Appendices to catalyst loading
“CATALYST CIRCULATION AND HEATING PROCEDURES”
6.5.4 Putting the unit into service
6.5.4.2 Pressurization of the unit
After catalyst drying, the unit has been purged with nitrogen to be oxygen free, (less than 0,2% vol.) and is now under a slight positive pressure.
Inlet temperatures of the reforming reactors beds are now about 250°C.
• Preparation
Nitrogen lift gas circuit is pressurized with nitrogen up to 3.5 kg/cm² g at nitrogen lift gas compressor KO drum.
Regeneration circuit is pressurized with N2 up to 4.5 kg/cm² g at the suction of the regeneration loop compressors.
N2 seal gas lines are commissioned.
Pressurize the reaction and HP absorber sections with pure hydrogen (electrolytic H2).
The resulting nitrogen in these sections is about 25 vol. % which is favorable for a steadier catalyst circulation.
Set pressure controller of the separator drum at 0.3 kg/cm² g above the start-up pressure.
Increase the pressure of the separator drum up to start-up pressure via the recycle compressor discharge.
Commission the split range pressure control on the H2 rich gas compressor suction.
Check again all the flanges for leaks using an explosimeter.
All interlocks related to catalyst circulation are made operational.
• Operation
Refer to PIDs „REGENERATION LOOP COMPRESSOR“
„NITROGEN SYSTEM“
Start one nitrogen lift gas compressor at 100% capacity, the PIC at nitrogen compressor discharge set at design pressure.
Start one regeneration loop compressor and increase capacity to 100% (BIAS not in service).
The FICs of calcinations and oxychlorination gases are set in auto mode at 80% of design capacity.
Commission all oxygen analyzers. Remember that certain ranges have been changed during catalyst drying and information to DCS inhibited.
Commission the regeneration dryer.
Start the H2 recycle compressor. Increase the capacity up to the maximum allowed by manufacturer.
Commission the hydrogen purity on line analyzer.
Start the H2 rich gas compressor at 50% capacity and bring the HP absorber drum pressure to about 1.2 kg/cm² g, recycling all the gas to the separator drum through the spill back Pressure Control Valve.
All H2 users and lines to fuel gas are isolated, only the FV on reduction gas, the PDV at the tube side outlet of reduction exchanger and the HV at the tube side outlet of the hydrogen lift gas exchanger are closed but block valves are open.
6.5.4.3 Catalyst heating-up and reduction (See example of schedule, on attached diagram Fig. 15).
During this reduction step:
Additional leak tests can be made when the reaction section temperature is increased.
The pressure must be maintained by make-up of hydrogen or nitrogen. Nitrogen content in the circulating gas must not exceed 30% vol.
Some water will be released from the catalyst. This water will be collected in the separator drum.
Light the burners of the preheater and interheaters and increase the temperatures at the inlet of reactors up to 400°C at the rate of 40°C/h.
Switch-on the burning, calcination and oxychlorination electrical heaters, then increase the temperature at the heater outlet TC's, up to 300°C at the rate of 40°C/h.
Set the flow H2 FIC to reduction chamber at 80% of design capacity and PDIC between reduction chamber outlet and first reactor at 0.1 kg/cm² g.
Switch on the reduction chamber electrical heater and increase its TIC outlet temperature to 400°C at the rate of 40°C/h.
When the temperature of 400°C is reached in the reactors, start catalyst circulation first from the 4th reactor lift pot to the upper surge drum etc. (as described in “Catalyst circulation”).
Note however that either nitrogen or hydrogen will be used depending on the lift pot (nitrogen
Set the catalyst circulation flow at the maximum compatible with the ∆P in the reaction section.
Increase the temperature to 480°C at the reactors inlets and at the reduction chamber inlet at a rate of 40°C/h.
Maintain this temperature for a minimum of 12 hours until the total water drained at the low points is lower than 0.05% of the catalyst weight per hour.
Owing to the difficulty of sustaining a steady catalyst circulation when the reaction section is under hydrogen (low DP in reactors), this step shall be maintained long enough to ensure that the catalyst contained in the upper and lower hoppers has been reduced.
Whenever possible it is recommended to stop the catalyst circulation after a transfer from the upper surge drum to the lock hopper. The reason for leaving an empty surge drum is explained in regeneration start up (6.5.4.7 “Regeneration start-up”).
Decrease then temperatures at reactors and reduction chamber inlets down to 400°C at the rate of 40°C/hour.
Stop catalyst circulation: isolate the manual catalyst tight valves under the lower hoppers.
Close the remote operated ON/OFF valves on the catalyst pipes:
• Between first upper hopper and reduction chamber
• Between first lower hopper and lift pot.
• Between fourth reactor lower hopper and lift pot.
Keep in service the N2 lift loop and the regeneration loop compressor at 80% capacity at burning oxychlorination and calcination beds with the 3 electrical heaters in service (300°C outlet temperature). Note that water washing injection and caustic solution circulation are not yet in service. Both will be started after OIL-IN, before catalyst circulation start-up, when increasing temperature from 300°C up to 480°C.
The unit is now ready for oil in.
Note: during the reduction period the pressure indicated in the procedure must be maintained in the reaction section, by H2 make-up and in the regeneration section or N2 lift section, by N2 make-up.
Remark: When starting the reformer coked catalyst where catalyst reduction is not necessary, RIT’s are increased at the rate of 40°C/h up to 440°C and stabilized at this temperature at which OIL-IN will be performed.
6.5.4.4 Oil in
A Coordination with hydrotreatment start-up
The aim of this paragraph "A Oil in" is to give an overview of a combined hydrotreatment plus Aromizing start-up.
