Energy Density Of Various Fuel Types Compared With Fuel Oil (Standard Values); Principles Of Wood Pellet Combustion For Generating Heat; What Are Wood Pellets; Pellet Requirements - Viessmann VITOFLEX 300-UF Technical Manual

Principles of wood combustion
B Amount of fuel required in kg/h
Q Required rated heating output in kW
N
1

Energy density of various fuel types compared with fuel oil (standard values)

Tip/
840 kg/m³
Stack density
Fuel oil equivalent
0.84 kg
kilogram
Fuel oil equivalent
1.00 l
litre

1.2 Principles of wood pellet combustion for generating heat

What are wood pellets?

Wood pellets are made from 100 percent natural wood remnants. This raw material is waste matter created by the wood industry in large
volumes through planing or sawing. Wood remnants are compressed under high pressure and formed into pellets, i.e. pressed into a cylindri-
cal shape.
The raw material is stored and transported under completely dry conditions. System users should also ensure completely dry storage condi-
tions. This is the only way to guarantee optimum and effective combustion.

Pellet requirements

For heat generation, use wood pellets that have the following proper-
ties:
■ Diameter of 6 mm
■ Length of 3.15 to 40 mm (1 % up to 45 mm)
■ Max. moisture content of 10 %
Requirement
Diameter
Length
Bulk density in the delivered condition
Net calorific value in the delivered condition
Water content in the delivered condition
Fines content in the delivered condition
Mechanical strength in the delivered condition
Ash content, free from water
Viesmann
8
(cont.)
860 kg/t.m³ 650 kg/t.m³ 459 kg/t.m³
1.28 kg 2.16 kg 2.35 kg
1.49 l 3.33 l 5.11 l
ENplus-A1
H Net calorific value in kWh/kg
u
η System efficiency in %
297 kg/t.m³ 217 kg/t. m³
2.30 kg 2.25 kg
7.73 l 10.36 l
The wood pellets used for combustion in the solid fuel boiler must
correspond to the requirements of EN ISO 17225-2.
mm
mm A maximum of 1 % may be lon-
ger than 40 mm, but no longer
than 45 mm.
kg/m³
MJ/kg
kWh/kg
m-%
m-%
m-%
%
EN ISO 17225-2 quality A1
6 ± 1
600 to 750
≥ 16.5
≥ 4.6
≤ 10
≤ 1
≥ 97.5
≤ 0.7
VITOFLEX 300-UF
D06
3.15 to 40
BD600
Q16.5
Q4.6
M10
F1.0
DU 97.5
A0.7