What the flame pattern tells you about the lining

A refractory lining rarely wears evenly. There is almost always one section that is removed considerably earlier than the rest — and it is almost always where the flame strikes.

That is not a question of material. The same mass lasts two campaigns longer three metres away. The difference is the way the furnace is run, and that changes more often than any lining.

Three things you can read from the flame

• The length. A flame that is too long lies against the opposite wall instead of filling the chamber. The surface temperature there rises far above what the material was chosen for.
• The position. A flame that is not centred grazes one side. The reason is often banal: a distorted burner block, a shifted anchor, a repair that turned the outlet by a few degrees.
• The colour and shape. A restless, yellow, flickering flame indicates a lack of air. Unburnt material then reaches the wall and reacts there — a chemical attack on top of the thermal one.

The connection that gets overlooked

Burner settings are optimised for product and throughput, not for the lining. That is correct — nobody runs a furnace for the refractory. What is missing from the calculation is that a setting which saves one per cent of energy can shorten a wall section by half a campaign.

This only becomes visible at the inspection, months later, and by then the setting is no longer connected to the finding. That is why it is worth noting changes to burner control with a date in the same file as repairs.

What belongs in the inspection

Anyone climbing into a cold furnace should know beforehand where the flame stands. Then a surface you search becomes a surface with an expected spot — and you check specifically whether the expectation holds.

• Check the impingement area for glazing, melting and discolouration. A glassy surface means the material was at its limit.
• Check the burner block for cracks running towards the opening and for positional accuracy.
• Include the opposite wall, not just the burner wall. The damage occurs where the flame arrives.
• Compare the finding with the current setting, not with the one from commissioning.

That costs a few minutes during the inspection and changes the repair decision. A spot created by the way the furnace is run will be back in the same place with the same material in two years — unless you change either the material there or the setting.

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