Q&A

(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.

(2013) Question 51: For hydroprocessing reactor modifications that involve the addition or removal of distribution trays and flexible thermocouples, what is your Best Practice for welding support rings or support lugs on a reactor wall? What is your Best Practice for removal of these items when they are no longer required?

When you are trying to remove the attachments from the reactor, do not touch them unless it interferes with your process flow, catalyst loading, or internal installation or access. When the rings are welded to the support rigs, remove the rings and leave the lugs in its place.

(2013) Question 52: What is the configuration of thermocouples that can be used to effectively monitor radial temperature differences, and what is the acceptable radial temperature spread in hydrotreaters/hydrocrackers?

The UOP bed thermometry consists of a stab-in type of assembly with three thermocouples on top of the bed. Typically, a multipoint thermometer is provided in the case of the first bed of a hydrotreating unit and if the bed length is more than 11 feet for a hydrocracking bed. At the bottom of the catalyst bed, industry-standard flexible-type multipoint thermocouples are specified.

(2013) Question 53: With respect to hydrotreating, what is the typical (CO + CO2) impurity in hydrogen produced from pressure swing adsorption (PSA): 10 ppm or 50 ppm? What problems can be expected if the (CO + CO2) exceed this value? If the hydrotreaters can handle higher than (CO + CO2), is it possible to run the PSAs harder and produce more hydrogen?

UOP has designed around 1000 PSA units. For most of the refinery applications, the impurity limit has been set to less than 10 ppm. The table shows a comparison between specs when relaxed from 10 to 100 ppm. H2 recovery was also checked when specs were tightened from 10 ppm to 1 ppm.

(2013) Question 54: Please comment on both personnel and process safety concerns when transporting and receiving crude via rail and truck. What laboratory analyses support this effort?

We receive crude by truck and rail at two of our seven refineries. I have prepared three slides to share with you: one for personnel, one for process, and one for sampling. Most of the tight oils we bring in are from under-developed fields that do not have proper gas plants; therefore, they come in fairly wild.

(2013) Question 55: In a recent turnaround, we successfully de-gassed and de-greased our crude tower but discovered residual mercury. What techniques have been used to mitigate this issue?

We recommend pre-turnaround development of a PPE matrix that can be used during the turnaround which outlines the PPE required should you discover mercury during the outage.

(2013) Question 56: With the current domestic conventional and unconventional crudes available, what incompatibility issues are observed from the tank farm through the crude unit? What mechanical, operational, and chemical strategies are employed to minimize these impacts?

Incompatibility issues are mostly observed in the desalter and downstream pre-heat train and heater as the asphaltenes precipitate and cause stabilized emulsions. Some of our observations include salted crude carryover from the desalter. The water and contaminants exit the desalter and foul all of your downstream pre-heat exchangers and heaters.

(2013) Question 73: What is the current design philosophy in the lower section of a coker main fractionator (from tower bottoms up to first product draw) for controlling product quality and coke fines buildup?

The main objective is to keep the coke fines agitated and then efficiently remove them from the bottom of the fractionator. A properly designed coke drum with low vapor velocity helps minimize the coke fines carryover to the fractionator. Proper C factor for tower sizing is critical to achieving the HCGO quality in low pressure cokers.

(2013) Question 74: How effective are the following decoke methods in a delayed coker furnace: online spalling, mechanical pigging, and steam air decoking?

The way the panel decided to answer this question was for me to give an overview of the different methods and a few of the pros and cons. Then one of the other panelists will present his actual experience. The mechanical method employs metal studded pigs which are pushed in water.

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