Automation of Nsezi Water Treatment WorksProcess Automation

The PLC Computer,PLC programable logic controler for control device or process by scada system.

Mhlathuze Water is one of the leading water utilities in South Africa today, providing a world-class service to its customers. Based in KwaZulu-Natal, its area of supply covers 37000km² stretching from the uThukela River in the south and up the east coast to the Mozambique and Swaziland borders, around Vryheid and back to the uThukela River.

Within this region, Mhlathuze Water has built and operates an inter-basin transfer, major water treatment plants, an offshore wastewater disposal pipeline and it operates treatment and sewerage plants on an agency basis for local municipalities.

Project scope

The Project title was SCADA Phase 2 Electrical and Electronic Works. Its intention was to upgrade all MCC’s which are not able to be interfaced to the automation system. The ultimate end state envisaged by the employer was to fully automate the Nsezi Water Treatment Works to be at on par with international norms and standards. The automation of the plant encompassed the following unit processes i.e. the clarifloculator de-sludging, chemical dosing, filtration process and pumping systems amongst other processes within the water treatment plant.

This Contract covered the detailed design, manufacture, supply, factory testing, insurance, delivery, transport, handling, storing, erection, site welding and making good coatings, aligning, fixing, supporting, connecting, adjusting, guaranteeing, site testing, painting, commissioning, handing over in complete working order, providing drawings, operating and maintenance instructions in quadruplicate, instructing staff and attending to defects for 12 months after completion.

The works covered by this project included the following areas:

Motor Control Centre (MCC) and pump control automation

  • The existing lake intake Rockwell PLC system was interfaced to the SCADA system for full monitoring and control.
  • The upgrade of the pumps, associated MCC and HMI complete with soft starters.
  • Development of the SCADA system mimics to operate, control and monitor the pump station from the control room.

Dosing system automation

  • Supply, installation, testing and commissioning of all sodium hypo-chlorite dosing pumps, associated control panel and ancillary equipment.
  • Programming of the mini PLC to control the dosing functions of the sodium hypochlorite station and the configuration of the SCADA system.

Network design

  • Network design including the fibre optic installation, splicing and patch panel.

Filtration plant and ancillary equipment

  • Supply, installation, testing and commissioning of a new Actuator Sensor Interface (ASi) network for the rapid gravity sand filters actuated valves and instrumentation.
  • The ASi network role was to transmit feedback and control commands to the main PLC to allow the controlling, monitoring and operation of the backwash filtration process.
  • Development of the SCADA mimics to operate, control and monitor the filtration process from the central control room.

Backwash and sludge pump station

  • Supply, installation, testing and commissioning of PLC type RIO station to allow the interface between the backwash and sludge pump station signals to the primary chemical house PLC.
  • SCADA system mimics development to operate, control and monitor the backwash and sludge pump station from the control room.

PLC panel and centralized control work

  • Design, supply, installation, testing and commissioning of the redundant Main PLC panel and associated equipment.
  • Programming configuration to control the filtration process, scanning and obtaining real time information from the RIO stations, remote PLC and IEDs.
  • Loading the engineering workstation with all PLC and SCADA system programs to enable configuration, diagnostics, maintenance and software version updates from the central location.
  • Installation and testing of redundant SCADA server machines to enable logging, trending and alarm management functionality of critical process variables complete with peripheral equipment.
  • Development of the SCADA mimics including plant overview, all the unit processes and major plant equipment face plates.
  • UPS to power up the critical PLC and SCADA equipment, server machines and displays at the control room.

Miscellaneous works

  • Fibre optic cables including terminations and patch panels to buildings that were not connected to the plant wide fibre optic ring.
  • Interfacing and integration of all pump stations via the telemetry system to enable monitoring of the pump stations from the Nsezi WTW control room.
  • Extension of the optic fibre cable to accommodate the new nodes and integrating the nodes onto the existing wide fibre ring.
  • Provisioning of a comprehensive full set of plant P&ID drawings to show “as built” plant status.
  • Logging and connecting of the cathodic protection system at the Nsezi WTW and Middledrift pumping scheme (Mkhalazi pump Station and Madungela pump station).

Conclusion

The client’s envisage end state or objective allowed for the starting and stopping, opening and closing, and controlling of unit processes or equipment within the plant from the centralized control location.

All information was logged and trended on the SCADA System database at the centralized control room. The ultimate end state envisaged by the client was to fully automate the Nsezi Water Treatment Works to be at on par with international norms and standards was realized.

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