Now after providing Auto stop facility pump will stop if Regenerator parameters upsets. Stoppage of C2CL4 pump for longer time will result lower chloride fixation and will affect acidic function of catalyst.
If dosing pump trips on any of the interlock, then dosing pump running condition can been known from DCS and pump can be started after normalization of regeneration. This will help in uniform fixation of chloride on Pt based catalyst.
2.5.4 DRYER :
Gas coming out of the washing drum is saturated with water at a pressure of 3.6 kg/cm2. Dryer package unit includes two drums, one in operation and one in regeneration. Dryer ensures water content in the outlet to be less than 50 ppm vol. Dryer will have a cycle time of minimum 6 hours. Allowable pressure drop is 0.3 kg/cm2 with maximum limit of 0.5 kg/cm2.goes through a dryer 17DR-1 and then through filter 17G-3 before to compressor 17K-1.
2.6 CATALYST CIRCULATION :
CCRU OPERATING MANUAL
CRU- 02 – 10*
PART-C
This nitrogen gas ex 17-K-3 A/B going to the lift pot 17-V-34 is divided into two flows:
a. The primary gas through FIC-1711, which initiates the lift operation.
b. The secondary gas through PDV-1711, which governs the catalyst flow.
Within the proper operating range, the rate of catalyst flow is proportional to the secondary flow rate of gas. When the secondary gas is stopped, no catalyst can move in the lift. The pressure drop measured between the lift pot and the next upper hopper indicates the catalyst flow. Nearly equal to zero when there no catalyst flow, this pressure drop will increase to about 100 gr/cm2 when there is catalyst flow. This measure is used as indication of catalyst flow in the control used for the follow-up of the operation of the lifts.
2.6.1 CATALYST LEVEL CONTROL
Catalyst surge vessels (upper hoppers) 17-V-10/12/13 are provided at the top of each reactor in order to compensate for differences in catalyst flow between the lifts. It is also a protection against variations of void fraction of the catalyst in the reactors. Each upper hopper is equipped with gamma-ray level sensors.
One level sensor gives a continuous information for the control, the other gives on-off information for catalyst lift cut-off. The level will be adjusted at 50% and the measure will be used through a cascade to modify the set point of the PDIC used to monitor the catalyst flow.
In case of low level, detected by a cut-off, the PDICV will be automatically closed until the defect disappears.
Following Gama ray detection systems are provided:-17-V-1 Upper Surge Drum LT 1701, LSHH 1701
17-V-2 Lock Hopper LSH-1702, LSL-1703
17-R-1 Regenerator LT-1702, LSLL-1704
Catalyst circulation is carried out by means of gas lift system, which carries the catalyst from the bottom of each reactor to the top of the following reactor.
The catalyst then flows downward through each reactor bed by gravity hydrogen rich gas is used as carrier in the regeneration system.
Between reaction system and regeneration loop, the catalyst is carried by a specific Nitrogen circulation loop. Catalyst batches are transferred periodically to the regenerator for regeneration.
2.6.2 SEQUENCE TRANSFER:
CCRU OPERATING MANUAL
CRU- 02 - 11
PART-C
Spent catalyst (at approx. 200 deg C.) is stored in the regenerator upper surge drum 17V-1, which is at a pressure of 2.9 kg/cm2 slightly lower than the pressure of the last reactor 15R-3 (3.3 kg/cm2). When upper surge drum is full of catalyst, this amount of catalyst is transferred to the lock hopper 17V-2 and then from lock hopper to regenerator in batch operation. Transfer is carried out transfer sequence UC-1701, which is explained as below. The sequence is divided into two main operations Load and Unload.
