Application of Hastelloy Agitated Nutsche Filter Dryer (“Three-in-One” Equipment) in Strong Corrosion Conditions

January 29, 2024

In the past ten years, with the rapid development of the pharmaceutical and chemical industry, in harsh corrosive conditions, such as petrochemical, flue gas desulfurization, fluorine chemical, pulp and paper, aerospace applications, acid environments and other industrial fields, Hastelloy materials have been used more and more widely.

WUXI ZHANGHUA Pharmaceutical Equipment uses more advanced Hastelloy anti-corrosion materials to manufacture the key components on its agitated nutsche filter dryer ("Three-in-One" multi-functional equipment) in lieu of the traditional anti-corrosion ones. Considering the performance of Hastelloy, it can be widely used in various unpredictable harsh conditions to minimize unscheduled maintenance. Meanwhile, it also has good processing and welding performance, which eases on-site maintenance.

How the agitated nutsche filter dryer ("Three-in-One" multi-functional equipment) works: in a closed container, the solid-liquid mixture after crystallization is separated into solid and liquid by the pressure difference before and after the filter cake, and then it is filtered → slurry washed → re-filtered → re-slurry washed → filtered or pressure filtered → dryed, etc. The process of primary filtration and re-filtration after cleaning is to pass the solid-liquid mixed suspension of crystals and liquids through the porous sintered mesh by pressure filtration or suction filtration, so that the crystals (solid particles) are intercepted on the filter medium, and the mother liquid is isolated when passing through the medium.

At the same time, in the drying stage of the agitated nutsche filter dryer, the filter cake is heated to make the moisture evaporate quickly, and then dried. The evaporation speed is accelerated by means of vacuum inside the equipment, and the evaporated moisture is taken away by adding treated nitrogen and other media, which speeds up the drying process and improve the drying effect. In view of the fact that the equipment will be widely used in pharmaceutical, chemical, pesticide, food and other industries, different companies will process various materials in the equipment. Therefore, the internal construction of the equipment must be corrosion-resistance to various pharmaceutical and chemical raw materials under high temperature and high pressure. Compared with other anti-corrosion materials, Hastelloy has shown the better performance and is most suitable for the agitated nutsche filter dryer.

At present, there are two types of anti-corrosion materials, non-metallic materials and metal materials. The non-metallic materials include ceramics, glass fiber reinforced plastics, enamels, graphite, and plastics, etc. Their advantage is that almost no corrosion happens, while the disadvantages included: 1) it cannot withstand high temperature over 200℃ and high pressure; 2) welding operations are not allowed; 3) it suffers high maintenance costs; 4) it can only be used to manufacture relatively smaller equipment. Therefore, it is not suitable for the agitated nutsche filter dryer at all. The metal anti-corrosion materials include iron-based alloys (stainless steel), nickel-based alloys and active metals, and Hastelloy is a kind of high-grade nickel-based alloy.

Hastelloy B (B-2, B-3) and Hastelloy C (C-22, C-276) are commonly used, as they have good corrosion resistance performance in non-oxidizing inorganic and organic acids conditions, including dilute sulfuric acid at 70 ℃, all concentrations of hydrochloric acid, phosphoric acid, acetic acid and formic acid, even concentrated hydrochloric acid.

Hastelloy is stable in caustic and alkaline solutions, as well as in organic media and seawater.

For iron-based alloys (stainless steel), no matter what it is, ordinary 300 series stainless steel (304, 316L, etc.), or austenitic stainless steel (904L, 254SMO, etc.) with relatively better corrosion resistance, or duplex steel (2205, 2507, etc.), or the copper 20 alloy series, their overall corrosion resistance performance is not as good as that of nickel-based alloys (Hastelloy), and such gap is particularly evident in reducing environments, complex mixed acid environments, and solutions containing halide ions.

Although active metals (titanium, zirconium, tantalum) have very good corrosion resistance performance, especially titanium materials are widely used in China, mainly to replace the stainless-steel materials that cannot adapt to corrosive environments. However, titanium generally provides protection by a dense oxide film, and is easily corroded in the conditions (flange, gasket sealing surface) with strong reducibility or high tightness (lack of oxygen). In addition, it cannot be used at the temperature over 300 ℃. Although zirconium and tantalum are corrosion resistance, due to their high price, and the fact that all active metals cannot be used in fluorine-containing environments, they are applied in limited conditions.

In comparison, nickel-based alloys have more advantages. Since nickel has a face-centered cubic structure, its crystallographic stability enables it to accommodate more alloying elements (such as chromium, molybdenum, etc.) than iron-based alloys to adapt to various environments. In addition, nickel itself is corrosion resistance, especially, its resistance to stress corrosion caused by chloride ions is incomparable to all stainless-steel materials. Most types of Hastelloy can be used in a wider range of environments and temperatures, and they are also one of the few metal materials that can resist fluoride ions. Hastelloy itself is a nickel-based alloy, but it is different from ordinary pure nickel (Ni200) and Monel. It uses chromium-molybdenum as the main alloying element to improve the adaptability to various media and temperatures, and special optimizations have been made for different industries.

In conclusion, the agitated nutsche filter dryer ("Three-in-One" multi-functional equipment) produced by ZHANGHUA uses Hastelloy as the main component material, which ensures that various chemical materials can be safely filtered, washed, and dried in the conditions of high temperature, high pressure and strong corrosion, improves the endurance limit and work efficiency of the equipment, reduces the unplanned maintenance and various costs, and plays an important role in increasing production capacity and creating more profit margins for enterprises. It is of great significance to upgrade, innovate and develop such agitated nutsche filter dryer to gain the market share of the pharmaceutical and chemical equipment field.

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