Nanofiltration Station Permeate Recirculation for Phosphate Purification
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Solution Overview
Problem
Current phosphate-containing acidic solution purification processes, such as those using nanofiltration, face challenges in achieving both high yield and impurity removal rates, often requiring regular bleeds to manage increasing impurity levels and resulting in reduced economic viability, especially when the market price of phosphate is low.
Innovation Solution
A fully continuous nanofiltration process with a novel station design that includes multiple membrane units arranged in series, incorporating permeate recirculation loops to enhance both yield and impurity removal rates without the need for regular bleeds, by recirculating permeates back into the system to maintain low impurity levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple nanofiltration membrane units are arranged in series to increase impurity removal rate, then impurity removal rate is improved, but phosphate yield decreases
Solution Approach 1:
The system is divided into multiple functional segments: purification membrane units (M1-Mn) for impurity removal, recovery membrane units (Mr1-Mr2) for phosphate recovery, and exit membrane units (Me1-Me2) for final purification. Each segment performs a specific function, allowing the system to achieve both high impurity removal and high phosphate yield by optimizing each segment's contribution to the overall process.
Solution Approach 2:
Permeate recirculation loops are implemented where permeate from recovery and exit membrane units is fed back to the entry line. This feedback mechanism allows purified permeate to be reused as feed solution, maintaining low impurity levels in the input solution and enabling continuous operation at high phosphate yield without requiring periodic bleeds.
2Productivity
If retentate solutions are recirculated to enhance phosphate yield, then phosphate yield is improved, but impurity content in feed solution increases requiring regular bleeds
Solution Approach 1:
Instead of recirculating retentate (which contains high impurity concentrations), the system recirculates permeate (which contains low impurity concentrations). This inversion of the recirculation stream allows phosphate recovery and yield enhancement without reintroducing high levels of impurities into the feed solution, eliminating the need for regular bleeds.
Solution Approach 2:
Permeate recirculation loops provide feedback of purified solution to the entry line, continuously maintaining low impurity levels in the feed solution while recovering phosphate. This feedback mechanism sustains both high phosphate yield and low impurity content simultaneously through continuous operation.
3Manufacturing precision
If regular bleeds are performed to manage impurity levels, then impurity content is controlled, but phosphate yield and economic viability decrease
Solution Approach 1:
The system operates continuously without periodic interruptions for bleeds. Permeate recirculation loops maintain low impurity levels continuously, allowing the purification process to run at constant high phosphate yield. The useful action of phosphate recovery and purification continues uninterrupted, enhancing both productivity and economic viability.
Solution Approach 2:
Continuous permeate recirculation provides ongoing feedback that maintains impurity levels below thresholds requiring bleeds. This continuous control mechanism eliminates the need for periodic phosphate loss through bleeds, sustaining high phosphate yield and improving economic viability through continuous operation.
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
The process achieves a significant increase in phosphate yield and impurity removal rates, maintaining low impurity concentrations and reducing operational costs by eliminating the need for frequent bleeds, thus improving the economic viability of phosphate purification.
Implementation Method 1
Nanofiltration is a membrane filtration-based method using nanometre sized through-pores that pass through the membrane
Implementation Method 2
Nanofiltration membranes typically have pore sizes from 1-10 nanometers, smaller than that used in microfiltration and ultrafiltration
Implementation Method 3
The process comprises at least one permeate recirculation loop formed by including a fluid communication between the permeate sides of one or more of the first or second recovery membrane units or of the first exit membrane unit with the entry line
Data Source
Figure 1(a)~1(b)
Figure 1(c)~1(d)
Figure 2(a)~2(c)
AI summary
The present invention concerns a process and an apparatus for purifying a phosphate containing acidic solution comprising impurities through a nanofiltration station comprising a number of nanofiltration membrane units, each comprising a retentate side and a permeate side separated by a membrane, the process comprising feeding the phosphate containing acidic solution through an entry line to a first membrane unit of n 2: 1 membrane units arranged in series, wherein a nth permeate flowing out of the nth membrane unit forms a nanofiltered phosphate solution. The gist of the present invention is the provision of at least one permeate recirculation loop, branching off the retentate side of the first membrane unit and closing the loop at the entry line to combine at least one of three permeates with the phosphate containing acidic solution.