Process Description
Circulating hot oil is used in several process heaters in the Oil Terminal. These are:
- Crude Oil Heater E-102 (continuously)
- Slop Heater E-111 (as-needed)
- Stabilizer Reboiler E-331 (continuously)
Cooled oil returned from these process heaters is collected in Hot Oil Surge Drum D-921 and is supplied to Hot Oil Circulation Pumps P-921A/B. These pumps circulate oil through Hot Oil Heaters F-922 and F-924 which are fired heaters. Normally only F-922 is in operation and F-924 is on stand-by. Heated hot oil from the Hot Oil Heaters is then supplied to a header supplying the process heaters listed above.
Each Hot Oil Heater has a minimum flow line that returns circulating hot oil to the Hot Oil Surge Drum in case of low demand by the process heaters. This protects the Hot Oil Heater from a low-flow trip of the heater. Fuel gas is supplied from Fuel Gas KO Drum D-901.
Cooled oil returned from the three process heaters E-102, E-111 and E-331 that use hot oil for is combined with minimum flow streams from Hot Oil Heaters F-922 and F-924. This combined stream flows through isolation valve XV-920 into the Hot Oil Surge Drum D-921. The combined temperature of the returned hot oil is normally 289 DEG F. The hot oil system is a closed liquid system, and the Hot Oil Surge Drum is sized to accommodate expansion and contraction of the hot oil in the system. Therefore, the level of D-921 will change based upon the density changes, unless there is a leak in the system in which case it will decrease.
Fuel Gas KO Drum D-901 provides gas for blanketing the vapor space in D-921 through self-regulating control valve PCV-920A. In case of expansion of the hot oil, the vapor volume will be compressed and the pressure of D-921 will increase. If it gets too high, self-regulating control valve PCV-920B will release blanket gas to the LP Flare System. The pressure of D-921 is normally 4.5 PSIG.
Hot Oil Circulation Pumps P-921A/B are electric motor-driven centrifugal pumps which circulate hot oil from D-921 oil through Hot Oil Heaters F-922 and F-924. Normally, only one pump, P-921A, is in operation. The normal flow of hot oil to F-922 and F-924 is 15.2 MBPD. Normally, only F-922 is in operation.
Instrumentation
Hand switch XV-920 opens and closes inlet isolation valve XV-920.
TI-920 indicates the temperature of hot oil returning to D-921.
PI-920 indicates the pressure of D-921.
LI-921 indicates the level of hot oil in D-921.
LAHL-921 independently indicates the level of hot oil in D-921. It is used by interlock I-921.
Hand switches MOV-921A/B open and close the suction MOVs (motor operated valves) on P-921A/B, respectively.
Hand switches HS-921A/B start and stop the motors of P-921A/B, respectively. Normally only pump “A” is in operation. These switches are locked in the STOP position on activation of interlock I-921 to prevent operation on low level which could lead to pump damage.
FI-921 indicates the flow rate of hot oil from P-921A/B to F-922/F-924.
PI-921 indicates the discharge pressure of P-921A/B.
TI-921 indicates the temperature of hot oil from P-921A/B to F-922/F-924.
Hand switch XV-922 opens and closes inlet isolation valve XV-922.
FIC-922 controls the flow rate through F-922 by adjusting the position of FV-922. Normally, FV-922 is fully closed because the flow through F-922 is above the setpoint of FIC-922 (10 MBPD).
FLL-922 is an independent indication of the flow rate through F-922. It is used by interlock I-922.
Hand controller HIC-922 adjusts the position of control valve HV-922. It is normally 100% open. HIC-922 is used to adjust the flow rate through F-922 when both F-922 and F-924 are in operation. Normally, only F-922 is in operation.
Hand switch XV-922 opens and closes inlet isolation valve XV-922.
FIC-922 controls the flow rate through F-922 by adjusting the position of FV-922. Normally, FV-922 is fully closed because the flow through F-922 is above the setpoint of FIC-922 (10 MBPD1,590 M3/H).
FLL-922 is an independent indication of the flow rate through F-922. It is used by interlock I-922.
Hand controller HIC-922 adjusts the position of control valve HV-922. It is normally 100% open. HIC-922 is used to adjust the flow rate through F-922 when both F-922 and F-924 are in operation. Normally, only F-922 is in operation.
TIC-922 controls the outlet temperature of F-922 by adjusting the setpoint of fuel gas flow controller FIC-923.
TAH-922 is an independent indication of the outlet temperature of F-922 and is used by interlock I-922.
ES-922 is a hand switch that indicates, trips and resets interlock I-922.
Hand switch XV-923 opens and closes fuel gas isolation valve XV-923. XV-923 is locked in the CLSD position when interlock I-922 is tripped.
FIC-923 controls the flow of fuel gas to F-922 by adjusting the position of control valve FV-923. FIC-923 is locked in manual mode with an output of 0% when interlock I-922 is tripped.
Hot Oil heater No.2 is identically instrumented to Hot Oil Heater No. 1 except the tag names differ. Refer to Hot Oil Heater No. 1 above for the respective instrument functions.
Normally, F-924 is not in operation and all valves are closed.
TI-925 indicates the temperature of the Hot Oil Distribution Header.
PI-925 indicates the pressure of the Hot Oil Distribution Header.