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.