Presented by: Chris Wills, Manager – New and Best Practice Technology and Joanne Ferry, Senior Contaminated Land Specialist, Tonkin + Taylor
Designed for landfill managers, supervisors and landfill gas technicians, the items covered will include the practical aspects of landfill gas extraction and advice on some of the issues that can detrimentally affect achieving good extraction rates.
This 60-minute webinar will cover:
- The importance of good gas collection – Jo:
- Global environmental concerns regarding the release of methane with a Global Warming Potential of 25
- Release of odours from Non-methane Organic Compounds (NMOCs)
- Cost of compliance with the ETS. 1 tonne of waste can produce methane with a carbon cost of $30. This can be reduced to $3 with good gas capture
- Biodegradation processes – Jo:
- Aerobic (in the presence of oxygen) as used in composting. Has a higher temperature during biochemical breakdown which can lead to spontaneous combustion
- Anaerobic (in the absence of oxygen) which produces valuable methane at a lower temperature (35-45 degrees C)
- Compaction – Chris:
- Reduces the air content in the waste and saves airspace
- Minimises the aerobic phase when waste can spontaneously ignite
- Keeping work areas as small as possible
- Cover – Chris
- Reduces the ingress of air and water into the waste.
- Minimises the chance of spontaneous combustion
- Reduces odour and stops access to waste by animals and insects
- Utilising daily, intermediate and final covers effectively
- Gas well types – Chris:
- Traditional form of well:
- Bored- significant loss of gas capture but ease of compaction and cover
- Slip formed – good gas capture but more difficult to work around
- Horizontal – often retrofitted to closed landfills. Can get blocked with leachate
- Hybrid – best capture rate because has both vertical and horizontal components to provide preferential flow paths for gas
- Gas wellheads, laterals and headers – Jo:
- Well heads need to be standardized for measuring gas constituents, flow rates, available vacuum and temperature. Adjustments made immediately depending on results
- Laterals typically 65mm diameter and slope away from well head
- Headers need to be designed for concurrent or countercurrent gas flow and have grading towards Knockout Pots
- It is desirable to have a ring main system with enough stop valves to allow additions and alterations to be made to the system while maintaining extraction
- Condensate and issues – Chris
- LFG is warm and saturated and condensate will form as gas cools at the surface
- This must be collected and drained off, otherwise the gas lines will become blocked
- Differing maximum gas velocities apply depending on whether the gas is flowing in the same direction as the condensate or in the opposite direction
- The most frequent failure of gas extraction systems is due to condensate blockages in the lines
- KOP’s – Chris
- Knockout pots are required at low points in the gas lines or if large volumes of condensate are expected.
- These can either be pumped out or drain back into the landfill
- Because gas velocities can be very high it is common to build in deflector plates or step-ups at KOPs to avoid condensate jumping across the pot
- Gas quality and quantity – Jo
- Gas contaminants and H&S issues
- Blowers – capacity and field monitoring
- Need to be designed for eventual demand and have duty and standby blowers each adequate to provide design vacuum at the most distant well head.
- Better to have blowers running at 50-60% capacity than 90-100% because gas flows can change with atmospheric conditions
- Gas destruction – Chris:
- Two main types of flares:
- Candle stick – used at smaller sites or in temporary situations. Have lower gas destruction capability and infrequently have gas flow measuring
- Ground flare – the ultimate in gas destruction with 99.98% gas destruction and fitted with combustion control louvres, flame-out warning systems, pilot ignition system and automatic slam shut valves
- Electricity generation sets either reciprocating or turbine
- Other opportunities e.g. leachate evaporation, ammonia stripping, greenhouse or building heating
The presentation will be followed by Q & A.
About the presenters:
Chris is the Manager – New and Best Practice Technology, Operational and Technical Services Division at Waste Management NZ. He has over 57 years’ experience in civil, mining and environmental projects and has conducted landfill operations training courses over the past 15 years in NZ and Australia. Chris was responsible for the start-up of Redvale Landfill in 1993, was Landfill Manager for many years, is still based there and has also been heavily involved in the start-up of a large landfill and award-winning transfer station servicing Adelaide. He has also been involved in landfill projects in Malaysia, Oman and China. Landfill gas systems have been an important part of his design and operational skill set and he was responsible for developing the hybrid gas extraction wells at Redvale, which have achieved LFG recovery factors of over 90% and are now extensively used at other sites.
Jo is a Principal Environmental Consultant within the Environmental Engineering and Management Team at Tonkin + Taylor. She has more than 16 years’ experience working in the waste and contaminated land sectors in New Zealand and Australia. Jo has worked extensively on the management of risks from closed landfill across New Zealand, including identifying landfill gas risks and developing controls to address risks to human health. Jo also works with operational landfill sites to maximum their landfill gas collection and destruction efficiency, and advises landfill operators on regulatory and legal compliance requirements in relation to landfill gas emissions. One of her speciality areas includes the application of the NZ Emissions Trading Scheme to landfill sites, and assisting landfill operators to manage their obligations under the scheme.