Chelating resin tower of the best regeneration cycle of

Hu Hu Ming-Ming

(Chongqing Wintinwe Chlor-alkali Chemical Co.Ltd,Changshou 401221, China)

Abstract:Combined with the examples ofchelating resin tower’s regeneration cycle,do detailed analysis for the factors that affecting regeneration cycle and find the best regeneration cycle at different load conditions .The calculating of regeneration cycle and regeneration economy show that finding the best regeneration cycle of  resin tower not only can greatly reduce the production cost, but also can reduce environmental emissions.

Key Words:Resin exchange capacity   Regeneration cycle  Chelating resin tower

1. Foreword

Chongqing Yingtianhui Chlor-Alkali Chemical Co., Ltd. Ion-exchange membrane caustic soda plant capacity.15million tons/In 2002, it has been put into production. Due to the impact of the financial crisis, the production scale is5million tons/Year. The refining of secondary brine uses Nantong Jiuxin chelating resin tower, bleachS930/4757Chelating resin, two-tower process, series operation, when the first tower needs regeneration, one tower runs, and after regeneration is completed, it goes online and series operation. The diameter of the resin tower is3mSingle tower resin loading9.89m³,To go out of the salt waterCa² ,Mg² ,Fe² ,Mn² , Yes² ,Sr² ,Ni² such as heavy metal ions. Design resin tower per24hours to regenerate, regenerate12Hours to complete, after completion as a protection tower to participate in operation. In order to ensure the complete regeneration of the resin tower, the amount of acid and alkali added is excessive, and the resulting acid and alkali wastewater is discharged into the sewage pool.

The company has now entered a stable production, how to save energy and reduce consumption has become a major research topic of the company. The regeneration wastewater of the secondary brine process is the main source of sewage discharge in chlor-alkali enterprises, and the cost of regeneration is relatively high, how to make the secondary brine device more reasonable operation, and tap the maximum economic benefits and minimum environmental discharge of the device, has become an important research topic. The purpose of this paper is to study the best regeneration time of the chelating resin tower under the condition of the same device. If the time is prolonged, the wastewater discharge per unit time will be small, and the economic benefits and environmental protection will be raised.

Analysis of 2. regeneration cycle

The regeneration cycle of the resin tower refers to the time required from the start of operation as the first tower to the offline regeneration. Theoretically, the resin is regenerated when it reaches saturation. The regeneration calculation formula is:

regeneration cycle=Resin working exchange capacity × resin volume/load concentration

resin working exchange capacity=Total resin exchange capacity × regeneration exchange rate × resin utilization rate

load concentration=Medium flow × impurity content

Total Exchange Capacity: Represents the total amount of chemical groups per unit amount of resin that can undergo an ion exchange reaction.

Working exchange capacity: indicates the ion exchange capacity of the resin under certain conditions, which is related to the type of resin and the total exchange capacity, as well as the specific working conditions such as the composition of the solution, flow rate, temperature and other factors.

Regenerated exchange capacity: indicates the exchange capacity of regenerated resin obtained under certain regeneration dose conditions,It shows that the degree of regeneration and recovery of the original chemical groups in the resin.

Regenerated exchange rate: The ratio of the regenerated exchange capacity to the total exchange capacity, usually50~90%(controlled in70~80%）。

Resin utilization: the ratio of working exchange capacity to regeneration exchange capacity, usually30~90%.

It can be seen from this formula that under the condition that the device is unchanged, the regeneration cycle is proportional to the total exchange capacity of the resin, the regeneration exchange rate, and the resin utilization rate, and is inversely proportional to the medium flow (production load) and impurity content. The following analysis of these factors one by one:

1The working exchange capacity of the resin is related to the type of resin, the full volume exchange capacity, the regeneration efficiency and the resin utilization rate, and the type of resin and the full volume exchange capacity are determined by the purchased resin, such as bleach.S930/4757The full volume exchange capacity of the chelating resin (Ca² ) ≥1.3meq/ml(Wet)Of course, during operation, the resin may come into contact with free chlorine to be oxidized or destroyed.FeSuch as heavy metal pollution caused by the attenuation of the resin, the total exchange capacity of the resin will be reduced. The regeneration efficiency depends on the regeneration effect. If the regeneration dose is not well controlled during regeneration, the regeneration will be incomplete and the regeneration efficiency will be low. The resin utilization rate is related to the working conditions at that time, if the temperature, pressure,PHSuch as good control, to achieve the best operating conditions of the resin, then the utilization rate of the resin will be relatively high.

2The medium flow is related to the production load. Under the condition that the scale of the device is unchanged, the greater the production load, the greater the medium flow.

