Revamps 2022 Issue

Tools for FCC unit troubleshooting Strategies, resources, and technology can help to rapidly identify potential operational problems in FCC units targeted for upgrading and optimisation of existing units

Warren Letzsch Warren Letzsch Consulting PC

T he fluid catalytic cracking unit (FCC unit or ‘cracker’) is fundamental to the successful operation of a fuels refinery. It is important that the cracker runs every day without any artificial limits. A well-trained technical staff is purposed with the responsibility to make this hap- pen. Tools are available to troubleshoot any unit problems to provide clues to the solutions required to restore order. A new process engineer on the FCC unit is often left to his own devices to learn the needed knowledge for the job. Table 1 is a checklist for the engineer in preparation for an FCC unit assignment. All these items are available or can be obtained during normal operations. Advanced preparation for many emerging problems can shorten the time it takes to identify the cause and make the necessary changes to alleviate the situation. A set of up-to-date FCC unit drawings is necessary to ensure the right numbers are being used in calculations. These should be the ‘as built’ drawings verified by field inspection. Cameras are very useful since they can record the unit as it stands versus the memories of people who think they know. The computer programs for the unit, which make many of the calculations, need to be updated after every modification. The source code should be avail- able so it is clear just what numbers and methodology are being used. Procedures and strategies Valid data from the unit test runs providing the material bal- ances is a must. The yields should not only weight balance, but also carbon and hydrogen balance. Pressure balances are needed as well as heat balances to have a picture of the entire unit when it is operating correctly. These provide checks against the current values and should be compared to design numbers. It is helpful to have the balances done at different feed rates since it is better to make comparisons at constant feed conditions. These balances need to be made after every equipment modification or when there are changes in catalyst or feed type to evaluate their effect on the unit performance. Single gauge pressure surveys are used to troubleshoot standpipe problems and can locate the source of flow issues. The instrumentation design scheme needs to be reviewed to understand the numbers. Maintenance records for the FCC are a vital source of information. These contain a chronological list of repairs made to the cracker and their frequency. Any items that were not made during the last turnaround (TAR) should be

noted since a problem can occur before the next scheduled shutdown. Data that might be pertinent to questionable equipment and locations should be monitored to quickly spot and alleviate any problem. Inspection reports can be used the same way. Any signs of unusual wear, coke formation, or other anomalies can provide clues to the underlying causes of the problem. It is essential that the causes of recurring issues be identified as design, operational and/or procedural so that changes can be made that resolve the problem. Identifying trends The equilibrium and fresh catalyst analyses should also be monitored. Fresh catalyst samples can be analysed by the company doing the equilibrium catalyst (ecat) analy- ses, which eliminates lab differences when comparing individual values of each analysis. Catalyst samples from the wet gas scrubber, ESP or flue gas line should be taken

Checklist for new FCC unit process engineers

  1 Heat balance   2 Material balance: Log sheets

Meters (meter factors)

  3 Pressure surveys:

Air blower --- flue gas stack Reactor-regenerator- main column Gas plant  4 Gas plant details (t. P. design)   5 Impact of other units: Desalter Crude unit Alkylation Polymerisation   6 Important calculations: Velocities Densities Levels Catalyst   7 Gauging tanks and hoppers   8 Torch oil guidelines   9 Unloading trucks and rail cars   10 Equilibrium catalyst analyses   11 Steam circuits   12 Water circuits   13 Feedstock analyses   14 Start-up and shutdown procedures

Table 1

Revamps 2022