(35a) Debutanizer Bottoms Recycle for Enhancing Gasoline/ Water Separation in the Quench System

Deficiencies in raw pyrolysis gasoline (RPG) can be experienced when processing larger volumes of light feedstocks. Beside challenging the process abilities in maintaining RPG product specifications, it may affect the water/ hydrocarbons separation in the quench water settler. This could likely result in premature fouling of the dilution steam system. Poor separation can be cause by emulsion and/ or low RPG/ water ratio below the immiscibility compositions. While emulsion problems can be handled with emulsion breaker and proper pH control; operating below the liquid/ liquid immiscibility region can only be resolve by increasing the RPG/ water ratio. Recycling Debutanizer bottoms is one way of increasing the critical mass of gasoline in the settler within the RPG/ water immiscibility region. However, the stream contains a number of known fouling pre-cursors, which depending on the recycle location may increase fouling propensity in certain area of the plant. This paper discusses the expected distribution of fouling precursors relative to the recycle location in the Quench system and the effectiveness of the recycle in increasing the RPG/ water ratio.