BF Furnace Aerodynamics

DP – Delta Furnace Pressure

If the furnace total DP (hot blast pressure – top pressure) exceeds the aim limit as set out in the WEEKLY OPERATING PARAMETERS, for 5 min or more – or sooner if the furnace stops moving, then the blast volume is to be reduced in steps of 200m3/min or more until the maximum DP constraint is satisfied. Exceeding the DP constraint can result in fluidisation in the stack and/or flooding and loading of the bosh. Both can precipitate unstable furnace operation. If having followed the rules of DP wind restrictions the blast volume has been reduced to 4500m3/min, and the furnace charging rate shows the furnace to ‘owe’ a minimum of 1.5m then checking practice is to be instigated.

Slips and Channels

Slips and channels result in a loss of metal quality and requires compensation according to the table in the furnace compensation.

If the instability is a continuing problem, reduce in blast volume and changes to burden and fuel rate may be necessary.

When a slip/channel of more than 3m has been experience, the blast volume is to be reduced by 300m3/min for 1 hour whilst the aerodynamics trends is monitored.

Hearth Liquid Levels

An increased level of liquids in the hearth will result in a changed wind pattern in the furnace and poor bosh permeability. It is therefore important to monitor the iron balance, the amount of time that slag is being cast, casting delay and occurrence of ‘not dry’ cast. If changes to casthouse operation do not remedy the melt balance within 2 hours, the blast volume is to be reduced at the discretion of Control Room Team Leader to a level at which control over hearth liquid levels can be regained.

Charging Fault

In the event of a fault on the charging system that reduces the charging rate, the blast volume is to be reduced to a level at which the stockline can be regained and maintained, taking the furnace off blast if necessary. If a low stockline is caused by charging fault the coke compensation found in furnace compensation is to be applied.

If distribution control is not possible, the furnace is to be taken off blast as soon as is safely possible.