One of the most spectacular and watched demolition projects of our time was the felling of the eight 137-metre chimneys at Hazelwood’s coal-fired power station. As buildings, process plants or electricity generating assets such as Hazelwood Power Station reach the end of their design life, the challenge is generally not how to prop them up, but how to safely bring them back down to earth.
The felling of the chimneys at Hazelwood’s retired 1,760-megawatt coal-fired power station in the LaTrobe Valley is an engineering feat that took approximately eight months of planning, modelling and analysis. Watch the chimneys come down in the video below.
Engaged by site owners ENGIE in May 2018, ABB, which has decades of consultant experience in successful demolition work throughout Europe, began by validating and verifying the site features for demolition: the monumental chimneys, their squat boiler houses, and massive mechanical dredgers on the adjacent brown-coal mine, are among the gargantuans of the Hazelwood site that must succumb for the site to be successfully remediated.
Subsequent to scoping the site for decommissioning, ABB helped to prepare the prequalification and tender documents to ensure the best demolition contractor was chosen for the project, assisting to verify the capabilities of the selected Delta Group to carry out the works. As works progress, ABB continues to support the project in helping to identify all potential hazards and risks, verifying best practice, and ultimately setting new standards of safety for an era in which thousands of power stations around the globe are gradually ceding their reign to cleaner electricity generation.
ENGIE demolition manager Tom McDowall and Stephen Smith, consultant demolition project manager with ABB’s Energy Industries division were in the incident event-management area of the Hazelwood site, close to the perimeter of the 500-metre exclusion zone. McDowall’s phone gave constant updates of the weather and wind speeds as all indicators converged, a few hours after the 11am scheduled moment, to meet the ideal conditions compliant with Environmental Protection Authority guidelines under the Section 38 application for a license to carry out the event.
It’s not about blowing stuff up
Part of the risk analysis and design process is to establish the least possible number of explosives that will ensure structure failure, and in this case that enabled the chimneys to fall in the desired direction. The process is engineered to minimise the fly of debris, reduce potential damaging over-air pressure and vibration which result in noise, and to minimise the amount of generated dust.
“We do as little as possible to induce the fell,” says ABB’s Late Life, Decommissioning and Demolition manager Steve Andrew. “And then let gravity and its own weight do the business.”
Keen observers of the felling of Hazelwood’s iconic chimneys will have noticed that the structures wore industrial-strength aprons for the occasion.
The blast-protection secured to the skirts on chimneys one and eight were made from conveyor-belt material salvaged from the site, and were arranged over a layer of geofabric mesh, at an angle to contain ‘fly’ but let the force of the 36 kilograms of explosives drilled into 196 core holes per chimney force its way through the structures. The blast protection for chimneys two to seven was similarly constructed, but minus the conveyor-belt overlay.
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In addition to water sprays to help contain the dust, four rows of 10 pools of water at the south-easterly aspect of the chimneys were on a manual timer controlled by the Shot Firer to explode just after the main felling charges, generating electrostatically charged water droplets that would bond with and help drag down the dust generated by the blasts. Dust monitoring installed by the project and the EPA showed this strategy to be extremely effective with no adverse results recorded.
The 4.6 seconds between detonation of each chimney’s explosives, and the angles at which the columns fell towards a central point, were modelled using several parameters to arrive at the optimal timing and aspect, says McDowall, who adds that impacts to the local cemetery and surrounding agricultural grazing lands were prime considerations.
Detailed options analysis and risk assessment had been carried to achieve the preferred method of chimney removal. Again, observers may have noticed that chimney number five failed at around the 40-metre level as it fell, confirming the team’s conclusions that the second most likely option to demolish out of the seven rigorously examined methods for demolishing the chimneys had been correctly ruled out.
That option was to tackle the structures from the top down, using cranes fitted with demolition attachments for pulverising, but analysis indicated that such disturbance could result in a potential failure of the chimney putting people at risk of injury and reducing the ability to contain asbestos in preformed concrete vent pipes inside the chimneys.
Although the roughly 23,000 tonnes of rubble created by the chimney felling contained a small proportion of non-friable asbestos material — it makes up 0.00021 per cent of the fallen mass — all of the chimney remains are being removed under wet conditions over a period of six to eight weeks, to an EPA-approved onsite containment cell.
The milestones ahead
The next stage of the program for the combined teams on this project is the demolition of eight massive pieces of mining equipment including dredgers and stacker reclaimers that fed Hazelwood power station over its 50-odd years of operation.
Four large mining machines are being demolished by conventional mechanical means, however the remaining four are of a size and complexity that requires demolition using specialist cutting charges, which will bring them down to a height that can then further be managed by large excavators fitted with hydraulic cutting attachments, says McDowall.
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Because these behemoths of machinery are located within the open-cut mine, risk mitigation measures must be closely followed to ensure there is no risk of causing a coal-fuelled fire. The first dredger to be demolished, “has been very carefully modelled to ensure that when they do cut the controlling wires with explosives, they also cut with charges to the superstructure that force the machinery to rotate away from the batter,” explains Smith, or coal slope.
Gravity, the new growth industry
Demolition is a highly specialised process. Andrew explains that Europe began developing its expertise when it had to deal with partially destroyed or compromised structures in the aftermath of World War II bombings.
Hazelwood, says McDowall, “puts Australia on the map from a demolition perspective”. The project has exceeded standards in onsite hygiene and air monitoring in relation to asbestos control — just one aspect of the project’s achievement that will contribute to Australia’s demolition code of practice and the expectations of regulators in future.
Andrew says, “As we go towards net-zero emissions from energy generation, it’s estimated that around 1000 generating plants, including a number of nuclear, will close and be demolished in Europe alone, so it’s a developing industry.”
In Australia, too, he says, there will be increased demand for both experienced and younger people to enter the demolition industry — engineers, digital modellers, hygienists and project managers like McDowall, who have a passion for dealing with complexities and with the community’s need to understand why gravity must eventually be assisted in having its day.