Drying out the unit .1 Introduction

Reaction, catalyst circulation and regeneration sections must be dried out prior to catalyst loading, firstly to avoid damaging the catalyst with water, secondly to shorten the duration of the low severity operation after first oil in.

Unit dry out is conducted simultaneously with the heater refractory drying. AXENS representative will consult with the heaters manufacturer representative to agree on a procedure (chiefly rate of temperature rise and duration of steps) mutually acceptable.

The description of the unit dry out, below, reflects AXENS's requirements only.

The dry out operation is carried out using hot nitrogen circulating in two loops, physically separated.

The first loop uses the recycle compressor, the hydrogen rich gas compressor and the nitrogen lift gas compressor and includes the reaction section, absorber section and nitrogen section as defined in chapter 6.4.3.6 "Recommended sections for leak tests". The fired heaters are used for warming up.

The second loop is the regeneration section (regeneration section as defined in 6.4.3.6

"Recommended sections for leak tests") and uses the regeneration loop compressor to circulate nitrogen which is heated in the electrical heaters (burning, oxychlorination and calcination heaters). The regeneration drying loop is isolated from the previous one by the special gas tight valves between the lock hopper and the upper surge drum and the valve on the seal leg between the first lower hopper and its lift pot.

6.4.4.2 Preparation and lining up

All TIs and TRs (in the firing box, in the process fluid, tube skin) have been checked. The burners, dampers, control and safety systems have been checked. All safety measures and control normally involved in the firing of heaters must be followed in agreement with Unit Owner or heaters manufacturer procedures.

Make a list of required instruments and check that they are connected and in service.

Check that orifices plates are installed where required and correctly calibrated (coefficient adjusted for nitrogen) check that all safety valves are installed and connected to atmosphere or flare collector isolated by blind in B/L..

Make sure that all blinds between reaction section and HP absorber section are removed.

The following compressors must be commissioned prior to start (blinds will be removed and left in open position):

• Recycle compressor.

• Regeneration loop compressors.

Note: To initiate the dry out of the reaction section, the recycle compressor only is required.

Commission also cooling water to:

• H2 rich gas compressor suction cooler

• Recontacting trim cooler

• Interstage coolers.

• Reduction gas trim cooler.

• Nitrogen loop trim cooler.

6.4.4.3 Reaction, HP absorber and nitrogen sections dry out Re: Drawings: on following pages

• Reaction section pressurization (reaction section as defined in 6.4.3.6

“Recommended sections for leak tests") check that:

- The reaction section is blocked in at the feed filters.

- The separator drum bottom pumps are isolated.

- The off gas line to flare is blinded.

Nitrogen is introduced at recycle compressor and the reaction section is pressurized to 2 bar gage. The pressure controller on separator drum is commissioned and set to 2 bar gage. Off gas discharge to atmosphere.

Special precautions must be followed concerning the welded plates heat exchanger (see note 2).

• HP absorber section pressurization:

This section is pressurized simultaneously with the reaction section, provided the following blinds have been removed in due time.

- On H2 rich gas kick back line to H2 compressor KO drum.

- On H2 rich gas line to catalyst reduction.

• Nitrogen section pressurization:

The equipment of the nitrogen section are lined up (refer to 6.4.3.6 "Recommended sections for leak tests" for definition of this equipment).

The section is pressurized to 2.0 kg/cm² g.

Then reactor and absorber sections on one hand, nitrogen section on the other hand, are connected while the following isolating valves are opened:

- On first upper hopper to reduction chamber.

- On last reactor lower hopper to its lift pot.

- On start up line between separator drum (reaction section) and nitrogen loop trim cooler.

• Nitrogen circulation and dry out initiation:

Open suction and discharge valve of recycle compressor and start the machine according to manufacturer's instructions. This initiates nitrogen circulation through the reaction section.

Once the section is on line, start draining free water from all low points.

Light small fires in the preheater and heaters according to manufacturer's instructions and increase reactor inlet temperature at a rate of 40°C per hour up to 200°C.

The following steps must now take place to circulate nitrogen in the HP absorber section and nitrogen section:

– Line up the H₂ rich gas circuit to reduction and to 1st, 2nd and 3rd reactors lift pots. Note that hydrogen purification unit is isolated and by passed.

– Start the H₂ rich gas compressor at 25% capacity, all the compressed gas being recycled to H2 rich Gas compressor KO drum, the spill back PCV is full open in manual. KO drums PCV's are set in auto mode.

