By Kody Cook, Journalist, Pump Industry Magazine

Northern Territory utility provider Power and Water has completed a refurbishment of the Tiwi Sewerage Pump Station as the third facility in its pump station renewal program, which is ensuring that critical infrastructure across the Territory is regularly assessed and maintained.

A renewal of the Tiwi Sewerage Pump Station was undertaken in order to maintain the delivery of safe and reliable water and sewerage services to its customers, which include the Darwin Hospital Precinct (Royal Darwin Hospital and Darwin Private Hospital), Tiwi and parts of Brinkin.

The new Tiwi Sewerage Pump Station is expected to prolong the life of the asset by 50 years as well as reducing the risk of failure and overflows and minimising potential safety and environmental incidents and compliance breaches.

The project required approximately 15 specialised subcontractors and during peak construction periods there were close to 30 people working onsite to deliver the upgrade.

Unpacking the upgrade

Power and Water’s Manager Infrastructure Delivery, Water Services, David Rossi, explained that the existing pumps at the facility, KSB Ajax K200/360 fixed speed units, had water cooled motors and that the cooling circuits were prone to blockage.

Power and Water also noted that during site tests, the motors would run quite hot on these units. As well as this, the old switchboard was not up to Power and Water’s standards and needed to be replaced, along with all of the pipework.

Mr Rossi said that the pumps selected for the station refurbishment, N series Flygt impellers provided by Xylem, were chosen for their high-efficiency, glycol closed loop cooling systems and their innovative self-cleaning ability.

“When solid objects such as stringy fibrous material and modern trash enter the inlet of a conventional pump, it tends to get caught on the leading edges of the impeller vanes.

“This material build-up reduced the impeller’s efficiency, resulting in a reduced flow rate or an increased power draw. Both of these consequences lead to drastically reduced pump efficiency and higher pumping costs.

“As solids continue to build-up inside the impeller, motor thermal protection may trip the pump, causing it to stop and this can lead to costly, unplanned service calls.

“When a conventional wastewater pump runs intermittently, the solids build-up will often be removed by the naturally occurring back flush each time the pump is shut off at the end of the operating cycle. When the next pump cycle begins, efficiency typically returns to its initial value since the impeller is free from solid objects.

“The high efficiency of a Flygt N-pump is sustained over time due to its self-cleaning ability, keeping energy costs to a minimum and reliability to a maximum.”

The typical inflow to the Tiwi Pumping Station is in the order of 14L/s. At 50Hz, single pump operation flow is in the order of 80-160L/s. The station is considered to be somewhat oversized for typical dry season inflows, but in the wet season the pumping capacity may be necessary to prevent overflows.

Mr Rossi said that the DN375 rising main requires a flow in the order of 110L/s for 1m/s cleansing velocity and 70L/s for the minimum 0.65m/s.

To minimise the pumping costs, three of the same Flygt variable speed drive (VSD) units were used for normal pumping at a minimum speed of 50Hz. These new variable speed pumps provide an efficient operating range with single pump operation between 110L/s and 160L/s.

Additionally, the control program was altered to run the VSD pump at no less than 50Hz and bring on additional VSD pumps in peak periods as needed.

Figure 2 illustrates the system curves for the Tiwi Pumping Station with the Flygt Pump running at 50Hz and a KSB unit running alone at 50Hz.

Figures 3 and 4 below show the curves for single pump and two pump systems based on pumps similar to those used in the renewal.

“You can see for both scenarios that the pumps are running near peak efficiency,” Mr Rossi said.

Renewal impact and what comes next

The renewal was completed within the expected timeframe and within budget, and has successfully increased the lifespan of the pumping station by up to 50 years.

Mr Rossi said that the upgrades to the station’s suction and discharge pipework were conducted with future growth in mind, enabling it to be further enhanced should the need arise.

“Power and Water is committed to providing safe and reliable water and sewerage services in urban and remote locations across the Northern Territory.

“Our sewerage pump station renewal program ensures that critical infrastructure is regularly reviewed and continues to operate safely and without impact to customers, stakeholders and the environment.”

Power and Water’s CEO, Djuna Pollard, visited the project site to see firsthand the advanced technologies and innovative

“I am really impressed with the safety and design features of the new Tiwi Sewerage Pump Station. Readings can be taken remotely from Ludmilla and air-conditioning has been installed in the switch room, providing a better working environment for our people,” Ms Pollard said.

“Congratulations to our Water Services Infrastructure Delivery Project Manager, Phillip Lo Castro, and the project team for their dedication and efficient project management to deliver the works on time, within budget and without any incidents.”

With the works on the Tiwi Sewerage Pumping Station now complete, the renewal project will move on to its next phase, the Mindil Beach Sewerage Pump Station. Works on the Mindil station are expected to begin in June 2024.

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