scholarly journals A CFD strategy to retrofit an anaerobic digester to improve mixing performance in wastewater treatment

2020 ◽  
Vol 81 (8) ◽  
pp. 1646-1657 ◽  
Author(s):  
D. Dapelo ◽  
J. Bridgeman
Keyword(s):  
Wastewater Treatment ◽  
Gas Flow ◽  
Biogas Production ◽  
Continuous Phase ◽  
Mixing Efficiency ◽  
Mixing Times ◽  
Cfd Modelling ◽  
Mixing Performance ◽  
Quantitative Results ◽  
Computational Fluid Dynamics Cfd

Abstract To date, mixing design practice in anaerobic digestion has focussed on biogas production, but no adequate consideration has been given to energy efficiency. A coherent, comprehensive and generalized strategy based on computational fluid dynamics (CFD) modelling is proposed to improve mixing efficiency of a full-scale, unconfined gas-mixed digester for wastewater treatment. The model consists of an Euler–Lagrange (EL) model where biogas bubbles are modelled as the Eulerian dispersed phase, and non-Newtonian sludge as the Lagrangian continuous phase. Robustness tests show that mixing predictions are independent of bubble size. The CFD strategy comprises the assessment of different mixing geometries and a range of input gas flow rates. Quantitative results show that simple retrofitting measures are able to achieve a significant improvement in the degree of mixing with reduced mixing times, and consequently recommendations for best mixing geometry and gas flow rate are given. A generalization to a generic digester is discussed in a form that is readily usable by professionals and consultants.

Multieffects on Mixing Quality of an Active Micromixer

2007 ◽  
Author(s):  
Thien X. Dinh ◽  
Yoshifumi Ogami
Keyword(s):  
Flow Rate ◽  
Pressure Loss ◽  
Rotation Speed ◽  
Mixing Efficiency ◽  
Mean Velocity ◽  
Mixing Performance ◽  
Convective Mixing ◽  
Wide Range ◽  
Computational Fluid Dynamics Cfd

The convective mixing performance of an active micromixer is analyzed by using computational fluid dynamics (CFD). The mixer consists of a Y-shaped channel and an N-paddle (3, 4, and 5) rotor with radius R suspended in the junction of the channel. Numerical simulations are performed for a wide range of rotation speed of the rotor, ω, and mean velocity in the mixer, U. The asymptotic mixing performance is investigated by means of Lagrangian particle tracking simulation, stretching of a material line, dispersive and distributive mixing efficiencies. The results show that the mixing performance depends on the combined variable ωR/U, whereas paddle number has ignorable effects. Physically, the convective ratio of rotation speed to mean velocity governs the mixing process in the mixer. Contrastively, paddle number affects significantly to pressure loss and fluid torque exercising on the rotor. The time-averaged fluid torque depends linearly on rotation speed regardless of flow rate. Pressure loss relates linearly to flow rate, negligibly to rotation speed. It shows that a smaller paddle number produces lesser pressure loss and fluid torque for the same mixing efficiency.

scholarly journals Influence of Modification of the Geometry of the Wave-Plate Mist Eliminators on the Droplet Removal Efficiency—CFD Modelling

Processes ◽  
2021 ◽  
Vol 9 (9) ◽  
pp. 1499
Author(s):  
Łukasz Makowski ◽  
Jakub Łaskowski ◽  
Mariusz Tyrański
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Removal Efficiency ◽  
Continuous Phase ◽  
Physical Parameters ◽  
Drainage Channel ◽  
Cfd Modelling ◽  
Wave Plate ◽  
Drainage Channels ◽  
Computational Fluid Dynamics Cfd

This study is concerned with droplet separation using wave-plate mist separators. The influence of continuous phase velocity, droplet size, and geometry on droplet removal efficiency has been investigated. The following modifications were analysed: drainage channel presence, length, angle, and modification to the streamlined shape. Furthermore, the influence of the physical parameters of the separated substances on separator efficiency was investigated. Calculations were conducted using computational fluid dynamics (CFD). The results were compared with the experimental data from the literature. Based on the results obtained, a new shape of drainage channels was proposed, which is characterised by high droplet removal efficiency with relatively low pressure drop.

