Salt extraction from hydrogen-sulfide scrubber solution using electrodialysis

The buildup of undesirable sulfur compounds(sulfates and thiosulfates) reduces the scrubbing effectiveness of the LO‐CAT I autocirculation sulfur recovery process from acid‐gas stream. Among various processes, withdrawing and disposing of a portion of the scrubber solution and replacing this “blowdown” with fresh solution have been the practice in the industry. The application of the electrodialysis system to recycle the blowdown is presented. Experiments were carried out using electrodialysis to separate salts (sulfates and thiosulfates) from the LO‐CAT I autocirculation scrubber solution containing organic chelating agents, iron, and various alkali‐metal inorganic salts. The results indicated that the electrodialysis was successful in removing 50% of the salts from the scrubber solution with less than 8% loss of organic and 8% loss of carbonates. The fluxes of the undesired salt species were high even at low current densities (200 to 400 A/m2).