Q&A

(2012) Question 20: What is the industry experience with managing cracked feedstocks to avoid hydrotreater problems such as fouling, and pressure drop?

Some of the mitigation options can be summarized in four areas. The first is feed logistics. We would say that if you are going to handle this, you need to do as much direct feeding as possible.

(2012) Question 21: High pressure strippers are an option for controlling VOCs in process condensate and managing export steam quality in a steam methane reformer hydrogen plant. What types of pH controls are being used?

Most hydrogen plants take the process condensate, send it to a deaerator to clean it up, and then reuse that condensate while mixing it with some boiler feedwater internally. There are configurations that have high pressure strippers where they will bring in some steam and do some initial stripping.

(2012) Question 22: What preventative maintenance program is applied to safety instrumented systems on a steam methane reformer that are Safety Integrity Level (SIL) rated?

Safety instrumented systems (SIS), as defined by ANSI/ISA-84.00.01-2004 Part 1(IEC-61511-1 Mod), are required to have components functionally tested and/or replaced/ refurbished under preventative maintenance (PM) to provide the reliability required to have a Safety Integrity Level (SIL) rating. SIL-rated safety systems are often required when a greater degree of protection layers is required then that offered by standard design.

(2012) Question 23: What are some options for increasing the cetane index (CI) of diesel to more easily meet export market requirements?

Cetane improvement chemistry mechanisms available to us are aromatic saturation and naphthenic ring opening (hydrocracking), both of which allow us to further take advantage of low-cost hydrogen to provide cetane upgrades and liquid volume gains.

(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.

(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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