Effect of Calcium and Phosphorus on Interactions between Quartz Sand and K-Salt-Doped Wood under Both Steam Gasification and Combustion Atmospheres

Effects of Ca and P on the interactions between quartz sand as the bed material and wood loaded with K2CO3, K2SO4, or KCl salts were studied in a lab-scale, fixed bed reactor at 900 degrees C under a combustion (5%, v/v, O-2) and steam gasification (50%, v/v, steam) atmosphere. The addition of calcite to these salt-loaded wood samples decreases the K retention in agglomerates and reduces the size of agglomerates. The extent of these effects depends upon the salt species. Steam increases the K retention in agglomerates. For wood loaded with salt mixtures of K2CO3/KH2PO4, K2SO4/KH2PO4, or KCl/KH2PO4, agglomerates dominated by K silicates are formed when the content of P in the wood samples is high, while agglomerates dominated by K phosphates are formed when the content of P in the wood samples is low. Both the addition of calcite at 1 wt % Ca to the wood samples loaded with the K salt mixtures and the addition of Ca(PO3)(2) at either 0.5 or 1 wt % Ca to the wood samples loaded with K2CO3, K2SO4, or KCl salts result in the formation of K-Ca phosphates (KCaPO4, K2CaP2O7, or other phases) within the silicate coating layer. Further increasing the Ca(PO3)(2) concentration to 3 wt % Ca leads to the formation of agglomerates dominated by partially molten K-Ca phosphates (K2CaP2O7 or other phases), which is inhibited by steam. With the addition of Ca(PO3)(2), the K retention in agglomerates is increased by the formation of K-Ca phosphates while decreased by the inhibition of K silicates. The domination of the two opposite effects depends upon the concentration of Ca(PO3)(2) and the types of K salts.