatus into a beneficial resource by using it as the heating source for membrane distillation. The hot gas stream, which would otherwise be wasted, is directed through a heat exchanger to provide thermal energy for Na2SO4 recovery, thereby eliminating the need for additional external energy input while maintaining high purity product recovery.

Inventive Principle:

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

Solution Approach 2:

The invention employs membrane distillation which utilizes phase transition of water from liquid to vapor through a hydrophobic membrane. The hot side of the membrane causes water to evaporate and pass through the membrane pores, while the cold side condenses it, leaving Na2SO4 concentrated in the feed stream. This phase transition mechanism enables high purity separation at lower energy costs compared to conventional evaporation.

Inventive Principle:

Principle #36Phase transitions

2Productivity

If waste heat from drying apparatus is discharged without utilization, then the drying process can be completed, but energy waste occurs

Engineering Contradiction:

Improvedrying process completionVSAvoidwaste heat loss

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The invention merges two separate processes - the drying apparatus and the Na2SO4 recovery system - by connecting the waste heat stream from drying to the heat exchanger of the membrane distillation unit. This integration allows the waste thermal energy to be captured and utilized for concentrating Na2SO4, transforming an energy loss into a productive resource that simultaneously achieves waste heat utilization and product recovery.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The system achieves self-service by using its own internally generated waste heat to power the Na2SO4 recovery process. The hot gas from the drying apparatus, which is already part of the system, serves as the heating source for the membrane distillation unit, eliminating the need for external energy inputs and making the overall process energetically self-sufficient.

Inventive Principle:

Principle #25Self-service

3Ease of manufacture

If membrane distillation is implemented without heat source, then Na2SO4 recovery is possible, but the process cannot be sustained economically

Engineering Contradiction:

Improveeconomic viabilityVSAvoidenergy requirement

Core Design Contradiction:

Ease of manufactureVSUse of energy by moving object

Solution Approach 1:

The invention converts the harmful waste heat discharged from the drying apparatus into a beneficial resource by using it as the heating source for membrane distillation. The hot gas stream, which would otherwise be wasted, is directed through a heat exchanger to provide thermal energy for Na2SO4 recovery, thereby eliminating the need for additional external energy input while maintaining high purity product recovery.

Inventive Principle:

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

Solution Approach 2:

The system achieves self-service by using its own internally generated waste heat to power the Na2SO4 recovery process. The hot gas from the drying apparatus, which is already part of the system, serves as the heating source for the membrane distillation unit, eliminating the need for external energy inputs and making the overall process energetically self-sufficient.

Inventive Principle:

Principle #25Self-service

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 reduces energy consumption and provides an economically advantageous route for Na2SO4 recovery, achieving high purity and concentration of Na2SO4, potentially as a solid, while utilizing waste heat efficiently.

Implementation Method 1

providing heat to water stream W0 in a heat-exchanger by means of the flow of hot gas to obtain water stream Wi at a temperature Ti

Methodology Applied

Scientific EffectHeat exchange: Heat Exchanger

Implementation Method 2

feeding water stream Wi comprising Na2SO4 at a concentration Ci to the feed side of the membrane distillation unit at a temperature Ti greater than the temperature Tp at the permeate side of the membrane distillation unit to obtain a water stream Wf containing Na2SO4 at a concentration Cf > Ci

Methodology Applied

Scientific EffectMembrane distillation: Distillation

Data Source

PatentEP3328523B1Process for the recovery of sodium sulfate

Publication Date: 2020.05.20 RHODIA OPERATIONS SAS

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AI summary

A process for the recovery of sodium sulfate from water, in particular from water deriving from a silica manufacturing process.