Potassium behaviour during combustion of wood in circulating fluidised bed power plants

Dissertation

Tuomas Valmari

Research output: ThesisDissertationCollection of Articles

2 Citations (Scopus)

Abstract

The behaviour of potassium during circulating fluidised bed combustion of wood-based fuels was studied experimentally in pilot-scale and industrial scale combustors. Aerosol measurement techniques were used for sampling fly ash and inorganic vapours from the flue gas, upstream and downstream of the convective pass. Elemental analysis methods and scanning electron microscopy were used for sample characterisation. The factors affecting in-duct impactor operation in elevated temperatures are discussed in detail. The fly ash released from the combustion chamber consisted of i) coarse particles (1-100 µm) that contained all the non-volatile species, including alkali silicates and CaSO4, as well as of ii) sub-micron K2SO4 particles. KCl was released from the combustion chamber as vapour, and was condensed on the fly ash particles in the convective pass. The fraction of K ending up in the fly ash as alkali silicates was found to depend on the fuel Si-content. A high fuel Si-content also resulted in depletion of K in the bottom ash. About 60-70 % of the fly ash entering the convective pass was deposited on the heat exchanger surfaces in the convective pass, and was removed during the soot-blowing period. The deposition efficiency correlated clearly with the ash-particle size. The largest particles, including alkali silicates, were deposited most effectively, and the deposition efficiency decreased with decreasing particle size. The physical state (vapour, fine particle or coarse particle) of the ash species was shown to have a remarkable effect on the form and rate of ash deposition in the convective pass. When the different fuels were compared, the variation in the deposition efficiency was the most remarkable for sulphur.
Original languageEnglish
QualificationDoctor Degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Kauppinen, Esko, Supervisor, External person
  • Jokiniemi, Jorma, Supervisor, External person
Award date30 Jun 2000
Place of PublicationEspoo
Publisher
Print ISBNs951-38-5569-4
Electronic ISBNs951-38-5570-8
Publication statusPublished - 2000
MoE publication typeG5 Doctoral dissertation (article)

Fingerprint

power plant
fly ash
potassium
combustion
ash
silicate
particle size
bottom ash
soot
fluidised bed
particle
scanning electron microscopy
sulfur
aerosol
sampling
temperature

Keywords

  • fluidized beds
  • biomass
  • wood
  • wood fuels
  • combustion
  • CFBC
  • fluidized bed combustion
  • ashes
  • alkali metals
  • potassium
  • deposition
  • heat exchangers

Cite this

Valmari, T. (2000). Potassium behaviour during combustion of wood in circulating fluidised bed power plants: Dissertation. Espoo: VTT Technical Research Centre of Finland.
Valmari, Tuomas. / Potassium behaviour during combustion of wood in circulating fluidised bed power plants : Dissertation. Espoo : VTT Technical Research Centre of Finland, 2000. 91 p.
@phdthesis{e2887b7bcd8b495d8f9607153d3449d3,
title = "Potassium behaviour during combustion of wood in circulating fluidised bed power plants: Dissertation",
abstract = "The behaviour of potassium during circulating fluidised bed combustion of wood-based fuels was studied experimentally in pilot-scale and industrial scale combustors. Aerosol measurement techniques were used for sampling fly ash and inorganic vapours from the flue gas, upstream and downstream of the convective pass. Elemental analysis methods and scanning electron microscopy were used for sample characterisation. The factors affecting in-duct impactor operation in elevated temperatures are discussed in detail. The fly ash released from the combustion chamber consisted of i) coarse particles (1-100 µm) that contained all the non-volatile species, including alkali silicates and CaSO4, as well as of ii) sub-micron K2SO4 particles. KCl was released from the combustion chamber as vapour, and was condensed on the fly ash particles in the convective pass. The fraction of K ending up in the fly ash as alkali silicates was found to depend on the fuel Si-content. A high fuel Si-content also resulted in depletion of K in the bottom ash. About 60-70 {\%} of the fly ash entering the convective pass was deposited on the heat exchanger surfaces in the convective pass, and was removed during the soot-blowing period. The deposition efficiency correlated clearly with the ash-particle size. The largest particles, including alkali silicates, were deposited most effectively, and the deposition efficiency decreased with decreasing particle size. The physical state (vapour, fine particle or coarse particle) of the ash species was shown to have a remarkable effect on the form and rate of ash deposition in the convective pass. When the different fuels were compared, the variation in the deposition efficiency was the most remarkable for sulphur.",
keywords = "fluidized beds, biomass, wood, wood fuels, combustion, CFBC, fluidized bed combustion, ashes, alkali metals, potassium, deposition, heat exchangers",
author = "Tuomas Valmari",
note = "Project code: K0SU00207",
year = "2000",
language = "English",
isbn = "951-38-5569-4",
series = "VTT Publications",
publisher = "VTT Technical Research Centre of Finland",
number = "414",
address = "Finland",
school = "Aalto University",

}

Potassium behaviour during combustion of wood in circulating fluidised bed power plants : Dissertation. / Valmari, Tuomas.

