RG compressor
QR1B1
H make-up 1
Feed mix
R1
H mix
Feed 1 Feed 2 Feed 3
H make-up 2
QR1B2
RG purge
H purge
Scrubber (Optional)
H S removal
QR2B1
HPS
R1
C C
QR2B2
LNAPH
HPS liquid
HNAPH
DIST
NH removal
Recycle oil
Bottoms product
Figure 1 Hydrocracker model configuration in HYSYS V.11
Process simulation and analysis The technical limitation of reactor simulation allows hydro - processing reactors in the simulation environment to deal only with process streams defined using the HCRSRK fluid package. The proposed solution is to try to exchange any not well-defined and incompatible process streams, espe - cially WLO and WCO, with an indirect defining method by transferring a suitable fluid package of Peng-Robinson and NRTL to the hydrocracker equation of state HCRSRK. Modelling and simulation usually propose the advantage of process flexibility that enables us to predict product yields, reaction conversion, and operating cost based on utility con- sumption. Product quality can also be predicted using the simulation model; most of the expected physical properties are considered good enough, especially molecular weight, heat transfer properties, boiling range, and API density. The RefSYS supported packages in HYSYS from V.7 up to V.11 are generally used to simulate most refining processes such as the DCU, hydrocracking unit (HCU), naphtha reform - ing unit (NRU), naphtha hydrotreating unit (NHT), FCC, and sulphur recovery unit (SRU). This package is an advanced tool for expecting and calculating reaction kinetics on a lump sum basis, depending on feed properties, product proper- ties, product yields, and reaction retention time provided in the calibration model. The hydrocracker model is usually built using the built-in hydrocracker configuration model or using (the hydropro - cessing bed) to install a given process configuration if it is widely varied from the built-in configuration (hydrocracker model). Figure 1 shows the hydrocracker configuration built-in model. The first step in building any RefSYS model
pump to the heat exchangers and charge heater. After liq- uid hydrocarbon feed enters the heat exchangers, make-up and recycle hydrogen flow are mixed with this liquid feed. Once the feed and hydrogen are mixed and heated to the required temperature, the feed mixture enters from the top of the reactor through an inlet distributor. As the reactants move downward in the reactor, hydroprocessing reactions occur as illustrated before, and the temperature increases gradually. The first reactor is divided into three beds, each supported by a steel beam and support grid. The support system is sep- arated from the next bed of catalyst by a quench gas distrib- utor and vapour-liquid redistribution tray. The second reactor is divided into two beds, and each is supported by a steel beam and support grid. The support system is separated from the next bed of catalyst by a quench gas distributor and vapour-liquid redistribution tray. As the reactants and prod- ucts mixture leave the second reactor, the flow through the heat exchangers is to be sufficiently cooled before entering the high-pressure separator. In the cold high-pressure separator, hydrogen recycle gas is separated and sent back to the reactors through the recy- cle gas compressor. Further, recycle gas flow is considered high flow with a considerable design purge flow of 10%, which increases hydrogen consumption. It is recommended to use an amine sweetening unit to treat recycle gas from acid gas contaminants such as CO, CO₂, and H₂S sulphide that reduce catalyst activity. Liquid from the cold high-pres- sure separator is sent to the cold flash drum, then the liquid from the cold flash drum is sent to the fractionation section to be separated into LPG, naphtha, kerosene, diesel, and unconverted oil.
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PTQ Q4 2023
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