magazine

“Rotary dryers are the most proven and
preferred method to dry frac sand…a
rotary dryer allows the user to vary the
mass air flow for different moisture content
levels or operation at lower throughputs.
deposits are already being exploited because
of the numerous uses for the material
in a variety of industrial applications, including
glass making and filtration media.
The way in which frac sand is mined
and processed depends on the location
and quality of the sand deposit. In general,
though, a typical frac sand flow sheet
is made up of wet flow and dry flow. The
goal of wet flow is to eliminate clay slimes
and disintegrate any agglomerates, or
clumps of material.
This portion of the flow sheet can also
act as a preliminary sizing by rejecting excess
fines—a process that is much more cost-effective
if performed wet instead of dry. The
first step in wet processing is to remove any
clay. The sand is washed with water and then
pumped to a cyclone for “desliming.” Slimes
are materials that are usually in the form of
clays or very fine silica. Since these materials
are often harmful to frac sand processing,
they must be removed through the use of
classifiers.
In the dry flow portion, the sand is sized
into a variety of products and any magnetic
contaminants are removed because they
would impede both crush and acid solubility.
Sizes vary, but the most commonly used
for frac sand are 12/20, 20/40, 40/70 and
70/140 mesh.
Shape and size have a significant effect
on the sand’s final permeability through the
fracture. A wide variety of particle shapes
and sizes will result in a tight packing arrangement,
reducing conductivity and permeability.
A controlled range of sizes and a
spherical shape, however, will lead to greater
conductivity.
Frac sand drying
solution
Rotary dryers are the most proven and
preferred method to dry frac sand. A varying
total petroleum hydrocarbons (TPH) rate
can often have a substantial effect on the efficiency
of the drying process. A rotary dryer
allows the user to vary the mass air flow for
different moisture content levels or operation
at lower throughputs.
In contrast, a fluid bed dryer features a
drying gas medium that must produce heat
for the drying process while also conveying
the material. Because the mass air flow
must stay constant, a fluid bed dryer can only
be turned down by decreasing the inlet gas
temperature, which has a detrimental effect
on efficiency. Fluid bed dryers also require
an increase in fluidizing velocities for larger
particles, resulting in high power usage and
lower evaporation and efficiency.
Rotary dryers, however, are far more efficient
and capable of enduring the varying
production requirements that accompany
different drying projects. A rotary dryer
is a sturdy piece of equipment that, when
well-built and maintained, can have maintenance
costs that are comparable to a fluid
bed dryer.
Dryers are available in countercurrent and
concurrent flow models. In concurrent flow,
the burner and feed system are located on the
same end of the dryer and the material and
exhaust gas exit the dryer on the opposite
end. The primary advantage of using a concurrent
flow dryer is the direct relationship
between the dryness of the product and the
temperature of the exhaust gas. This allows
the dryer to adjust to changes in feed conditions
in seconds, rather than minutes.
Dryers can be used at both the beginning
and the end of the fracking process. Prior to
its transportation to and use at a job site, frac
sand must be dried and treated. After the
process is completed, the waste fluids that
remain form a sludge. Dryers can extract the
liquid from this sludge and then turn it back
into a solid for proper disposal.
Custom-built Vulcan rotary dryers are
available from companies like Worldwide
Recycling Equipment Sales, LLC. The line of
rotary dyers can be manufactured to suit any
job site or drying application, including frac
sand. The units are available in direct or indirect
heated models and feature burners ranging
from one to 30 MMBtu and rotary drums
ranging from 18 to 70 feet with a variety of diameters.
Vulcan rotary kilns are ideal for quick
and efficient drying of numerous materials in a
wide range of industries, from soil remediation
to food processing to mining.
GET TO KNOW OUR
EXPERTS
SAVANNAH COOPER
Savannah Cooper attended Lincoln
University and works at Worldwide Recycling
Equipment Sales, which focuses on
the waste processing, recycling and environmental
process equipment industry.
BASIN BITS | Spring 2014 71