Choosing Test Methods
In recent months, I have been repeatedly asked to explain the difference between the various test methods available for testing solid biomass fuels. Fortunately, this isn’t as difficult as it once was, as now most of the European national standards such as the German DIN, Austrian Önorm, and others have been replaced by the CEN/EN methods. It is still rather confusing, but I will try to make sense of it for you.
Within the U.S., ASTM International has historically been the primary provider of test methodology for solid fuels including coal, refuse-derived fuels (RDF) and wood. Unfortunately for the biomass industry, most of these methods focus on coal and RDF with only a small number pertaining to wood. The lack of standards dedicated to biomass has resulted in many labs selecting coal or RDF methods to analyze biomass samples, and they may or may not be adequate for the purpose, especially when it comes to sampling and sample preparation. For example, all coal methods cite coal preparation standards to generate the sample to be analyzed. Unlike coal, wood does not pulverize under pressure, meaning that the coal preparation standards are essentially useless for biomass samples.
Inconsistencies like these are generally left up to the lab to determine how to compensate, and it is unlikely that all labs that come across the same inconsistency will identify the same solution. The end consequence is that test results may differ between two labs citing the same test method.
This same problem also resides within ISO test methods. Most of the historical test methods available within ISO are for—you guessed it—coal and other fuel types. Obviously, the same problem applies.
When the Pellet Fuels Institute Standard Specifications for Residential/Commercial Densified Fuel were being developed, these inconsistencies were understood and taken into consideration. Note, however, that some of the cited methods have been modified by PFI in order to make them applicable to pellets, and in some cases, PFI had to develop its own methods. Despite our best efforts to select ASTM methods that are applicable to pellets, in many cases these methods have not been updated in decades. That is not obvious, however, and a perfect example is ASTM E871 for total moisture in wood. While the method states that it was updated in 2006, the only update is the safety disclaimer in the scope.
Around the year 2000, the European Union identified the lack of test methodology for solid biofuels and in response created a new technical committee within their normalization body—CEN. Over the course of a decade, and with an investment of around 10 million euros, CEN TC 335 created about 30 technical specifications including terminology, specifications, chemical and physical test methods as well as sampling and sample preparation procedures. Most of these technical specifications have now been published as EN methods. These European standards are the best documents we have available today when it comes to test methodology for analyzing solid biofuels, but there are still concerns. Since the U.S. is not part of the EU, we had no input on these standards during their development. Therefore, they are very Eurocentric, and that’s apparent when comparing test methods for fines and durability in pellets. In addition, when performing the CEN/EN methods in our lab, it has become apparent that not all of these methods are as well researched.
The best news is that we now have a voice in further developing these solid biofuel standards. In 2007, the CEN/EN methods were forwarded to ISO to convert them to true international standards. ISO responded by creating a new technical committee—ISO TC 238. Lead by ASABE, the U.S. is actively participating in ISO TC 238 to develop true international standards for solid biofuels. For the past four years I have had the privilege of sitting on the U.S. Technical Advisory Group for ISO TC 238 and also on five of the six working groups. As such, I have great confidence in the work products that are moving forward, and I encourage all who are interested to participate in their development.
The ISO solid biofuel standards are still in various stages of development, and currently more than 50 standards development projects are being discussed. The first of these new standards should be published within the next year, with the rest being published in the next one to three years. Hopefully, the world will embrace them when they are published.
Author: Chris Wiberg
Manager, Biomass Energy Laboratory