When the Southern Seawater Desalination Plant (SSDP) doubled in capacity, its water transfer system required upgrading to accommodate the increased flow and address developing instabilities.
A team from OneStone Consulting and Water Corporation modelled and optimised the control system for Ravenswood Pump Station, achieving stable flow with significant infrastructure and operational savings.
Ravenswood Pump Station consists of two separate banks of variable speed pumps that can simultaneously deliver water to Tamworth and Dandalup. Its control system uses closed-loop feedback control based on flow and pressure measurements, allowing a remote operator to control the flow of each bank and manage the water transfer to Perth.
In preparation for the increase in SSDP production, the water transfer system was upgraded to a transfer capacity of 100 GL/a. This was achieved by constructing a second 32ML tank, duplicating 27 km of pipeline upstream of Ravenswood Pump Station, installation of a fourth pump in the Tamworth Bank, and four new pumps in the Dandalup Bank.
The pipeline duplication resulted in three issues:
- Issue 1: Changed system dynamics increased the risk of instability for the flow control systems. To find new tuning settings for the PID controllers, the project team saw the value in building an accurate model of the pump station’s control system, rather than treating the control logic like a black box
- Issue 2: Increased gravity flow to Tamworth causes the Tamworth Bank pumps to operate further ‘off their curves’ during start-up, particularly if the fourth pump is not available. The project team identified an opportunity to remove a complicated valve-assisted throttled start procedure
- Issue 3: Optimised system transfer capacity requires SCADA operators to operate a complex system at near 100% capacity for parts of the year. The team identified an opportunity to develop an operator tool to optimise the flow split between the Tamworth and Dandalup banks for water transfer to Perth
Gary Munns, Commissioning Director SSDP Integration Project, Water Corporation
Solving Issue 1: PID Controller Investigation
- Investigation into actual PID (proportional-integral-derivative) control logic programmed into PLC (programmable logic controller)
- Validation of the control system model against actual system response
- Development of new PID controller tuning settings using the model
- Testing and implementation of new PID tuning from the Operations Centre
Solving Issue 2: Tamworth Bank Throttled Start Removal
- Desktop assessment of potential mechanical issues during start-up (pump imbalance, bearing ‘skidding’ and vibration)
- Risk assessment for testing the ‘un-throttled’ start-up procedure
- On-site vibration monitoring while operating the pumps ‘off their curves’
- Testing new PID tuning settings and control system response for the ‘un-throttled’ start-up procedure
Solving Issue 3: SCADA Operator Tool
- Development of MS Excel based tool using simplified hydraulic equations
- Validation of operator tool against SCADA monitoring points in the actual system
- Building in an ‘energy optimiser’ and visualisation of bank duty points and hydraulic grade lines
Outcomes Issue 1:
Accurate model of Ravenswood Pump Station’s PID control logic.
New PID tuning settings tested and implemented from the Operations Centre, with minimal risk and effort.
Outcomes Issue 2:
Successful removal of cumbersome and overly complicated throttled start-up procedure.
Capital cost saving of $1M by proving that there is no need for a spare pump as start-ups could be managed with 3 pumps if required.
Outcomes Issue 3:
SCADA Operator Tool provides assistance and increased understanding on how to set up a complex system.
Operating strategy optimised with Operator Tool 14% more energy efficient than previous operating strategy.