Arto Laari

Wet oxidation of concentrated wastewaters of paper mills for water cycle closing

Experimental research into wet oxidation of concentrated wastewaters from paper mills was undertaken. Evaporation and membrane concentrates from paper mills were selected as experimental objects. The aim of the wet oxidation of the paper mill concentrates was to reduce the concentration of organics and to improve biodegradability of the concentrates. The effect of temperature, pH and the influence of homogeneous and heterogeneous catalysts on the rate of the wet oxidation process was studied. The experiments were carried out in stainless steel batch reactor at temperatures from 130 to 200°C and at pH 2, 5 and 10. The partial pressure of oxygen was maintained at 1 MPa for all experiments. The results showed COD and TOC removal increases of 50 to 80% at temperatures from 160 to 200°C. The best results with respect to the improvement of biodegradability were, however, observed under milder conditions. By the use of both homogeneous and heterogeneous catalysts, a biodegradability of 60 to 78% was achieved with wet oxidation at 150°C. Operational cost estimation for the wet oxidation process was also done and showed that the cost of wet oxidation of concentrated water by air is less expensive than an oxygen-based process.

Modelling of Chlorophenol Treatment in Aqueous Solutions. 2. Ozonation under Basic Conditions

Abstract Ozonation of 2-chlorophenol (2-CP), 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) in basic aqueous solutions is discussed. In such conditions (pH=9.5), ozonation of chlorophenols proceeds rapidly due to the presence of the dissociated form of the phenolic compound. No ozone occurs in the bulk of the liquid and, in modelling, it becomes necessary to account for the reactions in the liquid film. Two approaches were tested: 1) the film and bulk balances were solved sequentially, and the diffusional fluxes coupling the balances were obtained by solving numerically the concentration profiles in the film; 2) the bulk mass balances were solved without the film mass balances by applying the enhancement factor calculated from existing correlations. The results of both approaches are compared with experimental data. The formation mechanism of an aromatic quinone, hydrogen peroxide and chloride ions during the ozonation appeared to differ under basic conditions from that under acidic conditions. Hy...

Determination of the Henry's Coefficient and Mass Transfer for Ozone in a Bubble Column at Different pH Values of Water

In this study, the ozone gas-liquid mass transfer into water in a bubble column was investigated for different pH values. The ozone volumetric mass transfer coefficient and the Henrys coefficient were determined simultaneously by parameter estimation using a nonlinear optimization method. A sensitivity analysis was conducted to obtain information on the reliability and identifiability of the estimated parameters. A minor dependence of the Henrys law constant on pH was detected at the pH range 4 to 9.

Selective Removal of Lipophilic Wood Extractives from Paper Mill Water Circulations by Ozonation

Abstract Circulation waters from paper mills and TMP production were treated by selective ozonation to remove lipophilic wood extractives (LWEs). In the reaction model, ozone was assumed to react with overall organic matter measured as COD with one global reaction rate coefficient. The target compounds, LWEs, are a part of the overall organic matter and they react with ozone with a specific reaction rate coefficient. Reaction selectivity, defined as the ratio of reaction rate coefficients of the reactions of ozone with the LWEs and COD, describes how efficiently ozone is used to remove the LWEs compared to removal of COD. The reaction selectivity was determined from experimental results and it was found to vary from 3 to 20 for different sets of water and for different fractions of LWEs. However, the ozone dose needed for removal of extractives was found to be rather high, about 100–300 mg/dm3 for 50% removal. The reason is the high concentration of organic matter in the waters leading to excessive usage of ozone despite the high selectivity of the reaction. A reactor model was developed to predict the behavior of industrial ozonation reactors. The reactor model takes into account the variation in the rate coefficient with respect to the reaction extent.

Valorization of Lignin by Partial Wet Oxidation Using Sustainable Heteropoly Acid Catalysts

The production of carboxylic acids by partial wet oxidation of alkali lignin at elevated temperatures and pressures was studied experimentally. Two different heteropoly acids, phosphotungstic acid (H3PW12O40) and phosphomolybdic acid (H3PMo12O40), were used to catalyze the oxidation of lignin under hydrothermal conditions. Factors influencing the total yield of carboxylic acids formed during the partial oxidation of lignin were investigated. Formic, acetic and succinic acids were the major products identified. Of the two catalysts used, phosphomolybdic acid gave the most promising results, with carboxylic acid yields and lignin conversions of up to 45% and 95%, respectively.

