Tube Tech has developed a robotic fired heater convection bank cleaning technology (shown in Figure 4) to specifically address the issue of poor or limited access encountered when attempting to remove fouling from the convection banks of fired heaters.
The robot acts as a delivery vehicle for one or two lances, capable of delivering the range
of cleaning media shown in Table 1. The choice of cleaning medium (see Table 1) is dependent on the nature of the deposit. The blast medium cleaning radius is delivered within a distance of one inch from the fouled surface.
As a consequence, the robot can remove the hardest of deposits and can do so between every tube row while providing 360 degree tube surface contact, regardless of whether the design is square or triangular pitch.
In contrast to the conventional cleaning methods detailed earlier, robotic fired heater convection section cleaning physically penetrates deep inside and between every row of finned or studded convection tubes.
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Figure 4. The robotic fired heater convection section cleaner developed by Tube Tech

The robot can either use one lance for cleaning and one for inspection – allowing
inspection to follow immediately after to verify cleanliness without delay, conversely two lances can be used for cleaning, resulting in twice the productivity per robot. Productivity can be further enhanced and downtime reduced further by the simultaneous deployment of multiple robots, at multiple levels.
The robotic cleaning procedure begins with the placing of the robot on top of each
convection bank via existing access doors. If new doors are required, they can be cut in whilst the furnace is running prior to shut down, thereby removing this element from the shut down period, reducing down time further. The door size can be as little as 150 mm x 200mm in dimension and as large as 24 in².
The robot is equipped with cameras allowing it to be remotely controlled from an operator
external to the convection bank in which the robot has been placed. The lances are remotely
activated and are preset to the technical drawings provided by the client, ensuring that each
row of each convection bank is cleaned at every level (see Figure 5). The robot can negotiate a convection bank with as many as 20 rows from top to bottom. It can also operate
vertically upwards.
Once cleaning has been completed, the robot inspects between each row with a flat,
blade shaped camera and records the data for cleanliness, and integrity evaluation whereby
images and video clips are recorded for archive purposes. The resulting archives can be used
by clients to be used as a benchmark, for post contract evidence and for future cleaning and
inspection assessments which can be matched to overall fired heater performance before and after future cleaning exercises.

 

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Figure 5. Images showing the manner in which the robot can access deep between
every tube row for the very first time regardless of depth.
Regardless of whether the convection bank is square pitch or triangular pitch, the blast
cleaning pressure emitted from the nozzles does not hit the refractory as the angle of the jets
is such that they deflect off the tubes first where the pressure is dissipated quickly. There is
therefore no danger of refractory damage, as witnessed by Shell Global Solutions, worldwide
independent consultants.
The refractory will only ever get damp and the moisture is easily evaporated during the normal run up procedures. A shroud can be easily attached to the lance to provide plant operators with extra confidence that the high pressure blast medium such as liquid ice, CO2, water, etc., does not make contact with the refractory wall.
The robot delivers any cleaning medium e.g. air, steam or water at pressures ranging
from 600 psi to 60,000 psi (4000 bar) with volumes as low as 2.5 litres per minute and can be collected below the last convection bank and removed to an awaiting tanker or straight to the plant’s interceptor tank.
The development of robotic cleaning systems means that fired heater operators now have
the choice between either manual or static lancing (both of which in many cases struggle to
remove the more tenacious and fused deposits) or robotic fired heater convection section
cleaning which ensures removal of any form of deposit no matter how hard delivering a far
superior clean combined with inspection within a window of just two days. This is made possible by the way the robot runs up, down and across every row and physically penetrates every deposit across every tube row.
As the rate of deposit formation is often dependent on surface roughness, with rough
areas providing nucleation sites for new deposits (9), the better the finish on the finned
convection bank tubes, the slower the fired heater’s performance will degrade, allowing the
operator to delay the unit’s next clean for longer.
When selecting the cleaning method for a fired heater’s convection bank – it is crucial to
consider the risk of cleaning failure, which is particularly high when the fouling is in the form of harder deposits. Should a standard lancing technique fail, the operator will be forced to take the unit offline sooner, adding lost production to the cost of cleaning.
Robotic fired heater convection section cleaning is extremely cost effective considering the improvement from an average of 2% surface coverage to near 100% surface area coverage.