Key performance indicators The FCC unit has many variables that need to be monitored on a regular basis. Many refiners call some of these vari - ables key performance indicators (KPIs). Table 2 lists some of these values. Each refinery has its own values, depend - ing on what is important to its operation and needs. It is important to be familiar with the indicators and their impact on FCC unit performance to see if this may be the source of a particular problem. Other tools for troubleshooting can be called on to pro- vide important clues to problems and their causes. Some of these are listed in Table 3 . Tracking the feedstock analy- ses and product properties is important since the largest single variable for any process is the quality of the material processed. Changes in feed properties will affect the yields and product properties of the FCC unit. It is imperative that the process engineer understands the significance of all the feed tests being run so countermea - sures can be taken to fix any issues with the operation. The unit test runs can be used to generate graphs showing the effect of each feed variable. The operating manual should also be checked for the licensor’s correlations. Reaction mix sampling Reaction mix sampling allows for direct sampling of the reactor effluent in the overhead vapour line and determining the yields without having to wait for the gas plant to come into equilibrium under the new conditions. These give the as-produced yields from the unit’s reactor. Samples can be taken every two hours when making changes to operating parameters to evaluate the impact of variations in feed rate, dispersion steam, feed temperature, and stripping steam. Samples from the stripper can give insight into the effec - tiveness of stripper performance and help identify the hydrocarbons going to the regenerator. Samples taken from the end of the riser and the overhead vapour line will show the cracking that takes place in the dilute phase, cyclone system, plenum chamber, and vapour line. These tests will provide the basis for justifying a revamp to the reaction separation system. RMS testing gives information on the feed injection sys - tem. Turndown capabilities, plugged nozzles, changing the number of nozzles, and/or the type of nozzle can all be evaluated. If there is more than one feed location, the split- ting of the feed can be tested. Lift gas injected at the bottom of the feed riser is used in some FCC operations. The amount used can be evaluated easily with RMS testing. More steam in this service, which is not effective, is reducing the overhead condensing capa- bilities and adding to the load on the sour water stripper. The stream used as lift gas can also be examined. Recycle to cat crackers can be very important. Streams that might be recycled are gasoline, heavy cycle oil, decant oil, and even LCO. If separate nozzles are available, the location in the riser can be studied along with the rates of each stream. The impact of changes in the cut-points of various streams can also be explored. New units should be designed with taps in the appropriate locations to facilitate RMS testing. The testing itself is shown in Figure 1 .
Key performance indicators
Feedstock analyses API gravity IBP 650ºF point EP
Flue gas temperature Flue gas analyses Air rate Wet gas compressor rate Performance indicators Conversion, V% Dry gas, wt%
1050ºF point Sulphur, wt% Conradson carbon, wt% Operating variables Feed rate Feed temperature Reactor temperature Regenerator temperature Cyclone temperature
C 3 =, V% C 4 =, V% Gasoline, V% Octanes LCO (diesel), V% Coke, wt%
Table 2
periodically as well as from the main column bottoms to determine catalyst losses. A separate sheet for the individual samples makes it eas- ier to spot variations and the location of changes. Twice a month should be adequate to capture any trends and give confidence in the numbers. Sampling might be increased when issues arise. Catalyst additions and losses should be checked and recorded regularly. Automatic loading systems can gener- ate additions to the cracker. The losses are calculated from the concentration of the catalyst multiplied by the appro- priate exit stream rate. If any equilibrium catalyst is being added, the amounts and analyses of this material should be known. The volatility of the fresh catalyst (moisture, sulphates, chlorides, and ammonia) needs to be calculated to get the actual weight of the catalyst added. This number usually ranges from 7 to 13 wt%, depending on the final calcination received at the catalyst plant. Catalyst may pick up mois- ture after it leaves the manufacturer before it is injected into the unit. Any additives should be treated the same way. The amounts and analyses of the material can help explain changes in platinum, CO index, magnesium, calcium, and phosphorus contents and are essential in calculating their retention and where they are leaving the FCC unit. All pur- chased ecats should be checked for compatibility with the desired operation.
Other tools for troubleshooting
1 Feedstock analyses 2 RMS (reaction mix sampling) testing 3 Radioactive tracers 4 Gamma scans 5 Cold flow modelling 6 Computational fluid dynamics 7 Pilot plants infrared scans 8 Process tomography 9 Leak detection 10 Metallurgical testing 11 Acoustic imaging
Table 3
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Revamps 2022
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