Waste incinerators are a common cause of corrosion

Domestic garbage as fuel, has the characteristics of high moisture content, low calorific value, large changes in component composition, etc., in the process of operation of the garbage incinerator, its unique combustion conditions corrode the metal heating surface of the boiler, mainly due to the following reasons:

(1) In the process of combustion in the furnace, domestic garbage decomposes a mixture of chloride, alkaline metal, pyrosulfate and some heavy metals related to corrosion and lower melting point, and its compound effect is mainly to produce high-temperature corrosion on the metal heating surface at the superheater position under the condition of high temperature flue gas and high metal pipe wall temperature.

(2) The ash scale on the pipe wall contains K2SO4 and Na2SO4, which reacts with iron oxide on the surface of the pipe wall to form alkali metal composite sulfate K3Fe (SO4) 3 and Na3Fe (SO4) in the flue gas containing SO3, which will melt into a liquid state in the range of 550 °C ~ 570 °C, which is strongly corrosive to the metal pipe wall, and the corrosion is more serious at the wall temperature of 600 °C ~ 700 °C. Therefore, the working fluid of the early waste incineration boiler was saturated steam with low parameters, which slowed down the corrosion rate of the metal tube wall on the heating surface at a lower temperature. With the improvement of the incineration process and the application of some new corrosion-resistant materials, most of the working fluid parameters of the waste incineration boiler have been selected below 4.0MPa/400°C, and the wall temperature of the superheater has been controlled below 130°C.

(3) The solid particles carried in the flue gas and frequent soot blowing cause the erosion and corrosion wear of the metal pipe wall on the heating surface.

(4) The uncertainty of the garbage composition will cause the combustion temperature and working fluid parameters of the garbage incineration boiler to fluctuate in a large range, which will accelerate the fatigue of the metal on the heating surface, produce fatigue cracks, and external corrosive gases will erode the crack gaps and accelerate the corrosion of the pipe wall.

(5) The deterioration of the quality of the boiler feed water makes the inner wall of the heating surface tube scaled, resulting in the local overtemperature of the pipe wall, accelerating the creep rate of the metal and the high temperature corrosion of the outer wall.

(6) The structure of the superheater is poor, and the shape of the superheater bundle or the fin root of the fin superheater will cause the pipe wall to rupture in the form of creep and high-temperature corrosion at the stress concentration.

(7) When the waste incineration boiler starts and stops the furnace, the wall temperature of the metal heating surface is lower than the dew point of the acid in the flue gas, and low-temperature corrosion occurs.