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 °C under a combustion (5%, v/v, O2) 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)2at 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)2concentration to 3 wt % Ca leads to the formation of agglomerates dominated by partially molten K–Ca phosphates (K2CaP2O7or 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)2and the types of K salts.