Washington, DC: How To Keep A Digester Successful

A webinar presented by the American Biogas Council (ABC), based on a session at BioCycle REFOR16, focused on how to keep a digester successful. The three presenters — Brian Langolf, AD manager for the University of Wisconsin Oshkosh Foundation, Brian Meek, director of plant operations for Avant Energy’s Hometown BioEnergy Facility in Le Sueur, Minnesota, and Andrew Austin, AD manager for Scenic View and Brook View Dairies in Michigan — agreed that the bigger struggles to achieving a successful AD project tend to be procedural or economic rather than technical. For example, Langolf noted that its biggest technical challenge to operating a dry fermentation, plug flow and complete mix digester, has been to change out some piping installations to better withstand harsh Wisconsin winters. “The economic standpoint is really the area where we have had bigger struggles,” he continued, noting that the foundation wanted to build a 3 to 4 MW complete mix digester but could only secure a power purchase agreement (PPA) for 1.4 MW. “We got a PPA at 9 cents per kilowatt hour, but the economics aren’t quite the same now.” He adds that expired PPAs are being offered for renewal at only 2 to 4 cents per kilowatt hour in Wisconsin, which is not sufficient to keep an AD project operating.
Being a power merchant owner of a digester helps to mitigate the problem of a low or nonexistent PPA, said Meek: “We designed Avant Energy’s 45,000 dry ton, 8 MW Hometown BioEnergy AD facility to include three large gas storage vessels on site, so we can strategically runs the generators during periods with higher electric prices. It makes the project more economically advantageous than if we were running at a steady rate around the clock.”
Among best practices that can ensure success regardless of a digester’s ownership or circumstance:
• Keep the equipment and technology piece of the puzzle as simple as possible. “We found the simpler the process for these projects, the better,” suggests Austin. “The fewer flow meters, bells and whistles, the less maintenance.
• Austin also recommends that in cold climates, preheat the substrate going into the digester during the winter months. Scenic View and Brook View dairies both use hot water from the cogenerator jacket to preheat manure, yielding “a big increase in gas production, which paid for the heaters.”
• Hire staff with backgrounds in biological processes than electrical generation. “At a digester, the complications come from the biology of the digester,” noted Meeks.

Queensland, Australia: Bananas To Biofuels

More than 331,000 tons of bananas are grown in Australia annually, mainly in northern Queensland. About 20 percent of the banana crop, some 66,000 tons/year, are damaged or bruised during harvesting and transport to packing facilities and cannot be sold, according to a January 2017 article in the North Queensland Register. The Queensland horticultural industry trade group, known as Growcom, became involved in a Banana Waste-to-Energy project, about 10 years ago, to produce and harvest methane gas from banana waste, funded by the Sustainable Industries Division of the Queensland Environmental Protection Agency (EPA). This followed a University of Queensland laboratory study in collaboration with the Australian Banana Growers’ Council and Ergon Energy in 2005-2006 that showed bananas could yield about 240 liters of biogas per kilogram of dry banana. The biogas was of sufficient quality to be used as a substitute for diesel in combustion engines, containing about 40 percent methane and insignificant amounts of hydrogen sulfide and other contaminants. The digestate was suitable for use as fertilizer.
Growcom’s project demonstrated the feasibility of constructing a low-cost on-farm anaerobic digester to convert banana waste to biogas, to be used to run on-farm machinery and return power to the grid. Infrastructure, including a 122,000-gallon anaerobic digester with capacity to process 2,760 tons/year of banana waste and produce about 3 million cubic feet of methane, was built on a banana plantation near Tully in northern Queensland around 2008. This level of output could be used to continuously generate about 35 kilowatts of electrical power or provide much of the fuel requirements for a fleet of about 100 gas-converted vehicles. Growcom estimates that the amount of waste produced by the Queensland banana industry could sustain the operation of 10 similar-sized digester units.

