Causes of low-temperature corrosion in CFB combustion of bituminous coal

A4 Conference proceedings


Internal Authors/Editors


Publication Details

List of Authors: Emil Vainio, Tor Laurén, Patrik Yrjas, Mikko Hupa, Edgardo Coda Zabetta, Kyösti Vänskä
Editors: Wojciech Nowak, Marek Ściążko, Paweł Mirek
Publication year: 2017
Book title: Proceedings of the 12th International Conference on Fluidized Bed Technology
ISBN: 978-83-62079-16-2


Abstract

Maximizing energy recovery by keeping flue gas temperatures as low as
possible is of great interest in the power business, as higher recovery leads
to higher plant efficiency. However, minimum allowable temperature is often limited
by the presence of sulfuric acid. Condensation of sulfuric acid on steel
surfaces could lead to severe corrosion. Hygroscopic deposits may also cause
severe corrosion by taking up water and thus leading to wet corrosion. In this
study, the risk of sulfuric acid corrosion and corrosion caused by hygroscopic
deposits was studied in a full-scale circulating fluidized bed (CFB) boiler.
The boiler was run both with and without limestone addition to reveal the
effect of limestone on sulfuric acid corrosion and the effect of limestone on
wet deposit corrosion. Furthermore, the effect of load on corrosion was
studied. The measurements were performed before and after the electrostatic
precipitator (ESP). A KCl salt method, which has been developed to detect trace
concentrations of gaseous sulfuric acid, was used to study the risk of sulfuric
acid corrosion. Furthermore, an acid dew point meter was used to determine the
dew point temperature in the flue gases. Additionally, an air-cooled short-term
corrosion probe was used to measure the corrosion rate of carbon steel at
various material temperatures. Windward, side, and leeward side deposits were
collected from the probe and analyzed by means of scanning electron microscopy
with energy dispersive X-ray spectroscopy (SEM-EDX). Fuel and fly ash samples
for the different test cases were collected and analyzed. The work revealed new
interesting findings on the causes of low-temperature corrosion in combustion
of bituminous coal. The different operational parameters of the boiler had a
significant impact on deposit composition and on expected corrosion risk. In this
paper, we discuss the risks of sulfuric acid corrosion as well as corrosion
caused by hygroscopic deposits. Furthermore, the influence of boiler parameters
on deposit composition and chemistry will be discussed.


Last updated on 2019-18-10 at 03:31