Due to improper operation of the water treatment equipment and poor water quality control of the plate heat exchanger, circulating water that does not meet the water quality standards is injected into the heat exchanger. The calcium magnesium carbonate in the water is decomposed into calcium carbonate and magnesium hydroxide precipitates when heated. Impurities dissolved in water in the form of ions or molecules are harmful to the plate heat exchanger.
(1) The main components of calcium salts in water are Ca (HCO3) 2, CaCl2, CaSO4, and CaSiO3. Calcium salt is the main component that causes fouling of heat exchangers. CaSO4 is a kind of hard, fine crystalline scale with loose structure and low adhesion. It is a relatively soft sludge. It is separated from water and has fluidity and is easy to remove even if it adheres to the heated surface.
(2) The main components of magnesium salt in water are Mg (HCO3), MgCl2, and MgSO4. After magnesium is dissolved in water, it is heated and decomposed to form Mg(OH)2 precipitation, and Mg(OH)2 is also sludge scale. MgCl2 and MgSO4 dissolved in water will cause acid corrosion of the metal wall due to hydrolysis when the water pH is less than 7.
(3) Sodium salts are mainly composed of NaCl, Na2SO4, and NaHCO3. NaCl does not generate scale, but the presence of free oxygen in the water will accelerate the corrosion of the metal wall. If the content of Na2SO4 is too high, salt will form on the accessories behind the evaporator, which will affect safe operation. The NaHCO3 in the water will decompose NaCO3, NaOH, CO2 under the action of temperature and pressure, which will damage the metal crystal grains.