Landfill Gas Utilisation Case Study

Presentation by Graeme Alford, CEO, LGP

Queensland Landfill Conference, Gold Coast, November 2008

Our Vision: “To be the most efficient & innovative global provider of Renewable Energy.”

Slide 1: To better explain the processes involved in providing a gas extraction system for a landfill, a case study will be presented.  The landfill and power station subject of this case study is Tamala Park located in the northern suburbs of Perth Western Australia.

Slide 2: At Tamala Park, the environmental landfill operational licence requires the capture of landfill gas and its combustion.  It is about ensuring the safety of the local community and the environment.

Slide 3: The Tamala Park landfill is operated by the Mindarie Regional Council on behalf of its seven member local governments covering a population of over half million people.  It is the largest landfill in WA receiving some 350,000 tonnes of waste per annum and since commencing operations in 1991, more than 4 million tonnes of waste has been deposited.

Slide 4: Tamala Park is located on the coastal plain less than 2km from the Indian Ocean.  The land is limestone and sand.  Stage 1 is unlined, whilst stage 2 is fully lined.  The completed stage 1 has a plastic capping in place.

When Tamala Park was constructed it was located several kilometres north of the urban development.  The development is now up to its southern boundary and has leap frogged over the site and is continuing up the coast.  The passenger railway line has been extended beyond the landfill site and divided roads are now located on the east and west sides of the site servicing these new urban communities to the north.

Slide 5: The landfill gas capture system works away silently in the background and is the same irrespective of the method of combusting the gas, that is, electricity generation or flaring.  This comprises the installation of a series of wells on a grid layout to collect the gas. 

Post closure, vertical wells are drilled into the landfill.  When installed whilst the landfill is active, a combination of horizontal wells as filling progresses and vertical wells upon completion of the cell ensures the maximum collection of gas over the life of the landfill.

Slide 6: The design of the layout of wells is determined by a number of parameters:
Waste composition and moisture content.  How much greenwaste and inert materials are going into the landfill?
The landfilling operations including:
Type of compaction equipment used and number of passes
Cell construction.  How long does it take to fill the active cell?  Suggest maximum of 18 months based on delivery rates
Age of the waste.  Best gas comes from the new waste, so prefer to install wells as landfilling operations progress.

Slide 7: The other key factors influencing the design of the grid of wells are:
Surface area and side slopes.  How accessible is the surface to install wells post closure?
Depth of waste,  greater than 20 metre desirable whilst greater than 10 metre is an absolute minimum, and
Type of final cover provided by the landfill operator.  Clay goes through a seasonal wetting and drying cycle and gas escapes when it is dry.  Plastic liners are better as there is less opportunity for the gas to escape.

These landfill wells are connected by pipes to the manifold, which delivers the gas to power the station via a vacuum pump.  The well field operates under a slightly negative pressure to draw the gas out.

Slide 8: The gas is prepared for consumption in the engines modified for landfill gas combustion by a gas pre-treatment facility.  The gas must meet the engines manufacturer’s specifications to ensure maximum life from the engines.  These processes will vary depending on the contractor as each has developed their own expertise from operating these plants over many years.  This is where a competitive advantage can be gained and thus the intellectual property involved is closely guarded.

Slide 9: The engine/genset is located within an acoustic module inside the Tamala Park power station building to minimise noise to the surrounding land uses.  Likewise, the roof top exhaust mufflers are designed to minimise noise escaping from the site as the power station operates 24 hours per day.

The other form of construction is to put the engines in their own individual module and this would be the preferred option for sites with only 1 to 2MW generation capacity over the life of the power station.

Slide 10: All electrical works must comply with the local electricity grid company and include their protection equipment to isolate the power station if required.

Slide 11: Most major landfills will require a flare to cater for the infrequent times when the power station is in-operative.  It may be a condition of the landfill’s environmental operating licence.

Methane combusted is 23 times less damaging to the atmosphere.  The flare must be operated independent of the power station, in case of failure of the later and be regularly tested to maintain it in operational readiness if used as back up.

Slide 12: All landfills with MSW produce leachate, although the amount can vary from site to site.  The proper management of leachate in the gas collection pipework is critical to its success.  We are presently advising an international landfill operator on this very aspect that has shut down their electricity generation operations.

Leachate will be drawn out of the landfill with the gas and has to be suitably managed.  It is removed from the pipework and then recirculated or otherwise discharged as required by the landfill operator and their environmental licence.

Slide 13: There will be damage to the surrounding native vegetation from the mitigation of the methane from the landfill.  At Tamala Park, this was typical coastal plains vegetation.  The methane had killed the surrounding vegetation until the gas capture system was installed. 

With the collection of the methane, it is no longer migrating beyond the landfill and destroying the vegetation.  Now it is regenerating naturally and as a result of increased plantings.  Dead vegetation and grass is a sure sign methane is present beyond your landfill.

Slide 14: Power station operations can be monitored from a remote central location and thus the stations can be down the street, across the country or even overseas.  It is possible to diagnose an engine problem from a remote location, address the problem and to re-start the engine from your computer and without visiting the site.

On site personnel are required to attend to well field monitoring and undertake routine maintenance works.

Slide 15: When initially commissioned in January 2004, Tamala Park had an installed capacity of 2.65MW from three Caterpillar engines.  With the additional gas capture, a further two 1MW Caterpillar engines were added resulting in an increased capacity of 4.65MW at the site. 

Slide 16: In conclusion, there are several points I want to leave you with:
Use proven systems.  There are several companies in Australia who are able to undertake this work.  Use their experience to ensure you get a system that will work efficiently
Install the wells as early as possible to maximise the amount of gas collected.  Put in horizontal wells as landfilling progresses
The maximising the gas collection is an art.  Like most things in life, experience teaches us what we should do and what not to do.  The same applies to landfill gas extraction.  It is an art.  It cannot be learnt from a textbook.
The amount of electricity generated from your site will depend on the amount of gas collected.  The more efficient your collection system the more electricity generated.  The number of engines will increase and then decrease with gas flows before and post closure.
Leachate management is crucial to a properly run gas extraction system.  Get this wrong and you will have problem with your pre-treatment facilities and engines

Slide 17: Landfill operators have an obligation to operate their landfills in an environmentally sustainable manner.  One key aspect is the collection and proper disposal of the landfill methane gas created by the breakdown of the waste.