Mark D. Fowley

BLENDING TIME AND VELOCITY VARIATIONS DURING BLENDING IN A TANK USING DUAL OPPOSING JETS

Blending times are required for many process industries, and statistical analysis of the measured blending times was used to determine a relationship between CFD (computational fluid dynamics) predictions and experiments. A 95% blending time occurs when tank contents are sufficiently blended to ensure that concentration throughout the tank is within ±5% of the total change in concentration. To determine 95% blending times, acid and base tracers were added to an eight foot diameter tank, and the pH data were recorded to monitor blending. The data for six pH probes located throughout the tank were normalized to a range of 0 to 1. Then the blending time was established when the pH converged between 0.95 and 1.05 on the normalized graphs. Evaluation of results from 79 different tests concluded that the maximum blending time occurred randomly at any one of the six pH probes. The research then considered the calculated 95% blending times, which had uncertainties up to more than 100% at a 95% confidence level. However, this uncertainty is considered to be an actual variation in blending time, rather than an experimental error. Not only were there significant variations in the blending times, but there were significant variations in the velocities measured at different points in the blending tank.Copyright

WEAR LOCATIONS IN STAINLESS STEEL PIPE FITTINGS FROM THE TURBULENT FLOW OF A LIQUID-SOLID SLURRY

The United States Department of Energy (DOE) is building a Waste Treatment Plant (WTP) at the DOE Hanford Site in the state of Washington to process stored radioactive wastes for long-term storage and disposal. The Savannah River National Laboratory (SRNL) is helping resolve technical concerns with the WTP, which are related to piping erosion/corrosion (wear). SRNL is assisting in the design of a flow loop to obtain long term wear rates that will use prototypic simulant chemistry, operating conditions, and materials. The challenge is to accurately measure slurry wear to a pipe wall thickness tolerance of 47 microns/year anywhere in the test flow loop in a timely manner. A first step in such a test is to secure knowledge of high wear locations so that highly sensitive measurement techniques can be incorporated and properly located. Literature exists to help locate such wear locations in pipe and pipe fittings but most of the information deals with slurry flows that have significantly different velocities, different flows steams, e.g., steam, gas-liquid-solids, or made from different materials. To better estimate these high wear rate locations under the WTP conditions a separate pre-test flow loop was constructed and operated. This loop is referred to as the paint loop because it was internally coated with paint, which wears faster than the steel pipe, when a solids-laden slurry is circulated. The test flow conditions were a slurry velocity of 4 m/s in a 0.0762 -m (3-inch) Schedule 40 pipe system, resulting in Reynolds number just above 3 × 105, i.e., turbulent flow at a temperature of 25°C. The slurry was a mixture of water and sand, d50 ∼ 199 microns. This paper describes the test paint loop, its operation, and indicates the high slurry wear locations, as well as a comparison of those locations to existing literature sources.Copyright

Comparison of Experimental Results to CFD Models for Blending in a Tank Using Dual Opposing Jets

Research has been completed in a pilot scale, eight foot diameter tank to investigate blending, using a pump with dual opposing jets. The jets re-circulate fluids in the tank to promote blending when fluids are added to the tank. Different jet diameters and different horizontal and vertical orientations of the jets were investigated. In all, eighty five tests were performed both in a tank without internal obstructions and a tank with vertical obstructions similar to a tube bank in a heat exchanger. These obstructions provided scale models of several miles of two inch diameter, serpentine, vertical cooling coils below the liquid surface for a full scale, 1.3 million gallon, liquid radioactive waste storage tank. Two types of tests were performed. One type of test used a tracer fluid, which was homogeneously blended into solution. Data were statistically evaluated to determine blending times for solutions of different density and viscosity, and the blending times were successfully compared to computational fluid dynamics (CFD) models. The other type of test blended solutions of different viscosity. For example, in one test a half tank of water was added to a half tank of a more viscous, concentrated salt solution. In this case, the fluid mechanics of the blending process was noted to significantly change due to stratification of fluids. CFD models for stratification were not investigated. This paper is the fourth in a series of papers resulting from this research (Leishear, et.al. [1- 4]), and this paper documents final test results, statistical analysis of the data, a comparison of experimental results to CFD models, and scale-up of the results to a full scale tank.

Irradiation and Temperature Effects on Anti-Foam Agent Performance in a Non-Newtonian Waste Slurry Simulant

Foaming tests were performed in a bench-scale foam column and 1/9th-scale mechanically-agitated mixing system at the Savannah River National Laboratory (SRNL) for a simulant of waste slurry from the Hanford Tank 241-AZ-101. This featured additions of DOW Corning Q2-3183A antifoam agent (AFA) to prevent foaming, especially in the evaporators. These waste slurries (typically 15 wt% solids) are particularly prone to particle-stabilized foaming. Previous studies have shown that up to 20% of the polydimethyl siloxane (PDMS) portion of the AFA mixture is degraded by radiation. The high temperature (90°C) for 48 hrs of a caustic leaching process may have a similar effect on the polymer. The objective of this study was to determine how well degraded AFA works. Key results are that: • Without addition of this AFA, the 1/9th -scale system had about 100% foaming at 1 mm/s air velocity and the bench-scale system had over 400% foaming for an air flow of 10 mm/s. • The effect of irradiating 350 ppm AFA was to increase foaming from 6% to 30% in the foam column and 7.6% to 13.7% in the 1/9th -scale system at an air flow of 1 mm/s at room temperature. • The effect of heating the AFA to 90°C was to increase foaming by a factor of 1.6 in the foam column. But while the effectiveness of the irradiated AFA was reduced, it still provided a significant reduction in foaming. AFA additions required to mitigate the combined effects of high temperature and radiation were also determined.Copyright