3. Conceptual approach

The basic idea behind the UBET terminology is to create a suitable framework for the identification of the amount and type of wood energy flowing from different supply sources to meet end user needs. Thus the fuel or product used to transport energy is the basic parameter to be accounted and properly classified. Either in commercial or non-commercial terms, these fuels should always be seen as goods or commodities that are valuable and capable of meeting demand effectively.

A conceptual view of bioenergy systems, showing how biofuels physically flow in order to meet demand is presented in Figure 2.

Figure 2: Production chain of bioenergy

To cover the objectives of UBET three different points of view are considered:

• the sources of biofuels. This covers the initial location of the input material (biomass) in the economic and environmental cycles (like forest wood, energy forest trees, logging by-products, landscape management by-products, agricultural by-products, agro-industrial by-products, etc.);

• the types of biofuels. This covers the nature/origin of the biofuel in the same structure as the biomass sources (e.g., woodfuels, herbaceous fuels), and the most important trade forms (i.e. fuelwood, charcoal, producer gas, chipped biofuels, bundled biofuels);

• the most relevant biofuel parameters (e.g., moisture, total ash), and terms of sampling, testing, and classification.

Those aspects are covered in more detail in the following chapters. The relevant terms (always written in italics) are indexed in chapter 6 and definitions are given in chapter 7 in alphabetical order. A glossary is provided in chapter 8 with main terms given in English, French and Spanish.

This current version still contains weak points and overlapping areas and these will need clarification in the future. In the light of recent technical developments in the bioenergy sector, some terms commonly used in current literature and bibliography have been eliminated. For example, non-commercial energy has been eliminated and the earlier definition of biofuel, which used to refer to biomass processed to obtain ethanol, esters, etc., has been revised in order to give a more suitable definition. It should be noted that the term energy plantations is at present used to refer to both forest and agro-energy plantations; in this new classification, energy plantations will refer to forestry energy plantations, while agricultural plantations will simply be called energy crops.

In other cases new terms are proposed. For example agrofuels, which refers to biofuels derived from non-forest activities. It includes energy agricultural by-products, animal by-products, and agro-industrial by-products. As a general rule, it is proposed that the term wastes and residues be replaced by by-products.

3.1 Biofuels supply sources

To cover all the different statistical database requirements, a number of aspects need to be addressed. These include trading operations and biofuel and bioenergy balances for the terminology of biofuel sources information on pattern of supply demand and use, environmental resource requirement, and biofuel quality. Therefore different classification aspects have to be taken into consideration, including classification by production systems, economical sectors and class of material (see table 1).

Table 1: Relevant aspects for classification

In Table 2 those different aspects are brought together and illustrated by some examples. The term “by-products” includes the improperly called solid, liquid and gaseous residues and wastes derived from biomass processing activities. According to the structure in Table 2, Table 3 gives a more detailed overview of the different sources. The main biofuel sources used in developing countries are fuelwood, charcoal, agricultural by-products and dung.

The main definitions of biofuel supply sources employed in UBET include three types of biofuel: woodfuels, agrofuels, and municipal by-products.

The biofuel supply sources are put in different biofuel preparation processes. The output of those processes is different types of biofuels (i.e. solid, liquid and gaseous fuels) which are finally converted into heat and power. A detailed scheme for classifying biofuel types is presented in Table 5 (see chapter 4).

Table 2: Classification of Biofuel sources by different characteristics

*The term “by-products” includes the improperly called solid, liquid and gaseous residues and wastes derived from biomass processing activities.

Table 3: Overview on the most important biofuel supply sources

3.2 Trade in biofuels

Biofuels in general, and woodfuels in particular, are largely traded energy carriers in both formal and informal markets. In most commercialised cases, there are two major types (or forms) of biofuels: primary (unprocessed) biofuels, and secondary (processed) biofuels.

• Primary (unprocessed) biofuels are those where the organic material is used essentially in its natural form (as harvested). Such fuels are directly combusted usually to supply cooking, space heating, or electricity production needs, although there are also small- and large-scale industrial applications for steam raising and other processes requiring low-to-medium temperature process heat.

• Secondary (processed) biofuels in the form of solids (e. g. charcoal), liquids (e. g. alcohol, vegetable oil), or gases (e. g. biogas as a mixture of methane and carbon dioxide), can be used for a wider range of applications with higher efficiency rates on average, including transport and high-temperature industrial processes.

