Fluidized Catalytic Cracker - FCC

Process description

A Fluid Catalytic Cracker is often the center piece of an oil refinery. The process is designed to 'crack' the gas oil fraction of the distillation process. The cracking is done by means of a catalyst which behaves like a fluid when aerated with vapor. Typical FCC feed stocks are atmospheric gas oil, vacuum tower bottoms or coker gas oil. The hot feed is contacted with steam and then with the catalyst. This process changes its carbon molecule structure from heavier to lighter. FCC output products are mostly alkylation unit feed stocks (propylene, isobutene, gasoline, diesel fuel).

Importance & Technical Challenge of flow measurement

The FCC’s feed rate (see #1 above)must be optimized against other operating parameters (such as catalyst circulation, alkylation capacity, gas compression capacity etc.) The feed liquids are mostly hot.

The slurry oil measurement (see #2 above) ) is a very important indicator of how well the cracking process runs. This liquid is difficult to measure as it contains traces of the catalyst and is very abrasive.

Conventional meters

Conventionally both of these liquids are measured with DP (Differential Pressure) devices such as orifice or wedge meters . This technology is prone to measurement errors: the orifice plates in the slurry oil application erode and misread the flow. They are also maintenance intensive in that the liquid enters and clogs the pressure impulse lines causing false readings. Cleaning these lines becomes a regular maintenance routine and can be dangerous because of the liquid temperature.