There are several things which can cause a pressure drop within the bed of the catalyst. These things can vary from dust or grime building upon it, mishaps during the normal course of operating, or even the catalyst itself deteriorating. These factors will eventually affect the bed to such a degree that the plant itself will need to be shut down and the catalyst will need to be screened so that the bed can be restored to its normal functioning condition.
The first layer of the catalyst will need to be screened more often because any dirt which enters the reactor will go through this layer first. Operational problems may also result in a crust forming over the bed of the catalyst. If this happens, the pressure drop will increase very rapidly over a short period of time. The entire catalyst may need to be removed so that proper cleaning can begin. This is an important factor in catalyst property management. This state is particularly common in post and grid type of converters where occurrences of grid support collapsing may occur.
Vacuuming is the usual method of removing the catalyst from the converter. There are also methods used to remove the catalyst by hand but this is usually restricted to smaller types of converters and is far more labor intensive. Most screening is done well after the catalyst has reached a cooling point so that there is no special protective clothing needed. Screening is capable of being performed while the catalyst is still hot but there are strict procedures which must be followed and special clothing which must be worn.
As you can see, managing catalyst property and ensuring proper screening is performed is no task for amateurs. This is a very important job and must be performed with the utmost of care.