Wood to Energy - Biomass Gasification at Kisatchie

Biomass.  It can be a renewable resource, especially in the pine forests of northern Louisiana where moisture levels are high and growing seasons are long, where the logging industry practices "sustained-yield forestry" and where the US Forest Service's mission is "sustaining healthy forests."  But beyond sustainable, harvesting biomass can be regenerative.  Removing invasive trees and thinning timber stands are central to restoration of southern pinelands, in Kisatchie and nearby east Texas.



Biomass, therefore, is quite a prevalent by-product in such a forested region.

Enter Biomass Gasification, a process that converts this resource into electricity.   The Winn Ranger Station in Kisatchie National Forest has an experimental biomass plant where they've been researching the feasibility of this technology with local sources.[1]   Let's take a tour with Ranger Gregory Cohrs for a rundown of the 10-step gasification process.



1. Feedstock – A fancy word for woodchips.  Southern pines (longleaf, shortleaf, loblolly and slash) are readily available in the region, as well as the invasive Chinese tallow tree.


Records of biomass origin and species.

2. Drying Bins – Giant blow-driers remove any moisture from the chips to prepare them for gasification.


3. Sorting Screen – Hoppers release the chips out of the drying bins and onto a chute with a sifter, which discards chips that are too large or too small. A uniform diameter of around 2” ensures proper gasification without jamming machinery.


4. Feeder – Sorted chips are dropped into the gasifier.


5. Gasifier – The workhorse of the operation, it heats the chips to 800-900 C in a low-air environment, extracting synthesis gas, or "syngas."


6. Heat Exchanger – Gas is then cooled from 650 to 110 C.


Doo-dads and whizpoppers

7. Filter Drums – Gas is purified, removing ash and char.


Drum that catches ash

8. Flare - Excess gas is burnt through a vent on the roof. (for photo, consult satellite imagery)

9. Engine – Clean gas is then pumped back into the 20th century, where it fuels what appears to be a V6 engine from some guy's Ford Ranger. This in turn powers the final component:


10. Generator – Produces up to 25kw of electricity.



When operational this system powered the entire Winn District Ranger Station, a 4,000sq foot office building with outlying structures and a campground. It also contributed excess power back onto the grid, earning them credits.

“It was really neat to see in action,” said Greg. “I wish we could fire it up and show you.” But we didn't have the manpower. “You'd need a mechanic, a chemist and a computer whiz,” he joked. The system first arrived about seven years ago,[2] around the same time Greg did. He said it was used substantially in its first five years or so, mostly by grad students. But it hasn't run in almost a year, since research has concluded and attention has withered.


Geopolitics and macroeconomics have also lent a tentacle. With petroleum prices so low, alternative energy has become relatively less cost-efficient. Natural gas could power the same generator without the first seven steps.

On the bright side, production of fuel chips for gasifiers is growing. The paper industry historically opposed any competing demands for timber, but their power has waned thanks to e-mail and online news.

Now American companies are utilizing American forests for fuel chips, which are mostly shipped to Europe. The demand is high there, given their short supply. According to Greg, when visiting German foresters toured a recently-cleared timber stand they were shocked by the amount of debris left behind. In the Black Forest of their homeland, everything is gathered and used.  Large scale gasification plants are already operational in Europe, such as G├╝ssing, Austria and Svenljunga, Sweden. Forests of the US south supply 40% of European fuel pellets, 3.6 million metric tons in 2014.[3]

And gasification efforts in the U.S. haven't exactly run out of syngas either. Mr. Cohrs mentioned a few biomass plants nearby also powered by wood chips, such as a 44MW plant in Lufkin, TX, and A 100MW plant in Nacogdoches, TX, which powers 70,000 homes and is part of Austin's goal of supplying 30% of the city's energy with renewable sources by 2020.[4]  But that's just the tip of the pellet pile. According to a magazine and website devoted to the topic, there are 228 sites throughout the country, generating a total of 7,473MW of electricity.[5]


References
[1] "2009 Research Update: Wood to Energy," USFS [link] [2] James Skains, "Kisatchie Wood Chip Gasifier Formally Launched," The Piney Woods Journal [link]
[3]  Katie Fletcher, "Report Concludes US Pellet exports no Threat to Southern Forests," Biomass Magazine (Nov. 23, 2015) [link]
[4] "Nacogdoches Wood-fired Power Project," power-technology.com  [link] [5] "Biomass Plants," Biomass Magazine [link]

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