As one of the world’s largest producers of carpets and, not surprisingly, one of the largest producers of carpet waste, Shaw Industries Inc. faced rising energy and landfill disposal costs. In the late ’90s, the Dalton, GA-based company began searching for alternatives. After years of failed research and experiments, a partnership between Siemens Energy and Environmental Solutions (Siemens Building Technologies Inc.), and Primenergy Inc. found a profitable answer.

Primenergy’s gasification equipment supplies the key component of the system. The Tulsa, OK-based company specializes in the engineering and construction of turnkey energy conversion and recovery facilities. Gasification recovers energy that can create heat, steam, and electricity. Commercial systems vary in size and purpose, converting from 70 to 550 tons of biomass per day—providing hot air for drying or steam for various process applications including the production of up to 12.8 MW of electricity.

“It’s a patented process, but we’re not saying it’s a black box,” explains Clark Wiedetz, Siemens business development director. “Folks have been trying to burn carpet [unsuccessfully] for years, but in essence it is somewhat of a petroleum product, and part of the engineering was finding an environmentally friendly process.”

Although Wiedetz uses the term “burn,” the carpet scrap isn’t thrown to the flames. Instead it’s heated to a temperature of 1,400° F in a sub-atmospheric chamber. The gasifier acts like an oven, and once the carpet ignites it becomes a self-fueling process that produces gas and a low percentage of ash.

“You could say it’s carpet fusion,” adds Wiedetz, “but you are converting it into a synthetic gas, plus an ash byproduct.” The ash varies in volume from 5% to 10% of feedstock volume and traps the nitrogen and sulfur pollutants. Still, the gas has enough reactors in it to earn the designation of “dirty.” It would require a scrubbing process if Shaw wanted to use it to generate electricity with a turbine, but no special handling is needed to burn it in a waste heat boiler.

For Gary Nichols, Shaw’s corporate energy manager, Siemens’ gasification idea sounded like the perfect solution to years of searching—if the process succeeded where others had failed. “It was a frustrating search, and I was about ready to give up,” recalls Nichols. “I looked at boilers for a long time, and the industry has been working on them for years, but boilers have problems with carpet and the emissions are really bad, so it’s hard to get them permitted.” Wiedetz and Nichols visited Primenergy’s demonstration facility to see how the process worked and if it would meet emission standards

Primenergy has tested more than 25 different feedstocks. Some are recognized as the most difficult for energy conversion, such as rice hulls and straw, sugar cane bagasse, tire-derived fuel, refuse-derived fuel, paper-plant pulp sludge, and sewage sludge (biosolids). For all biomass materials tested, the process required no auxiliary fossil fuel to maintain continuous operation. And the same was true for the carpet scraps. “Carpet has a high thermal value and once you get the gasification started it supplies 100% of thermal power with no auxiliary fuels introduced,” says Bill Scott, president of Primenergy.

The demonstration showed that carpet also burns clean enough to meet EPA standards, as confirmed by a third-party company that conducted stack compliance testing in accordance with USEPA test methods and reporting protocol. The fact that the system had no problems gasifying wood byproducts was an additional bonus. Shaw owns a wood processing plant for making laminate flooring and creates plenty of “wood flour” that it formerly paid to have disposed of in landfills.

Next came an unusually long but necessary preconstruction phase. Siemens and Shaw spent about five years in planning and development, according to Nichols. “We tried to solve as many of the problems up front before either of us committed to spending the money putting the effort into it.” Most of the focus was on getting the carpet scraps into a form that would feed into the gasifier.

“Carpet is funny,” notes Nichols. “We make the carpet and yarn so it will tend to stick together. But that’s not what you want when you shred it and transport it.” The wood flour had similar problems. It changes density quickly and can easily double from 20 lbs per cubic foot to 40 lbs per cubic foot just from being trucked 20 miles. “It’s not a problem in transit, but the density of material going into the gasifier changes your energy specification feed rate,” explains Nichols.

Changes to the discharge chamber under the carpet silo and the auger that moves the scraps solved part of the problem. Next, the feeder’s conveyer and controls were modified to better regulate the feedstock entering the heating chamber. Nichols wasn’t surprised by the feeder problems, but he was surprised by the lack of problems in constructing the plant.

The facility went up in 16 months and construction stayed on schedule. It was an impressive feat, considering the amount of work. The project required a 10,000-square-foot building to house the carpet shredding equipment. Four silos were needed: one each for feeding carpet fiber, carpet backing, and wood flour, and one for capturing the ash. The system feeds about 80 to 100 tons of feed per day into Primenergy’s
gasifier.

The synthetic gas travels to a waste heat boiler that Wiedetz describes as “just a little different from a standard package boiler.” He notes that though it’s a custom design, there’s a wide choice of such boilers on the market and finding a match isn’t near as intricate as choosing gasifier.

The boiler creates 50,000 lbs of steam per hour, enough for 80% of the plant’s color-dyeing needs. “The reason it’s 80% is to keep the system base-loaded and to avoid handling peaks and valleys,” says Wiedetz. The plant also was designed to operate at a minimum level of staffing.

According to Wiedetz, the entire operation should require a maximum of two people to monitor the boiler and feeding activities. “We know of systems similar in size where they need six to seven people doing different things, but that’s a deterrent. One to two people per shift is reasonable for a company and part of the savings equation.”

Speaking of savings, Siemens and Shaw are predicting energy cost reductions of up to $3.5 million per year. With a total investment estimated at $10 to $15 million, the payback could come in less than five years. Moreover, it’s done without any state or federal subsidies. Shaw is leasing the plant from Siemens, and buys the energy at a fixed rate. The gasified energy has a lower emissions value and the company plans on selling the ash byproduct as filler for road paving material, and other uses.

According to Nichols, the financial benefits of gasification will make the facility the most economical in Shaw’s chain of 15 factories. “We will take the process to other plants,” says Nichols. “The only problem right now is that this plant will use all of our post-industrial carpet waste.”

Nichols expects the waste to increase when Shaw acquires another factory in the Augusta, GA, area. And now that Shaw is sold on gasification, the company has plans to buy oil from an independent gasification plant that uses automobile tires for feedstock.

As for Siemens, Wiedetz already sees many opportunities coming from the Shaw project. “Energy prices are driving the need,” he notes, “and if companies are looking at their fuel possibilities, we can help them from an economic, environmental and marketing perspective.”

ED RITCHIE specializes in energy, transportation, and communication technologies.

DE - July/August 2006