Content Limits For Non-Combustable Substances; Other Information - Viessmann Vitoflex 300-UF Series Installation And Operating Instructions Manual

Vitoflex 300-UF Installation & Operating
Wood Fuel Requirements
Content limits for non-combustible substances
- No wood fuels may contain any foreign bodies, such as pieces of metal, stones, masonry remnants or plastics.
The following limits (per mg/kg of dry fuel) of contained non-combustible substances apply [ash analyzed at a
temperature of 1500°F (815°C)]:
Substance
Chlorine (Cl)
Sulphur (S)
Total Cl, S
Ash content, total
Alkali oxides in the ash (K2O and Na2O)
Sintering point of the ash
If fuel does not comply with these limits, there is a risk of corrosion within the heat exchanger and early sintering and
melting of the ash which leads to:
- Shortened life of the heat exchanger
- Increased maintenance costs (firing, combustion chamber door)
The maintenance instructions need to be complied with in order to avoid a process, which will increasingly cause
damage to the boiler.
If maintenance instructions are not complied with the following process may occur:
- Cinders change the airflow
- Temperature peaks
- More slag is produced
- More cinder builds up and changes the airflow more
This process leads to damage by overheating and may affect refractory materials.
Additives in remnant and used wood have to be free of heavy metals and halogen compounds.

Other information

- Ash and cleaning:
Untreated wood without bark produces less than 0.5% ash of the fuel mass supplied. All the specifications
regarding cleaning are based on untreated wood with bark attached with an ash amount of 0.8% of the fuel mass.
If the ash content is higher and/or the ash melting point is lower, increased maintenance and/or cleaning are required.
- Changing fuels:
A substantial change in fuel quality, such as bulk density, water content, dust proportion or ash content might require
a manual correction of the firing parameters (see Operating section).
(continued)
Limit
max. 300 ppm (300 mg/kg)
max. 1000 ppm (1000 mg/kg)
max. 1000 ppm (1000 mg/kg)
max. 0.25 oz/lb (15.0 g/kg)
max. 0.016 oz/lb (1.0 g/kg)
min. 1800° F (1000° C)
General Information
Comparative value untreated forest wood
10 ppm (10 mg/kg)
120 ppm (120 mg/kg)
130 ppm (130 mg/kg)
0.08 oz/lb (5.0 g/kg)
0.006 oz/lb (0.35 g/kg)
approx. 2200°F (1200°C)
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