Innovative Technology to Restore the Performance of Ionites after their Long-term Operation

Studies conducted by scientists at our company have shown that the number and composition of functional groups (that is, the criteria that determine the basic technical characteristics of ionites) remain almost unchanged for both the new and the “old” ion exchanger (see Table 1, which indicates the potential to bring the performance of ionites after long-term operation to the quality of the new ion exchanger).

Table № 1.

Comparative Characteristics of Ion Exchangers at Various Stages of Operation

Exceptions are cases where the ion exchanger was operated at temperatures above the maximum permissible, which could lead to the irreversible destruction of the ion exchanger matrix due to low mechanical strength. In all other cases, the performance of the reduced ion exchangers depends solely on the effectiveness of the applied methods of reduction treatments.

Per the annotated information below, about the results of research conducted by the authors of this work, in the case of qualified selection of recovery treatment technology, the further operation of the restored ion exchanger does not differ practically from the operation of the new ion exchanger.

Based on the above theoretical prerequisites, the following technological mode of remedial treatments was developed. This developed recovery treatment mode is based on the completeness of the removal of contaminants that have accumulated the ion exchanger matrix, which initially had degraded kinetic characteristics. We have shown that, with all other options (modes) of restorative treatments, their effectiveness will be of short duration.

Table № 2.

Comparative Characteristics of the New KU-2-8 and after Two Years of its Operation

As can be seen from the materials in Table 2, during the operation of the ion exchanger, its main performance characteristics underwent significant deterioration: the DOE value deteriorated by ~40%, from 0.68 to 0.42 mEq / ml, and the specific water consumption for washing from regeneration products by ~30%, from 4.5 to 6.2 м³/м³).

For this ion exchanger, a multistage regenerative treatment technology was selected. At the same time, despite the fact that, according to the results of laboratory monitoring, during processing at the first stages, a significant amount of impurities was removed from the ion exchanger matrix (determined both visually and by chemical analysis), its kinetic characteristics, determined by main standardized indicators, slightly deteriorated.

On the initial filter cycles, after the subsequent stages of the reduction treatment, the kinetic characteristics (including DOE) improved by 20–55%, which was of fundamental importance for the operation. However, during the next 3-4 filter cycles, they were re-reduced to almost the original state, which made it economically inefficient to further operate these filters.

The subsequent operation of the restored cation exchanger confirmed this conclusion: for 6 months of observation of the filter in which the restored cation exchanger was in operation, no deviations were observed, compared to the operation of the new monofunctional sulfo cation exchanger.

The Approximate Program of Work to Restore Performance Characteristics of Ionites of the TLU for Heat and Power Characteristics Deteriorated Due to Prolonged Operation

During operation, the performance of standard ion exchangers of the gel structure deteriorates. The deterioration of the performance characteristics of ion exchangers is manifested in the form of a drop in their working exchange capacity, and an increase in the specific consumption of reagents for regeneration and water for the filter's own needs, including due to a significant increase in the duration of filter washing, deterioration in the quality of softened water.

Studies of the characteristics of “spent” ion exchangers show that the number and composition of functional groups (i.e. the criteria determining the value of the total exchange capacity) remain almost unchanged for both the new and the old resin. The fractional composition of the new and old ion exchanger TLU is almost the same for the TLU of most thermal power plants. The cost of restoration treatment of this cation exchanger is significantly lower than the cost of purchasing a new cation exchanger. All this testifies to the expediency of restoring the performance characteristics of ionites loaded into the filters of the TLU heat and power enterprises after their long-term operation to the quality of a new ion exchanger.

Restoration of the performance characteristics of the cation exchanger consists of the following two stages:

The 1st stage is cleaning the outer surface of the cationite grains from sorbed mechanical impurities that have good adhesion to their surface. An alkaline dispersing agent is used to clean the outer surface of cationite grains. Part of the dispersing additives for the first phase of processing is used for the correction of the solution on the second stage second stage processing.

The 2nd stage is a deblocking treatment inside the gel pores of the cationite from irreversibly absorbed impurities. A reagent is used for deblocking treatment inside the gel pores of the cation exchanger. Processing of the 2nd stage is carried out in two stages - Stage 1: removal of irreversibly absorbed heavy metal ions by forming water-soluble complexates at relatively low pH values; Stage 2: inside the gel purification of the cation exchanger from difficultly soluble forms of alkaline-earth metals by forming water-soluble complexonates at elevated pH values.

Processing conditions.

Recovery is carried out directly in the filters. Pre-material is discharged from the filter, the state of the lower DRU is checked by supplying water to it and visually determining the uniformity of flow distribution over the filter section. At the detection of defects of in the DRU, they are eliminated.

For processing, air is needed (supplied via a flexible hose and the filter transforming sampler).

Required processing reagents are introduced through the top hatch.

For processing, a specific temperature is needed. It is to be expected that the water in front of the TLU is not heated or is not heated enough. For regenerative treatments of cation exchanger and regeneration processes, the use of heated water (30-50 ^оС) is highly desirable.

Process progress 1st stage

1. Cation is in the filter in the swollen state.
2. The water from the filter is pre-drained.
3. Pour 15-20 g / l volume of water a first composition (pH> 9).
4. Add heated water to a level of 100-200 mm over a layer of cation exchanger.
5. Apply air for loosening. Visually, a uniform boiling of the cation exchanger layer should be observed without throwing the cation exchanger grains onto the filter walls.
6. The duration of treatment with air is 4-6 hours.
7. After cessation of the air supply, carry out intensive loosening flushing (intensity is maximal, but removal of working fractions should be excluded).
8. Flush until the water is completely clarified.
9. Open the filter. Cut (remove) the upper layer of small (non-working) cation exchanger fractions.
10. Visually determine the residual contamination of the outer surface of the cation exchanger. If there are traces of dirt, the operation according to p. 1.2.-1.8. Repeat, for what use part of the remaining portion of the reagent.
11. Take a sample of cation exchanger for transmission to the analysis.

2nd stage

1. The cation exchanger is in the filter in a swollen state. The water from the filter is pre-drained.

Stage 1: removal of irreversibly absorbed heavy metal ions

1. Pour ~ 20 g / l of the second reagent solution (control in accordance with clause 1.6, taking into account clause 1.4).
2. Add heated water to a level of 100-200 mm over a layer of cation exchanger.
3. Apply air for loosening. Visually, a uniform boiling of the cation exchanger layer should be observed without throwing the cation exchanger grains onto the filter walls.
4. During processing, control the pH value, which should be 4-5 units (by litmus paper or alkalinity by mixed indicator) (in processing the PH will grow, it is necessary to strive to keep it in the specified range by adding fresh portions of the second reagent).

Note: Lower pH values are undesirable due to corrosion of the case, which is not protected. The frequency of control and correction is hourly. The processing time is 6-8 hours.

Stage 2 - inside the gel cleaning of the cation exchanger from difficultly soluble forms of alkaline-earth metals.

1. Rinse with water, add a new portion of the reagent (~ 15g / l) + reagent of the first stage to Rn> 8 units.

2. Monitor and adjust the pH value by introducing the first reagent.

3. The processing time is 10-12 hours or until the full utilization of reagent stocks.

4. Take a sample of cation exchanger for transmission to the analysis.