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Texas Tower (VCFE Platformer) Drilled From Below

VCFE tubes cleaned with only 2m head room and top header in place

Summary

A Vertical Combined Feed Exchanger (VCFE/Texas Tower) at a refinery on a Caribbean island was suffering badly from blockages and constrictions in some of its 2,006 x 24 metre tubes. Tube Tech mobilised to the Caribbean and successfully cleaned the exchanger, even though details of restricted top access were somewhat lost in translation. By modifying its automated technology, however, Tube Tech continued the work from below and the tubes were successfully pressure jetted.

Challenge

At full operating efficiency, the refinery meets a substantial proportion of the island’s energy needs.
The refinery 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 VCFE (Texas Tower) was running at significantly reduced performance, due to an unknown number of tubes being either blocked or severely constricted.
The client estimated that approximately 12% of the 2006 tubes were blocked.
This estimate was based on the number that local contractors had previously been unable to clean.
Once the exchanger was opened up, it was found that the number of blockages was closer to 50%.
Tube Tech’s target was to unblock approximately 250 tubes in the time available.
Planning for the project was complicated by a language barrier problem, as a result of which there was unexpectedly limited access to the top of the exchanger.

Solution

With the project located many thousands of miles from base and its additional resources, the Tube Tech team put many hours of work into planning and preparation.
This included creating a full-scale mock-up of the bottom end of the exchanger, to ensure that safe man entry and access to the tube face would be possible.
When the equipment to be used was all packed there were several different but complementary systems being shipped to the Caribbean to ensure that all eventualities were covered.
A unique ‘pulsed jet” system – specially developed to locate blockages, where pulsed air/water is used to calculate back pressure. This is excellent for locating and calculating the severity of the restrictions as well as blocked tubes.
A unique, heat-treated, multi-lance to deliver ultra-high pressure water within the small tubes but with sufficient flexibility to clear blockages, backed up by the SafetyBossT, which prevents the lance head exiting the tube whilst under pressure.
Once the VCFE was opened up, a variety of deposits were discovered: hard mud, gum-like deposits, ferrous oxide scale, PCA and ammonium salts.
With access to the top of the VCFE limited to an 18″/450mm flanged access port, drilling of the 300 x 24 metre long tubes had to be carried out from below, which was itself a considerable challenge – and a world first.
Tube Tech was up against the clock in getting the project completed in time. In just five days, however, over 300 tubes were unblocked sufficiently to return the tower to production.
With a few more modifications, Tube Tech feels confident of being able to clear the remaining 750 tubes on a return visit, in a similar time.

Client Comment

T/O Coordinator: “We planned the clean of the Texas Tower carefully to minimise downtime, but we did not expect the number of tubes that were found to be constricted or blocked when the exchanger was opened. Once support services had finished modifying the scaffolding and supplies to Tube Tech’s requirements, cleaning progress was very good. It was unfortunate that the right information about the top of the exchanger was lost in translation, but Tube Tech showed great resourcefulness in adapting to the situation. Our VCFE was cleaned and inspected to production standard without overrunning the shutdown period.”

Tube Tech Comment

Mike Watson, Technical and Managing Director: “Whilst it was disappointing that the plant could not spare the time for us to unblock the remaining tubes, this particular project represents yet another world first. I am confident of this, because I am sure no other company can claim to have drilled vertically and continuously – without reconnecting and disconnecting extensions – over a 25 metre length through 14mm i.d. blocked tubes. What is more, we achieved all of this within a headroom of just 2 metres – a very confined, restricted space indeed.

This project was a classic case of how important clear and accurate communication is. We have since used interpreters on our conference calls to avoid any such ambiguity happening again. Our experience on this occasion vindicates our policy of taking several alternative cleaning systems to these international jobs. If we hadn’t been so well equipped, the discovery that the top header of the V.C.F.E. could not be removed would have been a very severe setback.”

Clients can be contacted via Tube Tech for references.

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