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KHABAROVSK REFINERY HYDROPROCESSING PROJECT PROCESS THEORY

KHABAROVSK REFINERY HYDROPROCESSING PROJECT PROCESS THEORY. TRAINING COURSE. APRIL 29th – MAY 3rd 2013, MADRID, SPAIN. CONCEPTUAL BLOCK DIAGRAM. CLAUS PROCESS DESCRIPTION. CLAUS PROCESS. Modified Claus Sulphur Recovery Process foresees two process steps:  Step No.1, thermal step:

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KHABAROVSK REFINERY HYDROPROCESSING PROJECT PROCESS THEORY

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  1. KHABAROVSK REFINERY HYDROPROCESSING PROJECT PROCESS THEORY TRAINING COURSE APRIL 29th – MAY 3rd 2013, MADRID, SPAIN

  2. CONCEPTUAL BLOCK DIAGRAM

  3. CLAUS PROCESS DESCRIPTION CLAUS PROCESS Modified Claus Sulphur Recovery Process foresees two process steps: Step No.1, thermal step: The acid gas is burnt in the thermal reactor where only one third of H2S has to be oxidised (substoichiometric conditions) to SO2. Ammonia (NH3) in the SWS sour gas is burnt almost completely to N2. Step No.2, catalytic step: The SO2 formed in the combustion step reacts with the unburned H2S to form elemental sulphur and water. • PURPOSE OF CLAUS PROCESS: • To remove hydrogen sulphide and sulphur compounds from acid gas, producing elemental sulphur. • As a second effect, NH3 content of the SWS stream will be highly reduced.

  4. FEED STREAMS TO CLAUS SECTION PROCESS STREAMS CHEMICAL SPECIES AMINE ACID GAS (AG):Hydrogen sulphide Hydrocarbons Water SWS SOUR GAS (SWS): Hydrogen sulphide Ammonia Water COMBUSTION AIR: Oxygen Inerts SOUR WATER STRIPPER ACID GAS AMINE ACID GAS

  5. CLAUS REACTIONS MAIN REACTIONS THERMAL STEP Main Oxidation H2S + 1.5O2 H2O + SO2 CATALYTIC STEP Conversion2H2S + SO2 1.5S2 + 2H2O  Overall REACTION Total Balance 3H2S + 1.5O2 3H2O+ 1.5S2

  6. CLAUS REACTIONS AMMONIA DESTRUCTION • NH3 decomposition • 2NH3+ 3/2O2N2+ 3H2O Ammonia (NH3) in the SWS sour gas is burnt almost completely to N2. Incomplete destruction of ammonia in the reaction furnace can lead to the formation of ammonium salts in cooler downstream part of the Unit (plugging).

  7. CLAUS REACTIONS SIDE REACTIONS The following side reactions can occur in the thermal step: H2S H2+ 0.5S2 H2S Dissociation CnH2n+2 + O2nCO + (n+1)H2O CO Formation/HC combustion CnH2n+2 + O2nCO2 + (n+1)H2O CO2 Formation/HC combustion CO2 + H2S COS + H2O COS Formation CO2 + 2H2S CS2+ 2H2O CS2 Formation

  8. CLAUS REACTIONS SIDE REACTIONS COS AND CS2 FORMATION CO2+H2SCOS+H2O CO2+2H2SCS2+2H2O COS AND CS2 FORMATION DEPENDS ON CO2 CONTENT AND HYDROCARBONS CONTENT, WHICH ARE INCLUDED IN THE PROCESS GAS FED TO THE CLAUS THERMAL REACTOR.

