Drying, an indispensable process for linings with castables

Our advice and recommendations:

Planned summer shutdowns and the associated maintenance work are a challenging and stressful time for the foundries: the work must be completed to the full extent and in the shortest possible time.

From the point of view of refractory maintenance, after the demolition and total or partial reconstruction of the linings of the various furnaces and installations, we reach the stage of drying and commissioning, the last step in concluding the summer shutdown.

Drying is an indispensable process after the use of concretes that are mixed with liquids, especially hydraulically bound concretes.

The aim of drying is to remove the water from the lining in a controlled manner and under the best economic and safety conditions, avoiding explosions due to the conversion of liquid water into vapor and achieving the best properties of the installed refractory materials.

During the drying of a hydraulically bonded concrete, as the temperature rises, the water disappears, decomposing the calcium aluminate hydrates formed during the setting process and thus gradually cutting the bonds of the hydraulic bond. The water added during mixing disappears in its entirety at around 600°C.

Drying is a time and control intensive temperature cycle (drying and start-up curve), but a key stage in lining or repair projects, and should therefore be considered from the early planning stages of the work.

Our advice and recommendations:

  • The drying process should be considered from the first project phases (quotation and engineering).
  • Time constraints, availability of suitable equipment and other considerations will affect the lining design in terms of material choice and geometric configuration.
  • In multilayer linings, the drying curve (gradients, maintenance and times) is always limited by the most restrictive material used.
  • The heating system must guarantee the degree of temperature regulation needed at each stage of the curve.
  • During drying, it is important to ensure
    o Constant positive pressure
    o Convection
    o Frequent air rotation.
  • Do not use radiant heat for drying.
  • In complex geometries, control and avoid "cold spots".
  • Ensure complete temperature mapping using regulation and control and monitoring thermocouples.
  • The use of thermocouples embedded in the different layers of the lining will help the monitoring of the drying process.
  • Monitoring both the temperatures and the evacuation of steam and water in real time will allow decisions to be made and the curve to be readjusted if necessary.
  • The use of thermography techniques and pressure sensors can help to complete the monitoring information in real time.

NOT carrying out a correct drying process can lead to situations like this…

Avoid it …. The consequences are … STARTING OVER with all that entails: shutdown of the start-up, complete cooling down, demolition, installation of the new lining, new drying, …. And non-operation of the kiln at an incalculable cost.

Don't gamble with the DRYING of the linings.