The choice of cleaning agent, currently used is pickling, which includes organic acids and inorganic acids.Organic acids mainly include oxalic acid, formic acid and so on.Inorganic acids mainly include hydrochloric acid, nitric acid and so on.According to the Heat Exchanger scaling and process, material and scale composition analysis:
1) the flow area of the heat exchanger is small, the internal structure is complex, and the cleaning liquid is not easy to be discharged if it produces precipitation.
2) The material of heat exchanger is nickel-titanium alloy, and hydrochloric acid is used as cleaning fluid.Easy to produce strong corrosion on the plate, shorten the service life of the heat exchanger.
1) Dissolution: acid solution is easy to react with calcium, magnesium and carbonate scale to generate soluble compounds, so that scale is dissolved.
2) peeling effect: acid solution can dissolve oxides on the metal surface.Combination of damage and scale.Thus the scale attached to the metal oxide surface is peeled off.And it comes off.
3) air lift effect: acid solution and calcium, magnesium, carbonate scale reaction, produce a lot of carbon dioxide.The carbon dioxide gas is escaping.For the scale layer that is difficult to dissolve or dissolves slowly, it has a certain lifting power to make the scale fall off from the heat exchanger's heating surface.
4) loose effect: for the mixed scale containing silicate and sulfate, because the oxides of calcium, magnesium, carbonate and iron dissolve in the acid solution, the residual scale will become loose, and it is easy to be washed down by the flowing acid solution.
1) Pickling temperature: increasing the pickling temperature is conducive to improving the descaling effect.If the temperature is too high, it will aggravate the corrosion of the pickling solution to the Heat exchanger plate. Through repeated tests, it is found that the pickling temperature should be controlled at 60~E.
2) Acid lotion concentration: according to repeated tests, acid lotion should be based on formic acid 81. O %, water 17. O %, buffer 1.2%, 0.8% of surfactant concentration preparation, cleaning effect is excellent.
3) pickling method: the pickling method should be carried out by the combination of static immersion and dynamic circulation.
4) Pickling time: Pickling time is static immersion for 2 h, and then dynamic cycle for 3 ~ 4 h.During the pickling process, samples should be taken frequently to test the pickling concentration. When the concentration difference between two adjacent tests is less than 0.2%, the pickling reaction can be considered to be over.
5) Passivation treatment: after pickling, most of the scale and metal oxides on the surface of the Plate heat exchanger are dissolved and shed, exposing new metals, which are easily corroded. Therefore, after pickling, the plate of the heat exchanger is passivated.
1) washing: before pickling, the heat exchanger is first washed in the open type, so that there is no mud, scale and other impurities in the heat exchanger, which can not only improve the effect of pickling, but also reduce the acid consumption of pickling.
2) the cleaning liquid will be poured into the cleaning equipment, and then injected into the heat exchanger.
3) pickling: static soaking of the heat exchanger filled with acid solution for 2h.Then the dynamic cycle continued for 3 ~ 4 h.During this period, positive and reverse cleaning is carried out alternately every 0.5h.After pickling, if the pH value of the acid solution is greater than 2, the acid solution can be reused, otherwise, the acid solution should be diluted and neutralized.
4) alkali washing: after pickling, NaOH, Na, Po, softened water is prepared in a certain proportion, and the heat exchanger is alkali washed by dynamic cycle to achieve acid-base neutralization, so that the plate of heat exchanger is no longer corroded.
5) washing: after the alkali washing, use clean softened water.Rinse the heat exchanger repeatedly for 0.5h, and rinse the residue thoroughly in the heat exchanger.
6) Record: During the cleaning process, the time of each step should be strictly recorded to check the cleaning effect.In short, after cleaning, pressure test should be carried out on the heat exchanger.Only qualified can use.
1) Strictly close the water quality in the operation. Strictly test the water quality in the system and the softened water in the softening tank. Only after passing the test can it be injected into the pipe network.
2) when the new system is put into operation, the heat exchanger should be separated from the system for a period of time, and then the heat exchanger is put into the system.To avoid the impurities in the pipe network into the heat exchanger.
3) in the whole system, in addition to the pollution device and filter should be irregularly cleaned, but also should be kept clean in the pipe network, to prevent heat exchanger clogging.
So that's all.It is an important guarantee for the normal operation of the production to clean strictly in accordance with the scale cleaning 456 of the plate heat exchanger.
