Revamps 2022 Issue

Cold flow modelling Many licensors of technology will do cold flow modelling in the laboratory to test new designs or the revamp of an existing unit. Small-scale equipment is fabricated, and the expected catalyst flow is used to look for potential prob- lems. This is more likely to be necessary for revamps since a new unit has all the required space and sizing for the technology. To ensure a positive outcome, the equipment being simulated should be at least one-third the size of the planned size. Computational fluid dynamics Computational fluid dynamics uses heat, mass, and fluid dynamic equations to simulate unit operation under all possible rates. Today, the better models yield good results and should be a routine part of any revamp or unit modi- fication. Earlier use of these models was hit or miss. The main problem was a lack of computer memory and speed. To make the solution converge, larger deltas for the vari- ables were used that gave inaccurate solutions. Pilot plants Pilot plants can be an effective way to look at changes in catalyst or feedstock. Small-scale ACE units are used as well as circulating pilot plants. Both can give excellent results if equilibrium catalyst from the commercial unit is used. The operation of the pilot plant is tuned to the cur- rent feed, and new catalyst candidates are run at those

conditions. The ACE unit should be at a reactor temperature between the large unit’s riser bottom and top temperatures to consider the heat of reaction. Delta cokes far exceeding the base operation make a direct scale-up of the data more tenuous. The larger cir- culating pilot plant allows for the determination of product properties and is easier to correlate with the existing oper- ation. This may be a much cheaper way of evaluating feedstocks than using the large FCC unit as a pilot plant. Catalyst testing will give meaningful results if the catalyst is deactivated artificially in a way that simulates what will happen in the commercial FCC unit. The preferred method of deactivating fresh catalyst is the cyclic propylene steam- ing (CPS) method, which can be adapted to both low and high metals (Ni and V) loading. The hydrogen produced is a marker for how effectively the deactivation will mimic the equilibrium from a commercial cat cracker. These and other tests can provide the necessary infor- mation for troubleshooting the FCC unit. Against this back- drop, another article in the development stages will discuss typical problems encountered in the FCC unit and how some of these tools help in their resolution.

Warren Letzsch is President, Warren Letzsch Consulting PC. He has 53 years’ experience in refining catalysts, petroleum refining, and engi- neering design and technology development for a major technology licensor.

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Revamps 2022