End User:

Renaissance Village Duqm, Oman

Scope:

Design, Engineering, Manufacturing, Supply and commissioning of MCC cum PLC panel & SCADA system for a ‘Membrane bioreactor’ (MBR) wastewater treatment plant.

Background:

MBR is an innovative wastewater treatment method which combines two technologies – membrane filtration and biological treatment. In order to automate the entire sewage treatment plant including MBR transfer pumps and mixers, a control system was required.

The major three units- Pre-treatment unit, Dewatering unit and Aeration unit had to be controlled and there were several valves and flow meters involved in the process as a whole. The customer wanted to have a PLC & SCADA based control system to automate the entire operation of the plant.

System Description:

The plant has a sequence of operations starting with the collection of wastewater at raw storage tanks, after pretreatment the water is transferred to various tanks to perform various processes like Anoxic, Aeration & MBR treatments. The processed water after these treatments are then taken to sludge removals and finally they are chlorinated and polymerized before storing in the treated storage tanks.

Each MBR process has characteristic flow rate, time duration, direction and stream of flow. Desired flow rate in MBR system is achieved through PID control of permeate pumps and their associated valves. Direction and stream control are achieved through Electro-pneumatic valves.

Each MBR cycle has a deaeration, backwash & ventilation sequence till the desired cycle is reached and then filtered and chemically dosed before feeding the treated water to storage tanks.

The PLC & SCADA based control system takes care of the automatic operation and monitoring of the entire plant. The system comprises M340 PLC from Schneider Electric, InTouch SCADA from AVEVA, DoL & Star Delta Starters from Schneider Electric and VFDs from Fuji Electric. The PLC, motor starters and other auxiliary devices are housed in a Modular Enclosure System from Rittal.

We implemented a centralized MCC panel to manage the pump and mixers operation in an efficient way. Also installed a Control System for the whole plant consisting of PLC, I/O modules and other components. We brought about Cumulative Flow Calculations for each stream.

The system is designed in such a way to generate visual alarms and prioritizes their visibility according to the criticality. The system also captures various critical parameters like Pump Status, Overload status, Power Parameters (Voltage, Current, Energy Consumptions etc). A solution for Unattended Trip Changeover, Duration based Changeover, and other configuration for blowers and mixers are also enabled. Moreover, we installed Tank Level based interlocks for motors, configurable from SCADA and equipped with different access levels for security.

Result:

• Presentation of the SCADA pages helped the operator to monitor all the operation sequences in a single window.
• The settings were provided nearby the control window which is easy for the operator.
• Our customer now has a well-designed control system which is not only reliable and stable but there are possibilities of expansion and adaptation in the future.