Research identifies processes and factors to produce best biomass pellets.
Small scale pelletizer machines are available on the market today that are intended to produce “biomass pellets” that are ready for use. These pellets can be used as a combustion fuel or as a feedstock to be converted to biofuel. However, successful operation of these pelletizer machines has proved to be somewhat problematic, i.e. with operations being characterized by poor pellet quality and/or chronic plugging of the device’s extrusion die.
Creating high quality pellets is more of an art form at this point rather than an exact science. At Penn State, we are working to help farmers and small operators to understand how to successfully produce high quality pellets from crop residues, perennial grasses, and other readily available biomass feedstocks. We are doing this by testing small scale pelletizers using a variety of feedstocks and operating conditions, and looking for the key characteristics that control pellet quality. In this way, we will be able to take some of the guess work out of the process and make it a little more of a “science” than an art. We’re also working to develop estimates of labor and energy budgets to run a pelletizer for these small scale operations.
2012 Summer Report - Purpose: to determine the most effective running conditions for a small scale pelletizer that creates pellets made primarily of switchgrass. The two characteristics monitored were overall pellet quality and the tendency for the die to plug. The factors investigated for their effect on pellet quality and die flow are: die temperature, speed of machine, moisture content, feed rate, and additives such as distilled dry grains, canola oil, and cornstarch. These factors were varied over the course of testing and the resulting pellet quality and tendency to plug were evaluated.
Results suggest that higher quality pellets occur if you run the machine at half speed and use two separate mixes; the initial mix having switchgrass mixed with DDGs at a ratio of 3:7; test mixture containing switchgrass with a moisture content between 11 and 16 percent and 1-4 percent canola oil.
2012 Fall Report - Purpose: to determine the optimal conditions for feedstock made primarily of switchgrass for use in a small scale pellet mill. The variables that were considered were moisture content of the feedstock, canola oil concentration, and distiller dried grains (DDG) concentration. These variables were each tested for two different size grinds of base switchgrass material. The quality of the pellets that were made as well as the tendency of the die to plug was measured on a subjective scale.
Results suggest that the pellets are made most effectively when a two phase approach is used, incorporating the use of a plugging mixture followed by input of the material to be pelletized. The best pellets were made using the more finely ground material at a moisture content of 15 to 20 percent, with the addition of about 1 to 3 percent canola oil.
2013 Spring Report - Purpose: to investigate the impact of feedstock properties on densification performance of a small scale pellet mill. The variables studied were two grind sizes of the base switchgrass material and moisture content of the feedstock. The quality of the pellets was assessed subjectively using a referenced numerical scale, as was the tendency of the die to clog. Power usage was measured for feedstocks of several different moisture contents.
It was confirmed that the moisture content of the feedstock was the variable with the most significant impact on pellet formation, and that a range of 15-25% moisture resulted in the highest quality pellets and least tendency for the die to clog. Preliminary results indicate that pellet quality is positively correlated to power consumption.
Many farmers and entrepreneurs are interested in producing biomass fuel pellets from crops like switchgrass, miscanthus, or other biomass. Not only is this a valuable market opportunity, it also allows producers to be more energy independent by growing and processing their own pellet fuel.
Our results will help to make pelletizing readily available to those who are looking to make the switch and go green by using alternative and renewable energy to effectively heat their homes and other needs. This project is supported by a grant from the Northeast Sun Grant Initiative
As we continue to test and develop recommendations for creating ideal pellets we will publish them on the project website: Penn State Pelletizing Biomass.
Scholars in the Penn State Department of Agricultural and Biological Engineering: Clay Swackhamer, Brian Wright, Ryan Hilton, Drew Swomley, Brian Gray, and David Rooney.
This report is not peer-reviewed and the researchers have sole responsibility for the content.
This research was initiated with funding from the Northeast Regional Sun Grant Center at Cornell University through a grant provided by the US Department of Transportation, Office of the Secretary, Grant No. DTOS59-07-G-00052.