“There’s a big difference between a pilot plant and a commercial demonstration facility,” says Brian Appel, chairman and CEO of New York-based Changing World Technologies Inc. (CWT). CWT has developed one of the few waste-to-energy technologies to reach the commercial level, but commercialization is just one of many factors that distinguish this company. The company was named to Scientific American’s 50 in 2003 in the energy category for its work to devise a method of turning solid waste into oil.
CWT’s process sets the company apart from the rest of the pack. Many waste-to-energy technologies successfully produce electricity and methane by using a form of combustion. CWT’s thermal conversion process (TCP), patented in 1993, is unique because it successfully recaptures the hydrocarbons and converts it into a renewable fuel without producing emissions.
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In the process, organic waste material is converted into renewable diesel, solids and specialty chemicals. The renewable diesel is different from biodiesel because it doesn’t contain alcohol. The process applies indirect heat and high pressure to emulate the Earth’s geothermal process of converting organic matter into fuel. Thus, instead of changing the chemical composition through incineration, it simplifies the existing complex polymers into their smallest units, which can then be converted into new fuels.
Here’s how the TCP works. The feedstock is first prepared with water and ground into slurry. The slurry is preheated to reaction temperature using high-pressure steam energy. Appel says the use of pressure makes the process efficient, with a net energy balance greater than seven. The heat comes from a boiler, which is powered by renewable diesel produced at the plant. The boiler heats water, which is contained in large pressure vessels.
The process is efficient because the water isn’t allowed to vaporize. “It doesn’t take a lot of energy to heat water up to the boiling point,” Appel says. “It takes all the energy to cross that threshold from the liquid to the vapor phase, where you’re constantly losing that energy to that vapor phase when you make steam. Instead of spending all that energy evaporating the water, we use it as part of the process.”
Keeping the water under pressure enables the boiler to heat the water up to 500 degrees Fahrenheit, which creates 600 to 700 pounds of pressure. “Once you’re done cooking the material—when you let that pressure down—you get all of that energy released in the form of steam, which is used to preheat the incoming material,” Appel says. “So not only are you not wasting energy evaporating off water that’s in everything, but you’re also then using that high-value steam as an energy source."
From the preheating treatment, the slurry is placed into a depolymerization reactor, where high pressure and heat separate out the bulk of the inorganic material. That organic material is then subjected to even higher temperatures and pressures in the hydrolysis reactor. Here, the water acts as a hydrogen donor to further break down complex molecules into shorter, useful and similar hydrocarbon molecules.
Finally, the molecules are separated into gases, renewable diesel, water and remaining solids. “After you go through the hydrolysis reactor, you then go through a series of polishing steps that are filters, dehydrators and normal steps that would be at a typical refinery to meet final product specification,” Appel says.
Because the TCP doesn’t incinerate or combust the waste, it doesn’t produce harmful emissions. “Whatever is in the material is going to come out in its elemental form as a hydrocarbon,” Appel says. “The typical bad actors we associate emissions regulatory policy around usually are from incineration- or combustion-type technologies.” Chlorine, for example, isn’t bad in itself, but when it’s exposed to an open flame, toxic complex chlorine compounds are formed. Because nothing hits an open flame in the TCP, no such emissions are created.
The process is currently being used at CWT’s commercial demonstration facility, Renewable Environmental Solutions LLC (RES) in Carthage, Mo. The facility, developed in partnership with ConAgra Foods and commissioned in 2004, processes agricultural waste—mostly turkey fat, bones and feathers. It has a nameplate capacity of 8 MMgy but is currently producing at approximately 70 percent capacity.
Though Appel says the fuel has performed well in blendability tests, the company isn’t selling to the blend market at this time. RES diesel is used unblended in commercial industrial boilers within 100 miles of the facility. “We don’t need a lot of customers because these are large boilers,” Appel says. A customer with a 1,500-horsepower boiler uses more than 2 million gallons of fuel per year to make steam.
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