Computational Simulation of Mixing Performance in the Circulating Jet Mixing Tank

2016 ◽  
Vol 14 (2) ◽  
pp. 621-636
Author(s):  
Yan-Fang Yu ◽  
Xiu-Hui Jiang ◽  
Hui-Bo Meng ◽  
Jian-Hua Wu ◽  
Zong-Yong Wang ◽  
...  
Keyword(s):  
Turbulent Mixing ◽  
Mixing Time ◽  
Computational Simulation ◽  
Mixed Volume ◽  
Hot Water ◽  
Mixing Times ◽  
Jet Mixing ◽  
Mixing Performance ◽  
Computational Fluid Dynamics Cfd ◽  
Temperature Equilibrium

Abstract Computational fluid dynamics (CFD) was used to investigate the turbulent mixing performance in a vertical CJT in the range of Re=3,668−18,342. Energy source of hot water was centrally placed just below the top of the tank and temperature instead of concentration measurements were used to quantify mixing performance. The 95 % criterion for temperature equilibrium was employed to evaluate the local mixing degree, and the global mixing performance was evaluated based on the ratio of well-mixed volume to total fluid volume. It was obviously observed from the axial distributions of t95 % that the macro-mixing times decreased slightly for z/H < 0.6 and a deep downward trends appeared with the increase of z/H with given r/R. The macro-mixing time in the jet mixing boundary layer were uniform which were a little longer than those in the bulk zones below z/H=0.5 and decreased sharply by 37.5−87.5 % than that in the bulk zone above z/H=0.5. The values of 95 % mixing time increased with the increase of r/R. The global t95 % decreased with the increasing Reynolds number, and a power correlation between the global t95 % values and Re was proposed. With the increasing logarithm of mixing time, the logarithm of segregation intensity rapidly decreased linearly in the slopes from –0.996 to –0.955. The segmentation intensity first decreased then increased with the increasing values of θ.

BIOGAS PRODUCTION IN THE CONCENTRATED DISTILLERY WASTEWATER TREATMENT

2018 ◽  
pp. 51-59 ◽  
Author(s):  
N. Golub ◽  
M. Potapova ◽  
M. Shinkarchuk ◽  
O. Kozlovets
Keyword(s):  
Wastewater Treatment ◽  
Dry Matter ◽  
Ph Value ◽  
Biogas Production ◽  
Anaerobic Sludge ◽  
Methane Formation ◽  
Maximum Output ◽  
Processing Technologies ◽  
Spent Wash ◽  
Distillery Spent Wash

The paper deals with the waste disposal problem of the alcohol industry caused by the widespread use of alcohol as biofuels. In the technology for the production of alcohol from cereal crops, a distillery spent wash (DSW) is formed (per 1 dm3 of alcohol – 10–20 dm3 DSW), which refers to highly concentrated wastewater, the COD value reaches 40 g O2/dm3. Since the existing physical and chemical methods of its processing are not cost-effective, the researchers develop the processing technologies for its utilization, for example, an anaerobic digestion. Apart from the purification of highly concentrated wastewater, the advantage of this method is the production of biogas and highquality fertilizer. The problems of biotechnology for biogas production from the distillery spent wash are its high acidity–pH 3.7–5.0 (the optimum pH value for the methanogenesis process is 6.8–7.4) and low nitrogen content, the lack of which inhibits the development of the association of microorganisms. In order to solve these problems, additional raw materials of various origins (chemical compounds, spent anaerobic sludge, waste from livestock farms, etc.) are used. The purpose of this work is to determine the appropriate ratio of the fermentable mixture components: cosubstrate, distillery spent wash and wastewater of the plant for co-fermentation to produce an energy carrier (biogas) and effective wastewater treatment of the distillery. In order to ensure the optimal pH for methanogenesis, poultry manure has been used as a co-substrate. The co-fermentation process of DSW with manure has been carried out at dry matter ratios of 1:1, 1:3, 1:5, 1:7 respectively. It is found that when the concentration of manure in the mixture is insufficient (DSW/manure – 1:1, 1:3), the pH value decreases during fermentation which negatively affects methane formation; when the concentration of manure in the mixture is increased (DSW/manure – 1:5, 1:7), the process is characterized by a high yield of biogas and methane content. The maximum output of biogas with a methane concentration of 70 ± 2% is observed at the ratio of components on a dry matter “wastewater: DSW: manure” – 0,2:1:7 respectively. The COD reduction reaches a 70% when using co-fermentation with the combination of components “wastewater: DSW: manure” (0,3:1:5) respectively.

