Design Considerations for Reactor Maintenance

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Handling such removable items such as relief valves and valve drives for off-site repair and catalyst loading can be achieved by fixing handling devices or by mobile equipment.

Fixed handling devices can be davits or for structure mounted reactors, trolley beams.

Following drawings shows a typical davit and trolley beam arrangements.

Catalysts are loaded through the top-head maintenance access of the reactor after removal of the inlet nozzle if integral to the maintenance access cover flange.

If the catalyst is not supported on a fixed grating and screen assembly, which would be fabricated with the vessel, the first step is to load the bottom head and unload the nozzle with inert material.

The inert material could be silica pellets or alumina balls, which are usually larger than the catalyst and support the catalyst bed.

The inert material is then covered with bottom floating screen.

The catalyst is first sieved through a mesh screen to remove the finer particles.

It is then loaded into a bucket or sock and lowered through the maintenance access, where it is manually distributed in layers until the reactor is filled to the capacity.

The top and bottom layers of the catalyst are usually a larger mesh than the main bed.

The top floating screen is then installed and covered with an additional layer of inert material that is used to hold down the screen assembly during regeneration and eliminates the inert gas turbulence during operation.

The catalyst is remove infrequently.

Removal is accomplished during shutdowns after cool-down by allowing the catalyst to exit through the bottom unloading nozzle.

After removal of the flange cover on the unloading nozzle, the catalyst can be allowed to free fall to a temporary containment area or be removed using an industrial vacuum or a temporary valve may be used to control the unloading rates.

Following drawings show less common reactor arrangements.

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