Water treatment processes are used to remove impurities, both biological and chemical, as well as balance pH levels. In the vast majority of installations, on-site staff can monitor and maintain the equipment to ensure continuous operation. However, in remote locations, regular on-site interventions are not practicable, so reliability has to be built-in to the equipment.
Setting the standard
RSE is a market-leader in the design, fabrication and delivery of innovative modular water treatment plants to supply high quality water to remote communities. Using specialist processes, such as reverse osmosis, Nanofiltration and Ultrafiltration, and automated process control equipment, the company is an expert in developing and delivering robust and reliable water treatment plants for their clients.
Water quality is determined by standards and specifications and it is the responsibility of the local water authority to deliver these standards. Significant geographical areas within the UK experience high pH levels within their surface water, due to organic matter within the soil, so there is a need for a simple and reliable control process.
RSE uses carbon dioxide (CO2) to reduce the pH of the water to increase the mineral content through reaction with limestone/remineralisation media. Primarily, it is a gas that is easy to handle, non-corrosive and its most appealing feature is that it will not lower the pH of water below 4.0. In addition, the only maintenance required for the dosing system is to replenish the gas cylinders periodically.
The design and parameter settings for the pH control process are determined by the local water authority. On each site the process control loop consists of a pH sensor, some solenoid control valves and a mass flow controller (MFC) supplied by Bürkert.
A Bürkert Type 8711 MFC is used in each application. In contrast to a simple flow control device, the measurement is independent of pressure and temperature, making it more accurate in varying conditions. When used with CO2, the Type 8711 has an impressive nominal flow range, from 0.02 LN/min up to 40 LN/min.
The MFC is calibrated by Bürkert for the gas being controlled before it is delivered to the customer. For those involved in more complicated applications, the Type 8711 can be set up to measure two different gases.
In this application, the changeover solenoid valves control the CO2 bottle banks to provide a duty/standby changeover system. The CO2 gas flowrate is accurately adjusted to control the target pH of the water treatment works using Bürkert’s Type 8711 MFC.
Mass Flow Controller for Gases (MFC)
- Nominal flow ranges from 0.010 lN/min to 80 lN/min
- High accuracy and repeatability
- Very fast settling times
- Optional: Fieldbus interface
Craig Kerr, Sales Manager for Bürkert, explains: “Bürkert has been chosen to supply these components because of their easy integration, accuracy and reliability. Operating in such remote locations and providing such a vital service, means that the equipment must be reliable above all else. To date, of the units installed on RSE Water treatment sites, there have been no failures, ensuring that the residents continue to receive high quality water supplies. RSE propose to use this system on six future water treatment projects in 2019."
Paul McCloskey, Senior Technical Manager at RSE, concludes: “We design these compact treatment plants for optimum performance with minimal maintenance. The Bürkert mass flow controller is central to maintaining the correct pH and it is delivered as a ‘plug & play’ component, which minimises our installation and configuration time.”
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