Q&A

(2012) Question 85: What is the state-of-the-art design used to minimize the impact of coke in the FCCU main fractionator bottoms and remove coke from the bottoms draw and circulating circuit?

In general, reducing fractionator bottoms coking starts with an optimum slurry system design to minimize the column residence time and bottoms temperature. We typically target around 680°F in the bottoms. This design should include the fractionator soft area, as well as the entire slurry exchangers train.

Question 86: What test method (e.g., ASTM D86, D1160, or D2887) do you currently use to determine the distillation of FCC gasolines, cycle oils, and fractionator bottoms?

I put distillation methods into two different categories. One is simple distillation or acts of distillation, which is either a D86 or D1160. D86 is at atmospheric conditions; the D1160 would be at a vacuum.

(2012) Question 87: What is typical light cycle oil/fractionator bottoms distillation overlaps, and what can be done to improve separations to increase LCO recovery?

The distillation overlap of LCO bottoms product varies somewhat. In our experience, it is in the range of 20ºF to 60ºF. We also have a few units that report distillation overlaps.

(2012) Question 88: What is the variation in fresh catalyst chemical and physical properties for your refineries? How do you determine acceptable tolerances for your fresh catalyst quality control?

There are large numbers of chemical and physical properties that can be measured. I am really just going to focus on the ones that are most typical. First of all, in the metals’ category will be the sodium, alumina, and rare earth.

(2012) Question 89: With the increase in rare earth costs, many units have decreased the rare earth oxide (REO) content or used rare earth substitutes in their FCC catalyst. What is your experience with these in terms of activity maintenance, delta coke, conversion, attrition, and yield selectivity's? How have operating conditions changed?

Rare earth stabilizes zeolite and increases hydrogen transfer. Reducing the rare earth on zeolite will decrease the catalyst activity at the same zeolite content and matrix activity.

(2012) Question 90: Can ZSM-5 be used to make propylene from high metal resid feeds? What is the effect of nickel and vanadium on this kind of operation?

ZSM-5 usage is widely used in FCC units trying to maximize propylene. ZSM-5 usage is just as popular in resid units as it is with gas oil units. We have seen high propylene yield units, resid units with feeds greater than 6 Conradson carbon residue, and e-cats that exceed 10,000 ppm nickel plus vanadium.

(2012) Question 91: What FCC turnaround intervals are refiners achieving for units that do not take mini turnarounds? Do longer intervals mean lower reliability between turnarounds?

Most of BP’s units are now transitioning from about a four-year turnaround cycle to a five-year. We have some units already running five years between turnaround cycles without necessarily showing evidence of higher wear and tear.

(2012) Question 92: Describe the turnaround scope of work for the combustion air blower. Does it differ for units with turbo expanders? Do you work on the air blower every turnaround? Is this work performed by a general turnaround contractor or by the manufacturer? How often does this work become critical path?

Most sites replace the internals of the expander during every turnaround. The stator veins are thoroughly inspected and replaced on as-needed basis.

(2012) Question 93: How do you manage regenerator cyclone life to ensure that you reach target turnaround intervals? Do you consider superficial velocity, inlet velocity, inlet loading, outlet velocity, etc.?

At KBR, we specify design parameters that will allow the operator to achieve extended regenerator cyclone life for several turnaround intervals. Based on our experience, it was shown that most cyclone problems are attributed to operating above the maximum recommended velocities. KBR recommends that Operations maintain a cyclone inlet velocity below 70 fps and 80 fps for the first- and second-stage cyclones respectively.

(2012) Question 94: What is your experience using specially designed automated isolation valves on the reactor overhead line for your de-blinding operation during the start-up of the FCCU? Will they dependably provide positive isolation after being in operation? How did you justify the installation cost (e.g., safety and economics)?

We have quite a few units that use valves in the vapor line and others with just simple blocked valves in that service. Two more units now have a newer style: a double disc valve which relies, in part, on a steam purge to provide positive isolation. Because that valve was very successful, two more valves are going to be installed soon.

Find the answer to your technical question in AFPM's extensive Q&A database.

Q&A