FOULING

Fouling is a phenomenon that ash condense, adheres and building up on super heater or reheater surface where heat transfer takes place in connective manner. Sometime it bridges the tubes and jeopardieses heat conductivity. Depending on nature of ash being built up, it can normally be removed by shootblower. 1. Influence of alkaline in ash :

Chemicals ingradients which have severe impact on fouling are alkalines such as Na2O, K2O and CaO. Particularly for the coal having high Na2O content in ash, special consideration on fouling is to be taken. In general term, young coal such as lignite and low rank subbituminous coal, have relatively high alkaline content in ash.

2. Influence of Sulphur Sulphur in coal has propensity to combine with alkaline to form sulphate thus promotes fouling.

3. Fouling Index (see attached below) For your information Berau Coal is categorized in lignitic type ash coal,

A. Bituminous type ash ( Fe2O3 > CaO + MgO )

Fouling Index RF = AB x Na2O content

AB =

2TiO3O2Al2SiOO2KO2NaMgOCaO3O2Fe

++++++

Index RF Fouling Propensity < 0.2 Low 0.2 – 0.5 Medium 0.5 – 1.0 High > 1.0 Severe

B. Lignitic type ash ( Fe2O3 < CaO + MgO )

Fouling Index R’F = 6

O2Na

Index R’F Fouling Propensity < 0.5 Low to Medium 0.5 – 1.0 High > 1.0 Severe