  9. ELEMENTAL SULPHUR SPECIES • The liquefaction of sulphur – which is produced in thermal reactor • and Claus reactors- is performed in the sulphur condensers, from where it is separated by means of hydraulic seals. Elemental sulphur vapour can exist as four separate species, hence it is important to consider the reactions: S2 S4 S4 S6 S6 S8 S8 Sliq Most of the sulphur vapour formed in the thermal reactor exists as S2. As the temperature of the process gas decreases, the sulphur shifts partially to S4 and then to nearly all S6 and S8. HIGH TEMPERATURE  LOW TEMPERATURE S2 S4 S6  S8

  10. INSIGHT ON CLAUS PROCESS - 1 • OVERALL REACTION: 3H2S + 1.5O2 3H2O+ 1.5S2 MAIN OBJECTIVE: TO DRIVE THE OVERALL REACTION TO NEAR COMPLETION IMPORTANT PARAMETERS REACTANTS RATIO IN THE CATALYTIC STAGE H2S/SO2=2 MINIMUM FLAME TEMPERATURE TO HAVE STABLE COMBUSTION AND COMPLETE AMMONIA DESTRUCTION

  11. CLAUS THERMAL STEP - overview The conversion of the oxidation reaction is affected not only by the reactants’ ratio and by the temperature, but also by the residence time. CLAUS BURNER: To reach a suitable temperature.  CLAUS THERMAL REACTOR: To provide the proper residence time at high temperature in order to obtain the desired conversion.  CLAUS BURNER CONTROL SYSTEM: To ensure that the reactants are in the proper ratio. WASTE HEAT RECOVERY (CLAUS BOILER) To recover the heat available in the process gas from the thermal reactor and to produce steam. HEAT RECOVERY

  12. INSIGHT ON CLAUS PROCESS - 2 REACTANTS RATIO The combustion of AAG and SWS AG must be carried out with the proper amount of oxygen in order to obtain a ratio of H2S/SO2=2 in the tail gas from the Claus section. COMBUSTION CONTROL SYSTEM The amount of oxygen to be fed to the Claus Thermal Reactor is evaluated and controlled by DCS facilities. DCS facilities have been foreseen to perform:  substoichiometric combustion of H2S fed to the thermal reactor   H2S/SO2=2 in the tail gas from the Claus Section.

  13. INSIGHT ON CLAUS PROCESS - 3 COMBUSTION AIR CONTROL SYSTEM • In the Feed-forward part: • the required quantity of air is calculated by measuring the individual acid gas flows and multiplying these flows with their required ratios air/acid gas; • the resulting air demand signal sets the flow control system in the main air line supply, through main control valve • In the Feed-back part: • the flow control system is adjusted by the H2S/SO2 analyzer controller located in the Claus tail gas line; • the feed back control ensures an H2S/SO2 ratio equal to 2 in the tail gas, in order to obtain the optimum sulphur recovery efficiency of the unit

  14. INSIGHT ON CLAUS PROCESS - 4 The stability of the combustion in the Thermal reactor is strongly dependent on the temperature of the flame. The flame temperature depends mainly on the composition of the acid gas: the higher is the concentration of H2S, the higher is the temperature of the flame. COMBUSTION STABILITY The minimum temperature that guarantees a stable flame inside the Thermal Reactor and complete ammonia destruction is 1420°C. The minimum adiabatic flame temperatures to achieve flame stability and impurities destruction in a Claus burner are summarized here below: HC NH3 Flame Temp. (°C) 1400 1500 1300 1200 1100 900 1000 BTX

  15. INSIGHT ON CLAUS PROCESS - 5 Temperature of the Claus Thermal Reactor 1st zone shall be kept at 1450°C in order to have the almost complete Ammonia destruction (to be burnt as N2). The oxidation reaction of Ammonia is: 2NH3 + 1.5O2  N2 + 3H2O AMMONIA DESTRUCTION The temperature control of Claus Thermal Reactor 1st zone is achieved by means of a partial bypass of the Amine AG from the 1st to the 2nd zone. The more the bypass, the more the exothermic reactions in the first zone will proceed, thus causing an increase of temperature in the first zone. This is due to the fact that the same amount of air finds a minor amount of Amine AG in the 1st zone and leads to the same SO2 but within less flowrate (1st zone higher temperature). The final temperature after the 2nd zone does not depend on the bypass ratio.

