Iron-based non-crystalline composite coating for protecting heat exchange pipes in flue gas waste heat recovery system of power station boiler and laser re-melting and moulding technology thereof

Abstract

The invention discloses an iron-based non-crystalline composite coating for protecting heat exchange pipes in the flue gas waste heat recovery system of a power station boiler, and a laser re-melting and moulding technology thereof. The iron-based non-crystalline composite coating is composed of the following elements in percentage by weight: 55.1 to 66.2 wt% of Fe, 24.4 to 34.3 wt% of Cr, 2.4 to 3.4 wt% of B, 1.5 to 2.9 wt% of Si, 1.7 to 3.9 wt% of Mo, and 1.6 to 3.8 wt% of Nb. The moulding technology comprises the following steps: preparing iron-based non-crystalline cored wires, adopting an ultrasonic electric arc spraying method to prepare an iron-based thermally-sprayed alloy coating on the surface of a heat exchange pipe; and then adopting neodymium-doped yttrium aluminium garnet (YAG) laser as the heat source to carry out laser re-melting and moulding on the positions, which are prone to low-temperature acid dew point corrosion, on the thermally-sprayed coating so as to form compact iron-based non-crystalline composite coating; wherein the coating and the substrate are combine through metallurgy, and no crack and gap exists between the substrate and the coating. The provided coating prevents the transfer of the low-temperature acid dew point corrosion, thus prominently improves the service life of the flue gas waste heat recovery system, relieves the symptom of low-temperature acid dew point corrosion, and has a great application potential.

Description

Technical field [0001] The invention belongs to the field of surface protection of power station boilers, and specifically refers to an iron-based amorphous composite coating used for protection of heat exchange tubes in a power station boiler flue gas waste heat recovery system and its laser remelting molding process. Background technique [0002] In order to make full use of flue gas waste heat, reduce exhaust gas temperature and improve boiler thermal efficiency, most power plant boilers are equipped with flue gas waste heat recovery systems such as air preheaters and economizers. However, as the air preheater and low-temperature economizer at the tail of the boiler, it is usually a low-temperature flue gas area containing water vapor and sulfuric acid vapor. The working conditions are relatively harsh, and low-temperature corrosion and ash blocking are prone to occur. There are two reasons: one is the presence of sulfur trioxide in the flue gas; the other is that the metal wa...

AI Technical Summary

Problems solved by technology

The air preheater and low-temperature economizer in the low-temperature area of ​​the boiler, once low-temperature corrosion and ash blocking occur, it will cause blockage of the flue gas channel, increase the resistance of the induced draft, and cause the boiler to burn under positive pressure.

This not only reduces the output of the boiler, but even causes the boiler to be shut down.

[0004] As a result of corrosion, the pipes of the air preheater and the low-temperature economizer will leak and be damaged, resulting in serious air leakage and deterioration of combustion conditions

In severe cases, the heating surface has to be replaced frequently, which not only increases the maintenance workload and material loss, but also affects the normal operation of the boiler. Cold air entering the flue gas side will also reduce the flue gas temperature, and accelerate the speed of low-temperature corrosion and ash blocking, thus Affect the safe operation of the boiler

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