Simultaneous SO₂/NO_x Removal and SO₂ Recovery from Flue Gas by Pressure Swing Adsorption

The feasibility of employing pressure swing adsorption (PSA) for simultaneous SO₂/NO_x removal from flue gas and concentrating the SO₂ in the desorption stream (expressed as enrichment ratio) is established by model simulation. A weak-base macroreticular resin is used as the sorbent. Concentrating the adsorptive is a new and promising application for PSA. This work also delineates the underlying principles for concentrating the adsorptive. The purge/feed ratio is a key parameter for the adsorptive enrichment ratio, which reaches a peak value at a certain purge/feed ratio. Effects of the other PSA cycle parameters on the enrichment ratio are also illustrated. For a simulated power-plant flue gas containing 0.5% SO₂, 0.13% NO₂, and 18% CO₂, a simple Skarstrom cycle can produce a purified stream with 0.035% SO₂, and 0.069% NO₂, while the desorption stream contains 7% SO₂. Further improvement can be obtained by employing a more complex PSA cycle by which a purified stream with 0.064% SO₂, and 0.055% NO₂, and a desorption stream with 9% SO₂ can be produced. The desorption stream can be readily converted to elemental sulfur by commercial processes. Preliminary experiments performed in this laboratory using polymeric sorbents instead of macroreticular resins suggest the validity of this work and indicate that the results of the present work can be further improved by using these polymeric sorbents.