Efficient management of water is crucial to maintaining supplies and a driving factor behind industry investment. Much of the water that we use every day is actually on a continuous loop - processed after use, returned to the environment before it is extracted again, treated and re-used. This process is heavily dependent upon precise process control, monitoring and data recording to ensure that all the regulatory standards are maintained as well as ensuring that the environment and the general population is protected.
Sewage treatment consists of screening, primary filtration, secondary filtration and tertiary treatment. On entering a sewage treatment works, water passes through screens to remove paper, wood and other large articles that could damage machinery or block pipe systems. Before the treatment stage, iron or aluminium salts are added to assist in the removal of phosphorus, while biological processes remove the nitrogen, both of which originate from industrial and agricultural practices.
The process of chemical dosing has to be very carefully controlled and monitored with records kept to ensure compliance with local water quality standards.
The remaining processes involve further settlement and filtration before the water can be returned to the local water course, from where it may be extracted to undergo further purification. The water is carefully dosed with aluminium sulphate, a coagulant, which helps to bind the impurities together to form particles. This process requires careful monitoring of the pH levels as well as effective mixing. Removing taste and odour, as well as disinfection, ensure that the final product which appears from the tap meets all the necessary regulations.
In general, the water treatment industry prefers to operate a centralised control system for each site, making it quicker and easier for operators to assess the equipment and processes on the site. With such a wide array of sensors, valves and pumps installed around the site, the most efficient controller will be one that is capable of multiple tasks while still being simple to operate.
One example is Bürkert’s type 8619 multiCELL transmitter/controller, (Figure 1) which is suitable for a range of applications in water treatment using pH, conductivity and flow sensors, ORP and temperature measurements. The major advantage of this controller is its versatility; it is compatible with most common sensors and has a modular design, allowing additional hardware and software to be added easily.
Each controller can be configured for a range of sensors as well as having up to six pre-configured I/O boards to accommodate any signal requirements. In addition, the controller can be configured as a datalogger, using the built-in SD card slot for data storage. This slot can also be used to save sensor parameters and control application settings to allow the same settings to be replicated in another multiCELL controller in another site.
The multi-function controller has been designed with both the installer and the operator in mind. The range of features and the modular design allows the system to be customised to the clients’ exact requirements, while the user interface can be configured in four different views to display the most relevant information to a particular application. Users can configure different views, depending on the area of control they are interested in.
Designing a system such as this reduces costs in the processing applications. A systems engineer can, in many instances, replace an entire control cabinet with one controller with a built-it display, eliminating the need for a separate enclosure, rack mounted PLC, I/O, cabling, power supply and HMI.
The advantage of this modular expansion facility is that users only pay for the features that they require and a single controller/transmitter across a range of applications minimises inventory and training costs. In the long term, the total cost of ownership is reduced compared to those systems currently in use, says the company. This unit is designed specifically to be panel-mounted, either internally, or on a door or bulkhead; so although a panel may be downsized, it can be technologically ‘up-sold’.
Similar principles have been used in the design of the mxCONTROL multi-function controller, type 8620, which has the additional benefits of Ethernet or modem communication as well as the ability to control digital dosing pumps. The flexible programming capabilities enable integrators and end users to make fast program modifications during commissioning, upgrades and maintenance.
Again, there is an SD card slot for data logging and saving parameter settings to save time when installing a number of units across different sites. By using a simple user interface, configurable control programs and common sensors, the whole process from design to implementation is streamlined, reducing training time and inventory.
Both controllers allow direct connection to existing SCADA systems and other methods of site-wide monitoring and supervisory control. Adding connectivity to PH sensors and flow meters, for example, can add to the automation efficiency of a plant, while supporting the case of the panel builder or integrator for a smarter solution.
As this area of process control develops, it is important to understand the client's difficulties with legacy equipment to design and implement the best solutions.
Using knowledge of process control and working with the end user, the panel builder and the installer, it is possible to create a package that delivers an efficient, cost-effective solution
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