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Tai Po Water Works DCS System

Hong Kong

The largest water treatment plant of Water Supply Department (WSD) in Hong Kong.  A three-stage treatment is used comprising:

  • Coagulation, flocculation and clarification by Dissolved Air Floatation (DAF)
  • Primary Aerated Biological Filtration (PABF) for ammonia removal
  • Secondary Rapid Gravity Filtration (SRGF) followed by final de-infection using chlorine.

The incoming raw water flows from Tai Po Tau ‘D’ Pumping Station provides a maximum capacity of 1200 Mld to the Tai Po Treatment Works when two parallel mains are in service.

The treated water is pumped and delivered to the service reservoirs via the treated water pumping station.  In the ultimate stage of the Tai Po Water Treatment Work, ten pumpsets of capacity 200 Mld each will be installed and operated.

VL Automation Limited (VL)’s responsibilities included system configuration, hardware supply, Human Machine Interface and control logic development, testing as well as training. VL is a sub-contractor to Cheavlier Envirotech Ltd.

Project Details

The Distributed Control System (DCS) supplied by VL controls and monitors the various treatment processes within the Taipo Water Works as well as two off-site pumping stations and reservoirs via telemetry connections.  The DCS system presents dynamic graphic display of the treatment process, equipment status, alarms, event recording, trends and reports to the operator on very high resolution screens. It also feeds data to Management Information System (MIS) for optimisation and maintenance.

[DIAGRAM]

All together five CS3000 Human Interface Stations (HIS) are installed in the central control room for remote control and monitoring of the treatment works.  One redundant Field Control Station (FCS) together with a local HIS is assigned for each of the twelve process areas.  To enhance system reliability and for peer-to-peer communication, the Yokogawa’s high-speed deterministic redundant control network, V net is used to connect all the FCS, local and remote HIS stations.  The communication media in this case being fibre-optic cable.

Two redundant database server computers store and manage historical data in SQL compliant database. They also provide removable storage and backup facilities for plant and process data.  Management client computers residing on the same MIS Ethernet network can easily access reports using off-the-shelves license free internet browser such as Netscape.

Redundancy and modularity is design into the system architecture such that no single failure or fault can affect or bring down the system.  For instance, at the filter plant, the biological aeration, filtering and backwash sequence of each filter is managed and controlled by its own Rockwell Automation ControlLogix PLC automatically.  The PLC of each filter is then interconnected on the ControlNet network to a dual redundant PLC-5, which controls the queuing of filters, common backwash facilities and interfaces to the CS3000 DCS.

It is worth noting that in Taipo Water Works, S&I intelligent Motor Managers are used for all MCC and connected to the DCS system using the interface computer – CMAC.  This eliminates all traditional hardwire connections and allows useful information such as running hour, current, kWh, cause of trip in additional to control and monitoring status to be relayed to the DCS and MIS system.

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