Chemical Engineering September 2020 - 61

factors, including, of course, the
bulk properties of the powder or
granulate being dosed.
Figure 5. Preferential drawdown of solids material
develops from the first pitch of a constantcapacity
screw feeder
conditions. Again refer to Figure
3, where the peaks and troughs in
the data are a direct function of the
agitator blade proximity to the feed
screw during rotation. A good-quality
feedback-control loop for screw
speed should be able to largely iron
this out and, of course, it should be
borne in mind that the magnitude of
variation will be strongly influenced
by many design and operational
Pitch spacing and flow
Taking screw and auger feeders as
a specific example of a constantvolume-type
feeder, the defining
feature for a standard unit in most
cases will be that of constant pitch
spacing and constant-diameter
flights along its length. The unit
would typically, but not necessarily,
also feature a central shaft along its
length to which the flights attach.
Some types are shaftless and consequently
have a helical appearance.
These design features parallel
those found in screw conveyors,
which are used to transport material
either horizontally or at an inclined
angle over distances of up to 9-12
ft (before transfer to an additional
unit is required).
Therein lies a very important difference
in the function of the feeders
and conveyors, namely that the
former type operates with each
Figure 6. evidence of a preferential flow channel
can be seen in this agitated dosing system
(the screw visible through a bed of compacted
material)
" pocket " filled to capacity, while the
latter would typically run at below
45% volume. Consider now the operating
of a standard (constant-volume)
screw feeder under a vessel.
During each rotation, a void opens
up at the back end of the screw,
into which material can be drawn.
The subsequent rotation creates
another void at the back end of the
screw and pushes the previously
filled volume forward, but since all
of the volumes along the screw are
identical, it follows that no further
capacity can be generated to draw
BUNGARTZ
MASTERPIECES
Where can you find all your
CPI solutions in one spot?
Written for engineers by engineers, Chemical
Engineering delivers solid engineering essentials
and developing industry trends to keep its
readers abreast of everything they need to keep
their facilities running smoothly.
START OF THE DRY SEASON
Nickel-base alloy and polyetrafluoroethylene on cast iron
A loan from a loyal customer
Missing archived issues or what
to share Chemical Engineering
with your colleagues?
Visit www.chemengonline.com/
chemical-engineering-magazine
for more information.
27584
For details visit adlinks.chemengonline.com/76994-30
ChemiCal engineering www.Chemengonline.Com September 2020
61
In some cases, a modern creation manages to become an instant classic.
This is the case with the MPCHDryRun horizontal centrifugal pump.
Thanks to it being safe to run dry despite its magnetic drive, it fascinates
due to its excellent reliability. Other details also catch the eye: it is hermetically
sealed, requires only low maintenance and can also be used flexibly
with liquids that are laden with solids as well as those that are hot.
More under +49 (0) 211 57 79 05 - 0 and: www.bungartz.de/masterpieces3
Visit uns at ACHEMA 2021, Hall 8, Stand C 1
http://www.chemengonline.com/ http://www.bungartz.de/masterpieces3 http://adlinks.chemengonline.com/76994-30 http://www.Chemengonline.Com
Chemical Engineering September 2020

Table of Contents for the Digital Edition of Chemical Engineering September 2020