Possibilities of joint treatment of spent sugar beet pulp and waste water from a sugar factory

2012 ◽  
pp. 756-761 ◽  
Author(s):  
Miroslav Hutnan ◽  
Štefan Tóth ◽  
Igor Bodík ◽  
Nina Kolesárová ◽  
Michal Lazor ◽  
...  
Keyword(s):  
Wastewater Treatment ◽  
Sugar Beet ◽  
Pilot Plant ◽  
Biogas Production ◽  
Sugar Beet Pulp ◽  
Spare Capacity ◽  
Anaerobic Reactor ◽  
Sugar Factory ◽  
Beet Pulp ◽  
Joint Treatment

The possibility of joint treatment of spent sugar beet pulp and wastewater from a sugar factory was studied in this work. Works focused on processing of spent sugar beet pulp separately or together with other substrates can be found in the literature. In the case of some sugar factories, which have spare capacity in the anaerobic reactor on an anaerobic-aerobic wastewater treatment plant, joint processing of spent sugar beet pulp and wastewater from the sugar factory might be an interesting option. The results of the operation of a pilot plant of an anaerobic reactor with a capacity of 3.5 m3 are discussed. Operation of the pilot plant confirmed the possibility of cofermentation of these materials. The organic loading rate achieved in the anaerobic reactor was higher than 6 kg/(m3·d) (COD), while more than half of the load was provided by spent sugar beet pulp. The addition of sugar beet pulp decreased the concentration of ammonia nitrogen in the anaerobic reactor and it was even necessary to add nitrogen. However, the nitrogen content in sludge water depends on the C:N ratio in the processed sugar beet pulp, therefore this knowledge cannot be generalized. About 1.5 to 2-fold biogas production can be expected from the cofermentation of wastewater with sugar beet pulp in an anaerobic reactor, compared with the biogas production from just wastewater treatment.

scholarly journals Dependence of the Flue Gas Flow on the Setting of the Separation Baffle in the Flue Gas Tract

2021 ◽  
Vol 11 (7) ◽  
pp. 2961
Author(s):  
Nikola Čajová Kantová ◽  
Alexander Čaja ◽  
Marek Patsch ◽  
Michal Holubčík ◽  
Peter Ďurčanský
Keyword(s):  
Particulate Matter ◽  
Flue Gas ◽  
Gas Flow ◽  
Negative Impact ◽  
Combustion Process ◽  
Cfd Simulations ◽  
Piv Measurements ◽  
Computational Fluid Dynamics Cfd ◽  
Particle Imaging ◽  
Combustion Of Solid Fuels

With the combustion of solid fuels, emissions such as particulate matter are also formed, which have a negative impact on human health. Reducing their amount in the air can be achieved by optimizing the combustion process as well as the flue gas flow. This article aims to optimize the flue gas tract using separation baffles. This design can make it possible to capture particulate matter by using three baffles and prevent it from escaping into the air in the flue gas. The geometric parameters of the first baffle were changed twice more. The dependence of the flue gas flow on the baffles was first observed by computational fluid dynamics (CFD) simulations and subsequently verified by the particle imaging velocimetry (PIV) method. Based on the CFD results, the most effective is setting 1 with the same boundary conditions as those during experimental PIV measurements. Setting 2 can capture 1.8% less particles and setting 3 can capture 0.6% less particles than setting 1. Based on the stoichiometric calculations, it would be possible to capture up to 62.3% of the particles in setting 1. The velocities comparison obtained from CFD and PIV confirmed the supposed character of the turbulent flow with vortexes appearing in the flue gas tract, despite some inaccuracies.

scholarly journals The Hydrodynamics and Mixing Performance in a Moving Baffle Oscillatory Baffled Reactor through Computational Fluid Dynamics (CFD)

Processes ◽  
2020 ◽  
Vol 8 (10) ◽  
pp. 1236
Author(s):  
Hamid Mortazavi ◽  
Leila Pakzad
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Dispersion Coefficient ◽  
Velocity Ratio ◽  
Axial Dispersion ◽  
Shear Strain Rate ◽  
Turbulent Length Scale ◽  
Mixing Performance ◽  
Axial Dispersion Coefficient ◽  
Computational Fluid Dynamics Cfd

Oscillatory baffled reactors (OBRs) have attracted much attention from researchers and industries alike due to their proven advantages in mixing, scale-up, and cost-effectiveness over conventional stirred tank reactors (STRs). This study quantitatively investigated how different mixing indices describe the mixing performance of a moving baffle OBR using computational fluid dynamics (CFD). In addition, the hydrodynamic behavior of the reactor was studied, considering parameters such as the Q-criterion, shear strain rate, and velocity vector. A modification of the Q-criterion showed advantages over the original Q-criterion in determination of the vortices’ locations. The dynamic mesh tool was utilized to simulate the moving baffles through ANSYS/Fluent. The mixing indices studied were the velocity ratio, turbulent length scale, turbulent time scale, mixing time, and axial dispersion coefficient. We found that the oscillation amplitude had the most significant impact on these indices. In contrast, the oscillatory Reynolds number did not necessarily describe the mixing intensity of a system. Of the tested indices, the axial dispersion coefficient showed advantages over the other indices for quantifying the mixing performance of a moving baffle OBR.

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