Technical Details for the Sand Washing Process

The use of ultrasonic energy for processing slurries containing sand and other fine granular materials has been in use for many years. Historically, the ultrasonic equipment available for this application, while providing exciting results were unreliable, required considerable maintenance and oversight, discharged the processed slurry at atmospheric pressure, and did not provide a reasonable service life. Advanced Sonic Processing Systems now manufactures a new generation ultrasonic slurry processing system; the Quad-Frequency Tubular Reactor, which addresses all of these issues and is ideal for these applications. Advanced Sonics offers a 10-Year transducer warranty for equipment placed into service for these demanding applications.

Benefits of Using Ultrasonic Energy for Sand Cleaning are:

Ultrasonically cleaned Jordan Sandstone

Ultrasonically Cleaned Sand with 0.7 seconds of Exposure Time

(Photographs courtesy of Phoenix Environmental Reclamation, LLC)

The above photographs show sand samples Before and After Ultrasonic Cleaning of Jordan complex sandstone, (ultrasonic exposure time less than 0.7 seconds @ 175 GPM and 25% Solids). Note how the Ultrasonic Cleaning Process is effective in removing clays and slimes encasing the individual sand particles. Ultrasonic Cleaning with just water (no additives) is very effective in reducing the Turbidity to acceptable levels. Ultrasonic Cleaning is the answer to attaining a higher quality product with a lower production cost.

The Effects of Ultrasonic Energy on Particles and Slurries

When ultrasonic energy is transmitted into a fluid, pressure waves move through the fluid that are produced at the same frequency, alternating in high and low pressure transients in the fluid. As the applied energy, or power is increased sufficiently, the vapor pressure of the fluid will exceed the pressure of the fluid in the low pressure transients, producing microscopic bubbles that will collapse during the high pressure phase of the transmission. At the point of collapse, the localized temperatures, pressures and fluid velocities have been calculated to be significant. This collapse is referred to as cavitation. When this cavitation occurs near the surface of a particle, material adhering to the particle can be removed from the surfaces of the particle. Once removed from the surface of the particle, the effect has been shown to remain in effect long enough to allow subsequent solid/liquid separation techniques to be more efficiently employed. The very high localized temperatures and pressures produced by cavitation likely result in chemical reactions that reduce the potential for immediately revering the separation. In typical applications, hydrated clays attached and envelop individual particles, modifying the physical attributes of each particle: the apparent specific gravity, cohesive attachment, and the physical size of a particle is affected. Cavitation, produced by ultrasonic transmission into a slurry, is effective in reducing, if not eliminating the clay association, suspending the clay in the fluid pending separation of the particles from the fluid in the slurry. Separation of the fluid from the particles and subsequent drying of the particles become more efficient unit operations. As a result of applying ultrasonics as a
pre-treatment to the slurry:

ultrasonically clean frac sand for a turbidity of <10 NTU's
the product is more easily and efficiently separated from the fluid in the slurry
the cost of drying is reduced
quality and recovery of the product is improved
the dried product will be more uniformly sized
the dried product will be more free flowing
the dried product will generate less dust during product handling
the dried product will exhibit reduced agglomeration potential
the dried product will be more efficiently beneficiated, separating product from gangue
the clay remains in suspension in the fluid, pending disposal or further processing

Cavitation is effective in uniformly dispersing reagents throughout the fluid. In most applications, ultrasonics can reduce reagent dosage. This attribute has particular application to froth flotation systems. The combination of a cleaner particle surface and a more uniform dispersion of the reagents in the fluid produces a situation where both product quality and recovery are improved. Particles stripped of clay exhibit an elevated settling velocity which accelerates separation of solids in settling ponds and typically increases the density of the settled solids.

Cavitation is an effective method for eliminating dissolved gases in a fluid. This phenomena can be useful for controlling the growth of algae.

Ultrasonic Application for Processing Sand Used in Well Bore Fracturing

The petroleum industry has developed and is currently dependent on several techniques used to recover oil and gas from wells drilled in shale formations. Directional drilling and formation fracturing increase the productive capacity from a location. Of particular interest is the fracturing of the formation and the method used to maintain the fracture after the process is complete. Sand or a similar material is pushed into the newly formed fracture to maintain the permeability and porosity required for the oil, gas and brine to migrate to the bore and ultimately pumped to the surface.
The fine grained sand is composed of particles typically smaller than 0.2 mm (0.0083 inch). The sand injected into the fractures of the formation is intended to maintain the fracture and provide a conduit for oil, gas and brine to migrate from the formation to the well bore. Size distribution and purity of the sand is critical. A wide range of particle sizes will reduce the void volume between particles. Clay, the most likely contaminant associated with the sand can fill the void volume. Both uncontrolled size distribution and sand contaminants such as clay reduce the porosity and thus the permeability of the sand injected into the fracture. This reduces the flow of oil, gas and brine to the well bore.

Sand with an appreciable distribution of clay is difficult to size, representing the genesis of issues limiting the ability to provide a sand product with superior properties. Conventional techniques employed to process sand produce marginal results. Washing sand does not adequately reduce the clay association, resulting in difficult unit operations for screening and drying. Dry screening does not materially address the clay associated with sand. Ultimately, the dried clay coating the surface of the conventionally processed sand may be difficult to wet uniformly, result in agglomerated particles, and expand after injection into the fractures and occlude the injected sand.

Processing the sand slurry prior to screening and drying can result in a final sand product more uniformly sized and free of the clay that can expand after injection. Particle wetting and agglomeration are eliminated making slurry preparation for well bore injection into the formation fractures trouble free.

Frack Sand Processing Using the Quad-Frequency Tubular Reactor

The Quad-Frequency Tubular Reactor offers all of the processing advantages provided by previous generations of slurry processing configurations, but represents a quantum step up regarding reliability, service life, and pressurized flow capability. This reactor can process slurry continuously for extended periods without continuous supervision. The slurry can be presented under pressure, discharging the slurry at near inlet pressure. Indeed, Advanced Sonics, LLC offers the unit with a 10 year transducer warranty. Capital and operating costs will be recovered quickly, based on typical feed and product sand quality: additional considerations should be given to increased high quality sand recovery. The standard 6 inch Quad-Frequency Reactor, can process about 350,000 tons of solids per year with an operating cost of less than $0.03 per ton of solids processed.

Written for Advanced Sonics, LLC by:

Harry Bonner
23 Country Estates Drive
Sheridan, WY 82801
Phone: 406-855-4841
E Mail: hsbonner@earthlink.net

Laboratory Sand Washing Trials and Photographs by:
Gary Liubakka
Phoenix Environmental Reclamation, LLC
2624 3rd Avenue East
Hibbing, MN 55746
Phone: 218-403-1866
E Mail: liubakkagary@yahoo.com

Ultrasonic Equipment is Available from Advanced Sonics, LLC
David Hunicke
Advanced Sonics, LLC
324 Christian Street
Oxford, CT 06478
Phone: 203-266-4440
Email: d.hunicke@advancedsonics.com
Website: www.zhendechuan.cn