Central VFD for Reverse Osmosis Membrane Protection

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Solution Overview

Problem

Existing reverse osmosis systems with high-pressure pumps require expensive and unreliable medium voltage Variable Frequency Drives (VFDs) for power management, and existing solutions are inadequate for gradual pressure control during startup and shutdown to prevent membrane damage, especially in large-scale facilities.

Innovation Solution

A central Variable Frequency Drive (VFD) system is used to control multiple reverse osmosis trains equipped with High-Efficiency Motor Interface (HEMI) and energy recovery turbos, allowing for gradual speed ramp-up and ramp-down of motors, eliminating the need for multiple VFDs and optimizing pressure control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If a direct online (DOL) motor start is used to start the high-pressure pump motor, then the motor reaches synchronous speed quickly (in a few seconds), but the pressure rise is too fast causing damage to membrane surfaces and spacers

Engineering Contradiction:

Improvemotor speedVSAvoidmembrane damage

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a Variable Frequency Drive (VFD) as an intermediary device between the power supply and the motor. The VFD gradually adjusts the frequency of the power supply to the motor, enabling controlled ramp-up of motor speed from zero to synchronous speed over 15-30 seconds. This intermediary control mechanism prevents sudden pressure rises that would damage membranes, while still achieving the required operating speed.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If a VFD is installed on each high-pressure pump motor in large-scale RO facilities, then gradual pressure control during startup and shutdown is achieved, but the capital cost and operating cost increase significantly

Engineering Contradiction:

Improvemembrane protectionVSAvoidVFD quantity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent applies a single VFD to control multiple high-pressure pump motors sequentially. The VFD serves multiple functions: it can ramp up one motor while keeping others at synchronous speed via DOL starters, and can ramp down motors during shutdown. This multi-functional approach eliminates the need for individual VFDs on each motor, reducing capital costs by 60-70% while maintaining membrane protection capabilities.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The system dynamically switches between two operating modes: during normal operation, motors run at synchronous speed via DOL starters; during startup/shutdown transitions, the VFD provides gradual speed control. This dynamic approach allows the system to use the simpler and more reliable DOL method for steady-state operation while reserving VFD control for transitional phases, optimizing both cost and performance.

Inventive Principle:

Principle #15Dynamics

3Ease of operation

If medium voltage VFDs are used for large motors in SWRO systems, then speed control capability is provided, but the VFDs are very expensive, dissipate up to 4% of electrical energy as heat, and can be unreliable

Engineering Contradiction:

Improvespeed controlVSAvoidenergy dissipation

Core Design Contradiction:

Ease of operationVSLoss of energy

Solution Approach 1:

The patent segments the speed control function into two parts: the VFD handles only the transitional ramp-up and ramp-down phases (typically 15-30 seconds), while the motors operate at synchronous speed via direct online starters during steady-state operation. This segmentation minimizes the duration and magnitude of VFD operation, reducing energy dissipation to a negligible level while maintaining necessary speed control capability.

Inventive Principle:

Principle #1Segmentation

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 solution reduces capital and operating costs, enhances membrane protection by gradual pressure management, and improves the reliability of large-scale reverse osmosis systems by using a single VFD to control multiple RO trains, thereby extending membrane life and reducing energy losses.

Implementation Method 1

Methodology Applied

Scientific EffectVariable Frequency Drive:

Implementation Method 2

A portion of the hydraulic energy from the high-pressure brine is used to energize pump section 8 of turbo 33

Methodology Applied

Scientific EffectEnergy recovery:

Implementation Method 3

The remaining hydraulic energy energizes pump section 4 of turbo 34

Methodology Applied

Scientific EffectHydraulic energy:

Implementation Method 4

The reverse osmosis (RO) process uses a set of membrane elements that allow solvent (e.g., water) to pass through the membrane but blocks dissolved solids (e.g., salts)

Methodology Applied

Scientific EffectReverse osmosis: Reverse Osmosis