Extruded double-base (EDB) propellant rocket motors are used to propel conventional munitions from a variety of tri-Service platforms. Nitroglycerin (NG) emissions are generated during propellant annealing operations from the EDB rocket-motor manufacturing plant at the Naval Surface Warfare Center, Indian Head Division (IHD). Conventional technologies have been deemed unacceptable for controlling NG emissions due to the inherent hazards associated with the explosive-laden vapors. The objective of this demonstration was to show that air-phase photocatalytic oxidation is a viable treatment technology for the destruction of NG air emissions. Photocatalytic oxidation is a low-temperature, destructive process that uses ultraviolet light and a titanium dioxide semiconductor photocatalyst to generate highly reactive species for destruction of organic molecules.
A full-scale photocatalytic pollution control unit was installed at the IHD's annealing oven and tested between July and October of 1998 using a combination of simulated and actual production operations. Photocatalytic oxidation worked but performance objectives were not met. At the design flow rate of 650 scfm, the system was unable to remove 10 ppmv NG from an air stream that also contained lesser amounts of inert plasticizers. When challenged with low NG inlet concentrations (0.7 ppmv or less) and operated at half the design flow rate (324 scfm), the system was able to maintain a destruction and removal efficiency of 96 percent or greater.
Installed equipment cost was estimated at $608,000. The total annual operating costs were estimated to be $935,000 per year. This is equivalent to $3 per pound of propellant annealed or $14,650 per pound of NG destroyed. Approximately 95 percent of the operating costs were related directly to replacing the catalyst cartridge, which would be necessary at the beginning of each annealing oven cycle due to catalyst fouling.
The high operating cost for photocatalytic oxidation at the performance level observed during the demonstration compared to estimates of $50-70 per pound of NG destroyed by alternative technologies of carbon absorption or incineration, which have safety concerns. However, it is unlikely that the operating cost of photocatalytic oxidation could be reduced to a comparable low level by process optimization and increasing the catalyst cartridge life. In its current configuration, photocatalytic oxidation is not an economical solution to the Navy's problem.