Objectif
To increase the solid content of sugar beet slices to +/- 30% in a second pressing stage subsequent to mechanical drying, using a recently developed press.
Assuming an 80 day harvest, expected energy saving is estimated at +/- 730 TOE per pressing unit/y.
The new element introduced was to dewater the pre-pressed pulp again in a second compression stage. For this purpose, the press is designed with a series of compartments along the pressing stretch. The screws are mounted one above the other in an alternating sequence of squeezing stages and breaking-up zones to prevent excessive compaction of the pressed material and at the same time redistribute the pulp. The pulp is fed to the energy-intensive dryers only after this second pressing stage which is designed to raise the dry matter content by about 7%.
The plant came on-stream as scheduled, for the harvest at the end of September 1981.
The performance test following the running period indicated that the working capacity of the press corresponds to a throughput of 1,627 T/d, with an increase in solid content of 4.63%. Another performance test followed a comprehensive plant inspection, and showed that the solid content increase drops significantly with an increase in speed: throughput capacity however, increases by the same range. By contrast, the amount of water pressed out indicates a maximum speed of 1000 RPM. As a result of very low harvest in 1983, the plant was in operation for only 51 days, during which time an increase of 2.1% in solid content was achieved at optimum speed.
In order to obtain an improved yield of white sugar the use of calcium chloride as a pressing aid was reduced.
The results of the 3 processings indicate an effective mean annual energy saving of 277 TOE.
The throughput of the press is already inadequate for today's requirements. An excellent pressing performance involves such a drop in throughput that a factory would require a large number of presses, at least given our initial dry matter content of about 20%.
The situation would improve with higher dry matter content, e.g. 25%.
There are now presses on the market which can raise the dry matter content of pulp after extraction from between 9 and 10% to over 30% in a single pressingoperation with a througput equivalent to between 2.000 and 3.000 tonnes of beet.
The two-stage pressing procedure therefore does not appear justified in view of the greater technical effort required, when identical results can be obtained with a single press.
Payback period for this project has been calculated to be +/- 10 years.
To date, extracted sugar beet slices of +/- 9% solid content have been mechanically dried (pressed) prior to thermal drying. By using modern presses it is possible to achieve up to 24% solid content (and without the addition of chemicals).
The dewatered slices are then dried to a solid content of +/- 90% in oil-fired rotary driers, at a much higher expenditure of energy than that required for the mechanical drying process. For this reason, this project is intended to increase solid content from +/- 19% to 26% by use of a new type of press at the second pressing stage. In addition, the use of chemical agents to stimulate dewatering is being investigated with regard to dosage and effect on the desired solid content.
The machine in question is a horizontal twin-screw press, type HP 2000 from Messrs Selwig und Lange in Braunschweig. It was designed to press the equivalent of 1.800 tonnes of beet per day. The high performance slicing press with infinitely variable drive, its operational efficiency verified by use in several previous sugar beet harvests, was integrated into the existing plant for demonstration purposes.
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DEM - Demonstration contractsCoordinateur
3342 SCHLADEN
Allemagne