Regeneration - Spent Hydroprocessing Catalysts - page 174

Figure 6.34: Flowsheet of in-situ regeneration plant: 1 and 2: reactors; 3: furnace; 4: heat
exchanger; 5: pump; 6, 11, 12, and 14: tanks; 7 and 8: vaporizers; 9: air cooled exchanger; 10:
water cooled exchanger; 13: tower; 15: piston compressor; I: air; II: inert gas; III: fresh sodium
carbonate solution; IV: spent solution [From ref. 449 . Reprinted with permission].
including the sodium carbonate system for scrubbing sulfur oxides from the gas exiting
regenerator.
There are reports on significant problems, such as temperature runaways and mal-distribution
of oxidizing gas, during the in-situ regeneration [13] . Also, fines that are usually formed
during regeneration complicate the subsequent hydroprocessing operation due to the
development of pressure drops and mal-distribution of liquid and gaseous streams through the
bed. In some cases, this required unloading the catalyst from reactor for the removal of fines
and subsequent reloading. All these problems were encountered during the in-situ regeneration
of catalysts used for hydroprocessing of light feeds. Of course, even more complications could
be envisaged for heavier feeds. Therefore, it is not surprising that most of the petroleum
refiners prefer to have their catalysts regenerated off-site. In fact, there is little information
suggesting that in recent years, any petroleum refinery would make an attempt to perform
in-situ regeneration of the catalyst fixed bed after hydroprocessing of heavy feeds.
The method for the in-situ regeneration of spent hydroprocessing catalyst described by
Tamayama [450] may be used to illustrate the complexity of the process. It involves de-oiling
the catalyst by shutting down the feed supply lines and flushing the fixed bed with a recycle
gas for about 2 h at temperature and pressure approaching those employed during the
operation. A typical recycle gas has a high content of H 2 in addition to H 2 S and volatile