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• What is your experience with utilisation of internals in Riser? What are the expected benefits in delta pressure and yields?

  Apr-2022

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Answers

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• Erick D Gamas, The Business Shop-Chemical Engineering Services, edgamas@hotmail.com

  The effectiveness  in chemical conversion in a riser reactor relies strongly on the contacting efficiency of feed and catalyst.  It is well known that there is downflow of spent catalyst particles at the reactor walls; the actual catalyst/oil ratios deviate from design values leading to operations not in specifications with design yields. A core-annulus diluted flow is present with a dense flow downward at the riser wall.

  An economic approach to determine the need for internals for a riser in an FCC unit, or any unit operating as a fluidized bed, is to determine the flow hydrodynamics via CFD Modelling or by actual measurements using tracer studies. Both methods can be contracted in the industry at a significantly lower cost than measuring hydrodynamics building a mock-up pilot or full scale unit simulation

  There is a significant amount of information in the open literature about the effect of internals to improve contacting between catalyst and feed in  a riser. Overall views indicate that there is a significant increase in delta P, sometime doubling the delta P in the conventional riser without internals.

  Another very important aspect of the use of internal is the effect that the catalyst particles have on the structure of internals hardware . Any equipment present in the reaction environment is expected to last the time-on-stream until a scheduled T/A of the unit. It is then necessary, in addition to the study on enhanced hydrodynamics by adding internals, to do proper diligence in studying the abrasive effect of particles impacting the surface of internals at  flow conditions in the riser. In most cases either the internals are destroyed by the catalyst, causing a period of high catalyst fines production, or the cost of using expensive ceramic  materials makes the unit upgrading prohibitive. Clearly having pieces of metal/ceramics dislodged due to abrasion moving at high speed inside a riser is to be avoided completely.

   

  May-2022