1st stage K.O. drum
2nd stage K.O. drum
1st stage wet gas compressor
2nd stage wet gas compressor
Ovhd condensate receiver
C - gas
Main fractionation column
Naphtha stripper
HP receiver
Primary absorber
LCO stripper
Stripper
Steam generator
Reactor vapours
Main column bottoms product
To debutaniser
Figure 1 Flow diagram of the MFC and GCU systems
failure. Unplanned shutdowns due to equipment failures are associ- ated with significant revenue losses. Shutdown of an FCC unit may incur operational losses of up to $1.5 mil- lion per day. Loss-risk of such a magnitude can be mitigated with a moderate investment in a high- fidelity digital twin capable of simu - lating all key equipment. Figure 1 presents a basic flow dia - gram of the MFC and GCU systems in the FCC unit. Gas from the GCU is compressed and combined with primary absorber bottoms and strip - per overhead gas. This combined stream is then cooled and sent to the high-pressure receiver. Gas from this separator is routed to the pri- mary absorber. Based on economic analysis and production planning, the operator modified the production targets of the FCC unit. The plan included an increase of the throughput by 15% (Case A), which is 5% above the design capacity. Additionally, more propane and light product would be produced, reflecting a weaken - ing market for naphtha whilst the market for petrochemicals was seen to be strengthening. The strategy involved increasing the ZSM-5 cat - alyst addition to the existing inven - tory (Case B) and increasing the
oline and light hydrocarbons in the MFC overhead stream are routed to the gas concentration unit (GCU). Due to the low pressure of the MFC, the overhead stream produces gas that contains a significant concen - tration of heavy hydrocarbons, whilst the overhead liquid product contains light hydrocarbons. The resulting vapour stream is sent to the GCU with a wet gas compres-
sor for high-pressure recontacting and separation. Poor separator design and inap- propriate selection of internals can cause excessive liquid car - ry-over. This liquid carry-over propagates through the process, affecting downstream equipment. Ultimately, it can lead to progres- sive degrading of compressor per - formance and premature machine
Vessel geometry and specifications
Separator
Configuration
Nozzles Inlet: 32in
Internals
MF
Vessel orientation: Horizontal
Vane type for inlet device
condensate Separation type: 3-phase with boot Gas outlet: 24in
No demisting device
receiver
Vessel ID: 3962mm
HC liquid outlet: 20in
Vessel T-T length: 11888mm
Water outlet: 3in
Boot ID: 1524mm Boot height: 2362mm
1st stage
Vessel orientation: Vertical
Inlet: 24in
Half pipe for inlet device No demisting device
compressor Separation type: 2-phase
Gas outlet: 24in Liquid outlet: 2in
K.O. drum
Vessel ID: 2515mm
Vessel T-T length: 5029mm
2nd stage
Vessel orientation: Vertical
Inlet: 12in
Half pipe for inlet device Mesh pad demisting device
compressor Separation type: 2-phase
Gas outlet: 12in Liquid outlet: 4in
K.O. drum
Vessel ID: 1575mm
Vessel T-T length: 4750mm HP receiver Vessel orientation: Horizontal
Inlet: 10in
Vane type for inlet device
Separation type: 3-phase with boot Gas outlet: 8in
No demisting device
Vessel ID: 2210mm
HC liquid outlet: 10in
Vessel T-T length: 8840mm
Water outlet: 2in
Boot ID: 686mm Boot height: 1219mm
Table 1
28 PTQQ 2 2022
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