Effect of Flue Gases' Corrosive Components on the Degradation Process of Evaporator Tubes.

Mária Hagarová,Miroslav Pástor,Miloš Matvija,Milan Vaško,Gabriela Baranová

doi:10.3390/ma14143860

Mária Hagarová, Miroslav Pástor + Show 3 more

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https://doi.org/10.3390/ma14143860

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Abstract

Corrosion of boiler tubes remains an operational and economic limitation in municipal waste power plants. The understanding of the nature, mechanism, and related factors can help reduce the degradation process caused by corrosion. The chlorine content in the fuel has a significant effect on the production of gaseous components (e.g., HCl) and condensed phases on the chloride base. This study aimed to analyze the effects of flue gases on the outer surface and saturated steam on the inner surface of the evaporator tube. The influence of gaseous chlorides and sulfates or their deposits on the course and intensity of corrosion was observed. The salt melts reacted with the steel surface facing the flue gas flow and increased the thickness of the oxide layer up to a maximum of 30 mm. On the surface not facing the flue gas flow, they disrupted the corrosive layer, reduced its adhesion, and exposed the metal surface. Beneath the massive deposits, a local overheating of the inner surface of the evaporator tubes occurred, which resulted in the release of the protective magnetite layer from the surface. Ash deposits reduce the boiler’s thermal efficiency because they act as a thermal resistor for heat transfer between the flue gases and the working medium in the pipes. The effect of insufficient feedwater treatment was evinced in the presence of mineral salts in the corrosion layer on the inner surface of the tube.

Highlights

Published: 10 July 2021In the heating industry, a boiler device is a whole group of devices used to convert the chemical energy contained in a solid fuel such as coal, biomass, or municipal waste, into thermal energy in the form of water or steam
The specific conditions of corrosion in thermal power devices result from the fact that while the outer surface of heat-exchange tubes is affected by the oxidizing effect of the flue gases or other combustion products with different temperature levels, the inner surface is affected by the oxidizing effect of feedwater, saturated or superheated steam
The superposition of Cl and its compounds manifested itself in the reaction of flue gases with the steel surface by the following mechanisms: 1

Summary

Introduction

A boiler device is a whole group of devices used to convert the chemical energy contained in a solid fuel such as coal, biomass, or municipal waste, into thermal energy in the form of water or steam. The specific conditions of corrosion in thermal power devices result from the fact that while the outer surface of heat-exchange tubes is affected by the oxidizing effect of the flue gases or other combustion products with different temperature levels, the inner surface is affected by the oxidizing effect of feedwater, saturated or superheated steam. The boiling system of the boiler represents an evaporator in which the phase conversion of the feedwater into saturated steam takes place by heat transfer from the flue gases through the heat-exchange surface areas of the water wall tubes. The material of the water wall tubes differs depending on the temperature of their outer surface.

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