TGTU Catalyst In-situ Presulphiding. Fernando Maldonado Business Manager Gas Treating Catalysts

Transcription

1 TGTU Catalyst In-situ Presulphiding Fernando Maldonado Business Manager Gas Treating Catalysts

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4 Forms of TGTU Catalyst Oxide CoMo Blue Oxide NiMo or CoMo Black Presulphurized, Presulphided or Sulphided Sulphated Presulphurized/Presulphided Or Sulphided 4

5 Tail Gas Treating Unit Catalyst Activation The Co-Mo catalyst that is used in the TGTU reactor is manufactured in a metal oxide form. Before the catalyst is utilized in a TGTU it must be made active by converting the metal oxide sites to metal sulfide sites. Delivered Oxide Form CoO MoO 3 States of Catalyst Sulfiding 200 C 315 C (390 F 600 F) In H 2 and H 2 S environment Oxidization/Regeneration T>150 C (300 F) in an oxidizing environment with no sulphur components added to recycle gas CoS MoS 2 Active Form Reduction Reduced Bad S/U Co Mo Inactive Form T>200 C (390 F) in H 2 environment with no H 2 S Not possible due to metals agglomeration Reduction Even with low H 2 PP, reduction to base metal is possible at T>200 C (390 F) in a H 2 environment with no H 2 S

6 Tail Gas Treating Unit Catalyst Activation What is the effect on TGTU catalyst operated in an oxidizing environment with sulphur compounds entering the reactor? Delivered Oxide Form CoO MoO 3 CoS MoS Active Form T>150 C (300 F) in an oxidizing environment with sulphur components entering Sulphated Catalyst

7 Sulphiding Chemistry The active form of the catalyst is the intimate mixture of the cobalt sulfide and molybdenum sulfide. Cobalt oxide is sulphided in a one-for-one exchange of the sulfur CoO + H 2 S CoS + H 2 O The molybdenum is reduced from the Mo (VI) oxide to the Mo (IV) sulfide; hydrogen is required. MoO 3 + 2H 2 S + H 2 MoS 2 + 3H 2 O 7

8 TGTU Catalyst Activation: In-situ versus Ex-situ Sulphiding The catalyst is converted from the oxide form to the sulphide form via either an in-situ sulphiding process or an ex-situ third party sulphiding process. In in-situ sulphiding process fresh catalyst is loaded into the TGTU reactor and activated using hydrogen sulphide from Claus feed or Claus tail gas. In ex-situ sulphiding, the oxide catalyst is sent from the manufacturing plant to the facilities of a 3 rd party (Porocel or Eurecat) where the catalyst is converted to the sulphide form. The two best known ex-situ sulphiding methods are Porocel s ActiCat TG process and Eurecat s TOTSUCAT TG process. Criterion TGTU catalysts have been successfully activated by both of the above named ex-situ processes. 8

9 TGTU Catalyst Activation: In-situ versus Ex-situ Sulphiding Is a presulfurized TGU catalyst the same thing as a presulfided TGU catalyst? No It is important to be precise with nomenclature Porocel s ActiCat TG process converts ~ 50% of the metal oxides to metal sulphides and provides sulphur within the catalyst pores to complete the conversion of the remaining metal oxides sites to metal sulphide sites. A catalyst that has undergone this ex-situ sulphiding process is referred to as a presulphurized catalyst. Eurecat s TOTSUCAT TG process converts 100% of the metal oxides to metal sulphides. A catalyst that has undergone this ex-situ sulphiding process is referred to as a presulphided or a fully sulphided catalyst. 9

