| American Fuel & Petrochemical Manufacturers

Question 3: How are you managing your units to mitigate risk of HTHA (High Temperature Hydrogen Attack)? What are monitoring best practices? Should we be concerned about short term operating periods such as startup, shutdown, hot stripping, etc.?

HTHA is a form of degradation of metal caused by hydrogen reacting with carbon in the metal to form methane in a high temperature environment, typically above 400 deg F and 50 psia H2 partial pressure.

Question 2: In hydrocrackers, how are your sampling systems designed to safely obtain inter-reactor / reactor effluent samples?

Inter-reactor sampling can be important for monitoring catalyst performance, troubleshooting, and measuring yields. In a hydrocracker, such a sampling system allows measurement of nitrogen slip from the pre-treat section into the hydrocracking stage.

Question 1: Do any of you place an alarm or upper limit on the operating pressure drop (dP) through a hydrotreater reactor circuit (preheat exchangers to High Pressure Separator)? If yes, what is the basis for the maximum dP?

One of our refineries has developed limits for pressure drop through the reactor circuit. The maximum allowable pressure drop is determined by the difference between the upstream reactor or heat exchanger design pressure and the set pressure of the relief valve on the high-pressure separator. The purpose of the alarm is to ensure that the upstream vessel’s design pressure will not be exceeded before the pressure at the downstream relief valve reaches the set pressure.

Question 104: How are radioactive surveys and/or gamma scans utilized to optimize FCC operation?

Monitoring parameters of the FCC such as density and height of catalyst beds, gas and/or solid distribution of the cyclones, air distributor, slide valves and standpipes are accomplished through measurements of pressure, pressure drop and temperature at various locations.

Question 103: We increased reactor severity and noticed an increase in oxygenates in LPG and sour water. Can you explain the mechanism by which phenols and other oxygenates form in the riser?

Since increasing reactor severity will result in an increase in catalyst circulation, it is likely that the increased oxygenate production being observed is from the higher catalyst circulation which is increasing the entrained molecular oxygen carryover to the riser.

Question 102: What benefits have you realized by installing packing in their FCC strippers? How did this equipment impact your catalyst circulation and unit pressure balance?

What benefits have you realized by installing packing in their FCC strippers? How did this equipment impact your catalyst circulation and unit pressure balance?

Question 101: What factors influence butylene selectivity in the FCC LPG? What is the relative role of feedstocks, catalysts, additives, and operating conditions?

A number of factors influence butylene selectivity in the FCC LPG stream. Figure 1 summarizes the fundamentals of butylene selectivity and maximization.

Question 100: How do Nitrogen compounds distribute in the product streams of FCC Units? What effect does riser severity and feed properties have on this distribution?

How do Nitrogen compounds distribute in the product streams of FCC Units? What effect does riser severity and feed properties have on this distribution?

Question 99: We are struggling with high afterburn in the regenerator. What hardware changes (spent catalyst distributor, air distributor, etc.) have you implemented to improve afterburn? What commercial experience exists using computational fluid dynamics (CFD) to resolve such issues?

CFD has been successfully used to predict afterburn in FCC regenerators. A published example was presented as part of the CFD Case Studies workshop at the 2012 AFPM Cat Cracker Seminar.

Question 98: What are the options for removing catalyst fines from the main fractionator bottoms product? Which, ifany, can reduce the ash content to 50 ppm or less?

Slurry oil catalyst fines Settling Aid chemistries have been used for many years in this type of application. Electrostatic precipitators and filtration equipment is also available for minimization of ash content in slurry oil.