The ideal situation to start an Aromizing is when a source of hydrogen of adequate purity, independent from the unit is available. In this case the pretreatment unit will be started with this hydrogen gas, and once the pretreatment effluent is on specifications (with respect to sulphur nitrogen and water mainly) it will be fed to the reforming unit.
Generally, however, this is not the case. A batch of desulfurized naphtha will then be used as start up feed for the Aromizing unit. All possible precautions must be taken to ensure this naphtha batch is free of water. It is recommended to store it in a fixed roof tank nitrogen blanketed, or in a floating roof tank.
All precaution must be taken to ensure this naphtha is free of water before being sent to the reformer unit.
Two types of integrated start-up sequences shall be considered according to the type of the hydrotreater unit:
• Hydrotreatment of whole naphtha. In such a case the unit is equipped with a stripper followed by a splitter where light and heavy naphthas are separated. This sequence will be taken into account.
• Hydrotreatment of heavy naphtha. In such a case the unit is equipped only with a stripper.
In both cases it is necessary to thoroughly drain the desulfuring and raw naphtha tanks and start-up lines low points to remove any free water.
• Whole naphtha hydrotreater startup
- Using the reaction section by-pass line, establish a circulation of desulphurized naphtha to the stripper then from stripper bottom to the splitter and from the splitter bottom to the aromizer stabilizer (by by-passing the reaction section) and from the stabilizer bottom back to the storage tank. After one hour stop the circulation. Let the water settle down for two hours. Drain again tank bottom and startup lines low points.
Restart again the circulation and bring the stripper and splitter to total reflux conditions. Drain the water recovered in the reflux drum.
- When the splitter bottom product reaches a water content equal to 10 wt ppm switch it to the reformer reaction section. When its operation is steady enough to
B Preparation and feed introduction
• Preparation
The Aromizing unit will be started with desulfurized naphtha as shown on Fig. 17.
The specifications of the feed acceptable for the start-up are:
- feed with similar ASTM distillation than design feed and impurities according to the following:
Poisons Max. level (wt) Source
Arsenic 5 ppb max Cracked Naphthas
Lead 5 ppb max Recycled slops
Copper < detection limit Corrosion
Mercury 5 ppb max Naphtha - condensates
Iron < detection limit Corrosion
Silicon < detection limit Additives (foaming)
Nickel < detection limit Corrosion
The status of the Aromizing ® unit is as follows:
• The stabilizer is operating on total reflux, its pressure being maintained by H2 injection if required.
• Reaction section is under H2 at start-up pressure.
• Check that blinds have been removed: at separator bottom pump (suction and discharge) and at LPG absorber pumps.
• The recycle gas compressor is operating at full capacity.
• PCV split range valves on H2 compressor suction KO drum are in service.
• Catalyst circulation is stopped.
• The regeneration loop is in stand-by: electrical heaters are in service (300°C outlet temperature), the regeneration loop compressor in service (75% capacity), air injection is carefully closed.
• The N2 lift gas compressor is in operation.
• The following ON/OFF valves on catalyst are also closed:
– Between first upper hopper and reduction chamber.
– Between first lower hopper and lift pot.
– Between 4th reactor lower hopper and lift pot.
• Manual valves on all seal legs are closed.
• Reactors inlet temperatures are steady at 400°C in auto mode.
• Outlet temperature of the reduction heater is maintained at 400°C, and the flow is about 80% of design capacity.
• Separator bottom pump is commissioned and ready to start.
• Air coolers fans are in service.
• Cooling water is in service on all users.
• Differential pressure between the reduction chamber and the first reactor is set at 0.1 kg/cm².
• All instruments of the HP absorber section are commissioned. A last check of all other instruments in the reaction section and nitrogen section is made.
• Commission the moisture analyzer on the recycle gas.
• Prepare a batch of chlorine solution (2% vol. of chloriding agent in hydrotreated naphtha).
• Commission chlorine pump for injection in the feed.
• Remove blinds from the feed filters.
• Drain water from the feed filter.
Note: During the oil in, when the water content of the recycle is within the range of the analyzer and until the reaction section operating conditions are stabilized, the water content in the recycle gas must be recorded every hour.
• Feed introduction
Feed is introduced in 10 minutes at 60% capacity. Injection must be done simultaneously in order to avoid unbalance in the welded plates heat exchanger, and quickly enough to insure a minimum flow on the fresh catalyst.
Stop the H2 rich gas make-up, if any.
As soon as the PV to flare on the separator drum and start opening, increase the pressure at H2 rich gas compressor discharge and bring the pressure up to design conditions in the Recontacting drum.
The export gas PV, in auto mode, will at the beginning of the operation send part of the H2 rich gas to the pretreater section, part elsewhere, depending upon local facilities. When the spill back PV tends to close increase the capacity of the H2 rich gas compressor,first to 75%
then to 100%.
Commission the H2 rich gas chloride guard drum.
When liquid appears in the separator drum, and the level is above 50%, start the separator bottom pump and send the product to the Recontacting drum section (control valve in manual mode).
When liquid appears in the Recontacting drum and the level is above 50%, start to feed the LPG Absorber drum.
When liquid appears in the LPG absorber, start the LPG absorber pump and feed, as smoothly as possible, the stabilizer column (control valve in manual mode).
Commission the stabilizer bottom LV/FV and route the reformate to slop.
Route the LPG to off spec. LPG.
Start chloriding agent injection to feed, starting rate 25 wt ppm of pure component related to feed.
Start DMDS injection to feed as to have a sulfur content in feed equal to 0.2 / 0.3 wt ppm.