Load operation transfers batch of catalyst from upper surge drum to lock hopper in approximately 20 minutes and is carried out automatically as given below:
1. Verify the conditions are good to start the load operation i.e. valves UV-1701, 1702, 1703, 1704 and 1708 are close and that enough place is available in lock hopper 17V-2 (LAL-1703 ON)
2. Open valve UV-1707 to equilibrate pressure between the upper surge drum and lock hopper.
3. Wait for the pressure equilibrium {ABS(PI1701-PI-1702)<0.3 kg/cm2}
4. Wait for enough catalyst in the upper surge drum level.
5. Open valve UV-1702 and UV-1701. The catalyst will fill up the lock hopper.
6. Wait for high level in lock hopper (LAH1702 ON). The lock hopper is full now.
7. Close valve UV-1701.
8. Wait for 10 secs.
9. Close valve UV-1702 and UV-1707.
10. Go to UNLOAD.
Unload operation transfer a batch of catalyst from lock hopper to the regenerator and will take approximately 20 minutes and is carried out automatically on the completion of load operation as given below:
1. Wait for the conditions are good to start the unload operation i.e. valves UV-1701,1702, and 1707 are close. Enough place in the regenerator top head is ensured.
2. Open valve UV-1708 to equilibrate pressure between the lock hopper and regenerator 17R-1.
CCRU OPERATING MANUAL
CRU- 02 – 12
PART-C
5. Wait for low level in lock hopper (LAL1703 ON). The batch of catalyst has been transferred to the regenerator.
6. Close valve UV-1703.
7. Wait for 10 seconds.
8. Close valve UV-1704 and UV-1708. The lock hopper is empty and ready for a new catalyst batch.
9. Go to LOAD.
The catalyst is achieved by means of a gas lift system. Hydrogen rich gas is used as carrier in the reaction section, Nitrogen is used as carrier between the reaction and the regeneration section.
The catalyst is lifted from the bottom of the regenerator to the top of the 1st reactor by nitrogen lift, flows downward in the reactor by gravity, from bottom to the next by hydrogen lift and from bottom of the last reactor to the regenerator by nitrogen lift.
The catalyst is transferred periodically from the upper surge drum to the lock hopper and from the lock hopper to the regenerator. Catalyst surge vessels are provided at the top of each reactor in order to compensate for differences in catalyst flow between the lifts.
The lift gas controls catalyst flow. It is achieved by Primary gas, which initiates the lift operation (FIC control). Secondary flow, which governs the catalyst flow (PDIC control) When the total gas flow is constant, the rate of catalyst flow is proportional to the secondary gas flow rate. The total gas flow is controlled by action on primary gas. When secondary gas is stopped no catalyst can move in the lift. The pressure drop measured between the lift pot and the next upper indicates the catalyst flow. This will be nearly equal to zero when there is no catalyst flow and will increase to 100 gm/cm2 when there is catalyst flow.
2.7 TRANSFER SEQUENCE:
2.7.1 DRYER
The Dryer 15-DR-1 can be used during the start-up operations. According to the actual design, it is estimated that this dryer has to be regenerated three times during a unit startup.
In drying service, part of the recycle gas goes down stream through 15DR1. The regeneration of the dryer is performed in two times:
Heating by a part of the produced hydrogen gas. The gas is heated in 15-EH-1 (controlled by TIC-1558), goes through the dryer and is cooled in cooler 15-E-12 before feeding into the KO drum 15-V-6.
CCRU OPERATING MANUAL
CRU- 02 – 13
PART-C
Cooling down. One part of the produced hydrogen gas is introduced downstream in 15-DR-1 and is cooled in 15-E-12. During the regeneration, the water from the is condensed in E-12 and separated in Knock out drum, 15-V-6.
2.7.2 Use of 15-DR-1 as Chloroguard for removing Chlorides :
** In S/D 2010 this Dryer (15-DR-1) was loaded with New Alumina based catalyst (Chloroguard). Top and Bottom loaded with Ceramic balls(Top for reducing impact on catalyst and bottom acts as support). and Now it is used for purifying 15-V-2 overhead gases. Hydrogen rich gas from 15-V-2 (25,000 NM3/hr, having a composition of (H2-90%, C1-2.5%, C2-3.0%, C3-2.0%, C4-1.0%, C5+ -0.5%) after heat exchange in 15E-4 at a temp of 36 deg.C and pr. of 5.3 kg/cm2 is routed to Dryer. Rich gas enters on top of Dryer and chlorides presents in Rich Gas (H2+HC) is adsorbed on the catalyst. From Dryer gases comes in downstream of 15-E-4 and from here it goes to either H2 unit PSA for purification or to FG/Flare through PIC -1507.