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Fouling, Slagging and Sintering During Combustion of Coal

Bed Agglomeration in Fluidised Bed Combustion

The bed agglomeration may proceed through several different sintering mechanisms. depending on the components in the ash and their interaction with the bed material, two types of mechanisms have been identified viz., partial melting and bed sintering

Partial Melting, occurring when using lignite rich in sodium, sulfur and chlorine whereby a molten coating of bed particles is formed which leads to bed agglomeration

Bed Sintering, occurring when burning coals and other fuels rich in potassium and calcium in a quartz bed. In this case aluminum silicate and calcium aluminum silicate are formed. Potassium aluminum silicates has a first meting point of 628C.

Coal As Fuel

Fouling Slagging and Sintering

Fouling is defined as the deposit formation where no only a small percentage of molten phase is present in the deposit.

Slagging is defined as deposits formed with higher melt percentage in the ash

Sintering is commonly used ti describe particle to particle agglomeration under heating

Predictability of Sintering

  • About 70% of of power generation in India is through coal.

“it had emerged that coal quality (its energy values, particle sizes and dryness) was a major problem for just about every power station at present....as proving to be the major reason for many of the unplanned outages or lower-than-normal generation performance”

Sintering

  • Sintering is Coalescence of solid particles. The process by which fly ash produced in combustion of fuels such as coal is baked (sintered) at a very high temperature.
  • The sintered material is used in the manufacture of cinder blocks and other ceramic products.
  • This term is also relevant to the enrichment of low grade ores and preparation of the charge for, e.g. a blast furnace.
  • The sinter plant may be a significant source of pollution while serving to aid in the abatement of pollution for the blast furnace usually called sintering. Catalysts often suffer during use from a gradual increase in the average size of the crystallites or growth of the primary particles. This is also usually called sintering.

Prediction of sintering inclusive of fouling and slagging behavior of ash before coal is combusted is very important.

Different laboratory scale predictive methods have been used for ash slagging and fouling, which provide information used in comparative way. For this comparison different computational indices as well as predictions obtained experimentally. the computational indices include: Silica Ratio, Silica to Aluminum ratio, Total acid, Total base, base to acid ratio, ferric percentage etc.

A number of sintering tests are also used as predictive tool such as dilatometry, electric conductivity measurements and compression strength tests of ash pellets.

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