scholarly journals Modelling Mechanically Induced Non-Newtonian Flows to Improve the Energy Efficiency of Anaerobic Digesters

Water ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 2995
Author(s):  
Andrew Oates ◽  
Thomas Neuner ◽  
Michael Meister ◽  
Duncan Borman ◽  
Miller Camargo-Valero ◽  
...  
Keyword(s):  
Power Consumption ◽  
Anaerobic Digester ◽  
Full Scale ◽  
Operating Conditions ◽  
Cfd Model ◽  
Total Solids ◽  
Helical Ribbon ◽  
Newtonian Flows ◽  
Solids Concentration ◽  
Water Glycerol

In this paper, a finite volume based computational fluid dynamics (CFD) model has been developed for investigating the mixing of non-Newtonian flows and operating conditions of an anaerobic digester. A CFD model using the multiple reference frame has been implemented in order to model the mixing in an anaerobic digester. Two different agitator designs have been implemented: a design currently used in a full-scale anaerobic mixing device, SCABA, and an alternative helical ribbon design. Lab-scale experiments have been conducted with these two mixing device designs using a water-glycerol mixture to replicate a slurry with total solids concentration of 7.5%, which have been used to validate the CFD model. The CFD model has then been scaled up in order to replicate a full-scale anaerobic digester under real operating parameters that is mechanically stirred with the SCABA design. The influence of the non-Newtonian behaviour has been investigated and found to be important for the power demand calculation. Furthermore, the other helical mixing device has been implemented at full scale and a case study comparing the two agitators has been performed; assessing the mixing capabilities and power consumption of the two designs. It was found that, for a total solids concentrations of 7.5%, the helical design could produce similar mixing capabilities as the SCABA design at a lower power consumption. Finally, the potential power savings of the more energy efficient helical design has been estimated if implemented across the whole of the United Kingdom (UK)/Austria.

scholarly journals Enhancing Efficiency of Anaerobic Digestion by Optimization of Mixing Regimes Using Helical Ribbon Impeller

Fermentation ◽  
2021 ◽  
Vol 7 (4) ◽  
pp. 251
Author(s):  
Buta Singh ◽  
Kornél L. Kovács ◽  
Zoltán Bagi ◽  
József Nyári ◽  
Gábor L. Szepesi ◽  
...  
Keyword(s):  
Model Simulation ◽  
Biogas Production ◽  
Scale Up ◽  
Anaerobic Digester ◽  
Operating Conditions ◽  
Mixing Efficiency ◽  
Dead Zones ◽  
Helical Ribbon ◽  
Significant Difference ◽  
Mixing Intensity

The appropriate mixing system and approach to effective management can provide favorable conditions for the highly sensitive microbial community, which can ensure process stability and efficiency in an anaerobic digester. In this study, the effect of mixing intensity on biogas production in a lab-scale anaerobic digester has been investigated experimentally and via modeling. Considering high mixing efficiency and unique feature of producing axial flow, helical ribbon (HR) impeller is used for mixing the slurry in this experiment under various conditions. Three parallel digesters were analyzed under identical operating conditions for comparative study and high accuracy. Effects of different mixing speeds (10, 30, and 67 rpm for 5 min h−1) on biogas production rate were determined in 5-L lab-scale digesters. The results demonstrated 15–18% higher biogas production at higher mixing speed (67 rpm) as compared to 10 rpm and 30 rpm and the results proved statistically significant (p < 0.05). Biogas production at 10, 30, and 67 rpm were 45.6, 48.6, and 52.5 L, respectively. Higher VFA concentrations (7.67 g L−1) were recorded at lower mixing intensity but there was no significant difference in pH and ammonia at different speeds whereas the better mixing efficiency at higher speeds was also the main reason for increase in biogas production. Furthermore, model simulation calculations revealed the reduction of dead zones and better homogeneous mixing at higher mixing speeds. Reduction of dead zones from 18% at 10 rpm to 2% at 67 rpm was observed, which can be the major factor in significant difference in biogas production rates at various mixing intensities. Optimization of digester and impeller geometry should be a prime focus to scale-up digesters and to optimize mixing in full-scale digesters.

Prediction of full-scale dewatering results of sewage sludges by the physical water distribution

2001 ◽  
Vol 43 (11) ◽  
pp. 135-143 ◽  
Author(s):  
J. Kopp ◽  
N. Dichtl
Keyword(s):  
Sewage Sludge ◽  
Water Content ◽  
Water Distribution ◽  
Free Water ◽  
Full Scale ◽  
Water Release ◽  
Total Solids ◽  
Solids Concentration ◽  
Free Water Content ◽  
Sludge Cake

The dewaterabilty of sewage sludge can be described by the total solids concentration of the sludge cake and the polymer-demand for conditioning. The total solids concentration of the sludge cake depends on the physical water distribution. The various types of water in sewage sludge are mainly distinguished by the type and the intensity of their physical bonding to the solids. In a sewage sludge suspension four different types of water can be distinguished. These are the free water, which is not bound to the particles, the interstitial water, which is bound by capillary forces between the sludge flocs, the surface water, which is bound by adhesive forces and intracellular water. Only the share of free water can be separated during mechanical dewatering. It can be shown, that by thermo-gravimeteric measurement of the free water content, an exact prediction of full-scale dewatering results is possible. By separation of all free water during centrifugation the maximum dewatering result is reached. Polymer conditioning increases the velocity of the sludge water release, but the free water content is not influenced by this process. Furthermore it is not possible, to replace the measuring of the water distribution by other individual parameters such as ignition loss.

