Local build: best option for turbine cooling system retrofit
22 December 2017
An Origin Energy gas turbine peaking plant in Adelaide South Australia, has just undergone a successful replacement of critical oil cooling system components using a local supplier.
The project is a great example of where, sometimes, buying local is better.
However, the project was not without risks and failure to properly plan and execute could have left the State vulnerable.
Failing cooling radiator
Gas Turbine number 5 (GT5) at Origin Energy’s Torrens Island (Quarantine Station) is the largest of five open cycle gas turbine generators installed at the power station.
A challenging operating environment (being close to sea water) contributed to the early decline of the turbine lubrication oil cooling radiators which began to leak due to excessive corrosion, necessitating the decision to replace all three radiator units.
Local manufacturer AR Industrial was contracted to supply replacement radiator cores (coils and fins) as a preventative measure to ensure reliability over South Australia’s summer season.
Window of opportunity
The power station is configured as four 24 MW gas turbines (installed in 2002) and one 120 MW GE Frame 9E Gas Turbine set, later installed in 2007. Total plant output is 224 MW generating capacity.
The plant is a peaking plant; only providing power at times of high demand.
The intermittent operating cycle provided a window of opportunity to swap out the damaged cooling radiator cores when the main turbine set (GT5) was least likely to be required.
The project was planned and supervised by Conway Blacker, Origin Energy’s Plant Technical Manager.
"With the demanding summer season looming, and the poor state of the cooling system, we identified a compelling business case to schedule the retrofit. We had to ensure reliability over summer."
"However, taking 120 MW of generating capacity out of the system required careful timing and selecting a high-performance contractor” said Conway.
Turbine lubrication oil cooling
The GE Frame 9E turbine lubrication oil is cooled via a two-stage heat exchanger system.
The first stage is an oil-to-water tube heat exchanger transferring heat to cooling water which is then cooled in the (second stage) water-to-air heat exchangers consisting of three large fan forced remote radiators.
The radiators dissipate energy, achieving a 10-degree water temperature drop maintaining the lubricating oil in the primary circuit at an optimum temperature of 54 degrees C.
A large radiator system is required to ensure adequate heat rejection capacity on very hot days when ambient air temperature can reach as high as 45 degrees.
Failure of the radiators would require an immediate turbine shut down as it cannot operate without continuously flowing cooled oil pumped into the main shaft bearings and other parts of the turbine.
Maintaining the oil at the correct operating temperature is critical, serving to both cool and lubricate.
The turbine spins at 3,000 rpm with internal operating temperatures of (approx.) 1,000 degrees C. The demands on the main bearings are considerable with the high temperatures and the full rotating mass of the turbine ‘sitting’ on the pressurized oil.
The replacement project presented several challenges requiring careful project management and the selection of the right contractor…
1. South Australia’s electricity generation is highly dependent on wind generators with back-up from mainly gas turbine peaking plants. The optimum schedule required timing the radiator changeover when wind generation was least likely to be off line either due to inadequate or excessive wind speed.
2. Replacement had to be completed before the summer peak demand.
3. Despite choosing an optimum time of the year, GT5 needed to be out of service for the minimum time possible in case it was needed.
4. The cooling units are unusually large remote industrial radiators purpose built with long lead times. Finding manufacturers with the required capability is challenging.
Radiator core replacement
The radiator cores, each measuring 13 metres X 2 metres, were replaced while maintaining the original surrounding steel framework, plumbing, motors and fans in place.
Manufacturing like-for-like replacement radiator cores was contracted to local firm AR Industrial, a specialist industrial radiator manufacturer with expertise in large remote radiator cooling systems for gas turbine and diesel generator sets.
The replacement cores were manufactured to a high tolerance to ensure an exact fit within the existing radiator framework.
A less than perfect fit at changeover, would leave GT5 unserviceable while adjustments were made. Worst case, the turbine could have been offline for months; failure was not an option.
AR Industrial commenced manufacturing the cores 3-months ahead of installation in their manufacturing facility in Gillman, roughly 6 kilometres from the Power Station.
The replacement radiator cores were completed within schedule including ‘Blygold coating’ to provide advanced corrosion protection.
The scheduled changeover date on the calendar was the critical project stage.
“We had planned a 120-hour window to take GT5 out of service, remove the deteriorated radiator cores and slide in the new units. This was the moment of truth; would the new units be a precise fit?” Said Conway Blacker, Origin Energy’s project lead.
“I am happy to report the retrofit went like clockwork. We completed the changeover well ahead of schedule and handed back GT5 two days before deadline” said Conway.
Initial performance data showed a successful “change out” with cooling performance identical to specification.
GT5 is back online ready for the summer.
“Working with a local supplier provided many benefits. Origin Energy prefer to engage with local suppliers where ever possible and, in this case, we were able to achieve competitive pricing, outstanding project performance and the comfort of knowing local support and back-up is just around the corner.”
While potentially a high-risk project, careful planning, a close working relationship, and attention to detail de-risked the program and ensured delivery on time and within budget.
“It was a huge relief to see the final unit slide into position, we knew then we had executed a successful project.”
AR Industrial supplies power generation companies throughout Australia, Asia and the Pacific Islands from its 16,800 m2 manufacturing facility in Gillman (a suburb in Adelaide).