The Upside of Downdraft Gasification

Waste to energy requires feedstock flexibility, but offers economic opportunity.
By Luke Geiver | October 08, 2012

David Gordon’s resume may show he’s a veterinarian by trade or the mayor of a small town in western Tennessee, but after his involvement with an innovative downdraft gasification project, he might have to add a new title to the list: waste-to-energy spokesman.

Through a partnership with Tennessee-based, two-and-a-half-year-old, PHG Energy, Gordon conquered the complex balancing act of wastewater remediation, biosludge removal, wood waste utilization and the always ballooning landfill tipping fees and transportation costs associated with all three. The city of Covington is already known as the Charm Pops capital of the world, Gordon says, and is the future home of the world’s largest ice cream production facility. But those catchy claims are already losing ground to the city’s project that utilizes a series of modular downdraft gasification units designed to produce electricity from a combined feedstock of woody biomass and biosludge that until PHG Energy came around, would have cost the city time and money to dispose of.

Surrounding communities faced with similar waste-based issues are taking notice, Gordon says, calling for information on how the veterinarian mayor of Covington turned his self-proclaimed interest in technical stuff, into a model of converting dirty into dollars. Money saved from the $2.25 million project paid for through a bond issuance from the Tennessee Municipal Bond Fund and a grant from the Clean Tennessee Energy Grant program offered by the state’s Department of Environment and Conservation, will pay for some things any mayor would gladly promote: new soccer fields, baseball fields and a walking trail for the city of 9,000.

“I’m already getting contacts from municipalities that want to see how this is working,” he says of the close-to-construction project, some calls coming from nearly 500 miles away. The excess revenue generated through the tipping fees and in-house electrical generation is nice, he says, adding however, that “the project is positive for other reasons.”

Pursuing Renewable Revenue

The city of Covington currently transports wastewater and dewatered sludge to a landfill that requires a two-hour round trip. Wood waste created in the city is also hauled out of the city, requiring a one-hour trip. Because of the costs associated with hauling and disposal, Gordon began looking into better alternatives for the city. “When I first heard about biomass gasification, I was at a Tennessee Renewable Energy and Economic Development Corp’s seminar,” he says. “I listened to a gentlemen talk about biomass gasification and it really got my interest.”

Through a mutual business acquaintance and more research, Wilson got in touch with the team from PHG Energy. There were other firms he spoke with and even other options discussed for utilizing the waste, one that included converting the sludge to a class A sludge, which would allow the city more leniency for disposal methods. Now, Gordon and the team at PHG Energy can point to several takeaways from the Covington project and why downdraft gasification not only won out in the small Tennessee town, but why it can succeed in other places at larger scales.

The most glaring reason downdraft gasification makes sense is that it fits into a popular belief in the biomass industry, that conversion technology should be feedstock flexible. Turns out, mayors like that idea as well. “In Covington,” says Chris Koczaja, vice president of sales and engineering for PHG Energy, “the biosolids alone would not work.” By taking a gasification approach, however, PHG was able to combine the biosolids with wood waste to create an acceptable feedstock, a situation Koczaja says helps to highlight PHG’s technology offering.

“If we put a gasifier on the ground and someone says I have a bunch of woodchips that I want to gasify today, but three years from now I have this other opportunity waste stream, the equipment doesn’t have to change,” Koczaja says. That facet of the conversion approach helps not only PHG but other similar companies pursue projects, allowing users to hedge not just on what is available today, but what the future may bring as well. “That is one of the big pieces that I think people grab hold of,” he says. “It’s not just what is in front of me today, but what may be in front of me tomorrow.”

The feedstock flexibility of the technology played only one part in Gordon’s decision. PHG Energy outperformed expectations, he says. In addition to helping Gordon land a state grant worth $250,000 (PHG is also helping Gordon seek out more), the company provided a plethora of information to Gordon to make the project make sense. Along with several emails, phone calls, information packets, directions to websites, and a trip to Florida to see the Organic Rankine Cycle generator that will be used to create electricity, Gordon says the PHG team found a way to make complex concepts manageable from an operational viewpoint, and most importantly, an economic standpoint.

“This had to make economic sense,” Gordon says, “I couldn’t go into it just as an environmental program that was going to be nice and fuzzy and warm.” To do that, PHG provided Gordon with adaptable spreadsheets that allowed him to change variables or inputs into a financial equation, and, information that allowed him to show the city alderman proof that the process would pay for itself over time. Because of all the research and time devoted toward understanding the merits of downdraft gasification, Gordon now says he tells people, “I haven’t made it to geek status, but I’m a confirmed nerd.”

The first iteration of the project involved the Tennessee Valley Authority, Wilson says. The project would have provided 1 MW of electricity to TVA in return for 3 cents per kilowatt (kW) for 10 years. Unyielding construction deadline clauses didn’t allow Gordon to pursue the project, but on the fifth iteration, PHG and Gordon finally found a way to make it all work.

