Environmental Engineering Reference
In-Depth Information
The next step is processing the biomass materials. These materials are dried,
compressed, fermented into alcohol, converted into biogas, pelletized or processed
into fuel in chemical plants. The aim of the processing is to produce useable
biomass fuels.
This biomass fuel has the same spectrum of use as fossil fuels like coal, crude oil
and natural gas. Biomass power plants can use biofuels to generate electricity;
biomass heating can satisfy heating needs; and biofuels can be used to run cars and
other vehicles.
The versatility of biomass use has led to a real interest in alternative fuels. In many
industrialized countries like Germany and Britain, however, biomass falls far short
of becoming a complete replacement for fossil fuels. Nevertheless, biomass fuels
will play an important role in the renewable energy sector in the future.
12.2 Biomass Heating
With traditional biomass, the focus has been on the generation of heat for cooking
and heating. Even today the use of biomass for heating is one of its key applications.
Wood, straw and biogas are the commonly used fuels. Vegetable oils and bioalcohol
are also used in some heating systems.
12.2.1 Wood as a Fuel
Wood is by far the main fuel used for biomass heating. It is available in different
processed forms (Figure 12.5). As the fi rst step, felled trees are cut to a common
length to produce round wood. High-quality woods are not used as fuel but are
processed further by the timber industry.
The round wood is then cut up, either by hand or by machine, to produce fi rewood.
Wood scraps or inferior-quality wood may be processed into wood shavings, which
can be made into wood briquettes or wood pellets. Special compression techniques
are used to press the wood into the right shape for burning. The natural lignin of
the wood serves as a binder, so no additional binders are required.
Because of their uniform shape and small size, wood pellets are an ideal fuel. They
can easily be delivered in bulk tankers and then blown into special pellet stores.
This eliminates the need for time-consuming manual loading. Automated feeding
systems enable wood pellet heating systems to provide the same level of heat and
ease of operation as natural gas or oil heating systems.
Some isolated quality problems existed in the early days of wood pellet production.
Pellets that are the wrong size can get stuck in conveyor systems. If the pellets have
not been compressed suffi ciently, they can disintegrate too quickly and block up a
system. Therefore, wood pellets should comply with European standards such as
the Austrian Ö standard M 7135 or the German DIN plus standard. Wood pellets
must conform to the following specifi cations:
