Selection and Industrial Application of Scale and Corrosion Inhibitors

corrosion inhibitor

Nowadays,most production enterprises use the recycling of industrial water as the main method of resource conservation. Different proportions of scale and corrosion inhibitors are used according to the quality of the cooling water.

This will not only improve the use of water treatment chemicals, but also support environmental protection to a certain extent. In this way, the water quality of the circulating water is purified and the harm of water pollution is reduced.

1. The Development Process of Scale and Corrosion Inhibitors

1.1  The Significance of Studying Scale Inhibitors

In the industrial production, cooling water accounts for a large proportion of total industrial water. The ratio is between 60% and 90%. Direct use of cooling water can cause corrosion and scaling problems in pipes and equipment.

Therefore, how to treat the cooling water has become a key issue in the production enterprises. In detail, the cooling water treatment mainly refers to the selection of scale inhibitors according to the water quality characteristics of the circulating water, the materials of the equipment, and the industrial production conditions. By matching and processing the reagents containing different components, the appropriate process is used to control the treatment process, and the recycle cooling water is processed in a basic and normal operation.

1.2 The Using Purpose of Corrosion and Scale Inhibitors

Cooling water can cause electrochemical corrosion to pipes and equipment during the circulation. The different recycled water quality, different circulatory conditions, and different over-water metal surface materials will cause different corrosion.

Generally speaking, the main purpose of adding a corrosion inhibitor includes the following three aspects.

First, the characteristic of the cathode and cathode in the corrosion inhibitor is used instead of the water-containing metal to participate in the reaction of circulating cooling water. In this way, the rate at which the metal material is corroded in industrial circulating water is reduced.

Secondly, the use of a large number of corrosion inhibitor molecules to play a molecular shielding effect in the circulation space. This indirectly hinders the electrode reaction.

Third, by adding a corrosion inhibitor to the cooling water, it is possible to form a film-like surface layer on the metal surface, thereby suppressing corrosion of the metal pipe and equipment.

Most of the dirt in industrial water belongs to composite materials. It is usually deposited together in a mixture of scale, biological mud, corrosion products, etc. Finally, it accumulates on the metal surface.

1.3 Different Stages of Scale and Corrosion Inhibitors

Scale and corrosion inhibitors were put into use in the 1980s. So far, it has experienced three periods of inorganic corrosion inhibitors, organic corrosion inhibitors and polymer corrosion inhibitors. At present, high-efficiency, environmentally friendly, and green composite corrosion inhibitors have become the main force in the treatment of industrial circulating water.

The scale inhibitor was invented later. In industrial cooling water, the formation and accumulation of scale generally goes through three stages. That is, the formation of the original seed crystal, the formation of crystal nuclei and the crystal growth. The scale inhibitor treatment was developed to control one of the three stages to achieve the purpose of controlling scale accumulation.

The development of scale inhibitors has evolved from inorganic, organic to high-polymer, from high phosphorus to low phosphorus to non-phosphorus. For the development of new varieties, the general idea is to combine more different monomers such as phosphono, amine, hydroxyl, amino, sulfonic acid groups to synthesize more efficient and multifunctional agents.

2. Problems with the Use of Current Scale Inhibitors

2.1 Lack of Systematic Research on Factors Affecting Scale and Corrosion Inhibitors

At this stage, in the use of corrosion and scale inhibitor water treatment chemicals, a systematic research system has not yet been formed on the factors affecting its function.

In the application of the treatment chemical, the same kind of medicament has different treatment effects in circulating water with different working conditions, different equipment materials and different water quality. The same kind of chemical sometimes has different treatment effects of scale inhibitors in different cycle periods of the same cooling water system. In the end, the desired effect of the treatment chemical cannot be achieved.

In order to improve the actual use of the water treatment agent, the actual use conditions of the scale inhibitor should be fully understood. On the basis of summarizing and summarizing the experimental data, systematically study the influencing factors affecting the water treatment effect.

2.2 The Ratio of Scale Inhibitor Is Easily Affected By External Conditions

When selecting industrial anti-scaling inhibitors, industrial production enterprises should select and evaluate the chemicals according to the actual water quality and working conditions of the cooling water. Once the selected water treatment agent is not up to standard, it will not only reduce the recycling efficiency of circulating water, but also affect the quality of industrial production.