The aim of biofuel processing is to provide fuels with clearly defined fuel characteristics and ensure a technically simple and environmentally sound conversion into useful energy. Such clearly defined fuels can then be used with fewer problems to meet a supply task efficiently and comfortably. To ensure this the conversion processes noted in Figure 3 can be used.

• Thermo-chemical conversion summarizes all conversion processes of biomass based on thermal energy. Thus gasification, pyrolysis and charcoal production are all relevant. From these various possibilities only charcoal production is currently widely used. Gasification for electricity production seems to be a quite promising option which might become available on the market the next few years. Pyrolysis with the aim of providing a liquid fuel useable in power units is an option for the future.

• A physico-chemical conversion process provides a liquid fuel based on physical and chemical processes. The most important process so far is vegetable oil production from oil seed, and the esterification of this oil to fatty acid methyl ester as a substitute for diesel fuel. This technology is used on a large scale within Europe.

• Bio-chemical conversion summarizes conversion processes using biological processes. The most important possibilities are alcohol production from biomass containing sugar, starch and/or celluloses, and biogas production from organic waste material. Both technologies are state of the art and widely used for energy provision.

These upgraded biofuels can be used in specially adapted engines, turbines, boilers, or ovens to provide thermal and/or mechanical energy, which in turn can be converted into electrical energy. Additionally, liquid and (potentially) gaseous fuels can be used directly, or after treatment, as transportation fuels.

Heat production and electricity generation are the most important uses worldwide for biomass fuel. Direct combustion devices are widely distributed with thermal capacities ranging from a few kW in household stoves up to heating plants with several tens of MW. The conversion efficiencies vary from 8 to 18 % for simple stoves used traditionally in developing countries, up to 90 % and above for modern heating units with high-end technology. Electricity production is based mainly on the conventional steam cycle with efficiencies around 30 % and capacities of several hundreds of kW and above.

Figure 3: Possibilities to provide heat and/or power as well as fuels from biomass.

Table 4 evaluates the differences among the various conversion routes for biomass upgrading concerning feedstock availability. Some conversion technologies are only possible based on specially grown biomass (i. e. energy crops). This provides an important obstacle to wider use since there is considerable effort needed to produce the biomass, and there is limited available arable land. Based on availability of different feedstocks, only gasification and pyrolysis seem to be promising options.

Widespread commercial and industrial applications are for example direct combustion of different woody biofuels as well as combustion of wood based charcoal, conversion of food processing industry by-products, municipal by-products, and certain agricultural by-products into biogas by anaerobic digestion for application in combined heat and power plants

Table 4 indicates that some routes are very promising for technology and system technology. This is especially true of the production of charcoal or vegetable oil and esterification as well as, with some restrictions, for alcohol production. In some developing countries the charcoal chain is well developed, as is the Biodiesel provision chain (i. e. vegetable oil esterification and use of the fuel for transportation purpose) in some industrialised countries (Austria, Germany, France and USA).

The term System aspects concerns the possibilities of the integration of these conversion routes into the energy system, the given or expected environmental benefits, the present costs and the possible cost reduction potentials. The table indicates that for some options the costs are quite high, but the cost reduction potentials are also high. The data makes it clear that most of these options can be considered to have promising to very promising environmental aspect. Therefore biomass could make a substantial contribution to meet energy demand in an environmentally sound way. This is especially true for the options of providing energy with modern conversion technologies. Additionally most of the biomass-based options could be easily integrated into the existing energy system. This would allow an easy transfer from the current energy system based mainly on fossil fuel energy to a more sustainable energy system based on biomass.

Table 4: Comparison of biomass conversion routes

Evaluation: + less promising; ++ promising; +++ very promising

Source: Smith, K.R.; Kaltschmitt, M.; Thrän, D. 2001 [19]

Use of biofuel differs significantly throughout the world. By-products concentrated at industrial processing sites (like bark and saw dust in saw mills) are currently the largest commercially used biomass source. For example bagasse, the fibre remaining after juice extraction in sugar cane processing, often provides energy for extracting the juice and processing to pure cane sugar or alcohol at the sugar mill and, in addition, surplus bagasse is used to supply electricity for the local grid.

In developing countries, biomass (particularly fuelwood and charcoal) is used mainly in open combustion devices for cooking and, to a lesser extent, space heating.