JPH039797B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating condensate, and more particularly, to a method for treating condensate containing ammonia from a power generation boiler or the like using a mixed-bed ion exchange resin column. In thermal power plants, etc., boiler condensate is desalted in a condensate treatment device and then PH-treated with ammonia.
The value is adjusted to a predetermined value and the water is recycled again as boiler feed water. Condensate treatment equipment usually consists of mixed bed towers (mixed bed type ion exchange resin bed towers) arranged in parallel, and the mixed bed towers contain hydrogen-form strongly acidic cation exchange resins (hereinafter referred to as
The tank is filled with a mixture of a free base type strongly basic anion exchange resin (hereinafter referred to as an OH type anion resin) and used for removing ions from condensate. Condensate contains sodium ions, chloride ions,
In addition to impurities such as iron ions, it contains a large amount (usually 0.5 to 10 mg/) of ammonium ions for pH adjustment, so when condensate is passed through a mixed bed column, H-type cation resin contains not only impurities but also ammonium ions for pH adjustment. , this ammonium ion is also captured, and after saturation, ammonium hydroxide eventually leaks from the mixed bed column. At this stage, the flow of condensate is stopped, the mixed bed tower is regenerated, and the mixed bed tower is used again for condensate treatment, commonly known as H-type operation. Since the condensate contains a large amount of ammonium ions, when the mixed bed column is operated in the H type, regeneration must be performed frequently, resulting in waste of regenerant and ammonia. Therefore, even after the H-type cation resin in the mixed bed column captures ammonium ions and becomes saturated, condensate water continues to flow, and impurities in the condensate are replaced in the form of ammonium hydroxide. , this is commonly known as NH ₄ type operation. Thermal power plants sometimes suspend operation at midnight, on weekends, during Obon, end of the year, and New Year's holidays to meet power demand.During shutdown periods, a large amount of hydrazine (0.5 to 500 mg/) is placed in the boiler can. It is added to prevent corrosion. Further, as an oxygen scavenger, hydrazine may be constantly added to the water supply in an amount of approximately several μg/kg. This hydrazine is captured in the mixed bed column during H-type operation, but if H-type operation is transferred to NH ₄ type operation without regeneration, a large amount of hydrazine leaks during the transition. If a large amount of hydrazine leaks, it becomes difficult to control the concentration of hydrazine in relation to the water supply flow rate at the inlet of the economizer.
Only type operation was adopted, followed by H type operation.
There was a problem that the _NH4 type could not be operated. The present invention was made to solve the above-mentioned problems, and it can be done without adding new equipment or mechanically modifying existing equipment.
The purpose of the present invention is to provide a method for preventing temporary large-scale leakage of hydrazine. That is, ammonia-containing condensate is passed through a mixed-bed column filled with a mixture of a hydrogen-type strongly acidic cation exchange resin and a free-base-type strongly basic anion exchange resin, and the condensate is treated. In a method in which condensate water continues to flow even after the hydrogen-type strongly acidic cation exchange resin captures ammonium ions and becomes saturated, water is sampled until hydrazine begins to leak into the treated water of the mixed bed tower, and then water is sampled. This condensate treatment method is characterized by stopping the water flow, stirring the mixed bed, and then restarting water flow. The mixed bed may be stirred within the mixed bed column or outside the column. As the stirring means, a conventional air stirring method can be employed. Next, cases in which stirring is performed outside the tower are listed. FIG. 1 is a schematic diagram showing an apparatus for carrying out the present invention, in which condensate flows down from line 1 to a mixed bed tower 3 filled with ion exchange resin 2 (H type cation resin and OH type anion resin). Supplied in countercurrent. A water collection device 4 is installed at the bottom of the mixed bed tower 3, and the treated water flows out. When hydrazine begins to leak into the treated water, the water flow is stopped and the ion exchange resin 2 is transferred to the regeneration tower 7 via the line 5. In conventional mixed bed towers, to prevent hydrazine leakage,
The hydrazine adsorbed on the ion exchange resin 2 was discharged from the resin to the outside of the system through a line 9 through a regeneration operation using chemicals such as acids and bases injected through a line 8. The resin in mixed bed towers used for ascites desalination at thermal power plants only replaces and adsorbs ammonia and hydrazine, which are normally injected into the material to prevent corrosion.
It is undesirable from the viewpoint of resource conservation to elute and discharge these components from the resin using chemical agents. Therefore, in the method of the present invention, the ion exchange resin 2 transferred to the regeneration tower 7 is subjected to a physical agitation treatment by introducing pure water and air through the line 8.
At this time, a metal oxide such as iron oxide may be discharged from the line 10. Mixed by pure water and air,
The cleaned ion exchange resin 2 is returned to the mixed bed column 3 via the line 6, and water flow is resumed. When condensate is passed through the mixed bed column, ammonia and hydrazine in the condensate are removed, and an amount of H-type cation resin corresponding to the amount thereof is converted to ammonia and hydrazine forms, forming an adsorption zone. FIG. 2-a shows a schematic diagram of the state of the adsorption zone of the H type cation exchange resin in the mixed bed tower when hydrazine begins to leak out from the mixed bed tower. On the other hand, in normal operation of a thermal power plant, condensate contains ammonia, but only a very small amount of hydrazine, so ammonia-type operation of a mixed bed column is carried out. At that time, if the power generation boiler is repeatedly stopped and restarted according to the electricity demand,
The hydrazine added in the holding tank flows into the mixed bed tower and begins to leak into the treated water. The schematic diagram of the state of the adsorption zone of the ion exchange resin in the mixed bed column at this point is shown in the second diagram.
-b Shown in figure. Figures 3-a and 3 show schematic diagrams of the state of the adsorption zone of the cation exchange resin when the mixed bed in the state shown in Figure 2-a or Figure 2-b is stirred in the manner shown in Figure 1 above. -b Shown in figure. The concentration of hydrazine leaking from the mixed bed tower depends on the content ratio of hydrazine in the lower layer and the pH of water in the lower layer. As is clear from Figure 3-a,
The distribution of hydrazine in the resin layer is uniform from the top to the bottom, the peak state disappears, the temporary large amount of leakage of hydrazine is prevented, and the H-type operation is stopped.
Smooth transition to _NH4 type operation. In addition, as shown in Figure 3-b, the amount of hydrazine leaking into the treated water can be kept at a stable low value against the temporary inflow of hydrazine during ammonia type operation, and the condensate of the boiler that is repeatedly stopped and restarted can be kept at a stable low value. Even when processing, NH ₄ type operation can be carried out smoothly. That is, the present invention has the effect of making a temporary sudden change in the water quality of condensate into a long-term gradual change in the water quality of treated condensate water. Example 1 4.0 of strongly acidic cation exchange resin (Diaion PK228: manufactured by Mitsubishi Chemical Industries, Ltd.) regenerated into H-form
and strong basic anion exchange resin (Diaion PA312; the same) 1.9% regenerated into OH form.
A mixed bed column was formed by filling an 80 mmφ column, with a condensate inlet at the top of the column and a condensate outlet at the bottom of the column. A portion of the condensate containing 0.7 ppm of ammonia was passed through this mixed bed column 12 for 25 days. During this period, the boiler operation was stopped for one day, the fourth day, and hydrazine as a preservative was mixed into the condensate at a concentration of 0.65 mg/day. 16. After 2 days of water passage, the cation exchange resin becomes mostly ammonia, and hydrazine is present in the treated water.
0.010 mg/ was detected, so water flow was stopped, the resin layer was mixed with air, and purified water was washed in an upward flow twice. Finally, after mixing with air, water flow of condensate was resumed. . The quality of the treated water at this time was as shown in the table below.

