Corrosion Inhibitor In Water Treatment

In the industrial production process, a lot of heat is often generated, so that the temperature of the production equipment or products increases, so the equipment must be cooled in a timely manner, so as not to affect the normal operation of the equipment and the safety of production. Water is a good medium for absorbing and transferring heat, and water is used in industry to cool production equipment and products. Therefore, the proportion of cooling water in industrial enterprises (electricity, petroleum, energy, chemical, steel, etc.) is very large, which basically accounts for more than 90% to 95% of the total industrial water consumption. Industrial cooling mostly uses once-through cooling water systems in half a century ago, which waste a lot of water resources. Now the recirculating cooling water system has replaced it and is widely used in most industrial fields, which can greatly save water resources and be friendly to the environment. In general, the proportion of supplementary water in the circulating cooling system can be as low as less than 5% of the circulating water. At present, the circulating cooling water system has become the consensus and standard in the industry.

The heat exchanger is the core part of the circulating cooling water system, and the circulating water takes away the excess heat of the equipment through the heat exchanger. However, the cooling water is constantly recycled in the circulation system, due to the rise in water temperature, the change in water flow speed, the evaporation of water, the concentration of various inorganic ions and organic materials, the cooling tower and cold pool are exposed to sunlight outdoors, the wind and rain, the entry of dust and debris, and the comprehensive effect of many factors such as equipment structure and materials. There will be serious sediment attachment, equipment corrosion and a large number of microorganisms, as well as the resulting mud and dirt blocking the pipeline and other problems. Without special treatment, the cold heat transfer effect of the system will become worse, and due to salt concentration and other effects, the heat exchanger and system pipes will produce corrosion, scaling and microbial growth and other problems. Therefore, the water quality treatment of circulating cooling water is the prerequisite and basic requirement to ensure the safe operation of the system.

• Scaling

Ca(HCO₃)₂= CaCO₃↓+CO₂↑+H₂O

Generally, dissolved bicarbonate exists in natural water, and this salt is the main component of scale adhesion in cooling water. In the DC cooling water system, the bicarbonate concentration is very low, but in the open circulating cooling water system, the bicarbonate concentration increases with the evaporation concentration. When the concentration reaches the supersaturated state, or when the water temperature rises through the heat transfer surface of the heat exchanger, decomposition reaction occurs and calcium carbonate precipitation occurs. Calcium carbonate deposits on the surface of the heat exchanger, forming a dense calcium carbonate scale, its thermal conductivity is very poor, thereby reducing the heat transfer efficiency of the heat exchanger, affecting the output, and serious will make the pipeline blocked.

• Corrosion

Positive: Fe=Fe₂⁺ + 2e

Cathode: O₂+H₂O+2e=2OH-

In water: Fe₂⁺+2OH-=Fe(OH)₂ / Fe(OH)₂ +ОH-=Fe(OH)₃

These reactions cause the metal in the anode region to dissolve continuously, resulting in corrosion. The corrosion of the equipment is related to the characteristics of the water and the properties of the metal in the system. Corrosion will shorten the life of the metal, and the deposition of corrosion products will also affect the heat transfer and water flow.

What Is Corrosion & Scale Inhibitor And Their Types

Corrosion and scale inhibitor is composed of organic phosphine, excellent copolymer and copper corrosion inhibitor, etc. It has excellent corrosion inhibition properties for carbon steel, copper and copper alloy, and excellent scale inhibition and dispersion properties for calcium carbonate and calcium phosphate. Mainly used in open circulating cooling water treatment systems, especially suitable for systems containing copper equipment. It can be used for water quality with high pH, high alkalinity and high hardness, and is one of the ideal water treatment agents for pH alkaline operation.

It's one or more single chemical compound ratio of water treatment agents, it has the following characteristics: synergistic effect, can simultaneously control the corrosion of a variety of materials, while controlling the formation of corrosion and scale.                                                                                                                                                                                                                 

The effect of corrosion inhibition

The effect of scale inhibition

There're many kinds of corrosion and scale inhibitors, usually the combination of some compounds with special structures, and the types should be selected according to the metal surface condition, the composition of the corrosive medium and the operation condition. The corrosion and scale inhibitors commonly used in water treatment are inorganic polyphosphate, organic phosphonic acid, phosphonic acid, organic phosphonic acid, polycarboxylic acid and so on.

The main chemical agents with corrosion inhibition and scale inhibition function are:

• Organophosphorus scale inhibitors and corrosion inhibitors: such as ATMP、HEDP、DTPMPA、EDTMPS、HPAA etc; 

• A few other polymers also contain certain corrosion and scale inhibition functions, such as phosphonyl carboxylic acid copolymers, green scale and corrosion inhibitors.

Corrosion & Scale Inhibitor Applications

Corrosion and scale inhibitor is a chemical widely used in the industrial field, and its application scope mainly includes the following aspects:

• Petroleum and petrochemical: scaling is one of the most serious problems encountered in oilfield water quality control. Scaling can occur in all parts of the formation and wellbore, some Wells and reservoirs are prematurely abandoned due to scaling deposited in the production layer of the wellbore perforation hole. Scaling can also occur in gravel filling layers, downhole pumps, tubing strings, oil nozzles and storage equipment, gathering and transportation lines, crude oil processing equipment, cooling towers, boilers, water injection and sewage lines, and any part of the water treatment system. Scaling will bring serious harm to production because scale is a bad conductor of heat, the formation of scale greatly reduces the heat transfer effect of scale deposition will cause local corrosion of equipment and pipelines, perforation and destruction of scale in the short term will also reduce the cross-sectional area of water flow, increase the flow resistance and transport energy, increase the cleaning cost and maintenance time. In these fields, corrosion and scale inhibitors can be used to prevent corrosion and scaling inside the pipeline by acidic or alkaline media, to protect the safe operation of equipment.

• Water treatment industry: corrosion and scale inhibitors can be used to prevent pipes and equipment from being affected by scale and corrosion, and improve the purity and treatment effect of water.

• Metallurgical industry: corrosion and scale inhibitors can be used to prevent the inner wall of the pipe of the cooling system, boiler and steam generator from being corroded and scaled to ensure the stable operation of the equipment.

• Steel production: In the process of steel production, corrosion and scale inhibitors can be used to prevent production equipment from being affected by corrosion and scaling, improve production efficiency and equipment service life.

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