7.1. SUMMARY OF SHUTDOWN
In order to proceed to a proper and safe shut down of the crude distillation unit, the next steps and recommendations shall be followed:
• Inform all concerned of the time of the shutdown.
• Reduce the crude rate as indicated in Section 7.2 Automatically, firing on heater will be also reduced.
• Product streams will be routed back to crude tankage, via crude recirculation header, or to appropriate off-spec storage in case of LPG. Then, the heater H-1101 can be shutdown, as described in Section 7.3, and the stripping steam to the main fractionator, T-1101, and to T-1103 and T-1104 (LGO and HGO strippers respectively) also shutdown.
• Drainage philosophy during unit shut down shall be as follows:
o Once the Unit is in turndown mode, all off-spec products are diverted to crude recirculation header, except LPG which has to be routed to LPG off-spec storage.
o The crude recirculation line can be used for rundown of the atmospheric residue back to the crude storage area. This practice is covered in Refinery Shutdown Philosophy Document. So, slopping of huge quantities of residue to slops system shall not be considered. In fact, crude recirculation line can be considered the preferred way to maximum 60% of the design flow)
o During normal operation, products should be sent to the LSO/HSO header after cooling in the heat exchangers upstream battery limit.
Rundown temperature should not exceed 70 ºC. The connections to slops placed before final rundown coolers are provided to push the full line inventory to Slops, after the operator ensures that product has been cooled down, and uses flushing oil to dilute it (in case HGO, Crude and Residue).
o Note that only one product at a time shall be routed to the same slop header (light or heavy). In the case that two products must be routed to the same slop system, the unit shall be rather put under recirculation back to the storage tank, as hydraulic will not allow sending the two products to the same header.
o As a reminder, off spec products can be rundown to storage or downstream Units provided that they are not to far from the specification and provided that the normal situation can be recovered in a reasonable timeframe. Also, the first instruction to the operator, in case of a product is really off-spec, with no hope to recover soon, should be to decrease unit capacity.
• Reduce T-1102, T-1103 and T-1104 bottom level controller Set Point to 20%
• Stop desalter wash water.
• Reduce the crude preheat train inventory by displacing the crude oil from one of the desalters, A-1101-D-01 or D-02, by means of level controller 011-LIC-506 and 011-LIC-503 Remember to isolate electricity FIRST. Refer to chapter 2.3 alternatives operations for “one desalter operation” mode and also to the chapter 8 of “Desalters operations and maintenance manual”: 8474L-011-A5016-0814-001-001.
• Maintain unit pressures with fuel gas or nitrogen during cool down.
• Cut crude oil feed by stopping the crude charge pumps P-6001A/B/C and crude booster pumps, P-1101 A or B, and close the feed and product battery limit valves.
• Stop pump arounds on the main fractionator, by stopping the pump around pumps: P-1102 A/B, P-1103 A/B, P-1104 A/B, P-1105 A/B.
• Stop reflux to the naphtha stabiliser, T-1107 by stopping the P-1114 A/B.
• Pump out liquid inventories to crude tankage, by means of reducing level controller Set Point of T-1105, T-1106, D-1103 and D-1104, via crude recirculation header and off-spec tankage for LPG.
• Stop the corrosion inhibitor injection pumps
• Vent T-1107 overhead system to the flare.
• Flushing the Unit as indicated in Section 7.4.
• Steaming out the Unit as indicated in Section 7.5.
7.2. REDUCTION OF FLOWRATES
In order to achieve a proper reduction of unit flow rates, the following steps must be followed:
• Confirm that all concerned have been informed of the time of the shutdown.
• Over approximately one shift (8 hours) reduce the feedstock flow rate to 50%
of the design by reducing FIC-069 Set Point 5% by step.
• When the crude rate is lower than 650 m3/h,
o Reduce FQIC020 (LGO to storage) Set Point to 160 m3/h and then to 108 m3/h.
o Reduce FQIC033 (Kerosene to Storage) Set Point to 33 m3/h.
o Reduce FQIC028 (HGO to Storage) Set Point to 42 m3/h.
o In the same time reduce the UIC031 Set Point from 2.8 to 1.4 MW and reduce the stripping steam flowrate.
