Page 71 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

50 Biomass Gasification, Pyrolysis and Torrefaction

specification (EN 14961) and quality assurance (EN 15234) of biomass.
Based on their origin, it classified biomass under four broad categories:

1. Woody biomass
2. Herbaceous biomass
3. Fruit biomass
4. Blend and mixtures.
Trees, bushes, and shrubs fall under woody biomass, but not the fruits or
seeds that some of them bear. Herbaceous biomasses are those plants that die
at the end of the growing season. These biomasses, however, include grains
and cereals that grow on such plants. Fruits, though classified as a separate
group, are part of woody plants. Additionally, we also have mixture or
blends of biomass. Blends are intentional mixing of biomass, while mixtures
are unintentional mixing of biomass.
Loosely speaking, biomass includes all plants and plant-derived materials,
including livestock manures. Primary or virgin biomass comes directly from
plants or animals. Waste or derived biomass comes from different biomass-
derived products. Table 3.1 lists a range of biomass types grouping them as
virgin or waste. Biomass may also be divided into two broad groups:
1. Virgin biomass includes wood, plants, and leaves (lignocellulose), and
crops and vegetables (carbohydrates).
2. Waste biomass includes solid and liquid wastes (municipal solid waste
(MSW)); sewage, animal, and human wastes; gases derived from landfill-
ing (mainly methane); and agricultural wastes.

3.2.2.1 Lignocellulosic Biomass
A major part of biomass is lignocellulose. So this type is described in more
detail. Lignocellulosic material is the nonstarch, fibrous part of plant materi-
als. Cellulose, hemicellulose, and lignin are its three major constituents.
Unlike carbohydrate or starch, lignocellulose is not easily digestible by
humans. For example, we can eat rice, which is a carbohydrate, but we can-
not digest the husk or the straw, which is lignocellulose. Lignocellulosic bio-
mass is not a part of the human food chain, and therefore its use for biogas
or bio-oil does not threaten the world’s food supply.
A good example of lignocellulosic biomass is a woody plant—i.e., any
vascular plant that has a perennial stem above the ground and is covered by
a layer of thickened bark. Such biomass is primarily composed of structures
of cellulose and lignin. A detailed description of wood structure is given in
Section 3.3.1. Woody plants include trees, shrubs, cactus, and perennial
vines. They can be of two types: (1) herbaceous and (2) nonherbaceous.
A herbaceous plant is one with leaves and stems that die annually at the
end of the growing season. Wheat and rice are examples of herbaceous