Furnace Technology
Presence of SO₂ in furnace gases attacks the ferrous metal by way of

Causing metal embrittlement
Attacking the grain boundaries; particularly severe on low carbon and nickel bearing steels at high temperature
All of these
Accelerating the rate of scaling

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Furnace Technology
In a furnace employing forced draught as compared to induced draught,

Positive pressure exists in the furnace
Air is sucked in, so air leaks are more and hence the furnace efficiency is reduced
None of these
The fan operates hot and hence blades are liable to corrosion and erosion

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