DEVELOPMENT AND DETERMINATION OF THE EFFICIENCY OF ANTI-SCALANT REAGENTS FOR THE PROTECTION OF WATER SUPPLY SYSTEMS
[3. Технічні науки]
Автор: Tetyana Shabliy, Doctor of Technical Sciences, Professor, National Technical University of Ukraine «Igor Sikorsky Kyiv Polytechnic Institute», Kyiv; Olena Ivanenko, Doctor of Technical Sciences, Associate Profess, National Technical University of Ukraine «Igor Sikorsky Kyiv Polytechnic Institute», Kyiv; Yuliia Nosachova, Candidate of Technical Sciences, Associate Professor, National Technical University of Ukraine «Igor Sikorsky Kyiv Polytechnic Institute», Kyiv
In order to improve the efficiency of the water circulation cycles of enterprises, to reduce the costs of water consumption and discharge, as well as to minimize operating costs, it is necessary to use water as efficiently as possible.
The efficient use of the enterprise's water resources is ensured by the multiple use of water in the production cycle, which includes the stage of cooling heated as a result of the use of technical water. Cooling of water, as a rule, occurs due to its evaporation in cooling towers. As a result of evaporation, soluble and insoluble impurities contained in water are concentrated; at the same time, there are conditions for the formation of deposits of hardness salts on the inner surfaces of pipelines of the water circulation cycle. The greatest damage is caused by deposits of hardness salts in heat exchangers, which leads to a decrease in the efficiency of heat transfer, an increase in energy consumption of production and to the stoppage of the main production for expensive and long-term cleaning of the equipment. In addition, the formation of deposits provokes the occurrence of subsurface corrosion, which leads to premature wear of equipment.
That is why, in addition to the preliminary stabilization treatment of water for water circulation systems, the removal of the already existing scale layer from the surfaces of pipelines and equipment is an urgent issue.
The scale layer is contains calcium compounds, mainly sulfates and carbonates. As you know, the solubility of calcium sulfate precipitates in acids is much lower compared to the solubility of calcium carbonates. That is why the research was conducted using calcium sulfate. Solutions of orthophosphoric, hydrochloric, sulfamic and phosphonic acids, as well as compositions based on these reagents, were used as washing reagents. The results of determining the solubility of calcium sulfate are presented in Table 1
Solubility of calcium sulfate in various media
It should be noted that orthophosphoric acid has the lowest efficiency in relation to the solubility of calcium sulfate compared to other inorganic and organic acids and is 11.4–11.9 g/dm3 for a 10% solution (Table 1).
Hydrochloric acid has the highest solubility of calcium sulfate. Thus, for hydrochloric acid with a concentration of 30 g/dm3, this indicator is 24.5–24.9 g/dm3. In a more concentrated solution (10%), the solubility increases to 36.2–36.7 g/dm3. However, the use of hydrochloric acid is not advisable due to significant corrosive effects even in low concentrations.
The solubility of calcium sulfate in phosphonic and sulfamic acids is 2.0–2.5 times lower than in hydrochloric acid. For their solutions in concentrations of 10%, this indicator is approximately 18 g/dm3. However, their use for washing equipment is appropriate, as these compounds are effective scale stabilizers and metal corrosion inhibitors . Their stabilization effects for tap water at 90 °C are 69.9% and 86.7%, respectively. But they are expensive and their use for large cooling systems is economically unprofitable.
In previous studies  it was shown that the composition of thiourea and urotropin exhibits a synergistic effect in protecting the metal surface from corrosion. Therefore, compositions of pickling solutions based on hydrochloric, sulfuric, and phosphoric acids in the presence of urotropin or urotropin with thiocarbamide were used in the work. In order to reduce the excessive use of these reagents, a new composition P-33 was developed - a reagent to prevent sediment formation.
This mixture showed effective results under the same harsh conditions (Т=90 °С, τ=5 h), but in environments with a significantly higher salt content (Table 2).
Dependence of stabilization and anti-scale effects on the concentration
of the P-33 reagent and the composition of the initial solution
Even with such high initial water hardness (230–490 mg-eq/dm3), the P-33 reagent at a concentration of 20 mg/dm3 provides a stabilization effect at the level of 56.0–93.3%, and an anti-scale effect – 95.5–99 .3%. With an increase in the concentration of the reagent to 50 mg/dm3, the stabilization and anti-scale effects reach 100%.
As a result of the research, the ability of various acids to dissolve lime scale in water circulation systems was studied. The proposed composition is based on phosphonic acids, which provides both effective cleaning of the surface of the equipment and a significant anti-scale effect.
1. Gomelya, N. D., Shabliy, T. A., Trohymenko, A. G., Shuryberko, M. M. (2017). New inhibitors of corrosion and depositions of sediments for water circulation systems. Journal of Water Chemistry and Technology, 39 (2), 92–96.
2. Nosachova, Yu. V. (2006). Stvorennia novykh zasobiv i tekhnolohii dlia zabezpechennia resursozberezhennia u promyslovomu vodospozhyvanni. Kyiv: National Technical University of Ukraine «Igor Sikorsky Kyiv Polytechnic Institute», 166.