The primary content of various phosphate treatment methods

The primary content of various phosphate treatment methods

(1) High phosphate treatment: If the water treatment process is backward, many calcium and magnesium ions often appear in the boiler water. Danto prevents boiler fouling. A large amount of phosphate has to be added to the boiler to remove the hardness of the boiler water. With the improvement of boiler parameters and the progress of water treatment technology, the use of high phosphate to treat boiler water has become less and less. At present, this treatment method is only used in low-pressure industrial boilers.

(2) Coordinated phosphate-PH treatment: Most of the phosphate-treated boilers have a hidden phenomenon of phosphate, and when remote, free NaOH is generated, and it tends to concentrate on the surface of high-temperature metal or deposits and cause alkaline corrosion. The purpose of coordinating the phosphate treatment is to prevent free NaOH from the boiler water. When R is less than 2.85, even if the hidden phenomenon of phosphate occurs and the solid phase of hydrogen phosphate is precipitated, free NaOH will not be produced in the boundary layer of the water wall. However, to prevent acid corrosion of the furnace tube, the pH value of the furnace water must be high, so the lower limit of R should be greater than 2.2. Therefore, the R-value should be controlled within 2.3-2.8 when coordinating the phosphate-PH treatment.

Because the corrosion characteristics of acid phosphate are similar to alkaline pitting corrosion, it was previously mistaken for alkaline pitting corrosion, but it was not recognized until recent years. Recent studies have found that when the R ratio is lower than 2.5, acidic phosphate corrosion is prone to occur once the phosphate is hidden. However, if R is equal to 3 or even slightly higher than 3, alkaline corrosion will not occur. Therefore, the new coordinated phosphate-PH treatment R control index is 2.6-3.0.

(3) Equal-component phosphate treatment: Equal-component phosphate treatment is a treatment method to maintain the same R-value in the solution and solid components. Generally, the R-value is controlled between 2.3 and 2. 6, and the boiler water is not Free; NaOH is allowed. However, it is difficult to maintain the PH value of boiler water due to the change of boiler load during operation under this water condition. Significantly when the load drops, the pH drops more, which often leads to acid phosphate corrosion.

(4) Low phosphate treatment: For high-parameter boilers, the higher the phosphate content in the boiler water, the more likely local concentration deposits and hidden phenomena will occur, which is very harmful to the safe operation of the boiler. Therefore, a low-phosphate treatment method has been proposed. At this time, the lower control limit of P0 43- in the boiler water is 0.3-0.5mg/L, and the upper limit generally does not exceed 2-3mg/L. Using the principle of soft phosphate, the buffer of the boiler water is insufficient, and it is not easy to control when the cooling water leaks into the boiler. It is only suitable for boilers where the boiler water has no hardness for a long time.

(5) Balanced phosphate treatment: The basic principle is to reduce the phosphate content of the furnace water to the minimum concentration required to react with the hardness components, that is, the "equilibrium" concentration; at the same time, the furnace water is allowed to contain less than 1mg of free NaOH To ensure that the PH value of the boiler water is within the range of 9.0—9.6.

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