Continuous Miniaturized Draft Tube Baffle Crystallizer with Particle Screw for Supportive Suspension Discharge

The effect of the ratio of draft tube diameter to reactor diameter (Di/Do) on the efficiency of nitrogen removal from domestic sewage is discussed based on liquid-circulating flow rate and continuous treatment data. More than 2.5 minutes of circulation time in the annulus part, which is required to create an anoxic zone, could be maintained under operating conditions in which air flow rate per reactor volume was 2 m3/(m3 · hr) and Di/Do was 0.19. When Di/Do was set at 0.19, the average total organic carbon (TOC), total nitrogen (TN) and dissolved nitrogen (DN) removal efficiencies were 83.2%, 72.1% and 71.6%, respectively, which were higher than those when Di/Do was at 0.26 or 0.36. From these results, it is concluded that 0.19 is the best Di/Do for nitrogen removal in a draft-tube type reactor with an effective depth of 4.0m under the treatment condition in which the BOD volumetric loading rate is in the range 0.22 to 0.46 kgBOD/(m3 · day). More than 80% nitrification and denitrification efficiencies can be achieved simultaneously when both conditions, the aerobic zone ratio being more than 0.2, and the anoxic zone ratio being more than 0.3, are satisfied.

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Proper orthogonal decomposition of turbulent swirling flow of a draft tube at part load

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/774/1/012091 ◽

2021 ◽

Vol 774 (1) ◽

pp. 012091

Author(s):

S Kumar ◽

S Khullar ◽

M J Cervantes ◽

B K Gandhi

Keyword(s):

Proper Orthogonal Decomposition ◽

Swirling Flow ◽

Draft Tube ◽

Orthogonal Decomposition ◽

Part Load ◽

Proper Orthogonal

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Effect of Air Injection on the Internal Flow Characteristics in the Draft Tube of a Francis Turbine Model

Processes ◽

10.3390/pr9071182 ◽

2021 ◽

Vol 9 (7) ◽

pp. 1182

Author(s):

Seung-Jun Kim ◽

Yong Cho ◽

Jin-Hyuk Kim

Keyword(s):

Flow Rate ◽

Draft Tube ◽

Pressure Fluctuations ◽

Flow Characteristics ◽

Internal Flow ◽

Air Injection ◽

Low Flow ◽

Francis Turbine ◽

Navier Stokes ◽

Vortex Rope

Under low flow-rate conditions, a Francis turbine exhibits precession of a vortex rope with pressure fluctuations in the draft tube. These undesirable flow phenomena can lead to deterioration of the turbine performance as manifested by torque and power output fluctuations. In order to suppress the rope with precession and a swirl component in the tube, the use of anti-swirl fins was investigated in a previous study. However, vortex rope generation still occurred near the cone of the tube. In this study, unsteady-state Reynolds-averaged Navier–Stokes analyses were conducted with a scale-adaptive simulation shear stress transport turbulence model. This model was used to observe the effects of the injection in the draft tube on the unsteady internal flow and pressure phenomena considering both active and passive suppression methods. The air injection affected the generation and suppression of the vortex rope and swirl component depending on the flow rate of the air. In addition, an injection level of 0.5%Q led to a reduction in the maximum unsteady pressure characteristics.

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