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Sasol, in Moers, Germany, asked its in-house contractor Schliemann to come up with a safer and more automatic system to clean its heat exchangers. Schliemann, an independent contractor in Germany, decided to turn to Peinemann of Holland, a leader in specialised heat exchanger cleaning and extraction equipment.

As approximately 33% of all accidents with high-pressure water occur with flexible lances, the latter have always been a concern all over the world. In The Netherlands, regulations for high-pressure cleaning of exchangers prescribe the use of automated equipment as much as possible. These regulations, first officially installed in 2009 and created by the Waterjet Foundation of The Netherlands (SIR), have now been adopted by the Dutch health and safety executive (ARBO) law, which protects all conditions for workers. These special regulations have resulted in a few special heat exchanger cleaning machines with single-, dual- or triple-lance feed mechanisms. As many plants in The Netherlands have already seen a dramatic increase of heat transfer by using automated equipment versus manual cleaning, it was an easy step to adopt a system that also provides a safer environment for the operator.

The basic problem with manual cleaning of exchangers is the following: in order to be able to clean tubes in a safe way, the waterjets must always have more backward jets than forward jets to move the nozzle away from the operator during cleaning. These reverse waterjets are used for propulsion of the nozzle and not much for actual cleaning of the tubes. Another issue is that most operators are not allowed to pull the nozzle back under pressure, which results in a one-way cleaning path. As the speed of the nozzle is inconsistent compared with that of a machine, the cleaning quality differs in the tube, resulting in a non-smooth surface where contamination easily builds up.

When tubes are blocked, there is another serious threat: hydraulicing of the nozzle. This occurs when the water coming out of the nozzle is able to build up pressure inside the tube, which can result in the nozzle shooting back. Normally, when high-pressure water leaves the small hole in the nozzle, water pressure is converted into high speed. For example, when 1,000 bar is used, the speed of the water leaving the nozzle is around 1,000km/hour. We have also seen (fatal) accidents with flexible lances coming back out of the tube due to damage on the thread of the nozzle or broken fittings on the high-pressure hose.

Cleaning the Vertical Bundles at Sasol in Moers, Germany
The results were very clear after cleaning the heat exchangers at Sasol. While the manually cleaned bundles often had to be cleaned every four to five weeks, the cleaning cycle increased to eight to nine weeks after switching to the machine.

This result was thanks to the special nozzles, which were used at a 90º angle (instead of having to move the nozzles) in order to use the water as efficiently as possible for cleaning the tube. Another reason was that the machine moved the nozzles at a constant speed in and out of the tubes under pressure, cleaning the tubes twice.

When tubes are cleaned properly, it can result in a 30–40% additional heat transfer for the plant owners. This results in better production, mostly close to the values achieved when the plant was new. Studies have shown that a 1mm layer of scaling can result in 10% additional fuel required to reach the same amount of heat transfer as a 100% clean tube. In these days, with rising oil prices, these costs can be substantial.

The heat exchanger that had to be cleaned was a large-diameter (3.2m) vertical bundle with around 2,000 tubes that are fixed in place (see Figure 1). Inside the tubes, which have an internal diameter of around 16mm, there was a medium-hard contamination with some blocked tubes. Cleaning was performed with a pressure of around 800–1,000 bar with a flow of around 40l per flexible lance, and thus 120l in total for the three flexlances.

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