Q&A

(2012) Question 73: What is your experience with coke bed instability?

We have seen coke beds collapse during the beginning stages of the quench water addition. We have had operational problems because we were not able to get the quench water into the coke bed. We even tried alternating back and forth between the stripping steam and the quench water, but we were not able to penetrate the coke bed with the quench water.

(2012) Question 74: We have experienced leak issues around gaskets in cyclical and hot temperature services. What solutions have you developed to eliminate these issues?

At one of our two cokers, we use ring joint flanges from the coker heater outlet to the coke drum inlet and have had no leak issues. At the other coker, we have a short section of piping at the coke drum feed inlet that had raised face (RF) with spiral wound gasket drum (SPWD) that would occasionally leak.

(2012) Question 75: Please describe your best turnaround practice for cleaning and inspecting heat exchanger bundles versus replacement.

KBC is a nonoperating company, so we do not operate any equipment or conduct turnarounds. However, we do know that the bundle must be cleaned for inspection. We are accustomed to seeing hydrolancing or chemical cleaning for less severe services.

(2012) Question 76: The check valve on the air blower discharge line is designed to protect the blower from hot catalyst that backs into it when the blower fails. What type of valve is used in this service, where is it located, and what is done to ensure that it closes properly?

UOP specifies two special check valves in the blower discharge line. The first special check valve is installed a minimum distance from the blower discharge downstream in the snort (or anti-surge) valve in a horizontal pipe run.

(2012) Question 77: For our emergency interlock system, we employ two-out-of-three voting systems for slide valve differential pressure transmitters. We use dedicated transmitter taps for each transmitter, but we get inconsistent readings. What can we do, regarding design and maintenance, to ensure that these transmitters read more consistently? What should we do if we are unable to achieve consistent readings?

To obtain a more consistent reading, plant personnel should examine three phases: the transmitter, its physical location, and its instrument gas system. As for the transmitter, the technician should analyze it to ensure that it is within the accuracy specified by the manufacturer.

(2012) Question 78: What inputs or trips are typically included in FCC flue gas expanders and CO (carbon monoxide) boilers' safety interlock systems? Are there any governing standards [(e.g., API and NFPA (National Fire Protection Association)] that apply?

I would like to address this question as two different parts, beginning with the flue gas expanders. BP has three flue gas expanders in its system. These expanders are all set up with slightly different configurations. We have one FCCU flue gas expander that is directly coupled to the main air blower.

Question 79: What tools are being used to monitor FCC performance? What are the key performance indicators and expectations?

These are two broad categories for the use of these indicators. The first category is capacity utilization and yield performance, which covers process performance, operating constraints, and optimal use of any inherent design margins.

(2012) Question 80: We are considering severe hydrotreating of our FCC feed. What yield shifts or unusual operating problems might we expect? What can be done to address these issues?

Processing Hydrotreated Feed: First of all, let’s define what ‘severely’ hydrotreated feed means. One unit in our system hydrotreats the feed down to 50 ppm sulfur and 50 ppm nitrogen, so you can see that processing that type of feedstock has tremendous yield benefits.

(2012) Question 81: Is there experience with continuous torch oil and/or air preheater firing; and if so, for what reasons? What are the demonstrated effects from doing either of these processes?

We do not have much experience with continuous torch oil firing. We do have one unit that fires torch oil if the bed temperature drops below 1250ºF.

(2012) Question 82: Do you have any experience with the recycle of C4/C5 streams from the FCC gas plant back to the FCC? If so, what was your motivation? What is the system configuration, and what are the key operating parameters?

We have some experience recycling BBs (butane-butylenes) from the gas plant back to the FCC reactor, and even some C5s. I will start by saying that this is a very unusual operation.

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