Interactions between Quartz Sand and Wood Doped with either K or Na Salts under Steam Gasification and Combustion Atmospheres

Abstract

The interactions between quartz sand and wood, which was doped with either K or Na salts, were investigated in a lab-scale, fixed-bed reactor under either a steam gasification or a combustion atmosphere at 900 °C. For the cases of the potassium/sodium phosphate salts, the interaction was found to be melting induced, while for the cases of the other salts, it was found to be coating induced. Large agglomerates were found to have already been formed during the early stages of steam gasification for the wood samples doped with potassium/sodium carbonate and acetate. However, the agglomerates obtained under the combustion atmosphere were found to be insignificant for the wood samples doped with potassium/sodium chloride. Both the reaction atmosphere and the types of salts were found to affect the formation of potassium/sodium silicates in the agglomerates and the interactions between the quartz sand with gaseous K or Na significantly.

Interactions of Olivine and Silica Sand with Potassium- or Silicon-Rich Agricultural Residues under Combustion, Steam Gasification, and CO2 Gasification

“…Therefore, the K components from grape marc were mostly retained in the solid agglomerates, which implies that the retention ratio of K in the silica bed is closely associated with agglomeration processes. It has been previously suggested that the presence of steam facilitates hydrolysis of K salts, − which was found to favor the reaction with silica sand and therefore retained more K in the agglomerates under a steam gasification atmosphere compared with that of the combustion atmosphere . In contrast, for the cases with olivine as the bed material, K was found to retain in the bed in the solid ash particles other than reacting with the bed material under the combustion or the steam gasification atmosphere.…”

“…It has been previously suggested that the presence of steam facilitates hydrolysis of K salts, 71−73 which was found to favor the reaction with silica sand and therefore retained more K in the agglomerates under a steam gasification atmosphere compared with that of the combustion atmosphere. 9 In contrast, for the cases with olivine as the bed material, K was found to retain in the bed in the solid ash particles other than reacting with the bed material under the combustion or the steam gasification atmosphere. In this context, the retention of K in the olivine bed under the two atmospheres would then be solely reliant on the ash transformation characteristics of grape marc.…”

“…The reactor design was adapted to better handle biogenic residues and waste as input material. Nevertheless, some agricultural residues have already been reported to exhibit challenging fuel properties for thermal conversion processes in DFB reactors. , This is because agricultural residues generally contain higher ash contents, especially potassium (K), which is of concern for fluidized beds as the high K retained in the bed will increase the propensity for agglomeration . A high level of gas-phase potassium in the flue and/or producer gases can also lead to fouling and corrosion of the heat exchange surfaces or downstream processes .…”

“…The bed agglomeration characteristics using silica sand as the bed material under combustion have been extensively studied, ,,,, while those under steam gasification are rather limited. Gasification with steam has been suggested to promote bed agglomeration , because steam can alter the formation of alkali silicates in the agglomerate, ,, the melting behavior of alkali salts, and the retention of K, all of which promote reactions between alkalis and silica sand. However, little information is available about the effect of CO 2 on the interaction between alkalis and silica sand.…”

“…7,8 This is because agricultural residues generally contain higher ash contents, especially potassium (K), which is of concern for fluidized beds as the high K retained in the bed will increase the propensity for agglomeration. 9 A high level of gas-phase potassium in the flue and/or producer gases can also lead to fouling and corrosion of the heat exchange surfaces or downstream processes. 10 The magnitude of each issue is closely associated with the transformation of K, combined with its interaction with the bed material, which varies depending on the chemical composition of each fuel.…”