Espoo : VTT Technical Research Centre of Finland, 2000. 91 p.

Research output: ThesisDissertationCollection of Articles

TY - THES

T1 - Potassium behaviour during combustion of wood in circulating fluidised bed power plants

T2 - Dissertation

AU - Valmari, Tuomas

N1 - Project code: K0SU00207

PY - 2000

Y1 - 2000

N2 - The behaviour of potassium during circulating fluidised bed combustion of wood-based fuels was studied experimentally in pilot-scale and industrial scale combustors. Aerosol measurement techniques were used for sampling fly ash and inorganic vapours from the flue gas, upstream and downstream of the convective pass. Elemental analysis methods and scanning electron microscopy were used for sample characterisation. The factors affecting in-duct impactor operation in elevated temperatures are discussed in detail. The fly ash released from the combustion chamber consisted of i) coarse particles (1-100 µm) that contained all the non-volatile species, including alkali silicates and CaSO4, as well as of ii) sub-micron K2SO4 particles. KCl was released from the combustion chamber as vapour, and was condensed on the fly ash particles in the convective pass. The fraction of K ending up in the fly ash as alkali silicates was found to depend on the fuel Si-content. A high fuel Si-content also resulted in depletion of K in the bottom ash. About 60-70 % of the fly ash entering the convective pass was deposited on the heat exchanger surfaces in the convective pass, and was removed during the soot-blowing period. The deposition efficiency correlated clearly with the ash-particle size. The largest particles, including alkali silicates, were deposited most effectively, and the deposition efficiency decreased with decreasing particle size. The physical state (vapour, fine particle or coarse particle) of the ash species was shown to have a remarkable effect on the form and rate of ash deposition in the convective pass. When the different fuels were compared, the variation in the deposition efficiency was the most remarkable for sulphur.

AB - The behaviour of potassium during circulating fluidised bed combustion of wood-based fuels was studied experimentally in pilot-scale and industrial scale combustors. Aerosol measurement techniques were used for sampling fly ash and inorganic vapours from the flue gas, upstream and downstream of the convective pass. Elemental analysis methods and scanning electron microscopy were used for sample characterisation. The factors affecting in-duct impactor operation in elevated temperatures are discussed in detail. The fly ash released from the combustion chamber consisted of i) coarse particles (1-100 µm) that contained all the non-volatile species, including alkali silicates and CaSO4, as well as of ii) sub-micron K2SO4 particles. KCl was released from the combustion chamber as vapour, and was condensed on the fly ash particles in the convective pass. The fraction of K ending up in the fly ash as alkali silicates was found to depend on the fuel Si-content. A high fuel Si-content also resulted in depletion of K in the bottom ash. About 60-70 % of the fly ash entering the convective pass was deposited on the heat exchanger surfaces in the convective pass, and was removed during the soot-blowing period. The deposition efficiency correlated clearly with the ash-particle size. The largest particles, including alkali silicates, were deposited most effectively, and the deposition efficiency decreased with decreasing particle size. The physical state (vapour, fine particle or coarse particle) of the ash species was shown to have a remarkable effect on the form and rate of ash deposition in the convective pass. When the different fuels were compared, the variation in the deposition efficiency was the most remarkable for sulphur.

KW - fluidized beds

KW - biomass

KW - wood

KW - wood fuels

KW - combustion

KW - CFBC

KW - fluidized bed combustion

KW - ashes

KW - alkali metals

KW - potassium

KW - deposition

KW - heat exchangers

M3 - Dissertation

SN - 951-38-5569-4

T3 - VTT Publications

PB - VTT Technical Research Centre of Finland

CY - Espoo

ER -

Valmari T. Potassium behaviour during combustion of wood in circulating fluidised bed power plants: Dissertation. Espoo: VTT Technical Research Centre of Finland, 2000. 91 p.