Therefore, proper filtration of the water treatment chemical before use, improvement of the reagent test method, and scientific test means are essential for selecting the agent.

2.3 Leakage of High Sulfur Crude Oil

High-sulfur crude oil is a substance that will cause serious corrosion to cold-exchange equipment during industrial production and processing. It sometimes even leaks into the water circulation system, which has a serious impact on the stable treatment of the water circulation system.

On the one hand, the corrosion of the water system equipment is increased, and the biological slime is increased. On the other hand, the effect of the water treatment chemical is lowered. It is a hidden danger to the normal production of industrial equipment.

3. Selection Test and Research Direction of Corrosion Inhibitor and Scale Inhibitor

3.1 Scale and Corrosion Inhibitor Selection Test

(1) An orthogonal compounding test focused on corrosion inhibition.

Five reagents with excellent corrosion and scale inhibition properties were selected in the composite formulation. They are polyol phosphates, ZnCl2, HEDP, AA/AMPS, sodium hexametaphosphate. They are divided into five components: A, B, C, D, and E. The concentrations of the components tested were 15~25 mg/L, 5-10 mg/L, 10-18 mg/L, 5-10 mg/L, and 1-5 mg/L, respectively. The five factors were divided into four levels in the corresponding concentration range, and the L16 (45) orthogonal test table was used for the compound test.

(2) Test target for scale inhibitors.

The experimental water is the standard water. Weigh 7.35g of CaCl2•2H2O, 4.93g of MgSO4•7H2O, and 6.58g of NaCl in about 7L of water. After completely dissolving, mix well. Also weigh 1.68g NaHCO3 dissolved in about 1L of water, completely dissolved, and mix. Transfer to the above solution, dilute to 10.0L with water and mix. The formulated water contains Ca2+ 2000mg/L, Mg2+ 480mg/L, and HCO3- 4778mg/L.

(3) Experimental materials and equipment.

Experimental materials and equipment include test piece: A3 carbon steel; rotating coupon corrosion instrument; large beaker.

(4) Experimental method.

The method used in this test is the rotating coupon weight loss test method. The conditions under test are as follows。

First, the temperature of the test solution is 40°C; second, the linear velocity of the test piece is 0.35 m/s (error is not more than 0.02); third, the area ratio of the test piece is 30 mL/m 2 ; fourth, test time It is 72 h.

(5) The static scale inhibition evaluation test of the scale inhibitor is selected.

The test water is on-site water, and a washing plant supplies supplementary water to the air separation circulating water system. The water has strong corrosion and scale forming factors. The water quality analysis data is shown in Table-1. The test was carried out using calcium carbonate deposition.

3.2 The Direction of Corrosion Inhibitors and Scale Inhibitors

In the 21st century, water treatment chemicals are gradually developing towards green environmental protection. The non-toxic, degradable and environmentally friendly aspects of corrosion inhibitors have become the focus of research and development. The main research and development direction of the scale inhibitor at this stage is high efficiency, universality and stability.

On this basis, the compound formula can exert more significant effects than a single reagent. In particular, it can make up for the lack of function of a single formula, and the composite formula has become the key to the future development of water treatment preparations. Through in-depth study of metal corrosion problems, the development and treatment of metal corrosion and scale deposition reduction from both macro and micro perspectives.

The accurate ratio of compounding agents and screening of high-efficiency, environmentally friendly, multi-functional, cost-effective scale inhibitors will become an important development direction to enhance water recycling efficiency and improve environmental protection.

4. Conclusion

According to the compounding experiment of the water treatment chemical, not only the industrial cooling water treatment preparation can be selected, but also the quality and safety of the industrial production can be ensured.

In the existing problems of water treatment agents, relevant research departments should select appropriate compound formulas through experiments to provide strong support for the treatment of industrial circulating water.

Table-1: supplementary water quality analysis data
alkalinityCa2+ClironturbidityhardnessECpH
100.28 mg/L97.99 mg/L16.99 mg/L0.17 mg/L1.62 mg/L132.71 mg/L210.48 u S • c m-17.15
2018-11-08T00:51:12+00:00 October 16th, 2018|Tags: , |