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Capturing methane generated from rotting household waste to produce energy has to be a win-win situation for ‘renewables’ and greenhouse gas emissions. By ALAN TITCHALL.
When opened in 1993, after years of progressing through planning and resource consent hurdles, Redvale Landfill was the very modern model of an engineered landfill development, taking out the Institution of Professional Engineers Environmental Award in 1994. Lined with stone walls and mature trees, the entrance to Redvale on State Highway 17 in community of Dairy Flat (about 30 kilometres north of Auckland), looks more suitable for a ritzy real estate project than the principal refuse disposal facility for the Auckland area. Inside the main gates, there’s a parkland setting of native tree stands, landscaped ponds for storm run-off, and rolling grassland to shield visitors from the ‘working’ end of the project. It is only the constant stream of heavy vehicles coming and going across the weighbridge that gives away the scale of waste handled at the site. Redvale was a greenfields project based around an exhausted lime quarry that offered around three million cubic metres of air space. The quarry owners initially offered the site to the Auckland Regional Authority who thought the site was too small. Waste Management (now a division of Transpacific Industries Group NZ) then stepped in and wisely bought land around the sides of the old quarry to make a viable landfill with a resource of 20 million cubic metres of air space. The site occupies about 80 hectares, has a total capacity of about 16 million tonnes, and is about halfway through the process of filling the resource, with closure expected in 2023. There are about 16 landfills throughout the country and Redvale is the largest in terms of waste input. The operation is self-contained and run by Waste Management’s Landfills and Project Development Division, made up of 57 fulltime staff; 20 tertiary qualified. “From a landfill view, it’s a perfect site,” says operations manager Chris Wills. “It was the flagship of modern landfills in New Zealand and, at over 80 metres deep, is an intensive use of the designated resource area by international standards.” Landfill gas managementBy early 1996, landfill gas was being ‘passively’ extracted (under natural pressure) from five gas wells around the landfill and flared. Active gas extraction with a central flare was installed in November 1998, and by the beginning of 2000 Redvale was generating and selling renewable electricity into the grid. “We are currently drawing off around 5000 cubic metres an hour of landfill gas made up of between 55 to 65 percent of methane. This will eventually be increased to a maximum of between 12000 and 14000 cubic metres an hour,” says Wills. Current generating capacity is just over nine megawatts using nine, 48 litre, V20, GE Jenbacher 320 landfill gas engines supplied by Clarke Energy. Run on methane, each generator is connected via an integrated 415V circuit breaker to a 33kV step-up transformer, from which high voltage electricity is exported to the grid. Each generator is housed in an acoustically lined GE Jenbacher, 13 metre (40 ft) standard container that also houses the control room. The cooling radiator and exhaust gas silencers are mounted on the roof. The gas is drawn from the landfill under vacuum through a concept where perforated pipes and wells are constructed into the landfill body and interconnected by a system of reticulation pipes. The system has been ‘Kiwi-ised’, says Wills, with both horizontal and vertical components that provide extraction rates of around 90-95 percent. Another innovation at Redvale is drawing off gas while building up the waste pile. Conventional practice, both here and overseas, is to reach final height and then drill down to install the wells. “But at 80 metres, it would take years and years to reach final height, which would result in a lot of lost gas in the meantime. Being able to draw off the gas while building the waste pile up is a very efficient way of doing things. Other landfills are now replicating this concept.” Thin operating marginsNot so efficient is the local network into which Redvale feeds its electricity. The first three generators over heated the 11kV low-grade local network, and the company had to make a huge investment in its own new 33kV line to allow export to the grid. However, the local network is still nowhere as secure as Redvale would like. “We have had outages of up to 48 hours. A real problem. Because we can’t generate, the gas has to be destroyed through the flare. It’s a wasted resource, and it happens more than we would like.” A large flare on standby is capable of burning off 3000 cubic metres an hour, if necessary. Not surprisingly, operating margins are thin. “When you have to burn gas occasionally due to outages, and then get charged to put power into the grid at other times, and it is costing $40 to $45 a MWh to run a generator – then you start to ask, ‘what are we doing this for’?” Pricing difficulties experienced by Waste Management include line charges, lack of real nodal pricing and reluctance on the part of many line companies to provide for embedded generation – except at exorbitant rates. Redvale could build its own connection to the local GXP, but under the country’s convoluted electricity rules the company would not be eligible for transmission benefits, as it wouldn’t be taking power ‘off’ the line. “These generation rules need a big shake up because, without a great deal of goodwill from Vector, this project would be too difficult and we would simply flare the gas,” says Wills. “We should be getting more credit for generating at the point of demand and consequently reducing the need to transmit power from further a field with the associated line losses.” It is these anomalies that makes the Government’s push for renewable energy sound hollow, says Wills. You would think any business that converts methane to energy, that would otherwise simply be flared under the requirements of the National Environment Standard for large landfills (and methane is considered 21 times worse that CO2 as a greenhouse emission), would be getting as much Government encouragement as possible. However, Wills says renewable generation in New Zealand still has to match the market at the same spot rate as conventional generation, and gets no real incentives or financial motivation from the corridors of power in Wellington. “We have turned down projects here because they are only have a one or two megawatt potential, which is too marginal in New Zealand.” In Australia (and Transpacific is an Australian company) there’s an incentive to chase after just 500kW of renewable energy because of credits for greenhouse gas abatement, with up to A$85 a MWh hour boost on your generation, plus a spot rate on top, says Wills, that changes the whole economics of a marginal project. “If the government is serious about renewables, then its should provide incentives for smaller embedded generation projects, not just rely on the big ones. It wouldn’t take much to change the situation,” says Wills. “There are so many other areas in New Zealand perfect for small scale renewable energy generation with the right encouragement.” Accessing the meritsIan Kennedy, the manager of the Landfills and Project Development Division at Waste Management, reiterates the question whether renewable landfill gas operations in New Zealand are actually worth the investment under current legislation. “We were voluntarily capturing landfill gas and generating renewable energy as an industry early starter, before the government’s initiatives to reduce greenhouse gases,” he says. Since then, the Government has introduced the National Environmental Standard that requires all large landfills to capture and destroy methane. “While we support the concept and the environmental benefits, this effectively ‘nationalised’ our ability to trade carbon credits on the international market.” says Kennedy. Then there is the proposed Waste Levy of $10/tonne of waste going to landfill, starting from July 2009, followed by the proposed government’s Emissions Trading Scheme (ETS), which imposes a further tax on fugitive methane emissions. “One can’t help wondering about this ‘stick’ approach in the absence of any ‘carrot’ to encourage or incentivise generating renewable energy from landfills, rather than simply flaring this resource.” he says. “Considering the volatility of the spot price and the lack of influence that we have over that, one would normally require a higher rate of return on investments of this nature.” Kennedy says if the return is not there, the company may have to reassess the “merits of generation” against alternative commercial opportunities. “Such as disconnecting our containerised landfill gas generators and shipping them to Australia where there are incentives.”
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With the potential of producing around 60 megawatts, the country’s landfills already generate around 20MW of electricity, and almost half of that is produced from Redvale, just north of Auckland.