• Reduce the number of operating burners in the H-1101 to maintain the T-1101 bottoms temperature but maintain all the pilots lit. During the cool down of unit a maximum of three burners in each cell can be taken off-line, in order to avoid a furnace trip.
7.3. SHUTDOWN OF HEATERS AND HEAT OFF.
• Stop product transfer having first advised all receiving units of imminent shutdown. Route product streams back to tankage.
• Shutdown the crude charge heater H-1101, following the next recommendations:
- Put heater firing control onto manual mode.
- Reduce fuel gas flow until closure of 011-PV-092, minimum fuel gas flow will be maintained by the 011-PCV-072.
- In case of H-1101 is operating with fuel oil, change 011-FIC-504 set point to cero. Minimum fuel oil stop will ensure enough flow to burners.
- In case of H-1101 is operating with fuel oil, the atomizing steam will be reduce automatically to the oil burners.
- Isolate each burner
- Maintain the pilots lit for a short time in order to burn any flammable substance could remains in the heater.
- Turn light off the pilots by closing each isolating valve. It is strongly recommended to light off one or two pilots on one cell and then one, or two, pilot on the other cell to compensate the loss of heat on the chambers.
- Keep the blowers B-1101 A or B running in order to cool down the heater.
• Stop flow of High pressure Steam to the E-1121, naphtha stabiliser reboiler.
• Cut the flow of Medium Pressure Steam to the vacuum package, A-1102.
• Cut the electricity of the desalter, transformer, which remains in operation and drain it to slops.
7.4. FLUSHING OF UNIT
• The atmospheric residue, coming from the main fractionator bottoms, will have been partially diluted by unheated crude coming forward. This product shall be pumped away to crude tankage (see drainage philosophy described in Section 7.1).
• Open up S.R. flushing oil to the fractionator, T-1101, and establish a normal level in the bottom part (via 2’’ flushing connection). Reopen the crude unit battery limit valve and pump SR flushing oil with the feed pumps from the tank farm through the crude feed line to the CDU. Flush the crude feed line to the desalters and fill them.
• With the P-1101 A / B, pump the flushing oil from the desalters through to the T-1101 bottoms and out to crude tankage or to heavy slops, via P-1106 A /B.
• Continue with this circulation until displace the remaining oil, which will be detected via operator monitoring sampling. Shutdown then the crude feed pumps and close the CDU battery limit valves.
• Re-establish SR flushing oil flow to the T-1101 bottoms. Circulate through short path to the heater, and through long path to the start of the preheat train, bypassing the crude booster pumps, P-1101 A and B. Pump this away to heavy slops. Repeat as required over 4 or 8 hours. For short and long path refer to marked-up P&ID’s included in attachment 2.
7.5. STEAMING OUT AND PREPARATION FOR MAINTENANCE
Any section of pipe, equipment item such as a vessel, heat exchanger or pump which needs to be accessed or opened up for maintenance must be thoroughly cleaned and prepared before work commences.
In order to ensure a proper and safe operation proceed to follow the next steps:
• Using block valves, isolate the smallest practical volume of oil bearing pipe and / or equipment containing the item to be maintained. Drain as much oil as possible to the light or heavy slops system.
• The black oil section of the plant must first be thoroughly flushed to heavy slops. Drain the flushing oil. Black section of the plant covers Crude Oil, Residue and Heavy Gas oil.
• Open vents on tower and drums and start steaming out the flushed item to remove traces of flushing oil. Periodically drain condensate while steaming, and run the contaminated condensate to the oily water sewer.
• The white oil section of the plant must be drained thoroughly to light slops.
Open vents on tower and drums and start steaming out the item. Drain the condensate periodically to the oily water sewer. White section covers: Light Gas Oil, Kerosene and Naphtha sections.
• In order to prevent the cooling of steam in air fin exchangers and heaters, damper should be closed and fan stopped.
