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riser outlet temperature to 540ᵒC (1004ᵒF) to increase conversion (Case C). Rating calculations were required for all equipment, includ - ing separators around the MFC. This case study investigated the performance of the following four separators in the FCC unit: 1. The condensate receiver of the main fractionation tower 2. Two compressor K.O. drums in the gas plant 3. The high-pressure separator To accommodate the increase in gas production from the MFC, the operator added a third compression train, identical in size and capacity to the two existing ones. This case study was conducted to determine the adequacy of the existing equipment, particularly the overhead condensate receiver, both compressor suction K.O. drums, and the HP separator. A key oper - ational requirement involved limit - ing both the maximum droplet size and excessive volume of entrained liquid. These efforts helped prevent cumulative damage to costly rotat - ing equipment and minimised the risk of an unplanned shutdown. Outline specifications of the four vessels under investigation are pre - sented in Table 1. Figure 2 illustrates the configuration of the original MF condensate receiver vessel. Petro-SIM process simulator, MySep Studio, and MySep Engine were used to investigate the per - formance of these four vessels. The simulation results are presented in Tables 2 - 5 . It is intended that liquid carry- over from the MFC overhead con - densate receiver be captured by the first-stage K.O. drum. The higher volumetric flow rates for cases B and C result in higher mist flow rates and small droplets enter - ing the MFC overhead conden - sate receiver. Analysing the flow regimes reveals annular mist flow in both horizontal and vertical pipes. In addition, the first-stage K.O. drum has insufficient capac - ity to handle the excessive mist load. It was therefore concluded that the condensate receiver would require retrofitting with a demist - ing device. This would avoid any problems associated with excess
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Figure 2 MF condensate receiver original configuration
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Simulation results for theMFC overhead condensate receiver
Feed rate
Pressure drop,
Liquid carry-over,
Droplet size,
increment,%
kPa-psi 2.1-0.31 3.2-0.47 3.5-0.50
kg/h-lb/h 92.3-204 1944-4285 2719-5994
μm 107 137 142
Case A Case B Case C
+ 15 + 27 + 29
Table 2
Simulation results for the first-stage compressor K.O. drum
Pressure drop, kPa-psi
Liquid carry-over, kg/h-lb/h
Droplet size, μm
Case A Case B Case C
0.23-0.03 0.45-0.07 0.49-0.07
---
216 299 310
11.0-24.2 20.1-44.4
Table 3
Simulation results for the second-stage compressor K.O. drum
Pressure drop, kPa-psi Liquid carry-over, kg/h-lb/h
Droplet size, μm
Case A Case B Case C
0.99-0.14
---
15 14 13
1.5-0.22 1.8-0.27
0.08-0.17 0.17-0.36
Table 4
Simulation results for the HP receiver
Feed rate
Pressure drop,
Liquid carry-over,
Droplet size,
increment, %
kPa-psi 2.5-0.36 2.5-0.36 3.4-0.49
kg/h-lb/h 0.63-1.4 5.9-13.0 44.1-97.2
μm
Case A Case B Case C
+ 15 - 4 + 9
33 38 41
Table 5
liquid in flare gas and capture use - ful product. A droplet size of 100 µm enter - ing a compressor is considered excessive. Moreover, the predicted volume of entrained liquid would damage the process compressors. Figure 3 shows the volume fre -
quency distribution of the mist flow in the inlet and gas outlet streams for the MFC overhead receiver, showing all three cases. Although the separator removes all droplets of 150 μm and larger for all cases, the predictions reveal significantly higher carry-over in the gas outlet
PTQQ 2 2022 29
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