Spark erosion restores Shell plant's capacity

Edited by the Engineeringtalk editorial team Jul 19, 2004

Innovative use of Furmanite's spark erosion technology applied at Shell's Stanlow petrochem plant at Ellesmere Port has helped to increase production efficiency, restoring design capacity.

Innovative use of Furmanite's spark erosion technology applied at Shell's Stanlow petrochem plant at Ellesmere Port recently, to remove metal deposits threatening to block reactor vessel nozzles, has helped to increase production efficiency, restoring design capacity.

Spark erosion is usually deployed for metal disintegration to remove seized or broken studs and bolts, and dismantle and remove old, damaged or disused plant.

Its use in this instance to remove metal laydown now opens up the potential for this technology in broader applications.

The product passing through the catalyst in the 40ft reactor vessels in the Neodol and Linevol plants at Shell Stanlow produces a byproduct which builds up as hard deposits in the pipelines and particularly the nozzles, restricting flow and reducing production efficiency.

"Clearly the deposits need to be removed, and in the days when outages were longer this metal laydown (which has a value in itself) could be chipped off by hand", Furmanite Sales Engineer Neil Hibbert explains.

"Today's short and tightly scheduled shutdowns mean this is no longer a viable option, but there's still a need to remove the deposits which would otherwise create a severe restriction, and eventually a blockage".

"Traditional machining is one option but the deposits being very hard means that conventional machining methods would cause loading on the nozzles and possible weakening of the welds", Hibbert continues.

"The other option to remove and replace the nozzles would incur significant time and high expenditure due to the inconnel lining, and complicated weld procedures".

Engineering solutions specialist Furmanite was called in and put forward an alternative solution using spark erosion.

As a specialised cutting technique that breaks down almost any metal or other fully hardened material into minute particles, spark erosion does not generate cutting forces and can be used where conventional processes are difficult, damaging or dangerous to use as in this case.

The operation involves an electrode held in the cutting head of the disintegrator, and combines a cutting action with a continuous series of high frequency electric arcs.

A nonhazardous coolant is pumped through the electrode to wash out the powdered waste material.

Moreover, the process is relatively quick and highly efficient, thus meeting the need to complete the work within the one-week shutdown.

The flexibility of the system the cutting head can be set up at any angle, including inverted was also important in this application.

The nozzles to be cleared included a 3in drain at the base of the reactor (treated vertically using a 50mm electrode) and three 2in inlets at the top of the reactor column (which were treated horizontally, using a 38mm electrode).

As the technology had not previously been used for such an application, trials were set up at Furmanite's Kendal workshops, demonstrating that the objective could be achieved; the deposits were successfully removed by being turned to dust, with no load on the pipes.

The work was then successfully completed during the scheduled seven-day shutdown in September.

Shell's Engineering Services Manager Chemicals Sean Figov commented: "We were delighted with the job Furmanite undertook for us".

"We have never cleared the nozzles so effectively with any previously tried methods".

"The reactors had developed a pressure drop that was some three times the design value".

"A combination of this spark erosion and replacement of piping has reduced this pressure drop to the expected design value, returning the unit's capacity to its original design capability".

"Moreover, subsequent NDT inspections have shown that there has been no damage to the pipe walls or lining".

"It really has proved an excellent solution to the problem".