NO{sub x} Emission Abatement Technologies

The Hanford Waste Vitrification Plant (HWVP) will convert Hanford Site high-level liquid defense waste to a solid vitrified (glass) form suitable for final disposal in a geological repository. Future process flow sheet developments may establish a need for a NO, scrubber in the melter off-gas system. Consequently, a technology review has been conducted to identify and compare applicable off-gas processing alternatives should NO, emission abatement be required. Denitrification processes can be separated into two distinct categories, wet or dry, depending upon whether or not NO{sub x} is absorbed into an aqueous solution. The dry methods of removal are generally more efficient (>90%) than wet scrubbing approaches (>60%); however, most dry approaches are applicable only to NO,. Of the dry removal methods, selective catalytic reduction (SCR) using NH3 reductant and a hydrogen zeolite catalyst appears to be the most suitable technology for reducing HWVP NO{sub x} emissions should emission abatement be required. SCR is a relatively simple, well established technology that produces no secondary waste stream and is applicable to a wide range of NO{sub x} concentrations (500 to 30,000 ppm). This technology has been successfully applied to uranium dissolver exhaust streams and has, more recently, been tested and evaluated as the best available control technology for reducing NO, emissions at the Idaho National Engineering Laboratory's waste calciner facility, and at DOE's West Valley Demonstration Project. Unlike dry NO, scrubbing methods, the wet techniques are not specific to NO{sub x}, so they may support the process in more than one way. This is the only major advantage associated with wet technologies. Their disadvantages are that they are not highly efficient at low NO{sub x} concentrations, they produce a secondary waste stream, and they may require complex chemical support to reduce equipment size. Wet scrubbing of HWVP process NO{sub x} emissions is an option that is justifiable only if the technology is needed to eliminate other process emissions and scrubbing compatibility can be established