– Establish flow of gas (up to normal flow taking into account you are handling nitrogen) to the 1st, 2nd and 3rd reactors lift pots and to the reduction chamber.

– Line up the N₂ lift gas circuit to the regenerator and last lift pot, upper surge drum

– at 3.0 kg/cm² g.

– Start N₂ lift gas compressor and load the valves to circulate the gas at 100%

capacity.

– Establish flow of gas to the regenerator and last lift pot up to the normal flow.

When the above steps are completed, the nitrogen circulation for drying purpose is fully established, as shown on the attached drawings.

The reduction electrical heater is then switched on and reduction chamber inlet temperature is progressively increased at a rate of 20°C per hour up to 200°C.

• Follow-up and end of drying (Re: Reaction section dry out diagram).

Purge water from separator drain and all low points (air cooler and trim cooler outlets,

The system is considered dry, at this temperature (200°C), when the water draw-off is less than 10 liters per hour.

Then the temperatures are increased to 400°C at a rate of 20°C per hour. When the amount of water drained is lower than 5.0 liter per hour the temperature is increased to 500°C and maintained until the total water draw-off is less than 1.0 liter per hour.

Note that the reduction heater outlet temperature is increased to 450°C only.

The 500°C temperature must be reached in the reaction section in order to check if any problem, due to the thermal expansion of the reactor internals, occurs.

When the system is dry, lower the temperature to 200°C (50°C/h). Then stop firing or stop electrical heaters and circulate nitrogen until the reactors are cooled down to 40°C. The doors of the heater boxes could be opened in order to speed-up the cooling process.

Stop then the recycle and H2 rich gas compressors and close the block valves at suction and discharge. Depressurize and repressurize the unit with air, to remove nitrogen. Check that the atmosphere is suitable for entry into the vessels.

Notes:

1. During the temperature rise, watch the skin temperatures of the heater tubes and flue-gas temperature to avoid any overheating of the tubes. Check also the temperature of each equipment in order not to exceed the design figures.

2. Welded plates heat exchanger (feed/effluent)

The following precautions must be carefully observed:

• Owing to the narrow space (2.5 mm) between plates, the upstream piping must be thoroughly flushed prior to flow through the exchanger.

• During shell or bundle flushing (to remove air or process fluids) the differential temperature between the feed stream and the effluent stream must not exceed 50°C.

• The plate are stainless steel. Presence of chloride and liquid water for an extended period must be avoided.

• Ensure that the feed side pressure always exceeds the effluent side pressure.

Consequently:

– the exchanger must be pressurized only from the feed inlet (recycle compressor discharge).

– the exchanger must be depressurized only from the effluent outlet (separator drum).

• Introduce the naphtha feed at a linear rate in order to reach 60% of the design within ten minutes. Ensure that both inlet flows are balanced.

6.4.4.4 Regeneration section dry out Refer Drawing: on following pages

The regeneration section is defined in 6.4.3.6 "Recommended sections for leak tests".

The section is fully isolated from the reaction- absorber - nitrogen section by the special tight valves on top of the lock hopper and by the valve on the seal leg (on the lower hopper bottom pipe).

When the equipment of the regeneration loop is lined-up, the regeneration loop compressor is pressurized up to 6.0 kg/cm² g with nitrogen, open the valves at suction and discharge of the regeneration compressor.

Start the machine and load the valves to circulate the gas, establishing flows equivalent to design values, to the burning and to the oxychlorination/calcination zones.

When circulation is established, drain free water from low points.

Switch-on the burning, oxychlorination and calcination heaters and bring temperatures up, at a rate of 20°C per hour, until the regenerator inlet temperature reaches 200°C.

• Follow-up and end of drying:

(Re: Regeneration section dry out diagram).

A procedure similar to the reaction section drying will be followed (rate of temperature increase: 20°C per hour), except that the temperature is limited to 400°C for the regeneration section.

After reaching 400°C with a total water draw off less than 1.0 liter per hour, the temperature is lowered to 200°C, then heaters are switched off and nitrogen circulation continued until the regenerator cools down to 40°C. Then nitrogen is replaced by air and the atmosphere checked suitable before allowing entry to the vessels.

Reactors, regenerator and vessels are now ready for inspection (thermal expansion of internal devices) and for catalyst loading.

Note: Typically, the drying of all the sections take place at the same time. However the drying of the regeneration section may also be carried out separately.

FIGURES AND DRAWINGS ATTACHED TO