On the coking problem in gasoline hydrogenation units

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Prolonged storage of coker gasoline can induce the polymerization of dienes. Dienes are highly prone to polymerization even under normal temperature and pressure; however, the polymers formed are oligomers that remain dissolved in the gasoline. After storage, the coker gasoline, under high hydrogenation temperatures and pressures, causes the oligomers of dienes to rapidly transform into polymers, resulting in severe scaling. According to relevant literature, unsaturated hydrocarbons such as dienes in coker gasoline undergo significant condensation reactions at around 220°C. During storage, it is not possible to completely isolate the storage tanks from air; as a result, the coker gasoline feedstock comes into contact with oxygen and undergoes oxidative condensation reactions, which alter the properties of the oil. The gel content in the oil increases significantly. This gel can further undergo polymerization reactions when it enters the hydrogenation unit and the temperature rises in the heat exchange system, leading to scaling in the heat exchangers located before the reactor. Therefore, the deterioration of the properties of crude oil coker gasoline during storage and transportation is the main cause of fouling in heat exchangers.