In order to monitor the process of reverse osmosis and ensure that deposits do not clog up membranes and reduce system efficiency, Martens, a member of the GHM Group, has joined the forces with its Condix 4623 digital 4-electrode conductivity converter and the GHM-ONE multi-function HMI controller.
The conductivity device detects whether the untreated water is unsuitable for operation in the system, whilst the multi-function device provides the measurements to the superordinate PLC via a Profinet fieldbus, where it is easily integrated by means of a GSDNL device description file.
Reverse osmosis does not only produce the permeate that is the filtered raw water, it also produces retentate, a concentrate that is unable to pass the membrane. It is an effect that can reduce the efficiency of the system and result in damage if the scaling effect of dissolved contents exceeds the solubility limit and deposits accumulate. An over-saturation of calcium carbonate must also be prevented.
In order to counteract both of these effects, an antiscalent is added to reduce the precipitation level and the water to be treated is adjusted to an acidic level in order to prevent oversaturation with calcium carbonate.
Jan Grobler, managing director of GHM Messtechnik South Africa says, “The pH value at this point is the measured variable for the correct dosing. The objective is to minimise the use of additives with maximum filter effect. The development of ammonia, which is toxic for fish, must be avoided. The concentration increases and decreases analogously to the prevailing pH value, therefore, the pH value is monitored in the process input and upstream from the discharge and conditioned as necessary.
“The combination of the Condix 4263 and the GHM-ONE multi-function controller offers a superior analysis technology specifically for process water monitoring in order to prevent membrane clogging and system under performance. Accurate analysis protects the material of the system from undesired deposits that require cleaning with the benefits of reduced downtime and increased productivity.”
The relevant results are visualised by the GHM-ONE, which is connected to the measuring probes via RS-485 (Modbus RTU) and the measured values can be read at any time on its display, so that conclusions can be made about the system status throughout the entire process cycle.
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