• Steam out shall be maintained for more than one hour.
• Pumps in LPG service, P-1114 A and B and P-1115 A and B, should be isolated, vented to the flare and nitrogen purged.
• Swing the spectacle blinds or replace the ring spacer with spades.
• If the closed valves were passing, re-steam or re-purge the blinded section or equipment.
• Check the residual hydrocarbon vapours.
• Release the plant for maintenance under a Permit-to-Work.
7.6. KEROSENE STRIPPER REBOILER FOR MAINTENANCE To take E-1110 out of service, proceed as follows:
• Route stripped kerosene to crude recirculation header by line K-110259.
• Introduce stripping steam into the column by opening valve 011-FV-015. Prior to open the inlet valve, low point drain and 1.5” vent valve will remains opened until all the steam condensate have been removed from the line and line work is at superheated steam temperature.
• Close the inlet and outlet valves on the circulating HGO (lines HGO-110175 and HGO-110176), heating medium. Leave some time for the exchanger to cool down.
• Close the inlet and outlet valves on the kerosene to and from reboiler (lines K-110241 and K-110242).
• Drain the kerosene to the closed drain by CD-118550.
• Drain the HGO to the closed drain by lines CD-118551 and CD-118552.
• Blind the reboiler tubeside and shellside from all process lines.
• Open the vents on the tubeside and shellside, and steam both sides of the reboiler, routing oily condensate to the OW.
• Continue steaming, checking the tubeside and shellside regularly for hydrocarbons.
• When checks are satisfactory, stop steaming, allow vessel to cool, recheck atmosphere for hydrocarbons and hand over to maintenance.
7.7. DESALTERS ISOLATION FOR MAINTENANCE 7.7.1.1. First desalter isolation
To take the first stage desalter out of service, the following steps have to be followed:
• Switch the desalters level control by 011-HS-001 (at this moment the level control 011-LIC-506 in the second stage desalter is controlled by 011-LV-003, instead of 011-HY-003).
• Close the water outlet from A-1101-D-01 to ETP (line DEW-110265).
• Stop pump P-1118.
• Open water outlet from A-1101-D-02 to ETP (DEW-110271).
• Open the interlock valve 011-SP-815 on line PL-110104.
• Close the crude inlet valve to the desalter (line PL-110003).
7.7.1.2. Second desalter isolation
To by-pass the second stage desalter, the following steps have to be followed:
• Set FIC-004 and FIC-005 in manual mode.
• Open water inlet line upstream 011-FV-021 (line SW-116614).
• Stop pump P-1118.
• Set FIC-021 controller to manual and output zero.
• Open the interlock valve 011-SP-815 on line PL-110105.
• Close the crude inlet valve to the desalter (line PL-110012).
7.7.1.3. Desalter maintenance
To remove the oil from the desalter being taken out of service, proceed as follows:
• Isolate and pull the fuses from the electrostatic precipitators (refer to vendor’s manual).
• Adjust the oil / water interface upwards beyond the LIA high alarm by mud wash water lines (SW-116618 and SW-116619 depending which desalter is going to be taken out of service).The crude will be displaced by the mud wash water to the second desalter, if the fist one is bypassing and to the crude booster pump, if the second desalter is bypassing.
• Sample the try cocks (SCC-5B-013 or SCC-5B-014) until the desalter contains water only.
• Close the valve on the crude outlet line (PL110012 or PL110015) from the desalter. Close the water inlet valve to the desalter.
• Vent the desalter and dispose of as much of the water as possible to the desalter effluent (lines DEW-110265 and DEW-110271). Drain the remaining water to the closed drain.
• Remove any sludge, using service water.
• Blind the desalter from all process lines.
• Ensure vent is open, and steam out routing oily condensate to the oily water system.
• Continue steaming, checking desalter atmosphere regularly for hydrocarbons.
• When checks are satisfactory, stop steaming, open manways, allow vessel to cool, recheck atmosphere for oxygen and hydrocarbon and hand over to maintenance.