PTQ Q2 2022 Issue

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


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



Nozzles Inlet: 32in



Vessel orientation: Horizontal

Vane type for inlet device

condensate Separation type: 3-phase with boot Gas outlet: 24in

No demisting device


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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