10 TGTU Catalyst Activation: In-situ Sulphiding 1. Load catalyst in air. 2a. Purge system with N 2, or 2b. Run in-line burner near stoichiometric air/fuel ratio 3. Warm catalyst bed to 200 C (390 F) with burner. Care should be exercised that the provisions for adding H 2 S to the system are ready to operate, otherwise the exposure of the catalyst to H 2 in the absence of H 2 S can result in irreversible damage to the catalyst. Also, impaired catalyst activity can result if the catalyst is exposed to hydrogen sulphide for extended periods without hydrogen being present. 4. Switch to substoichiometric conditions, adjust so gas entering reactor contains 2 10% H 2 + CO. 5. Bleed in H 2 S (1 2%). Hold conditions for 30 minutes and observe catalyst bed temperatures. 6. Ramp catalyst bed temperature to 250 C (475 F) at 15 C (25 F) per hour. Adjust temperature ramp rate to keep temperature difference between reactor inlet temperature and maximum bed temperature below 25 C (50 F). 7. Before heating catalyst bed past 250 C (475 F), verify H 2 S concentration in reactor outlet gas stream is greater than 1000 ppm. Ramp catalyst bed temperature to 315 C (600 F) at about 15 C (25 F) per hour. 8. Continue sampling the reactor outlet gases at one hour intervals. If H 2 S concentration in the reactor outlet gas falls below 1000 ppm, hold reactor inlet temperature until H 2 S level rises above 1000 ppm, then resume ramping temperature. 9. When the catalyst has been fully sulphided the reactor outlet gas H2S concentration equals the reactor inlet gas H2S concentration. Hold the catalyst bed temperature at 315 C (600 F) for 4 hours. Do not exceed 350 C (650 F) catalyst bed temperature. 10. Cool reactor to less than 280 C (535 F) and prepare for normal operation. 10

11 Simplified Diagram In-situ Sulphiding Procedure via Acid Gas Bypass PC Incinerator Acid Gas FC Incinerator To Amine Absorber Fuel Gas Steam Air Tail Gas from SRU Steam RGG TGTU Reactor S/U Gas Ejector Utility N 2 Quench Tower Opened LC Closed Reactor Effluent Cooler Sour Water 11

12 In-situ Sulphiding Procedure via Acid Gas Bypass 1. Load catalyst in air. 2. Isolate TGTU from SRU (verify SRU tail gas valve is closed). 3. Isolate reactor section from amine section of the TGTU (verify quench tower outlet gas valve to amine absorber is closed). Line up quench tower overhead to front of TGTU. 4. Establish quench tower water circulation. 5. Start the start-up gas steam ejector and establish recycle rate of 30% of process design flow. 6. Add N 2 to begin purging reactor system. 7. Set the quench tower pressure controller at ~0.2 barg. 8. Start the RGG burner slightly above stoichiometric air/fuel ratio. 9. Warm catalyst bed to 200 C (390 F) with RGG burner. 10. a. Adjust RGG to substoichiometric operation; target 2% - 10% H 2 + CO (reducing gas) to reactor. Prior to adding H 2 S rich acid gas, verify O 2 content in recycle gas is <0.5% by volume. b. Slowly add H 2 S rich acid gas via the acid gas bypass line. c. Target 1% H 2 S by volume at reactor inlet. Upon addition of acid gas, sample reactor inlet and outlet process gases. A hand-held Draeger tube sampling system that provides immediate H 2 S concentration in % or ppm values is recommended. 11. Hold conditions for 30 minutes and observe catalyst bed temperatures. 12. Ramp catalyst bed temperature to 250 C (475 F) at 15 C (25 F) per hour. Adjust temperature ramp rate to keep temperature difference between reactor inlet temperature and maximum bed temperature below 25 C (50 F). 13. Before heating catalyst bed past 250 C (475 F), verify H 2 S concentration in reactor outlet gas stream is greater than 1000 ppm. Ramp catalyst bed temperature to 315 C (600 F) at about 15 C (25 F) per hour. 14. Continue sampling the reactor outlet gases at one hour intervals. If H 2 S concentration in the reactor outlet gas falls below 1000 ppm hold reactor inlet temperature until H 2 S level rises above 1000 ppm, then resume ramping temperature. 15. When the catalyst has been fully sulphided the reactor outlet gas H 2 S concentration equals the reactor inlet gas H 2 S concentration. Hold the catalyst bed temperature at 315 C (600 F) for 4 hours. Do not exceed 350 C (650 F) catalyst bed temperature. 16. Cool reactor catalyst bed to 280 C (535 F) and prepare for normal operation. 12

