Critical changes of inorganics during combustion of herbaceous biomass displayed in its water soluble fractions

In order to clarify the key factors of problems in combustion of herbaceous biomass, soluble and insoluble fractions of corn stover, wheat straw and rice straw pre and post combustion were prepared and examined. Elemental contents, components of the samples and mass-loss/heat-effect at heating stage of the samples were measured using X-ray fluorescence (XRF), X-ray Diffraction (XRD), and simultaneous thermal analysis (STA). Supplementary STA experiments on water soluble fraction of raw biomass, mixtures of KCl, K₂SO₄, and ash/FeS₂ were analyzed to explain some phenomena. Results show that: 1) The change of solubility from pre to post combustion varies significantly with elements. 2) Congruent melting of KCl and K₂SO₄ occurs at 680 °C during combustion of herbaceous biomass. 3) Changes and release of KCl is the major cause of mass loss of biomass ash at temperature below 900 °C.