Thermal cleaning: Not an alternative, but a better way of cleaning

It is actually quite simple to thoroughly clean your heat exchangers. After all, if the cleaning method used succeeds in pulverising the organic contamination to only a few percent of the original amount more specifically in the form of easily removable dust, then cleaning thoroughly is child’s play. While this all sounds very simple; is it also achievable in practice?

By Robert Mol, CEO of Thermo-Clean Group

To answer this question, it is important to know a little more about the technique that makes all of this possible: thermal cleaning. This technique involves the use of special ovens in which the combination of heat and low oxygen levels will ensure that the organic components in the fouling are converted into pyrolysis gases and dust residues. During the process, these gases are used as a source of energy with which the furnace plant is brought up to adequate temperatures and to maintained the heat. Thus, most of the pollution is already processed in an environmentally friendly and useful way. What remains is dust consisting of ash residues and inorganic components, which can be easily removed afterwards by hosing down the previously polluted area.

As this thermal cleaning method features the combination of heat and the fact that a kilo of dirt is converted into 50 grams of dust, it is now possible to clean all those hard-to-reach places.

Advantages of thermal cleaning

With thermal cleaning, it is therefore possible to simultaneously remove contamination both inside pipes, around pipes, between pipes and jackets, and even in pipes with static mixers. As a result, the areas can be thoroughly cleaned and this has many advantages:

• Improved heat exchanger performance
• Improved heat transfer
• Reduction of greenhouse gas emissions
• Saving on operating costs
• Fewer maintenance shutdowns
• Longer operating hours
• Less wastewater

A cleaning technique that can return a heat exchanger close to its original design values is a very important asset today. It automatically results in far fewer maintenance shutdowns and also makes a huge difference to the energy consumption of the production process. This can really save hundreds of thousands of euros or dollars per year per cleaned heat exchanger; a nice result for an initially slightly more expensive cleaning method. A clean bundle transfers heat much better and, as a result, much less energy is needed to keep production running properly.

Practical considerations

When using this cleaning method, it is of course important that the parts can withstand the temperatures used. A normal treatment is generally carried out between 400 and 450°C (752 °F and 842 °F), and the metal components of the material must be able to withstand this. Aluminium exchangers are thus already ruled out for thermal cleaning.

For special alloys which cannot withstand this temperature, such as duplex steel or Monel, two-stage cleaning is often performed. Here, the contamination is first thermally cracked at a lower temperature, after which the residue will be removed by hydro blasting. As the fouling becomes somewhat more brittle due to the thermal treatment, it is relatively easy to completely remove the residue using water blasting. A thermal test with the fouling will soon reveal whether this is a feasible cleaning option or not.

Ideal candidates

The broad range of parts can be treated by thermal cleaning: heat exchangers with pollution in and between the tubes; heat exchangers with fixed housings and pollution between tubes and the shell; compablocs, heat exchangers plates, spiral heat exchangers; vane decks, demisters, mellow packs; pipe work (also with static mixers); extruder screws & parts; polymer & refinery pumps; flame arrestors, sieve packs, valves; filters, spin packs, die plates, hot runners, and so on.

In principle, all parts resistant to the temperatures used, polluted with organic material, can be thermally cleaned. Note: inorganic fouling can only be removed if it is part of a fouling mix with organic components. In such cases, thermal cleaning will remove the organic part (the adhesive in this case), leaving the inorganic part loose and ready to be removed by the post-treatment technique.

Comparison between hydro blasting and thermal cleaning, based on heat transfer performance

Downsides

As with any technique, there are some drawbacks with this cleaning method. Aside from the materials having to be able to withstand the high temperatures, pyrolysis furnaces are not mobile, so only offsite cleaning is possible. In that case, your proximity to a potential supplier possessing this technology in-house obviously plays an important role.

Moreover, thermal cleaning is a highly specialised niche, and not all pyrolysis furnaces are suitable for it. Perfect temperature control, the ability to heat up and cool down slowly, and the creation of a low-oxygen environment are important prerequisites for using this technique properly and safely. Not only does the pyrolysis furnace need to be installed correctly, but the necessary expertise is also required to bring the cleaning to a successful conclusion. Because of these restrictions, only a few companies in the world can offer this in a professional manner. As a result, the current capacity is quite low, and it is sometimes difficult to clean all parts with this technique within a few days or weeks during a major shutdown. In practice, such capacity problems usually mean that thermal cleaning is only used for the bundles that will benefit most from this excellent cleaning quality.

Looking forward

Thermal cleaning is not an alternative, but simply a much better cleaning method for a very large spectrum of contaminated parts. The technique itself has been around for years and is increasingly being used to bring dirty heat exchangers from various industries to a higher level of clean. The fact that this method generates much less waste and, additionally, could result in a huge reduction in CO2 emissions, are huge assets that make thermal cleaning even more appealing for the future.

Practice shows that thermal cleaning is now widely used, and the method is fortunately becoming more and more familiar to the general public. Choosing the right cleaning technique is very important, as it largely determines the efficiency of your production process in the future.

About the author

Robert has been the CEO of the Thermo-Clean Group since 2005. What started as a company with only three employees is now a network of ten sites in total, scattered across Europe. Robert regularly lectures about thermal cleaning and there are numerous articles in various trade magazines about the cleaning technique.