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E.T. Baars

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12 records found

Drinking water pellet softening

Prediction the terminal settling velocity of natural particles

Conference paper - O.J.I. Kramer, O.J.I. Kramer, O.J.I. Kramer, P.J. de Moel, P.J. de Moel, P.J. de Moel, E.T. Baars, W.H. van Vugt, J.P. van der Hoek, J.P. van der Hoek

Natural particles are frequently applied in drinking water treatment in up-flow fluidisation processes. Additionally, sedimentation processes are applied to clarify water and to concentrate solids. To estimate the terminal settling velocity of single solid particles in a liquid s ...

Accurate voidage prediction in fluidisation systems for full-scale drinking water pellet softening reactors using data driven models

Journal article - O.J.I. Kramer, O.J.I. Kramer, O.J.I. Kramer, O.J.I. Kramer, P.J. de Moel, P.J. de Moel, P.J. de Moel, J.T. Padding, E.T. Baars, Yousef M.F. El Hasadi, E.S. Boek, J.P. van der Hoek, J.P. van der Hoek

In full-scale drinking water production plants in the Netherlands, central softening is widely used for reasons related to public health, client comfort, and economic and environmental benefits. Almost 500 million cubic meters of water is softened annually through seeded crystallisation in fluidised bed reactors. The societal call for a circular economy has put pressure on this treatment process to become more sustainable. By optimising relevant process conditions, the consumption of chemicals can be reduced, and raw materials reused. Optimal process conditions are feasible if the specific crystallisation surface area in the fluidised bed is large enough to support the performance of the seeded crystallisation process. To determine the specific surface area, crucial variables including voidage and particle size must be known. Numerous models can be found in the literature to estimate the voidage in liquid-solid fluidisation processes. Many of these models are based on semi-empirical porous-media-based drag relations like Ergun or semi-empirical terminal-settling based models such as Richardson-Zaki and fitted for monodisperse, almost perfectly round particles. In this study, we present new voidage prediction models based on accurate data obtained from elaborate pilot plant experiments and non-linear symbolic regression methods. The models were compared with the most popular voidage prediction models using different statistical methods. An explicit model for voidage estimation based on the dimensionless Reynolds and Froude numbers is presented here that can be used for a wide range of particle sizes, fluid velocities and temperatures and that can therefore be directly used in water treatment processes such as drinking water pellet softening. The advantage of this model is that there is no need for applying numerical solutions; therefore, it can be explicitly implemented. The prediction errors for classical models from the literature lie between 2.7 % and 11.4 %. With our new model, the voidage prediction error is reduced to 1.9 %.@en

Fluidisation characteristics of granular activated carbon in drinking water treatment applications

Journal article - O.J.I. Kramer, O.J.I. Kramer, O.J.I. Kramer, O.J.I. Kramer, C. van Schaik, C. van Schaik, P.D.R. Dacomba Torres, P.J. de Moel, E.S. Boek, E.T. Baars, J.T. Padding, J.P. van der Hoek, J.P. van der Hoek

Granular activated carbon (GAC) filtration is an important unit operation in drinking water treatment. GAC filtration is widely used for its filtration and adsorption capabilities as a barrier for undesired organic macro- and micro-pollutants. GAC filtration consists of two succe ...

Prediction of the terminal settling velocity of drinking water pellet softening particles

Conference paper - O.J.I. Kramer, P.J. de Moel, P.J. de Moel, E.T. Baars, W.H. van Vugt, J.P. van der Hoek, J.P. van der Hoek

The literature provides a comprehensive collection of equations to estimate the terminal settling velocity of single solid particles in a liquid system. The settling velocity for perfectly round spheres can accurately be calculated. In the contrary for natural imperfect particles ...

