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A voluminous liquid waste stream is generated as sodium nitrate (NaNO3) solution in Spent Nuclear Fuel Reprocessing Plants. Fluidized bed thermal denitration is a strong contender among various disposal options for this stream. In the present work experimental investigations on thermochemical denitration of NaNO3 have been carried out in an 80 NB laboratory scale fluidized bed reactor. Carbon based reductant was utilized to convert NaNO3 to sodium carbonate (Na2CO3) as well as to reduce denitration temperature. The operating parameters were optimized for maximum conversion of NaNO3 and 99.13% denitrification has been achieved. Pressure fluctuation across bed was also recorded and analysed in the state space domain employing attractor comparison technique. This technique computes a statistical metric ‘S’, as a measure of the fluidization state in the fluidized bed reactor and can be used for early detection of agglomeration in the bed. The sensitivity and early agglomeration detection capability of S-statistics are illustrated with experimental results for a liquid-sprayed gas fluidized bed.

A non-invasive ultrasonic technique (UT) is developed to determine gas-liquid-solid composition inside digester of a biogas plant. The technique involves sweeping a contact type UT probe along the wall of pipes to determine the relative fraction of gas, liquid and solid phases under segregated conditions. The technique is validated at laboratory scale for two-phase (air-water) and three-phase (air-water-solid) systems. The average absolute error in prediction of segregated interfaces is ∼2.5%. Field trials are done on horizontal pipe sections (5 coils) of digester in the plant. More than 50% of the top most pipe run is occupied by gas. For second/third pipe runs solid fraction is around 20–25% while gas fraction is 10–15%. However, for the 4th and 5th pipe rows, the solid fraction is around 40–55%. A gradual increase of gas hold up towards the top regions and larger accumulation of solids at the bottom is expected because of waste feeding at the bottom. The described UT based system represents a novel way forward in use of ultrasound technology to detect segregated multiphase phases in digesters of biogas plants.