PROCESS DESCRIPTION
The system is designed to reduce the hardness in the thin juice coming from beet or cane. The softener uses a weak cation exchange resin in the sodium form.
The system incorporates a three-cell design with two cells being exhausted on thin juice simultaneously. These are staggered with respect to exhaustion so that both do not require regeneration at the same time. The third cell is being regenerated or is in standby.
The high resin capacity and the fast flow rates makes it possible to process the entire factory stream with a very small installation compared to other processes using strong cation exchange resins.
The exhaustion cycle length varies with the hardness concentration. A minimum cycle length of eight hours is necessary to properly turn around a cell and preserve the continuous operation.
The cycle is so dimensioned, that the cell is removed from service before a hardness leakage takes place, at this time the next cell is placed on line.
During the sweetening-off step the juice is pushed across the resin and delivered to the evaporation plant.
The cut-off point is determined by volume totalizing of treated thin juice. As a result very little water is being send forward to the evaporators.
The regeneration is carried out counter-current to the juice flow.
Sulfuric acid is the regenerant of choice so it can be recycled to the diffuser.
Since the calcium sulfate formed during regeneration is only sparingly soluble, care must be taken to insure that the solubility of this product is not exceeded. To prevent this from happening the acid concentration must be below 0.5% and the flow rate should be kept high enough.
A relative disadvantage here is that a large volume of spent regenerant is produced. However, it can all be used back in the process, but must be metered into the diffuser supply at a rate which gives the desired quantity of pressing aid or pH to the diffuser supply.
The weak Cation exchanger system can be regenerated very efficiently with only 110% regenerant on capacity to give complete conversion to the hydrogen
form. Sulfuric acid may be used to adjust the pH of the diffuser supply water. Therefore any excess regenerant reduces this requirement and is not wasted.
Following regeneration a rinse step takes place.
After the rinsing step the resin is put in the sodium form by up-flow percolating the resin bed with a 2% NaOH solution.
The system works very well and produces a thin juice with an average of less than 2% of hardness inlet value when the cells are exhausted to the point of leakage.
The major advantage of this softening process is that the molasses produced from the treated juice are of excellent quality, as far as decalcification is concerned, for further processing in an ion – exclusion plant without any further softening.
