Preventing ammonium salt fouling and corrosion.
The presence of chlorides or salt formation can lead to damage or production losses in oil refineries. Usually, these salts are ammonium chloride (NH4Cl) or ammonium bisulfide (NH4HS). Process units suffering salt fouling or corrosion are crude distillation units, hydrotreaters, hydrocrackers, FCC units and reformer units. Salt formation is frequently observed on the tube walls, fractionator trays, piping and heat-exchanger surfaces. The salt deposit formation leaves a highly concentrated, thick, acidic, viscous solution. This can result in under deposit corrosion (pitting corrosion) as the salt deposit absorbs moisture. Ammonium chloride or ammonium bisulfide salts are highly corrosive. Wash water systems are installed for the reduction of a salt deposit risk. It is certainly a good step in the right direction to remove as many salts as possible. Ammonium salts are generally readily soluble in water. But in the presence of hydrocarbons salt deposits often cannot be completely removed.
Kurita has developed a unique chemical treatment programme, known as ACF Technology. Liquid formulations of a very strong organic base are used to avoid acid corrosion or salt formation. The organic base ACF reacts preferentially with strong acids such as hydrochloric acid (HCl) or its ammonium salts. The favoured reaction of ACF with HCl is a significant benefit in process units with naturally high H2S concentrations. At locations, where salt formation occurs, ACF displaces the weaker base ammonia by forming a liquid ACF salt. The reaction products have very high moisture absorption characteristics (highly hygroscopic). ACF salts have a very low corrosivity and can be removed easily with free water.
ACF treatment programmes are used continuously for the prevention of salt formation and corrosion attack. ACF reacts immediately with acidic components and minimises the salt deposit potential. This allows refiners to run the distillation units with a higher productivity and higher reliability.
FCC units frequently suffer from ammonium salt fouling. In many cases, ammonium chloride salts increase the pressure drop or cause flooding of the top trays. Removal of deposited salts during normal process operations is particularly very useful in crude oil refinery processes. Traditional tower washing procedures may remove water-soluble salts. But the feed rate must be significantly reduced during this time. Produced naphtha, sometimes also light cycle oil(LCO), goes off-specification. It must be reprocessed with increased costs. When ammonium salt fouling is detected, an online cleaning with ACF is the first choice to dissolve the deposited salts from the top trays. Throughput reductions are not required. Deposited salts are dissolved and mobilised in a short period of time. A rapid decrease of the differential pressure typically demonstrates the success of the online treatment.
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