Despite their wide usage, the existing coating options doesn’t offer long term solutions for addressing corrosion issues. “We are working on a coating specifically for the hydrotreating process within refineries. Hydrogen is used to improve the product and reacts with impurities such as Sulphur, Nitrogen, and Chlorine in the feed and goes to the scrubber to remove impurities before returning to the recycle compressor. The problem that can occur is the build-up of hydrogen chloride and ammonium chloride. And it causes severe pitting of even 17-4 PH stainless steel,” says Derrick Bauer, Materials Engineering Manager, Elliott Group.

Derrick Bauer shared his presentation titled, ‘Specialty coating for hydrogen recycle compressors in the refining and petrochemical industry’ at the NextGen Chemicals & Petrochemicals Summit 2021 organized by Indian Chemical News on 7-8 October, 2021.

“Operators of compressors are always looking for the solutions. One option is injections of Naptha. However, customers report mixed results with some cases making the problem worse. Ammonium Chloride has very low solubility to Naptha. Water injection could be an effective option as it has a very good success while using detergents to clean during shutdowns. Ammonium chloride is soluble in water and thus is an additional positive point. However, it can result in severe corrosion if not done properly. Given that the other options aren’t fully satisfactory, coatings offer easy solutions that can be implemented any time. Coatings may not completely solve the problem but will at least provide directional improvement. It also doesn’t affect the process," says Bauer while talking about the problems with current coating options.

“Among the currently available options, Organic Coatings offer excellent corrosion resistance and fouling resistance. However, these are not sufficiently durable for a 5-7 year operational period. Another is Electroless Nickel which offers good corrosion resistance and fouling resistance besides excellent durability. At the same time these coatings have not been tested for behavior with salt type foulant. Industry standard coatings include PTFE coating over a corrosion resistant base coat. This is a 30-40 year old technology and widely utilized in hydrocarbon service. Variations of topcoat exist within the industry," adds Bauer.

Talking about the solutions, Derrick Bauer says, "We conducted the Foulant Adherence Test for testing the coating. In the process, the plate sample is mounted to a holder (chloride spray on to a coating panel) situated rig and there is a heater behind it that blows 100 degree Celsius. Gravity feed spray nozzle is mounted to an actuator which moves and a solenoid valve is opened every 30 seconds to intermittently spray foulant. At the end of the 24 hour period, there would be an air blade that would tend to blow off foulant. The coatings were compared to see how much of the foulant was removed. Pos-E Coat Protect coating the best performer (81 percent clean) during the process. 20 different coatings were tested and it was found that industry standard coatings were okay in the process but not very effective. Similarly the other tests such as EIS Test was done as well and Pos-E Coat Protect performed well there too. It offers the best combination with continuous operations at 280 degree Celsius temperature. It has the best anti-fouling properties, corrosion and water resistance. It outperformed currently available coatings in Hydrogen Recycle Compressor environments.”