Troubleshoot FCC Reactor Level Control with Fluidization Principles
In the latest issue of Catalagram, Grace’s signature publication for the refining industry, we dive into the Fluid Catalytic Cracking unit (FCCU) to troubleshoot changing reactor level controls. Maintaining the correct catalyst levels in an FCCU is critical for the effective operation.
Why Reactor Levels Matter
In the FCCU, low or high catalyst levels may trigger elevated catalyst losses or other non-optimal conditions such as regenerator afterburn or higher dry gas. Today’s modern riser termination devices require the catalyst level to be within a prescribed range to ensure optimal operation and product yields.
Regenerator level in a valve controlled single regenerator configuration will increase as catalyst is added into the unit, requiring catalyst be periodically withdrawn from the unit to avoid excessive bed level. Reactor or disengager level is controlled by action of the spent catalyst slide valve or plug valve in a valve-controlled unit.
Short- vs. Long-Range Instrumentation
Many units are equipped with both long and short (sometimes referred to as wide and narrow) range level instrumentation for managing catalyst levels.
Reactor level is often controlled by the short-range instrument during normal operations to ensure level is precisely regulated. The long-range level instrument is available to the operator but often is not used for control purposes during normal operation.
Short-range instruments can provide excellent precision when controlling the reactor level, ensuring the correct burial amounts of the riser termination device or cyclone diplegs.
Recognizing inconsistencies between the long- and short-range level instruments can give insights to the FCC engineer or operator regarding problematic operations that may need to be remedied. Shifts in catalyst particle density may require a revision of target LI values or control set points to maintain the same physical catalyst level.
Fluidization Principles in Action
Interestingly, in a typical FCCU, long range level instrument readings will shift while the short-range level instrument readings remain steady. Even the seasoned FCC engineer or operator may be challenged to explain how these two levels can become inconsistent.
Read the case study in Catalagram, where we review the fluidization principles used to measure catalyst level in an FCC unit and offer recommendations to resolve the issue.