Quality of biomass

Three years ago, FPInnovations began a multi-year project to unravel everything there is to know about woody biomass. Research efforts  so far have focused on identifying critical biomass attributes, quantifying new opportunities to increase the fibre basket, defining best practices and testing the most promising technologies related to producing, storing and supplying woody biomass.

In some cases, feedstocks that have been finely broken down are delivered at higher than optimum moisture content and their addition to other drier biomass may compromise overall biomass quality.

Knowledge leads to savings
One element that has proven to be important is what FPInnovations’ Fibre Supply researcher Sylvain Volpé calls feedstock quality.

“The definition of a high quality feedstock depends ultimately on its end use. For example, because of the way they are designed, different types of biomass boilers require different types of biomass. Small boilers ideally need small wood chips of uniform size with low moisture content (MC) whereas big boilers can use bigger chips with higher MC and more contaminants,” explains Sylvain Volpé.

FPInnovations’ focus is to identify and test cost-effective, low energy strategies for measuring and reducing moisture content of biomass at various points along the supply chain.

Identifying the optimal quality characteristics for each use and product can benefit the industry. Boiler efficiency, for example, can be improved by up to five per cent if biomass moisture is reduced from 50 to 40 per cent. For a single boiler using 25 green tonnes/hour of biomass at 50 per cent moisture content (≈210,000 GMt/yr), improved feedstock management can save up to $1.2million/year. This includes transportation fuel costs and emissions since less weight is being transported.

Apart from moisture content, the characteristics that make up forest biomass quality include particle size distribution, called granulometry, as well as shape and calorific value, but also the presence of specific elemental chemicals, bark, foliage and inorganic contaminants. Recognizing these characteristics is important, Volpé says, when considering the efficiency of the supply chain for delivering fibre to the end user in the most appropriate form.

These characteristics depend on a number of parameters such as source (log, branches), equipment (chipper or grinder, operating conditions), initial moisture content, local climate, log dimension, wood species, contaminants as well as equipment operator experience.

The power of dry
As demonstrated earlier, moisture content is one of the key characteristics in determining the calorific value of biomass. An important part of FPInnovations’ focus in this field is to identify and test cost-effective, low energy technologies and strategies for measuring and reducing moisture content of biomass at various points along the supply chain. With the financial support of Natural Resources Canada, FPInnovations has demonstrated the potential to reduce moisture content by 10 to 30 per cent in harvest residues by using proper piling and covering techniques. However, because of the need to rehabilitate and renew roads or to minimize fire risks, not all forest residues can be left in place for seasoning. In these cases, feedstocks that have been finely broken down are delivered at higher than optimum moisture content and their addition to other ‘drier’ biomass may compromise overall biomass quality.

If biomass is not stored properly, there can be excessive loss of biomass through biological and chemical degradation, notwithstanding the very real risk of fire.

Practical ways of economically drying this biomass to the desired moisture content are needed in order to ensure optimal conversion efficiencies. Other industrial activities involve biomass drying. For example, low energy driers are commonly used for drying peanuts and other agricultural products, and OSB flakes are routinely dried before they’re used to make panels and there are many new technologies that claim to dry biomass. However, doing so in an efficient, economical and timely manner requires specialized equipment and handling.

Storing biomass
Storage also influences the quality of woody biomass. If this is not done properly, there can be excessive loss of biomass through biological and chemical degradation, notwithstanding the very real risk of fire. Current thinking on biomass pile management to reduce losses during storage have been summarized in an FPInnovations guide entitled ‘Hog Pile Management.’ While a very good practical synopsis of best practices, this document also highlights the need to understand the degradation processes, and how to monitor and manage them.

Searching for new ways to characterize, produce, manage and store biomass from the forest is one of FPInnovations’ important ongoing mandates. Future research efforts related to biomass quality include the development of methods to recover biomass from sawmill heritage piles, log yards and other forest-origin sources while reducing the presence of contaminants as well as monitoring of tarping and in-woods storage drying efficiency practices and technologies.