When Heat Transfer International President David Prouty met gasification veteran Robert Graham, he recognized a great, but also somewhat risky, opportunity. Historically, the development of a renewable energy industry in the U.S. had not been consistent. Hot streaks of interest erupted briefly, but generally faded away as quickly, Prouty tells Biomass Magazine. “In the ’70s, people began to care about energy after the oil embargo and they spent some time in alternative energy, but interest was lost after awhile,” he explains. “So they went back to doing what they did. In 1979 to ’81, people became interested again. At that time, Bob’s work revolved around improving gasifiers for the destruction of waste. No one cared about the extra energy so they threw away a great deal of energy, but interest in those areas soon died down again.”

When Prouty became acquainted and familiarized himself with Graham’s work, he decided the third time just might be the charm. “Come 2003, I asked myself if the world would once again shy away from alternative energy and gasification and turn back to fossil fuels, or if interest would stick this time,” he says. Prouty went with his gut feeling, which was indicating to him that this time the world was finally ready to forge ahead with alternative energy.

Graham had spent the bulk of his career working in the field of waste gasification and high-temperature combustion equipment, dealing with materials such as precious metals and army munitions—things which Prouty says nobody else in the world would touch—to develop the means to destroy the products or capture anything usable in the ash. Soon after Prouty purchased Graham’s intellectual property and design rights, HTI emerged. The company moved Graham and his wife to Kentwood, Mich, where HTI is based.

At 78, senior application engineer Graham still comes into the office every day, Prouty says, and his 50 years of experience in the field has been invaluable to HTI’s growth.

SALT System Benefits
HTI is a designer and manufacturer of starved-air/low-temperature (SALT) retorts, which are biomass gasification systems that convert biomass, through a thermal process, into synthesis gas.

By properly controlling the air injection arrangement the feedstock pile temperature is kept below the sublimation, vaporizing or melting temperatures of the noncombustible solids, and at the same time vaporizes the volatiles using the energy from partial combustion of the wastes. The resulting syngas is sent to a chamber, or “low NOx (nitrogen oxide) oxidizer,” where it is combusted much like natural gas or propane and is then used to make heat, which can be converted into steam, power or hot water.

Prouty says the key benefit of the SALT system is that a hot air turbine is used instead of water for power generation. The company has a partnership with Walled Lake, Mich.-based turbine manufacturer Williams International, and has spent the past three years working with Williams to optimize a biomass turbine. The companies’ collaborative work was showcased in the fall of 2009 with the commissioning of a project at Sietsema Farm Feeds in Howard City, Mich., which now hosts the state’s first gasification plant and the world’s first hot air turbine powered by biomass.

Projects, Partners and Progress
Sietsema Farms Feeds owner, Harley Sietsema’s goal is to completely remove his operation from the power grid, with a 90 percent reduction in energy costs
The Sietsema project utilizes about 70,000 pounds (two semi-truckloads) of turkey litter a day as the fuel source. Uniquely, electricity and steam are produced at the Sietsema plant, but none of the steam is used to generate electricity—instead, 100 percent is used to soften grain that is used in the feed mill to make turkey and hog feed.

HTI also has a partnership with Morbark Inc., a manufacturer of size-reduction equipment for organic materials, to provide chipper/grinder/shredder equipment for feedstock material preparation and handling, a logistic which Prouty describes as the “Achilles’ heel” of gasification. “Feedstocks like industrial sludges, sewer sludges and municipal solid waste are complex because there is a wide variety of chemicals in them, typically a high ash content, and they are often not uniform in size, so you need to have a way to deal with those issues,” he says.

For further testing, HTI is constructing a $3.5 million biomass development center, which Prouty says will house four different styles of gasifiers and different forms of power generation. The machines will be larger than pilot scale—big enough to prove formulas for a smooth transition to full-sized machines. “What we want to be able to do is, when a customer brings in a material, we can prove out exactly what the right recipe of waste should be, and determine which full-scale gasifier will work best with it,” Prouty says. “We’ll prove the process and the air emissions, so that as they move into their permitting and design phases they know exactly how the material will perform in the gasifier.”

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