Gas Refining

CO2 Removal

In this process step, the CO2 is removed from the process gas with physical or chemical absorption. The residual CO2 content typically ranges between 50 and 3000 ppmv. In chemical absorption, the solvents mostly used are aqueous amine solutions (MEA and aMDEA), or hot potassium carbonate solutions. In physical absorption, typical solvents are glycol dimethylethers (Selexol), propylene carbonates and others (IPTS/EC, 2007). The heat requirements in a modern chemical absorption plant range between 30 and 60 MJ.kmol-1 CO2. A physical absorption plant can be designed to have zero heat requirements. However, mechanical energy requirements will have to be taken into account (EFMA, 2000). 

A promising development, pressure swing absorption (PSA), can combine the CO2 removal step and the methanation step into one. When a pure stream of CO2 is required, solvent scrubbing can be used for CO2 recovery (IPTS/EC, 2007).

Methanation

After CO2 removal there are still small amounts of CO and CO2 that can poison the ammonia synthesis catalyst and need to be removed. In this process CO and CO2 are transformed into methane in a reactor filled with a nickel containing catalyst. The reactions are the following:

CO + 3H2 → CH4 + H2O,     ΔΗ = - 206 kJ/mol

CO2 + 4H2 → CH4 + 2H2O,   ΔH = - 165 kJ/mol

The water produced needs to be removed before entering the converter. This is done by cooling and condensation downstream of the methanator (IPTS/EC, 2007 p.42).

Gas RefiningTechnologies & Measures

Technology or MeasureEnergy Savings PotentialCO2 Emission Reduction Potential Based on LiteratureCostsDevelopment Status
High Pressure Water Power Recovery Turbine

Investment costs are reported to be 150 million Yen for a 330,000 t ammonia/year plant, providing annual revenues of 36 million Yen and resulting in a payback time of 4.1 years (199 values) (ECCJ, 1999. p.155).

Commercial
Use of Enhanced CO2 Removal Solvents

Investment costs of improved solvents are estimated at €15 per GJ saved annually (de Beer et al., 2001.,  p.22).

The investment for the use of improved solvents for CO2 recovery are estimated to be around €3/GJ (Nieuwlaar, 2001. p.22).

Japanese flag For a 300 000 tonne/y plant, the investment costs for switching over to Selexol are reported to be around 1 200 millon Yen, providing yearly savings of 470 million Yen and resulting in a payback time or  2.5 years (ECCJ, 1999. p. 160).

Indian flag The cost of revamping from MEA to aMDEA in the Indian plant totaled  US $ 1.25 million (Vaish and Patel, 2002).

Commercial
Heat Recovery from Solvent Regeneration in CO2 Removal

Not available. 

Commercial
Pressure Swing Adsorption for Purification

Not available. 

Commercial
Two Stage Regeneration in CO2 Removal System

Indian Flag Implementation costs for a 1 500 tpd plant are estimated to be in the range of US 3.6 million [2005 values](FAI, 2013)

Commercial
High Efficiency Packings and Internals for CO2 Removal ColumnsIndian Flag Depending on the scope of upgrading work – , i.e. replacement of packings, and other modifications, for example to the.distributor – the costs are estimated to vary between US $ 50 000 and 200 000 [2007 values](FAI, 2013). Commercial