Company builds ‘Grassifier’ prototype

By | October 26, 2010

A Buffalo, Minn., company wants to scale up a residential-sized biomass energy system and develop turn-key power plants that could supply grid power and hot water for space heating, process heat or other applications.

Development of the “Grassifer” began about two years ago, when Mel Moench, president of Moench Inc., became interested in combusting biomass—in particular, warm season grasses.

Moench determined that the major challenges for biomass combustion systems was moisture content, particle size and efficiency. “I decided to eliminate the densification process and combust the material without preprocessing, to save energy,” he said. “I wanted the unit to be automated, compact and highly efficient.” 

Moench also sought to eliminate any special equipment needed to prepare the feedstocks for combustion. “We’ve combusted grassy materials with moisture content of up to 25 percent, which is close to ‘as harvested’ condition,” he said. “Our unit also contains a cyclone to extract excess water vapor in the flue gas.”

After three prototypes and scores of modifications, Moench completed a unit that achieved two of his top priorities—reaching more than 1,850 degrees Fahrenheit consistently, and overcoming the issue of grate clogging by using a patent-pending, grateless configuration. “I also had to use a proprietary fuel feeding system that virtually eliminates issues with fuel compaction and subsequent auger jamming,” he said. “The prototype can also utilize multiple, dry coarse-chopped materials interchangeably.”

After the chopped biomass is conveyed to the in-feed auger, it drops into a screw auger and is pushed into the combustion chamber as needed to maintain the proper temperature. Negative pressure is supplied by a vacuum blower so no smoke or gasses escape, and primary and secondary burning occur at a high temperature, ensuring the complete combustion of all particles and gases. While the ash continues forward and drops into the ash collection drum, the hot gases leave the heat containment chamber and enter the heat exchanger that transfers the heat to the antifreeze solution surrounding the tubes. A circulating pump keeps the hot antifreeze solution moving through insulated underground pipes to a plenum heat exchanger, baseboard unit, in-floor radiant tubing or other heating systems.

Moench said that although his company believes the Grassifer is technologically and environmentally advanced, it is a working prototype at this point. “We’re searching for partners to continue improvements and other applications, including sizing up the unit for trigeneration, district heating or combined-heat-and-power applications,” he said.