Multidimensional Numerical Modeling of Combustion Dynamics in a Non-Premixed Rotating Detonation Engine with Adaptive Mesh Refinement

2021 ◽  
pp. 1-32
Author(s):  
Pinaki Pal ◽  
Gaurav Kumar ◽  
Scott Drennan ◽  
Brent Rankin ◽  
Sibendu Som
Keyword(s):  
Performance Optimization ◽  
Adaptive Mesh Refinement ◽  
Design Space Exploration ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Full Scale ◽  
Operating Conditions ◽  
Cfd Model ◽  
Combustion Dynamics ◽  
Frequency Wave

Abstract In the present work, a novel computational fluid dynamics (CFD) methodology was developed to simulate full-scale non-premixed RDEs. A unique feature of the modeling approach was incorporation of adaptive mesh refinement (AMR) to achieve good trade-off between model accuracy and computational expense. Unsteady Reynolds-Averaged Navier-Stokes (RANS) simulations were performed for an Air Force Research Laboratory (AFRL) non-premixed RDE configuration with hydrogen as fuel and air as the oxidizer. The finite-rate chemistry model along with a 10-species detailed kinetic mechanism were employed to describe the H2-Air combustion chemistry. Three distinct operating conditions were simulated, corresponding to the same global equivalence ratio of unity but different fuel/air mass flow rates. For all conditions, the capability of the model to capture essential detonation wave dynamics was assessed. An exhaustive verification and validation study was performed against experimental data in terms of number of waves, wave frequency, wave height, reactant fill height, oblique shock angle, axial pressure distribution in the channel, and fuel/air plenum pressure. The CFD model was demonstrated to accurately predict the sensitivity of these wave characteristics to the operating conditions, both qualitatively and quantitatively. A comprehensive heat release analysis was conducted to quantify detonative versus deflagrative burning for the three simulated cases. The present CFD model offers a potential capability to perform rapid design space exploration and/or performance optimization studies for realistic full-scale RDE configurations.

Prediction of full-scale dewatering results by determining the water distribution of sewage sludges

2000 ◽  
Vol 42 (9) ◽  
pp. 141-149 ◽  
Author(s):  
J. Kopp ◽  
N. Dichtl
Keyword(s):  
Sewage Sludge ◽  
Water Content ◽  
Water Distribution ◽  
Free Water ◽  
Full Scale ◽  
Water Release ◽  
Total Solids ◽  
Solids Concentration ◽  
Free Water Content ◽  
Sludge Cake

Dewaterability of sewage sludge can be described by the total solids concentration of the sludge cake and by the polymer-demand for conditioning. Total solids concentration of the sludge cake depends on the physical water distribution. The various types of water in sewage sludge are mainly distinguished by type and intensity of their physical bonding to the solids. In a sewage sludge suspension four different types of water can be distinguished. These are free water, which is not bound to the particles, interstitial water, which is bound by capillary forces between the sludge flocs, surface water, which is bound by adhesive forces, and intracellular water. Only free water can be separated during mechanical dewatering. It can be shown, that thermo-gravimeteric measurement of the free water content leads to an exact prediction of full-scale dewatering results. Maximum dewatering results are reached by separating all free water during centrifugation. Polymer conditioning increases the velocity of thesludge water release, but the free water content is not influenced by this process. Furthermore it is not possible, to replace the measuring of the water distribution by other individual parameters such as ignition loss.

A pilot web former designed to study retention-formation relationships

2010 ◽  
Vol 25 (2) ◽  
pp. 185-194
Author(s):  
Anna Svedberg ◽  
Tom Lindström
Keyword(s):  
Pilot Scale ◽  
Operating Conditions ◽  
Montmorillonite Clay ◽  
Speed Ratio ◽  
Good Reproducibility ◽  
Total Solids ◽  
Retention Aids ◽  
Solids Content ◽  
Relationship Of ◽  
The Relationship

Abstract A pilot-scale fourdrinier former has been developed for the purpose of investigating the relationship between retention and paper formation (features, retention aids, dosage points, etc.). The main objective of this publication was to present the R-F (Retention and formation)-machine and demonstrate some of its fields of applications. For a fine paper stock (90% hardwood and 10% softwood) with addition of 25% filler (based on total solids content), the relationship between retention and formation was investigated for a microparticulate retention aid (cationic polyacrylamide together with anionic montmorillonite clay). The retention-formation relationship of the retention aid system was investigated after choosing standardized machine operating conditions (e.g. the jet-to-wire speed ratio). As expected, the formation was impaired when the retention was increased. Since good reproducibility was attained, the R-F (Retention and formation)-machine was found to be a useful tool for studying the relationship between retention and paper formation.