In November, construction will begin at the current wastewater treatment facility where a system will be installed that includes a downdraft gasifer, thermal oxidizer and an 125 kW ORC generator that will produce electricity for the wastewater facility and heat to dry the woody biomass portion of the feedstock used in the process. Koczaja says the electricity will offset the facility’s utility bill, and the overall footprint of the facility will be roughly one and a half acres.

Every day, 12 tons of biomass will be converted, biomass that would otherwise be landfilled, according to Mike Webb, business development director at PHG. Roughly 360 tons of waste will be deflected from the landfill per month. The gasifiers can convert feedstock blends up to 35 percent moisture, but the team prefers to convert at 25 percent. The mixture also has to have a minimum organic compound percentage.

Webb says each gasifier consumes 8 tons of feedstock per day, producing roughly 4 million Btu per hour. The noise of the units will be very little, allowing for casual conversation while standing next to the system, he says. The part of the equipment that people can see is clean (something that surprises most people Webb points out) and nothing like incineration. There are air blowers and air compressors, and a cyclone to handle particulates (mostly carbon fines) created in the closed loop process. The majority of the maintenance will be on the feedstock handling side, in addition to general work to inspect valve seats and conditions. The producer gas, as PHG calls it, combusts at a lower temperature than natural gas, so there is reduced thermal nitrogen oxide potential.

Koczaja says the project team looked at several possibilities for the Covington location, but in the end decided to work on what made the most sense for the city inside the fences of the wastewater treatment plant. After holding several city meetings with the public, Gordon says his city is excited about being out in front of the waste-to-energy opportunity he and PHG believe exists in the region.

The Downdraft Secret

Most of Koczaja’s sentences describing the benefit of PHG’s technology begin with “the beauty of,” but, there is proof behind the PHG technology. At a brick production facility in Gleason, Tenn., PHG was able to put an early version of its technology to the test. At the facility, which has since gone under but graciously allowed PHG to continue operations of its six gasification units as a pseudo R&D lab and feedstock testing facility, PHG was able to prove the benefits of a gravity-based system.

“We have taken the proven downdraft gasifier and made two significant changes,” he says. First, the team converted the technology to allow for industrial use by implementing SiC refractory lining in the entire gasifier box and stainless steel for the grate and residue box. Second, the team made the whole system scaleable by creating modular units. According to Koczaja, the scalability is related to the ability of up to three or four units to run off one materials-handling operation. The same handling operation needed to run one, can run four.

The downdraft nature of the units also allows for greater conversion rates, as gravity forces the material to flow through the entire gasification chamber, which, Koczaja also says, can reach very high temperatures. The process creates biochar, but only 2 percent by weight of the feedstock. Because the feedstock travels through the entire chamber due to the downward path, the producer gas is much cleaner, according to Webb, and doesn’t require the need for gas cleanup typically used in fluidized bed or updraft gasifiers.

The secret to PHG’s success isn’t just its technology. They’ve also developed an application strategy that is used for every project. “There are two big things we look at for every project,” he says. “What is the feedstock and what is the application? That is how we kind of tailor our offerings to that specific project.”

In Gleason, the downdraft gasifiers weren’t used to take advantage of a waste stream, they were used to offset the costs of another energy application: natural gas. Brick kilns, which require a high volume of natural gas for heat production created in the long corridors that turn liquid mixtures into solid bricks, can benefit from woody biomass. PHG used wood waste from a nearby hardwood flooring manufacturer as a feedstock to feed the gasifiers, which in return created thermal heat for the kilns.

The price for natural gas has since dropped (drastically), and although PHG is looking at projects interested in a different energy application as opposed to propane or fuel oil, the waste-based energy crop (as Webb calls it) is where the company sees a huge market. “A lot of things are not what people think of as energy crops,” Koczaja says. “Once you start asking the questions and you start looking, there is a lot more biomass available than initially meets the eye.” When Webb talks about the number of feedstocks they've tested, he says with a chuckle, “several.”

The company performs the majority of the work required in a waste-to-energy project in-house, but does contract out some engineering and feedstock analysis testing, Webb says. And although the company doesn’t want to “outrun its headlights,” Koczaja explains that more people like Gordon are calling all the time about downdraft gasification technology. A customer in the Caribbean will produce 5 MW from agricultural waste with PHG’s technology and forest waste from federal land thinning will utilize downdraft gasification, potentially supplied by PHG. As Koczaja would say, that is the beauty of waste-to-energy technology. The waste-based portion provides flexibility of feedstock now and in the future for project applications from the Caribbean to the Blow Pop capitals of the world.

Author: Luke Geiver
Features Editor, Biomass Magazine
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