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Each cell is constructed from clay, is about 100 metres wide and 350m long.
Each cell is constructed from clay, is about 100 metres wide and 350m long.
 










Generating power from ‘holey’ ground

When all the quarry’s work is done, what do you do with the old void? Is landfill the answer? Boral, with Energy Power Systems Australia, has developed a solution for tapping power from landfill waste. Damian Christie and Mandy Parry-Jones report.
Of late, there have been some innovative schemes to do with quarries. In Scotland, the Rubislaw quarry may be turned into a commercial deep-water diving site. China is going a step further with a massive hotel that seems to spill down the sides of a quarry to the water.

Both are interesting ideas but surely the best idea is to make electricity from a disused quarry using landfill. Not only will the land be reclaimed but in the process it will reduce reliance on fossil fuels, get rid of rubbish, reduce greenhouse emissions and be economically beneficial to the site owner.

One of the four G3516 1.1mW gas-to-energy modules located at Boral’s Deer Park biogas facility.
One of the four G3516 1.1mW gas-to-energy modules located at Boral’s Deer Park biogas facility.
Biogas is not a new idea. The practice has been common since the 1970s but generating reliable electricity has been the problem. In Australia, quite a few sites produce electricity from landfill and sell it back to the power grid, now that it has become more reliable.

Research and development by companies such as Caterpillar and its dealers like Energy Power Systems Australia (EPSA) have led to stationary engines that will produce that electricity unmanned and consistently.

According to studies by the Australian Bureau of Agricultural and Resource Economics and Sciences (ABARES), landfill gas accounted for 24 petajoules of renewable energy projects in Australia in 2008-2009.

What makes Boral’s Deer Park quarry stand out from other landfill sites is that Boral, as the owner, is also running the site. Usually, it will be a power supplier on behalf of the landfill operator that puts in the facilities to produce electricity through biogas. The power supplier then pays the landfill operator a royalty.

Melbourne’s west is a virtual “Mecca” for industry and it has spawned a great deal of new housing, roads and infrastructure. In 1999, Boral Waste Solutions began operating the 10 million square metre site at Deer Park. Today, it is one of the largest landfills in Australia.

Approximately five per cent of the Deer Park site is set aside by Boral Waste Solutions for converting the old quarry void into landfill.

Conservative estimates are that around 500,000 tonnes of waste goes to the Boral site every year, including commercial and industrial waste, municipal solid waste, green waste from local councils and smaller quantities of construction and demolition materials. Other prescribed waste such as Category C soil are approved by the Victorian Environmental Protection Agency (EPA). In the 13 years since its inception, Boral Western Landfill has accepted over 6.5 million tonnes of waste.

CELLS THAT BURY THE BAD SMELL

The waste is essentially placed and compacted into landfill cells on the quarry floor. Each cell is constructed with a composite liner, is about 100 metres wide and 350m long. Nick Stuhlener, Boral Waste Solutions’ business development manager, estimates that five per cent of the whole quarry site - or 53 of 1055 hectares – is comprised of these landfill cells.

“This quarry here is a basaltic rock quarry about eight metres in depth,” Stuhlener said. “Underneath that, there’s a layer of clay, it varies depending on where we are in the quarry. We excavate that clay and then utilise it in the construction of our liner. It’s an excellent material for us, as we don’t have to import clay from anywhere. It’s all sourced here.”

Caterpillar’s generators are traditional lean burn spark ignited engines – similar to a common car engine.
Caterpillar’s generators are traditional lean burn spark ignited engines – similar to a common car engine.
Lining the base of the clay cell is thick plastic and then a geo-textile underlay is positioned, followed by rocks to limit contaminated water or leachate draining down to the clay base.

“When the waste breaks down, the water comes into the cell and creates leachate,” Stuhlener explained. “It’s just water from the process, it can be acidic and salty and you don’t want it to contaminate your ground water, so that’s why we build lined cells. The engineered channels mean the leachate drains into one area and we can then pump it to the surface and put it into a leachate pond where it can evaporate.”

Compacted waste is laid down, followed by a layer of compacted soil, followed by another layer of waste and soil and so on. A cutaway view would look a little like an unattractive terrine.

When the cell is full, it receives a clay cap and finally a layer of soil on which trees and vegetation can be planted. However, within two years, the waste starts to emit very unpleasant gases. Methane gases form 45 to 60 per cent of the gases generated. Methane has greenhouse warming potential over 21 times that of carbon dioxide.

“There’s a lag time between when we put the waste in the ground to when it starts generating gas,” said Stuhlener. “The methane generation starts in two years, that’s after it’s been in the ground for two years, and the rule of thumb is that one million tonnes of landfill gas is the equivalent of one engine.”

TAPPING INTO THE CELLS
Traditionally landfill gases were burnt with above ground flares but these gases are well suited to powering engines and producing electricity. Boral has recognised the value of tapping into these cells for renewable energy and so it engaged EPSA, the Australian dealer for Caterpillar’s range of gas and diesel fueled engine generator sets.

“Caterpillar’s been producing gas engines for decades. Probably the first major landfill site in Australia using Caterpillar G3516 engines was done by Energy Developments Limited (EDL) at Berwick in 1992.

