California cement plant uses biomass with coal in kilns

By Lisa Gibson
Mitsubishi Cement in Lucerne Valley, Calif., has acquired a Rawlings Manufacturing Wood Hog, enabling it to use both coal and biomass in its cement kilns.

The wood waste recovery system will use construction waste, according to Judi Tyacke, Rawlings Manufacturing, as Mitsubishi's location makes other feedstocks difficult to procure. "They're in the middle of the desert," she said. "There isn't a lot of slash, so they're using construction wood waste." Rawlings has been making and selling the wood hog design for 30 years, according to Tyacke. It can reduce various types and sizes of wood waste to biomass fuel six inches or less in size, she said. Once the wood has been processed through the hog, the metal is removed by an overhead self-cleaning magnet and conveyed to a moving floor stoker storage system, according to Rawlings. To ensure optimal size, the wood is then processed over two vibrating finger screens and transferred to the kilns by a blower system.

The wood will already be ground when it's shipped to the company, Tyacke said. Mitsubishi is working toward a 50:50 coal to biomass ratio, according to Scott Smith, plant manager. The system has been operating at the plant for about a month, he said.

Rawlings is developing a railroad tie separator to expand the types of biomass feedstocks that can be fed into the wood hog, Tyacke said. Ties would have to be ground before being put into the wood hog system.

"We're hoping we can do this at quite a few more cement plants," Tyacke said. A study conducted by scientists in Spain showed using biomass in cement kilns decreased the carbon dioxide emissions by 144,000 tons between 2003 and 2006, according to a journal article written by the researchers. The study evaluated the effects of using sewage sludge to generate 20 percent of the thermal energy needed in the cement manufacturing process at a plant in Vallcarca. Smith said the system will reduce carbon dioxide emissions at the Mitsubishi plant, but didn't have specific amounts to cite.