A ‘Torrefic' Energy Solution

Similar to cellulosic ethanol, there have been challenges to overcome in developing and advancing torrefaction. Now on the brink of commercialization, the thermochemical treatment process has the potential to serve as a substantial upgrade for coal and biomass combustion, co-combustion and gasification applications.
By Anna Austin
Torrefaction, a process commonly used to dry and roast coffee beans, has evolved into a promising bioenergy innovation. Traditional biomass and coal may soon be playing second string to torrefied feedstocks, if companies striving to commercialize torrefaction technologies are successful.

Torrefaction involves using extreme heat on biomass-most companies developing torrefaction technologies are currently centered on wood-in a low-oxygen environment, during which volatile organic compounds, water and hemicellulose are separated from the cellulose and lignin. These changed properties produce a fuel that is easier to transport and store and is carbon neutral.

Several companies say they will soon achieve commercialization. One of those companies is South Carolina-based Agri-Tech Producers LLC, which expects to have a torrefaction technology commercialized within the next year.

Agri-Tech Advances
According to Agri-Tech, torrefaction can overcome the challenging logistics associated with using woody biomass as an energy source. Utilizing a technology developed at North Carolina State University in Raleigh, Agri-Tech is in the midst of scaling up a torrefaction technology that the company believes is more cost effective than typical torrefaction processes.

"This process densifies, adds value to and improves the characteristics of woody biomass, making it a much better feedstock to co-fire with coal, and producing superior pellets and briquettes to use in gasifier operations," says Joseph James, president of Agri-Tech. "It also allows treated biomass to be shipped more economically, and for greater distances." Agri-Tech expects to have an exclusive license for NCSU's process before the end of the year.

Agri-Tech completed a prototype in the summer of 2008, and is now engaging outside engineering and manufacturing capabilities to scale the technology up for commercial use. "We are in discussions with companies that could potentially produce these machines for us," James says. "Everyone we are talking to says they could increase the throughput and enhance the workability of the machine-and we're hopeful that after we make an engagement, we will have machinery available for sale within six to 12 months."

James says Agri-Tech's technology is relatively simple and straightforward. "Our research shows we have fewer moving parts compared with others that are making torrefaction technologies," he says. The process is also attractive because it's powered by the products extracted from the wood, making it nearly self-sufficient. "We use some of the organic and volatile compounds in the wood-the gases-as a fuel to run the process, so it is very fuel efficient," James says. "We use very little outside fuel for the process."

Bringing the Heat
In Agri-Tech's torrefaction process, wood is heated to 300 to 400 degrees Celsius (572 to 752 degrees Fahrenheit), in a low-oxygen environment. The volatile organic compounds and hemicellulose, which are separated from the cellulose and lignin along with water, are combusted to generate 80 percent of the torrefaction process heat. The remaining warm lignin acts as a binder once the torrefied wood is pelletized.

Water removal is a key factor in the economical use of wood as a biomass source. The moisture content of fresh biomass is about 50 percent, according to NCSU and Agri-Tech. Transporting water requires 20 percent to 50 percent of the delivered cost; 10 percent to 25 percent of the total delivered cost. Water may also reduce the heating value of biomass by roughly 50 percent.

Torrefied wood is dense when it's pelletized, reducing transportation costs of the otherwise bulky material. NCSU and Agri-Tech have found that it costs 23 cents per ton per mile to transport chips and torrefied wood.

The torrified wood is also dry and water resistant because at the high temperatures used in the process, the lignin becomes plastic and is transformed into a binder for individual wood particles. In addition, torrefied wood, which has a low sulfur and mercury content and is carbon neutral, can be easily crushed and doesn't rot.

Furthermore, torrefied wood has a heating value of 11,000 British thermal units (Btus) per pound, compared with coal at 12,000 Btus per pound, according to NCSU and Agri-Tech. Similar to coal, torrefied wood generates electricity at 35 percent fuel to electricity, compared with untreated wood which has a conversion rate of 23 percent fuel to electricity.

Quantity of Customers
Although Agri-Tech is focused on supplying its technology for large, fixed facilities, it is also interested in providing mobile torrefaction equipment. "In regards to the mobile units-in terms of hurricane recovery or disaster recovery-we think we could deploy these units to areas with lots of downed trees to create value, which helps offset recovery costs," James says.

That would further expand the customer base for torrefaction, which is already considerably wide, James says. "We have several [potential customers]," he says. "One is electric utilities which currently burn coal. Typically, coal is pulverized. The material we produce will crush just as easily as coal and at the same particle size that coal is normally crushed to, for that same purpose."

Other customers, are those who are already involved in the pellet-making business, according to James. "Those customers are currently making pellets for U.S. consumption and for export," he says. The third customer group, although small, are companies that are making cellulosic ethanol using gasification processes. "We think that will grow in the future," he says. "Some are telling us that torrefied material is a superior feedstock to them, over and above the raw wood and raw cellulosic material; it's drier and it has more carbons available for conversion. Now we now think there are other applications as well."

When it comes to competition, James says he's not aware of any commercial torrefaction plants operating in the U.S., although many companies are developing research and working toward commercialization.

In addition to wood, the company is also torrefying switchgrass. "We've been working with one of the largest switchgrass producers east of the Mississippi, and look forward to continuing that exploration of switchgrass as a source of torrefiable material," James says. "We're also looking at other biocrops, which are not food crops. We think that in addition to wood, these are the feedstocks of the future, along with other cellulosic material."

Although torrefaction may be new to some, it is really an old process that researchers are breathing new life into, James says. "Torrefaction research is old-30 to 40 years," he says. "Similar to other research, such as biodiesel, it was sort of shelved when the not-so-renewable alternative fuels were entering the marketplace. We are looking for innovations to that basic research to make it a competitive process."

Anna Austin is an Biomass Magazine staff writer. Reach her at aaustin@bbiinternational.com or (701) 738-4968.