Reverse Osmosis Desalination instrumentation and control
The level of instrumentation and control of a plant is determining in a plant operation. The more instruments, the easiest the control.
Instruments measure relevant values used to evaluate plant performance (inputs) based on which pumps and valves (outputs) can be regulated either manually or automatically by a PLC.
Typical I&C features are the following:
|Instruments||indicator / switch||transmitter|
|High pressure pump frequency||fixed||variable|
|Feed/ concentrate valve||manual||proportional|
Lenntech provides several level of instrumentation and control (I&C), depending on the application, the type of end-user and the plant size:
Basic I&C consists in indicating instruments. Flows and pressure are measured with simple local indicator that do not require any power. Only the conductivity meter gives an analog signal since it is the main performance criteria of the plant. The high pressure pump is not equipped with a variable frequency drive, so flows and pressure have to be adjusted manually if the plant is subject to temperature variations. These plants are controlled by a ready-made micro-controller with limited amount of outputs.
Standard I&C includes a permeate flow transmitter, ORP and/or chlorine sensors to make sure the chlorination and/or dechlorination steps are effective. Temperature and pH measurement are added to monitor the permeate quality. The HPP can be equipped with a variable frequency drive if the temperature variations are important, but the concentrate or feed valve remains manual
Advanced I&C is recommended for industries with DCS. All instruments are analog and monitored via the PLC or a datalogger. Such a plant is controlled via a touch panel through a PLC with analog and digital inputs and outputs. Therefore the HPP is often frequency controlled and the concentrate valve proportionally regulated.