Cleaner Technology Projects in Denmark 1997
Use of Fluid (air and water) in the Cleaning of Sugar Beets
Anvendelse af fluid (luft eller vand) til rensning af sukkerroer
Arbejdsrapport nr. 41, 1997, Miljøstyrelsen
In 1993 Danisco Sugar Development Center Nakskov introduced the project "Clean Beets", which aims at making sugar beets so clean that further cleaning in the factories becomes unnecessary. In this connection the fundamental conditions concerning the cleaning of beets were investigated, including the importance of the beet material and the consumption conditions with focus on fluid cleaning. This report deals with the application of fluid (compressed air or water) in the cleaning of sugar beats and focuses on experimental testing of energy and water consumption of the single beet.
The purpose of the investigations in 1996 was:
 | To investigate and optimise the energy- and water consumptions for cleaning of sugar beets by air and by water, respectively. |
| To investigate the influence of external conditions (type of soil, humidity of soil, variety of beet, etc.) on fluid cleaning. |
For investigations on fluid cleaning under controlled conditions a test rig was developed and built where the parameters: time of exposure, pressure, nozzle diameter, and distance can be adjusted very precisely. In this test rig single beets are cleaned by air or by water. The results are expressed as specific energy/water consumptions, and wastes of energy and water, which would appear in practice, are disregarded.
For investigations on the optimal set-up of the parameters: time, pressure and nozzle diameter multiple level factorial experiments were carried out on beets from several fields. On the basis of the results, 2 models were made. In model 1 the residual soil is expressed as a function of time of exposure, pressure, and nozzle diameter, and in model 2 as a function of the same parameters including the type of soil. The specific energy consumption was calculated on the basis of time of exposure, pressure, and nozzle diameter and is indicated as the standard beet.
Residual soil as a function of the energy consumption shows a curve area in the form of an exponentially decreasing function, where the residual soil lies between 1% and 50% for an energy consumption of 10 kJ/beet and 0.2 kJ/beet, respectively. In order to obtain the most energy-economical cleaning, a correct set-up of the parameters is important. The type of soil and the consistency of the soil are also of great importance to the minimisation of residual soil.
Other parameters were investigated as well. Parameters that are most important to the subsequent mechanical construction are:
| The speed of the nozzle should be as high as possible (tested up to 6 m/s). |
| The residual soil grows exponentially at a given cleaning when the distance between nozzle and beet increases. Distances below 50 mm are of lesser importance to the residual soil. |
The main parts of the tests were made on beets dug up by hand. The beets were only exposed to a gentle mechanical pre-treatment.
Experiments with a manual pre-treatment of the beets show that there should be as little soil as possible on the beets before the cleaning by air, and the soil must not be too compressed.
Tests with cleaning of different varieties of beet show that the cylinder beet gives the smallest amount of residual soil for the lowest energy consumption. The energy consumption was measured effectively on the part of the beet containing soil.
A 3-row beet harvester lifts 13.3 beets per second. It is assumed that:
| 8 kJ per beet should be used for cleaning by air |
| The efficiency of the compressor is 0.6 |
| The cleaning is effective (no waste) |
The necessary installed effect on the harvester will then be 177 kW.
In January 1997 tests were made with water nozzles from KEW. Tests were made with 4 different nozzles at different pressures.
The tests with water on the test rig show that if the water consumption is between 40 and 70%, the residual soil will be between 5 and 1%. The energy consumption will be between 3.0 and 7.5 kJ/beet. Tests were made with pressures between 26 and 160 bar, where 160 bar results in a high-energy consumption. At a too high pressure (for a specific nozzle and distance) the water may damage the surface of the beet.
If the residual soil (1-50%) is illustrated as a function of the energy consumption (0.2-10 kJ/beet), a curve area like an exponentially decreasing function will appear.
More set-ups of time, pressure, and nozzle diameter may give the same energy consumption, but varying cleaning efficiencies.
The calculations show potentials (in the form of lower energy consumption for the same amount of residual soil) in using large nozzle diameters and higher pressures.
In order to avoid the use of too much energy for cleaning, a pre-cleaning is necessary. Tests have shown that the pre-cleaning should clean the beets to the lowest possible amount of residual soil and at the same time avoid compression of the residual soil.
The water tests indicate consumption of more than 40% water and between 3.0 and 7.5 kJ/beet.
The mentioned energy and water consumption are specific and effective. By upscaling to use in practice some waste of energy and water may take place due to the efficiency of the equipment and to the actual conditions.
Author/ institution
Frank B. Hansen, Bjarne Fallesen og Flemming Hansen
Danisco Sugar
This report is subsidised by the National Council for Recycling and Cleaner Production
ISSN no. 0908-9195
ISBN no. 87-7810-798-9