Environmental Engineering Reference
In-Depth Information
According to CERCLA or “Superfund” which was promulgated by EPA, refining industry
may be forced to a cleanup wherever spent catalysts were disposed of in the past.
The RCRA subtitle C requires the installation and operation of the ground water monitoring
system for evaluation of the performance of TSDFs unless the owners of such facilities can
demonstrate that there is no and/or low potential of migration of hazardous species to ground
water [296,297] . This includes establishment of a ground water sampling and analysis
program as well as a ground water quality assessment plan. Regulations require at least one
up-gradient and three down-gradient wells for obtaining samples of ground water. The RCRA
provides details of the maintenance of the wells and water sampling procedures [296] .
Monitoring is required during the operation of the facility, during its closure, and during its
postclosure period if necessary. Postclosure monitoring, usually lasting 30 years after closure,
is required in the case that hazardous solid was not removed from the facility after the closure.
This may apply to landfills and surface impoundments that were closed but waste solid left in.
In view of the complications discussed above, it may be wise to conduct a thorough
assessment of the site before a landfill facility is constructed. A similar assessment was made
by a company before constructing a new metal reclamation plant [317] . In this case, the
company commissioned a third party environmental audit, which also included the previous
site operation. The audit comprised of the evaluation of the potential impact on ground water
and soil contamination as well as the review of the permit status and files to assess potential
liability of the site. As part of the audit, a shallow, confined, permeable deposit was discovered
about 10m under previous site. This zone was confined by clays and silts. The water samples
taken from it revealed that all metals were at the background level or at the level of the nearby
river. As the result of the audit, the new plant was constructed on top of very tight formation of
clays and silts, having very low permeability.
5.1.4 Handling of Spent Catalyst on Refinery Site
When the decline in catalyst activity cannot be offset by adjustment of operating parameters
(e.g., temperature), the operation has to be discontinued. In some cases, such actions have to
be taken because of a high-pressure drop caused either by accumulation of solids on the front
of fixed bed or due to the attrition of catalyst particles and formation of clumps caused by
temperature excursions. The problems may be alleviated by skimming the front of the bed and
replacing it with fresh catalyst. In more complicated cases, whole bed may need to be
unloaded, screened, and reloaded. If no other action can restore the operation, catalyst has to
be removed from reactor, which is then reloaded with either fresh or regenerated catalyst. The
catalyst removed from reactor at this point is referred to as spent catalyst. It should be noted
that such situations might be encountered during the operation of fixed bed reactors rather than
moving bed reactors. In fact, avoiding problems with high-pressure drops was the main reason
for the development of the latter reactors.
 
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