Hydrocarbon Processing - February 2022 - 65

Plant Turnarounds and Project Management
wrapped around its surface before being
inserted into the tube. This ceramic fiber
paper keeps the ferrule flexible to move
within the tube and does not allow the
refractory to stick to the tube.
The ceramic fiber paper was found
in unbroken ferrules but was missing in
cracked pieces. After checking with the
field supervisor, it was discovered that
the ceramic fiber paper stock fell short,
and workers went ahead without
it.
Therefore, the ferrules bonded with the
inner wall of the tube during application
of the refractory and during curing. Since
the ferrules were rigidly bonded, they
broke during curing.
Refractory anchors in furnaces. Refractory
anchors play an important role
in holding the castable refractory during
hot and cold conditions.
Various refractory anchor designs and
shapes are used for different applications.
These anchors are welded to the furnace
body at a specified pitch. The welding
pattern and pitch of these anchors differs,
depending on the refractory thickness,
weight and orientation in the furnace.
A strong anchoring system is key to
maintaining monolithic refractory lining
integrity-even when it is cracked-to
prevent a total structural collapse.
The tips of the anchors experience the
highest temperatures. To allow expansion
of the anchor tips, they are covered
with plastic caps or dipping wax. The tip
burns out, allowing the anchor to expand
without causing cracks in the refractory.
The following are common mistakes/
omissions regarding anchors and related
field work:
* The mix-up of anchors: Mix-up
of different metallurgy or type.
* Anchor pitch or orientations
not followed: Anchor pitch varies,
based on the anchor's location
in the side furnace. Sometimes,
a worker misses this aspect and
starts welding on the uniform
pitch and orientation.
* Anchor weld joint hardness:
Welding the anchor, using high
heat input, makes the joint brittle.
Since these are welded sequentially,
the work is easy. However, if any
anchor breaks in between, repair
is quite difficult. A typical mockup
should be made and tested by
knocking the anchor, adjusting
the welding current and making a
procedure for each type. The joint
should be ductile and not break.
* Missing anchor expansion caps:
Any missing caps should be put
in place prior to application of
refractory.
Refractory
drying out. The WHB
tubesheet ferrule design is important to
protect WHB tubes. If a crack develops,
hot process gas may reach the tubesheet
and/or tubes, resulting in high-temperature
sulfide corrosion and eventually
tube failure.
Refractory curing heating rates are
normally provided by refractory vendors.
Speeding up the commissioning
process results in refractory failures,
leading to hot spots on the metal shell
and breakages in refractory.
Refractory linings must be dried very
slowly prior to the introduction of acid
gas to ensure that moisture is completely
removed. If not properly dried, embedded
moisture may form steam, resulting
in a crack in the refractory (FIG. 3).
Catalyst slippage from the converter.
Converters are horizontal vessels that
support catalysts on bar-type gratings
(FIG. 4A). Normally, the top of the grating
contains stainless-steel mesh held under
the weight of ceramic balls, with the catalyst
on the top.
On a project, catalyst leakage was
found in large quantities in the downstream
sulfur condensers. On investigation,
it was noticed that the wire mesh
above the grid did not cover the grating;
it had slipped out from its place, creating
an opening near the side wall.
To overcome this, the design was modified.
An overlap of 4 in.-6 in. of mesh on
the vessel wall was used and held in position
by additional stud anchors and a
clamping plate (FIG. 4B).
Sulfur condensers (mist eliminators
and inclined nozzles). Sulfur condensers
are conventional shell-and-tube heat
FIG. 3. Refractor damage caused by dry-out.
FIG. 4. View of converter mesh (A) and
clamping plate (B).
FIG. 5. Modified sulfur condenser demister box.
Hydrocarbon Processing | FEBRUARY 2022 65
Hydrocarbon Processing - February 2022

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