Pellet Quality Characteristics; Types Of Pellet Delivery; Principles Of Woodchip Combustion For Generating Heat; What Are Woodchips - Viessmann VITOFLEX 300-UF Technical Manual

Principles of wood combustion
Requirement
Ash softening temperature
This value is only binding for pellets certified to ENplus.
It indicates the temperature at which the wood ash is
deformed and can therefore cause fusions in the com-
bustion chamber.
Chlorine content, free from water
Sulphur content, free from water
Nitrogen content, free from water
m-% = percentage by mass

Pellet quality characteristics

Good wood pellets:
■ Smooth, shiny surface
■ Uniform length
■ Low proportion of dust
■ Sink in water

Types of pellet delivery

In their loose form, wood pellets are transported by silo tanker and
pumped into the storage room via a hose system.

1.3 Principles of woodchip combustion for generating heat

What are woodchips?

Woodchips are made from 100 percent natural wood from forests
and plantations. This raw material comes from tree trunks or
branches.

Definition of woodchip size classes according to EN ISO 17225-4

Size class Main percentage (at
least 60 % of the
mass), a)
Size in mm
P16S 3.15 to 16
P31S 3.15 to 31.5
P45S 3.15 to 45
a) The number in the size class refers to the maximum particle size in the main percentage. The particles have to pass through a strainer
with a circular mesh (ISO 17827-1 standard), in which the sieve apertures are of the specified size for the size class. The lowest possible
property class should be specified.
b) Only determine the length and cross-sectional area of particles in the coarse fraction. In a sample of about 10 l 2 pieces at the most can
exceed the maximum length if the cross-sectional area is < 0.5 cm
c) To measure the cross-sectional area, you are advised to use a transparent set square, arrange the particles at right angles behind the set
2
square and use a cm grid to estimate the maximum cross-sectional area of these particles.

Woodchip requirements

For combustion in the solid fuel boiler, use woodchips of size class
P31S that have the following properties:
■ Max. coarse fraction of 6 % (> 45 mm)
■ Max. cross-section of 4 cm²
VITOFLEX 300-UF
(cont.)
ENplus-A1
°C
m-%
m-%
m-%
Note
EN 14961-2 was superseded by the new standard EN ISO 17225-2
in September 2014. It describes the essential properties of wood pel-
lets.
Low quality wood pellets:
■ Cracked rough surface
■ Widely varying length
■ High proportion of dust
■ Float in water
Careful handling of wood pellets ensures a low proportion of dust,
trouble-free boiler charging and a constant heating output by the
solid fuel boiler.
The wood is then processed with high speed cutting tools in accord-
ance with EN ISO 17225.
Fine fraction Coarse fraction (in
(≤ 3.15 mm) brackets particle
length)
In % of the mass In % of the mass
≤ 15 % ≤ 6 (> 31.5 mm)
≤ 10 % ≤ 6 (> 45 mm)
≤ 10 % ≤ 10 (> 63 mm)
2
.
■ Max. length of 15 cm (1 % up to 45 mm)
■ Moisture content (see product description)
EN ISO 17225-2 quality A1
≥ 1200
≤ 0.02
≤ 0.04
≤ 0.3
Maximum particle Maximum cross-sec-
length, b) tion area of the coarse
fraction, b) c)
in mm 2
In cm
≤ 45 ≤ 2
≤ 150 ≤ 4
≤ 200 ≤ 6
Viesmann
–
1
Cl0.2
S0.04
N0.03
9