Image of a water lance cleaning the carbon build-up off the inside of gas pipes.

Coke build-up was removed using water lances however, this proved ineffective.

Step-by-step approach unblocks operations' heart

Researchers investigating techniques for removing carbon fouling from gas outlet tubes discovered that the water-lancing technique being used ‘was a bit like squirting a garden hose into a tornado’.

  • 20 February 2008 | Updated 14 October 2011

Carbon build-up poses problem

Carbon build-up in gas pipes is a problem akin to suffering blocked arteries for the reactor units critical to processing operations.

But a change of ‘diet’ to combat the condition is not an option for companies such as Syncrude, which produces synthetic crude oil from bitumen-bearing sands – an especially low-grade and heavy feedstock.

Instead, the Canadian company has been working with CSIRO since 2001 to better understand the problem and improve the cleaning technique for carbon (or coke) fouling at its upgrading plant.

Research Scientist Dr Seng Lim says overall drivers for the study (from Syncrude’s point of view) are to improve plant performance, minimise downtime and eliminate hazards for operators doing the cleaning.

Coke fouling is an expensive problem

The research focuses on fouling in FLUID COKING™ units, where bitumen is mixed with extremely hot carbon as part of the upgrading process that takes place at the Syncrude plant prior to downstream refining operations.

Dr Lim says coke released as a by-product of the reaction in the FLUID COKING™ units builds up on various reactor components, but the most critical fouling involves the gas outlet tubes, creating a major bottleneck.

'The reactor is the heart of the process and if you have things blocking it up then, just like a heart artery, you can’t go on,' Dr Lim says.

He says Syncrude’s coke fouling problem forces expensive plant shutdowns when the blocked pipes are cut out and replaced.

If CSIRO’s findings were able to help the company extend running time between such shutdowns it would save millions of dollars in costs and boost plant productivity.

Cleaning technique studied

Syncrude tackles the coke build-up in its gas outlet pipes through a program of water jet cleaning, carried out while the reactors remain online.

Contractors use a flexible lance to apply a high-pressure water jet to blast the coke build-up.

Dr Lim’s team has implemented a series of experimental and computational approaches to help Syncrude understand the behaviour and performance of that cleaning technique.

Scale model reveals limitations

Dr Lim says a carefully designed scale model reflecting the hydrodynamics within the gas outlet pipes has played a key role both in carrying out the required research and being able to clearly demonstrate findings to the client.

'The scale model showed strong interaction of the gas flow in the gas outlet tube with the water jet cleaner, clearly revealing the true limitation of the existing technique. It was a real eye-opener for the plant operator.'

With gas coming out of the outlet pipes at about 60 to 80 metres per second, or well over 200 kilometres an hour, the tests showed that trying to direct a water lance inside was 'a bit like squirting a garden hose into a tornado'.

Dr Lim says a large test-facility was also built to help understand the cleaning process using the commercial-scale lancing at high temperature, emulating the plant environment.

Innovative approaches key to understanding difficult problem

“The reactor is the heart of the process and if you have things blocking up there then, just like a heart artery, you can’t go on.”
Dr Seng Lim, Research Scientist, CSIRO Minerals

'The ability to design and then perform such testing is the key strength of the CSIRO team – tackling practical, industrially relevant problems,' Dr Lim says.

Dr Larry Hackman, a senior research associate at Syncrude, says Dr Lim’s team has provided innovative approaches to developing experimental methods and interpreting the results.

'Seng has done an outstanding job in taking a very complex industrial process and developing experimental techniques to understand such large-scale systems in a laboratory environment,' Dr Hackman says.

'This includes a hot pilot plant that was able to reproduce the removal process at operating conditions.'

Call for assistance gets unexpected response

When Syncrude originally issued a call for assistance with its coke problem, sending out a general request for research proposal (RFRP) to understand what was happening with its cleaning system, the response from CSIRO took an unexpected form.

Dr Lim says that rather than responding to the request as outlined in the original RFRP, CSIRO proposed a different approach and strategy.

'There was a risk of not getting the project because we went outside the scope of the request and suggested a way we thought would be more useful.'

'To our surprise they accepted and commended us for our originality with genuine intention to address their true need,' Dr Lim says.

'We think outside the square a bit – coming up with different approaches to addressing the problem.'

CSIRO goes 'back to basics'

The approach was to carve up the job into different stages, creating a number of experiments and models to ‘demystify’ some company thoughts about how water-lancing worked.

Essentially it was a ‘back to basics’ approach, Dr Lim says. 'That way we could try to understand, step-by-step, the underlying causes of the problem.'

The resulting research contract built on a relationship CSIRO had already developed with Syncrude, aided by links Dr Lim established when he completed postdoctoral studies at the University of British Columbia, in Vancouver, Canada, in the early 1990s.

And while the initial project assessed the water-lancing technique in use at the Syncrude plant, a newly-approved contract is set to take that work a step further, with the aim of establishing a more effective approach.

Outcomes

Dr Lim says the CSIRO team is very pleased with the project outcomes and the relationship it has built with Syncrude.

'The most important outcome is that they fully understand and appreciate the current limitations, reinforcing the real need to look for better, more effective and safer alternatives, which is the emphasis of the newly negotiated contract.'

Read the resume of Dr Seng Lim: fluidised bed specialist.

  • This article originally appeared in the February 2008 issue of Process magazine.
  • FLUID COKING™ is a trade mark of Exxon Mobile.