For conductivity>2000 μ For the raw liquid with S or PH not between 3.5 and 10.5, the method of single column separation shall be adopted to fully use up the resin exchange capacity. The acidic solution is exchanged by the anion column first, and the alkaline solution is exchanged by the cation column first. However, solutions with high calcium or magnesium content (such as xylose neutralization solution and sucrose sugar refining saturated solution), no matter what the pH of the solution is, should first undergo hydrogen cation column exchange or sodium cation column softening. The presence of calcium or magnesium will pollute the anion resin and cause hardening of the anion resin, affect the exertion of exchange capacity and even damage the resin. For conductivity<2000 μ The raw liquid of S can complete the ion exchange process at one time by using the string column exchange method.

There are two methods of column arrangement: 6 columns in series and 4 columns in circulation exchange and 8 columns in series and 5 columns in circulation exchange. Generally, the fully automatic continuous separation (rotary table type or simulated moving bed type) adopts the string column exchange mode, which can achieve the dual purpose of fully using the resin exchange capacity and ensuring the quality of material exchange. Six columns are connected in series and four columns are used for cyclic exchange, that is, six separation columns are used: 1 # cation column, 2 # anion column, 3 # cation column, 4 # anion column, 5 # cation column and 6 # anion column. The failure of the exchange column is judged by the discharge conductivity index of 2, 4 and 6 # columns. The feed liquid is first exchanged through No. 1 - → No. 2 - → No. 3 - → No. 4. The No. 1 and No. 2 columns fail first, and the exchange is stopped for regeneration; The flow direction of feed liquid is changed to No. 3 - → No. 4 - → No. 5 - → No. 6 for exchange, and No. 3 and No. 4 columns fail first and stop exchange for regeneration; The flow direction of feed liquid shall be changed to No. 5 - → No. 6 - → No. 1 - → No. 2 for exchange. The No. 5 and No. 6 columns shall first fail, and the exchange shall be stopped for regeneration.

In this way, exchange and regeneration are carried out in turn. If the feed liquid is obviously acidic, the six columns can also be arranged in the form of yin, yang, yin, yang, yin and yang. Eight columns are connected in series and five columns are used for cyclic exchange. Eight separated columns are used: 1 # cation column, 2 # anion column, 3 # cation column, 4 # anion column, 5 # cation column, 6 # anion column, 7 # cation column and 8 # anion column. The discharge conductivity indexes of 2, 4, 6 and 8 columns are used to judge the failure of the exchange column. First, the feed liquid is exchanged through No. 1 - → No. 2 - → No. 3 - → No. 4 - → No. 5, and No. 1 and No. 2 columns fail first, and the exchange is stopped for regeneration; The flow direction of the feed liquid is changed to No. 3 - → No. 4 - → No. 5 - → No. 6 - → No. 7 for exchange. The No. 3 and No. 4 columns fail first, and the exchange is stopped for regeneration; The flow direction of feed liquid shall be changed to No. 5 - → No. 6 - → No. 7 - → No. 8 - → No. 1 for exchange, and No. 5 and No. 6 columns shall fail first and stop exchange for regeneration; The flow direction of feed liquid shall be changed to No. 7 - → No. 8 - → No. 1 - → No. 2 - → No. 3 for exchange, and No. 7 and No. 8 columns shall fail first, and the exchange shall be stopped for regeneration. 

In this way, exchange and regeneration are carried out in turn. If the feed liquid is obviously acidic, the 8 columns can also be arranged in the form of yin, yang, yin, yang, yin, yang, yin and yang. Whether six columns in series with four columns are used for circulation exchange or eight columns in series with five columns for circulation exchange depends on whether you want the final discharge column to be a positive column or a negative column, that is, whether you want the final discharge column to be slightly acidic or alkaline. We attach importance to the main role of ion exchange in addition to deashing (desalination), but we can not ignore its auxiliary role in adsorbing and decoloring (or adsorbing harmful organic impurities) and regulating material PH.