Desalination Intake System with Segmented Wedgewire Screens
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Solution Overview
Problem
Desalination plants face significant environmental issues due to fish and larvae entrapment and entrainment in intake systems, with existing solutions like screened intake systems and wedgewire screens being inefficient or impractical for large-scale commercial operations near ecologically sensitive coastal areas, leading to high mortality rates and habitat destruction.
Innovation Solution
An integrated intake and reef system that uses a grating with a baffle to prevent surface water entry, accelerates seawater flow through a raceway with wedgewire screens to minimize entrainment, and employs a recovery system with fish-friendly pumps to return residual seawater to a reef ecosystem, optimizing habitat impact and reducing impingement losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If screened intake systems are used to reduce entrainment and entrapment, then fish and larvae losses are reduced by 85-90%, but significant losses still occur due to high concentration of sea life in near shore environment
Solution Approach 1:
The intake system is divided into multiple screens arranged in series (first screen, second screen, third screen) with different orientations and mesh sizes. This segmentation allows progressive filtering of fish and larvae, with each screen capturing different sizes and types of organisms, thereby reducing overall entrainment and entrapment more effectively than a single screen system.
Solution Approach 2:
The system employs screens with varying orientations (vertical, angled, horizontal) and positions (above and below the water surface). By introducing dimensional diversity in screen arrangement, the system captures fish and larvae from multiple spatial dimensions, increasing overall removal efficiency while maintaining adequate water flow for desalination.
2Object-affected harmful factors
If travelling screens with fine mesh are used to achieve 85% removal efficiency, then fish and larvae are removed, but a fish return system is required that routes recovered fish away from the intake system
Solution Approach 1:
The system extracts fish and larvae from the water flow using multiple screens, and the captured organisms are collected in fish buckets attached to the screen structure. This extraction mechanism eliminates the need for complex separate fish return systems, as the fish are directly collected and can be periodically removed or returned to the water body in a simple manner.
Solution Approach 2:
The travelling screen system is self-cleaning through its continuous movement and backflush mechanism. The screens automatically remove accumulated debris and fish, maintaining their filtering capability without requiring external cleaning systems. This self-service feature reduces operational complexity while maintaining high removal efficiency.
3Object-affected harmful factors
If travelling screens are used to remove fish and larvae, then removal efficiency is achieved, but mortality rate is high due to stress of impingement and reduced oxygen content in water
Solution Approach 1:
The system uses screens with different mesh sizes (fine mesh, medium mesh, coarse mesh) at different positions to create localized filtering zones. The first screen with fine mesh captures small larvae, while subsequent screens with progressively larger mesh sizes capture larger fish. This local quality variation reduces impingement stress on different organisms, improving survival rates while maintaining removal efficiency.
Solution Approach 2:
The system performs preliminary sorting of fish and larvae using multiple screens before they enter the desalination plant. By pre-separating organisms of different sizes and types, the system reduces the stress of impingement on vulnerable larvae and allows larger, more resilient fish to be handled differently, thereby improving overall survival rates of captured organisms.
4Object-affected harmful factors
If wedgewire passive screens are used to achieve 85-90% effectiveness, then fish and larvae are removed, but significant screen surface area is required which is impractical due to site restrictions
Solution Approach 1:
Instead of using a single large screen, the system segments the filtering function across multiple smaller screens arranged in series. This segmentation achieves the same total removal effectiveness (85-90%) while requiring less total screen surface area and fitting within constrained waterfront sites. Each screen handles a portion of the filtering load, making the overall system more space-efficient.
Solution Approach 2:
The system utilizes vertical and angled screen arrangements to maximize the use of vertical space rather than horizontal space. By orienting screens at angles and stacking them vertically, the system achieves high removal effectiveness without requiring large horizontal footprints, thereby accommodating site restrictions at industrial waterfront locations.
5Object-affected harmful factors
If subsurface intakes are used to prevent entrainment and entrapment, then sea life is filtered by the sea floor, but high porosity sea bed is required which is not available at many locations
Solution Approach 1:
The multiple screen intake system serves multiple functions: it filters fish and larvae effectively, maintains water flow for desalination, and can be installed in various waterfront locations regardless of sea bed porosity. Unlike subsurface intakes that require specific high porosity conditions, this screen-based system is universally applicable to different sea bed types and locations, enhancing adaptability and versatility.
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 system achieves minimal impingement and environmental losses, with less than 10% fish and larvae entrainment, and supports a healthy reef ecosystem, reducing habitat damage and operational costs compared to conventional designs.
Implementation Method 1
cross-flow filtering system...wedgewire screens...permitting the flow of screened cross flow water
Implementation Method 2
A baffle at the top of the grating prevents fish and larvae rich surface water from entering the raceway
Implementation Method 3
accelerates seawater flow through a raceway with wedgewire screens to minimize entrainment
Implementation Method 4
recovery system with fish-friendly pumps to return residual seawater to a reef ecosystem
Data Source
AI summary
An environmentally supportive seawater intake system includes a first filtering system in communication with raw seawater for providing a flow of seawater in a first direction into a raceway. A second filtering system is also in communication with seawater in the raceway and is adapted to receive a portion of the seawater in the raceway and directing it in a second direction away from the flow of residual water in the raceway. An input device receives the second portion flowing in the second direction, and a recovery system receives and returns the first, residual portion to the sea environment.