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Texas Tower (VCFE Platformer) Cleaning Improves Heat Transfer

Arabian VCFEs cleaned despite wide variety of deposits

Summary

Flow through two vertical combined feed exchangers (VCFEs/Texas Towers) at a middle eastern refinery of one of the world’s largest Arabian oil companies had become severely restricted. Just how restricted became apparent when Tube Tech’s cleaning teams started working on them. Original estimates of 400 to 600 tubes blocked out of 6,000 x 21M long x 14mm bore, vertical tubes, turned out to be 3,000 tubes. In five days of gruelling conditions, Tube Tech successfully cleaned every tube in the two VCFEs to inspection standard, except for just three that were blocked by metallic debris, thought to be fragments of jetting lances and nozzles left behind by previous contractors.

Challenge

The refinery of one of the world’s largest Arabian oil companies includes a processing stage found in the most productive and successful refineries anywhere – the Continuous Catalytic Reforming unit or CCR Platformer.
Texas towers or VCFEs (vertical combined feed exchangers) play a vital part in the platforming stage of the refinery process.
Platforming product in its last stage of processing is passed into the Texas Tower to cool it down against cold feed.
The special design of Texas Towers minimises heat loss, thereby improving the fuel consumption of the unit’s furnaces.
It is therefore vital that the VCFE is operating as efficiently as possible and that means it needs to be cleaned thoroughly – both tube side and often shell side – to the highest possible standard.
The two Texas Towers at this particular refinery contain a combined total of 6,200 steel tubes.
The tubes are 21 metres long, with an internal diameter of 14mm.
Tube Tech was contracted to clean between 200 and 300 tubes in each VCFEwhich were belived to be blocked.
The client also stated that production standard would be quite satisfactory for the clean.
As the VCFEs were opened, it became clear that the client had underestimated the level of fouling.
Instead of 200-300 blocked tubes, there were almost 3,000 – practically half of the total.
In the face of high ambient temperatures, Tube Tech faced a significant challenge to meet the new objective in the time available, particularly as there were to be numerous operational delays that were beyond the company’s control.
An early obstacle was to be the lack of scaffolding that should have been provided by the client, due to the erection teams being fully engaged elsewhere on the site.

Solution

As always with major international cleaning projects, Tube Tech airfreighted not just one but several different cleaning systems to the client’s site – with just one week’s notice – to cover any unforeseen operational eventualities.
This meant that the lack of scaffolding did not prevent the clean from going ahead, thanks to Tube Tech’s inherent versatility and its ability to deploy a third, fall-back system.
The heavy gum found in approximately 30% of the heat exchanger tubes required frequent cleaning head re-configuration, as the system originally intended to clear this type of blockage could not be deployed, due to the absence of scaffolding.
With normal cleaning heads, the gum jetted out tends to solidify behind traditional jet nozzles and trap the lance, which means it can then become irretrievable.
In one of the VCFEs, Tube Tech found that three tubes contained metallic blockages that could well have been previous contractors’ broken flexible and rigid lances, drills or cleaning tips caught in just this way.
Apart from the three blocked tubes, all the others were successfully cleaned and unblocked.
In five days and nights of intensive working in 40DegC heat, the Tube Tech teams were able to clean both VCFEs to inspection standard, well in excess of the production standard expected.

Client Comment

Quote from Site Engineer: “Following the Tube Tech clean of the VCFEs, the heat transfer between the exchangers’ tubes and shell increased, thereby reducing the delta T between ROT and HIT. This is shown by the drop in temperature on the ‘after’ plot. The cleaning therefore led to hotter feed going to the downstream heater inlet. ”

Senior Shutdown Manager: “We negotiated carefully with Tube Tech’s local agent for many months in order to satisfy ourselves that the company could clean our Texas Towers to the required standard. We have used local and international contractors before, but with mixed results and the VCFEs have not performed as well as they could have, for nearly long enough following the clean, so we were willing to consider the Tube Tech alternative. For the first time since the refinery was commissioned, the Texas Towers on the CCR Platformer are giving us near-to-original efficiency and productivity.

Tube Tech Comment

Martin Byford, Operations Director: “Rarely do we encounter such a wide variety of deposits. We found literally everything – from a coke-like substance to rubbery gum-like full-length blockages. I am very proud of our teams for doing such a superb job in the limited time available, particularly considering the high working temperatures. We have completed several Texas Towers this year and we are confident that we can tackle such jobs successfully, no matter what we find when we get to site.”

Clients can be contacted via Tube Tech for references.

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