Chemical Engineering August 2021 - 49

expertise and technology to perform
this work (Figure 2).
Loading and unloading encompasses
a wide range of operations.
Pre-bagging is basically transferring
the catalyst material from its original
packaging to intermediate hoppers.
Screening and sieving normally involves
removing the catalyst from a
reactor, sieving the different-sized
particles and removing the undersized
solids, dust and fines from the
catalyst. The screening step may be
required due to a blockage at the
top of the reactor, which can cause
pressure-drop and flow problems.
Sieving is also used to remove other
materials, such as ceramic balls that
can be used as an inert support in
catalyst beds. In the majority of instances,
the loading method is dictated
by the manufacturer.
Fixed-bed reactor catalysts are
usually dumped out of the reactor
via a reactor catalyst dump chute,
or vacuumed out from the top manway
of the reactor via a catalyst
vacuum truck. The materials are
unloaded into drums, supersacks,
flow-bins or roll-off boxes. The
methods used here are generally
determined by the user.
Loading methods
The following sections discuss various
methods for loading solid catalyst
materials.
Vacuum loading. This consists of
pneumatically conveying the catalyst
directly from approved packaging
types into the reactor via a vacuum
system. The vacuum system creates
a negative vacuum on the reactor
containing the catalyst material,
which is then conveyed into
the reactor. This method minimizes
operator exposure and environmental
impact, as well as eliminating the
requirement for crane support.
Direct loading. The catalysts are
placed in bags and the bags are
lifted with cranes. They are made
to pass through a dust containment
system before being loaded into the
reactor. There are two types of catalyst
loading methods for fixed bed
reactors, namely, dense loading or
sock loading. Sock loading would be
the least expensive loading method.
Dense loading. In dense loading, a
device is used to spread the catalyst
evenly in the reactor, in order to
reduce void space, reduce channelling
and to achieve a greater catalyst
density gain. Dense loading technologies
differ in their approach, with
some using rotating equipment and
others relying on air as a propellant
to spread the catalyst. Nitrogen can
be used in place of air for self-heating
catalysts. Dense loading methods
require constant operator attention
to regulate the feed rate and
avoid surges. It would normally require
an operator inside the reactor
to follow loading. Periodic checking
of the level and evenness is required
during loading.
The dense loader is set-up to load
catalyst through the top manway on
the reactor, if the reactor is a multibed
reactor. The loader is set up at
the inner bed tray section, loading
into the lower bed.
Sock loading. Sock loading is a
method in which the catalyst is
transferred from a loading hopper at
the top of the reactor into the catalyst
bed via a flexible sleeve or sock.
It typically consists of a rigid pipe
attached to the discharge nozzle of
the hopper at the top, and a flexible
sock at the bottom. This equipment
allows the catalyst-loading technician
to keep the loading sock full
of catalyst and prevent the catalyst
from free-falling a maximum of three
feet from the discharge area while
loading the catalyst bed to the correct
level. The sock is shortened as
the loading operation continues and
as the solid level increases toward
the desired level of the catalyst bed.
The same technique is also used to
load multi-bed reactors.
Tubular reactor/reformer loading.
Loading a tubular reactor requires
directly filling the catalyst into each
individual tube. In the past, this has
been a highly labor-intensive operation,
so numerous multi-tube-loading
devices have been developed
and are available.
Loading tubular reactors has historically
presented many challenges
for contractors to address. During
the infancy of efforts to address the
unique challenges of emptying thousands
of tubes ranging in size from
0.5 to 1.5 in. in diameter, a significant
portion of those efforts were focused
on reductions in manpower,
and reducing exposure to dust and
injury, as well as lessening the physiCHEMICAL
ENGINEERING WWW.CHEMENGONLINE.COM AUGUST 2021
Maviro
FIGURE 3. Modern catalyst loading requires equipment
like the breathing mask shown here being
tested for use inside a reactor
cal labor the work involved.
These challenges were compounded
by the need to maintain a
clean, climate-controlled work environment,
and the need to recover
precious metals from catalysts.
Also, the fines generated during catalyst-handling
activities can present
health hazards.
The objective of the loading operation
is to consistently load fresh
catalyst into the tubes while meeting
the requirements for exact outages
and narrow ∆P tolerances across
the tube-sheet (typically 3 to 5%),
without bridging the varied sizes and
shapes of the catalyst particles.
In more recent years, catalysthandling
contractors have invested
significantly in the development of
new technologies, equipment and
methods for the removal and replacement
of these expensive catalysts
(Figure 3).
Among the innovations resulting
from the push to improve the loading
of tubular reactors are multi-tube
fish-tape and recovery troughs, as
well as electronic differential pressure
(DP) measuring devices, airlance
unloading equipment and vibratory
loaders. The term " fish tape "
refers to catalyst guide tubes used to
unload catalysts with maximum dust
containment and catalyst recovery.
By employing the newer tools,
reactor contractors that once used
simple templates with openings
matching the pitch and inner diameter
of tubes observed reductions in
the time required to perform catalyst
changes. They also saw improvements
in spent catalyst and precious
metals recovery, product yields, catalyst
life and the quality of the overall
run cycle.
Current technology
The predominant technology employed
in the U.S. tubular market
47
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