Systematic Studies of Ash Composition During the Co-Combustion of Rapeseed Cake and Bark

• Agglomeration occurring during the firing of phosphorus-rich biomass is not fully understood. It has become clear that the ash-forming matter in agricultural biomass (e.g., rapeseed cake) is phosphorus dominated and that phosphate species are involved in agglomeration. Understanding the agglomeration mechanisms would provide valuable insight into possible strategies for preventing defluidization. The objective of this work was to study the ash composition resulting from the combustion of a phosphorus-rich fuel, in particular, the phosphorus compounds formed; the focus was the effect of ash composition on the formation of sticky ash particles, which cause defluidization. Eleven mixtures of rapeseed cake and bark with varying Ca/P molar ratio were studied. Using a 5 kW quartz BFB reactor operated at approximately 800 °C, eight‐hour combustion tests were performed prior to each agglomeration experiment. Fly ash and bottom ash samples were extensively analyzed with SEM/EDX, and the fuel properties were also determined. Rapeseed cake ash consists of particles containing different K/Na-Ca/Mg-P compounds. The ash composition responsible for low defluidization temperatures was found to lie in the region of the ternary diagram containing 30-40 mol% P2O5, 20-40 mol% (CaO+MgO), and 30-50 mol% (K2O+Na2O). Sodium probably formed CaNaPO4, but it was also found in mixtures with other phosphates. The addition of bark favoured the formation of orthophosphates containing 40-50 mol% (CaO+MgO), which increased the first melting temperature of the ash.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Kemiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Chemical Engineering (hsv//eng)

Nyckelord

rapeseed cake

bark

co-combustion

phosphorus

agglomeration

Publikations- och innehållstyp

ref (ämneskategori)

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