Enhancing flexibility in two-stage hydrocrackers Shifting markets and refined product priorities compels refiners to find the flexibility for shifting from middle distillate to naphtha for petrochemical feedstock
A Mediterranean refinery recently installed Topsoe catalysts in a two-stage hydrocracker. Taking an unconventional approach and using a zeolite- based catalyst in the second stage provided product flex- ibility while maintaining high selectivity in diesel mode. The required temperatures in the second stage are lower than for amorphous-based catalysts. This one solution solved three challenges: it satisfied the need for naphtha flexibil- ity, it relieved limitations due to tight heat integration, and it tempered the build-up of heavy polynuclear aromatics (HPNA), thereby leading to significant operational benefits in the hydrocracking unit. Unit description T he hydrocracking unit (HCU) comprises three reactors: Reactor 1 contains guard and pretreat catalysts, Reactor 2 contains the zeolite-based first-stage hydrocracking Devansh Dhar, Pronit Lahiri and Paul Ronald Robinson Topsoe
catalyst, and Reactor 3 contains the zeolite-based second- stage hydrocracking catalyst. In addition, post-treatment catalyst is loaded in the hot high-pressure separator pre- sented in the block flow diagram (see Figure 1 ). The operating pressure exceeds 150 bar, and the target conversion level is 99.5 wt%. The primary aim is to maxi- mise middle distillates while processing heavy vacuum gas oil (HVGO), coker gas oil, and other heavy streams. In addi- tion, the refiner desires flexibility to increase naphtha yields in response to changes in market demand. The product slate from this unit comprises LPG, light naphtha, heavy naphtha, kerosene, diesel, and unconverted oil (UCO). Feedstock challenges Thanks to its Mediterranean location, the refinery has ready access to many crudes. In a given year, more than 25 dif- ferent crudes are processed. Consequently, the feed to the
Treat gas
2nd stage feed drum
Pump
Filtration
Fresh feed
F/E exchange
Furnace
Pump
Fractionator bottom
R1 pretreat
R3 2nd stage hydrocracking
Quench
Quench
Naphtha
R2 1st stage hydrocracking
Kerosene
Separation section
Fractionator
O gas
Diesel
Naphtha
UCO
To 2nd stage
Figure 1 HCU flow
29
PTQ Q3 2022
www.digitalrefining.com
Powered by FlippingBook