Author: Mike Watson, Managing and Technical Director, Tube Tech
Abstract: A review of polymer fouling challenges, the limitations of traditional polymer removal techniques and an assessment of new innovative polymer removal methods.
An End to Polymer Removal Desperation
Often deemed impossible to remove and most definitely impossible to ignore – polymer fouling is the cause of many a maintenance professionals headache. Having used innovative technology to removal polymer from a variety of plant equipment Mike Watson, Managing Director of Tube Tech, discusses common challenges found within all polymer removal contracts, the limitations of traditional polymer removal techniques and highlights case studies demonstrating new polymer techniques used within a cross section of industries.
Common Polymer Removal Challenges
Polymer fouling not only damages equipment and impacts on heat transfer efficiency but also adds expense to plant operation due to frequent shutdowns.
The potentially hazardous nature of polymer fouling creates a number of challenges to those aiming to remove it. In the main non-man entry is a prerequisite for polymer removal from vessels due to the potentially hazardous nature of the fouling and fume.
The removal of polymer from heat transfer equipment can also include access issues. If tubes are plugged or gaps between the tubes on the shell side are blocked the challenge becomes creating an entry point to make direct contact with the fouling.
Another challenge is ensuring no damage is made to the coils, blades, paddles etc within tanks and vessels. By default the cleaning techniques used to remove polymer have to be forceful yet the fragile internal mechanisms of the vessels have to be taken into consideration.
Traditional Polymer Removal Techniques
Solvents and chemicals have been used to try to remove polymer based fouling for a number of years with limited success. These techniques are expensive, create a huge amount of waste and can cause serious environmental damage.
Some companies are still using hammers, chisels and even chain saws to remove polymer blockages. These methods are dangerous, exceptionally time consuming and often needs to be used in conjunction with another method to achieve a reasonable level of cleanliness.
Numerous drilling methods have also been tried to remove polymer from within tubes including turbine drills, pneumatic drilling methods and dry drilling. The drilling of polymer unfortunately carries with it the risk of damage to equipment.
Traditional high and even ultra high pressure water jetting can remove polymer blockages but can take a huge length of time. Traditional water jetting techniques often just ‘bounce’ off the deposit.
Innovative Polymer Removal Methods
Severe raw polyethylene shell side fouling on reactor tubes was like having a 1m cube solid block of high density polymer surrounding the stainless steel tube external surfaces. The client urgently required passage between the tubes. The biggest challenge was not only removing the polymer deposit from the external tube surfaces but overcoming the problem of “access between the 5mm gap between the tubes” . Traditional high pressure water jetting and band saws could only create a gap the width of the saw blade and nothing more.
Tube Tech made design modifications to their Shell Jett system, originally designed to clean the shell side of Texas Towers (VCFE/Platformers). The system removed a staggering 95% of the polymer fouling from the shell side compared to 20% removed by traditional cleaning contractors. The process was applied using semi remote equipment to minimise the fatigue element making the cleaning process far safer and therefore quicker.
A 5m high x 2.5m diameter polymer mixing vessel became unserviceable following a process error that caused its contents to fuse into a solid mass of styrene. The plant’s operators tried chiselling the hard styrene out, but after several weeks had made little impression on it. Replacement of the vessel would be expensive, take too long and be problematic structurally. Cleaning could be complicated by the heating coils around the wall of the vessel, as any cleaning solution would have to be able to reach behind them to remove the styrene.
Until there was room in the vessel for an operative, the work started with a remote head, removing styrene from the manway. Once the manway was cleared, Tube Tech used a WysperJeTT™, running at up to 60kpsi but producing very low water volumes. This combination is extremely powerful but has little reactive force, so is not tiring for the operator. The lance does have to be held very close to the target, as the water’s energy dissipates rapidly. Much of the 2-3 litres-per-minute jetting water actually disperses as vapour, leaving relatively little to be pumped out of the vessel. Having an operator working safely in the vessel meant that it was possible to cut away the styrene behind the heating coils and around the central mixing shaft and paddles completely. The vessel went back into production quickly without the trauma and expense of replacement.
Operators risk huge financial losses while trying to remove polymer using inadequate traditional cleaning techniques. “I get so frustrated with those who hold a ‘this is the way we have always done it so let’s carry on doing it this way’ attitude. Traditional techniques, especially those that are ineffective and costly, need to be challenged constantly,” says Mike Watson. Tube Tech believe that the polymer production sector stand to benefit greatly from innovative specialist cleaning contractors who are willing and able to utilise bespoke polymer removal techniques.