PTQ Q3 2023 Issue

Overall pumparound heat duties

215

Non- condensable cracked gas/air

Vacuum system

Service

Test run

Revamp

LVGO PA MVGO PA HVGO PA

87.0 87.5

107.0 128.5 140.0

210

Slop oil

125.0

LVGO PA

275

LVGO (diesel)

Crude oil & n-fan & CW

Much higher reux

Table 5

LVGO PA duty condenses reux & LVGO product

RGO

section. The higher top temperature increased conden- sable oil to the ejectors; however, this was offset by routing part of the RGO to the atmospheric column and improving CV1 atmospheric column bottoms stripping. The vacuum column has a 38 ft-diameter column sec- tion above the HVGO PA, which makes distributing liquid to the LVGO/MCGO fractionation bed difficult. Prior to the revamp, a leaky LVGO draw tray and very low reflux rate resulted in low packing efficiency and low LVGO product (diesel) yield. In order to have enough reflux to properly wet the large diameter bed, a significant heat balance shift from MVGO PA to LVGO PA was needed (see Figure 9 ). With this heat balance shift and the elimination of the leaky tray, MVGO draw temperature increased by more than 50°F. HVGO draw temperature increased by 20°F. The combination of higher MVGO and HVGO draw tem- peratures, along with small investments in control valves and piping bypasses, enabled maximum pumparound cir- culation. These changes allowed for heat balance optimi- sation, which was needed to increase crude preheat and external AR heating. Energy optimisation CV1’s overall energy use per barrel of feed decreased even as higher-valued product yields increased and external RGO and AR processing increased. Energy improvements were essential to avoid costly heater modifications. Both the atmospheric and vacuum heater outlet temperatures were increased by 15°F and +20°F, respectively, to increase dis- tillate yield, which was done without increasing the heater firing. Both crude and vacuum heater inlet temperatures increased by 20°F and 41°F, respectively, by recovering more heat to oil vs generating steam. Overall 250 psig steam con- sumption was reduced by more than 37,000 lb/hr by reduc- ing process and motive steam to the first-stage ejectors. Pumparound heat was optimised between crude preheat and external AR heating. More heating of the external AR stream was required to offset higher vacuum heater outlet temperature. The combined AR feed to the vacuum heater was increased from 587°F to 628°F to keep the vacuum heater firing constant. External AR feed stream tempera - ture increased from 481°F to 567°F. The last two services in both crude and external AR feed streams are VR/VR Quench and HVGO PA/product streams. Figure 10 shows a simplified PFD of the last two services for these streams. Higher HVGO draw temperature, higher pumparound flow rate, which was achieved by installing short piping runs to partially bypass exchangers, and optimisation of the VR quench location aided in increased heat recovery with no additional exchanger area. 11

M VGO PA

Hydrocracker or FCC

Crude oil & steam & n-fan

MVGO

HVGO PA

HVGO

FCC

Crude oil & external AR & steam

780

AR from heater

Temperature, ˚F 780

Stripping steam

VR External AR & crude oil

Figure 9 Vacuum column heat shift

shortcomings led to less-than-optimal pumparound heat balance. Lower top pressure, higher heater outlet temperature, and improved bottoms stripping increased HVGO cut- point. More gasoil was being lifted from the vacuum resid. This, coupled with increased RGO processing, would increase the overall pumparound heat duty requirements by 25% (see Table 5 ). Optimisation of the heat balance was necessary to remove the additional heat and maxim- ise LVGO production. A combination of higher MVGO and HVGO draw temperatures, along with small investments in control valves and piping bypasses, enabled maximum pumparound circulation A long-term fix for the leaky LVGO tray was needed to reliably maximise LVGO recovery and meet crude preheat targets. The LVGO section experienced heavy corrosion from tramp amines. The corrosion byproducts plugged the LVGO/MVGO fractionation section distribu- tor and corroded the packing, collector tray, and vessel top section. The revamp increased the vacuum column overhead temperature from 120°F to 215°F to prevent corrosive material from being formed in the LVGO PA

PTQ Q3 2023