Ammonia CO2 Removal Systems

CO2 Removal - Process Technology for Ammonia Plants By: Gerard B. Hawkins Managing Director, CEO

Why Remove CO2 ?         

Poisons Synthesis catalyst Can be used downstream in Urea production If allowed into the loop would Also act as inert in loop Increase the compression costs Used as a product in its own right Carbonated drinks Refrigeration units Can be exported to methanol plant

Systems for Removing CO2    

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Started with Monoethanolamine Chemical absorption Highly corrosive High energy consumption (14% of total plant) Modern plants use MDEA Other options include physical solvents Selexol (UOP) Benefield (hot potassium carbonate) Vetrocoke

MDEA 

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Uses diethanolamine with an amine activator No corrosion inhibitors required No solvent degradation is observed Acts as a combination of physical and chemical solvent CO2 can be recovered by flashing only

Typical System for MDEA Treated Gas

Feed Gas

CO2

Advantages of MDEA   

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Some stated above Can use MDEA to retrofit plants using MEA Can tailor balance between physical and chemical Allows for versatility especially in retrofit cases

Benfield System Treated Gas

Lean 75°C

CO2 and H2O

Semi Lean 120°C Regenerator Feed Gas Reboilers Absorber

CO2 Removal issues 

Benfield Problems

• Dirty solution • Foaming due to contaminants or degradation products • DEA degradation products • Difficulty of oxidizing V4+ to V5+ 

Results

• Low DEA concentration • Poor corrosion protection • Reduced CO2 removal capability

Vanadation 

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Method of protecting stable magnetite layer from corrosion Must reduce V5+ and deposition on surface Steady state is reached when V5+ : V2O5 is 0.4 If ratio less than 0.3 - rapid break down and corrosion High levels can lead to degradation of DEA Most plants have a slow reduction of V5+ to V4+ Can counter by addition of KNO2

Benefield - Water Balance  

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Large volumes of solution being circulated Must keep water balance right to ensure strength of solution is between 27 and 30% >30% - crystallisation and vessel corrosion