Page 72 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

Chapter | 3 Biomass Characteristics 51

plants that develop hard stems with vascular bundles. Herbaceous plants do
not have the thick bark that covers nonherbaceous biomass like trees.
Nonherbaceous plants are not seasonal; they live year-round with their
stems above the ground. These include trees, shrubs, and vines. Nonherbaceous
perennials like woody plants have stems above the ground that remain alive
during the dormant season and grow shoots the next year from their above-
ground parts.
The trunk and leaves of tree plants form the largest group of available
biomass. These are classified as lignocellulosic, as their dominant constitu-
ents are cellulose, hemicellulose, and lignin. Table 3.2 gives a percentage of
these components in some plants. Section 3.3.2 presents further discussions
of the lignocellulose components.
There is a growing interest in the cultivation of plants exclusively for
production of energy. These crops are called “energy crop,” and they are lig-
nocellulosic in nature. Such crops typically have a short growing period and
high yields and require little or no fertilizer, so they provide quick return on
investment. For energy production, woody crops such as miscanthus, willow,
switchgrass, and poplar are widely utilized. These plants are densely planted.
They have high-energy yield per unit of land area and require much less
energy for cultivation.

3.2.2.2 Crops and Vegetables
While the body of a plant or tree (e.g., trunk, branches, and leaves) is ligno-
cellulosic, the fruit (e.g., cereal and vegetable) is a source of carbohydrate,
starch, and sugar. Many plants like canola and mustard also provide fat. The
fruit is digestible by humans, but the lignocellulosic body of the fruit tree is
not. Some animals, however, can digest lignocellulosic biomass because of
special chemicals in their stomach. The use of crops or vegetables for the
production of chemicals and energy must be weighed carefully as it might
affect food supplies.

TABLE 3.2 Composition of Some Lignocellulose Wood

Plant Lignin (%) Cellulose (%) Hemicellulose (%)
Deciduous plants 18 25 40 44 15 35
Coniferous plants 25 35 40 44 20 32
Willow 25 50 19
Larch 35 26 27
Source: Adapted from Bergman et al. (2005, p. 15).