OCR Text |
Show contact times to absorb the NO, AR type NOx scrubbers have not been developed to prototype scale. The cost compared to OAR type NOx scrubbers may be about equal. Any advantage for the AR type would have to come from a new, more efficient, less expensive absorbing fluid. Oxidation-absorption (OA) type processes attempt to absorb the NOx and convert it into nitric acid or dispose of NO. OA type processes have all the disadvantages of the OAR type and introduce new problems: high ozone use and scrubbing fluids that have not been used in FGD scrubbers. One OA type scrubber has been applied to power plant NOx removal (33.3 megawatts). Absorption-oxidation (AO) type processes use very expensive liquid oxidizers to absorb and oxidize NOx. They were conceived to avoid the use of a gaseous oxidizer. S0_ must be removed from the flue gas prior to NOx scrubbing to avoid excessive consumption of the expensive oxidizer which also reacts with SO . AO type processes use scrubbing fluids not used in FGD scrubbers and have all the disadvantages of OAR type NOx scrubbers. The AO scrubbers have not been developed to prototype scale. The cost compared to OAR type NOx scrubbers may end up about equal for NOx but the advantage of simultaneous SO and NOx scrubbing is lost. Four of the more promising processes which have been operated at prototype scale are described below: Oxidation-Absorption-Reduction Type (OAR) Ishikawajima-Harima Heavy Industries (IHI) Process Moretana Calcium Process Moretana Sodium Process Oxidation-Absorption Type (OA) Tokyo Electric-Mitsubishi Heavy Industries (MHI) Process Of these four processes, the Tokyo Electric process was developed for SO -free gas and therefore applies only to natural gas-fired boilers. The three OAR processes were developed for simultaneous NOx and SOx removal and are applicable to gas or oil fired units. Of these the Moretana calcium process is reported to be the most economical. The Moretana sodium process is not recommended by the developers for large installations because 4-27 P-233 |