They call her Miss Piggy.
About the size of an SUV, the metal and white refractory brick structure sits on a concrete slab behind the research facilities off Lake Wheeler Road.
She was built to convert materials to energy by burning them at temperatures between 1,000 and 2,000 degrees. Technically, “she” is a gasifier.
“Whatever you can fit in that chamber you can gasify. The mafia would have loved that machine,” R. Preston Burnette said with a laugh.
The project engineer for the Department of Animal Science reaches into the square chamber and picks up a handful of fine white ash — once turkey bone — now sterile and soft. He sifts it between his fingers, and patiently explains the ins and outs of the contraption. Burnette and others at the Animal and Poultry Waste Management Center are working to give agricultural waste like pig manure, chicken litter and scrap wood a place as feedstock in the production of energy — with help from machines like Ms. Piggy.
As feedstock, or raw material used for processing or manufacturing industry, these products which were once waste could become, instead, profit. And that profit would not be contained within the farming community.
Agricultural biomass is a relatively untapped energy source in North Carolina, and through temperature controlled cooking processes such as gasification, researchers like Burnette and Chris Hopkins, outreach associate for the Department of Forestry and Environmental Resources, plan to utilize this supply. And they hope to make the environment a little cleaner along the way.
“People have called [N.C.] the Saudi Arabia of biomass. We have more biomass here than anywhere in the country,” Burnette said. “We have a lot of animals, we have a lot of manures, we have a lot of agricultural crops and we have a tremendous source of wood.”
But Burnette doesn’t mean chopping down standing trees for energy, he means using the leftover tops, wood chips and branches of trees that have already been harvested for lumber and other purposes. According to Hopkins, the research they are conducting is different because so much of the discussion of biomass energy is in regards to growing and using dedicated energy products, such as corn, switchgrass and woody crops.
“Some of the technologies overlap, but it’s a whole different mind set,” Hopkins said. “What we are talking about at this [research] location is almost uniquely waste products and getting energy out of the waste products.”
These waste products are leftovers farmers have to dispose of anyway, and by using existing waste rather than forcing a huge change in crop growth specifically for energy production, farmers aren’t required to choose between growing foodstuff and growing feedstock.
“In those cases the energy crop has to carry all the freight, all the expense, all the financial worries, from a farmers point of view,” Hopkins said. “They don’t have any other options, they have to sell it for energy. What we’re providing is another revenue stream on top of what people already have.”
And some of the methods they are using to convert this waste into energy, methods like gasification and torrefaction, are processes that have been around for quite some time. Patents for torrifiers, which are also used in coffee bean processing, go back to the early 1800’s, and gasifiers are already being used in power plans to process coal.
Not quite combustion
More efficient than direct combustion, which occurs above 2,000 degrees Farenheit, gasification takes place between 1,000 and 2,000 degrees, and can occur with or without oxygen present. It is a method of burning the material lower and slower, so that actual combustion never takes place and all of the elements can be retrieved and utilized.
Burnette likened the process to putting wood chips inside a pot on the stove and creating a tiny hole in the top to allow the gas to escape. As the wood heats, the gas, such as hydrocarbons and methanes, burns off. Once all the gas has burned off, all that’s left in the pot is a little bit of carbon and sterile mineral ash.
Gasifiers recreate that process in large scale, with a variety of feedstocks. Gasifiers can process anywhere from a few hundred pounds a day to a few tons, and Burnette said the processors themselves differ based on the needs of the user.
Batch gasifiers are capable of handling different feedstocks, but can only run one batch at a time. They must be shut down before being reloaded. Continuous feed-type gasifiers can only process one type of feedstock, but are capable of a continuous run cycle. Continuous batch gasifiers have a series of chambers, each of which can be loaded with a different feedstock every thirty minutes.
“Heat something up, vaporize all the organic material,” Burnette said. “How you get that or how you do that or what you do with the gas afterwards is what makes each gasifier different.”
Cooking wood like coffee
Torrefaction is essentially the process of cooking wood, and is more of a conversion of energy than a creation of it, according to Burnette. This process occurs below the 2,000 degree mark with no oxygen present, and eliminates excess water from the feedstock, allowing for cheaper transportation and consolidation of energy.
“Water is always almost a burden. It’s a heat sink,” Hopkins said. “It’s a huge problem all the way through the process. Anything you can do to get the water out of the system early, earlier is better.”
According to Hopkins, it takes about a quarter of energy content to turn water into steam and then send it up the stack. That’s a lot of wasted energy when the feedstock being processed is wood.
“Wood, when it’s fresh cut, is about 50 percent water. So you’re spending a lot of fuel hauling water down the road, which does you no good,” Burnette said. “If you can employ at torrefaction system, which would get the water out and turn the wood into coal substitute, now you’re hauling energy down the road, not water.”
Wood is very fibrous, and because of that can be hard to process. Torrefaction breaks the glue that holds the wood together, and the charcoal created by torrefaction can be burned in place of coal, creating a cleaner burn.
“Now coal plants won’t have to do anything but empty one of their fuel bins and place this in it,” Burnette said.” It’ll burn just like coal, essentially, with nearly the same energy content. its a way to better utilize the waste biomass that we have.”
The direct path to energy production
Another reason these processes work well for agricultural waste is that they allow researchers to bypass the biofuel stage, simplifying the system by converting the feedstock directly to a synthetic gas which is then turned into thermal energy. According to Burnette, agricultural waste, when gasified, produces a syngas that is harder to clean for biofuel production.
“You would spend a lot of money on cleaning up your syngas to create ethanol, so we decided to drop the ethanol and go with just direct energy like electricity or steam,” Burnette said.
So instead of collecting the syngas to create those fluids, researchers are combusting the gas directly into the system, heating it and keeping the system running on it’s own energy. That heat produced can create hot water, steam for processing and elecricity.
The big picture
By effectively recycling agricultural waste products, farmers could eliminate the cost of removing those wastes from their property and help sustain their own land.
“Imagine if you got all the energy out. Farmers could provide 20 or 30 percent of their own energy on a farm,” Burnette said.
According to Burnette, the average small chicken farmer in the area owns four to six barns and spends anywhere from $4,000 to $6,000 to heat a single barn. Just by putting a gasifier on the property and processing the chicken litter and mortalities they could offset at least one barn, saving the heat cost as well as the cost to safely eliminate the chicken waste.
And gasification is such a sterile process, it would help reduce unnecessary harm to the environment.
“It’s just one more step toward making our environment cleaner, and putting more money in these peoples pockets and helping the economy,” Burnette said.
The cost of energy has been consistently increasing, and according to Burnette that isn’t going to change anytime soon.
“Our parents’ generation, they were very fortunate to have cheap energy. Our generation will not be so fortunate. So we’ve got to find alternative sources of energy,” Burnette said. “Now are any of these technologies the end all be all, this is it, this is our solution? No … but combined, they can help.”
