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    Energy Balance: Hydrogen Production

    Uploaded by

    Mohit Mangal
    The document summarizes the energy and material balances for a steam methane reforming process to produce hydrogen. Key steps include: 1) A primary reformer converts methane and steam into hydrogen, carbon monoxide, and heat. Additional natural gas is used to preheat the air and provide heat to the reformer. 2) Heat from the primary reformer is recovered to generate high pressure steam. 3) Shift converters further convert carbon monoxide into carbon dioxide and more hydrogen, using steam. Heat is recovered between stages. Cooling and condensation are required after each stage to remove heat and condense steam. Heat exchangers use water for cooling and generate steam to preheat the feed.

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    © All Rights Reserved
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    Energy Balance: Hydrogen Production

    Uploaded by

    Mohit Mangal
    136 views7 pages
    The document summarizes the energy and material balances for a steam methane reforming process to produce hydrogen. Key steps include: 1) A primary reformer converts methane and steam into hydrogen, carbon monoxide, and heat. Additional natural gas is used to preheat the air and provide heat to the reformer. 2) Heat from the primary reformer is recovered to generate high pressure steam. 3) Shift converters further convert carbon monoxide into carbon dioxide and more hydrogen, using steam. Heat is recovered between stages. Cooling and condensation are required after each stage to remove heat and condense steam. Heat exchangers use water for cooling and generate steam to preheat the feed.

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    Original Title

    Energy Balance

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    The document summarizes the energy and material balances for a steam methane reforming process to produce hydrogen. Key steps include: 1) A primary reformer converts methane and steam into hydrogen, carbon monoxide, and heat. Additional natural gas is used to preheat the air and provide heat to the reformer. 2) Heat from the primary reformer is recovered to generate high pressure steam. 3) Shift converters further convert carbon monoxide into carbon dioxide and more hydrogen, using steam. Heat is recovered between stages. Cooling and condensation are required after each stage to remove heat and condense steam. Heat exchangers use water for cooling and generate steam to preheat the feed.

    Copyright:

    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd
    Download as docx, pdf, or txt
    136 views7 pages

    Energy Balance: Hydrogen Production

    Uploaded by

    Mohit Mangal
    The document summarizes the energy and material balances for a steam methane reforming process to produce hydrogen. Key steps include: 1) A primary reformer converts methane and steam into hydrogen, carbon monoxide, and heat. Additional natural gas is used to preheat the air and provide heat to the reformer. 2) Heat from the primary reformer is recovered to generate high pressure steam. 3) Shift converters further convert carbon monoxide into carbon dioxide and more hydrogen, using steam. Heat is recovered between stages. Cooling and condensation are required after each stage to remove heat and condense steam. Heat exchangers use water for cooling and generate steam to preheat the feed.

    Copyright:

    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd
    Download as docx, pdf, or txt
    of 7

    Hydrogen production

    ENERGY BALANCE
    PRIMARY REFORMER:
    Reactions taking place in primary reformer are:
    (1) CH
    4
    + H
    2
    O CO + 3H
    2
    H
    298
    = +206 kJ/mol
    (2) CO + H
    2
    O CO
    2
    + H
    2
    H
    298
    = - 41 kJ/mol
    Inlet temperature : 500C
    Outlet temperature : 860C
    H
    1133
    = H
    298
    +
    }


    1073
    298
    Cpi xi dT
    (H
    1133
    )
    1
    = 20600+ {(3*14.71*2 + 1*1.12*28) - (1*3.44*16 + 1*2.102*18)}*(1133-298)
    = 226726.6 kJ/kmol
    (H
    1133
    )
    2
    = - 41000 + {(1.05*44 + 2*14.71) - (1.12*28 + 2.102*18)}(1133-298)
    = - 36021.4kJ/kmol
    Thus ,
    Heat required by first reaction : Flow rate of methane (H
    1133
    )
    1

    1493.12*226726.6 kJ/hr

    = 33.85 10
    7
    kJ/hr
    Heat liberated by second reaction : Flow rate of carbon monoxide (H
    1133
    )
    2

