Fate of Phosphorus During Co-Combustion of Rapeseed Cake with Wood [chapter]

P. Piotrowska, M. Zevenhoven, M. Hupa, K. Davidsson, L. E. Åmand, E. C. Zabetta, V. Barišić
2009 Proceedings of the 20th International Conference on Fluidized Bed Combustion  
Recent studies show that deposit formation and agglomeration in fluidized bed boilers may be aggravated by a high phosphorus content besides alkali metals, chlorine and sulphur in a fuel. This paper presents the fate of phosphorus during co-combustion of wood chips and wood pellets with rapeseed cake pellets, a high phosphorus fuel in a 12MW CFB boiler. 12 hour tests with 12% and 18% (energy basis) of rapeseed cake with wood were performed with and without limestone addition. All fuels were
more » ... All fuels were characterised by means of standard fuel analyses combined with chemical fractionation. Retrieved ash samples were analysed using wet chemical analysis complemented with SEM/EDXA. Gaseous alkali metal chlorides as well as HCl and SO 2 were measured upstream of the convective pass at a flue gas temperature of 800 o C where also the deposit samples were collected with a deposit probe. The composition of deposits was studied with SEM/EDXA. Analyses of bed material particle cross-sections showed phosphorus compounds present within a K-silicates matrix between the agglomerated sand particles, indicating direct attack of gaseous potassium compounds on the bed surface followed by adhesion of rich in phosphorus ash particles. Build-up of the deposits took place mainly on the windward side of the probe; where up to 9 wt-% of phosphorus was present. SEM/EDXA shows that rapeseed cake addition caused an increase of K, Na besides P indicating presence of low melting phosphate salts in the deposits. During limestone addition in the deposit samples the increase of Cl could be noticed however no significant change in P content was observed. This paper shows that agglomeration and fouling when co-firing rapeseed cake may be linked to its high content of organically bonded phosphorus -phytic acid salts; together with high content of water soluble fraction of alkali metals chlorides and sulphates in the fuel mixture.
doi:10.1007/978-3-642-02682-9_152 fatcat:ytajpwxpmbbc7cog2sxturdsnm