1, the choice of cleaning agent
The choice of cleaning agent, currently used for pickling, includes organic and inorganic acids. Organic acids are mainly oxalic acid, formic acid and the like. The main inorganic acids are: hydrochloric acid, nitric acid and the like. According to the heat exchanger fouling and process, material and scale composition analysis:
1) The heat exchanger has a small flow area and a complicated internal structure, and it is difficult to discharge if the cleaning liquid is precipitated.
2) The heat exchanger is made of nickel-titanium alloy, using hydrochloric acid as the cleaning solution. It is easy to produce strong corrosion to the plate and shorten the service life of the heat exchanger.
Through trial and error, it was found that the choice of formic acid as the cleaning solution is the best. The addition of a buffering agent and a surfactant to the formic acid cleaning solution provides a better cleaning effect and reduces the corrosion of the cleaning solution on the sheet. Chemical tests on scale samples have shown that formic acid is effective in removing scale. Through acid immersion test, it was found that formic acid can effectively remove the scale attached to the sheet, and its corrosion effect on the heat exchanger sheet is also small.
2, the basic principle of removing scale
1) Dissolution: The acid solution easily reacts with calcium, magnesium, and carbonate scale to form a soluble compound, which dissolves the scale.
2) Peeling effect: The acid solution can dissolve the oxide on the metal surface. Destruction and scale bonding. Thereby, the scale adhering to the surface of the metal oxide is peeled off. And fell off.
3) Air enthalpy action: After the acid solution reacts with calcium, magnesium and carbonate scale, a large amount of carbon dioxide is generated. Carbon dioxide gas is in the process of overflow. For the scale layer which is difficult to dissolve or dissolve slowly, it has a certain enthalpy power, so that the scale falls off from the heated surface of the heat exchanger.
4) Loose effect: For the mixed scale containing silicate and sulfate, since the oxides of calcium, magnesium, carbonate and iron are dissolved in the acid solution, the residual scale becomes loose and the acid solution is easily flowed. Washed down.