Improved bed support for molecular sieve dehydrators and adsorbers
Adsorbent beds supported by a support grid traditionally use ceramic rope packing to fill an expansion gap between the vessel shell and the bed support grid. This gap allows the bed support grid to move under thermal expansion. The bed support grid would be constricted from thermal expansion without this gap, causing it to buckle or fail during process heating operations.
An unobstructed expansion gap is critical for proper performance of the bed support grid. Preventing molecular sieve granules and fines from filling around the rope packing is crucial to long-term bed support performance in molecular sieve dehydrators. Granules and fines converge into an incompressible mass once they are in the expansion gap, preventing bed support grid expansion upon heating. An annular mesh screen or bolted cover plate typically covers the rope packing as the primary sealing mechanism. Nevertheless, gaps between the vessel shell and the annular mesh screen or bolted cover plate allow fines and granules into the expansion gap.
This paper provides details of an improved adsorbent bed support design that utilizes a superior sealing mechanism that features a fixed hold down ring design. The fixed hold down ring design provides an innovative method of sealing the expansion gap that will effectively eliminate the pathway by which molecular sieve granules and fines enter the expansion gap. This is accomplished by welding the hold down ring directly to the vessel shell above the bed support grid. Additionally, the rope packing is moved from the expansion gap to the gap between the hold down ring and the top of the bed support grid. A relief gap is provided in the bottom of the banding around the periphery of the bed support grid to allow expulsion of fines from the expansion gap. These features provide an expansion gap sealing mechanism that eliminates the chronic failures experienced by conventional bed support grid sealing mechanisms. While the fixed hold down ring design has been specifically developed to resolve the thermal expansion issues associated with molecular sieve dehydrators, it can be used for many types of packed beds requiring modified bed support designs.