The Snares of Pelleting Mahogany Residues

There are more variables to take into account when it comes to different types of wood. We all know how to handle soft wood like pine and spruce, and even hardwood such as oak and beech, but what about mahogany residues?
By Holger Streetz | October 02, 2018

Following my introductory column in Pellet Mill Magazine, I received some direct feedback from an unexpected place: China. Not only does China plan on increasing its wood pellet consumption for cofiring at coal power plants, like other Asian countries, it is also busy building pellet plants. From what I learned from my conversation with a plant manager of a pellet plant in inland China, there are more variables to take into account when it comes to different types of wood. We all know how to handle soft wood like pine and spruce, and even hardwood such as oak and beech, but what about mahogany residues, in a mixture of two-third wood chips and one-third dust? With a Brinell hardness of 3.1 N/mm2, mahogany is almost as hard as oak (3.5 N/mm2) and beech (3.7 N/mm2). The big difference is that mahogany is a very oily wood, and therefore more difficult to pelletize. The high oil content does not allow high moisture levels. However, with low moisture, dust emissions increase, and cause a drop in efficiency of the production, decreasing pellet quality and increasing the risk of fire. So what to do?

Adding binders like starch is not a solution, because these binders don’t bind dust. However, there is a company that soon will be offering a dust-binding additive for wood pellets. Moisture level adjustment is one method of regulating dust, but there are restrictions to the moisture level—not only from a pellet standards point of view, but also because buyers don’t want to pay for water. One  way to get to a better product is to improve pretreatment. Installing a mixer prior to the feeder homogenizes the material, and thus leads to well-mixed feed for the pellet mill.

Due to biomass-supporting political framework, Japan and South Korea are currently the main drivers in the Asian biomass market, and have grown exponentially since 2012. With imports of 2.4 million metric tons of pellets, South Korea leads the Asian biomass demand. More than 80 percent is delivered from Southeast Asia, with Vietnam as the leading supplier for palm kernel shells, which make up a substantial amount of woody biomass used in Asia. Japan’s wood pellet demand of half a million metric tons annually is mainly supplied by Canada (71 percent). However, with 1.4 million metric tons, PKS account for the vast majority of biomass.

The positive trend in the Asian biomass market will continue for the longer-term, as the greener policy will not change in the short-term, and because the go-ahead has been given to six new biomass power plants.

I look forward to more feedback and questions for discussion in my next column.


Author: Holger Streetz
International Operations Manager, Bathan AG
h.streetz@bathan.ch
+491-735918-550