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PROJECT: CONSULTING SERVICES AND PLC SYSTEM INTEGRATION

Critical PLC System Replacement

PROBLEM

On 1 January 2024, the control system at the Baardskeerdersbos water plant failed beyond repair. The Modbus RTU communication line on the industrial computer stopped working, and all attempts to restore communication were unsuccessful.

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As a result, the plant could no longer operate correctly:

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  • None of the pumps could be started.

  • The ultrafiltration pump was unable to function.

  • The reservoir ran dry.

  • The community was left without water.

  • The municipality had to install temporary water tanks to provide drinking water.

 

The failure created an urgent operational and service delivery issue, requiring both an immediate temporary solution and a full replacement of the control system.

SOLUTION

The existing control system had to be replaced with a new PLC. However, due to the lead time required for procurement and delivery of the PLC equipment, an interim solution was implemented to restore partial plant operation as quickly as possible.

A temporary PLC was installed to allow three pumps to operate while the replacement PLC equipment was being sourced. The pump VSDs, which are integrated into the motors, required a device with an infrared port for setup and programming. Grundfos provided a suitable device, an older iPod, which was used to configure the VSDs.

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The VSDs were programmed to operate using hardwired start and stop signals, allowing the temporary PLC to be deployed for operator control until the permanent PLC equipment arrived.

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Once the new PLC equipment was available, the full system was:

  • Rewired.

  • Reprogrammed.

  • Integrated with the required instrumentation.

  • Loaded with the new control program.

  • Commissioned for normal plant operation.

 

The system was programmed to restore the plant’s previous operating sequence, based on the operator’s recollection of how the plant had functioned before the failure.

 

The commissioned control system now operates as follows:

  • When the reservoir on the mountain reaches a low level, the transfer pump starts and pumps water from the water tank up to the reservoir.

  • When the product tank reaches a defined level, the ultrafiltration plant starts. During the first step of the UF cycle, the system fills the backwash tank while filtering water into the product tank.

  • Water is disinfected with hypochlorite to make it safe for human consumption. Once the backwash tank is full, the backwash valve closes and the system continues filling only the product tank.

  • In filtration mode, the UF system runs for a fixed period before automatically initiating a backwash cycle to clean the filters.

  • Once the UF feed tank reaches the required level, one of the boreholes starts on a duty standby basis.

  • While a borehole is running, a dosing pump controls the pH to assist with impurity removal. At the same time, a blower starts to introduce airflow into the water.

 

The final system restored normal plant functionality and allowed the municipality to return the Baardskeerdersbos water plant to reliable operation.

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