Abstract:

The purpose of a hydrocracker is to convert vacuum gas oil and demetalized oil (DMO) to naphtha and diesel. Saudi Aramco has two total conversion hydrocrackers which operate at very high pressures. The hydrocracking catalyst plays an important role in a hydrocracking unit and its selection is very critical to the success of hydrocracker's performance. The premature failure of the previous hydrocracking catalyst in one of Saudi Aramco hydrocrackers intensifies the importance of hydrocracking catalyst selection. Thus Saudi Aramco develops an intensive catalyst selection program to safeguard the catalyst selection for refining catalytic processes.

This paper summarizes hydrocracking catalyst selection process which includes proposal evaluation, pilot plant testing program and economic evaluation. Detailed evaluation results including pilot plant test results and economic evaluation will be reported in the presentation.

INTRODUCTION

The hydrocracking technology plays an essential role in the world's refining economics by upgrading heavier and lower value vacuum gas oil (VGO), demetalized oil (DMO), or residuum into lighter and higher value naphtha and diesel. Hydrocracking catalysts selection is very critical to the success of the hydrocracker performance. Therefore, a refiner should implement a proper procedure in order to safeguard the catalyst selection to meet most of the operating objectives. The pre-mature failure of the previous hydrocracking catalyst in one of Saudi Aramco's (SA) refineries was the compelling starting point for developing a well structured procedure for selecting refining process catalysts.

Saudi Aramco Standard for Refining Process Catalyst Selection

Saudi Aramco has developed a standard to establish requirements for selection and quality assurance/quality control (QA/QC) of refining process catalysts. The catalyst selection procedure starts with development of the technical package and performance guarantee which we send to vendors to solicit catalyst proposals, and initial screening of all technical proposals by benchmarking them against the refinery desired criteria. The initial evaluation rules out some inappropriate proposals. If necessary, the selection process includes pilot plant (P/P) testing of potential catalysts. The P/P testing is conducted under the same operating conditions to mimic the commercial operations. In addition, the selection process includes a survey on users to get their feedback on performance of the proposed catalyst systems. Finally, an economic evaluation on the technically acceptable catalyst systems, together with the performance guarantee and users' comments, will determine the winning catalyst system. The standard also indicates that QA/QC tests on a pre-delivery sample are required before the catalyst is shipped to the refinery. If necessary the performance tests can be conducted during the catalyst cycle to validate performance guarantees. Any deviation from the standard will require a waiver from the appropriate authority.

Hydrocracker Catalyst Selection
Hydrocracker Unit Process Description

The hydrocracker unit (HCU) is a single stage, series flow unit with two parallel trains. Each train encompasses two treating reactors and two cracking reactors with a steam generator in between to recover waste heat and control the inlet temperature of the first cracking reactor. The fractionator bottom is sent to the vacuum tower in the crude unit to eliminate heavy polynuclear aromatics (HPNA) and is recycled back to the first reactor.

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