New innovative HPNA management process to achieve virtually total conversion in a hydrocracker

CATEGORY: HYDROCRACKING
JoP - The Journal of Petrotech, Vol. VIII Issue 8 January - March 2013
New innovative HPNA management process to achieve virtually total conversion in a hydrocracker
Raju Chopra, Mike Hunter, Raj Patel, Sylvain Verdier
Haldor Topsoe India Pvt. Ltd.
Abstract
Hydrocracking is well suited for selective middle distillate production from heavy vacuum gas oils and operation with recycle of unconverted oil for maximizing the conversion to middle distillate products is highly desirable. However, certain undesired side reactions that are characteristic of all catalytic hydrocracking processes result in the production of small quantities of highly condensed aromatic ring structures commonly referred to as Heavy Poly-Nuclear Aromatics or HPNA’s. Unless purged from the system the HPNA’s will build up to unacceptable levels. The undesired formation of HPNA therefore represents a practical limitation on the total conversion achievable in almost all hydrocracking processes. The new innovative and simple HPNA management process reduces the unconverted oil bleed requirement from a hydrocracker and thereby increases the total conversion to distillate products that can be practically achieved.
The new process can deliver substantial economic benefits depending on the relative value of distillate product over the value of purged oil. This benefit is realized by concentrating heavy poly-nuclear aromatics so that the steady state purge requirement can be lowered by 50 to 80%. The process equipment requirements are minimal and can be retrofit to existing units with a low cost modular approach to give a very high return on capital investment.
Introduction
Certain undesired side reactions that are characteristic of all catalytic hydrocracking processes result in the production of small quantities of highly condensed aromatic ring structures commonly referred to as Heavy Poly-Nuclear Aromatics or HPNA’s. Once they are formed, HPNA’s are very difficult to convert catalytically in the process and will build up in the unconverted recycle oil stream unless physically removed from the system most commonly by purging a small quantity of the unconverted oil from the hydrocracker. This bleed stream can represent as little as one percent to as much as 10 percent of the feed and is commonly in the range of two to five percent in many middle distillate hydrocrackers. The undesired formation of HPNA therefore represents a practical limitation on the total conversion achievable in almost all hydrocracking processes. The conversion of this incremental purge to diesel and lighter products can deliver substantial economic benefits depending on the relative value of distillate products over the value of the purged oil. Topsoe’s HPNA Trim™ process is a unique, compact and highly cost effective design to control HPNAs while achieving virtual total conversion in a hydrocracking unit.
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