Plate heat exchanger is an efficient heat exchange equipment. Because it has the advantages of high heat transfer efficiency, compact structure and convenient assembly, disassembly and cleaning, it has begun to be widely used in many fields in the 1980s. Due to the small cross-section of the plate heat exchanger, the heat exchanger efficiency is reduced due to fouling and clogging, which affects the heating effect. Therefore, choosing a reasonable cleaning method has become a necessary means to improve equipment heat exchange efficiency and extend service life. What are the causes of fouling in plate heat exchangers?
1 Impurities dissolved in water in the ionic or molecular state
(1) Calcium salts. The main constituents in water are Ca (HCO3) 2, CaCl2, CaSO4, CaSiO3 and so on. Calcium salts are the main component of fouling in heat exchangers.
(2) Magnesium salt. The main constituents in water are Mg (HCO3) 2, MgCl2, and MgSO4. After magnesium dissolves in water, it will generate Mg (OH) 2 precipitates after thermal decomposition, which will form sludge or scale.
(3) Sodium salt. The main components are NaCl, Na2SO4, and NaHCO3. NaCl does not generate scale, but the presence of free oxygen in water accelerates the corrosion of metal walls. If the content of Na2SO4 is too high, salt will be formed, which will affect safe operation. NaHCO3 in water will decompose NaCO3, NaOH, CO3 under the action of temperature and pressure, which will damage the metal grains.
2 Impurities present in a colloidal state
(1) Iron compounds. The main component is Fe2O3, which generates iron scale.
(2) Microorganisms. The water temperature and dissolved oxygen of the circulating water provide microorganisms with favorable conditions for reproduction, and microorganisms will multiply.When the temperature of the circulating water is high, adding phosphate and other agents to the water is just a nutrient for microorganisms. The proliferation of microorganisms not only blocks the plate passages, but also sometimes blocks pipelines and corrodes metals.
(3) Sludge. The sludge in the cooling circulating water originates from the dust in the air and suspended matter in the make-up water, and gradually deposits in the heat exchanger with a lower flow rate.
(4) Sticky dirt. It is mainly formed by the secretion of microorganisms with the sediment, corrosion products, and bacteria and algae debris in the water.