Ammonium bisulfide corrosion of reactor effluent air coolers (REAC) and stripper overhead is a reliability issue for the refining industry. This type of corrosion has already resulted in major equipment failures, fires and explosions.
Organic sulfur and nitrogen compounds are converted to hydrogen sulfide and ammonia in hydrotreater reactors. When the effluent is cooled below 250 F, the gases combine to form ammonium bisulfide (ABS) salt. To prevent accumulation of the salt, water is injected before the reactor effluent cools to the ammonium bisulfide deposition temperature. Downstream from the point of injection, the equipment is then subjected to a sour alkaline solution with high concentration of hydrogen sulfide, ammonium bisulfide, and contaminants such as chloride, cyanide, and dissolved oxygen. Change in feedstock, upset conditions and/or wash water injection problems result in plugging of some exchanger tubes causing under-deposit corrosion. The non-plugged tubes are then subjected to high effluent flow and experience severe erosion-corrosion. ABS corrosion has already resulted in major equipment failures, fires and explosions.