Reverse Osmosis Membrane Flow Control via Velocity PID
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Solution Overview
Problem
Conventional reverse osmosis membrane separation systems face challenges in maintaining a consistent flow rate of permeate water due to changes in water permeability coefficients caused by temperature variations and membrane degradation, leading to deviations from target flow rates and potential overconcentration issues.
Innovation Solution
A reverse osmosis membrane separation device equipped with a flow rate detecting unit, pressure pump driven by an inverter, and a control unit using a velocity-type digital PID algorithm to adjust the drive frequency of the pressure pump, ensuring the detected flow rate matches the target flow rate by averaging instantaneous flow rates and performing temperature feedforward recovery rate control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional flow rate feedback water volume control is used, then the flow rate of permeate water can be held at a target flow rate value under stable conditions, but when the water permeability coefficient rapidly changes, the system cannot sufficiently follow this change and the flow rate greatly deviates from the target value
Solution Approach 1:
The control system performs preliminary actions by detecting temperature changes and predicting permeability coefficient variations before they fully manifest. The system calculates anticipated flow rate deviations and pre-adjusts the pressure pump drive frequency to compensate for upcoming changes, enabling the system to follow rapid permeability changes without great deviation from the target flow rate value
Solution Approach 2:
The system employs dual feedback mechanisms: conventional flow rate feedback that monitors actual permeate water flow and adjusts pump frequency, and temperature feedback that detects supply water temperature changes and predicts permeability variations. This combined feedback approach allows the system to respond rapidly to permeability coefficient changes while maintaining flow rate stability at the target value
2Ease of operation
If pressure pump operates at constant operating pressure, then system operation is simple, but when temperature is low or membrane is blocked, permeate water volume becomes smaller than required production volume
Solution Approach 1:
The system uses flow rate feedback from the flow rate detector to continuously monitor permeate water production volume. When the detected flow rate falls below the target flow rate (indicating low temperature or membrane blockage), the control unit calculates the necessary drive frequency increase and adjusts the pressure pump accordingly, maintaining required production volume while building upon the simple constant pressure operation baseline
Solution Approach 2:
The system dynamically changes the drive frequency parameter of the pressure pump based on detected flow rate and temperature conditions. By adjusting the drive frequency, the system modifies the pump's operating characteristics to compensate for low temperature effects or membrane blockage, ensuring the permeate water production volume meets required production targets while maintaining operational simplicity
3Ease of operation
If pressure pump operates at constant operating pressure, then system operation is simple, but when temperature is high or membrane is degraded, overconcentration occurs easily at primary side of membrane
Solution Approach 1:
The flow rate feedback mechanism detects when permeate water flow exceeds the target flow rate, which indicates high temperature or membrane degradation conditions. The control unit responds by adjusting the pressure pump drive frequency to reduce the water volume fed to the membrane, thereby preventing overconcentration at the primary side and subsequent membrane blockage while preserving the simplicity of constant pressure operation
Solution Approach 2:
When overconcentration is detected through flow rate feedback, the system rapidly adjusts the pressure pump drive frequency to skip through the dangerous operating condition. This quick response prevents the accumulation of concentrated substances at the membrane primary side, avoiding membrane blockage while maintaining the overall simplicity of the constant pressure operation system
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 effectively maintains a stable flow rate of permeate water at the target value even with rapid changes in water permeability coefficients, suppressing deviations and preventing overconcentration, thus ensuring consistent water production and membrane health.
Implementation Method 1
a reverse osmosis membrane module (5) that separates supply water (W1) into permeate water (W2) and concentrated water (W3)
Implementation Method 2
a flow rate detecting unit (6) that detects a flow rate of the permeate water (W2) to output a detected flow rate value corresponding to the flow rate... the impeller (63) makes one rotation, the Hall integrated circuit (62) outputs a rectangular wave pulse signal
Implementation Method 3
a pressure pump (2) that pressure feeds the supply water (W1) to the reverse osmosis membrane module (5)
Implementation Method 4
an inverter equipment (3) that outputs a drive frequency corresponding to an input current value signal to the pressure pump (2)
Data Source
AI summary
A reverse osmosis membrane separation device includes: a reverse osmosis membrane module; a flow rate detecting unit configured to detect a flow rate of permeate water to output a detected flow rate value corresponding to the flow rate; a pressure pump configured to be driven at a rotation speed corresponding to an input drive frequency and to feed supply water to the reverse osmosis membrane module; an inverter configured to output a drive frequency corresponding to an input current value signal to the pressure pump; and a control unit configured to calculate a drive frequency of the pressure pump by a velocity type digital PID algorithm, such that a detected flow rate value output from the flow rate detecting unit becomes a target flow rate value that is set in advance to output a current value signal corresponding to a calculation value of the drive frequency to the inverter.