Q&A

(2011) Question 30: What is the recommended feed nozzle design for HF alkylation units to provide proper mixing of the feed, HF acid, and isobutane? What are the recommended materials of construction for these nozzles?

The licensor for HF alkylation is UOP and they should be consulted before changing the feed nozzles. Isothermal reactors that have feed injection in the reactor bundle utilize a feed pipe system with nozzles machined into the pipes.

(2011) Question 31: In HF alkylation units, do you have two vent gas or flare gas scrubbing systems, one for normal operation and one for a rapid acid dump system?

Each of our units has one system. Most units only route acid containing reliefs to the Acid Relief Header which has a Neutralizing system as part of that.

(2011) Question 32: What are your best practices for minimizing corrosion in aromatics extraction process from oxygen in the feed? Is the strategy to reduce oxygen ingress or treat the feed? Is the situation different for glycol, Sulfolane, Morpholine, or other solvents?

Udex unit uses Tetra Ethylene Glycol as solvent. The Udex performance w.r.t. corrosion was not so high initially after revamp, but we started experiencing severe corrosion from 2008 onwards in stripper reboiler, severe thinning of stripper bottom tray panels and unit had to be shut down repeatedly in 4-5 months interval for attending reboiler leaky tubes till M&I shut down was taken up.

(2011) Question 33: Are there any new technologies to control bromine index in aromatics streams? Do clay towers still provide the best operating value?

UOP has commercialized a selective hydrogenation for this application and Exxon Mobil offers an alternative catalyst that appears to be a direct replacement for clay.

(2011) Question 34: What is your best practice for minimizing octane losses based on unit operating parameters and/or catalyst types in FCC gasoline post-treat units?

Minimizing octane loss while hydro desulfurizing FCC gasoline implies minimizing olefins saturation with hydrogen. This is all about selecting the right operating conditions (temperature, pressure and H2/HC) so that the hydrodesulfurization reactions are fast enough, but the kinetics of the olefin's saturation reactions remain low.

(2011) Question 35: How far can the hydrogen to hydrocarbon ratios be decrease in gasoline hydrotreating units before experiencing high reactor pressure drops? Please provide some details of your experience with reference to the run length limitations and operating performance.

We have number of naphtha hydrotreatment units in our refineries, some operating with straight-run naphtha as feed and others in mix mode with significant cracked feedstock varying from 10% to 40%, to produce feedstock for catalytic reformers. I suppose, the question here is for hydrotreating units processing cracked components.

(2011) Question 36: What changes have you made to the C5/C6 Isomerization unit to comply with the new benzene regulations; what changes have you made to the refinery operation; and what have been your challenges and successes of implementing the new configuration?

More severe regulation in term of Benzene in the gasoline pool can lead to increase the Benzene content to the C5/C6 isomerization unit. This can happen in two different ways.

(2011) Question 37: To help manage fouling and pressure drop in a naphtha hydrotreater, do you rely on graded bed technologies or feed filtration (magnetic or other) or both? What is your experience with these options? What other means are being employed?

The countermeasures to pressure drop build-up in naphtha hydrotreaters units obviously depend on the cause of the fouling. The two main causes that we know in Naphtha HDT units of are corrosion particles usually coming from outside the battery limit and gums or coke. Axens addresses those two issues at design stage.

(2011) Question 38: What is your experience with rod baffle exchangers for naphtha hydrotreater or reformer preheaters?

There are a number of vertical RODbaffle® exchangers in ConocoPhillips Reformer preheat service. They have very good heat transfer and excellent reliability.

(2011) Question 39: What are some mitigating strategies for reducing corrosion in the fractionation section of a naphtha or light-ends unit?

The potential problems are most of the time located in the columns overhead where some water may condense locally. Corrosion inhibitor injections are systematically foreseen in strippers' overhead columns.

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