13 TGTU Catalyst Activation: In-situ Sulphiding Pitfalls BTX in acid gas Acid Gas FC PC Incinerator Incinerator To Amine Absorber Fuel Gas Steam Air Tail Gas from SRU Steam RGG TGTU Reactor S/U Gas Ejector Utility N 2 Quench Tower Opened LC Closed Reactor Effluent Cooler Sour Water What can be done to prevent or minimize catalyst damage? 13

14 TGTU Catalyst Activation: In-situ Sulphiding Pitfalls BTX in acid gas: Use Claus tail gas to activate the catalyst. Operate Claus unit at high ratio (>7:1) H 2 S:SO 2. Verify that SRU reaction furnace temperature is sufficiently high to insure BTX destruction. Be prepared to add ammonia or caustic to quench water to maintain ph above 6 until the catalyst activates. Bypassed acid gas can be used with temporary carbon bed to remove the BTX compounds. Utilize ex-situ processed TGTU catalyst. 14

15 TGTU Catalyst Activation: In-situ Sulphiding Pitfalls No acid gas flow How to activate the catalyst? 15

16 TGTU Catalyst Activation: In-situ Sulphiding Pitfalls No acid gas flow: Use high ratio (>7:1) H 2 S:SO 2 Claus tail gas to activate the catalyst. Be prepared to add ammonia or caustic to quench water to maintain ph above 6 until the catalyst activates. Prior to starting in-situ sulphiding verify line is not plugged and valves are operable. 16

17 TGTU Catalyst Activation: In-situ Sulphiding Pitfalls PC Incinerator Incinerator FC To Amine Absorber Acid Gas Fuel Gas Steam RGG TGTU Reactor No recycle gas system Utility N 2 Air Tail Gas from SRU S/U Gas Ejector Quench Tower Steam Opened LC Closed Reactor Effluent Cooler How to activate the catalyst? Sour Water 17

18 TGTU Catalyst Activation: In-situ Sulphiding Pitfalls No recycle gas system: Use once through nitrogen to heat bed. When catalyst bed temperature reaches 200 C (390 F) either bypassed acid gas or Claus tail gas can be utilized to activate the catalyst. Prior to starting in-situ sulphiding verify recycle gas system is operable. 18

19 TGTU Catalyst Activation: In-situ Sulphiding Pitfalls PC Incinerator Acid Gas FC Incinerator To Amine Absorber Fuel Gas Steam Air Tail Gas from SRU RGG TGTU Reactor S/U Gas Ejector Utility N 2 Quench Tower Quench water ph drops below 6 Steam Opened LC Closed Reactor Effluent Cooler Sour Water How to prevent or minimize catalyst damage and operational upsets? 19

20 TGTU Catalyst Activation: In-situ Sulphiding Pitfalls During catalyst activation, the quench water ph remains above 6 only through use of caustic or ammonia addition: If bypassed acid gas (H2S with no SO2) is utilized during catalyst activation and low quench water ph is observed this is caused by formation of SO 2 and air ingress into the reaction system is the likely cause. Check the following: 1. Verify proper RGG operation. Is the air to natural gas ratio correct? Typically 80% to 90% substoichiometric operation is targeted. 2. Verify air supply valves to start-up burners or pilots have not been left open. 3. Verify bleeders closed. 4. Verify air is not being drawn in through recycle blower seals. 5. Verify nitrogen is used in all instrument purges. What can cause low quench water ph if Claus tail gas is used for catalyst activation? 1. Air ingress 2. Non-activated catalyst 3. Hydrogen starvation 4. Incorrect H 2 S:SO 2 5. Catalyst bypassing 20

21 TGTU Catalyst Activation: In-situ Sulphiding Pitfalls Loss of Supplemental Hydrogen FC PC Incinerator Supplemental Hydrogen Incinerator FC To Amine Absorber Acid Gas Fuel Gas Steam RGG TGTU Reactor Utility N 2 Air Tail Gas from SRU S/U Gas Ejector Quench Tower Steam Opened LC Closed Reactor Effluent Cooler Sour Water How to activate the catalyst? 21

22 Loss of supplemental hydrogen: TGTU Catalyst Activation: In-situ Sulphiding Pitfalls If additional hydrogen is needed, lower substoichiometric operation of RGG to make more reducing gas. 22

23 TGTU Catalyst Activation: In-situ Sulphiding Questions? 23