Michael Dorsey - CB&I
Spent catalyst stripper in an FCC unit is quite a critical piece of equipment. Hydrocarbon vapors entrained with spent catalyst represent a loss of valuable product, increase in delta coke and regenerator temperature, resulting in further loss of conversion, and yields of desirable products. The disc and doughnut baffles or shed deck designs have been employed in many FCC grass-roots designs for several decades. In recent times, there has been a step-change development in spent catalyst stripper internals design. These advanced stripper internals significantly improve the stripping efficiency and hence increased FCC unit profitability.
Hydrogen in coke is traditionally used as a primary indicator for assessing the performance of FCC spent catalyst stripper. Normally the hydrogen in coke is calculated from regenerator flue gas composition data, combustion air flow rate, etc. Since the flue gas data is also the basis for the heat balance calculations, it will influence many of the calculated operating variables such as unit coke make, catalyst circulation rate, the heat of reaction and most important hydrogen in coke. Use of hydrogen in coke as stripper performance indicator may result in misleading conclusions. This paper discusses traditional stripper performance assessment method, performance indicators & associated influence on conclusions. This paper will also highlight the importance of using the measured variables for assessing the improvements due to modern stripper internals with some examples.