Radiotracer investigation in an aerobic digester of a wastewater treatment plant.

Radiotracer residence time distribution (RTD) methodology was used to determine the hydrodynamic parameters of the aerobic digester of an effluent treatment plant. Technicium-99m was used as a radiotracer. The concentration of radiotracer in the exit stream of the digester was determined using an on-line tracer monitoring method. The experimental mean residence time (MRT) of the digester was found to be 4 h, far less than the theoretical MRT calculated with respect to nominal flow parameters (volume and flow rate of material into the digester). The experimental MRT corresponds to a percentage effective volume of 11% translating into approximately 89% dead volume in the digester leading to the conclusion that the hydrodynamic performance of the aerobic digester of the effluent treatment plant was not efficient. A radioactive tracer (Tc-99m) was used to determine the flow type in the digester; an RTD Software was used to model the flow by curve fitting the experimental RTD with various non ideal flow models. It was observed from the radiotracer experiment that the perfect mixers in series with exchange model best described the flow type existing in the digester.

Radiotracer investigation in gold leaching tanks.

Measurement and analysis of residence time distribution (RTD) is a classical method to investigate performance of chemical reactors. In the present investigation, the radioactive tracer technique was used to measure the RTD of aqueous phase in a series of gold leaching tanks at the Damang gold processing plant in Ghana. The objective of the investigation was to measure the effective volume of each tank and validate the design data after recent process intensification or revamping of the plant. I-131 was used as a radioactive tracer and was instantaneously injected into the feed stream of the first tank and monitored at the outlet of different tanks. Both sampling and online measurement methods were used to monitor the tracer concentration. The results of measurements indicated that both the methods provided identical RTD curves. The mean residence time (MRT) and effective volume of each tank was estimated. The tanks-in-series model with exchange between active and stagnant volume was used and found suitable to describe the flow structure of aqueous phase in the tanks. The estimated effective volume of the tanks and high degree of mixing in tanks could validate the design data and confirmed the expectation of the plant engineer after intensification of the process.

Thermal neutron reflection method for measurement of total hydrogen contents in Ghanaian petroleum products.

A fast and non-destructive technique based on thermal neutron reflection was used to determine total hydrogen contents in petroleum products available in Ghana. A source holder consisting of an 241Am-Be neutron source and 3He neutron probe designed for detection of liquid levels was used to measure reflection parameter as a function of hydrogen contents in liquid hydrocarbons which served as standards. The measured data were fitted to two linear equations for two different geometrical arrangements. The trend of data was found to be consistent with theoretical analysis based on neutron moderation. The calibration lines were used to determine hydrogen contents in 10 petroleum products. The results agree favourably with those obtained using different experimental set-ups with other neutron sources and probes. The technique was also used to determine the quality of diluted petrol with aviation fuel.

Geometrical effects on thermal neutron reflection of hydrogenous moderators using 241Am-Be source.

The variation of thermal reflection parameter with thicknesses of water and paraffin moderators was measured using an instrument consisting of 1 Ci 241Am-Be isotopic neutron source and 3He neutron detector. Based on experimental data obtained from two different source-detector-sample geometries, analytical expressions were derived for calculation of reflection parameters for various moderator thicknesses. The measured data for the two geometries exhibit saturation curves with saturation achieved at about 8 and 16 cm when sample container was placed at top and side of the source holder, respectively. By locating the source holder along the vertical axis of the sample container, measurements showed that the reflection parameter was very sensitive with the axial location and was strongly dependent on the moderator and its thickness.