  16. CLAUS SECTION OVERVIEW AAG THERMAL STEP CATALYTIC TAIL GAS STEP H2S/SO2=2 1450°C LIQUID SWS SULPHUR FLOW RATE IN ORDER TO HAVE H2S/SO2 =2 IN TAIL GAS COMBUSTION AIR TAIL GAS

  17. CLAUS CATALYTIC STEP PURPOSE To drive the Claus conversion reaction to near completion producing liquid sulphur. CLAUS CATALYTIC STAGE The Claus catalytic conversion is performed in 2 stages (two reactors and one shell), each stage includes: process gas preheating catalytic reaction sulphur condensation CLAUS CONVERSION OF H2S AND SO2 TO SULPHUR HYDROLISIS REACTION OF COS AND CS2 CLAUS CONVERSION OF H2S AND SO2 TO SULPHUR 1st Claus Reactor 2nd Claus Reactor

  18. CLAUS CATALYST ARRANGEMENT 1ST CLAUS REACTOR 2ND CLAUS REACTOR  The typical arrangement for the 1st Claus Reactor is a double catalytic bed, where the top two-thirds of the bed is the Claus reaction catalyst (Activated Alumina). The hydrolysis catalyst is placed at the bottom layer (one-third) of the 1st Claus Reactor, where the best temperature for the hydrolysis is achieved. OPERATING TEMPERATURES TIN~240 °C, TOUT~306 °C In the 2nd Claus Reactor there is only the Claus catalyst. OPERATING TEMPERATURES TIN ~206 °C, TOUT ~228 °C

  19. The conversion of H2S and SO2 to elemental sulphur is an equilibrium reaction. CLAUS CATALYST The Claus reaction is supported by a specific Alumina Catalyst. EXOTHERMIC REACTION The reaction is exothermic, it’s favored at low temperature: there is an increase of temperature through the catalytic bed. CLAUS REACTION 2H2S + SO2 2H2O + 3/x Sx + 557 kcal/Nm3 of H2S EQUILIBRIUM REACTION

  20. HYDROLISIS REACTION in 1st CLAUS REACTOR CATALYTIC REACTION The reaction yield is enhanced by a special catalyst (titania catalyst) which promotes the hydrolysis of COS and CS2 at high temperature. HIGH CONVERSION The reaction, if performed on the special catalyst at high temperature, is practically complete. COS and CS2 react with water to form Hydrogen Sulphide and Carbon Dioxide. It’s an exothermic reaction, so it is thermodynamically favoured by low temperature HYDROLYSIS REACTION COS + H2O=>CO2 + H2S CS2 + 2H2O=>CO2 + 2H2S

  21. OPERATING TEMPERATURE The temperature must be higher than the dew point temperature in order to avoid Sulphur condensation in the catalytic bed with temporary catalyst deactivation. CLAUS REACTORS TEMPERATURE • The reactor inlet temperatures are automatically controlled by acting on the Hot gas by-pass for the first Claus Reactor and on the Claus Heater for the second Claus Reactor.

  22. SULPHUR DEGASSING STEP SAFETY The presence of H2S and H2SX during sulphur transport and handling represents a danger for safety and environmental problem Liquid sulphur produced from the sulphur recovery unit contains about 300 ppmw H2S, part simply as dissolved H2S and part in the form of polysulphides (H2Sx). The combination of sulphur atoms and H2S is called ‘polysulphide’. Cooling and agitation of the sulphur accelerate the release of H2S, and often occur during storage, loading, and transport of the sulphur. As H2S is released, an explosive mixture of air and H2S may be formed. Necessity to degas the liquid sulphur to reduceH2S content to a safety value of 10 ppm wt. (to remove the dissolved hydrogen sulphide and hydrogen polysulphide from the liquid sulphur). DEGASSING STEP

  23. SULPHUR DEGASSING STEP LIQUID SULPHUR CONTAINS H2S AND H2SX DISSOLVED: TOXICITY EXPLOSION HAZARD NECESSITY OF LIQUID SULPHUR DEGASSING PACKAGE. SAFETY VALUE: 10 PPM WT. Air stripping to sweepH2S from liquid sulphur. The Degassin Process removes H2S from sulphur through two mechanisms. Some of the H2S and H2Sx are oxidized to sulphur, some is oxidized to SO2, and some H2S is stripped from the sulphur. H2Sx=>H2S + S(x-1) • Below 120°C the margin between operating and sulphur solidification temperature of 115°C would become too small. • Above 155°C degassing is less effective due to the increased sulphur viscosity.