Improvement of voidage prediction in liquid-solid fluidized beds by inclusion of the Froude number in effective drag relations

Journal article - O.J.I. Kramer, O.J.I. Kramer, O.J.I. Kramer, O.J.I. Kramer, J.T. Padding, W.H. van Vugt, P.J. de Moel, P.J. de Moel, E.T. Baars, E.S. Boek, J.P. van der Hoek, J.P. van der Hoek

A novel effective drag relation for liquid-solid fluidisation is proposed, suitable for application in full-scale installations. This is achieved by presenting new insights related to the influence of the temporal-spatial heterogeneity on the effective hydrodynamic drag for large fluidised systems. While heterogeneous flow behaviour can be predicted increasingly accurately in CFD simulations that explicitly model the heterogeneous solids distribution, for the operation of many large-scale applications it is infeasible to perform such computationally intensive simulations. Therefore, there is a clear need for full-scale drag relations that effectively take into account the heterogeneous behaviour and irregular spatial particle distributions. Our new drag relation is based on a large set of experiments, which shows that the degree of overall expansion is not only dependent on the ratio of laminar-turbulent flow, but also on the amount of homogenous versus heterogeneous flow, which is not included in current full-scale drag relations. To include the effect of heterogeneity, the standard drag relation, based on the Reynolds number, is extended with a specific type of Froude number. Because fully turbulent flow regimes are rare in applications of liquid-solid fluidisation, our focus is not on the turbulent flow regime but instead on laminar and transitional flow regimes. In these regimes, three types of models are investigated. The first type is based on a theoretical similarity with terminal settling, the second is based on the semi-empirical Carman-Kozeny model, and the third is based on empirical equations using symbolic regression techniques. For all three types of models, coefficients are calibrated on experimental data with monodisperse and almost spherical glass beads. The models are validated with a series of calcium carbonate grains applied in drinking water treatment processes as well as data obtained from the literature. Using these models, we show that the voidage prediction average relative error decreases from approximately 5% (according to the best literature equations which use Reynolds number only) to 1-2% (using both Reynolds and Froude number). This implies that our new models are more suitable for operational control in full-scale fluidised bed applications, such as pellet softening in drinking water treatment processes.@en

Improvement of the Richardson-Zaki liquid-solid fluidisation model on the basis of hydraulics

Journal article - O.J.I. Kramer, O.J.I. Kramer, O.J.I. Kramer, O.J.I. Kramer, P.J. de Moel, P.J. de Moel, E.T. Baars, W.H. van Vugt, J.T. Padding, J.P. van der Hoek, J.P. van der Hoek

One of the most popular and frequently used models for describing homogeneous liquid-solid fluidised suspensions is the model developed by Richardson & Zaki in 1954. The superficial fluid velocity and terminal settling velocity together with an index makes it possible to determine the fluid porosity in a straightforward way. The reference point for the Richardson-Zaki model is the terminal settling velocity at maximum porosity conditions. To be able to predict porosity in the proximity of minimum fluidisation conditions, either the minimum fluidisation velocity must be known or the Richardson-Zaki index must be very accurate. To maintain optimal process and control conditions in multiphase drinking water treatment processes, the porosity is kept relatively low. Unfortunately, the Richardson-Zaki index models tends to overestimate the minimum fluidisation velocity and therefore also results in less accurate predictions with respect to porosity values. We extended the Richardson-Zaki model with proven hydraulics-based models. The minimum fluidisation velocity is acquired using the model proposed by Kozeny (1927), Ergun (1952) and Carman (1937). The terminal settling velocity is obtained through the model developed by Brown & Lawler (2003), which is an improved version of the well-known model developed by Schiller & Naumann (1933). The proposed models are compared with data from expansion experiments with calcium carbonate grains, crushed calcite and garnet grains applied in drinking water softening using the fluidised bed process. With respect to porosity, prediction accuracy is improved, with the average relative error decreasing from 15% to 3% when the classic Richardson-Zaki model is extended with these hydraulics-based models. With respect to minimum fluidisation velocity, the average relative error decreases from 100% to 12%. In addition, simplified analytical equations are given for a straightforward estimation of the index n.

