Corrosion mechanism of waste incineration and application of corrosion resistant 625 alloy surfacing
(HY-industry technical centre)
As an economical and rapid process for surface modification of materials, surfacing is increasingly used in the manufacture and repair of parts in various industrial sectors.The most widely used chemical equipment is the use of welding methods (such as belt surfacing) to weld corrosion-resistant austenitic stainless steel, nickel-based alloys, etc. on the inner surface of the equipment. such as:
The waste incineration power generation system needs to weld a layer of Inconel 625 alloy corrosion-resistant layer to protect the inner surface of the equipment from corrosion and prolong the service life of the equipment.
The inner wall of various hydrogenation reactors at high temperature and high pressure is welded with chromium-nickel austenitic stainless steel, which can effectively prevent high-temperature hydrogen corrosion of hydrogen on the steel surface.
The inner weld layer of the urea synthesis tower is made of ultra-low carbon molybdenum-containing austenitic stainless steel, which can greatly reduce the corrosion of urea on the equipment.
In order to reduce the overall engineering cost, all kinds of large-scale equipment and accessories are welded to the surface of common metal materials with 2~3mm thick Hastelloy C276, C22 or inconel 625 alloy layers.
In order to effectively exert the role of the weld overlay layer, the commonly used surfacing method has a smaller base metal dilution and a higher deposition rate to obtain an excellent weld overlay performance.High-quality, high-efficiency, low-dilution surfacing technology is increasingly used in a variety of industries, such as waste incineration systems, manufacturing and maintenance, ship engineering, power, machinery industry, petroleum and petrochemical industries. The carrier has valves, pipes, fittings, flanges and plates.
All anti-corrosion alloys can theoretically be used for surfacing: such as Inconel 625, Incoloy 825, C276, Monel 400 …
Controlling the welding process of these materials can economically use the corrosion resistance of materials and cost-effectively serve industrial enterprises. In recent years, there have been many applications in China for large-scale surfacing.
Waste incineration power generation is an effective way to deal with domestic garbage. It has the characteristics of volume reduction, harmlessness and resource utilization. Due to the complexity and heterogeneity of the waste components, various corrosive media, mainly chlorides and sulfides, are produced during the incineration process. After analyzing the contents of HCl and SO2 in the flue gas of the waste furnace, it was found that the HCl content was significantly higher than that of SO2, so the main corrosion was mainly chlorine.
Cl often appears in the incineration environment with gaseous HCl, Cl2 and metal chlorides such as KCl, NaCl, ZnCl2, PbCl2 and the like.
In the high-temperature chlorine-containing atmosphere of the incinerator, in addition to direct vapor phase etching, these metal chloride low-melting ash deposition salts and the oxide film of the metal surface layer undergo oxidation-reduction reaction to corrode the metal matrix. In addition, it will be deposited on the metal surface together with other inorganic salts in the flue gas to form a low-melting eutectic, which greatly reduces the melting point of the ash, and produces a molten corrosive salt on the high-temperature pipe wall. A local liquid phase is formed at the interface to form an electrochemical corrosion atmosphere.
The base metal is anodic dissolved, and the two oxidants O2 and Cl2 in the corresponding atmosphere are reduced, and the base metal is further oxidized and combined to form as loose oxide particles, or combined with Cl- to form chloride.
Thus, as the corrosion progresses, a loose outer oxide film is formed on the outer surface of the molten chloride. This electrochemical process severely erodes the water wall of the boiler and overheats due to the large diffusion rate of the metal ions in the molten salt. The metal components of the device and the like cause degradation and failure of the performance in advance.
In addition, the corrosion of sulfur on the heat exchange surface in the waste furnace can not be ignored. The corrosion of sulfur is mainly the hot corrosion of alkali metal salts, that is, the corrosion of Na3Fe(SO4)3 and K3Fe(SO4)3.
In summary, the waste surface of the waste furnace is gradually eroded and consumed in a corrosive environment. At the same time, a large amount of ash powder generated during the burning of the garbage scoured the heated surface tube, causing different degrees of wear on the outer surface of the heated surface tube. Under the combined action of multiple factors, the heated surface tube is continuously oxidized, corroded and worn from the outside to the inside, so that it is gradually thinned, and the tube is burst when the local water vapor pressure cannot be partially withstood.
In view of the corrosion problem of the heating surface tube of the waste heat boiler, the method of welding high temperature corrosion resistant nickel-base alloy material on the outer wall of the boiler tube is generally adopted. The traditional surfacing method has serious damage to the boiler tube substrate, and the dilution rate is 10%-20%. Between, it is difficult to meet the use requirements. The CMT (Cold Metal Transfer) welding system is used to weld a layer of high temperature and corrosion resistant nickel-based Inconel 625 material on the heating surface of the boiler, which can effectively solve the corrosion problem of the heated surface tube and prolong the service life of the boiler.
After the waste incineration power plant adopts CMT surfacing Inconel625 nickel-based material protection measures, the effect is remarkable:
Under high load operation, it is usually operated for about 1 year because of high temperature corrosion and bursting. After the protection, the service life of the protective layer can reach more than 5 years, and the safety of the waste power plant is realized. Production is stable.
Solving the problem of corrosion on the heated surface, the temperature limit of the heating surface of the boiler is obviously improved, and the daily waste volume can be increased by up to 30%, and good social benefits have been achieved.
The problem of ash accumulation on the pipe wall has been improved, and the heat conversion efficiency has been improved, thereby increasing the power generation capacity of the waste power plant and the economic benefits are remarkable.