Q&A

(2013) Question 68: For those refiners seeing an increase in vacuum overhead chloride concentration at constant desalted crude salt content, what are the consequences and how can they be controlled?

First, verify the chlorides found in the hot well water. Could the chlorides be from leaks from the vacuum system condenser cooling water? A hardness test will quickly identify water system leaks. Essentially, getting a high chloride concentration in the vacuum overhead at a constant salt content in the desalted crude implies either a change in the chloride type or in the operating conditions leading to more chloride hydrolysis.

(2013) Question 69: What are some of the advantages and challenges in processing FCC slurry in a vacuum tower along with conventional atmospheric residue streams?

If you feed FCC slurry to the vacuum unit, the major benefit is recovery of diesel range material. High temperature limits in the bottom of the heavy cycle oil slurry fractionation system limit diesel recovery from slurry. Typical limits in this section in the FCC are 720°F, or 382°C; above that, coking starts to be a major issue.

(2013) Question 70: What are the key areas to target when contemplating crude unit modifications to enable effective tight oil processing? In addition to these modifications, what other problem areas become evident once the actual processing begins?

We run tight oil in six of our seven plants, and it is mixed in the basket of the other 10 to 20 crudes normally processed. Tight oils are not the predominant crude in most places, so we have not needed many modifications. In two instances, we did have tray fouling from drilling mud; so, we installed low fouling trays.

(2013) Question 71: How do you rebalance your coker operation when processing atmospheric tower bottoms at your FCC during tight oil processing?

Our particular configuration for tight oil processing allows us to operate one of our cats with ARC (atmospheric reduced crude) without any impact to our coker operation. We typically have sufficient feed, but the obvious answer might be to purchase additional number 6 fuel oil or vacuum tower bottoms for operation.

(2013) Question 72: What are potential causes of damage to the top section of coker main trays? What mechanical and process considerations are used in designing the top section trays for more reliable operation?

Damages to the top section of the coker trays could be due to process-related reasons or mechanical or operational issues. One process-related reason is salt deposition. Usually, the salt is ammonium chloride. It is water-soluble, corrosive, and rapidly deposits at the right conditions, leading to severe loss of tray capacity and efficiency.

(2013) Question 46: What are the main considerations in converting a fuel hydrocracker into lubes services in terms of equipment modifications and catalyst selection?

The conversion of a fuel hydrocracker to a lube hydrocracker mainly depends upon the product quality requirements and unit constraints. If you are producing lube-based stock as your main product, then the operating parameter needs to be examined in detail.

(2013) Question 47: What evaluations are required for hydrocracking units to increase conversion due to processing heavier feedstocks?

Pilot plant studies should be done to evaluate catalyst performance with new proposed feeds. If you are planning to make revisions to your unit, you certainly want to consider catalytic changes, perhaps more selective to diesel or gasoline. Your operating cycle could possibly decrease or increase with conversion, depending on which way you are tending to go.

(2013) Question 48: What are the typical guidelines for reactor loading if the decision is to not fully load with catalyst? Is it acceptable to short load a reactor, and what are the recommended minimum and maximum distances below the inlet distributor?

First of all, it is a bit unclear why one would want to short-load the reactors. Can it be done? Yes, especially if it is a gas-phased operation. If it is a mixed-phase operation, then it probably could become an issue.

(2013) Question 49: What are the criteria for levelness during dense loading of a catalyst bed? What are the preferred monitoring techniques, and what is the best approached to correct an uneven bed profile if it is detected?

Really, it is not so much that you want to maintain a definite level bed, but what comes with that is making sure you are truly loading your reactor correctly and that you have an even distribution of densities through your entire bed. We also recommend that you check loading densities at some prearranged interval. Initially, it may be 10 or 15% of the start-of-run and then every 25% throughout the load until you are finished.

(2013) Question 50: What are the technology evaluations and engineering studies required for revamping a diesel hydrotreating unit to substantially increase throughput?

In any major revamp of throughput for a DHT (distillate hydrotreater), establishing a realistic design basis and engineering certainly never really exists. The idea is to look not just to the point but at deviations and feedstock properties, expected changes in compositions, and past history of contaminants.

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