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

Inputs

1. Components:  Carbon dioxide, Hydrogen sulphide, Methane, Ethane, Propane, 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: 1,817 m³/hr
2. Temperature : 37 °C
3. Pressure : 60 kg/cm²
4. Component composition: (CO₂: 4%, CH₄: 80%, C₂H₆: 12%, C₃H₈: 3.5%, Saturation: 100%, H₂S: 0.5%, All in mol%) 
   

Absorber Inputs

1. Tray type: Generic valve trays 
2. Number of trays: 20
3. Tray spacing: 0.6 meters
4. Number of passes: 1
5. Weir height: 0.05 meters
6. Foam derating Factor: 0.85     
7. Vapor flood & Downcomer flood: 70%
8. Pressure>>set pressure by feed stream: 2
9. Connect streams appropriately to absorber based on the flowsheet

Stream Information(Lean amine)

1. Inputs taken for the lean amine
2. Lean amine flow rate: 114 m³/hr
3. Temperature : 40 ° C
4. Pressure : 60 kg/cm²
5. Component composition: (CO₂: 0.003 loading,  H₂S: 0.001 loading, MDEA: 40 wt. %) 
6. Select the water specification as “Is Remainder(Solvent streams only)”

Run Simulation

1. Run simulation at base case i.e., MDEA concentration is 40 wt. %
2. CO₂ concentration in the treated gas in the base case is 1.244 mol%.
3. H₂S concentration in the treated gas is 2.199 ppmv.
   
4. However, outlet concentration of H₂S meets the objective but CO₂ didn't
   
5. So, let us increase the solvent strength from 40 to 50 wt.% and run the simulation.
6. CO₂ concentration in the treated gas at 50 wt.% MDEA is 1.251 mol%.
7. H₂S concentration in the treated gas at 50 wt.% MDEA is 2.971 ppmv.
8. CO₂ still haven't met the objective, then how can we meet CO₂ spec?
   
9. Bring the solvent strength to base case i.e., 40 wt.% and now increase the solvent circulation rate from 114 m³/hr to 136 m³/hr
10. Now run the simulation and note the concentrations of CO₂ and H₂S in treated gas
    

Results & Discussion

Output

1. CO₂ concentration in the treated gas at 50 wt.% MDEA is 0.845 mol%.
2. H₂S concentration in the treated gas at 50 wt.% MDEA is 1.814 ppmv.
   
3. Now, concentrations of both the components in the treated gas meets the objective

1. In the graph (MDEA concentration vs CO₂ concentration in the treated gas), we can clearly observe that up to 47 wt. % MDEA, the amount of CO₂ in the treated gas followed decreasing pattern and after that amount of CO₂ in the treated gas started increasing.
2. The main reason for this phenomenon is the natural viscosity of lean amine. It increases as the weight percent of MDEA in the lean amine after it crossed a threshold limit. (in this case: 47 wt.% MDEA)
   
3. So, in order to achieve the objective we have to maintain the amine strength at the base case and increase the solvent circulation rate to meet the objective.
   

Something to think about

1. How does the seasonal climatic changes impact the viscosity of amine/solvent?
2. For more detailed information about the reboiler duty and temperature profiles visit ___________________