Efficient On-Site Densification of Biomass

The goal of the Wisconsin project is to develop a one-pass biomass field machine that will both harvest a crop and produce a biomass cube. At the moment, most biomass is harvested by farmers and then transported to regional centers for further processing and densification. These centers may pellet or cube the material. The advantage of a one-pass, in-field machine is that biomass doesn't have to baled, which saves both energy and time. Also, a regional processing center won't have to de-twine the bales before processing. _USAgNet

The energy density of biomass is significantly less than that of coal or petroleum. If biomass energy is to become economically competitive, better ways of densifying biomass must be devised. Scientific and engineering personnel from the University of Wisconsin and Mississippi State University have teamed to develop machinery that can harvest and compress biomass in the field -- in a single pass. But there are significant challenges that must be overcome.

Since biomass cubing requires substantial horsepower and energy, it reduces its appeal as a renewable energy source. One of the main interests that the coal industry has is reducing its carbon footprint. Cofiring with biomass that requires significant energy to produce doesn't help the coal industry realize this goal because all energy expended in production is counted.

Moreover, biomass has several other limitations when compared with coal because cubes are not a perfect replacement. While coal contains 12,000 British thermal units (Btu) per pound, biomass alfalfa cubes only contain 7,350 Btu. Biomass cubes also are less dense. Therefore, they are more bulky and expensive to haul long distances. Finally, biomass cubes have a tendency to break apart. This makes handling the cubes with traditional coal industry equipment problematic.

Cubing technology is part science and part art. Biomass cubes are formed under high temperatures and pressure. In fact, the Wisconsin research team found that the temperature of the alfalfa was raised to near the boiling point of water while it was being processed. To start cubing, the John Deere machine had to "warm up." Generally, it took about 20 minutes of operation for the machine's internal temperature to rise enough to form stable cubes.

Another challenge is the moisture content of the alfalfa. The cubing operation requires that the biomass be as dry as possible. However, letting alfalfa lay outside increases the risk of rain damage and deterioration.

The Wisconsin and Mississippi research teams are confident these issues can be overcome. They are in the process of designing new equipment prototypes that are more tailored to cubing and densifying biomass instead of alfalfa _USAgNet

Various methods have been proposed for using sunlight to substitute for fossil fuels in the drying, densification -- and even gasification -- of biomass.

It is also likely that biomass "cubes" will have to be graded and priced according to energy density, moisture content, etc. as well as mass. As thousands of rural communities adapt to the coming biomass economy, there will be a significant spread in terms of quality of biomass. In each region, particular entrepreneurs are likely to stand out as providing the highest quality biomass feedstock for biofuels production or co-firing with coal. Those biomass entrepreneurs will likely become regional financial tycoons.

Biomass energy promises to help to rejuvenate rural and semi-rural economic localities and regions across Europe and North America. The potential is there to do the same for South America, Asia, Africa, and all the world's tropics and temperate areas -- if the rampant corruption in those areas can be moderated.