From Fluff to Fuel
Most people looking at the mountains of municipal solid waste (MSW) being generated these days view them as problems that should be dealt with as cheaply as possible. A quality end product is not as important as making the waste go away, according to Mark Brown, CEO of WastAway. “We take the opposite approach,” he says. “Our goal is to have a high-quality fuel and we ask, what amount of processing makes sense to get the high-quality fuel we desire, and we can sell?”
At WastAway’s facility in Morrison, Tenn., raw MSW is sorted and preprocessed in much the same way as other MSW systems, utilizing magnets, eddy currents and shredders. WastAway takes it another step. “A key part of our technology is our continuous flow hydrolyzer. It’s similar to the autoclaves they use in Europe, but they tend to be batch units,” Brown says. The hydrolyzer heats the material to about 350 degrees Fahrenheit at pressures of 125 PSI. “The material comes out sterile, so all the pathogens and odors are destroyed in the heating process,” he explains.
The refuse-derived fuel (RDF) also undergoes a physical change. What starts out as MSW shredded to an inch or less, is exposed to heat under pressure which is then quickly reduced. “It implodes the material and we end up with an intermediate material we call Fluff,” Brown says. The appropriately named and trademarked Fluff looks like cellulose insulation and is easy to pelletize, he adds. “We’re taking it down to extremely fine and consistent particle sizes so we can run it through a conventional pellet mill to make high quality pellets.” The Btu content is between 8,500 and 9,000 Btu per pound and moisture content is below 10 percent. The hydrolyzing process creates hygroscopic pellets that will not absorb atmospheric moisture, although they can’t sit in water and do need to be protected from rain.
The WastAway process is not new. “We’ve been processing Fluff here in Tennessee for 10 years and we have a plant on the island of Aruba,” Brown says. “We’ve taken in waste from literally all over the world for test runs. What all of that testing has shown is that, regardless of where the waste comes from, Fluff is extremely consistent in Btu content and moisture content. Any concerns about heavy metals or bad actors are all extremely similar, regardless of where the household garbage is collected.” While metals, glass and stones are removed, plastics are generally left in the fuel, at least until market prices make plastic recycling economical. With the main concern being the chlorine content of RDF, WastAway’s research has shown the biggest source of chlorine in RDF fuels is not plastics, he adds, but rather food waste. “Common table salt contributes more than the PVCs do.” WastAway-engineered pellets are lower in chlorine content than other RDF-sourced fuels, although higher than wood or coal and the ash content is typically 10 percent, lower than most RDF and comparable to most coals.
CanmetEnergy, the research arm of National Resources Canada, has taken a close look at the pellets’ potential for displacing coal in a report titled, “Co-firing process engineered fuel with high vale coal—combustion characterization and analysis.” The report finds that engineered RDF pellets could replace up to 10 percent of the thermal content at a coal-fired power plant, with no change in operations. CanmetEnergy estimates the greenhouse gas savings to be 2.75 tons CO2 equivalent per ton of coal displaced, mostly due to the avoided methane emissions from not landfilling the material. Methane is 25 times worse for atmospheric warming than CO2, Brown explains.
While WastAway has 10 years of experience with making Fluff, most of the production to date has been used by a horticulture supply company owned by parent company Bouldin Corp. as an amendment for potting soil. The company first developed its pellet product five years ago, just in time for the economic turndown that dried up project development. That has changed in the past 18 months, Brown says, along with greater interest in finding coal alternatives. In addition, new European and U.S. standards are facilitating supply contracts. “Users can now define the parameters of the fuel they’re purchasing,” he explains.
For the past year, the company has been making pellets for large-scale test runs at power companies and cement plants and other facilities using large amounts of coal. One such project in Alberta is close to being finalized. A proposed $22 million project to implement WastAway’s system at the Drayton Valley municipal landfill site has already received a $10 million grant from Alberta’s Climate Change and Emissions Management Corp. If the remaining details can be pinned down and the project given the final go-ahead, Brown expects the Drayton Valley project will be the third commercial installation of the WastAway process. In addition, there are a half a dozen domestic projects actively under development, as well as several in Europe.
“If you’re looking at a facility processing 200 tons per day of waste, the all-in capital cost for buildings and equipment will be around $20 million,” Brown says. While tipping fees and coal prices vary dramatically across regions, “In the majority of the U.S. and majority of international markets, we can compete favorably and give either the community or the third party an economic return on investment.”
Author: Susanne Retka Schill
Senior Editor, Biomass Magazine