Bed agglomeration behavior in biomass firing FBC conditions
Ladda ner
Typ
Examensarbete för masterexamen
Program
Materials chemistry (MPMCN), MSc
Publicerad
2020
Författare
Tropp, Frida
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
When fossil fuels are phased out and replaced with biomass in energy conversion in
fluidized beds, ash-related problems like fouling, sintering, and agglomeration are
likely to increase. Agglomeration in a fluidized bed can cause defluidization and
result in high operating costs. Biomass with high alkali content like agriculture
residue and waste is especially problematic. Since the composition of the fuel is
hard to change, a possible solution to the problems could be using alternative bed
materials that counteract the agglomeration tendency of the biomass fuel. Therefore,
this study focuses on agglomeration phenomena in fluidized beds using alternative
bed materials in an attempt to avoid defluidization of the bed.
In this study, two byproducts from the steel industry, blast furnace slag, and
oxide scales, were tested as bed materials in a laboratory-scale bubbling fluidized
bed reactor. Both fuel and salt experiments were performed at 850°C and 900°C.
Sunflower seed shell pellets were used as fuel and were fed to the reactor until
defluidization occurred or until 700 g had been fed. The salt K2CO3, a synthetic ash
component, was added to the reactor in batches of 0.5 g/10 min until defluidization
occurred or until a total of 10 g had been fed. The results from the experiments
with the two bed materials were also compared to previous studies performed in the
same reactor using silica sand as bed material.
After each experiment, the bed was examined and analyzed with scanning electron
microscope coupled with an energy dispersive X-ray analyzer (SEM-EDX). In
the experiments with blast furnace slag, bed agglomerates were found to have been
formed around sand particles and potassium silicate glued the particles together. In
the oxide scale bed, potassium gathered around the particles, and only very small
amounts of potassium silicate could be found after combustion with sunflower seed
shell pellets.
Both blast furnace slag and oxide scales proved to be able to withstand higher
weight percentages of potassium in the bed before defluidization occurred compared
to silica sand. This indicates that they could be more suitable bed materials than
silica sand for fuels with a high potassium content such as sunflower seed shell
pellets.
Beskrivning
Ämne/nyckelord
bubbling fluidized bed combustion , silica sand , blast furnace slag , oxide scale , sunflower seed shell pellets , potassium carbonate