[Table] Comparative Example 1 Using the same mixed bed tower as in Example 1, ascites desalination was carried out in parallel with Example 1, and even when hydrazine started leaking, water flow was continued without stirring the resin. However, the hydrazine in the treated water was as shown in the table below.

[Table] From this table, on the 17th day of water flow, the maximum
It can be seen that hydrazine leaked into the treated water, making it unsuitable for boiler feed water. Example 2 Continuing from Example 1, the boiler operation was stopped on the 26th day, and when the ammonia boiler operation was restarted on the 27th day, 0.65 mg/hydrazine suddenly flowed into the condensate for 5 hours. Immediately after that, the amount of hydrazine in the treated water was 0.005 mg/or less, but after 10 hours, the amount of hydrazine began to rise to 0.010 mg/.
Therefore, the water flow was temporarily stopped, the resin layer was agitated with air, and then the water flow was restarted. Immediately after restarting, the leakage concentration of hydrazine remained stable for 3 days, at 0.030mg/
It was hot. Comparative Example 2 In the condensate treatment following Comparative Example 1, the amount of hydrazine in the treated water immediately after 5 hours of inflow of 0.65 mg/hydrazine on the 27th day was 0.005 mg/or less, but the amount of hydrazine 10 hours later is 0.010mg/
It continued to increase and reached 0.14 on the 28th day.
mg/, and then gradually decreased.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of an apparatus for implementing the present invention. Figures 2-a, 2-b, 3-a and 3-b are schematic views of the state of the adsorption zone of the H-type cation resin in the mixed bed column. 2...Ion exchange resin, 3...Mixed bed column, 4...
Water collection device, 7... regeneration tower.

Claims (1)

[Claims] 1. Treating the condensate by passing ammonia-containing condensate through a mixed bed tower filled with a mixture of a hydrogen-type strongly acidic cation exchange resin and a free-base type strongly basic anion exchange resin, In a method in which condensate water continues to flow even after the hydrogen-type strongly acidic cation exchange resin in the mixed-bed tower captures ammonium ions and becomes saturated, water sampling is continued until hydrazine begins to leak into the treated water of the mixed-bed tower. death,
A condensate treatment method characterized in that water sampling is then stopped, the mixed bed is stirred, and then water flow is restarted. 2. The condensate treatment method according to claim 1, wherein stirring of the mixed bed is performed in a mixed bed tower. 3. The condensate treatment method according to claim 1, wherein the mixed bed is stirred by transferring the mixed bed to a separate column, performing the mixing in the separate column, and returning the mixed bed to the mixed bed column after stirring. .