The VLM Mixer™ uses vertical linear motion technology to create a distinct flow pattern that produces highly efficient mixing.
Due to the combined effects of oscillating velocity and pulsating pressure waves, true isotropic mixing keeps all grit in suspension with 100% axial flow patterns and low energy consumption.
Most conventional mixers, on the other hand, use a circular motion to “stir” liquid. This requires a large quantity of power, as well as expensive digester cleaning protocols to remove scum and sediment build-up.
The innovative cam-scotch-yoke electric motor system operates above the tank.
The shaft transfers the up-and-down motion to the hydro-disk.
The hydro-disk is the heart of the mixing process, producing 100% axial mixing through momentum exchange.
The energized currents continually flow, eliminating surface scum and floor sediment.
The oscillating velocity and pressure waves enhance mass transfer to produce a homogeneous mixture.
The Computational Fluid Dynamics (CFD) process is available to meet unique mixing needs.
The frequency (or oscillating speed), the stroke length, and the size and positioning of the hydro-disk control the force and velocity of the liquid core. By varying these four elements according to each tank’s configuration, we can meet the mixing needs of a wide variety of operations.
The CFD process allows for:
Parameter | Value | Comment |
Diameter (ft) | 90 | - |
Overall tank height (ft) | 52 | Cylindrical tank plus bottom |
Maximum sludge elevation (ft) | 38 | From bottom of cylinder |
Conical height (ft) | 8.5 | From bottom apex |
Cylindrical height (ft) | 40 | Total wall height |
Maximum tank capacity (gal) | 2,000,000 | Sludge bulk volume |
Parameter | Value | Comment |
Sludge inlet diameter (in) | (2) 6ӯ | TWAS & thickened PS lines |
Sludge Inlet Pipe Elevation above bottom wall (ft) | 8 | Changed from 16.11 ft |
Parameter | Value | Comment |
Sludge outlet diameter (in) | 6ӯ | - |
Sludge outlet pipe elevation (ft) | 2162.5 | 12.5 below bottom of the wall |
Parameter | Value | Comment |
Bulk density (kg/m3) | 1,034.2 | Typical value |
Viscosity (cP) | 265 | - |
Sludge flow rate (gpm) | 92.6 | Estimated |
Parameter | Value | Comment |
Density (kg/m3) | 2,650 | Grit particles (worst case) |
Solids content (% wt) | 3.5 | Average grit and organics |
Solids particle size (μm) | 100-150 | Typical grit size (worst case) |
Parameter | Value | Comment |
Bulk density (kg/m3) | 1,034.2 | Same as sludge |
Viscosity (cP)) | 265 | Same as sludge |
Concentration (mg/L) | 7.5 | Lithium Chloride solution |
Flow rate (kg/s) | 3.48 | - |
Injection duration (s) | 15 | - |
Elevation of injection location (ft) | 8 | At sludge intake |
Parameter | Value | Comment | |
Point 1 | Circulated sludge out, elevation(ft) | 2175.5 | Radial distance 44.5 ft |
Point 2 | Primary sludge out, bottom cone (ft) | 2163 | Tank axis |
Point 3 | Sampling port 1 elevation (ft) | 2212.5 | Radial distance 40 ft |
Point 4 | Sampling port 1 elevation (ft) | 2198.5 | Radial distance 40 ft |
Point 5 | Sampling port 1 elevation (ft) | 2176.5 | Radial distance 40 ft |
Point 6 | Sampling port 2 elevation (ft) | 2212.5 | Radial distance 10 ft |
Point 7 | Sampling port 2 elevation (ft) | 2198.5 | Radial distance 10 ft |
Point 8 | Sampling port 2 elevation (ft) | 2176.5 | Radial distance 10 ft |
Parameter | Value | Comment |
Outer diameter (in) | 96 | - |
Inner diameter (in) | 64 | - |
Stroke length (in) | 20 | Changed from 16 inch |
Oscillating frequency (cpm) | 32 | Changed from 30 cpm |
Bottom of stroke location (ft) | 20 | Above bottom tank cone |
Tracer concentration at sample probe locations. Results indicate that after 1 hour 50 minutes of mixing the sample probes depict asymptotic behavior of the tracer approaching mean concentration value “MEAN”. The asymptotic trend of all probe concentrations indicates complete mixing. (The MEAN concentration corresponds to 6.0E-5).
