How to solve the problem of cleaning the plate heat exchanger

    In recent years. The plate heat exchanger has the characteristics of light weight, small floor space, low investment, high heat exchange efficiency, flexible assembly and easy removal of scale. Gradually promote the use of crafts in all walks of life. However, due to the small cross section of the plate heat exchanger. After fouling, clogging is easy to occur, which reduces the heat exchange efficiency of the plate heat exchanger, thereby affecting the safety of the equipment and the normal use of the user. therefore. Solve the cleaning of the plate heat exchanger to prevent the formation of scale. It will become an important issue to ensure safe production and economic operation.

1. The basic principle of the plate heat exchanger to remove scale 1) Dissolution: The acid solution easily reacts with calcium, magnesium and carbonate scale to form a soluble compound to dissolve 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. 1, the choice of cleaning agent 2, the choice of cleaning agent, currently used is pickling, which 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.

  2, according to heat exchanger fouling and process, material and scale composition analysis: 1) heat exchanger flow area is small, internal structure is complex, if the cleaning solution is not easy to discharge. 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.

3, the process requirements for cleaning scale 1) pickling temperature: increase the pickling temperature is conducive to improve the descaling effect. If the temperature is too high, it will aggravate the corrosion of the acid heat treatment plate by the acid washing liquid. It is found through repeated tests that the pickling temperature is controlled at 60~E. 2) Pickling solution concentration: According to repeated tests, the pickling solution should be based on formic acid 81. O%, water 17. O%, buffer 1.2%, surfactant 0.8% concentration, the cleaning effect is excellent. 3) Pickling method and time: The pickling method should be carried out by a combination of static soaking and dynamic circulation. The pickling time is first static soaking for 2 h, then dynamic cycling for 3 to 4 h. The pickling concentration should be sampled frequently during the pickling process. When the difference between the two adjacent assays is less than 0.2%, the pickling reaction is considered to be complete. 4) Passivation treatment: After the acid washing is finished, most of the scale and metal oxide on the surface of the plate heat exchanger are dissolved and detached, exposing a new metal, which is highly corrosive, so after pickling, the heat exchanger plate The sheet is passivated.

    4, the specific steps to clean scale 1) Washing: Before pickling, first open the heat exchanger, so that there is no mud, dirt and other impurities inside the heat exchanger, which can improve the pickling effect, but also reduce The acid consumption of pickling. 2) Pour the cleaning solution into the cleaning equipment and then inject it into the heat exchanger. 3) Pickling: The heat exchanger filled with the acid solution is statically immersed for 2 hours. Then continuously cycle for 3 to 4 hours. In the meantime, the positive and negative alternate cleaning is performed every 0.5 h. After the acid washing is finished, if the pH of the acid solution is greater than 2, the acid solution can be reused. Otherwise, the acid washing solution should be diluted and neutralized and drained. 4) Alkali washing: After the acid washing is finished, NaOH, Na, PO and demineralized water are prepared in a certain ratio, and the heat exchanger is subjected to alkaline washing by dynamic circulation to achieve acid-base neutralization and heat exchanger plate. The piece no longer corrodes. 5) Washing: After the alkali washing is finished, clean the softened water. The heat exchanger was repeatedly flushed for 0.5 h to thoroughly rinse the residue in the heat exchanger. 6) Recording: During the cleaning process, the time of each step should be strictly recorded to check the cleaning effect. In short, after the cleaning is completed, the heat exchanger is subjected to a compression test. It can be used only after passing the test.

    5. Measures to prevent scaling of plate heat exchangers 1) Strictly check the water quality during operation. Strict water quality tests must be carried out on the water in the system and the softened water in the softening tank. After passing the test, it can be injected into the pipe network. 2) When the new system is put into operation, the heat exchanger should be separated from the system, and after a period of cycle, the heat exchanger will be merged into the system. To avoid impurities entering the heat exchanger in the pipe network. 3) In the whole system, the decontamination device and the filter should be cleaned occasionally, and the pipe network should be kept clean to prevent the heat exchanger from being clogged.