Reconciling Electrical Resistance Tomography (ERT) Measurements with a Fluid Mixing Model for Semi-Batch Operation of a Stirred Vessel

Abstract

I n chemicals manufacture, many stirred vessel reactors are operated semi-batch wise. In this mode, one liquid phase reagent is charged initially to the vessel. A second liquid reagent is then added continuously from a feed reservoir, usually with stirring during the addition. Semi-batch operation is used for safety reasons, since there is never an excess of the second reagent and in effect the rate of reaction is controlled by the rate of addition. This is important for highly exothermic reactions, which could otherwise undergo a dangerous thermal run-away reaction. The fl uid mixing in stirred vessels is generally diffi cult to describe and control. This is certainly true for the semi-batch mode. Moreover, because practical reaction rates are usually fast relative to the fl uid mixing rates, concentration gradients will invariably be present. This is usually manifested as a reagent 'plume' evolving from the point of addition, via a partially submerged dip pipe. House, Risley, Warrington, WA3 6AS, U.K. 3. Industrial Tomography Systems, 47 Newton Street, Manchester, M1 1FT, U.K. 3. Industrial Tomography Systems, 47 Newton Street, Manchester, M1 1FT, U.K. Reconciling Electrical Resistance Tomography British Nuclear Fuels (BNFL), HintonAn electrical resistance tomography (ERT) system retrofi tted to a 2.3 m 3 vessel has been used to image the vessel volume for single feed semibatch operation. Images reconstructed from the raw ERT measurements may be represented as time incremented 3-D iso-surface representations of the fl uid mixing. ERT derived mixing curves have been evaluated against a network of zones (NOZ) mixing model, which is able to compute the time evolving concentration fi elds. Like the ERT system, the NOZ model is also able to visualise the evolving feed plume and has the power to predict the corresponding time-wise reaction behaviour in space for a simple A + B → products reaction.On a eu recours à un système de tomographie à résistance électrique (ERT) adapté à un réservoir de 2,3 m 3 pour cartographier le volume du réservoir pour un fonctionnement semi-discontinu à alimentation unique. Les images reconstruites à partir de mesures d'ERT brutes peuvent être représentées sous forme d'une série chronologique d'iso-surface en 3-D du mélange de fl uide. Les courbes de mélange établies par ERT sont évaluées par rapport à un modèle de mélange à réseau de zones (NOZ), qui est capable de calculer l'évolution du champ de concentration dans le temps. À l'instar du système ERT, le modèle NOZ est également capable de visualiser le panache d'alimentation en évolution et de prédire le comportement dans le temps et l'espace d'une réaction simple A+B → produit.Keywords: stirred vessel, fl uid mixing, electrical resistance tomography, ERT, semi-batch Stirred vessels are notorious for their lack of instrumentation to reveal and quantify composition. However, we have recently shown that ERT can be applied to visualise both an inert tracer as well as an inert mimic of a reagent plume in semi-batch operation (Stanley...

Cavern Formation in Non-Newtonian Media in a Vessel Agitated by Submerged Recirculating Liquid Jets

“…This value was then used to analyze the measurements made for all previous time points 0 < t < t* to obtain the information on how the boundary of the active region spreads with time in three dimensions. This is similar to the previous approaches documented in the literature, 8,10 where an initial reference frame and a final well-mixed frame were used to process the intervening frames. This technique eliminates the need for external conductivity measurements for establishing a threshold for ERT.…”

“…computational fluid dynamics, CFD Mann et al 7 Stanley et al 8 Ricard et al 9 Stanley et al 10 Pakzad et al 5 Rodgers et al 11 Bhole et al 12 Harrison et al 13 Patel et al 14 positron emission particle tracking, PEPT Edwards et al 15 Simmons et al 16 flow visualization Simmons et al 16…”

Tomographic imaging during reactive precipitation in a stirred vessel: Mixing with chemical reaction

“…More specifically ERT has been used to image gas-liquid hold up (Wang et al, 2000); the distribution of solids in an agitated vessel (Mann et al, 2001); miscible liquid mixing following the addition of a continuous brine tracer (Stanley et al, 2002) as well as the validation and analysis of a fluid mixing model (Stanley et al, 2005a). Previous ERT-based studies of reactive crystallisation have been undertaken (on a larger scale vessel) although only effects due to impeller failure and two different feed rates were investigated (Stanley et al, 2005b).…”