Dynamic investigation on potassium migration and transformation during biochar combustion and its correlation with combustion reactivity

For agricultural biomass combustion, K migration and transformation is a key factor affecting boiler operation and reaction characteristics. In this study, dynamic K migration and transformation characteristics during rice straw char combustion process under different O2 concentrations were studied using chemical fractionation analysis (CFA), X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX). Furthermore, the correlation between K migration/transformation and char combustion reactivity was discussed. The results showed that most of K in rice straw char was H2O-soluble K. And the main forms of H2O-soluble K and insoluble K are KCl and KAlSi3O8, respectively. As reaction proceeded, the contents of H2Osoluble K and insoluble K decreased but those of NH4Ac-soluble K and HCl-soluble K increased. Most of the released K is H2O-soluble K. H2O-soluble K would be transformed into NH4Ac-soluble K and HCl-soluble K, and some insoluble K would be transformed into H2O-soluble K. The increase of O2 concentration would stimulate the transformation of H2O-soluble K into NH4Ac-soluble K, HCl-soluble K and released K. However, the reaction to form K-aluminosilicate was hardly found during the combustion process at 400 celcius. Ultimately, it is found that H2O-soluble K is the key occurrence form K affecting the combustion characteristics of rice straw char.

Automated summary

The migration and transformation characteristics of potassium (K) during the combustion process of rice straw char under different O2 concentrations were studied. It was found that most of the K in rice straw char is water-soluble K, which can be transformed into NH4Ac-soluble K and HCl-soluble K. The increase of O2 concentration promotes the transformation of water-soluble K. However, no reaction to form K-aluminosilicate was observed during the combustion process at 400 degrees Celsius. It was concluded that water-soluble K is the key form affecting the combustion characteristics of rice straw char.