Swedish Chemists Trace Heavy Metals In Wood Pellet Manufacture.

[NNadir]

Many people think of biomass burning as "risk free." With respect to fossil fuels, it is, of much lower risk, but it is not risk free.

Swedish chemists have analyzed some of the risks associated with the burning of pellet fuels, an increasingly popular approach to home heating and other energy applications. Here are some excerpts from a recent publication examining these risks.

An increasing interest for utilization of biomass as a CO2-neutral and sustainable alternative to fossil fuels for production of heat, power, and liquid fuels can today be seen globally. There is further a growing market for upgraded biomass fuels, in particular, the use of wood pellets in small- and medium-sized devices in the Nordic countries as well as in Middle Europe and North America.1,2 Fuel pellets are a dried, homogenized, and densified biomass fuel with several advantages during handling, storage, and combustion compared to unprocessed biomass fuels. Today, the raw material for fuel pellets is mainly stem-wood assortments such as sawdust, planer shavings, or dried chips from sawmills and the wood-working industry, while bark, agricultural residues, and other forest fuels only occasionally occur.3 The development of systems for production and use of biomass fuel pellets has been extensive during the past decade, mainly in Europe (e.g., Sweden, Austria, and Germany) and North America,1,2 with a significant further potential for conversion from heating by oil, wood logs, or electricity to fuel pellets within the residential sector. For example, the production of wood fuel pellets in Sweden has increased from 10 000 tons in 1990 to over 1 million tons (5 TWha) in 2005, of which 25% presently are used in the residential sector.4...

...The concerns regarding environmental dispersion of toxic heavy metals (e.g., Cd, Pb, and Hg) are today well-documented and constitute solid motives for the special focus of the fate and forms of these elements in different processes. The presence of different particle-associated transition metals (e.g., Cu, Zn, V, and Ni) has also been suggested to be one of several properties that may elucidate the link between different observed adverse health effects and exposure to particulate matter (PM) in the ambient air.17-20 The importance of combustion-related trace element pollution and its implications to human health have also been discussed. 21,22...

...Conclusions
The behavior of different trace elements relevant for woody biomass fuels during pellets production and use (combustion) was studied by field sampling of raw material, fuels, and particulates in two different pelletizing mills as well as by chemical-equilibrium calculations. It was shown that the use of a direct drying process with uncleaned combustion flue gases can imply a significant risk for contamination of the raw material by trace elements during the pellets production. A significant enrichment of the volatile trace elements Zn, Cu, Cd, and Pb was documented from the field-sampling campaign in the plant using bark combustion gases for drying of the sawdust and was also supported by the chemicalequilibrium results. This is caused by the volatilization of these elements from the bark fuel during combustion with subsequent formation of fine particles in the flue gases and, finally, capture in the pellet raw material.

The article is from the ASAP sections of Energy and Fuels.

The abstract for the article is found here: http://pubs.acs.org/cgi-bin/abstract.cgi/enfuem/asap/abs/ef050375b.html