Title:
Characterization and Quantification of Deposits Buildup and Removal in Biomass Suspension-Fired Boilers
Author(s):
Bashir, M.S., Jensen, P.A., Frandsen, F., Wedel, S., Dam-Johansen, K., Wolfe, T., Pedersen, S.T., Wadenbäck, J.
Document(s):
Paper
Abstract:
Utilization of biomass as wood or straw in large suspensionfired boilers is an efficient method to reduce the use of fossil fuels consumption and to reduce the net CO2 formation. However, the presence of chlorine and alkali metals in biomass (straw) generate ash with a low melting point and induce large problems of ash deposit formation on the superheater tubes. Full scale studies on biomass ash deposition and removal had been done on biomass grate boilers, while only limited data is available from biomass suspensionfiring. The aim of this study was to investigate deposit mass uptake, heat uptake reduction, fly ash and deposit characteristics, and deposit removal by using an advanced online deposit probe in a suspensionfired boiler using wood and straw pellets as fuel. The influence of fuel type and probe exposure time on the ash deposition rate, the heat uptake, the fly ash and deposit characteristics, and deposit removal have been investigated. The final deposit mass signal after a residence time of 3 to 5 days region was 1041, 1475, 1520 and 1670 g/m2 for 35, 65, 80 and 100% straw share respectively in the superheater region (flue gas temperature, 800900 oC), while the mass uptake was very small in the tube bank region (flue gas temperature, 550605 oC) during pure woodfiring. It was found that during suspensionfiring of pure straw at low boiler load, the overall weight uptake is comparable with gratefiring, even though the amount of fly ash generated was significantly higher during suspensionfiring. Deposit removal through debonding was the main mechanism of deposit shedding when no plant sootblower was in operation. Elemental analysis of fly ashes and deposit samples was made in order to determine concentrations of the major elements Al, Ca, Fe, K, Mg, Na, P, Si, S and Cl. It was identified that the straw suspensionfiring fly ashes contain high contents of Si and Ca, while gratefiring fly ashes contain higher contents of volatile elements K, Cl and S.
Keywords:
biomass, fly ashes, fouling, slagging, deposits
Topic:
Thermochemical conversion - Combustion and co-combustion
Subtopic:
Prediction and abatement of corrosion and gas emissions in large biomass combustion and co-firing plants
Event:
18th European Biomass Conference and Exhibition
Session:
OA5.1
Pages:
1094 - 1100
ISBN-13:
978-88-89407-56-1
ISBN-10:
88-89407-56-5
Paper DOI:
10.5071/18thEUBCE2010-OA5.1
Price:
FREE
