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Techniques For Troubleshooting FCC Regenerator Problems.

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Presentation on theme: "Techniques For Troubleshooting FCC Regenerator Problems."— Presentation transcript:

1 Techniques For Troubleshooting FCC Regenerator Problems

2 Overview Introduction Particulate Emissions: –CPFD Modeling –Catalyst attrition –Cyclone integrity –SEM analysis Afterburn Control –Analysis & control Gaseous Emissions Control –Control of SOx emissions –Control of NOx emissions Conclusion

3 Introduction There has been substantial experience gained in troubleshooting FCC regenerator operations during the last 68+ years Many important lessons learned – one of the most important is that: Effective troubleshooting requires a solid set of baseline data taken during normal operations Selective use of additives can also help enhance the performance of the regenerator Refer to reference section of associated paper for key landmark papers related to regenerator troubleshooting

4 Overview Introduction Particulate Emissions: –CPFD Modelling –Catalyst attrition –Cyclone integrity –SEM analysis Afterburn Control –Analysis & control Gaseous Emissions Control –Control of SOx emissions –Control of NOx emissions Conclusion

5 Particle Fluid Dynamics One of the most interesting tools to become available in recent years is CPFD Modeling –Computational Particle Fluid Dynamics Extremely computer intensive, has only very recently become a practical tool Using a very simple set of boundary conditions, these models can provide a whole new level of understanding of regenerator operations INTERCAT is grateful to Barracuda for the following simulation

6 Particle Fluid Dynamics Simulation is of a Model II Regenerator Spent Catalyst enters through the bottom nozzle Baffle plate above the catalyst inlet to deflect catalyst into the dense bed Three combustion air rings Single regenerated catalyst standpipe 12 pairs of cyclones

7 Particle Fluid Dynamics In this flowing simulation colour is used to represent catalyst density Simulation revealed several interesting features: –Catalyst entering regen is concentrated on outside bend of pipe –Deflector plate was ineffective at keeping catalyst in the bed –Much of the incoming catalyst bypasses the bed and enters the dilute phase directly –Bed is very unstable, with no clear level –Red area below air rings shows a large dead zone of defluidized catalyst

8 Particle Fluid Dynamics In this flowing simulation colour is used to represent catalyst density Simulation revealed several interesting features: –Catalyst entering regen is concentrated on outside bend of pipe –Deflector plate was ineffective at keeping catalyst in the bed –Much of the incoming catalyst bypasses the bed and enters the dilute phase directly –Bed is very unstable, with no clear level –Red area below air rings shows a large dead zone of defluidized catalyst

9 Particle Fluid Dynamics This view shows only catalyst that has been in the regenerator for less than 30 seconds Note large amount of unregenerated catalyst making its way to the very top of the dilute phase

10 Particle Fluid Dynamics This view shows only catalyst that has been in the regenerator for less than 30 seconds Note large amount of unregenerated catalyst making its way to the very top of the dilute phase

11 Particle Fluid Dynamics Close in view of bed shows catalyst from primary cyclone dipleg bypassing the bed, and directly entering the standpipe Explains salt and pepper appearance of ECat

12 Particle Fluid Dynamics Close in view of bed shows catalyst from primary cyclone dipleg bypassing the bed, and directly entering the standpipe Explains salt and pepper appearance of ECat

13 Particle Fluid Dynamics This view was generated to assess likely areas of erosion Green areas show time averaged areas of high velocity and high catalyst density This simulation was carried out before the unit was shut down When unit was opened up, wear was found to be in exactly the areas predicted by the CPFD simulation

14 Particle Fluid Dynamics This close match gave confidence in the model predictions Model could then be used to design a new deflector plate & internal configuration New design was implemented, and unit operation has been very stable since startup

15 Attrition in Regenerators All units have a low level of attrition occurring continuously Submerged jet attrition at the grid Attrition in cyclones Abnormal Attrition can be substantial Improperly designed, eroded, or missing orifices in steam lines Excessive velocities through air grid High turbulence caused by a broken air grid High catalyst velocities through slide valves Developing a good normal operating baseline is strongly recommended in order to prepare for troubleshooting any future loss problems

