KHABAROVSK REFINERY HYDROPROCESSING PROJECT PROCESS THEORY

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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: - PowerPoint PPT Presentation

Text of KHABAROVSK REFINERY HYDROPROCESSING PROJECT PROCESS THEORY

  • KHABAROVSK REFINERYHYDROPROCESSING PROJECT PROCESS THEORYAPRIL 29th MAY 3rd 2013, MADRID, SPAINTRAINING COURSE

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    CONCEPTUAL BLOCK DIAGRAM

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    CLAUS PROCESS DESCRIPTIONPURPOSE 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.

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    FEED STREAMS TO CLAUS SECTIONAMINE ACID GAS (AG): Hydrogen sulphide Hydrocarbons WaterSWS SOUR GAS (SWS):Hydrogen sulphide AmmoniaWater

    COMBUSTION AIR:Oxygen Inerts

    AMINE ACID GAS SOUR WATER STRIPPER ACID GAS

    CompositionH2O% mol8.41H2S% mol91.37NH3% mol0.08CH4% mol0.02C3H8% mol0.04H2% mol0.08

    Total% mol100

    CompositionH2O% mol27.68H2S% mol36.38NH3% mol35.94CH4% mol0.00C3H8% mol0.00H2% mol0.00

    Total% mol100.00

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    CLAUS REACTIONSTHERMAL STEPMain Oxidation H2S + 1.5O2 H2O + SO2

    CATALYTIC STEPConversion 2H2S + SO2 1.5S2 + 2H2OMAIN REACTIONS Overall REACTIONTotal Balance 3H2S + 1.5O2 3H2O+ 1.5S2

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    CLAUS REACTIONSNH3 decomposition 2NH3+ 3/2O2 N2+ 3H2O AMMONIA DESTRUCTIONAmmonia (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).

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    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

    CLAUS REACTIONS

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    SIDE REACTIONSCOS AND CS2 FORMATION DEPENDS ON CO2 CONTENT AND HYDROCARBONS CONTENT, WHICH ARE INCLUDED IN THE PROCESS GAS FED TO THE CLAUS THERMAL REACTOR.COS AND CS2 FORMATION

    CO2+H2SCOS+H2O

    CO2+2H2SCS2+2H2O

    CLAUS REACTIONS

    PROCESS GAS FROM WHB1.9427.110.0353.410.000.006.043.020.010.000.000.000.000.008.430.000.000.000.000.000.000.000.000.000.00

    Stream DescriptionComponent %molH2H2OCON2O2 CO2H2SSO2 COSCS2CH4 C2H6 C3H8 i-C4H10 S2-vapS4-vapS6-vapS8-vapS1-LIQ NH3 n-C4H10 i-C5H12n-C5H12 n-C6H14MDEA

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    ELEMENTAL SULPHUR SPECIESElemental sulphur vapour can exist as four separate species, hence it is important to consider the reactions:S2S4S4S6S6S8S8Sliq

    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 S4S6S8

    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.

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    INSIGHT ON CLAUS PROCESS - 1IMPORTANT PARAMETERSREACTANTS RATIO IN THE CATALYTIC STAGEH2S/SO2=2MINIMUM FLAME TEMPERATURETO HAVE STABLE COMBUSTION AND COMPLETE AMMONIA DESTRUCTIONMAIN OBJECTIVE: TO DRIVE THE OVERALL REACTION TO NEAR COMPLETION

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    CLAUS THERMAL STEP - overviewThe 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

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    INSIGHT ON CLAUS PROCESS - 2The 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 SYSTEMREACTANTS RATIOThe 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.

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    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 valveIn 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 unitINSIGHT ON CLAUS PROCESS - 3COMBUSTION AIR CONTROL SYSTEM

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    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 STABILITY1000 1100 1200 1300 HC

    1400 1500 900NH3

    BTX

    Flame Temp. (C)The minimum adiabatic flame temperatures to achieve flame stability and impurities destruction in a Claus burner are summarized here below:INSIGHT ON CLAUS PROCESS - 4The minimum temperature that guarantees a stable flame inside the Thermal Reactor and complete ammonia destruction is 1420C.