A Critical Look into the Deviation of Full Scale Performance from Design Expectations

1989 ◽  
Vol 21 (10-11) ◽  
pp. 1389-1402 ◽  
Author(s):  
R. Zaloum
Keyword(s):  
Expert Systems ◽  
Waste Treatment ◽  
Full Scale ◽  
Operating Conditions ◽  
Organic Load ◽  
Computer Assisted ◽  
Uniform Load ◽  
Effluent Quality ◽  
Simulation Techniques ◽  
Steady Level

Deviations from design expectations appear to stem from views which assume that a unique response should result from a given set of operating conditions. The results of this study showed that two systems operating at equal organic loads or F/M ratios and at the same SRT do not necessarily give equal responses. This deviation was linked to the manner in which the HRT and influent COD are manipulated to obtain a constant or uniform load, and to subtle interactions between influent COD, HRT and SRT on the biomass and effluent responses. Increases of up to 200% in influent COD from one steady level to the next did not significantly influence the effluent VSS concentration while an effect on filtered COD was observed for increases as low as 20%. Effluent TKN and filtered COD correlated strongly with the operating MLVSS while phosphorus residual depended on the operating SRT and the organic load removed. These results point to the inadequacy of traditional models to predict effluent quality and point to the need to consider these effects when developing simulation techniques or computer assisted expert systems for the control of waste treatment plants.

scholarly journals Evaporator Optimization of Refrigerator Systems Using Quality Analysis

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 555
Author(s):  
Sangkyung Na ◽  
Sanghun Song ◽  
Seunghyuk Lee ◽  
Jehwan Lee ◽  
Hyun Kim ◽  
...  
Keyword(s):  
Power Consumption ◽  
Operating Time ◽  
Cooling Capacity ◽  
Operating Conditions ◽  
Quality Analysis ◽  
Lubricating Oil ◽  
Optimal Operating ◽  
Compressor Piston ◽  
Refrigerator Temperature ◽  
Visualization Experiments

In this study, evaporator optimization, via both experimental and simulation methods was conducted. To evaluate the evaporator performance, under the optimal system, the compressor operating time and the effects of oil on the refrigerator system were studied. If the temperature of the refrigerator chamber reaches the setting value, the compressor stops working and it leads to the temperature of the refrigerator chamber slowly increasing, due to the heat transfer to the ambient. When the refrigerator temperature is out of the setting range, the compressor works again, and the refrigerator repeats this process until the end of its life. These on/off period can be controlled through the compressor piston movement. To determine the optimal compressor operating conditions, experiments of monthly power consumption were conducted under various compressor working times and the lowest power consumption conditions was determined when the compressor worked continuously. Lubricating oil, the refrigerator system, using oil, also influenced the system performance. To evaluate the effect of oil, oil eliminated and oil systems were compared based on cooling capacity and power consumption. The cooling capacity of the oil eliminated system was 2.6% higher and the power consumption was 3.6% lower than that of the oil system. After determining the optimal operating conditions of the refrigerator system, visualization experiments and simulations were conducted to decide the optimal evaporator and the conventional evaporator size can be reduced by approximately 2.9%.

A Transient 3D CFD Model of a Progressive Cavity Pump

2016 ◽  
Author(s):  
K. R. Mrinal ◽  
Md. Hamid Siddique ◽  
Abdus Samad
Keyword(s):  
Oil And Gas ◽  
Complex Geometry ◽  
Transient Behavior ◽  
Oil And Gas Industry ◽  
High Viscosity ◽  
Solid Content ◽  
Operating Conditions ◽  
Cfd Model ◽  
Ansys Fluent ◽  
Flow Variables

A progressive cavity pump (PCP) is a positive displacement pump and has been used as an artificial lift method in the oil and gas industry for pumping fluid with solid content and high viscosity. In a PCP, a single-lobe rotor rotates inside a double-lobe stator. Articles on computational works for flows through a PCP are limited because of transient behavior of flow, complex geometry and moving boundaries. In this paper, a 3D CFD model has been developed to predict the flow variables at different operating conditions. The flow is considered as incompressible, single phase, transient, and turbulent. The dynamic mesh model in Ansys-Fluent for the rotor mesh movement is used, and a user defined function (UDF) written in C language defines the rotor’s hypocycloid path. The mesh deformation is done with spring based smoothing and local remeshing technique. The computational results are compared with the experiment results available in the literature. Thepump gives maximum flowrate at zero differential pressure.

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