Chemical Engineering April 2012 - 46

Feature Report
Table 3. lisT of quesTions To
consider when selecTing a
sampler
Is the material free-flowing?
Is the material abrasive?
Is the material friable?
Does the material have a broad
size distribution?
Is the material dusty?
What is the largest particle
diameter
Is the material temperature sensitive?
Is
the process enclosed?
Are the particles dispersed in
gas phase?
Intersystems
Figure 4. Rotary chute sampler
As a rule of thumb, incremental
extraction errors can be minimized
by limiting the cutter speed to 0.6
m/s, an inner-wall sampler three
times the particle diameter (3d) for
coarse material, where d > 3 mm, and
at least 10 mm for finer material.
Sampling from gravity flow
As shown in Figure 5, gravity flow can
be any free-flowing powder or slurry
from a conveyor, hopper, launder or
unit operation under the influence of
gravitational forces. When sampling in
such systems, each increment should
be obtained by collecting the whole of
the stream for a short time. The width
of the receiver should be made at least
10 mm or three times the diameter
of the largest particles - whichever
is larger. The volume of the receiver
must be large enough to ensure that
the receiver is never full of material.
The length of the receiver should be
sufficient to ensure that the full depth
of the stream is collected. The ladle or
receiver should cross the whole stream
in one direction at constant velocity.
For heavy mass flow, a traversing cutter
as a primary sampler together with
a Vezin sampler as a secondary splitter
can usually be applied.
Is the process in a pressurized
enclosure?
Is the process at elevated
temperature?
Is the process wet or dry?
Is the powder in motion?
What sample size is required?
Are there any sanitary
requirements?
Is automatic sampling required?
Is a composite sample
required?
Heath & Sherwood Co.
Is the sample sensitive to
moisture?
Figure 5. Linear gravity flow samplers
collect samples from free-flowing powders
under the influence of gravity
Mechanical conveying systems
The conveyor types for mechanical and
pneumatic conveying of bulk solids include
belt conveyor, screw conveyor,
bucket conveyor, vibrating conveyor,
and dense- or dilute-phase conveyers.
The best position for collecting the
samples is where the material falls in
a stream from the end of the conveyor.
One can then follow the procedure for
gravity flow or free-falling streams as
46 ChemiCal engineering www.Che.Com april 2012
noted above. However, if the situation
is such that samples have to be taken
directly from within the conveying line,
several types of sampler have been developed.
An example of such samplers
designed to extract samples from belt
conveyor systems is illustrated in Figure
6. The mid-belt sampler uses a rotating
scoop that makes a pass across
the moving belt, thereby cutting a
clean cross section of material.
Sample requirements
Process conditions
Materiel properties
http://www.Che.Com
Chemical Engineering April 2012

Table of Contents for the Digital Edition of Chemical Engineering April 2012
