Sour Water Stripping-(Single stage) - Impact of HSS

Sour Water Stripping-(Single stage) - Impact of HSS

Instructions



  1. This article contains a series of steps to feed the data to the flowsheet, run the simulation, interpret the results

  2. A user can either follow the series of steps mentioned in this article to build the flowsheet, or download the ProTreat file attached to this article, review the inputs and run the simulation  

Simulation Set Up


Objective

  1. Target is  < 80 ppmw NH₃ in the stripped water

Flowsheet

 

Inputs

  1. Components:  Carbon dioxide, Hydrogen Sulphide, Hydrogen cyanide, Phenol, Ammonia, NaOH, Formate (HSS), Sodium ion, Water

Sour Water

  1. Gas flow rate>> 150000 lb/hr
  2. Temperature>> 135°F
  3. Pressure>> 70 psig
  4. Component composition>> (CO₂>> 0.1%, Ammonia>> 2%, H₂S>> 1.5%, Water>> 96.4%,  All in mol% | Phenol>> 100 ppmw, Formate>> 50 ppmw, HCN>> 100 ppmw) 

Feed/Btms

  1. Configuration
    1. Flow Type
      1. Countercurrent flow
    2. Shell side outlet
      1. Select "Stream number 7"
  2. Heat Transfer
    1. Calculation mode
      1. Select " Simple energy balance"
        1. Thermal Spec>>Tube outlet temperature>> 235°F
    2. Enable "Apply LMTD Correction factor (Ft factor)
      1. Select "Let ProTreat calculate"
  3. Pressure
    1. Shell side
      1. Select Pressure drop >>5 psi
    2. Tube side
      1. Outlet pressure>> 70 psia
  4. Thermo & Convergence
    1. Thermodynamic package
      1. Shell side>>Tube side>> OGT Gas Treating

SWS

  1. Configuration
    1. Select the check boxes that the column has reboiler and condenser, and has reflux to column (% return is 100%)
    2. Section
      1. 1 - Generic Value Trays
        1. Data 
          1. Tray data
            1. Number of trays>>40
            2. Tray spacing>> 2 feet
            3. Number of passes>> 1
            4. Weir height>> 2 inch
            5. Foam derating factor>> 0.7
        2. Size
          1. Diameter calculated
            1. %Vapor flood>> Downcomer flood>> 70%
        3. Pressure
          1. Enable "Specify pressure>> 15 psig >> Tray number 1"
          2. Enable "Calculate pressure drop"
  2. Cond/Reboil
    1. Condenser
      1. Temperature>> 180°F
      2. Select pressure drop>>0 psi
    2. Reboiler
      1. Select vapor return line pressure drop>>0 psi
    3. Select "Reboiler steam flow ratio"
      1. Reboiler steam flow ratio>> 1.3 lb steam /std US gallon
        1. Basis liquid stream for calc>> 1
        2. Pressure>> 50 psig
  3. Models
    1. Thermodynamic package>> OGT Gas Treating
    2. Reaction kinetic model for CO₂ and COS
      1. Select " ProTreat default (most columns)"
  4. Streams
    1. Feed & Draw streams
      1. Streams
        1. Stream 2>> connect>> above tray no. 6
        2. Stream 12>> connect >> above tray no. 35
      2. Top vapor stream
        1. Select " Rate stream"
      3. Bottom liquid stream
        1. Select "Rate Stream"

NaOH

  1. Connect the NaOH input stream to the regenerator above tray no. 35
  2. Recycle flow rate>> 0.1 USGPM
  3. Temperature>> 120°F
  4. Pressure>> 50 psia
  5. Component composition>> (NaOH>> 20 wt.%, Water>> 80wt.%)

Pump-1 

  1. Pump>>Pressure rise>>50 psi  
  2. Efficiency>>75%

Cooler

  1. Cooler>>Duty>>Outlet temperature>>120°F
  2. Pressure
    1. Pressure drop>>10 psi
  3. Thermo
    1. Thermodynamic Package>> OGT Gas Treating

Run Simulation

  1. Review all the inputs and run the simulation
  2. What is the concentration of Ammonia in the stripped water in ppmw?
  3. Increase the Formate (HSS) concentration in the sour water from 50 to 750 ppmw and observe ammonia concentration in the stripped water.
  4. Is the concentration of NH3 maintained below 80 ppmw?

Results & Discussion

Output-1

  1. Concentration of Ammonia in the stripped water @ 500 ppmw Formate(HSS) is 205.3 ppmw
  2. The outlet concentration of NH3 in stripped water increases as we increase the formate(HSS) concentration in the sour water 
  3. Does increasing reboiler duty decrease the NH3 concentration in the stripped water?
  4. At increased reboiler steam flow ratio of 1.7 lb steam/ std US gallon, concentration of Ammonia in the stripped water is 162.76 ppmw
  5. No appreciable results came on increasing the reboiler duty
  6. This happened because, NH3 is chemically bound 

Re-Run Simulation

  1. Now keep the reboiler duty at 1.3 lb steam/ std US gallon and increase the NaOH injection from 0.1 to 0.65 USGPM and RUN SIMULATION again
  2. Does it help in decreasing the NH3 concentration in stripped water?

Output-2

  1. An increase in NaOH injection decreased the ammonia concentration in the stripped water and made stripped water to meet the objective
  2. Concentration of Ammonia in the stripped water @ 0.65 USGPM of NaOH injection is 76.25 ppmw

Something to think about

  1. How much percent can a SW stripper contribute in enhancing sulphur recovery?
  2. Which one is most economical to use, single stage or two stage sour water stripper considering all the constraints and obtained product value ?
  3. For more detailed information about SWS visit ___________________












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