Cleaner Technology Projects in Denmark 1997
Effects of Soil, Green Materials and Washing Water on the Processing of Sugar Beets for Sugar
Effekter af jord, grønt og vaskevand i oparbejdningen af sukkerroer til sukker
Arbejdsrapport nr. 38, 1997, Miljøstyrelsen
The aim of this pilot project is to clarify the maximum level of soil and green materials that can be accepted in the extraction of sugar from beets and the juice purification without causing negative consequences for the product quality. In addition, the project aims at illustrating the possibilities of applying beet washing water in the process instead of pure condensate, which is used today.
The sugar factories in Denmark receive approx. 3.5 mio. tons of dirty beets per year to be cleaned at the factories for soil, stones and green material. The soil is by far the largest problem. It amounts to approx. 300,000 tons per campaign. If sugar beets should be processed without a preceding cleaning at the factory, they must be effectively cleaned in the fields, but how clean should they be?
Today, at the factories the beets are cleaned by large consumption of water to approx. 0.2% remaining soil (level 0-0.5% on beet). This might be the basis for the claim, but in reality only very little is known as to how and to which extent soil and green material affect the processing of sugar beets and, consequently, a more correct formulation of the claims for cleaning in the fields would be:
 | Cleaning to a level where processing conditions and/or product qualities (juice and pulp) are not worse than they are today. |
Consequently, it was decided to perform tests with a controlled addition of soil and green material to the processing of sugar beets in a pilot plant with a capacity of 300 kg beet per hour. Furthermore, tests were made with addition of beet washing water to the processing, because this recycling of water "loaded" with sugar might be a relevant alternative to the use of pure condensate, as done today.
The pilot plant was built in 3 sections completely analogous to the construction in a factory (scale 1:1500):
| Beet wash and water treatment |
| Juice extraction (slicing, diffusion and pressing) |
| Juice purification |
One experiment lasted approx. 24 hours (day-and-night working), and a total of 23 experiments were made: 6 references, 7 with addition of soil (up to 1% on beet), 1 with addition of green material (1% on beet), 1 with soil + green (1+1), 7 with wash water, and 1 with beets washed in the field.
The documentation of an experiment partly consisted of running samples and analyses from the operation and partly of samples/analyses from the end of the experiment (after 22 hours of operation), when all processes were supposed to be in equilibrium.
The effects of the impurities were documented on:
1. The products from the process: Pressed beet pulp and juice.
2. The actual processes: The extraction and the juice purification.
The relevant quality parameters in beet pulp are ash and hydrochloric acid insoluble ash (sand). The claims are max. 8% and max. 3.5% on dry substance, respectively. These critical border limits were reached already at soil levels of approx. 0.2% soil dry substance on cossets and, consequently, the claims on the purity of the beets - based on unchanged quality of fodder pills - are a remaining soil percentage of = 0.2% on cossets.
Soil in the diffusion will deteriorate the juice quality, especially as a consequence of washing out sodium, potassium and amino nitrogen from the soil. In the process these components act as molasses agents, meaning that they reduce the crystallisation abilities of sugar, thus drawing more sugar into the molasses instead of producing white sugar. On the basis of the experiments the loss of molasses was calculated to be 0.011% per percent soil on the cossets.
Soil and especially green material caused a decrease in pH in the diffusion of 0.3 units and 0.5-0.9 units, respectively. This is an expression especially for an increased microbial decomposition of sugar to lactic acid, meaning a loss. In the juice purification there were indications of reduced filtering properties with the presence of soil, but the picture was not unambiguous.
Green material - but apparently not soil - gave a higher colour in 2nd carbonation juice than the reference, presumably as a consequence of the content of invert sugar (glucose and fructose), which may enter into Maillard-reactions with N-connections in the heated sugar juice.
To some extent, addition of wash water had the same effect as addition of soil, because the water soluble salts are found in wash water as well, and it has been calculated that addition of wash water, despite addition of extra sugar, approx. 0.15% on beet, causes a net loss of sugar to the molasses compared to the reference.
With the assumption that the process conditions for processing of sugar beets and product qualities (fodder pills and juice) should not be deteriorated compared to the present level, it could be concluded that if sugar beets should be led directly to processing without previous cleaning at the factory, they should be cleaned in the fields to a remaining soil percentage of approx. 0.2% on the beets.
The use of beet washing water as diffusion water instead of condensate, as done at present, will give an increased loss of sugar to molasses, and if wash water should replace condensate as recycling water to the diffusion, it has to be treated in order to remove salts, while the main part of the sugar is maintained.
Author/ institution
John Jensen og Bjarne Fallesen, Danisco Sugar
This report is subsidised by the National Council for Recycling and Cleaner Production
ISSN no. 0908-9195
ISBN no. 87-7810-797-0