“Terra preta” means black earth. It is prized in the Amazon because of its high level of fertility compared with the surrounding red clay soils. The tremendous precipitation in the region washes away any nutrients not taken up by plants, leaving an impoverished soil that is ill-suited for agriculture. In contrast, the terra preta is highly productive year after year. How these soils kept producing good crops was a mystery until a few years ago. Researchers discovered the terra preta was largely man made. Over centuries, the ancient residents of the Amazon incorporated charcoal into the soil. Amazingly, radiocarbon dating showed that some of the terra preta sites were 1,500 to 2,000 years old.
The same properties that enrich the earth could also someday protect the skies. Now that it is known that charcoal can remain in the soil for millennia, some scientists think this may be a possible carbon sink to reduce greenhouse gases in the atmosphere.
Article Continues After Advertisement
Dark Matter
Char is the product of partially burned biomass. While charcoal has been produced for almost as long as man has controlled fire, the modern source of char is from a process called fast pyrolysis. In this process, biomass is heated to the point where volatile gases and liquids are driven off and condensed into a product call bio-oil. What remains is almost pure carbon, called char, pyrolysis char or biochar with a varying ash content that depends on the type of biomass used. Interest in the char has grown as more companies explore processing technology and new uses for biomass.
Heartland Bioenergy LLC is proposing to build a biorefinery in central Iowa. The company’s goal is to use corn stalks to produce transportation fuel. “We have been working on biomass issues for five or six years now,” says Lon Crosby, a researcher with Heartland Bioenergy. “If you are going to collect biomass to prove technology, you had better have a way to use the biomass.”
Heartland looked at a number of technologies as a base for its proposed biorefinery. “As we started to look for ways to use biomass, we looked at gasification, fast pyrolysis and a variety of other techniques,” Crosby says. “Probably the best approach we found was to start with fast pyrolysis, because it yields two products: bio-oil and biochar.”
Bio-oil is a relatively easy product to market as a bunker fuel, Crosby says. There is an existing demand for char, but finding new uses for it would make the whole process more economically viable. “Biochar is easy (to market) as long as you are interested in low-value applications,” he adds. “I happen to also farm, so looking at char’s agricultural applications was a natural choice.”
Heartland is testing char in a large-scale project to see how it impacts corn production. Dynamotive Energy Systems Corp. has provided Heartland with 14 tons of biochar. While working with the USDA National Soil Tilth Laboratory, Iowa State University, the Iowa Soybean Association and Prairie Rivers of Iowa Resource Conservation and Development, Crosby created a large-scale test plot to measure the impact of adding char to the soil. The plot consists of three strips that are 30 feet wide and 800 feet long. One strip is untreated while the others were treated with 2.5 and 5 tons per acre of char.
This experiment will overcome some of the deficiencies seen in small-scale char experiments. Crosby says char experiments are greatly affected by edge effects between treated and untreated soils. This skews the results from test plots that are a few meters across. By using large plots, edge effects are reduced producing more reliable data.
A Hot Product
Dynamotive has been producing bio-oil and char for several years in Canada, says Desmond Radlein, the company’s chief scientist. The company uses waste wood from the timber industry as a feedstock. Radlein views the bio-oil as the primary product and the char as a secondary product. “If you pyrolyze wood under fast pyrolysis conditions you might get 70 percent of a liquid as a product with some gas and some char as a byproduct,” he says. “Fast pyrolysis is a fairly well established technology. Several people are practicing it and trying to commercialize it. The basic idea is to make a liquid fuel. It isn’t a high-grade fuel. You can’t burn it in your car but you can burn it in boilers and gas turbines.”
Dynamotive began its work on fast pyrolysis at about the same time terra preta soils became a hot research topic. “It turns out that the conditions under which the char is made under pyrolysis seem also to be the optimal conditions to making a good char for soil amendment purposes,” Radlein says. “Char is a secondary product, but from that perspective, one is always looking to see what one can do with it.”
Sidebar Articles
| 1 2 3 | Next Page --> | |
| View Entire Article | ||