16 Attrition in Regenerators How Can We Check Catalyst Attrition Rates? –Capture & analyze fines samples regularly 3 rd stage separator or isokinetic sample –Need to request detailed PSD analysis –Plot wt% capture vs. PSD Normal Distribution: –One primary peak at μ –One attrition peak at 0-5 μ –One breakage peak at μ If Attrition Source Present: –Primary peak shifted to lower particle size & reduced in magnitude –Attrition peak increases & dominates

17 Cyclone Integrity Mechanically related problems: –Broken welds –Holes from erosion or high stress tears in the cyclone or dipleg –Dipleg valves which do not operate –Dipleg valves which do not close because of bent or lost closure plates Operationally related issues –Excessive mass flows in cyclones & diplegs –Insufficient dipleg length (Conceptual example) Note that PSD of catalyst is different at each point – this is key to effective troubleshooting

18 Troubleshooting Cyclones Primary cyclone hole –A secondary peak is observed to the right of the primary peak Positioned at >60 μ –The attrition & breakage peaks continue to be present

19 Troubleshooting Cyclones Secondary cyclone hole –A secondary peak is observed to the right of the primary peak Positioned at μ –The attrition & breakage peaks disappear Flooded cyclones –Primary peak shifts to the right of a typical unit –The attrition & breakage peaks continue to be present

20 Dipleg Pressure Balance Knowledge of cyclone dipleg levels can be very important Too high a dipleg level will cause catalyst entrainment –Minimum distance of catalyst level to cyclone vortex is approximately 600 mm (24 inches) –Increases in unit feed rate can increase required dipleg level beyond this minimum –Result: catalyst attrition, erosion in cyclone cones & hoppers, entrainment Higher catalyst levels occur in secondary cyclones lead to entrainment losses –Plot cyclone dipleg heights vs. catalyst losses to determine unit specific critical dipleg level ρ bed h bed h dl ρ dl

21 Filter paper SEM image Attrition vs. Fresh Cat Losses When losses increase, the first response is normally to ask if they due soft fresh catalyst If losses are from fresh catalyst: –Fines surface area > ECat –Fines metal levels < ECat If attrition source/hole: –Fines surface area = ECat –Fines metal levels = Ecat SEM check: –Acquire ESP, stack fines, etc. –Analyze particle morphology –Base line critical

22 SEM Fines Analysis Typical FCC fines –Note: well rounded equilibrium particles –Attrition fragments will vary by unit –Base lining normal operations critical –Particle size 1-3 µ –Magnification = 10,000X 20 µ Attrition fines Primarily sharp irregular morphology Particle size 1-2 µ –Magnification = 2,500X 5 µ

23 Overview Introduction Particulate Emissions: –CPFD Modeling –Catalyst attrition –Cyclone integrity –SEM analysis Afterburn Control –Analysis & control Gaseous Emissions Control –Control of SOx emissions –Control of NOx emissions Conclusion

24 Regenerator Afterburning Afterburning is any increase in flue gas temperature after leaving the dense bed –May occur in dilute phase, cyclones, or flue gas –Little catalyst present to absorb heat of combustion –May limit throughput or feedstock flexibility –Can result in serious damage to internals leading to premature shutdown & costly repairs Two types of afterburn observed: –Kinetically limited afterburn Due to insufficient regenerator bed residence time for complete combustion –Afterburn induced by poor catalyst and/or air distribution Frequently due to inherent design features &/or air grid mechanical failures Source: Jack Wilcox, RPS

25 Kinetic Limited Afterburning Characteristics: –Well dispersed afterburn across regenerator cross section –Commonly seen when there are: High superficial velocities Low bed levels Low bed temperatures Solutions: –Consider raising bed level –Use of CO Promoter Kinetically limited units generally respond well to CO Promoter use

