Instructions

1. This article contains a series of steps to feed the data to the flowsheet, run the simulation, interpret the results
   
2. User can either follow the series of steps mentioned in the article or download the ProTreat file attached to this article, review the inputs and run the simulation  
   

Simulation Set Up

Objective

1. Components:  Carbon dioxide, Hydrogen Sulphide, Thiosulfate(HSS), Nitrogen, MDEA, Water

Stream Information (Feed Gas)

1. Set up a conventional absorber & regenerator loop in ProTreat as shown in the flowsheet
2. Inputs taken for the exercise 
1. Gas flow rate: 6 MMSCFD
2. Temperature : 95 °F
3. Pressure : 1.6 psig
4. Component composition: (CO₂: 3.4%, N₂: 94.9%, H₂S: 1.7%, All in mol%, water %saturation: 100) 
   

Absorber Inputs

1. Tray type: Generic valve trays 
2. Number of trays: 14
3. Tray spacing: 2 feet
4. Number of passes: 1
5. Weir height: 2.5 inch
6. Foam derating Factor: 0.65     
7. Vapor flood & Downcomer flood: 70%
8. Pressure>>specify pressure below bottom: 1.6 psig
   
9. Select calculate pressure drop
   
10. Connect streams appropriately to absorber based on the flowsheet

Pump-1 Input

1. Pump>>Outlet Pressure>>25 psi  
2. Efficiency>>75%
   

Heat X-1 Input

1. HeatX-1>> Heat transfer>> Thermal spec>> Shell outlet temperature >>235 °F
2. Apply LMTD correction factor>>Let ProTreat calculate
   

Regenerator Inputs

1. Select the check boxes that the column has reboiler and condenser, and has reflux to column (% return is 100%)
2. Tray type: Generic valve trays 
3. Number of trays: 24
4. Tray spacing: 2 feet
5. Number of passes: 1
6. Weir height: 3 inch
7. Foam derating factor: 0.75     
8. Vapor flood & Downcomer Flood: 70%
9. Pressure>>specify pressure at tray no.1: 12 psig
   
10. Select calculate pressure drop
    
11. Connect streams appropriately to absorber based on the flowsheet
12. Connect feed stream above tray no.5
13. Condenser/Reboiler>>Condenser>> Temperature>>120 °F
14. Condenser>>Pressure Drop>>0 psi
15. Reboiler>> Vapor return line pressure drop>>0 psi     
16. Reboiler Steam Flow Ratio>>1.2 lb steam /std US gallon
17. Basis liquid stream for calculation>>Pump inlet stream
18. Pressure>>50 psig 
    

Cooler Input

1. Cooler>>Duty>>Outlet temperature>>100 °F

Amine Inputs in Control Block-1

1. Stream Flow rate: 85 USGPM
2. Composition: 40 wt. % MDEA, 0 wt.% Thiosulfate(HSS)
3. Select method for calculating make up as “Control Block In/ Out Streams”
   

Stream Information (Recycle block)

1. Select the preferred components and feed the input data in the perspective recycle block
2. Recycle flow rate: 85 USGPM
3. Temperature : 100 °F
4. Pressure : 10 psig
5. Component composition: (CO₂: 0.0001 Loading, MDEA: 40 wt.%, H₂S: 0.0001)
6. Select water specification as “is remainder (solvent streams only)”

Run Simulation

1. Firstly, run the simulation with no HSS and extract the concentration profile of the absorber
2. After, Add 0.5 wt.% of thiosulphate and extract the concentration profile of the absorber
3. Compare both the profiles, what significant observation can be noted?
4. In which case driving force for absorption dominates throughout the entire column?

Results & Discussion

Output

 H₂S concentration profiles at with no Heat stable salt

Interpretation-1

1. From the above graph we can say that there exist a significant driving force for absorption till tray number 4
   
2. Above tray 4 there is no bulk absorption taking place
   

 H₂S concentration profile at with 0.5 wt.% Heat stable salt

Interpretation-2

1. In this case, we can see that there exists a significant driving force for absorption throughout the column
   

1. Run the same simulation by varying the heat stable salt concentration from 0 to 1 wt.% 
   

Something to think about

1. Does HSS have an active role in reduced amine strength in solvent? If yes, what can be the precautionary measures?
2. For more detailed information about Impact of HSS on treating visit ___________________