  24. Degassing is achieved inside the Sulphur Pit by means of a packed tower where liquid sulphur is contacted with air stream. • The Stripping Airto the Degassing Column package is sent from the Combustion Air Blower. • Liquid Sulphur and process air flow through the DEGASSING COLUMN filled withpacking. Air is fed to the bottom part of the contactor by means of a distributor to ensure a good mixing with flowing sulphur. • The overhead gas is sent to the Incinerator. SULPHUR DEGASSING STEP

  25. TGT SECTION PURPOSE: To reduce all sulphur compounds in the tail gas from Claus Section into H2S by the reducing action of Hydrogen To absorb the residual H2S from the Tail Gas with Amines To recycle the acid gas obtained by amine regeneration to the Claus section

  26. TGT SECTION HYDROLISIS REACTIONS HYDROGENATION REACTIONS Sulphur Dioxide and sulphur vapours are reduced to H2S : SO2 + 3H2 H2S + 2H2O (SO2 reduction) Sx + xH2 xH2S (Svapor reduction)  CO, COS and CS2 react with water as the following: CO + H2O H2 + CO2 (CO shift) COS + H2O H2S+ CO2 (COS hydrolysis) CS2 + 2H2O  2H2S + CO2 (CS2 hydrolysis) FORMATION OF H2S, H2O FORMATION OF H2S, CO2

  27. TAIL GAS REDUCTION HIGH CONVERSION • To obtain a high conversion of both hydrogenation and hydrolysis reaction, two main parameters are important: • The presence of reducing reactant (H2) in the process gas fed to the reactor • Minimum inlet temperature to activate the catalyst  Hydrogen injection is expected upstream of TGT hydrogenation reactor. PREPARATION OF THE FEED TO THE HYDROGENATION REACTOR SPECIAL CATALYST FOR BOTH REACTIONS. CATALYST ACTIVE AT 280/330°C (SOR/EOR conditions) MINIMUM INLET TEMPERATURE TGT HEATER  The TGT Heater will allow the preheating of the feed to the reduction reactor.

  28. TAIL GAS COOLING STAGE To cool the Tail Gas before feeding it to the TGT absorber, since absorption is carried out at low temperature PURPOSE TGT HEATER TAIL GAS FROM CLAUS SECTION INDIRECT COOLING The Tail Gas is firstly cooled down in the TGT Gas/Gas Exchanger. TAIL GAS COOLING HYDROGENATION REACTOR DIRECT COOLING The Tail Gas is contacted with quench water with the purpose to saturate the tail gas and then to cool the tail gas.During the cooling step, heat and condense of sour water are removed from the system. TGT GAS/GAS EXCHANGER QUENCH TOWER QUENCH WATER TAIL GAS TO ABSORBER

  29. ABSORPTION STAGE PRINCIPLE OF ABSORPTION: H2S, CO2 IN SOLUTION (aqueous medium) dissociate to form AMINES IN SOLUTION (aqueous medium) dissociate to form FORMATION OF WEAK ACID FORMATION OF WEAK BASIS H2S + H2O H3O+ + HS- CO2 + H2O H+ + HCO3- [AMINE] + H2O OH- + [AMINE]H+ WEAK ACID + WEAK BASIS The absorption of acid compounds within amine solution is ensured by the correct inlet temperature of the amine coming from regeneration and correct MDEA %wt. FORMATION OF SALT BY CHEMICAL COMBINATION OF ACID/BASE WITH REMOVAL OF ACID COMPOUNDS

  30. ABSORPTION STAGE The most commonly used in the industrial processes are   Primary Amine RNH2 MEA (Monoethanolamine) Secondary Amine R2NH DEA (Diethanolamine) Tertiary Amine R2NCH3 MDEA (Methil diethanolamine)  where R= CH2CH2OH ISTANTANEOUS REACTION H2S ABSORPTION HIGH RATE REACTION FOR PRIMARY AND SECONDARY AMINES (MEA, DEA) CO2 ABSORPTION LOW RATE REACTION FOR TERTIARY AMINES (MDEA)

