The water to the harm of the heat exchanger impurities
1, in order to ion or molecules dissolved in the water the state impurities hazards
A, calcium salt in the water main composition have Ca (HCO3) 2, CaCl2, CaSO4 CaSiO3, etc. Calcium salt is a scaling the major components of the heat exchanger. Among them, the CaSO4 is a hard, crystallization of germplasm fine scale, structure is loose, adhesion is small, it is a more soft mud slag, separated from water with liquidity, even if in the attached heating is easy to remove.
B, magnesium salt in the water main composition have Mg (HCO3), MgCl2, MgSO4, etc. Magnesium dissolved in water, in the thermal decomposition to create Mg (OH) 2 precipitates, Mg (OH) 2 is also mud slag type scale. Dissolved in water, the MgSO4 MgCl2, in water ", because the pH 7 hydrolysis reactions can cause metal wall of acid corrosion.
C, sodium salt main composition have NaCl, Na2SO4, NaHCO3, etc. NaCl don't generate a scale, but in the water there free oxygen exist, will accelerate corrosion of metal wall; The content of Na2SO4 too high, it will in the evaporator of attachment "after salt, affects the safety operation; The water in the NaHCO3 under the effect of temperature and pressure can decompose the NaCO3, NaOH, CO2, can make the metal grain damaged.
2, dissolved oxygen gas hazard
The reason of corrosion of the heat exchanger happen a lot, but the most serious corrosion, the fastest or oxygen. In the atomic order sheet iron in hydrogen over potential, do not contain oxygen in the neutral water, system metal surface iron atoms lost in two price of electronic ion (Fe-2 e-Fe2 +), Fe2 + ions and water OH-ions in static under gravity with [Fe2 + + 2 OH- Fe (OH) 2], and set up the following in the water balance:
Fe2 + + 2 OH-= Fe (OH) 2
When the water there presence of oxygen, Fe (OH) 2 is further oxidized to insoluble hydrogen ferric oxide precipitation out:
4 Fe (OH) 2 + + 2 H2O-O2 4 Fe (OH) 3 press
Due to the Fe (OH) 3 precipitation, make the anode of iron ion around to water solution, accelerate the corrosion.
From the above reaction can see, water and oxygen is from corrosion of the necessary conditions for anode part is from corrosion place, cathodic site is piled up parts of the reaction of corrosion. When the metal surface corrosion in basic evenly, corrosion speed won't soon, so dangerous is not big, the corrosion called full corrosion. When corrosion focus on certain parts of the metal surface is called local corrosion. The local corrosion speed, easy to rust wear, the pit corrosion in the heat exchanger is common in the local corrosion, so very dangerous.
3 and colloid state is in the harm of the impurity to heat exchanger
A, iron compounds main component is Fe2O3, it will generate iron scale. When the water is iron compounds are too, water often yellow.
B, microorganism due to air conditioning cooling of the circulating water temperature, oxygen, and provide the nutrients of microorganisms to breeding conditions, microbial growth of reproduction. Microbes from soil and air cooling, the temperature of the water at the higher, after cooling tower aeration, increase oxygen in water to often dosing phosphate and potions, just as the microbial nutrition, cooling tower and mostly located in open-air, sun exposure to the algal growth, microbial propagation of the plate channel not only obstruction, and sometimes jam lines, still can make metal corrosion.
C, sludge of recirculating cooling water of the sludge, comes from the air and the supplement of water dust suspended. Air and water in the convective exchange process, a lot of air in tower accept circulating water spray, dust into the water, and gradually deposition in the low velocity in the heat exchanger.
D, stick is mainly secretion of the microbial scale and water sediment, and corrosion products, bacteria and algae binder debris into, they are often attached to the wall in heat exchanger, produce all sorts of organic acid, this acid can also cause corrosion.
Therefore, the heat exchanger fluid is very important the requirements, in operation management, should strengthen attention, equipped with some necessary and scale, anticorrosive equipment, prolong the service life of equipment.
