Erilaisten korjuuketjujen tuottaman metsä-hakkeen käyttö suurten voimaloiden leijukerroskattiloissa: PUUT08

When combusting wood fuels the chemical composition of woof fuels can cause fouling and high-temperature corrosion of the heat transfer and superheater surfaces of the boiler. Problems are caused especially by forest chips, which include high quantities of needles and thin branches. Even though low alkali metal and chlorine contents are typical for wood fuels, the problem is that they are easily vaporised during combustion. Depending on the combustion conditions, the alkali metals can be oxidised to alkali metal oxides or they can form sulphates or chlorides. When combustion pure wood the sulphur content in combustion process is low and alkali metal compounds form chlorides easily, which can be condensed on the heat transfer surfaces of the boiler and form a significant high-temperature corrosion risk. If the sulphur content of the combustion process is increased e.g. by additional utilisation of peat, the chemistry of alkali metals is directed to formation of alkali metal sulphates instead of chlorides, and the chlorine liberated in the furnace forms gaseous hydrogen chloride (HCl). Hydrogen chloride, formed in combustion of wood fuels, is transferred in low concentrations in flue gases out of the boiler so it does not cause significant chlorine corrosion or emission risk.