Q&A

(2011) Question 20: Pre-hydrotreated feeds and crudes look easy to process on paper. Why is it more difficult than expected to process pre-hydrotreated feeds in a hydroprocessing unit?

Pre-hydrotreated feeds are often the most difficult feeds to process in hydrotreaters primarily because the remaining molecules to be treated are the most refractory. Low sulfur feeds are not automatically the easiest to process; the sulfur species determines the difficulty of processing, not the total sulfur.

(2011) Question 21: What needs to be considered when processing LCO or increasing the amount of cracked feed in a hydrocracker?

It is important to ensure that sufficient H2 is available to satisfy the minimum required H2/oil ratio because hydrogen consumption will increase significantly.

(2011) Question 22: Which is the impact of feed asphaltenes content on hydrocracker cycle length?

The asphaltenes are high boiling, high molecular weight and hydrogen deficient materials that are the least reactive in a hydrocracking environment.

(2011) Question 23: What is the impact of HPNA (Heavy PolyNuclear Aromatics) on hydrocracking catalyst activity, stability. and yield selectivity?

The impact on hydrocracking catalyst deactivation and yield selectivity due to precipitation of Heavy PolyNuclear Aromatics (HPNA) is typically based on several criteria.

(2011) Question 24: Do you use Safety Instrumented Shutdown systems in gasoline units (reformers, alkylation, isomerization, hydrotreaters)? How many of you use DCS-based vs. dedicated hardware shutdown systems?

In order to comply with auto fuel policy of Govt. of India for introduction of Euro-III and Euro-IV in the country and in all major cities in India respectively, all IOC refineries (10 nos.) had to take up MS Quality Improvement Projects which included new units and revamp of existing units including catalytic reformers, isomerization units, selective hydrogenation units, benzene saturation units and hydrotreaters.

(2011) Question 25: How do you manage process hazard analysis (PHA) scenarios related to corrosion?

First, ConocoPhillips has developed generic PHA scenarios for each major technology to determine what scenarios are applicable to a particular unit. These tables contain initiating categories (such as Corrosion), potential causes and consequences, possible safeguards and suggested consequence rankings.

(2011) Question 26: When you test for free HF and organic fluorides in alkylation unit products (alkylate, butane, propane), what are your typical observed levels? After HF breakthrough in our butane product, why does our treater still have plenty of KOH remaining? Is there any way to regenerate KOH during the run? Do others maintain a heel of KOH in the bottom of the alkylate storage tank to neutralize traces of HF?

Our sites vary in the type of testing with most sites testing for combined (organic) fluorides in at least the propane and butane streams. Multiple stream points are typically tested dependent on what the monitoring goals are.

(2011) Question 27: What are the pros and cons of alkylating delayed coker butylenes (co-processed with FCC butylenes)? Does this require higher isobutane recycle? Should we consider processing them in a separate reactor? What are the economic alternatives to alkylation?

A more specific question is: “What is in Coker olefin that is problematic since a pure olefin is the same whether from a Coker or FCC unit?” A Coker derived olefin stream has more sulfur, diolefins and acetonitrile than FCC olefins.

(2011) Question 28: How is the acid soluble oil (ASO) disposal system operated in an HF alkylation unit? - where / how do you dispose of the ASO? - do you operate the rerun continuously or in batch mode? - do you have problems with the ASO line fouling or plugging? - is there a min velocity, min/max temperature or something else that controls your rate of ASO disposal from the rerun?

The summary response is: Collect the ASO, neutralize it in KOH or NaOH and then dispose of it in another refinery product stream.

(2011) Question 29: The relief valve on the acid storage drum on our HF Alkylation unit was designed to be rotated to relieve to the atmosphere during unit turnarounds when the unit flare system is unavailable. Is this still common practice, or have you made arrangements to provide access to another flare system during turnarounds?

Some refiners do disconnect the outlet of the acid storage drum relief valve from the relief header and align it to atmosphere during turnarounds. This situation is very similar to the acid truck that delivers the fresh acid to site.

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