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    Temperature of the Claus Thermal Reactor 1st zone shall be kept at 1450C in order to have the almost complete Ammonia destruction (to be burnt as N2).

    The oxidation reaction of Ammonia is:2NH3 + 1.5O2N2 + 3H2OAMMONIA DESTRUCTIONThis 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.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.INSIGHT ON CLAUS PROCESS - 5

    H2S/SO2 in process gas atFlame adiabaticat Thermal Reactor outlettemperature, C2.0about 1330

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    CLAUS SECTION OVERVIEWAAGTHERMAL STEP1450CCATALYTICSTEPLIQUID SULPHURTAIL GASH2S/SO2=2FLOW RATE IN ORDER TO HAVE H2S/SO2 =2 IN TAIL GASCOMBUSTION AIRSWSTAIL GAS

    Stream DescriptionComponent %molH2H2OCON2O2 CO2H2SSO2

    2.1836.590.0360.040.000.010.680.34

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    CLAUS CATALYTIC STEP1st Claus Reactor

    2nd Claus Reactor

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    CLAUS CATALYST ARRANGEMENT

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    EQUILIBRIUM REACTION

    2H2S + SO2 2H2O + 3/x Sx + 557 kcal/Nm3 of H2SCLAUS REACTION

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    HYDROLISIS REACTION in 1st CLAUS REACTOR HYDROLYSIS REACTION

    COS and CS2 react with water to form Hydrogen Sulphide and Carbon Dioxide.

    Its an exothermic reaction, so it is thermodynamically favoured by low temperature

    COS + H2O=>CO2 + H2S

    CS2 + 2H2O=>CO2 + 2H2S

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    CLAUS REACTORS TEMPERATUREThe 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.

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    SULPHUR DEGASSING STEPLiquid 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 reduce H2S content to a safety value of 10 ppm wt. (to remove the dissolved hydrogen sulphide and hydrogen polysulphide from the liquid sulphur).

    DEGASSING STEP

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    Below 120C the margin between operating and sulphur solidification temperature of 115C would become too small. Above 155C degassing is less effective due to the increased sulphur viscosity.SULPHUR DEGASSING STEPThe 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)LIQUID SULPHUR CONTAINS H2S AND H2SX DISSOLVED:TOXICITYEXPLOSION HAZARDNECESSITY OF LIQUID SULPHUR DEGASSING PACKAGE.SAFETY VALUE: 10 PPM WT.Air stripping to sweep H2S from liquid sulphur.

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    SULPHUR DEGASSING STEP

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    TGT SECTION

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    TGT SECTIONFORMATION OF H2S, CO2FORMATION OF H2S, H2O

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    TAIL GAS REDUCTION PREPARATION OF THE FEED TO THE HYDROGENATION REACTOR

    MINIMUM INLET TEMPERATURETGT HEATER The TGT Heater will allow the preheating of the feed to the reduction reactor.SPECIAL CATALYST FOR BOTH REACTIONS. CATALYST ACTIVE AT 280/330C (SOR/EOR conditions)

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    TAIL GAS COOLING STAGETAIL GAS TO ABSORBERTAIL GAS FROM CLAUS SECTIONQUENCH WATERQUENCH TOWERHYDROGENATION REACTORTGT HEATERTo cool the Tail Gas before feeding it to the TGT absorber, since absorption is carried out at low temperature

    PURPOSE

    INDIRECT COOLINGThe Tail Gas is firstly cooled down in the TGT Gas/Gas Exchanger.TAIL GAS COOLING

    DIRECT COOLINGThe Tail Gas is contacted with quench water with the purpose to saturate the tail gas and then to