Control parameters for circulating water quality

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1. pH: 7.0–9.2. At 25°C, water with a pH of 7.0 is neutral; therefore, water with a pH of 7.0–9.2 falls within the neutral or slightly alkaline range； The corrosivity of cooling water decreases as the pH value increases ； When the pH value of the circulating water is below this range, its corrosiveness increases, leading to corrosion of the equipment ； When the pH value of the circulating water is above this range, its tendency to form scale increases, which can easily lead to scaling in heat exchangers. 2. Suspended solids: ≤10 mg/L. Suspended solids will adsorb zinc ions in water, reducing their concentration in the water ； Under normal circumstances, the suspended solids concentration or turbidity of circulating cooling water should not exceed 20 mg/L; when plate, finned-tube, or spiral-plate heat exchangers are used, this value should not be higher than 10 mg/L. 3. Salt content: ≤2500 mg/L. The salt content can also be indirectly indicated by conductivity; the conductivity of natural fresh water is usually between 50-500 μS/cm ； Conductivity is roughly proportional to salt content; a conductivity of 1 μS/cm corresponds to a salt content of 0.55–0.90 mg/L ； In water with a high salt content, the concentrations of Cl-(*) and SO42-(*) are often high, resulting in greater corrosivity of the water ； In water with a high salt content, if the levels of Ca2+ (*), Mg2+ (*), and HCO3- (*) are high, the tendency for scaling in such water is greater ； When adding corrosion inhibitors and scale inhibitors, the salt content in circulating cooling water should generally not exceed 2500 mg/L. 4. Calcium ions: 30≤X≤200 mg/L. From a corrosion perspective, although soft water does not tend to form scale, it is quite corrosive; therefore, the calcium ion concentration in circulating water should not be less than 30 mg/L ； From the perspective of scaling, calcium ions are the primary scaling cations in circulating water; therefore, the concentration of calcium ions in such water should not be too high ； When a scale-inhibiting dispersant is used, the maximum allowable calcium ion concentration should not exceed 200 mg/L. 5. Mg2+ (*) ions: Magnesium ions are also a major scaling-causing cation in cooling water; the concentration of magnesium ions in circulating water should not exceed 60 mg/L or 2.5 mmol/L (based on Mg2+ (*)) ； Since magnesium ions readily form magnesium silicate scale similar in composition to serpentine with silicate ions in circulating water, which cannot be removed by acids, it is required that the concentration of magnesium ions in the circulating water comply with the following relationship: (mg/L)* (mg/L)