TY - JOUR

T1 - Ash transformation and deposit build-up during biomass suspension and grate firing: Full-scale experimental studies

A1 - Shafique Bashir,Muhammad

A1 - Jensen,Peter Arendt

A1 - Frandsen,Flemming

A1 - Wedel,Stig

A1 - Dam-Johansen,Kim

A1 - Wadenbäck,JOhan

A1 - Thaaning,Søren

AU - Shafique Bashir,Muhammad

AU - Jensen,Peter Arendt

AU - Frandsen,Flemming

AU - Wedel,Stig

AU - Dam-Johansen,Kim

AU - Wadenbäck,JOhan

AU - Thaaning,Søren

PB - Elsevier BV

PY - 2012

Y1 - 2012

N2 - An attractive option for reducing the net CO2 emissions is to substitute coal with biomass in large power plant boilers. However, the presence of chlorine (Cl) and alkali metals (K, Na) in biomassmay induce large operational problems due to ash deposit formation on the superheater tubes. The aim of this study was to investigate ash transformation and deposition behavior in two biomass-fired boilers, firing wheat straw and/or wood. The influence of strawfiring technology (grate and suspension) on the ash transformation, deposit formation rate and deposit characteristics has been investigated. Bulk elemental analysis of fly ashes revealed that fly ash from suspension firing of straw has high contents of Si, K and Ca, while fly ash from straw firing on grate was rich in the volatile elements K, Cl and S. Investigations of deposit formation ratesweremade in the superheater and convective pass regions of the boilers by use of an advanced online deposit probe. During straw firing on grate, the measured deposit formation ratewas close to 38 g/m2/h. Data fromstraw suspension firing showed a deposit formation rate of 41 g/m2/h. The deposit formation rates during straw suspension firing and straw grate firing were on similar levels. This was observed even though the concentration of fly ash in the flue gas was significantly higher during straw suspension firing. The influence of co-combustion of wood with straw on deposit formation rate, probe heat uptake and deposit characteristicswas also investigated during suspension firing conditions. Data from 35% straw suspension firing with wood showed a deposit formation rate of 33 g/m2/h for the first 12 h. The deposit formation rate increased to 41 g/m2/h with 100% strawfiring. The probe heat uptake reduction up to 40 h of exposure time was 3.0, 7.3, 8.4 and 16.5 kW/m2 during 35, 65, 80 and 100% straw firing, respectively.

AB - An attractive option for reducing the net CO2 emissions is to substitute coal with biomass in large power plant boilers. However, the presence of chlorine (Cl) and alkali metals (K, Na) in biomassmay induce large operational problems due to ash deposit formation on the superheater tubes. The aim of this study was to investigate ash transformation and deposition behavior in two biomass-fired boilers, firing wheat straw and/or wood. The influence of strawfiring technology (grate and suspension) on the ash transformation, deposit formation rate and deposit characteristics has been investigated. Bulk elemental analysis of fly ashes revealed that fly ash from suspension firing of straw has high contents of Si, K and Ca, while fly ash from straw firing on grate was rich in the volatile elements K, Cl and S. Investigations of deposit formation ratesweremade in the superheater and convective pass regions of the boilers by use of an advanced online deposit probe. During straw firing on grate, the measured deposit formation ratewas close to 38 g/m2/h. Data fromstraw suspension firing showed a deposit formation rate of 41 g/m2/h. The deposit formation rates during straw suspension firing and straw grate firing were on similar levels. This was observed even though the concentration of fly ash in the flue gas was significantly higher during straw suspension firing. The influence of co-combustion of wood with straw on deposit formation rate, probe heat uptake and deposit characteristicswas also investigated during suspension firing conditions. Data from 35% straw suspension firing with wood showed a deposit formation rate of 33 g/m2/h for the first 12 h. The deposit formation rate increased to 41 g/m2/h with 100% strawfiring. The probe heat uptake reduction up to 40 h of exposure time was 3.0, 7.3, 8.4 and 16.5 kW/m2 during 35, 65, 80 and 100% straw firing, respectively.

KW - Suspension-fired boiler

KW - Fly ash

KW - Wood

KW - Straw

KW - Grate-fired boiler

KW - Deposit formation rate

U2 - 10.1016/j.fuproc.2012.01.018

DO - 10.1016/j.fuproc.2012.01.018

JO - Fuel Processing Technology

JF - Fuel Processing Technology

SN - 0378-3820

VL - 97

SP - 93

EP - 106

ER -