Characterization of biomass using instruments – Measurement of forest and crop residues - Biomass as Energy Source: Resources, Systems and Applications - page 55

CHAPTER 3
Characterization of biomass using instruments - Measurement
of forest and crop residues
Robert Aulin
3.1 INTRODUCTION
In 2009, renewable energy made up for 47% of the entire energy consumption in Sweden where
two major sources of energy are biofuel and hydropower. In 2010, they contributed with
141.5TWh and 66.8TWh respectively. The corresponding shares of the entire 616.5TWh energy
supply in Sweden were 23% and 11%, respectively.
Due to the large forest areas in Sweden, wood and forest residue have been an important source
of energy for centuries. Since the early 1980s, they have increasingly been used as an energy
source in the combined heat and power plants (CHP's) that constitute a backbone in municipal
heating. According to the Swedish Energy Agency, wood, tops and branches extracted directly
from the forest contributed to 26TWh in 2010. In addition to this figure, e.g. stubs, residue from
pulp and paper plants, sawmills and recycled wood are used for energy production.
Since production capacity increases, there is a debate over a potential fuel shortage in the future.
Except for rising prices, another implication would be that the use of less desirable fuel sources
such as stubs and recycled wood is likely to increase. In this case, one might expect larger quality
fluctuations and problems with fuel shipments that do not meet up to the specifications agreed
upon by the buyer and seller. This, in turn, increases demand for quality control. Increasing
quality fluctuations will also have a negative impact on the plants themselves. With real-time
quality assessment of the fuel, adequate countermeasures may be taken through improved process
control.
This text is written from a Scandinavian perspective with a large demand for heat in the
winter and where the installed capacity of a single CHP often exceeds 100MW. As a result, the
implications of this text might be less applicable for countries with a warm climate and smaller
plants. However, these lines of reasoning may be useful since economies of scale suggest that
plant sizes will rise generally. Recent directives from the European Union will also enhance this
development.
This chapter discusses sources of moisture content variation, their magnitude and techniques
to measure moisture content in large material flows. Focus is put on forest residue such as tops,
branches, sawdust and bark. Many aspects and solutions might well apply for other materials
such as peat, recycled wood and household waste. Today, there is a fast development in the
technology for moisture measurement. Any detailed description of such technology is likely to
become outdated within a few years. Some examples of commercially available measurement
equipment are given but the emphasis of this chapter is on sources of quality fluctuation and
strategies for using the measurement results.
3.2 QUALITY ASPECTS AND SOURCES OF VARIATION
3.2.1 Volume, weight and moisture content
There are several parameters of interest with respect to fuel characteristics. In Sweden, volume,
weight and moisture content are three important parameters that are often measured for shipments
as small as the containers of a single truck.
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