Activities on standardization have to be followed by the development of quality assurance systems relevant for biofuel provision and utilization. Currently, there is no quality assurance system that takes into account the whole provision chain of solid biofuels. A standard for quality assurance will be developed within CEN/ TC335/working group II (see Table 11.3).

Theoretically, quality assurance systems can be introduced in all processes of the provision chain. Figure 11.1 gives an overview of the biofuel chain, the different processes, the basic conditions and an illustration of factors influencing quality along the chain. In practice, the first step is to identify the points where the relevant physical and/or chemical parameters can be measured and controlled easily.

A motivation for quality assurance is to guarantee that the processes follow environmental laws (e. g. emission limits) or meet technical requirements at the conversion plants (e. g. avoiding corrosion). The quality of the fuel can be controlled, for example, when chemical and/or physical parameters are modified in crop pro­duction processes (e. g. modifying the nitrogen content of whole grain crops by nitrogen fertilization) or in harvesting and fuel preparation (e. g. modifying the water content of wood by storage). At the conversion plant, technical solutions are available for emissions reduction (e. g. primary and secondary measures for NOx — emissions reduction).

Measures that affect quality should be identified preferably where the costs are lower along the chain. Although different control points are practicable, it is believed that a quality assurance system shall start at the combustion plant, in coopera­tion between the fuel traders and combustion plant operators, which will ensure a trouble-free and low emission business. Additionally, the manufacturers of equip­ment for biofuel handling and combustion should take quality assurance among their considerations in the technical development of their equipment.

Specific research is being conducted to optimize the biofuel production chains and to recommend the most promising biofuel classes (respectively supply chains) for different markets. In Germany, for example, various options to modify solid biofuel characteristics such as nitrogen and water content have been identified within the production and provision of certain biofuels. This includes fertilization and storage practices. Also, options to reduce emissions within biomass burning have been studied (Thran et al., 2001). An example for the case of straw is provided here to illustrate how quality improvements can be accomplished.

Theoretically, different options are available to modify the chlorine content of straw respectively, the HCl-emissions in crop production, harvesting/preparation as well as conversion. Figure 11.2 illustrates measures for reducing chlorine content in

straw. It follows the different steps of information along the chain of production, provision and energetic utilization of straw. The arrows give an overview of straw chlorine and HC1 reduction measures potentially available, especially within crop production and biofuel conversion. The first hatched rectangle describes the feasible chlorine content that can be achieved through crop production measures (0.1 to 0.6 per cent). The second rectangle indicates the maximum tolerable chlorine contents (0.1 to about 0.4-0.5 per cent), which are derived from technical limits set by plant corrosion problems and/or emissions regulations. These measures for chlorine reduction are discussed in turn.

Crop production. One way to modify chlorine content is to make a targeted selection of straw for energetic purposes. Investigations show that the chlorine content in wheat straw varies within a lower range than oats straw. Fertilization of the grain has an important influence on straw biofuel quality. A K2S04-fertilizer, for instance, reduces the chlorine content of straw by 0.3 per cent as compared to the application of a KCl-fertilizer (Vetter and Hering, 1999).

The harvest date also influences the chlorine content. Harvesting the grain at the time of dead ripeness[14], compared to the time of full ripeness, allows further chlorine reduction (Vetter and Hering, 2000). Another option is to extend the period between harvest and straw collection from the field. One reason why this can reduce chlorine is that the straw may be washed by rain. Vetter and Hering (1999) observed that the chlorine content from (winter) barley straw was reduced from 1.12 to 0.5 per cent based on a three week “storage” on the field before straw collection (baling). Comparable conditions provided a chlorine content reduction from 0.4 to about 0.13 per cent for triticale straw.

Preparation and harvesting. Within the process of straw preparation, the chlorine content may be washed out by technical means (Nikolaisen et al., 1998). Investment costs are on the order of DKK 200 million (Danish crowns)[15] for a plant that “cleans” about 125000 to 150000 tons of straw per year. Such high costs indicate that this measure is not very attractive as a first step, the reason why it is not considered in Figure 11.2.

Conversion. Filters are often required at the conversion plant to reduce dust emissions from the stack. At the same time, these filters contribute to reduce HC1 emissions. Another measure for HC1 reduction is the use of a sorbent (e. g. lime hydrate). This allows for about 90 per cent reduction of HC1 emissions, as the chlorine is incorporated in the ash.

The example of quality assurance of the chlorine content in straw shows that there are many options to accomplish improvements in the crop production field. A lower chlorine content reduces technical risks such as corrosion at the plant, as well as emissions. Thus a quality assurance system for straw has to include crop production measures besides the options available at the conversion plant.

However, a clear and detailed description of the various steps and aspects of a quality system has to take into account the local and regional conditions for crop production, the economic implications of the various measures, and the practical experiences of the various stakeholders (farmers, supervisor at the conversion plant). More knowledge on economic and technical advantages of the different measures and processes shall allow for a more specific discussion on the options available at the regional and national levels.