The histogram chart indicates that about 90% of the tank volume is fully mixed. The 90% mixed volume corresponds to the tracer concentration of 5.762E-5 (which is very close to the mean value of 6.0E-5). Also, the results indicate that about 8% of the tank volume has tracer concentration of 3.601E-5.
Two-dimensional view across a vertical plane parallel to the sludge intake. Zones of highest velocity (max 0.86 m/s) correspond to the hydro-disk location. The average tank (bulk) velocity is about 0.012 m/s and is distributed nearly uniform in the whole tank. This uniform velocity creates isotropic turbulence resulting in uniform mixing when coupled with oscillating pressure waves.
Two-dimensional view across a vertical plane at 5 meter high from tank bottom. The velocity is clipped at 0.012 m/s which corresponds to the tank mean (bulk) velocity. The flow pattern indicates that the mean velocity is uniformly distributed across the tank diameter, consequently providing uniform mixing of the whole tank.
The VLM Mixer™ is a top-entry mixer that can be installed in both new and existing tanks. When compared with conventional mixing systems, installation is simple and costs are low.
Installation features:
A. For a VLM Mixer™, the energy required for a given mixing performance (such as in an Anaerobic Digester) is only a small fraction of the energy that would have been consumed in conventional mixers. This is because the VLM Mixer™ produces a purely radial/axial circulation, whereas rotary mixers (such as impellers or turbines) produce rotary fluid motion.
A. When the reciprocating disk is located at the centre of a large tank, a circulation pattern is produced with a central up-flow above the disk and a central down-flow below the disk. The liquid circulates outwards through the tank and returns inwards towards the reciprocating disk. Two circulation loops are formed when the disk is located half-way in the fluid level. However, if the Hydro-Disk is moved closer to the bottom of the tank, a single circulation loop is formed.
A. The reciprocating hydro-disk which generates an upward-moving liquid core on each downstroke, and a downward-moving core of liquid on each upstroke. These high-energy cores (macro-eddies), which are continuously produced, dissipate into the liquid and create a steady bulk circulation in the tank. The tank volume can be several orders greater than the volume swept by the drive disk. Although the hydro-disk is oscillating, the majority of the liquid in the tank does not oscillate, but instead circulates in response to the directional movement from the hydro-disk.
A. Yes, the VLM Mixer™ can be installed on existing tanks, with any digester cover that can withstand the additional loads of the mixer. These can include concrete covers, radial beam steel covers (either floating or fixed) and truss covers. The mixer is designed for the center of the digester, so prior to installation, we verify the location of the gas collection piping, gas handling equipment and any other interior piping. Also, one should verify that the digester cover has sufficient structural strength to withstand the mixer’s loads.
A. With conventional mixers, scum and solids gradually build up in digesters. Over time, tank volume is reduced, mixing becomes less effective, and the entire digester needs to be shut down, emptied and professionally cleaned. Because VLM Mixers™ generate axial mixing, the continuous flow keeps grit in suspension and prevents sediments from accumulating. Companies with VLM technology report that these cleaning protocols, and the costs associated with them, are rendered almost completely unnecessary.
A. The shaft and hydro-disk are constructed out of stainless steel and have no mechanical parts below the mounting flange that would require regular maintenance. This means that the shaft and hydro-disk do not need to be removed from their mounting location for maintenance. Rather, all the components that will wear are easily accessible in the drive head, above the cover and outside the tank.