Metal-Fach GHT, Эксплуатационная и техническая документация, Страница: 10 / 32

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Altereco B1 type wood chips are delivered to the customer in plastic bags weighing
about 14 kg and transported on pallets (fig. 15), the packaging method protects them
from excessive moisture, but does not release them from storage under a roof, in order
to avoid the direct impact of adverse weather conditions that may reduce fuel quality.
1.4.1 Basic information on the combustion of wood-based fuel to produce heat.
General information.
Calorific value of wood-based biomass depending on water content
The energy efficiency of wood is determined by its calorific value (Hu). The calorific value is
the energy obtained by burning one kilogram of wet wood. The water contained in the flue gas
is transformed into steam. The calorific value (Ho) additionally contains the condensation heat
of the water vapour that is generated by cooling down to the initial temperature. The amount
of water contained in the fuel batch is the basic amount that affects the combustion. It
determines the energy efficiency and thus the potential energy yield during combustion. The
calorific value of wood-based fuels ranges in practice from 5.0 kWh/kg (18 MJ/kg) with a water
content of 5% to 1.5 kWh/kg (5.4 MJ/kg) with a water content of 60%. This value depends on
the species of wood and to a large extent on the water content or moisture content of the
wood. The water content has a decisive influence on the regulation of partial load and emission
properties of the installation.
Determination of water content
The water content shall be determined on the basis of the drying process in the dryer, on which
the CEN standard is also based. A fuel test is carried out using damp wood, the material is
dried for several hours in a cupboard dryer at a temperature of abou
t 105°C and then analysed
again. The amount of water in the fuel is given as water content (w).
Range of application of the fuel depending on water content
The boiler can burn wood-based biomass with a water content of 5 to 30%.
Table of calorific values of different types of wood.