Audited yield shifts after Shell Energy and Chemicals Park Singapore LRCC unit feed nozzle upgrade
Component
Yield shift * (wt%)
Dry gas
–0.4 –0.1 –0.5
Propylene/propane (PP) Butane/butylene (BB)
Gasoline
3.7
Light cycle oil (LCO)
–0.9 –1.8
Slurry oil
Conversion
2.7
* Audited at constant coke yield
Table 1
viscosity. The challenge was to increase long residue cata- lytic cracker conversion and yields. FCC unit operators will often tackle these challenges by using additional atomisation steam and higher feed preheat temperatures. Additional steam is generally effective if the feed nozzle is optimally designed for it; otherwise, the addi- tional steam can cause deterioration of the spray pattern. 1 Pursuing higher feed preheat temperatures can help feed atomisation, but it can also shift the heat balance, thereby reducing conversion and the yields of desired products. The solution involved implementing the Shell Max Atomisation Feed Nozzle at the site during its 2018 turn- around. The audited yield shifts after the upgrade are given in Table 1 . The slurry reduction was significant, and it was found that crackable components present in the slurry oil before the turnaround were ultimately cracked to lighter products following the feed nozzle upgrade. Figures 5 and 6 present the slurry oil quality shifts with respect to specific gravity and total aromatics. The new feed nozzles significantly increased the upgrad - ing of slurry and LCO to gasoline. Moreover, because the new nozzles had improved atomisation, there was better quenching of the regenerated catalyst, leading to a lower riser temperature above the feed zone. In addition, under certain conditions, the unit was feed-rate limited by the riser temperature one-third up from the feed injection zone.
Figure 4 Shell Max Atomisation Feed Nozzle design
Improving reliability Although high conversion and yield performance are important to feed nozzle design, reliability is the key to having consistent and sustained feed nozzle performance throughout the run. The Shell Max Atomisation Feed Nozzles are designed to fit inside a Shell riser cone that includes a protective shroud that shields the feed nozzles from the riser environment. The shroud protects the noz- zle slot and internals and prevents catalyst ingress into the nozzle during operation. Additionally, the feed nozzles experience minimal erosion, leading to consistently high performance over the entire cycle. Figure 4 shows a feed nozzle shroud with inserted feed nozzle after a complete FCC unit cycle. As can be seen from the picture, the feed nozzle slot and internal steam orifices show little to no deterioration, and although the shroud shows signs of typical refractory erosion, it is still fully intact and func- tional after the run. Audited Result 1: Shell Energy and Chemicals Park Singapore (formerly Pulau Bukom refinery) The refinery has a long residue catalytic cracking (LRCC) unit that was designed to crack feedstocks with a CCR value of about 5 wt%. The feed is particularly challenging to atomise as it can be quite heavy and have an elevated
65
1.10
60
1.08
Post-turnaround
55
Post-turnaround
1.06
50
Pre-turnaround
1.04
45
Pre-turnaround
1.02
40
1.00
35
30
0.98
Figure 5 Slurry oil specific gravity before and after the feed nozzle upgrade
Figure 6 Slurry oil aromatics content before and after the feed nozzle upgrade
41
PTQ Q3 2022
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