| OCR Text |
Show Oxidation-absorption-reduction processes use simple modifications of available flue gas desulfurization (FGD) technologies. NO is oxidized in the gas phase with ozone (0 ) or chlorine dioxide (CIO.). The scrubbing fluid may contain a catalyst to promote NOx removal efficiency. Reduction of the NO to N is done by soluble sulfite ions. The removal efficiencies are 95% for SO. and 90% for NOx. The waste water contains dissolved chlorides and nitrates. Absorption-reduction processes use iron chelates (for example) to absorb NO directly into a water solution. NO is reduced to N by sulfite ions. The removal efficiencies are 95% for SO- and 90% for NOx. No soluble nitrates are formed. Oxidation-absorption processes use a gas-phase oxidation and form water-soluble nitrates or dilute nitric acid. NOx removal efficiency is about 90% and little or no S0_ is scrubbed. 4. Absorption-oxidation processes use a liquid phase oxidant [KMnO , Ca(ClO) ] to form nitrate ions from NOx and also oxidizes any SO-to sulfates. The high cost of the oxidant makes the use of these processes prohibitively expensive if SO- is present in the scrubber feed gas. (71 Nineteen wet NOx processes were documented by TVA. Many of the processes have been proven unfeasible technically or economically in bench or pilot plant tests. Oxidation-absorption-reduction (OAR) type NOx scrubbers have the most advantages and are the most fully developed, with seven prototype units (10 to 40 megawatt) in operation. Absorption-reduction (AR) type processes were conceived to eliminate the need for a gas phase oxidizer and the presence of nitrates in the waste water. This leads to the use of an expensive absorption fluid (e.g., containing iron chelates) and requires long 4-26 P-233 |
