Application of duplex stainless steel in the field of environmental protection

With the development of the economy and society, the industrial production process and people’s lives produce more and more “three wastes” (waste gas, waste water, waste residue) that are threatening people’s homes to survive. The “three wastes” for recycling, purification treatment, or comprehensive use, to achieve standard discharge, to prevent environmental pollution, and waste into treasure, for the benefit of mankind. Duplex stainless steel, because of its unique physical and chemical properties, is one of the materials of choice for the manufacture of “three wastes” recycling and purification equipment and facilities.

Duplex stainless steel has the advantages of both ferritic and austenitic stainless steel, with good corrosion resistance, mechanical properties, and welding properties. Due to its excellent overall performance and manufacturing technology breakthroughs, in recent years has been used in large quantities for the manufacture of equipment under the conditions of chloride and hydrogen sulfide media, especially suitable for the manufacture of heat exchangers containing chloride-ionized water or brackish water cooling media, but also for the manufacture of dilute sulfuric acid solutions and storage and transportation of pure organic acid equipment. In place of 304 stainless steel in heavily loaded structural materials, it also improves the service life of the equipment and reduces material costs. In recent years, due to the development of industrial level and increasingly high requirements for environmental protection, duplex stainless steel in the field of environmental protection has also been widely used, especially in industrial waste gas, wastewater, and solid waste treatment is widely promoted.

Exhaust gas treatment

Exhaust gas pollution is one of the biggest environmental problems facing mankind, such as coal-fired boilers in power plants, gas furnaces in fertilizer plants, and coke ovens in iron and steel plants contain a large number of harmful gases and toxic dust particles such as sulfide, nitrides, chlorides, fluorides, etc., which need to be removed before discharge into the atmosphere, the most common method is to pass the exhaust gas through the absorption tower equipped with lime slurry or limestone The most common method is to neutralize the waste gas by passing it through an absorption tower with lime slurry or limestone, which generates corrosive gases containing HCl and HF, causing severe corrosion to the absorption tower. Therefore, in order to ensure the continuous operation of the system, it is necessary to use good corrosion resistance of stainless steel, and 2205, and 2507 duplex stainless steel has the advantages of this, so in the flue gas treatment absorption tower device is used in large quantities.

Statistics show that in recent years in Europe to build a number of sets of flue gas desulfurization devices are used in a large number of duplex stainless steel manufacturing. Canada Coleson Cove power plant is the first in North America at the top of the absorption tower using 360 tons of 2205 duplex stainless steel. In recent years, domestic industrial flue gas treatment equipment also began to use duplex stainless steel materials, such as Huadian International Zouxian Power Plant Phase III flue gas desulfurization absorption tower also uses a large number of 2205, 2507 duplex stainless steel as a manufacturing material. At the same time in the flue gas dust treatment system, the wet type electric dedusting technology (WESP) device system dust collection plate, anode plate, and cathode line using 2205 duplex stainless steel manufacturing. In the pharmaceutical enterprise industry organic waste gas treatment system, its pneumatic switching valve body is made of 2205 duplex stainless steel. Due to the requirements of the environment, ships, especially chemical ships’ flue gas desulfurization emission absorption towers also have a large number of 2205, 2507 duplex stainless steel manufacturing.

Wastewater treatment

With the construction of cities and towns and industrial processes at home and abroad, the discharge of wastewater has become the culprit affecting the deterioration of global water resources and needs to be treated harmlessly before it can be discharged. Municipal sewage, hospital sewage, livestock breeding sewage, etc. contain a large number of Cl- ions, phosphorus compounds, nitrogen compounds, organic compounds, etc., especially the content of these ions or compounds in the sludge is higher. The content of various metal ions, Cl- ions, phosphorus compounds, nitrogen compounds, organic compounds, etc. in industrial wastewater is also high. If these ions or compounds are discharged without treatment, they will cause significant pollution to the water environment and pose a major threat to human life.

As some of the equipment or piping systems in the sewage treatment system are permanently built, and urban and industrial sewage, sludge is corrosive, such as improper selection of materials not only to sewage treatment equipment, piping systems cause serious corrosion, sewage treatment equipment or piping systems maintenance difficulties, sewage treatment companies will also cause significant economic losses. So sewage treatment equipment and piping systems need to choose corrosion-resistant materials manufacturing.

Wastewater treatment equipment and piping systems are generally made of 304 stainless steel, but the sewage Cl- greater than 200ppm, wastewater, and sewage treatment equipment or piping systems are best used 2205 duplex stainless steel or better corrosion resistance 2507 super duplex stainless steel manufacturing, such as stainless steel pickling plant, auto parts plating plant, pulp or paper mills, mines, coal chemical industry, chemical fertilizer plant, the phosphate fertilizer plant, sugar plant, brewery and other industrial waste liquids, sewage treatment systems or equipment are manufactured using 2205, 2507 duplex stainless steel materials.

Waste treatment

The same as sewage treatment and waste fume treatment, duplex stainless steel in the solid waste treatment process is also used in large quantities, this is because the solid waste contains a large number of metal ions, a variety of complex organic substances, chlorides, fluoride, sulfides, etc., these substances are not only toxic but also acidic and alkaline, in the treatment process of serious corrosion of equipment. Solid waste treatment systems with strong corrosive properties of solid waste contact parts, and piping systems need to use duplex stainless steel material manufacturing.

Toxic, acidic, and alkaline chemical, petroleum, pharmaceutical, and other solid waste combustion process, the need for its harmless treatment, solid waste treatment system configuration of the scrubber tower, and wet electrostatic equipment are manufactured using 2205, 2507 duplex stainless steel. In the electroplating solid waste or other solid waste containing rare metals such as gold, silver, cobalt, etc., the use of mixing equipment, piping, and electrolytic purification equipment is used in a large number of 2205, 2507 duplex stainless steel manufacturing. In the Metallurgical manufacturing industry, such as carbon steel, stainless steel pickling solid waste treatment of mixing equipment, ball making equipment local parts also have used 2205 duplex stainless steel.

In summary, because of the excellent mechanical properties of duplex stainless steel, wear resistance, stress corrosion, chloride ion corrosion, and resistance to uniform corrosion performance and other comprehensive excellent performance, its application in the field of environmental protection is becoming more and more widespread.