1. Replace the resin. The reduction of pH value should be solved from the source. Although the effect of oil-contaminated resin has been improved to some extent after recovery, it is not a permanent cure. During operation, resin will release oil into boiler water continuously with make-up water, resulting in a vicious circle, and at the same time, the pH value will drop sharply during regeneration, which will aggravate the corrosion of boiler.

Based on the above situation, the resin of pre-cation bed and mixed bed was replaced in April 2005, and the pH returned to about 9 in a short time, but the periodic pH was unqualified, and the interval was basically 1 month.

2. Strengthen sewage discharge. Because the boiler is seriously polluted by heavy oil, it is difficult to completely remove the oil in some dead corners of the drum internals and header in a short time without stopping the machine. When the organic acid in boiler water accumulates to a certain extent, it will show a decline in pH value, so it is necessary to strengthen sewage discharge, which can be divided into two forms: intermittent sewage discharge and continuous sewage discharge.

Intermittent blowdown is located in the header under the water wall, and its task is to discharge slag impurities deposited at the bottom of the drum, which has a certain effect on discharging organic acids. However, normal blowdown depends on continuous blowdown, that is, part of boiler water is continuously discharged from the drum, and the continuous blowdown water intake point of fine or suspended water slag and organic matter in the discharged boiler water is located at about 100mm below the normal liquid level of the drum.

In the case of unqualified pH, the pH can be quickly recovered in a short time by strengthening sewage discharge.

3. Coordinate pH- phosphate control. When the pH value of boiler water is low, only increasing the dosage of Na and PO will help to improve the pH value, but it will often lead to misoperation. At this time, if the pH is controlled according to the routine, the actual dosage is much larger than the normal dosage.

If the PO of boiler water is controlled above 10 mg/L, if the pH value of boiler water is too high, it is easy to produce "soda water * * * rise", which seriously affects the safe operation of boiler, and it is also easy to produce "hidden" phenomenon of phosphate. The results show that when this phenomenon occurs, Na2. SHO。 SPO: Precipitates from the solution and deposits on the furnace tube, which is prone to tube explosion.

Therefore, pH- phosphate synergistic treatment is needed. In order to prevent alkali corrosion caused by excessive NaOH, the Na/PO (molar ratio) of boiler water should be controlled.

Extended data:

Cause analysis of low pH value;

I. Changes of water quality of make-up water

If the CODc of make-up water is high, the resin will enter the drum with the feed water because of its limited ability to remove organic matter. Under high temperature and high pressure, CODc will generate organic acids, which will accumulate in boiler water, resulting in low pH value of boiler water.

Considering the changes of the water quality of the Yangtze River after the closure of the Three Gorges, the water quality of the raw water is comprehensively analyzed and compared with that before the closure. In addition to the calcium hardness, it increased by about 10%, and the CODc was1.34 mg/L. Therefore, the raw water quality is not the main reason for the long-term unqualified pH of boiler water.

Second, the condensate recovery system water quality changes

1, condensate heat exchanger leaks. Generally speaking, the heat exchange of condensed water is cooled by circulating water. If the heat exchanger leaks, Ca't and Mg in the condensate will be higher. After all the condensed water enters the pre-Cation bed for treatment, a large amount of ca. Mg will be exchanged with cation resin, and a large amount of H will be exchanged, which will lead to the acidity of the effluent from the pre-cation bed and the acidity of the effluent from the subsequent mixed bed.

2. The condensate water quality fluctuates. If the water quality of incoming water condensate becomes worse, it will lead to high conductivity. According to the operation experience, the inlet water has high conductivity and is generally caused by NH. For example, when adjusting the pH value of boiler water, the ammonia concentration is controlled too high, or the main equipment is turned off. After all the condensate enters the pre-cation bed for treatment, a large amount of NH' is exchanged with cation resin, and a large amount of H' is exchanged, which leads to the acidity of the effluent from the pre-cation bed and the acidity of the effluent from the subsequent mixed bed.

The above two situations will also occur in operation, but after the leakage source is found or the condensed water is discharged, the pH value of boiler water immediately returns to normal in a short time. Therefore, the fluctuation of condensate water quality is not the main reason for the long-term unqualified pH of boiler water.

3. The change of condensate COD .. The condensate from urea process could not be recovered originally. In 2003, the enterprise established a recycling system to recycle condensed water to save water. The condensate of urea process contains a small amount of organic matter, and the CODc is 2.4 mg/L, which is basically similar to that in 2003. After it was put into operation in 2003, the pH value of boiler water was normal. In order to verify whether it is the CODc effect of this water, the water is discharged, but the pH has not improved, so this factor can also be ruled out.

Third, the steam system oil pollution

On June 20th, 2005, 65438+February 20th, 2005, due to the leakage of EB 10 1, a large amount of deoiled asphalt leaked into the boiler feed water, resulting in oil in the steam and serious blockage of the boiler sampling system pipeline. In order to prevent the slurry from blocking the circulation of boiler water, a large amount of slurry was found in the boiler water discharged from the continuous flash tank.

Adopt non-stop treatment scheme to strengthen continuous discharge flow and increase regular discharge frequency. The continuous discharge flow is increased from 2m/ furnace to 4m/ furnace, and the regular discharge is increased from weekly 1 time to each shift 1 time. Due to forced sewage discharge, the pH value of the system can be kept normal for about 2 months. However, the system oil can not be completely removed, and the oil is converted into organic acids under high temperature and high pressure and accumulated in boiler water, resulting in low pH value of boiler water.

Four. Resin pollution of pre-cation bed and mixed bed In order to find out the resin pollution situation, the oil content of steam turbine condensate was analyzed, the highest was 5.72 mg/L, and the oil content of mixed bed effluent was1.43 mg/L. The resin of pre-cation bed was seriously polluted by oil, and the batch of mixed bed operation was reduced from normal 65438+ 1 to current 6000t, so the exchange capacity was seriously insufficient.

In order to avoid mixed bed oil production, soaking with 10% alkali has certain effect, and the average batch of mixed bed is 50 thousand. However, after the mixed bed regeneration was put into operation, the pH value of boiler water dropped sharply to about 4, but returned to normal after 4 hours. The reason for the sharp drop in the pH value of boiler water is that the outlet valve of Q mixed bed leaks, and hydrochloric acid leaks into the outlet of mixed bed during regeneration, which leads to the drop in the pH value of boiler water.

References:

Baidu encyclopedia-boiler water supply

References:

Baidu encyclopedia-hot water boiler