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Cleaner Technology Projects in Denmark 1997
Forsøg med roerensning på en stationær rensestation
Arbejdsrapport nr. 39, 1997, Miljøstyrelsen
In 1993 Danisco Sugar introduced the project "Clean Beets", the aim of which
is to make the beets so clean that further cleaning in the factories becomes unnecessary.
Two preliminary reports on the subject concluded that cleaning in the field is better than
cleaning in the factory and that there is a need for developing new techniques for
cleaning. Moreover, it was concluded that the amount of residual soil on clean beets
should be no more than 0,2%. A development project with the aim of manufacturing a
prototypical-cleaning machine for beets was therefore completed.
The project is part of a three year-long project, which includes the following
three phases:
1994: The construction and testing of a stationary
cleaning station
1995: The construction and testing of a mobile cleaning station
1996: The construction and testing of a prototype of cleaning station
The present report describes the testing of the stationary cleaning station (phase 1)
Introduction of extra mechanical cleaning of the beets in the field
may fairly easily be implemented in the phase of loading and transporting beets to the
factory. During the past 10 years a development in the use of so-called cleaner loaders
for this extra cleaning has taken place abroad, but so far in Denmark the use has been
limited. Commercial cleaner loaders typically remove 30-50% of the soil on the beets, and
as a starting point it would be obvious to find techniques for improvements of this
cleaning efficiency.
As part of the first stage of the development, work on improved techniques for cleaning
of the beets in the field, a stationary module-built cleaning station was made. The
station gives the possibility of testing the cleaning efficiency in single mechanical
cleaning modules and in modules connected in series.
Three cleaning modules were used: Rollenrost, rubber fingers
and axial rollers. Each of them could be combined with overlapping
brushes. The axial rollers (always the last stage) were combined with water nozzles as
well.
The cleaning station with a capacity of approx. 25 tons per hectare beets was built at
Saunsøgaard where the beets are stored in the yard before transportation to the factory.
At that capacity all beets passed the cleaning modules in one layer in such a way that
there was always contact between cleaning module and beet.
A total of approx. 1200 tons beets were cleaned in the plant corresponding to approx.
50 tests. For each test the separated material was weighed and sorted out in order that
separated soil, green material and root tips could be calculated as a percentage of the
beet.
The harvesting conditions for beet lifting were generally good during the 1994 campaign
and, consequently, the beets were relatively clean (7-15% soil on beets) on delivery to
the cleaning station. During extreme years (very wet) and with extreme soil types (stiff
clay) the soil level may be more than doubled.
The very first cleaning takes place during reloading and transport to the actual
cleaning modules. Especially loose soil between the beets and looser soil on the beets are
removed (by a rubbing effect). 53 % of totally removed soil was removed in the feed
section for the cleaning modules where the residence time was approx. 5-7 times longer
than in commercial cleaner loaders.
The comparison of the two mechanical cleaning
modules: Rollenrost and rubber finger rollers showed
equality as regards removal of soil, but the Rollenrost was more gentle to the beets and
had a better removal of green material. Independently of type, in the first cleaning
module approx. 24% of totally separated soil was removed, while the second cleaning module
removed approx. 9%. The combination with brushes did not improve the cleaning essentially
in any of the two modules.
The axial rollers, which were intended for a final cleaning of the firm soil in the
root grooves appeared to have only a limited effect, since only approx. 9% of the total
removed soil was removed in this third stage.
During the transportation by lift from cleaning station to lorry approx. 5% of total
removed soil was removed.
It is seen that more than 80% of total removed soil is removed in the feed section, in
the first cleaning module and in the lift, while less than 20% is removed in the two extra
cleaning modules.
Correspondingly, it could be calculated that more than 60% of the root loss takes place
during cleaning in a one-stage cleaning while 40% is lost in the two extra cleaning
modules.
The use of water nozzles (at 7 bar) for cleaning of the beets in the third stage (in
combination with the axial rollers) gave only a limited effect (residual soil 2.9% on
dirty beets with water against 3.2% of residual soil on dirty beets without water) -
primarily due to too short a contact time.
If all experiments are considered together, the cleaning of the beets in the cleaning
station has given an improvement of 4 percentage points (from 83.7% to 87.4%) compared to
dirty beets delivered from Saunsøgaard.
The residual soil percentage for cleaned beets was on an average 3.2% on dirty beets,
corresponding to a removal of more than 50% of the soil on the beets before cleaning.
It may be concluded that the results from a multi-stage cleaning in 3 cleaning modules
averaged 3.2% residual soil on dirty beets with acceptable losses of roots (2.7% on dirty
beets). This is not a pronounced improvement compared to what commercial cleaner loaders
may perform when the cleaning is optimised.
Author/ institution
Flemming Hansen, Bjarne Fallesen and Torben Bøch Andersen
Danisco Sugar
This report is subsidised by the National Council for Recycling and Cleaner Production
ISSN no. 0908-9195
ISBN no. 87-7810-794-6
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