Banking is the term used for suspending operation of a blast furnace for an indeterminate length of time whilst preserving the lining in good condition.
To develop a hot silaceous slag to scour the furnace clean of limey deposits and to prevent the formation of a limey slag (which being viscous causes operating problems) when production is resumed, extra coke is charged and the amount of limestone reduced. Then a heavy coke blank is charged followed by greatly reduced iron ore and limestone, and sometimes silaceous additions. The dust catchers are emptied. When the coke blank reaches bosh, the final cast is made. A heavy blanket of ore is charged to reduce draught, the blast taken off and the tuyeres plugged with cflay, follwed by sand and lastly brick.
The stock level is inspected daily and if the burden descends, the exterior of the furnace is sprayed with clay sealant to minimise air infiltration which causes the coke to burn. After a month or two, water flow to the coolers is reduced and after three or more months only the hearth remains cooled.
Banking for days or a few weeks can be routine. There tends to be less experience of prolonged banking as it is far less frequently resorted to. Much of the complexity comes from the exact order of shutting down of the furnace auxilliaries (stoves, dust catchers, gas mains, cooling water, steam, etc) to ensure safety (some gas/air mixtures are explosive) and that the plant can be started up without pipework etc being blocked.