East Palo Alto, California: IKEA Expands Biogas Network

As part of its quest to generate and use as much renewable energy as possible in its retail locations, Swedish home furnishing retailer IKEA installed its sixth biogas-powered fuel cell system at its U.S. stores. The latest one is at IKEA’s East Palo Alto location in the San Francisco Bay area, making it the fifth installation at IKEA stores in California. (The sixth is in Connecticut.) The fuel cells are manufactured and installed by Bloom Energy, producing a total of 1.5 MW of biogas-based energy, according to IKEA spokesman Joseph Roth. The units are the size of a commercial back-up generator. All of the stores with fuel cells also have solar panels, and all power generated is directed to the store’s electrical load, together accounting for close to 60 percent, Roth notes, adding that IKEA still uses natural gas for heating.

Biogas-based fuel cells align well with IKEA’s push to reduce its carbon footprint. “We have solar at 90 percent of our U.S. locations, and we own two wind farms,” he adds. “We’re open-minded in terms of evaluating potential renewable sources. The potential to generate electricity from a fuel cell was attractive, but we decided we only wanted to pursue it if we could be carbon neutral.”
For 2017, IKEA contracted to buy biogas from a manure digester in Kansas to power its fuel cells. Beginning in 2018, under new 20-year contracts, the retailer will use biogas originating from anaerobic digestion of agricultural and industrial organics in Missouri and Arizona. Under these contracts, the biogas is “wheeled” from the point of generation to California, meaning that it is conditioned and put into the natural gas pipeline where it is produced, and an equivalent amount is pulled out by IKEA and used in the fuel cells. Despite using the carbon-free biogas, Roth says that IKEA doesn’t receive carbon credits under California’s cap and trade system because the credits are retired when the biogas is purchased. “It would be double-counting for IKEA to use carbon-neutral biogas and count a carbon credit,” he explains.
As for how many more biogas-based fuel cells IKEA might install, Roth is optimistic: “Our stores’ electricity bills dropped significantly. Everything Bloom said would happen came to fruition. We were cautiously optimistic and were pleasantly surprised at how successful it has turned out to be.” Besides solar arrays, wind farms and biogas fuel cells, IKEA also has installed electric vehicle charging stations at 16 stores and integrated geothermal projects at two store locations to help meet its goal of becoming energy independent by 2020. The electric vehicle charging stations serve simply to promote the technology.

London, England: United Kingdom Revises Feed-In Tariffs For AD Plants

In May 2016, the British government published its consultation on the support feed-in tariffs (FITs) for anaerobic digestion (AD) and combined heat and power (CHP) generators. The consultation closed in July 2016 with responses having been received from a broad range of stakeholders. The revised AD generation FITs were implemented on April 1, 2017, and vary based on the amount of electricity produced. The prices decline over the period between April 2017, and January 2019. The generation tariff ranges for each amount generated are as follows (all data in U.K. pence per kilowatt-hour): 0-250 kW—from 6.93 in April ‘17 to 6.58 in Jan. ’19; 250-500 kW—6.56 in April ’17 to 6.25 in Jan. ’19; 500-5000 kW-2.49 in April ’17 to 2.24 in Jan. ’19.
Ashfords LLP, a large British law firm with expertise in the renewable energy industry, offered this perspective on the revised tariffs: “Few expected there to be a significant upturn in government subsidy provided to AD and mCHP [micro combined heat and power] projects through the FITs and from that perspective the government’s response provides little in terms of surprise. Overall government support for AD has reduced just as it has already reduced for other renewables technologies. Consequently it is unlikely these changes will alter the outlook for those looking to invest in these technologies in the medium term. That said, now that the response to the consultation has been issued, it should enable final decisions to be made on the viability of projects currently in the pipeline. There may yet be one ‘last flurry’ of activity before institutional investors conclude that the risks of financially sponsoring an AD project outweigh the gains to be made by investing in such a project. …. The Government’s response also has the potential to affect prospective medium-scale AD projects around the 500 kW capacity figure, where there may be a notable incentive to remain below the 500 kW cut-off to access the higher level of tariff support. If there does prove to be a last flurry of activity from the institutional investors, one might expect the plants they are funding to be at the more modest end of the scale.”