26 Distribution Induced Afterburn Characterized by localized afterburning Induced by poor air &/or catalyst distribution –Due to mixing of CO & O 2 rich zones above bed –Responds less well to CO Promoter Monitor hotspot temp as Pt concentration increases Hotspot temperature will drop until O 2 is fully consumed in effected region Continued additions after temperature fails to drop has little effect on regionalized afterburn NOx emissions will continue to increase –A normally well behaved unit which begins to afterburn together with a change in losses or equilibrium PSD indicates air grid damage Maldistribution may be confirmed using a portable gas analyzer O 2 richCO rich O 2 rich CO rich Source: J.W. Wilson, AM-03-44

27 Gas Analyzer Verification Portable gas analyzers are effective at confirming maldistribution Typical equipment used: –Reaction Mix Sample (RMS) probe –Mott filter element used to remove catalyst fines from the gas stream Catalyst withdrawal #1 #2 #3 Spent cat entry

28 Overview Introduction Particulate Emissions: –CPFD Modeling –Catalyst attrition –Cyclone integrity –SEM analysis Afterburn Control –Analysis & control Gaseous Emissions Control –Control of SOx emissions –Control of NOx emissions Conclusion

29 Controlling SOx in Full Combustion Feedstock effect –About 10% emitted as SOx (range: 5-35%) To improve SOx additive efficiency: –Drive SO 2 to SO 3 equilibrium towards SO 3 Increase excess O 2 (up to ~2%) Reduce bed temperature Increase regenerator pressure Use of CO promoter –Enhance additive efficiency Increase cat circulation rate Factors reducing additive efficiency: –High catalyst losses –Large regenerator inventories –Poor stripper efficiencies –High Fe on equilibrium catalyst Total elimination of SOx emissions is achievable

30 Controlling SOx - Partial Combustion SO x additives in partial burn : –Majority of S is normally in reduced form e.g. COS, H 2 S –Oxidation of SSO 2 SO 3 limiting step –Tailored oxidation component required for maximum additive effectiveness Compare SO 2 in flue gas vs. stack prior to using additives –Normally only about 30% of S will be in oxidized state Partial burn guidelines: –There is a practical upper limit to SOx reduction with additives Monitor SOx concentration in flue gas upstream of CO Boiler thru trial –Monitor regenerator CO-to-CO 2 ratio as additive concentration increases Sulfur Species Data from European 7% CO Deep SOx reductions in partial burn are feasible

31 Controlling NOx Emissions NOx formation: –~10% of N in coke emitted as NOx –Excess O 2 is the most significant operating variable affecting NOx emissions Maldistribution of air & catalyst leads to high NOx emissions NOx reducing additives are effective in full combustion –There is an effective unit specific maximum concentration Exceeding this maximum will have no effect or may actually increase NOx –Additive efficiency is highly unit specific –Effectiveness in Partial Burn is limited

32 Designing for Low NOx Emissions Control of air-to-catalyst mixing critical to low NOx emissions –Combustor type regenerators with superior air- to-catalyst mixing control NOx emissions well Bubbling bed regenerators can be improved for reduced emissions: –Ensure counter current operation –Distribute spent catalyst uniformly across the top of the regenerator bed –Inject combustion air uniformly across cross section of regenerator Additives are normally effective for further reductions if needed Courtesy: KBR

33 CO Promotion & NOx Emissions NOx emissions increase as platinum content increases –Simultaneous control of afterburn & NOx emissions is possible via non-Pt promoters –Fully commercialized solution Be sure to use good additive loader technology for optimum performance –See example on right –Reliable additive injection is essential –INTERCAT offers loaders for all of its additives Example of enhanced additive effectiveness due to improved loader reliability

34 Overview Introduction Particulate Emissions: –CPFD Modeling –Catalyst attrition –Cyclone integrity –SEM analysis Afterburn Control –Analysis & control Gaseous Emissions Control –Control of SOx emissions –Control of NOx emissions Conclusion

35 Advanced troubleshooting techniques can help the FCC engineer monitor, troubleshoot, & optimize the FCC regenerator A good quality base case taken during normal operations is essential for swift troubleshooting Most catalyst companies have substantial hands on regenerator troubleshooting & optimization expertise –Take advantage of this expertise, and use it to ensure the baseline FCC operation is thoroughly understood –Will ensure that any operational problems can be quickly diagnosed whenever they arise


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