Whether in the final pelletised product or the raw material intake, the moisture level in the material during animal feed manufacture is an essential value to measure and control.

1. STORAGE
MOISTURE CONTROL
New Technology provides a simple and more accurate method of moisture control
W
hether in the final
pelletised product or
the raw material intake,
the moisture level in the
material during animal
feed manufacture is an
essential value to measure
and control.
A number of different
options present themselves when installing moisture control into
a grain and feed processing plant. These include measuring the
moisture of the incoming grain from the fields and also measuring
moisture in the feed whilst it is in the mixer or after it has been
pelletised.
Moisture measurement is often viewed as too complex to add to
a plant. Nuclear based and Near InfraRed solutions are expensive
to install and maintain and microwave based moisture sensors
have traditionally been seen as not accurate enough with limited
information available when compared against the cost of the sensor.
However recent developments in technology have enabled
Hydronix, a UK based company which designs and manufactures
digital microwave sensors, to include a set of new sensing modes
within its latest generation of sensors.
The new sensors take a digital measurement which is then
processed to give a number of different readings relating to the
electrical properties of the material. By selecting the measurement
mode most appropriate to the material and process, a much more
stable and precise reading of the moisture level can be obtained.
Mechanical installation is also a very important consideration
with microwave moisture sensors, as the consistency of the
material and flow stability is crucial to getting the best results.
The installations which achieve the best results have a bypass
system which diverts some of the material flow past the sensor
before returning it to the main flow. This prevents any interference
from turbulence changes or
changes in density in the previous
processes affecting the moisture
sensor.
To assist customers to achieve
the best results with mechanical
installation, Hydronix has recently
developed a new ducting system.
This is designed to be inserted into
existing plant ducting and is available for either vertical or angled
ducting.
This system enables a Hydro-Mix moisture sensor to be easily
positioned at exactly the correct angle against the diverted
material flow to achieve an extremely accurate, real time moisture
measurement. Any adjustment that is required to the material flow
is simple using the baffles provided.
As digital microwave sensors provide a much more reliable
and stable signal when compared with sensors based on older
technologies, there is no need to continuously monitor and adjust
the calibration of the material being measured. It is sufficient
to make a calibration when the sensor is first commissioned and
installed into the process.
It is important to take representative samples from the process
flow over the sensor at the same time as recording the average
corresponding sensor values. This is vital, as these points will
determine the accuracy of the material calibration point.
Of equal importance is the testing of the material samples. It
should not be assumed that another measurement technology is
good enough to give an accurate moisture value, as other sensors
are often not as accurate as they seem. The only scientific way to
find the material moisture is to test the sample in the laboratory by
heating it until completely dry and determining the loss in weight.
The calibration process itself when using a digital sensor (which has
a response which is inherently linear to the moisture change) is very
simple. Each step change in moisture gives the same step change in
the sensor reading. If you have two separate moisture sample points
then you can extrapolate the calibration line very simply by doing a
standard linear regression using the sensor setup software.
This software also provides the option to add multiple calibration
points which improves the accuracy of the sensors by cancelling
out some of the inevitable errors due to sampling errors and
laboratory handling procedures.
As moisture is the simplest component to adjust during the
manufacturing process, the
addition of digital microwave
sensors to a control system for
a feed plant has now become
a simpler, more accurate and
extremely cost effective method
for improving the final quality
of the product.
www.hydronix.com
76 | March 2016 - Milling and Grain
F