    2415.46*36021.4 kJ/hr
    = 8.7 10
    7
    kJ/hr
    Enthalpy content of outlet stream :
    E (F .x .Cp.1133) =
    (224*44*1.265)+(2415.46*28*1.208)+(2446.85*2*15.2)+
    (31.26*16*4.71)+(29.02*28*1.192)+(1167.16*18*2.375)
    = 179045.28 kJ/hr
    Enthalpy content of inlet stream :
    E (F .x .Cp.773) =
    (1493.12*3.84*16)+(29.06*1.116*28)+(4031.42*3444.3)
    = 1.398 10
    7
    kJ/hr
    Hydrogen production

    Thus,
    Additional heat required,
    33.85 10
    7
    + 179045.28 - 8.7 10
    7
    - 1.398 10
    7
    kJ/hr
    = 23.7710
    7
    kJ/hr
    Rest of heating is done in radiation zone of primary reformer using natural gas,
    Calorific value = 43000 kJ/m
    3

    Natural gas required =



    =5527.9 m
    3
    /hr
    = 246.8 kmol/hr

    Radiation section of reformer:
    CH
    4
    + 2O
    2
    CO
    2
    + 2H
    2
    O
    Oxygen required = 2242.74= 484.2 kmol/hr
    Air required =


    =2305.4 kmol/hr

    Energy to preheat air from 30C to 500C = m C
    p
    T
    = 3.35610
    7
    kJ/hr
    Natural gas required to preheat the air = 3.35610
    7
    kJ/hr/43000kJ/m
    3

    =780 m
    3
    /hr

    HEAT RECOVERY BETWEEN SMR REACTOR & HTSC:
    Effluent from secondary reformer is cooled to 673 K before being fed to HTSC. This heat is
    utilized for producing HP steam at 250C and 41 bar.
    Steam produced:
    s T Cp
    H
    + A
    A

    H = heat recovered = 179045*(860-400)
    = 8.23610
    7
    kJ/hr
    Hydrogen production

    o
    = 4.187-80 + 1703 = 4.067 10
    7
    J/kmol
    Steam produced = 8.23610
    7
    kJ/hr 4.067 10
    7
    J/kmol
    = 2245.16 kmol/hr

    HIGH TEMPERATURE SHIFT CONVERTOR:
    Inlet temperature: 693 K
    CO + H
    2
    O CO
    2
    + H
    2
    H = -41000 kJ/mol
    Additional steam required for reaction = 3507.3 kmol/hr
    Enthalpy of inlet steam = [(224.4*1.135*44) + (2415.4*1.112*28) + (2446.85*14.63*2) +
    (31.26*3.556*16) + (29.02*1.1*28) + (3507.3*2.071*18)] (673-298)
    =8.514 10
    7
    kJ/hr
    Let outlet temperature of HTSC = T
    Enthalpy of outlet steam = [(2085.8*1.135*44) + (553.7*1.112*28) + (4309*14.63*2) +
    (31.26*3.556*16) + (29.02*1.1*28) + (1645.53*2.071*18)] (T-298)
    =31142(T 298) kJ/hr
    Heat released by the reaction, H
    rxn
    = -41000kJ/kmol*2415.46kmol/hr
    = 9.9 10
    7
    kJ/hr
    Applying balance: 8.514 10
    7
    kJ/hr + 9.9 10
    7
    kJ/hr = 31142(T 298) kJ/hr
    T = 889 K
    Outlet temperature of HTSC = 889 K
    To maintain the temperature of reactor to 425

    C , water cooling is required


    Heat to be removed= 311482(889-698) = 5.94*10
    7

    Cooling water available at 30 C and leaves at 70 C
    Water required= 5.94*10
    7
    / (4.187* 40)*18
    = 19673.6 kmol/hr

    HEAT RECOVERY BETWEEN HTSC & LTSC:
    Inlet temperature = 698 K
    Outlet temperature = 573 K
    Hydrogen production

    Heat removed = 311482(698-523)
    =5.451 10
    7
    kJ/hr
    This heat is utilized for producing steam at 373 K and 1 atm.
    Amount of steam produced :
    s T Cp
    H
    + A
    A
    =

