The catalyst dosage is a very important parameter for the FCC unit daily routine. Therefore, it is important that it always fits the unit conditions, its goals and restrictions. Ill-functioning of the continuous catalyst loading can entail several impacts to the inventory quality and on its turn to the cracking unit yields.

Catalyst makeup should be done continuously allowing the unit to always operate under optimized profitability conditions. A batch loading, for example, can lead to a peak in activity which in turn leads to instant coke and fuel gas rise which could compromise the air blower and the gas compressor, therefore altering the unit yield profile. Besides, it can also lead to enhanced losses caused by a rise in the particulate material load in the cyclones and/or caused by a rise in breakdown caused by increased line rate.

The exhibited case shows a study of the unit profitability as a function of catalyst makeup. In this case it can be observed that both for the 4ton/day makeup and the 7 ton/day makeup the refinery is placed in a condition of profitability loss before the 5ton/day base case.

That is, even if the average makeup is 5 ton/day, in case the makeup is always out of the optimum level, the refinery is in a profitability loss condition. In the study case, it is found that the refinery had a 5ton/day makeup, even by oscillating between 0.6 and 14 ton/day. Thus, the refinery profitability for the same catalyst expenses is lower than in the case it would makeup 5ton daily.

In spite of the direct impact on the yield profile, many units have drawbacks in maintaining the catalyst continuous dosage. In order to minimize this problem a few good practices are suggested:

• Employ valve models and internals better fit to abrasive solids transportation.
• Employ instrument air or a drying air system dedicated to the dosage system.
• Control the air flowrate used to avoid catalyst breakdown and excessive abrasion of the loading lines.
• Prioritize the system preventive maintenance by considering the right value of the period between failures. Also, keep the prioritization of the corrective maintenance of this system in case of unscheduled failures and the availability of spare parts for change when required.
• Do not use air to fluidize the system during catalyst loading to the feeder since this hinders the catalyst flow from the silo to the feeder reservoir.
• Whenever possible, have redundancy between the load cell and the feeder reservoir level key. It is thus possible to execute a dosage double check avoiding sub-dosages or overflows, besides having an indication when a valve is giving way.

FCC S.A. has a team available to aid refineries in this kind of problem. If needed, please contact us.