PROCESS DESCRIPTION
The system is designed to reduce the hardness in the thin juice coming from beet. The softener uses a strong 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 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 high leakage hardness will appear compared to that designed, at this time the next cell is placed on line. The cut-off point is determined by volume totalizing of treated thin juice.
The regeneration phase includes all operating steps, which do not produce decalcified thin juice. All regenerating steps are done in an up-flow mode and use soft thin juice drawn from the product surge tank.
The regeneration sequence includes first an air – scouring step of the resin, followed by a backwash with soft juice, with the purpose of loosening the resin mass and freeing it from foreign matter. The backwash stream is collected in a buffer tank, from which it is continuously pumped to the filters after the second carbonatation.
The resin is then cooled to 35 oC with cold soft juice.
The resin is then regenerated up-flow with 35 oC cold soft thin juice containing 40-50 g/l NaOH (as 100%).
This is followed by a thorough displacement of the regenerant with 35 oC cold thin juice. The calcium-saccharate containing spent regenerant is collected in a buffer tank and from there it is continuously transferred to the lime milk preparation system.
The regeneration is completed by an up-flow rinsing of the resin bed performed with 80 °C hot soft thin juice. This operation has the purpose of washing away the sodium hydroxide and heating up the resin bed.
A closure step concludes the regeneration.
The outflow of the rinsing step is split between the regenerant collecting tank to first carbonatation and the backwash-collecting tank to the second filtration.
