A Little Independent Energy Experiment on the Prairie
If you can fight your way through the dirt storms of Madelia, Minnesota, you may be able to find the future of renewable energy
- By Maggie Koerth-Baker
- Smithsonian.com, April 06, 2012, Subscribe
(Page 3 of 3)
The system is both simple and delightfully clever. Pyrolysis is all about breaking down plants and other matter into a form better suited to usable commercial energy. Grasses, stalks, manure—any kind of organic material—goes in. That stuff gets heated to almost 950 degrees Fahrenheit in an oxygen-free environment, thus releasing a host of volatile gases. Condense the gas, and you get a liquid fuel. There are several ways to heat up biomass, but the university’s system is special because it relies on microwaves, stronger versions of the same technology you use to cook popcorn and leftover pizza.
It’s a handy method, because it’s already proven technology—easy to use and cheap to construct. Microwaves also make the entire biofuel production process simpler. Usually, before any biomass can be turned into fuel, it has to be ground into tiny pieces to make sure every bit can be evenly heated at the same time, but microwaves heat up the center of a solid object just fine.
In addition, there’s money to be saved in shipping costs. Moving biomass around isn’t very efficient. Organic material is generally bulky and not very energy dense. Transporting a ton of prairie grasses uses as much energy and costs as much money as transporting a ton of oil, but you get more energy out of the oil. By using microwaves—a heating technology that’s lightweight and can be scaled down to the size of a small camper trailer—the University of Minnesota hit on a way to make pyrolysis portable and bring the fuel factory to the farm. There, each farmer can load up the pyrolysis machine and produce a couple of different products on site. Batch process test runs in the lab took as few as fifteen minutes.
What the farmers get out is useful stuff. Fuel is the main product of microwave pyrolysis. The university’s system does produce enough combustible gas that, once started, it can power itself. In general, though, what you’re making is a liquid called biogas. It’s useable as is, fresh out of the tap, but for best results, it really needs a bit of cleaning up. Any engine will run on fresh biogas, but over time the acidic fuel would tear the engine apart. The university researchers are still working on methods to make biogas compatible with cars, but in the meantime, the stuff can be used in place of home heating oil or sold as a replacement for industrial petroleum.
In the fall test run of the microwave pyrolysis machine, the University of Michigan researchers found some problems with the syngas-powered generator, but they're going to return to Madelia this summer to test the system again with a new generator.
Biogas is not the only important product to come out of the system. Back up to the head of the production line, and you’ll find another output—one that can reduce the quantity of CO2 in the atmosphere and might be able to boost plant growth, too. When biomass is heated by microwaves, the parts that don’t turn into fuel transform into something akin to charcoal. Called biochar, it’s a bit different from standard barbecue briquettes, thanks to the oxygen-free environment where pyrolysis happens.
Biochar functions as a maximum-security prison for carbon. Charcoal can trap carbon, too, but not as effectively. Charcoal is chemically made up of carbon joined to lots of oxygen molecules but is primarily ash and has lost most of its carbon to burning. Like sorority girls in a slasher film, the oxygen is easily picked off by bacteria, which speeds up the process of decomposition, breaking the chemical bonds and leaving the carbon that does remain to drift back into the atmosphere.
Subtract the oxygen, however, and the carbon molecules get tough; they form ring structures that don’t easily shatter and are more resistant to microbial attack. Lab research suggests that these bonds have the potential to hold fast for anywhere from hundreds to hundreds of thousands of years. That means less carbon in the atmosphere. It’s also good news for anyone who’d like to see carbon-neutral or even carbon-negative biofuel production. Of course, that’s in a test tube—there aren’t many biochar studies being done in the (literal) field, and the real-world research hasn’t been conducted for very long.
That’s why—despite lots of crossed fingers—we don’t yet know whether biochar will make as good a fertilizer as it makes a carbon trap. The key question—“Does biochar-infused soil lead to more crops and better soil fertility?”—is still wide open. Yet some tantalizing data are coming out of those lab tests. It seems that by putting microbial life on slow-mo, biochar also works to trap nitrogen in the soil. Not only does that mean less nitrous oxide—another greenhouse gas—in the atmosphere, it could also mean less nitrogen fertilizer applied to the ground and less excess nitrogen leaching away into the water supply.
This is the Madelia Model in a nutshell: give farmers a reason to grow plants that are better for the land and the water supply than corn is, and then reap the benefits. In go prairie grasses, out come fuel, fertilizer, and economic development. It’s not enough fuel and fertilizer to supply the whole country or even the whole state, but that’s okay. It doesn’t have to do that. The primary goal is to prevent more of the local topsoil from blowing away, not to create a mini- empire of bio-oil production. The Madelia Model only has to work on a local scale.
Excerpted from Before the Lights Go Out: Conquering the Energy Crisis Before It Conquers Us, published in April, 2012 by John Wiley & Sons, Inc. Maggie Koerth-Baker is the science editor for boingboing.net.
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Comments (3)
Several topics that this article does not mention: How much energy goes into collecting and cooking the biomass vs. the energy output? How much Carbon is present in the liquid fuel and where does it go when burned? We desperately need alternative fuels but the bottom line will always abide by the laws of conservation of matter and conservation of energy. Simply track the Carbon and the BTU's to know if you have a real winner. There is no mention of the fact that SOYBEANS are a LEGUME that naturally fix their Nitrogen from the atmosphere. When SOYBEANS are converted to BIODIESEL there is a NET ENERGY GAIN of about 3.24:1. (Why did we loose the Biodiesel tax credit?) An analysis of net energy or Carbon cycle shows that Ethanol can't come close to the benefits of Biodiesel. In many parts of the U.S., farmers have long been using no-till practices that build soil and sequester Carbon. Crop residue stays on the surface where it protects the soil from weathering. Cover crops like Diakon Radish and Annual Ryegrass further protect the soil in the winter and recycle nutrients. It sounds like Minnesota needs no-till and cover crops. Native plants and wildflowers make good fodder for government programs and the media but if we really want to change our relationship with the planet, we need genetically modified plants - like Nitrogen fixing, drought tolerant corn and wheat.
Posted by Robbie Williams on April 22,2012 | 10:10 AM
"Charcoal is chemically made up of carbon joined to lots of oxygen molecules but" uh uh
Posted by Stuart21 on April 11,2012 | 11:24 AM
Somewhat confusing article: on page 2, the researchers are from Minnesota, on page 3, University of Michigan (maybe a collaboration?). And no links for further research. I found these: http://biorefining.cfans.umn.edu/ http://gekgasifier.com/ http://www.umb.no/statisk/umnumb/presentations/microwave_pyrolysis.pdf
Posted by John Valenti on April 9,2012 | 09:57 AM