We have about 110 of these units in Australia operating on landfill gas,” said David Moore, business manager for EPSA. “They are mainly in capital cities - Perth, Darwin, Adelaide, Brisbane, Sydney, certainly Melbourne, Launceston, across the board.

To extract the gases, Boral drills vertical wells 20m into the buried landfill.
To extract the gases, Boral drills vertical wells 20m into the buried landfill.
“On the sites managed by other landfill gas generator operators such as EDL and LMS Energy, the numbers of units have gone up and down. And that’s one reason they’ve all adopted a similar modular type philosophy.”

To be financially viable, landfill gas energy must produce electrical energy at a market competitive price, which means that the system and engine producing it must be low maintenance with good longevity built in. Building longevity into these engines is not easy as the chemicals and gases passing through can be very corrosive. Enter the Caterpillar G3516, a reliable and specially designed solution.

Four of the G3516 1.1 megawatt (mW) gas-to-energy modules are located at Boral’s Deer Park site. The first unit was installed in March 2006, the second in February 2008, the third in April 2009 and the fourth in 2011. By 2018, Boral expects to have eight units operational.

Moore explained the rationale behind the designations for each of the modules. “The G3516 – the 16 designates a V16 engine, the ‘G’ designates a ‘gas’ as opposed to the diesel model. The majority of the units we have in Australia on landfill are the G3516. There is the G3512 – which is a V12 engine – and the G3508 – which is a V8.”

The gas is measured by output and the size of the engine by output as well, so that is where the 1.1mW engine comes into it.

AVAILABILITY IS SIGNIFICANT
Caterpillar is not the sole engine manufacturer in the industry but certainly has the lion’s share of the landfill business. The product has a good reputation - and availability. Availability is a percentage of the work time that the machinery is available in a year and it takes into account the downtime for scheduled maintenance. Downtime can have an acute effect on any industrial operation and this is no different.

“Within Boral, we have an overall equipment effectiveness calculation which indicates 90 or 92 per cent availability,” explained Stuhlener.
“These units are specifically manufactured for landfill gas,” said Moore. “We have a different version of engine for natural gas. There are various components that are manufactured from different materials such as stainless steel for more resistance to corrosion.”

Moore explained how the engines received the waste gas. “The gas goes through various sets of filters incorporated in gas treatment skids that chill and filter the gas before it goes into the engine.

Landfill gas is a pretty arduous gas on the engines, it can have rather nasty corrosives,” he said. “What we can see are deposits on the cylinders that can accelerate wear, particularly if there’s corrosive components in there. It’s all about maximising output and maximising engine life.

“You can get hydrogen sulphide in the gas, which when it condenses you get sulphuric acid, and the other things you get are siloxanes. If you have a lot of siloxanes, it can turn into silica. You then basically have sand in an engine, which is not a good mix at all.”

Moore added that Caterpillar’s generators for landfill are traditional lean burn spark ignited engines that operate not unlike your common car engine. “You have the fuel system, you have a radiator coolant like a car, and you have the exhaust system, what we call lean burn technology,” said Moore.

“The units generate at 415 volts which is then stepped up to 22,000 volts.

The gen-set unit powers at 415 volts which is then stepped up to 22,000 volts.
The gen-set unit powers at 415 volts which is then stepped up to 22,000 volts.
“The generator set itself is manufactured in the US but pretty much everything else is manufactured locally. The radiators are the cooling package, that’s manufactured by a company in Geelong. The acoustic enclosures are manufactured by a company in Dandenong. The control panels are manufactured by a company in Hallam.”

EPSA prefers to offer a turnkey solution. “We will traditionally do as much or as little as the customer wants. For units two, three and four we took upon the turnkey element ourselves. Other than the civil works, EPSA are supplying the generator set, the acoustic enclosure, the switchgear, the radiator and the exhaust system. But the operation and maintenance is by a company engaged by Boral,” said Moore.

What Boral did was approach EPSA and asked for their best turnkey proposal. EPSA commissioned and built it, then handed the keys over to Boral.

“We employ electrical sub-contractors and other mechanical contractors and plumbers to pull it all together and we take total responsibility and offer a package,” said Moore.

“With some other landfill operators, we basically sell them the engine and they do everything else, they build the acoustic enclosure, etc. But they’ve set up their organisations to do that.”

POWERING THE GRID
As for the actual electricity, most landfill biogas facilities are putting the power back to the public grid for financial compensation.
“It goes onto the electricity grid, supplying approximately enough power for about 300 homes per unit,” said Stuhlener.

“Each unit produces 1115kW less parasitic loads. I’d say that each domestic house is about 3kW, about 300 plus homes per unit,” confirmed Moore.

During the last financial year, 22,000mW of export power came from the site, with that set to increase as additional modules are installed.

With about 60 per cent of Australia’s waste - approximately 20 million tonnes going to landfill every year - it makes financial sense as your quarry nears the end of its life to plan for a solution that benefits the operator, the environment and the electricity grid. Boral’s Deer Park site has shown that it can – and does – work.

Interview by Damian Christie.
Text by Mandy Parry-Jones.









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Wednesday, 18 September, 2019 12:46am
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