Environmental Engineering Reference
In-Depth Information
7.1.3.3 Solid Emissions
A breaking and crushing of the catalyst particles during operation cannot be avoided. This may
be evident after decoking of spent catalyst. It might be necessary to remove the crushed
particles from spent catalyst before rejuvenation. These aspects of spent catalysts were
discussed earlier. Fine particles formed during rejuvenation process end up in the leachate. If
removed from the leachates, the fine particles of catalyst have to be either stored or disposed
using methods ensuring environmental acceptance unless some other safe utilization options
were identified.
7.1.4 Rejuvenation Process Design
Important information to be considered during process design includes the process capacity,
operating conditions, and special precautions needed due to corrosion and environmental
regulations. All stages of rejuvenation process, i.e., spent catalyst de-oiling, mechanical
separation of catalyst particles, selective metal leaching, and decoking, have to be carefully
assessed. In addition, there might be requirements for water systems, fuel systems, and power
generation. Also, facilities for treatment of gaseous and liquid effluents have to be installed to
prevent release of harmful species into the environment. If integrated with petroleum refinery,
some facilities required for rejuvenation may be integrated with those used during refining.
Therefore, it might be more attractive to construct rejuvenation plant on or near the site of
petroleum refinery than a stand-alone rejuvenation operation.
7.1.4.1 De-Oiling
The aspects of de-oiling which are common for regeneration process were discussed in the
Chapter 6
. It was indicated that it is preferable that de-oiling is performed by spent catalyst
generator (e.g., petroleum refinery) unless rejuvenation process is integrated with refinery. It is
believed that an efficient mechanical separation cannot be achieved without prior de-oiling of
spent catalyst particles.
7.1.4.2 Mechanical Separation
It is desirable that particles that are non-regenerable and/or non-reusable are removed from
process streams before rejuvenation step. Two methods are employed for mechanical
separation of spent de-oiled catalyst particles, i.e., fines sieving and particle grouping
according to density or jigging. With efficient removal of fines, the emissions of particulate
matter are significantly reduced. Apparently, fines removal is much more critical for spent
catalysts removed from ebullated bed reactor than that from the fixed bed reactor. This results
from the small inside diameter (ID) of catalyst particles (1mm or less) used in the former
reactor compared with fixed bed reactors. Also, because of a continuous motion, a cracking of
catalyst particles may occur more readily in ebullated bed than in fixed bed.
Table 7.8 [12]
