| Crystallization fouling is the most common and difficult to be solved problem in industrial circulating water system. Crystallization fouling combined with corrosion and biological accumulating will result in a reduction in heat transfer and increase in operation and maintenance costs of heat exchanger. Calcium carbonate fouling is one of most common crystallization fouling in China. Mechanism of calcium carbonate in heat exchanger is extremely complex, which is often affected by the flow, temperature,pH value and super-saturation of fluid, and it also affected by surface roughness of the heat exchanger and other factors. In industrial production, in addition to strengthen the structure of the heat exchanger in design to reduce fouling deposition, the most common and effective method of scale controlling is the use of chemical additives as scale inhibitors. Scale inhibitors will slow down the fouling rate and reduce operation and maintenance costs of the heat exchanger.The fouling problems of industrial circulating water are studied experimentally from the two aspects in this paper. One aspect is a novel scale inhibitor of acrylic copolymer is synthesized in water phase from malefic anhydride(MAH), methyl acrylate(MA) and 2-acrylamido-2-methylpropane sulfonic acid(AMPS) as monomers, and ammonium persulfate and hypophosphite as the initiator. Orthogonal experiments show that when the molar ratio of monomers is n(MAH): n(MA):n(AMPS)=1.5:1:1, the molar ratio of ammonium persulfate to the total amount of monomers is 1:10,the molar ratio of hypophosphite to the total amount of monomers is 1:7, the optimal polymerization temperature is 60 oC, the optimal thermostatic temperature is 65 oC, and the optimal reaction time is 4 h, the acrylic copolymer with optimal scale inhibition is obtained. Static scale experiments show that the polymer is good at in inhibiting scales of calcium carbonate, calcium sulfate and calcium phosphate at low dosage. On the other hand, scale timeliness is good, when the concentrated ratio is 2,the inhibition efficiency of the polymer on calcium carbonate is still greater than 81%, as the pH value of the solution is less than 9.5 the scale inhibition ability of the polymer is excellent, and copolymer also has good corrosion inhibition.The other aspect is used PMA and calcium carbonate as the research object. The effect of the quality ratio of PMA to CaCO3 and concentration of the CaCO3 solution on the characteristic of fouling and its heat transfer of 316 L stainless steel tube are investigated in conditions which is closely to the actual operating conditions. Theresults showed that when CaCO3 concentration is no more than 800 mg/L, K/K0 is increasing with increase in dosage of inhibitor; in the lower dosage of inhibitor and higher CaCO3 concentration condition, there is a critical threshold effect in PMA inhibiting CaCO3 scale; with further increase in the dosage of the inhibitor, the tendency of inhibitor and Ca2+formed a polymer precipitate will increase; lattice distortion of CaCO3 crystal as well as loose degree of fouling will increase with increase the dosage of PMA, the amount of fouling increases gradually from inlet to outlet of the test tube, and the degree of lattice distortion increases. |
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