Cleaning method of scaling in plate heat exchanger

Cleaning method of scaling in plate heat exchanger

1. Selection of cleaning agent

At present, the choice of cleaning agent is pickling, which includes organic acid and inorganic acid. Organic acids mainly include oxalic acid, formic acid, etc. Inorganic acids mainly include hydrochloric acid, nitric acid, etc. According to the analysis of scale formation, process, material and scale composition of heat exchanger:

 1) The flow area of heat exchanger is small, the internal structure is complex, and it is not easy to discharge the cleaning liquid if it produces precipitation.

 2) The material of heat exchanger is nitinol alloy, and hydrochloric acid is used as cleaning fluid. It is easy to produce strong corrosion on plates and shorten the service life of heat exchanger.

Through repeated tests, it was found that formic acid was the best cleaning solution. Adding buffer and surfactant into formic acid cleaning solution, the cleaning effect is better, and the corrosion of cleaning solution to plate can be reduced. Through the chemical test of scale samples, it is shown that formic acid can effectively remove scale. Through the acid immersion test, it is found that formic acid can effectively remove the scale attached to the plate, and its corrosion effect on the plate of heat exchanger is also very small.

2. Basic principle of scale removal

1) Dissolution: the acid solution is easy to react with calcium, magnesium and carbonate salt water scale to generate soluble compounds, which make the scale dissolve.
2) Stripping effect: acid solution can dissolve oxide on metal surface, destroy the combination with scale. Thus, the scale attached to the metal oxide surface is peeled off. And fall off.
3) Air lift: a large amount of carbon dioxide is produced after the acid solution reacts with calcium, magnesium and carbonate scale. Carbon dioxide gas is in the process of spilling. For the scale layer which is difficult to dissolve or slow to dissolve, it has a certain lifting power, which makes the scale fall off from the heating surface of the heat exchanger.
4) Looseness: for scale containing silicate and sulfate mixture, as the oxides of calcium, magnesium, carbonate and iron dissolve in the acid solution, the remaining scale will become loose and easily washed down by the flowing acid solution.
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