Comparision Of Ozonation And Wet Oxidation For The Destruction Of Lipophilic Wood Extractives From Paper Mill Circulation Water

Abstract Lipophilic wood extractives (LWEs) are natural components of wood, which are liberated from softwood into process water in the production of mechanical pulp (TMP refining or groundwood grinding). These compounds are known to be toxic to aquatic life in the receiving waters. Also, when water circulations are closed these compounds are accumulated in the process waters leading to problems in process operation and in product quality. In this work two different oxidation methods, ozonation and wet oxidation, were studied for die removal of LWEs from circulation waters. Bom studied meuiods are capable of selectively removing the LWEs.

Experimentally Validated CFD Model for Gas-Liquid Flow in a Round-Bottom Stirred Tank Equipped with Rushton Turbine

Abstract Hydrodynamics of gas-liquid flow in a round-bottom stirred tank is modelled at two gas flow rates, constant bubble size and agitator speed of 300 rpm. A round-bottom tank equipped with four baffles and a Rushton turbine was chosen to represent a typical reactor used in hydrometallurgical processes operating under pressure. The applicability of different momentum interchange models and the Realizable k-ε, SST k-ω, and RSM turbulence models was studied using CFD software. The results were compared and validated against experimental data from Particle Image Velocimetry measurements by means of liquid and gas velocity distributions. In addition, energy balance between power input and dissipation energy was compared for the different turbulence models. The CFD model was found to be in good agreement with the measurements. Of the turbulence models studied, the Realizable k-ε model showed best agreement with the measured velocity profiles. Popular drag force models proposed in the literature were assessed, as was the influence of inclusion of non-drag forces. Gas flow was found to affect the liquid phase flow in the tank by generating an additional secondary circulation loop in the upper part of the reactor.

Erratum: Demesa, A.G.; et al. Valorization of Lignin by Partial Wet Oxidation Using Sustainable Heteropoly Acid Catalysts. Molecules 2017, 22, 1625

The authors would like to make the following correction to their published paper [1]. [...].

Experimental and Numerical Study of Multiphase Mixing Hydrodynamics inBatch Stirred Tank Applied to Ammoniacal Thiosulphate Leaching of Gold

Hydrodynamics of aerated slurry is studied experimentally and numerically using the example of thiosulphate leaching of gold concentrate. The studied milled concentrate has shear-thinning fluid rheology and it was imitated by water-based solutions of CMC. Presence of electrolytes, as in the case of the leaching slurry, has great influence on bubble size distribution. Primary phase flow is measured by Particle Image Velocimetry. Local gas hold-up in aerated CMC 50000 (0.15 w%) solution is measured by Electrical Impedance Tomography. Volumetric mass transfer is measured by dynamic method in different CMC solutions over a range of operational conditions in absence and presence of electrolytes. The experimental data was used in CFD modelling of the aerated slurry. Single phase hydrodynamics of shear-thinning fluid (CMC 50000 (0.15 w%)) have been modelled and validated against experimental data with reasonable agreement. Multiphase mixing of the thiosulphate slurry was modelled with the assumption of constant bubble size. The results of the simulations and measurements are presented and discussed.

Numerical Simulation of Bubble Coalescence and Break-Up in Multinozzle Jet Ejector

Designing the jet ejector optimally is a challenging task and has a great impact on industrial applications. Three different sets of nozzles (namely, 1, 3, and 5) inside the jet ejector are compared in this study by using numerical simulations. More precisely, dynamics of bubble coalescence and breakup in the multinozzle jet ejectors are studied by means of Computational Fluid Dynamics (CFD). The population balance approach is used for the gas phase such that different bubble size groups are included in CFD and the number densities of each of them are predicted in CFD simulations. Here, commercial CFD software ANSYS Fluent 14.0 is used. The realizable - turbulence model is used in CFD code in three-dimensional computational domains. It is clear that Reynolds-Averaged Navier-Stokes (RANS) models have their limitations, but on the other hand, turbulence modeling is not the key issue in this study and we can assume that the RANS models can predict turbulence of the carrying phase accurately enough. In order to validate our numerical predictions, results of one, three, and five nozzles are compared to laboratory experiments data for Cl2-NaOH system. Predicted gas volume fractions, bubble size distributions, and resulting number densities of the different bubble size groups as well as the interfacial area concentrations are in good agreement with experimental results.