Page 188 - Fluid Catalytic Cracking Handbook

160 Fluid Catalytic Cracking Handbook

• Increase the temperature of the fresh feed, recycle, and atomizing
steam from their preheated states to the reactor temperature
« Provide the zendothermic heat of cracking
• Increase the temperature of the combustion air from the blower
discharge temperature to the regenerator flue gas temperature
• Make up for heat losses from the reactor and regenerator to the
surroundings
• Provide for miscellaneous heat sinks, such as stripping steam and
catalyst cooling

A heat balance can be performed around the reactor, around the
stripper-regenerator, and as an overall heat balance around the reactor-
regenerator. The stripper-regenerator heat balance can be used to
calculate the catalyst circulation rate and the catalyst-to-oil ratio.

Heat Balance Around Stripper-Regenerator

If a reliable spent catalyst temperature is not available, the stripper
is included in the heat balance envelope (II) as shown in Figure 5-4,
The combustion of coke in the regenerator satisfies the following
heat requirements:

« Heat to raise air from the blower discharge temperature to the
regenerator dense phase temperature
• Heat to desorb the coke from the spent catalyst
• Heat to raise the temperature of the stripping steam to the reactor
temperature
• Heat to raise the coke on the catalyst from the reactor temperature
to the regenerator dense phase temperature
• Heat to raise the coke products from the regenerator dense tem-
perature to flue gas temperature
• Heat to compensate for regenerator heat losses
• Heat to raise the spent catalyst from the reactor temperature to
the regenerator dense phase temperature
Using the operating data from the case study, Example 5-5 shows
heat balance calculations around the stripper-regenerator. The results
are used to determine the catalyst circulation rate and the delta coke.
Delta coke is the difference between coke on the spent catalyst and
coke on the regenerated catalyst.