Environmental Engineering Reference
In-Depth Information
Figure 6.45: Simplified flowsheet of ReFRESH regeneration process [From ref.
433
. Reprinted
with permission].
The direct fire is a single shell vessel with rings added inside to slow the catalyst as it tumbles
from the inlet (elevated part) towards outlet (lower part). The oxidation medium flows
countercurrent to catalyst movement. The O
2
concentration in the medium will decrease in the
same direction because of its consumption. Therefore, the zone in the vessel located near the
inlet may function as a stripper of volatile components of coke. The kiln is fired by gas burners
directly against the outer shell of the vessel. The temperature inside the kiln is controlled by
adjusting the burner heat, varying concentration of O
2
in the oxidizing medium and its flow.
The indirect fire kiln comprises a double-shell cylinder vessel. The inner shell is similar as that
of the direct fire kiln. The space between the shells is heated either by combustion gas or
steam. In some cases, the inner cylinder shell is ebullated allowing hot gases or steam to enter
and contact the tumbled catalyst. The catalyst temperatures are controlled by monitoring the
temperatures of the inlet and outlet gases. It is believed that Eurocat process evolved from a
rotary kiln process by be improving the control of operating parameters such as temperature,
gas flow, speed of rotation, etc.
6.4.5 Comparison of Regeneration Processes
Obviously, at this point, it would be desirable to provide some comparison of commercial
processes that have been used for regeneration of spent hydroprocessing catalysts.
Unfortunately, this is prevented because of the limited information on details of the individual
processes available in open literature. It is believed that differences in the operating costs may
be more evident than that between the efficiency of regeneration processes. The information
on quantities of consumables, i.e., gases, electricity, chemicals, etc. as well as emissions such
