Environmental Engineering Reference
In-Depth Information
The incinerator attached to the former section converts volatile matter removed during
stripping. If necessary, the flue gas from incineration may be introduced to the scrubbing tower
attached to regeneration section. The off gas from regeneration is water quenched before
entering absorption tower (Packing) used for SO
X
and NO
X
emission control. The quenched
water is neutralized in the sump by caustic supplied from the adjacent storage tank. To
maintain pH necessary for scrubbing, the caustic can bypass sump and introduced directly to
the top of tower. Spent caustic is considered a hazardous waste because of corrosive nature
caused by pH exceeding 12. Also, some caustics may be reactive and on acidification can
release H
2
S
[470]
. Therefore, the spent caustic must be handled in accordance with
environmental and safety regulations.
6.4.4.2 TRICAT Regeneration Process
Simplified flowsheet of the TRICAT regeneration process (TRP) is shown in
Fig. 6.41
[471,472]
. In this process, screened spent catalyst enters the first of two ebullated bed reactors
shown in
Fig. 6.42
. The regeneration air entering at the bottom through distribution plate is
used as the fluidization medium. The design of ebullated bed ensures that regeneration
temperature is maintained below that observed in other commercial regenerators. This is
attributed to the fluidization hydrodynamics of the bed. Air is supplied to each reactor
independently. Temperature control is maintained through the number of independent
variables such as catalyst feed rate, air temperature, cooling coils and catalyst level in the
Figure 6.41: Simplified flowsheet of TRICAT regeneration process [From refs
471
and
472
.
Reprinted with permission].
