Electrochemical regeneration of iron-chelates for combined NOx and SO2 removal from combustion flue gas

The ThioNO_x process under development by Dravo Lime Company is an emerging post-combustion flue gas cleanup technology. It can simultaneously remove NO_x and SO₂ from boilers burning high-sulfur coals. In this process, SO₂ is removed by scrubbing the flue gas with slaked Thiosorbic lime (a magnesium-enhanced lime) slurry. The removal of NO_x is achieved by adding to the scrubbing liquor iron-EDTA, a metal chelate, which binds and removes NO from the flue gas. The ThioNO_x process is an attractive option for utility stations already equipped with wet scrubbers to reduce the emissions of SO₂. Results obtained from tests utilizing a bench scale wet scrubbing facility rated at 5 KWe are presented. The emphasis is on the utilization of an unique electrochemical regeneration technique to keep the iron chelate in the ferrous form. Description of the 5 kWe test facilities, the regeneration technique and results obtained from such tests are given. Data from recent 5 kWe tests showed that more than 50% NO_x removal had been achieved at an inlet flue gas oxygen concentration of 10 volume percent. Data obtained from bench and prototype scale tests have led to the successful design of full scale electrochemical regeneration units. Further testing of this technology will be conducted at DLC´s pilot plant to verify the process economics. Implications of this technology for retrofit applications to existing coal-fired boilers is also discussed