| American Fuel & Petrochemical Manufacturers

Question 82: For those operating units with electrostatic precipitators (ESPs), share your experience with using SOx (sulfur oxide) reduction additives and their impact on: 1) ESP performance, 2) stack opacity, and 3) filterable solids mass.

We have two ESPs in our system. One of them is on a unit currently using less than 2.0% of SOx additive. We have not seen any impact at all on performance, opacity, or filterable solids. The other ESP went through a retrofit within the past four years, going from a smaller, older version of an ESP to a larger ESP with more modern technology.

Question 81: How do CO (carbon monoxide) and NOx (nitrogen oxide) emissions change when you operate at low regenerator temperatures? What can be done to mitigate any increases?

I will initially address this question from a CO standpoint and then discuss the NOx. CO emissions typically increase if the regenerator falls below a certain temperature threshold. That temperature threshold will vary based on your regenerator configuration and definitely on the type of air distribution.

Question 80: We have coke deposits in the plenum chamber and vapor line and are concerned the deposits may spall off or ignite during refractory dryout. What precautions should be taken to avoid re-igniting these coke deposits during the dryout?

We prevent hot air from entering into the reactor system during the regenerator dryout. Subsequently, we will use initial catalyst circulation for the reactor side dryout. Prior to lighting the DFAH (direct fire air heater) for the regenerator refractory dryout, we will introduce dry steam into the reactor, feed distributors, reactor riser, reactor dome, and stripper section.

Question 79: How do you mitigate the risk of falling coke deposits from the reactor plenum chamber and vapor line during initial vessel entry?

We have not had the experience of falling coke deposits on vessel entry. We usually experience difficulty in removing the coke deposits, and we do this by mechanical means. Prior to entry into the reactor, a visual inspection is made from the manway. It is typical to see stalactites from the reactor plenum.

Question 78: What procedures (maintenance and operational) are being used to minimize risk when swinging the blind between the reactor/main fractionator?

There are two scenarios to consider: shutdown and startup. I will address the shutdown scenario first. For the shutdown scenario, catalyst is de-inventoried from the reactor and regenerator systems, and the main column and reactor are cooled down to 350°F. There are certain operational conditions that must be satisfied before the blind is installed.

Question 77: What are the consequences associated with continuing to operate the FCC without main fractionator bottoms cooling circulation?

We considered this question as three parts: What is the action to follow in the event of a loss of bottoms’ cooling? What is the consequence if you lose the net slurry product? What are the operational possibilities if you have a well-planned outage of the slurry circuit? In situations one and two where you have lost circulation or you have lost the net bottoms’ product in the system here, we expect that you would shut down the unit consistent with your licensure’s emergency shutdown procedures.

Question 76: What has been the industry experience in mitigating the impact of solids in the feed or coke fines in the fractionator side draws and recycled cutting water?

We use settling mazes in the water section to minimize fines without chemical injection, and then we vacuum out individual cells on a periodic frequency to recover the fines.

Question 75: What are the potential problems or negative impacts of utilizing FCC slurry/decant oil as coke drum OH (overhead) line quench oil?

Again, FCC slurry/decant oil has a similar distillation range to HCGO but a higher endpoint. Although it could possibly be used as just overhead quench, we caution that if the slurry/decant oil is not be filtered properly, it will contain catalyst fines that could accelerate the coke deposition by settling in equipment or piping.

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.

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.