The AFEX Has Almost Arrived
Researchers at Michigan State University, led by Bruce Dale, professor in the department of chemical engineering and materials science, have found a way to use the properties of lignin to their advantage. To do it, they’ve nearly perfected a process they call AFEX, ammonia fiber expansion. Using AFEX, the team has also shown that transporting biomass can be much more efficient if the properties of lignin, namely its binding qualities, are put to use to form (or bind) the biomass into easy to transport biomass packs that are similar to briquettes.
Dale, who has been working on the AFEX process for roughly 30 years, says that some people might be familiar with the process as a gaseous treatment to improve the material for animal feed. To form the biomass packs, here is how it works.
Starting with plant material that can contain moisture content as high as 50 percent, the process uses roughly a pound of ammonia for every pound of plant matter. The biomass (hay, straw, corn stover, etc.) is treated at 150 to 200 degrees Fahrenheit for approximately 15 minutes at a pressure of 200 pounds per square inch. After the treatment time is up, the ammonia evaporates and nearly 20 to 30 percent of the original amount is recovered. “One of the effects of the treatment is to break down the lignin into smaller pieces,” Dale says. “When the pressure is released, the mixture of ammonia, water and lignin migrates to the surface of the plant fiber and it leaves behind the lignin fiber, which is naturally sticky.” Essentially, the AFEX process breaks down the lignin into pieces that are more than capable of acting as a binding agent to hold the rest of the biomass together, making the biomass easily compactable and transportable.
The material, Dale says, “has about the bulk density of corn and it flows like corn and should store well in grain handling equipment.” And, because the AFEX-effected biomass holds those properties, Dale believes the system will allow for a more distributed process approach for biomass to biofuel biorefineries. The idea is to utilize regional biomass processing depots that perform this pretreatment step and densify the biomass. “We envision a series of these smaller distributors that maybe process a hundred tons a day of plant material that could be owned by rural interests.” This vision can all be made possible, he says, because of one of the greatest advantages to the AFEX process. “There are no other processes like the AFEX process” that would work, he says, on a distributed basis because, unlike the AFEX process, they all use heavy amounts of water. —Luke Geiver