@en

Environmental financial and quality assessment of drinking water processes at Waternet

Journal article - M Tapia, MA Siebel, A.W.C. van der Helm, E.T. Baars, HJ Gijzen

Optimal flow distribution over multiple parallel pellet reactors: a model-based approach

Journal article - KM van Schagen, R. Babuska, L.C. Rietveld, E.T. Baars

Optimal flow distribution over multiple parallel pellet reactors: a model-based approach

Journal article - KM van Schagen, R. Babuska, L.C. Rietveld, E.T. Baars

Modelling disinfection and by-product formation during the initial and the second phase of natural water ozonation in a pilot-scale plug flow reactor

Journal article - A.W.C. van der Helm, L.C. Rietveld, E.T. Baars, PWMH Smeets, J.C. van Dijk

Modelling disinfection and by-product formation during the initial and the second phase of natural water ozonation in a pilot-scale plug flow reactor

Journal article - A.W.C. van der Helm, L.C. Rietveld, E.T. Baars, PWMH Smeets, J.C. van Dijk

Use of on-line uv/vis-spectrometry in the measurement of dissolved ozone and aoc concentration in drinking water treatment

Conference paper - LJP van den Broeke, P.S. Ross, A.W.C. van der Helm, E.T. Baars, L.C. Rietveld

Contributed

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An improved model of calcium carbonate crystallization

An improved kinetics-model for the calcium carbonate crystallization in the fluidized bed softening reactors at the Weesperkarspel drinking water treatment plant

Master thesis - E. Chiou, J.P. van der Hoek, H.J.M. Kramer, O.J.I. Kramer, P.J. de Moel, E.T. Baars

One of the main targets of Waternet, the water-cycle company of Amsterdam, is to increase the sustainability of water treatment. To achieve this goal, it is necessary to improve the efficiency and to decrease the use of chemicals during pellet softening process. However, the model of Van Schagen et al. (2008 b,c) that is currently used to optimize the pellet softening process is not predicting accurately enough the pH and calcium profile over the height of the pellet softening reactor. The calcium carbonate crystallization is calculated, in this model, using a linear relationship between the rate of crystallization and supersaturation with an additional diffusion parameter to take into account the flow conditions inside the reactor.
To determine more accurately the rate of calcium carbonate during the pellet softening process, two types of experiments were conducted during this research: STR batch and PFR fluidized bed experiments. Firstly, the experimental results were compared with the predictions of two linear models: the model of Wiechers et al. (1975) from literature and the one-rate-constant model developed in this research. Based on the results, it was concluded that it is not possible to improve the prediction of calcium carbonate crystallization kinetics if a linear model with one-rate-constant is used as proposed by Van Schagen. When the rate of crystallization is plotted against supersaturation a bending of the curve is observed at low supersaturation due to a sharp decrease in the rate of crystallization. Other researchers, such as Dreybrodt et al. (1997) has also observed that the rate of calcium carbonate crystallization is not linearly related to supersaturation when water or seeding material with inhibiting compounds is used. To describe this bending of the curve, two models were considered: the exponential model of Lasaga (1998) and the two-rate-constants model that consists of two linear equations. In this research, the two-rate-constants model was chosen instead of the exponential Lasaga model because it is easier to fit to the experimental results and gives a better overview of the dependence of the rate of crystallization from supersaturation. The two-rate-constants model significantly improves the prediction of calcium carbonate crystallization in a pellet softening fluidized bed reactor. The average relative error of this model, for the prediction of the calcium profile in a full-scale reactor, is only 2-5% while the average relative error of the one-rate-constant model is approximately 15-30%. Therefore, the two-rate-constants model predicts better the calcium carbonate crystallization and can be used to describe much more accurately the pellet softening process compared to the models found in literature.
Based on the results of the research, it can be concluded that the performance of a pellet softening fluidized bed reactor cannot be significantly improved by increasing the height of the reactor. On the other hand, it is possible that performance is enhanced by removing inhibitors such as organic carbon from the water. Nevertheless, further research is necessary to determine the effect of inhibitors, such as organic carbon, on water softening. Also, in order to determine more accurately the model parameters, the experimental set up should be adjusted in order to represent better the conditions inside a pellet softening fluidized bed reactor. In particular, increasing the height of the reactor and mixing the caustic soda at the bottom of the column is necessary.