Two-Stage Reverse Osmosis for Produced Water Purification
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Solution Overview
Problem
Conventional methods for purifying produced water from oil and gas operations, such as reverse osmosis membrane systems, face challenges with scaling issues due to high hardness and contaminants, requiring extensive pretreatment and pH adjustments, which are costly and complex, and do not effectively remove boron and ammonia.
Innovation Solution
A method involving the use of ultrafiltration and reverse osmosis membrane systems in series, with ion exchange softening and pH adjustment, to produce purified water with reduced hardness and dissolved solids, while managing membrane scaling through retentate recycling and antiscalants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional reverse osmosis membrane systems are used for water purification, then water purification is achieved, but extensive pretreatment and pH adjustments are required which increase system complexity and operational costs
Solution Approach 1:
The invention divides the water purification process into distinct stages: a first reverse osmosis membrane system that operates without extensive pretreatment to produce permeate, followed by a second reverse osmosis membrane system that further purifies the permeate. This segmentation allows each stage to handle specific contaminants appropriately, reducing the need for complex pretreatment while achieving high purification effectiveness.
2Object-affected harmful factors
If high pH adjustment is applied to reduce scaling, then membrane scaling is reduced, but separation effectiveness of contaminants like boron and ammonia deteriorates
Solution Approach 1:
The invention dynamically adjusts the pH of the permeate from the first reverse osmosis system before it enters the second reverse osmosis system. By controlling and optimizing the pH level, the system prevents membrane scaling while maintaining effective separation of contaminants such as boron and ammonia, thus resolving the contradiction between scaling prevention and separation effectiveness.
3Object-affected harmful factors
If extensive pretreatment is applied to remove hardness and contaminants, then membrane scaling is reduced, but operational costs and process time increase
Solution Approach 1:
The invention performs preliminary removal of hardness and contaminants in the first reverse osmosis stage, which operates without extensive pretreatment. This preliminary action reduces the burden on subsequent stages and minimizes overall pretreatment requirements, thereby reducing both process time and operational costs while still preventing membrane scaling.
4Object-affected harmful factors
If conventional pretreatment methods are used to remove hardness, then membrane scaling is reduced, but system operational costs increase
Solution Approach 1:
The two-stage reverse osmosis system is designed to be self-regulating, where the first stage naturally removes a significant portion of hardness and contaminants without requiring extensive external pretreatment. This self-service capability reduces the need for additional chemicals and energy-intensive pretreatment processes, thereby lowering operational costs while still preventing membrane scaling.
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 method effectively reduces total dissolved solids, hardness, and boron levels in produced water, improving membrane performance and reducing operational costs by simplifying the pretreatment process and enhancing water quality for industrial and domestic use.
Implementation Method 1
passing a feed stream of the produced water having a temperature of at least 45° C. through an ultrafiltration membrane module
Implementation Method 2
The first permeate stream is passed to an ion exchange softener module comprising a plurality of ion exchange resin pellets to produce a soft water stream having a hardness less than 5 ppm
Implementation Method 3
The reverse osmosis feed stream is passed to a high temperature reverse osmosis membrane module having a plurality of membrane elements to form a purified water stream containing less than 500 ppm total dissolved solids
Data Source
AI summary
Produced water from a crude oil or natural gas production process is purified using a membrane purification system for petroleum production, agricultural, commercial and domestic uses. The produced water is pretreated to remove, at least, particulates and oil from the produced water. The minimally pretreated water is then purified in a membrane purification system, that is operated at conditions such that membrane scaling is reduced or prevented. In particular, the membrane purification system is operated to maintain the turbidity of clarified water feed to the system or intermediate aqueous streams that are cascading through the membrane purification system. Ensuring that the turbidity of the reject streams generated in the membrane system are useful in achieving long membrane operating life.