Recent laboratory and field data suggest that hydrates form very porous pipeline plugs which transmit pressure freely, while hydrates act as significant flow obstructions. The blocked flow causes an ocean pipeline to rapidly equilibrate to the ocean temperature at 4°C. When the hydrate plug is dissociated through total depressurization of the pipeline, the hydrate plug will be converted to an ice plug which significantly dissociates longer than the hydrate. This work formulates the first dissociation model in rectilinear coordinates. It indicates that there may be an optimum pipeline pressure for the most rapid dissociation of all solid phases resulting from hydrate pipeline blockages. Surprisingly, the high ice thermal diffusivity provides the highest heat flux when some ice is present.

Volume reduction of low-level mixed wastes from former nuclear weapons facilities is a significant environmental problem. Processing of these materials presents unique scientific and engineering problems due to the presence of minute quantities of radionuclides which must be contained and concentrated for later safe disposal. Low-temperature catalytic incineration is one option that has been utilized at the Rocky Flats facility for this purpose.This paper presents results of research regarding evaluation of bulk metal oxides as catalysts for low-temperature incineration of carbonaceous residues which are typical by-products of fluidized bed combustion of mixed wastes under oxygen-lean conditions. A series of 14 metal oxides were screened in a thermogravimetric analyzer, using on-line mass spectrometry for speciation of reaction product gases. Catalyst evaluation criteria focused on the thermal-redox activity of the metals using both carbon black and PVC char as surrogate waste materials. Results indicated that metal oxides which were P-type semiconductor materials were suitable as catalysts for this application. Oxides of cobalt, molybdenum, vanadium, and manganese were found to be particularly stable and active catalysts under conditions specific to this process (T < 650 degrees C, low oxygen partial pressures).Bench-scale evaluation of these metal oxides with respect to stability to chlorine (HCl) attack was carried out at 550 degrees C using a TG/MS system. Cobalt oxide was found to be resistant to metal loss in a HCl/He gaseous environment while metal loss from Mo, Mn, and V-based catalysts was moderate to severe. XRD and SEM/EDX analysis of spent Co catalysts indicated the formation of non-stoichiometric cobalt chlorides. Regeneration of chlorinated cobalt was found to successfully restore the low-temperature combustion activity to that of the fresh metal oxide.