| Popis: |
We have developed a laboratory procedure using FCC Ecat which quantifies the mobility of vanadium, relative to nickel, in a particular FCC unit. The procedure involves the separation of the Ecat into different density fractions, and subsequent measurement of the nickel and vanadium on each fraction. The results of these measurements are combined into what is referred to as a “vanadium mobility index” or VMI, which is a number between one and about 15. A VMI of less than five represents low mobility, whereas a VMI greater than eight represents high mobility. In this paper we present data on the VMI of a number of different FCC units, representing all types of catalysts and operation. We have found that units with high VMI tend to have more vanadium deactivation of their catalysts; however, vandium trapping technologies perform better in these same units. We will present results which show that the commercial performance of a Davison vanadium trap is well correlated with the unit VMI. We have also examined what specific factors affect the mobility of metals in an FCC unit. Our work on VMI has shown large variation in vanadium mobility; however, we have not been able to clearly correlate changes in VMI with specific unit operating conditions, such as full vs. partial burn, regenerator configuration, catalyst addition rate, unit type or carbon on catalyst. In order to take a more rigorous approach to understanding the effect of regenerator conditions on vanadium mobility, we have undertaken a laboratory study to evaluate the effect many of these conditions have on metal mobility. We have designed a bench scale regenerator [1], which simulates the essential elements of operation of an FCC unit regenerator, and can be used to study metal mobility. Using this apparatus, we can control the important operating parameters of the regenerator, such as temperature, contact time, oxygen content and steam partial pressure, and evaluate their effect on vanadium mobility. In this paper we discuss our recent results on the effects of these parameters on the mobility of vanadium on Ecat and lab deactivated catalysts. |
