The following events should occur automatically as the pneumatic operated valves go to their safety position (fail close or fail open) :
1. The fuel gas and pilot gas shutoff valves to all fired heaters will fail closed. The common stack damper 013-HV-620 will stay in its current position (with a tendency to open).
2. The CCR should go into a Hot Shutdown due to any one of a number of things. All valves will go to a fail safe position, except for B-type valves. The B-type will fail in their current position and can be manually closed.
3. Charge to the Platformer would stop as valve 013-FV-003 fails in the closed position.
4. The Recycle Compressor C-1301 should continue to operate.
5. The level control valves for all vessels and Debutanizer bottom will fail closed and these levels will begin to rise rapidly.
6. The net gas valves 013-PV-004A (to flare) and 013-PV-004B (to FG) from the Platformer will fail closed to maintain the unit pressure in the Reactor section.
7. The Debutanizer overhead receiver net liquid control valve (013-FV-0110) will fail closed and the reflux control valve (013-FV-011) will fail open placing the column on total reflux. The overhead pressure (net overhead vapor) control valve (013-PV-012) will fail closed to maintain column pressure.
8. Other pump minimum flow line control valves will fail open.
Action to be taken by Operators :
TRY TO RESTORE THE INSTRUMENT AIR SUPPLY AS QUICKLY AS POSSIBLE 1. Verify that the fired heaters H-1301 to 1304 have shutdown and the fuel gas and
pilot gas tight shutoff valves have closed. Block in the fuel gas at the burners/pilots.
2. Block in the feed naphtha block valves of 013-FV-003. Stop the injection of organic chloride and condensate if these were going before the instrument air failure (pumps P-1304 A/B and P-1305).
3. Verify that the Recycle Compressor C-1301 has continued to operate. If C-1301 has also shutdown for some reason, see procedure for loss of Recycle Compressor (§ 2.3).
4. Stop the Separator bottoms pump (P-1301 A/B) and block in its discharge valve.
Drain liquid to the closed drain if necessary to lower the level in the Separator (D-1301) to a safe level. The liquid levels in other drums can be lowered in the same manner if necessary.
5. Watch other drum levels and use control valve bypasses as necessary to control levels in safe ranges.
6. Conduct the remainder of the shutdown according to the normal shutdown procedures as much as possible (refer to Chapter 7).
3.2 COOLING WATER FAILURE
In the event of a cooling water failure, a complete shutdown of the unit is required. Since most of the heat is removed with aircoolers, the shutdown can be conducted in a
controlled and smooth manner, except stop heaters H-1301 to 1304 and charge to the unit immediately. However, the time for the shutdown is limited due to the loss of cooling for the lube oil systems of the compressors, the loss of interstage and spillback cooling of the Make Up compressors (unit 012), the loss of cooling in the condensing turbine which drives the Recycle Gas Compressor.
The Recycle Compressor C-1301 has to be shutdown (or will automatically trip) when the discharge temperature becomes too high (refer to § 2.3 for consequences of a loss of Recycle Compressor).
For a partial cooling water failure it may only be necessary to reduce the naphtha feed rate to the unit to the extend required to maintain reasonable receivers and products temperatures downstream of water cooled exchangers.
3.3 HP STEAM FAILURE
The following will happen simultaneously.
♦ The steam driven compressor C-1301 will stop (refer to § 2.3 for consequences of a loss of recycle gas),
♦ The reboiling of the Debutanizer T-1301 will stop.
Stop the Platforming unit according to the normal shutdown procedure (refer to Chapter 7).
3.4 BOILER FEED WATER FAILURE
Boiler feed water (BFW) feeds the steam generation in heaters H-1301 to 1304 convection zone. In case of failure of BFW supply from battery limit, the level in the Steam Disengaging Drum will decrease and will imply the stop of the Circulating Water Pumps P-1303 A/B.
The loss of the Circulating Water Pumps, detected by low low flow switches 013-FSLL-613 A/B (2 of 2 voting system), will automatically partially stop the heaters H-1301 to 1304 (after a time delay) by :
♦ Closure of the shutoff valves on fuel gas to the heaters H-1301 to 1304 (013-XV-603 / 605).
♦ Opening of the bleed valve 013-UV-604 to flare (the pilots will stay lit).
Stop the Platforming unit according to the normal shutdown procedure (refer to Chapter 7).
3.5 ELECTRICAL POWER FAILURE
In case of electrical power failure all pumps, air coolers and will trip. A sustained power failure will require a complete shutdown of the unit, using the following guidelines :
a. Block in the feed to the Combined Feed Exchanger E-1301 (by closing 013-FV-003). Reroute the NHDT Splitter (T-1202) bottoms to the storage area as necessary.
b. Shutdown all fired heaters and block in the fuel gas supply to each burner.
c. Keep the Recycle Compressor C-1301 (turbine driven) in operation to cool down the reaction section.
d. The separator D-1301 level (013-LIC-002) will increase if the Separator Pumps P-1301 A/B are shutdown. Lower this level to the closed drain, if necessary. This
level should not be allowed to increase high enough to cause liquid to accumulate in the Recycle Compressor suction line.
e. The overhead pressure for the Debutanizer will increase by the effect of loss of the reflux pumps P-1302 /AB (while the reboiler E-1307 is still in service).
In this case, the operator shall reduce and cut of the reboiler E-1307 (closure of the HP steam supply to the reboiler).
The Debutanizer column will cool down automatically.
f. Proceed with an orderly shutdown of the unit by following the normal shutdown procedures as much as possible (refer to Chapter 7).
3.6 LOSS OF REFRIGERANT
LOSS OF REFRIGERANT MAY BE A DANGEROUS SITUATION! The system should be shut down immediately, and the reason for the loss located. A leak to the atmosphere is hazardous and appropriate precautions should be made. The Lean Oil and Net Gas should be stopped and bypassed, and the system should be depressurized if the leak cannot be fixed immediately.
3.7 FUEL GAS FAILURE
In case of fuel gas failure, heaters H-1301 to H-1304 will automatically shutdown due to low low pressure detection at burners and pilots lines.
The reactors temperatures and the Debutanizer feed temperature will drop, thus leading to off-spec production.
The naphtha feed to the unit has to be stopped and the recycle gas circulation should be maintained. If the fuel gas cannot be restored rapidly, proceed with a normal shutdown.