Courtesy of Mark Severy and Schatz Energy Research Center
The Biomass Research and Development Initiative (BRDI) Waste to Wisdom project is studying various pathways to increase the value of forest residuals and decrease transportation costs to bring this underutilized resource into the renewable energy market. Densifying waste biomass into briquettes during forest operations may achieve both of these goals by converting it into a valuable heating fuel that is easily transported due to its high density and low moisture content.
[In April 2015], SERC engineers, alongside partners from Pellet Fuels Institute and RUF Briquetting Systems, operated a commercial briquetter with a variety of feedstocks at Bear Mountain Forest Products’ manufacturing plant in Cascade Locks, Oregon. Electricity consumption and biomass throughput data were collected in the field, while a pallet containing feedstock and briquette samples was shipped to SERC for material analysis. Back at SERC’s lab, the samples were sent through a suite of tests to assess the quality of each briquette and determine which feedstock properties influence the end product’s characteristics, such as density, durability, grindability, and moisture absorption.
Results show that this briquetting system increases the volumetric energy density of chipped biomass by nearly 250%, producing briquettes with an average packing density of 720 kg/m3. Feedstocks with moisture content exceeding 15% produce lower density briquettes, which expand in height after exiting the briquette press. High moisture content, however, does not significantly impact briquette durability. Instead, the feedstock’s particle size distribution has the greatest effect on briquette durability. Feedstocks comprising mainly large particles, especially chipped biomass, do not bind together as well as fine or ground particles. To improve durability, chipped biomass can be combined with sawdust, which increases briquette durability two-fold and results in briquettes with a binding strength similar to those produced from pure sawdust.
These results help frame and guide our future work with biomass densification. In the next stages of this project, the multidisciplinary BRDI research team will investigate whether the upstream energy investments in drying and particle size reduction are worth the payback when bringing briquettes to the heating market.
Biomass blocks are ok, but, densified briquettes with a central hole burn better due to the “Venturi effect”, creating an airflow which allows a total burn, with little ash and a Hot flame.
Hi John,
we did test round, blocks and hollow centered briquettes (or logs) in our small demonstration project using two-stage combustion hydronic heaters. Its not a definitive answer because it also depends heavily on the type of appliance and combustion controls it would have.
Hollow centered briquettes or logs have a much higher surface area ratio than a big block or a brick. They would definitely burn much quicker in an uncontrolled appliance (no primary or secondary air control) because of a higher surface ratio, but as we have seen so far, they release the same thermal efficiency thank blocks or bricks.
If there is any interest, I can post the links when its published. We should also have the CO data to compare if the emissions are better or the same.
Thanks
Terrence