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Operational cleaning of residual scale after pickling of industrial steam boiler

Update time : 2021-04-07 18:02:16

When the first question is raised, the scale removal area should reach more than 80% of the original scale coverage area. When cleaning silicate or sulfate scale, the scale removal area should reach more than 60% of the original scale coverage.

Boiler scale, especially sulphate scale and silicate scale, even if pickling is used, it is difficult to clean it all at once. The surface of the residual scale is rougher than the surface without scale. The rough surface has a lot of impurities, and the above-mentioned internal solution is the stagnant zone, and the scale is easy to concentrate, deposit and form here. Based on the above-mentioned unfavorable factors, after the industrial steam boiler is pickled, the treatment of residual scale is very necessary.

2 Descaling methods and principles 2.1 Method Salt and sodium humate can achieve a synergistic effect and achieve the purpose of removing old dirt during operation.

2.2 Principle The scale is converted into CaC3 water slag.

An I has a dissolving effect on silicate. NaOH reacts with insoluble silicate scale to produce soluble sodium silicate.

The higher the temperature of the pot water containing the lye, the easier the above reaction will proceed.

Utilize the chelating effect and lattice distortion of organic phosphonates. Can organic hydrochloride and Ca2 in aqueous solution? , Mg2? A stable chelate is formed, and it can also interact with CaCO3 crystals (phosphonium phosphonic acid), because of Ca2? The chelating coordination of CaCO3 makes the CaCO3 scale layer have many cavities, splitting the interaction force between the scale layers, and the hard scale becomes soft scale. When the pot water is boiling, it causes the effect of scouring and dispersion, and the sewage is discharged. Drain them together.

Utilize the regeneration and self-releasing membrane effect and descaling effect of organic polycarboxylate. The organic polycarboxylate can form a film that co-precipitates with the scale layer on the heat transfer surface. This film will rupture when it grows to a certain extent, and will leave the heat transfer surface with the scale and replace it.

Utilize the osmotic effect of sodium humate. Sodium humate has more osmotic effect, can penetrate into the surface of scale and metal contact surface with calcium, magnesium salt to undergo a metathesis reaction, so that the surface adhesion of old scale and metal is reduced instead.

3 Application Examples Example 1 A KZL2-8 horizontal quick-installation boiler in a certain factory, the raw water is groundwater, and the hardness is 10. Mg2+), there are often water treatment equipment, due to poor water quality, and improper operation, the formation of scale, covering an area of more than 90%, the average thickness is 45mm, and the thickest part is 11mm. After pickling, take the residual scale and pass the test to determine it as sulfate scale. According to its nature, the following scheme was adopted: (3), then Na2C3 was added to increase the alkalinity of the pot water to 18), and the dosage was calculated according to the sample: G = V° (D standard one D) MG? The amount of Na2C3, g; V? The water capacity of the industrial steam boiler, m3 (2t/h boiler is calculated as 4...) D is the required alkalinity of a pot of water, mmol/L (OH, D is the alkalinity of the pot water tested at the time, mmol/LM? NaC3 The molar mass of ± Na2C3 is that after adding according to the above scheme and dosage, the turbidity of the pot water is increased compared with that before adding the medicine. One is that the salt content of the medicine itself increases, and the other is that the scale gradually becomes water under the action of the pharmacist. Slag. As time goes by, the turbidity slowly decreases. After 6 months of operation, most of the residual scale has been removed and a small amount is replaced with the bottom of the drum, which becomes soft scale, which is easily turned into slag to remove it. .

Example 2 A KZL4-10 horizontal quick-installation boiler in a factory did not test the water quality before installation, the softening equipment was debugged incorrectly, and the water quality did not meet the standard requirements, which caused the newly installed boiler to run for 3 months at the water supply site The water wall was replaced by scale, and there were pipe bursts. Six of them were replaced. The thickness of the remaining part was about 4mm, and the thickness of some parts was 7~8mm. After pickling, residual scale accumulates. Since the natural alkalinity of the make-up water of the boiler is 3.5 mmol/L, the alkalinity of the industrial steam boilerr is mostly maintained at about 15-20 mmol/L (OH, female COt), so Na2C3 is not added, only HEDMP and HEMA are added. After 4 months of operation with sodium humate, the residual scale was greatly reduced. Most of the metal is partially exposed.

4 Problems that should be paid attention to. Adding chemicals to remove residual scale must be strictly controlled. The hardness of boiler make-up water or softened water must be strictly controlled within 0.03mmol/L (calculated as ±Ca2'" 1Mg2 ten) to prevent the hardness from entering the pot and forming , New scales and consumed reagents. Examples, in the first case, the softening equipment was re-commissioned, and in the second case, the softening equipment was directly replaced, and the analysis operators were trained.

5 In the case of the residual scale of the boiler after pickling and continuous pickling, the method of adding chemicals in the boiler can be used to solve it.a

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