Parametric analysis of velocity steam
Parameters
Unit
Baseline
Case 1
Case 2
Velocity steam flow rate
Mlb/hr
3.45
6.8
10.2
(+97.1%) 110.54 (+3.2%) 127.664 (+3.4%) 148.719 (+3.6%) 169.359 (+3.6%)
(+195.6) 112.22 (+4.7%) 129.734
Process absorbed duty
MMBtu/hr
107.15
Total absorbed duty
MMBtu/hr
123.459
(+5%)
Firing rate
MMBtu/hr
143.604
150.871 (+5%) 171.81
Total fuel gas flow
MSCF/hr
163.534
(+5%)
Efficiency (LHV)
% %
85.6 68.2
85.5 67.8
85.6 67.6
Per cent duty in radiant sections
(-0.6%)
(- 0.9%)
Bridge wall temperature (BWT)
°F
1471
1486 (+1%)
1,493
(+1.5%)
Flue gas stack entry temperature
°F
531
536
539
(+1%) 114.33
(+1.5%) 131.36 (+43.3%)
Process pressure drop
psi
91.67
(+24.7%)
TMT – Radiant coil top pass TMT – Radiant coil middle pass TMT – Radiant coil 2nd row pass TMT – Radiant coil bottom pass
°F °F °F °F
776 811 874 873
774 811 873 873
773 811 872 873 6.45
Simulation model maximum relative coking rate
-
8.1
6.9
(-14.8%)
(-20.37%)
Maximum inside film temperature
°F
837
835
833
(-0.25%)
(-0.5%)
Residence time
Second
94.3
84.5
79.6
(-10.39%)
(-15.6%)
Weight fraction vaporised at column
-
0.39
0.427
0.451
(+9.5%)
(+15.6%)
Table 1
match the operating conditions. The comparison will only focus on the process feed stream, as it is relevant to the cok - ing issue. However, the steam super heater (SSH) and boiler feedwater (BFW) will mainly affect the overall efficiency. Some parameters have larger variances from the operating data but can be explained as follows: • Bridge wall temperature: Although the simulation assumes an uniform radiant temperature based on well- stirred box approach, in reality the roof zone of the firebox measures a relatively colder bridge wall temperature com - pared to the actual temperature of the flue gas near the fire - box's middle zone. • Flue gas stack entry temperature: The SSH and BFW measured data were not reliable; therefore, the original inlet and outlet conditions were used. The variance can also be explained by a dirty convection section that might be limit - ing the heat transfer to the tubes, resulting in hotter flue gas leaving the convection section. • TMT – radiant coil bottom pass: The measured data are not reliable since the tubes and temperature elements are wrapped with a ceramic blanket, leading to false tempera - ture readings.
heaters, including complex processes, multiple fire boxes, most coil configurations, and transfer lines. To maximise vacuum heater run length, reducing coke for - mation rate and lowering start-of-run TMT are required to be achieved. In other words, reducing oil film temperature and oil residence time is essential to meeting the study’s objective. The simulation model for the vacuum heaters has been developed using the original process datasheets. Since the vacuum heaters are operating under different parameters compared to the original design, the simulation model needs to be recalibrated to achieve reliable results. An operating case representing the right proportion of crude blend and process input is used as a baseline. The oper - ating case of specific date is used as a baseline for future comparisons. This case is specifically chosen since it repre - sents the right proportion of crude blend, and can be con - sidered as a clean case since it was just after testing and inspection (T&I) after decoking. Simulation model validation The calibrated simulation model is compared to the base - line operating case to assess if the program can predict and
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