  31. ABSORPTION STAGE CO2 Absorption with MEA or DEA CO2 + 2 [AMINE] [AMINE] + + [AMINE]CO2- CO2 Absorption with MDEA (or tertiary amine) is not direct CO2+H2O+ R2NCH3HCO3- + R2NHCH3+ SELECTION OF THE RIGHT SOLVENT PRIMARY  SECONDARY  TERTIARY  Selectivity for H2S respect to CO2 increases Low T High T Low T High T

  32. ABSORPTION STAGE MDEA, WHY? • High concentration of CO2 with reference to H2S concentration • Necessity of SELECTIVE ABSORPTION  TAIL GAS FROM CLAUS SECTION: LOW H2S CONCENTRATION SELECTIVE ABSORPTION favoured by MDEA • MDEA: TERTIARY AMINE HIGHLY SELECTIVE TOWARD H2S • MDEA solution (50%) has been adopted for TGT section.

  33. ABSORPTION - REGENERATION STAGE The absorption reactions are EQUILIBRIUM REACTION: The direct reaction is favoured at LOW temperature The reverse reaction is favoured at HIGH temperature ABSORPTION AT LOW TEMPERATURE DESORPTION AT HIGH TEMPERATURE AMINE PROCESSES ARE REGENERATIVE The desorption of acid compounds from amine solution is realised by mean of heat input: the stripping of the rich amine solution is ensured with the amine vapours produced in the Regenerator Reboiler (LPS used to heat amine solution and generate vapour).

  34. INCINERATION SECTION PURPOSE • To transform all the Sulphur compounds contained in the tail gas to SO2 • To discharge the flue gas to the atmosphere via a stack THERMAL OXIDATION WITH EXCESS OF OXYGEN LOW OXYGEN CONTENT WILL NOT FAVOUR THERMAL OXIDATION TO SO2 HIGH OXYGEN CONTENT WILL FAVOUR SO3 AND NOX FORMATION. BEST COMPROMISE OXYGEN EXCESS IN THE FLUE GAS FROM THE STACK ~2% VOL (WET BASIS) MIN.

  35. THERMAL OXIDATION All Sulphur compounds will be transformed to SO2 by thermal oxidation at high temperature using excess of oxygen. POSSIBLE REACTIONS The possible reactions in the Thermal Incinerator are: S + O2 SO2 H2S + 1.5 O2 H2O + SO2 COS + 1.5 O2  CO2 + SO2 CS2 + 3 O2  CO2 + 2SO2 SO2+ 0.5O2  SO3 Oxidation reactions, not regarding S-compounds, are: H2 + 0.5 O2  H2O CO + 0.5O2  CO2 and the complete oxidation of fuel gas. OPERATING CONDITIONS INCINERATION SECTION • Oxygen excess required 2 vol.% min; • Operating temperature  650°C (normal condition); • Fuel gas sustaining combustion

  36. REGENERATION (ARU) SECTION All the reactions involved are EQUILIBRIUM REACTIONS: The direct reaction (absorption), being an exothermic reaction, is favoured at LOW temperature The reverse reaction (regeneration) is favoured at HIGH temperature and occurs at the boiling point of the solution in the stripping column (Regenerator). ABSORPTION AT LOW TEMPERATURE DESORPTION AT HIGH TEMPERATURE AMINE PROCESSES ARE REGENERATIVE The desorption of H2S from amine solution (DEA at 25 %wt) is realised by mean of heat input: the stripping of the rich amine solution is ensured with the amine vapours produced in the Regenerator Reboiler (LPS used to heat amine solution and generate vapour).

  37. SW STRIPPING (SWS) SECTION  H2S and NH3 are soluble in water. The solubilisation of H2S and NH3 in water is favoured at LOW temperature The separation is favoured at HIGH temperature. The separation of H2S and NH3 from sour water solution is realised in the Sour Water Stripper by mean of heat input: the stripping steam is produced in the Stripper Reboiler (LPS is used to heat the sour water and generate vapour).

  38. RomeViale Castello della Magliana 7500148 - ItalyPh. +39 06 602161Fax +39 06 65793002info@tecnimontkt.it – www.tecnimontkt.it

  39. THANK YOU FOR THE ATTENTION

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