3The impurity content is related to the front-end treatment. If the front-end treatment is good, the impurity content is relatively low.

From the above theoretical analysis, it can be seen that under the condition that the secondary brine device is unchanged, if the load production is reduced, the corresponding regeneration cycle needs to be extended. If the quality of primary brine treatment is good, the regeneration cycle can also be extended. If the working conditions are well controlled, the utilization rate of resin can be improved, and the regeneration time can also be extended. If the regeneration process is well regenerated and the regeneration rate is high, the regeneration time can also be extended.

Calculation and Practice of 3. Regeneration Cycle

1Known data

Unit scale:15million tons/Year100% NaOH

Production scale:5million tons/Year100% NaOH

Brine flow:60m³/h

Impurity content (in totalCa² calculation) ≤5mg/l

Resin used:S930/4757chelating resin

Full volume exchange capacity (Ca² ) ≥1.3meq/ml(Wet)

CaThe gram equivalent:20g

Regeneration exchange rate:70~80%

Resin utilization:30~90%

Diameter of resin tower:3m

Resin filling height:1.4m

2Calculation of regeneration period

regeneration cycle=Total resin exchange capacity × regeneration exchange rate × resin utilization rate × resin volume/Medium flow × impurity content=1.3×20×70%×30%×3.14×1.5×1.5×1.4×1000/60×5=180Hours

While the actual regeneration cycle is24Hours, difference7.5times, equivalent to an increase7.5times the cost and7.5Times the amount of wastewater discharged.

3Practical improvement

After the above calculation data came out, our company immediately carried out the practice, extended the regeneration time, and the analysis frequency became2Once an hour, at No.5In the sky, the analysis results were better every time,Ca² Mg² are less20ppb, at No.6In the weather, I was afraid of the static pressure of the resin tower and regenerated it, that is, the regeneration cycle was changed120hours of regeneration. Run according to this regeneration cycle4Months, a full range of follow-up analysis, brine quality, resin effect is relatively good.

4. regeneration process and economic analysis

After a regeneration cycle, the first stage chelating resin tower needs to be regenerated offline. Since there are only two towers in operation, each regeneration process only needs to be carried out.12hours, and put into operation immediately after regeneration. The regeneration process of chelating resin tower is shown in Table 1, and the discharge and treatment costs of each regeneration waste liquid are shown in Table 2. Brine flow is60m³/h.

As can be seen from Table 1,3mThe diameter of the resin tower each regeneration needs to discharge the waste liquid up.142.3m³,which consumes acid3.6m³(31%),alkali consumption3.3m³(32%). What can be recycled is not included in the cost, and it can be seen from Table 2 that the cost of discharge and treatment of recycled waste is as high6120.85Therefore, reducing the number of regeneration can effectively reduce emissions and reduce costs.

We start from24Once every hour is changed120Regenerate once an hour, work once a year8000hours per year can reduce wastewater discharge37947 m³, cost savings163Ten thousand yuan.

5. Conclusion

Through the above analysis, it can be found that the optimal regeneration cycle of the resin tower can be used to the greatest extent, and the regeneration cost can be saved and the environmental protection emission can be reduced. The factors affecting the optimal regeneration cycle are summarized as follows:

1Good and stable primary brine quality. The less impurities in the primary brine, the longer the regeneration cycle, the stable impurity content, and the easier it is to approach the optimal regeneration cycle.

2Adjust the corresponding regeneration cycle according to the brine flow of different loads. In the same device, because the load is different, the brine flow is not the same, then the regeneration cycle is not the same, need to follow the adjustment.

32. Control the working conditions of secondary brine and improve the utilization rate of resin. The resin provides the best temperature, pressure,PHUnder such conditions, the utilization rate of the resin will be higher and the regeneration cycle of the resin will be longer.

4The regeneration procedure is scientific and reasonable, consistent with the actual situation, and improves the regeneration rate. The concentration, flow rate and time of adding acid, alkali and pure water washing must be calculated well, not only to ensure good resin regeneration effect, but also not to add more acid and alkali to increase emissions.

53. Accurate analysis, increase the frequency of analysis. Analysis is the eye, and only through it can you understand the most real situation correctly.

References:

【1] Liu Zhixin, Luo Guihua, Discussion on Regeneration and Consumption Reduction Measures of Chelating Resin Tower[J], chlor-alkali industry,1996, (7）：5-6.

【2] Li Jie, Measures to Improve the Operation Capacity of Chelating Resin Tower, China Chlor-Alkali,2009(7）：14-15.

【3] Wang Fang, Standard Handbook of Ion Exchange Resin, Beijing: China Standards Press,2003.6,10-15.