Controls for a new effluent treatment facility
Votec designed, built and commissioned the controls for a new effluent treatment facility for First Milk and Cheese at the Haverford West Creamery in Wales. The plant treats 2,000 M3 of effluent each day, ensuring that the outfall meets stringent consent limits suitable for discharge.
Votec based the control system on the Allen-Bradley CompactLogix PLC range taking advantage of their Integrated Architecture. A single CompactLogix processor controls the whole treatment plant via an ethernet network which is linked to local panels at strategic points around the site. This ensured that site wiring was kept to a minimum, an important consideration given the size of the plant, and enabled fully comprehensive control and monitoring facilities from the main PLC in the control room.
Each of the local panels carries Allen-Bradley point I/O to collect local sensor signals, the drive controls for adjacent plant and an HMI to provide operator control and information.
Some of the panels contain variable speed drives, needed for a number of pumps and blowers, with sizes up to 160kW. These drives are individually linked and controlled from the main PLC via the network. All the VSDs are fitted with Safe Torque Off, giving safe stopping under emergency stop conditions without the use of expensive and space-consuming heavy contactors.
There are over 70 pneumatically operated valves installed across the plant. Valve islands are located in cabinets at key positions around the plant and are directly linked to the network. Bus addressing of the valves reduces panel wiring and helps to eliminate the errors associated with hardwire connections. To simplify the site installation, each valve is brought out to a push-in connector.
Remote monitoring facility
The system also includes a remote monitoring facility which has enabled the installer to optimise the treatment process during the initial period of operation without frequent trips to site. The facility has also enabled Votec to provide timely fault diagnosis and program changes using the remote access from our offices.
Votec has engineered many effluent and water treatment control systems, based on other PLCs including Siemens, Schneider, Mitsubishi and Omron.