Generating electricity from biogas is more difficult because constituents of the gas, such as hydrogen sulfide, are particularly corrosive. It is possible to clean up the gas by removing the hydrogen sulfide by exposing it to iron oxide (a process called hydrodesulfurization). The biogas can then be burned to produce electricity in generators such as the GE Jenbacher engines that Huishan uses. These engines have been modified to burn at compression levels particularly suited to biogas, and they have special coatings that resist corrosion.
Less than 1 percent of the dairies in the United States capture methane. Part of the challenge is scale. According to Don Wichert, director of renewable energy programs at Wisconsin Energy Conservation Corporation, producing electricity from biogas at a farm with about 100 cows costs twice as much as producing it at a farm with over 2,000 cows. Huishan is gathering manure from 20 farms located close together near Shenyang, China, to feed into massive digesters. Thomas Elsenbruch, marketing program manager for Jenbacher engines at GE, says larger systems can supply enough gas for a one-plus-megawatt engine. Such engines are more efficient than the 300- to 500-kilowatt systems used in many farms in Europe or the U.S.
But many other barriers remain, including a lack of capital investment. There are also few detailed models of the economics of using biogas systems at farms of various sizes that also have different feeding methods and manure-management techniques, says Ann Wilkie, professor of environmental microbiology at the University of Florida.
Regulations have also gotten in the way. In California, biogas generators funded since 2001 with government support were shut down last year because they produce too much nitrogen oxide (also called NOx).
Another major barrier is a lack of education about the possibilities of biogas, Wilkie says. The new project could draw attention to a technology that is long-overdue for wide deployment, she says. “It shows this is not a phantom technology we have to wait for in the future,” she says. “It’s something we can do now to deal with existing waste, and garner renewable energy.”