    *1/18
    =1486 kmol/hr

    LOW TEMPERATURE SHIFT CONVERTOR:
    Inlet temperature : 523 K
    CO + H
    2
    O CO
    2
    + H
    2
    H = -41000kJ/hr
    Inlet enthalpy = (2085.8*0.986*44) + (553.7*1.113*28) + (4308*14.51*2) +
    (31.26*2.889*16) + (29.02*1.056*28) + (1645.53*1.954*18)
    =292972.64 kJ/hr.K
    Outlet enthalpy = (2520*0.986*44 ) + (119.08*1.113*28) + (4743*14.51*2) +
    (31.26*2.889*16) + (29.02*1.056*28) + (1210.93*1.954*18)
    = 257272.6 kJ/hr.K
    H = -41000*553.7 kJ/hr
    =2.27 10
    7
    kJ/hr
    Applying balance: 292972.64(523-298) + 2.27 10
    7
    = 257272.6(T-298)
    T = 642 K
    Reactor has to be maintained at 250 C to prevent catalyst from over heating and steam from
    condensation.
    Cooling water available at 30 C will heat to 70 C
    Thus required water is
    T Cp
    H
    A
    A
    = 257272.6(642-523)/ 4.187*40*18
    = 10124 kmol/hr

    Hydrogen production

    CONDENSER:
    Exit stream from LTSC contains steam which is an unwanted load on absorber. In condenser,
    steam is condensed at 513 K. Further no sub-cooling of products takes place.
    Exit gases ( other than steam) are also cooled from 523K to 513K through a heat exchanger
    AH = E (F .x .Cp.(523-513)) + F
    H2O
    * = 3.76 10
    7
    kJ/hr
    Cooling Water at 30 C is heated to 70 C and required amount is =
    3.76 10
    7
    kJ/hr / 4.187*40*18kJ/kmol
    =12433.86 kmol/hr
    HEAT EXCHANGER BEFORE ABSORBER
    Finally remaining gaseous products are cooled from 250

    C to 40

    C
    Heat duty = {(2520*0.986*44 ) + (119.08*1.113*28) + (4743*14.51*2) + (31.26*2.889*16)
    + (29.02*1.056*28)}(250 - 40)
    = 4.51*10
    7
    kJ/hr
    Cooling water required =

    ()

    kmol/hr
    = 14954.74 kmol/hr

    FEED PREHEATER
    Feed at 50 C is heated to 210 C by saturated steam available at 600 psig.
    Inlet feed temp. = 50C
    Outlet feed temp. = 210C
    Feed flow rate = 1522.18 kmol/hr
    Methane flow rate = 1493.12 kmol/hr
    Nitrogen flow rate = 29.02 kmol/hr
    Cp (CH
    4
    ) = 41.8 kJ/kmol.K
    Cp(N
    2
    ) = 30.43 kJ/kmol.K
    Cp (mix) = 0.981*41.8 + 0.019*30.43
    = 41.59 kJ/kmol.K
    Heat received by feed = mCpT
    Hydrogen production

    = 1522.18*41.59*(210-50)
    = 1.01*10
    7
    kJ/hr
    Steam required = m kg/hr
    m = 1.01*10
    7
    kJ/hr
    m = 1.01*10
    7
    /2233.5
    = 4535.12 kg/hr = 251.95 kmol/hr

    FEED SUPERHEATER 1 and SUPERHEATER 2
    In superheater1 Feed is heated from 210 C to 380 C before fed to the desulfurizer.
    saturated steam available at 600 psig.
    Cp (CH
    4
    ) = 46.24 kJ/kmol.K
    Cp(N
    2
    ) = 30.43 kJ/kmol.K
    Cp (mix) = 0.981*46.24 + 0.019*30.43
    = 45.94 kJ/kmol.K

    Heat received by feed = mCpT
    = 1522.18*45.94*(380-210)
    = 1.189*10
    7
    kJ/hr
    Steam required = m kg/hr
    m = 1.189*10
    7
    kJ/hr
    m = 1.189*10
    7
    /2233.5
    = 5322.5 kg/hr = 295.7 kmol/hr

    In superheater2 Feed is heated from 380 C to 500 C before fed to the SMR reactor..
    saturated steam available at 600 psig.
    Cp (CH
    4
    ) = 56.9 kJ/kmol.K
    Cp(N
    2
    ) = 30.8 kJ/kmol.K
    Cp (mix) = 0.981*56.9 + 0.019*30.8
    Hydrogen production

    = 56.4 kJ/kmol.K

    Heat received by feed = mCpT
    = 1522.18*56.4*(500-380)
    = 1.03*10
    7
    kJ/hr
    Steam required = m kg/hr
    m = 1.03*10
    7
    kJ/hr
    m = 1.03*10
    7
    /2233.5
    = 4612.9 kg/hr = 256.3 kmol/hr

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