Electro-membrane processes for flue gas cleaning

摘要

Various techniques for NO removal in Membrane Contactor were considered. However the NO absorption in a liquid adsorbent with chemical enhancement and its ease for regeneration, was selected as the most practicable choice. Various different compounds for chemical enhancement were studied and Fe(II)-chelate enhanced adsorbent was selected for further studies. The technical feasibility of Fe(II)-chelate enhanced adsorbent for obtaining greater than 80% NO removal have been successfully established. Even though the membrane area required for greater than 80% NO removal has been found to be about 500 m(sup 2)/MW(sub c) (compared to 50 - 150 m(sup 2)/MW(sub c), for 95% SO(sub 2) removal, depending on the membrane characteristics), suitable Membrane Contactor design has been proposed for carrying out the process at an acceptable gas side pressure drop. The electro-membrane processes for the regeneration of adsorbents have been studied both theoretically and experimentally. The theoretical studies have concerned the study of basic functions of both the bipolar membranes and charge laden (anion/cation) membranes. Suitable experimental techniques have been devised for studying of these basic parameters (e.g. charge transport number, salt diffusion through membranes, current-voltage characteristics of bipolar membranes and electrical resistance of charge laden membranes). These parameters have further been utilized in the mechanistic model of combined membranes in an ED cell (electrodialysis). Based on these fundamental studies and analysis of process requirements, suitable configuration of ED cell has been developed and verified by experimental studies. The effect of both the stack design parameters (e.g. number of cells, membrane type and spacer design) and the operational parameters (e.g. temperature, electrolyte concentration, liquid velocity and current density) have been studied for optimization of energy consumption for regeneration of loaded adsorbents. As a result, the energy consumption for regeneration of 250 kJ/mole SO(sub 2), at a current density of 150 mA/Cm(sup 2) and 200 kJ/mole SO(sub 2), at a current density of 50 mA/cm(sup 2), have been achieved. This may be compared to the energy consumption of about 1200 kJ/mole SO(sub 2) for the conventional process (steam stripping) for regeneration. The problems arising from fouling of membranes due to the presence of impurities in the liquid have also been studied. These studies have then been used for evaluating the requirement for cleaning of liquids before regeneration. (EG) EFP-94. 95 refs.