High temperature degradation by erosion-corrosion in bubbling fluidized bed combustors

Abstract

Heat-exchanger tubes in fluidized bed combustors (FBCs) often suffer material loss due to combined corrosion and erosion. Most severe damage is believed to be caused by the impact of dense packets of bed material on the lower parts of the tubes. In order to understand this phenomenon, a unique laboratory test rig at Berkeley was designed to simulate the particle hammering interactions between in-bed particles and tubes in bubbling fluidized bed combustors. In this design, a rod shaped specimen is actuated a short distance within a partially fluidized bed. The downward specimen motion is controlled to produce similar frequencies, velocities and impact forces as those experienced by the impacting particle aggregates in practical systems. Room temperature studies have shown that the degradation mechanism is a three-body abrasion process. This paper describes the characteristics of this test rig, reviews results at elevated temperatures and compares them to field experience. At higher temperatures, deposits of the bed material on tube surfaces can act as a protective layer. The deposition depended strongly on the type of bed material, the degree of tube surface oxidation and the tube and bed temperatures. With HCl present in the bed, wastage was increased due to enhanced oxidation and reduced oxide scale adherence

Erosion–corrosion behaviour of Ni–20Cr plasma coating in actual boiler environment

“…The condition at which this layer forms depends on the amount of fine dust particles retained in the bed, which is closely related to the composition of the bed, the specimen and bed temperatures and the oxidation rate of the specimen. 4 Currently superalloys are being used to increase the service life of the boilers, especially in the superheater zones of the boilers. Although the superalloys have adequate mechanical strength at elevated temperatures, they often lack resistance to erosion-corrosion environments.…”

Porosity-Based Corrosion Model for Alkali Halide Ash Deposits during Biomass Co-firing

“…Previous work has included the development of custom experimental rigs, 20 which attempt to replicate fluidized-bed combustors, as well as tests in which samples are exposed to gas flows containing HCl or similar gases. 21,22 Work has also been conducted in which corrosion probes were placed in a biomass combined heat and power (CHP) plant.…”

“…Previous work has included the development of custom experimental rigs, which attempt to replicate fluidized-bed combustors, as well as tests in which samples are exposed to gas flows containing HCl or similar gases. , Work has also been conducted in which corrosion probes were placed in a biomass combined heat and power (CHP) plant . A review of recent research on ash-related issues in fluidized-bed combustion of biomass has been carried out by Hupa, while a review paper focusing specifically on the chlorine-associated corrosion in biomass boilers was carried out by Nielsen et al…”

Abrasion Resistance of Materials

“…Some of the outstanding characteristics are: excellent heat transfer, low emission of contaminants, good combustion efficiencies and good fuel flexibility. However, FBC units can suffer materials deterioration due to particle interaction of solid particles with the heat transfer tubes immersed on the bed (Hou, 2004, Oka, 2004, Rademarkers et al, 1990. Among other issues, some of the most important factors believed to cause wear problems are: the motion of slowly but relatively coarse particles, particles loaded onto the surface by other particles, erosion by relatively fast-moving particles associated with bubbles, and abrasion by blocks of particles thrown into the surface by bubble collapse.…”