Self-cleaning filter combined with medium and high pressure boiler pot dosing treatment

Guide: The medium and high pressure boiler feed water is generally treated with a relatively complete external water treatment, but it will still bring in various impurities that cause corrosion and scaling. Therefore, it is also necessary to add a chemical agent for the in-pot drug treatment. Commonly used agents are: trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate and sodium hexametaphosphate. This treatment is called phosphate treatment, also known as pot-assisted treatment.

The second is physical processing using a self-cleaning filter to intercept some impurities to reduce the concentration of suspended solids entering the pipeline. Phosphate treatment is divided into three modes: normal (constant) phosphate treatment, low phosphate treatment, and coordinated pH phosphate treatment.

Normal phosphate treatment is used for boilers with softened water as supplementary water, or for boilers with a hardness of usually about 0.O01mmol/L; low phosphate treatment and coordination of pH; phosphate treatment for demineralized water Boiler, or boiler with a feed water hardness of less than 0.001 mmol/L. In addition, there are methods such as total volatility treatment, which are described below. <

1) Phosphate treatment

Phosphate treatment is to add phosphate solution under the condition that the pot water is alkaline, so that the phosphate in the pot water is maintained within a certain range, and the calcium and magnesium ions in the water react, because the pot water is in a boiling state, and the pH value is higher. High, generally between 10 and 12, the basic calcium phosphate and serpentine produced by the above reaction are dispersed and soft water slag in the pot water, which is easily discharged with the boiler sewage, and does not form secondary scale on the heated surface. Moreover, phosphate can form a phosphate protective film on the metal surface to prevent metal corrosion.

When a certain amount of excess P field is maintained in the pot water, the concentration of calcium and magnesium ions in the pot water can be lowered very low, thereby avoiding the formation of scales of CaS04, CaSi03 and Mg3(P04)2. The content of PO3 in pot water is generally controlled within the range of 5-20 mg/L, and should not be too low or too high. Too low can not prevent anti-scaling and anti-corrosion; too high will increase the salt content of the pot water, affecting the steam quality; may also produce Mg3 (P04) 2 or Fe3 (P04) 2 scale; also the phenomenon of phosphate sequestration .

The so-called phosphate; hidden; phenomenon means that in the normal case of boiler dosing, when the boiler operating load increases, the phosphate concentration in the pot water will be significantly reduced, and when the boiler load is reduced or the furnace is shut down, the phosphoric acid in the pot water The phenomenon that the salt concentration rises again. The essence of this phenomenon is that when the boiler is under high load, the easily soluble phosphate is precipitated from the pot water and deposited on the water wall tube, and the phosphate concentration in the pot water is obviously reduced; when the boiler is under low load, it is deposited on the tube surface. The phosphate is dissolved again and the phosphate concentration in the pot water is significantly increased.

2) Low phosphate treatment

Some high-parameter steam drum boilers use a good water treatment method outside the boiler, the water quality of the make-up water is excellent, and the quality of the condensed water is very good. Therefore, there are very few impurities such as Ca2+ added to the pot with the feed water, and it is possible to reduce the water in the pot water as much as possible. The concentration standard, this water treatment in the pot is called low phosphate treatment. With this treatment method, the PO3-concentration in the pot water is generally controlled to be in the range of 0.5-5 mg/L, and the pH is maintained between 9 and 10. When this method is used, once the turbine condenser leaks, the phosphate dosage should be increased in time. Units with poor condensing accuracy and large leakage or frequent leakage should not be treated with low phosphate.

3) Coordination of pH phosphate treatment

The so-called coordinated pH value; phosphate treatment is a water treatment process in the pot by strictly controlling the total amount of phosphate and the pH value of the pot water to achieve the purpose of anti-corrosion and anti-scaling. It is suitable for high pressure and ultra high pressure drum boilers that use demineralized water (or distilled water) as make-up water.