Practice Makes Perfect

Texas company embarks on second AD project.
By Anna Austin | January 25, 2011

Hoffland Environmental Inc. has operated a 1-megawatt (MW) hog waste-fuelled power generation facility on the Island of Cyprus in Europe for the past three years. Marking the company’s U.S. debut is a second anaerobic digestion (AD) project currently underway in Fremont, N.C., near Goldsboro at White Oaks Farm.

Chemical Engineer Guy Weismantel says the 10-acre farm site hosts about 5,500 pigs, but manure from that operation alone will not be enough meet the electrical capacity goal of 2 MW without supplementary poultry waste or manure from nearby farms. Corn silage was originally considered as a partial feedstock, he adds, but is currently too expensive.

Hoffland is now working to firm up the feedstock requirements of the project, which will be implemented in two phases—first producing 1 MW of electricity, the second doubling capacity to 2 MW. Weismantel says when evaluating feedstock requirements, it’s not only necessary to look at the number of animals in an operation, but also the kind and size of animals, such as farrow-to-wean. “Animal units are important to consider,” he says.

A power line going through the project site belongs to an area power cooperative, with which the company is working to sell all of the electricity to the grid, Weismantel says.

On incentives, the $15 million project is subject to receive renewable energy credits under the state’s renewable energy and energy efficiency portfolio standard, but Weismantel says the main driver is North Carolina’s Senate Bill 3, requiring 12.5 percent renewable electricity by 2021; 0.2 percent of that amount must be generated from swine waste by 2018, after rising each year prior. “For the whole state of North Carolina, that amounts to about 14 MW in 2011,” Weismantel says.

Hoffland has also applied for Section 1603 funds, as the project qualifies as an open-loop biomass project.

Weismantel says that what sets Hoffland’s AD process apart from others is that it’s a unique, three-step process that involves a certain amount of recycling of “seed bugs” that optimize the mesophillic reaction. “So we are getting more biogas off the digester,” he says. “This gas is methane in nature and is nominally 600 Btu per cubic foot in heating value.”

There are a number of additional aspects that sets the process apart from other AD technologies, such as the sulfur removal system, which is undergoing patent writing, Weismantel says. “HEI fabricates much of the equipment in its own shop utilizing and maximizing clarifier performance, manure handling, manure measurement and key process control functions that interface simplified on-line measurements to optimize performance.” 

He adds that hardware and process performance complications have been ironed out during the three years of performance at the Cyprus plant. “It has provided an excellent learning curve,” he says.

—Anna Austin