Flue gas V
base
Regenerator T base
O N
Flue gas V ~ base
Flue gas V
base
Regenerator T base
Regenerator T base
CO
CO
O
O
Constant volume mode
Constant temperature mode
Figure 2 Constant volume vs constant heat balance/temperature mode of operation
by the combustion process in the regenerator, whereas N 2 remains inert and carries a substantial amount of heat released during the combustion process. This heat is typi- cally recovered to a large extent in the flue gas heat recov - ery section of the FCC process. In an ‘oxy-combustion’ (referred to as ‘synthesised air’ going forward) mode of operation, the combustion is facili- tated by synthesised air, which is a mixture of O 2 and CO 2 . The CO 2 replaces N 2 as the inert heat carrier to avoid exces- sively high temperature in the regenerator, as per Figure 1 . In the simplest form of synthesised air operation, every mole of N 2 in the air is replaced with an equal mole of CO 2 . This results in the number of moles of regenerator flue gas remaining the same as typical air operation. Hence, the crit- ical velocities in the regenerator, including vessel superficial In the simplest form of synthesised air operation, every mole of N 2 in the air is replaced with an equal mole of CO 2 velocity and cyclone velocity, can be maintained in a simi- lar manner to base air operation. This is the ideal ‘constant velocity operation’ in synthesised air operation. The complexity of synthesised air operation arises from the fact that the molecular weight of CO 2 is approximately 1.6 times that of N 2 . Due to higher molecular weight and consequent higher mass flow, heat carried away by CO2 will be significantly higher for the same moles of N2, which results in a substantial drop in regenerator temperature (assuming reactor temperature and feed quality are held constant). To achieve a ‘constant heat balance operation’ of the regenerator, the number of moles of CO 2 in synthe- sised air operation needs to be reduced without compro- mising the critical velocities. See Figure 2 for a pictorial representation. UOP performed a case study in 2023 a on the application of Synthesized Air FCC system for a European refiner oper - ating its FCC unit at a feed throughput of 65,000 BPSD,
with nearly 75% residue in the feed blend. The blended feed Conradson Carbon (CCR) concentration of the feed was 3.6 wt% (see ‘Case Study’ section). Based on the findings of this case study, conversion from normal air combustion to synthesised air operation is estimated to reduce the regenerator temperature from 738°C to 709°C. The drop in regenerator temperature and the reduced flue gas flow rate create additional coke burn capacity in the regenerator. This additional coke burn capacity provides an opportunity to increase residue con- tent in the feed blend from 75% to 100%. The resulting regenerator temperature for this operation was estimated to be 738°C, like the base case. The results of the 2023 case study produced by Honeywell UOP proprietary pro- cess models demonstrate the inherent potential of its Synthesized Air FCC technology to increase FCC profitabil - ity, apart from reducing direct CO 2 emissions (Scope 1) via an installed CCU, as shown in Figure 3 and detailed in the ‘Case Study’ section. Process description The principal components and general arrangement of the Synthesized Air FCC system are presented in Figure 3. It is comprised of a third-stage separator (TSS), power recov- ery turbine (PRT) section, heat recovery steam generator (HRSG), nViro FCC section, novel, proprietary, non-solvent Honeywell UOP FCC carbon capture section (CCS), and recycle blower. Note that an existing ESP/bag filter can be revamped to an nViro FCC unit, and a wet gas scrubber can be used in lieu of an nViro FCC unit. Flue gas from the FCC regenerator enters the TSS, where separation of the larger catalyst fines from the flue gas stream is accomplished. The TSS provides the necessary particulate removal to protect the expander internals from blade deposition or erosion. The clean flue gas exiting the TSS flows to the expander for power recovery. The larg - er-sized catalyst fines, separated from the main flow of flue gas in the TSS, are carried out of the bottom of the TSS with a slip stream of flue gas. The larger-sized catalyst fines are removed from the slip stream via, for example, a fourth- stage separator (FSS) before the slip stream merges with the main flue gas line upstream of the HRSG. The expander
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PTQ Q4 2023
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