PROCESS DESCRIPTION
The system is designed to continuously process molasses in order to produce an enriched sugar fraction and a raffinate fraction. The process used by IDRECO is the most improved and up-dated molasses separation process, and consists of the following operations:
Diluted molasses is passed through a pre-treatment step (Molasses Filtration) before it enters the chromatographic separator section, which consists of two stages. In the first stage, the “Crossover non sugars fraction” (Betain rich) and the “Upgrade fraction” are separated. Both fractions are to be concentrated. The concentrated “Crossover non sugars fraction” can be sold as such or mixed with the raffinate fraction and is sold as a by-product. The concentrated “Upgrade fraction” is processed in the second stage which produces the Extract (sugar fraction) and the Raffinate (non-sugar fraction).
The described system needs an amount of condensate (or water free of divalent cations) for the dilution of the incoming molasses, and for the chromatographic separation process purposes.
The molasses to be treated will have the following characteristics :
- Dry substance: 80%
- Purity: 60%
- Total hardness: 3 meq / % dry substance max.
- Invert sugar: 1,3 % dry substance max.
- Betaine: 5% dry substance max.
Each of the Process Steps is described below:
DILUTION
The molasses syrup is pumped from the day storage tank and diluted with condensate. It is then heated to an higher temperature of approx. 85 °C.
FILTRATION
After dilution the molasses is filtered through a precoat filter. The filtered solution is then pumped through check filters with 5-10 micron bags to the degasser.
DEGASSING
The molasses is reheated to 85 °C and passed through a degasser, which is connected to the surface condenser of the evaporation system.
CHROMATOGRAPHIC SEPARATION
After degassing, the molasses solution is pumped to the first stage column. In this stage the “Crossover non sugars fraction” is separated from the “upgrade fraction”. The two streams are then concentrated in the evaporation system.
The upgrade solution is check-filtered and then directed to the second stage.
The remaining nonsugars are excluded during the chromatographic process and the enriched sucrose fraction is recovered at a concentration of about 35 – 37 °Bx.
The recovered extract and raffinate fractions are then concentrated.
The concentrated “Crossover“ fraction can then be combined with the concentrated raffinate fraction.
The condensate outflows from both above-mentioned concentrations are returned to the system to be used as process water. For this purpose, the condensate streams are mixed with softened make up water, filtered and finally degassed before being used as eluant water.
Make up water can either be condensate or softened water. Alternatively to softened water, factory condensate may be used as make-up water.
PRODUCT QUALITY
- Extract: Dry substance 29-32%
- Overall sugar recovery: 82% (this is the crystal sugar recovered in a 3 boiling system from the crystallization of the extract).
- Raffinate: Dry substance 4.5
- Color removal: 90% or greater (based on material balance shown below).
The overall sucrose recovery of 82% is based on an elution water to feed ratio of 6.25 to 1 (volume to volume), assuming a feed molasses RDS of 80%. The only measurements used to determine the overall recovery would be the recovery of extract sugar across the separator and the extract purity.
Overall recovery (OR) is based on a secondary molasses (molasses remaining after crystallizing sugar from extract) purity of 60% and will be calculated according to the following formula:
Where R is the recovery or percent of the sugar in separator feed that remains with the extract fraction and Qe is the true purity of the extract. The above formula gives the various combinations of separator recoveries R and extract purities Qe that will meet the overall recovery of 82%.
The color removal is based on material balance of exiting materials and % Color elimination (CE) is calculated as follows:
