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(2017) Question 71: What are your recommended configurations for main fractionator flash zone thermocouples to measure the flash zone temperature under the slurry bed?

It is important to measure the main fractionator flash zone temperature in the proper location such that it provides meaningful information. Temperature indicators (TIs) located below the slurry bed are at risk of coking, subject to maldistribution of vapor entering the tower, and are at a location before the vapors have been de-superheated.
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(2017) Question 72: Current economics drive unit operation to minimum slurry production limits, as defined by physical properties and rundown velocities/flow rates. What are your typical slurry limits, and what are your options to overcome those limits to further reduce slurry?

It is fair to say that past, current, and future economics will almost always call for the minimization of slurry production. As slurry production is minimized, the risk increases to foul exchangers or plug lines due to low velocities. Additionally, as slurry is minimized, the quality of the slurry will degrade, which will also increase the risk of fouling.
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(2017) Question 50: From this list of your top FCC gas plant constraints, which area is your primary constraint: 1) main column (MC) overhead, 2) wet gas compressor, 3) primary or sponge absorber, 4) stripper, or 5) debutanizer bottoms or overhead?

Refining investments in alkylation expansions and gasoline octane improvements require production of additional feedstock for the alkylation unit. The primary source of olefin feedstock for the alkylation unit is the FCC unit. Operating conditions in the FCC unit can be adjusted to favor increased propylene and butylene production. The FCC wet gas compressor becomes the first major bottleneck in recovering the incremental propylene and butylene. Modifications may be required to the compressor, as well as associated cooling, inter-stage, or after-stage equipment. 
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(2017) Question 51: Can you comment on the safety aspects of placing catalyst in a standpipe to help isolate one vessel from the other? Does the existence of catalyst in a standpipe create a ‘seal’?

I would like to mention that we will have a P&P tomorrow on this topic, so I will try to keep my answer short. It is assumed that this question relates to using the slide or plug valve to form a seal between the regenerator and the reactor during shutdowns. I would like to point out that this is a standard practice in an FCC as there is really no other option; and for the most part, it does work. 
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(2017) Question 52: What challenges do you face for implementing safety-instrumented systems that result in closure of the FCC slide valves?

Systems are designed to meet a specific safety integrity level (SIL). Each operating company has a risk-based matrix specific to the company or site. This matrix has severity on one axis and probability on the other axis. High severity and high probability score the highest. Based on this ranking system, the company sets the SIL rating at SIL 1, 2, or 3. SIL 1 and 2 are the most commonly found in typical refinery processes.
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(2017) Question 54: What recent innovations have you made to instrumentation that has application in FCC units?

For level measurement, guided-wave radar level instruments have been gaining popularity and been successfully applied in numerous services, especially for interface levels. Nuclear-type level instruments have been more or less accepted in other processing units in refineries and have made their way into the FCCU for severe services, such as main fractionator bottoms level, and for hopper levels.
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(2017) Question 73: Gasoline octanes continue to have a high value for many refineries. What fractionation strategies do you apply to increase gasoline octane? What rules of thumb do you apply for estimating changes in octane with gasoline endpoint adjustments?

RVP and endpoint both have a minor effect on gasoline octane. With other operating parameter changes and repeatability of octane results in the lab (+/- 0.5 RON), it is difficult to quantify small changes in octane caused by fractionation changes. Literature suggests that for every 1.5 psi RVP increase, RON will increase 0.3. We have very little data to support the literature, because the octane and RVP value of mixed C4s is much greater as alkylate than on the frontend of FCC gasoline.
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(2017) Question 74: How do you mitigate aqueous corrosion in the main fractionator overhead and gas concentration unit? What contaminants do you test for in the sour water, and what limits do you impose? What are your concerns with using stripped sour water as waterwash?

Over the last six years, there have been a number of questions related to different aspects of overhead and gas concentration unit corrosion management, including design recommendations. For completion of the Answer Book, here is a brief summary of the topics covered.
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(2017) Question 75: What are your Best Practices in design and operation to achieve positive isolation of slurry/HCO equipment?

Technip’s practice is to specify gate valves with flushing connections at the base of the seat. To ensure positive isolation, the flushing connection can be used to remove any sediments that may be impact the contact of the gate with the seat. Another option is to orient the valve stem off of vertical in order to move the final seating location away from the low point, therefore reducing the chances of sediment to accumulate there.
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