Hydrocarbon Processing - August 2022 - 39

Catalysts
FIG. 9. Spiral inserts.
containers provided. The catalyst loading
must have a robust quality assurance/
quality control (QA/QC) process that
should include duplicate identification
and the counting of catalyst bins/bags/
drums loaded into the designated reactor/bed.
Each bin/bag/drum number, as
well as the catalyst batch number, should
be recorded against the respective reactor/bed.
This prevents any errors and provides
important information if a catalyst
performance issue occurs after startup.
The dense-loading technician will stop
loading at intervals to check the bed profile
and the catalyst density to ensure the
bed is loading consistently flat and not
dished or mounded. A dished or mounded
profile will affect liquid distribution
through the bed during operation. If the
bed must be levelled, it is important that
a uniform layer of the bed is disturbed
and levelled, resulting in a uniform layer
of the equivalent of sock-loaded catalyst.
Just pushing the mounded catalyst out or
filling the dished section into the middle
of the bed will cause distribution issues.
The dense-loading machine can only
load effectively up to 300 mm-500 mm
from the bottom of the distribution tray.
The final part of the bed must be sock
loaded.
The catalyst bed must be levelled and
confirmed as level at each catalyst layer
transition and at the top of the bed. This
should be verified by physical inspection
or, at the very least, a video inspection.
When the catalyst bed is accepted as
completed, the distribution tray and other
quench zone trays are cleaned again and
closed, along with the catalyst support
grid for the bed above. The closing of each
tray should be witnessed. The process of
loading the next bed is then repeated.
Physical filtration materials may be
used in the very top of the lead reactor, per
stage (i.e., the last layer loaded). This maFIG.
10. Controlling the pre-wetting exotherm.
terial is often awkward to load and spread
in the confined space between the top of a
catalyst bed and the distribution tray. Vendors
provide loading guidelines and catalyst-handling
contractors have developed
innovative ways for loading this material.
Restart. Standard preparations for startup
are commenced after the top elbow(s)
are reinstalled on the reactor(s) and the
reactor circuit is put into its startup configuration.
All equipment opened or
worked on should be handed back from
engineering or maintenance
has been completed; however, if this step
is incomplete, the catalyst temperatures
must be held to complete the dry-out.
Once all reactor skin temperatures are
above the MPT, the system can be pressured
to close to normal operating pressure
and temperatures can be adjusted
(as determined by the catalyst vendor)
for catalyst sulfiding. During this process,
pressure testing and leak detection steps
are completed to ensure the circuit is tight
before introducing liquid feed and/or
hydrogen sulfide (H2
S).
following
documented close-up and hand-over procedures,
and a detailed (piping and instrumentation
diagram) P&ID-based check
of the condition of the unit is performed,
including a cross-check that all blinds are
in their correct position.
The reactor circuit is freed of oxygen-
either by evacuation or nitrogen purging-prior
to rolling the recycle gas compressor.
When recycle gas circulation has
been established, the heater is commissioned
and the system pressure is raised
to 25% of normal operating pressure, with
hydrogen (H2
), until the minimum pressurization
temperature (MPT) is reached.
During this heating/hold phase, when
the mass of the reactor and catalyst is being
brought to the MPT, the catalyst is being
dried out. Any moisture the catalyst
has adsorbed during transport, storage
and loading is slowly driven off in this drying
step. Normally, by the time the reactor
has reached MPT, the catalyst dry-out
In liquid-phase sulfiding, the startup
oil-normally a low endpoint (< 370°C)
diesel-is introduced at 105°C-110°C.
During the introduction of the startup oil,
called pre-wetting (FIG. 10), there will be
an exotherm in each catalyst bed caused
by the heat of adsorption as the liquid
contacts and adsorbs onto the surface of
the catalyst. Type-II hydrotreating catalysts
must be kept below 140°C-150°C
until the catalyst is fully wetted to retain
the hydrotreating catalyst structure and
activity. The temperature limit for hydrocracking
catalyst (prior to the introduction
of H2
S) is 205°C to prevent reduction
of the metal oxides on the catalyst to
their base metallic (zero valence) state in
the H2
-rich conditions. Any reduced metal
sites cannot be regenerated and result in
permanent catalyst deactivation.
Traditionally, no quench has been required
to maintain the catalyst temperature
within the 140°C-150°C and 205°C
limits mentioned above; however, as
Hydrocarbon Processing | AUGUST 2022 39
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