Maintenance and Inspection - Catalyst
September 16, 2003

Introduction Raking Catalyst Sampling

Associated Links Catalyst Converter Maintenance Catalyst Loading Catalyst Unloading

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Introduction

Maintenance of the catalyst can only be done during a plant shutdown after the converter has cooled down and access to the inside of the converter is possible. 

Inspection

The inspection of a catalyst is relatively straight forward.  The primary concern is to ensure that the bed is level and uniformly distributed across the converter.  Areas to concentrate on are the gas inlets to the bed.  High gas velocities may cause the quartz rock to be blown away allowing the even lighter catalyst to be redistributed.  If this has occurred, the bed must be leveled agained and additional quartz rock placed on top of the catalyst to prevent the problem from occurring again.  Sometimes a stainless steel screen   can be substituted for or used in addition to the quartz rock to keep the bed from being blown around.

Access on top of the bed should be minimized as the movement of people on top will cause the catalyst to rub against each other and disintegrate.  If there will be a lot of activity in the converter, wooden boards should be laid across the catalyst to help distribute the weight across the bed resulting in less mechanical damage to the catalyst.  Just ensure that the boards are removed when all work inside the converter is completed.

Raking

Raking is a procedure that can be done when a catalyst bed exhibits  high pressure drop due to dust build up.  It is a temporary measure that can be done during a short shutdown when there is insufficient time to unload, screen and reload the catalyst back into the converter.  The procedure does require that the converter be cold enough for personnel to enter.

Most dust accumulates in the top layer of the bed while the remainder of the bed remains relatively dust free.  Raking of the bed disturbs the top section of the bed allowing the dust to migrate down further into the beds.  The distribution of the dust through a larger section of the bed reduces the pressure drop across the catalyst.

Pitch forks are inserted into the bed as deep as possible and shifted back and forth to ‘open’ up the bed and allow the dust to penetrate deeper into the bed.  The entire bed is disturbed in this manner.

If the raking procedure has been successful and reduction in the pressure drop across the bed should be seen when the plant restarts.   The catalyst bed should be fully screened during the next plant shutdown.

Catalyst Sampling

Catalyst should be sampled when it is first installed in the converter and during subsequent screenings of the bed or whenever performance of the catalyst is in question.  The catalyst should be retained for future reference or sent immediately for analysis.

Representative samples can be obtained by obtaining samples at four quadrants within the bed.  Samples should be taken from the top of the bed at each quadrant about 100 to 250 mm into the bed.  All four sample should be combined together.  Similar sample should be taken from the bottom of the bed about 100 mm from the bottom.

For Bed 1, an additional sample should be taken from the middle of the bed.

If a bed contains different types of catalyst separate samples should be taken of each layer.