Abstract
This work presents studies on the co-combustion of sludge and wheat straw (30 wt % sludge + 70 wt % wheat straw). Prior to the combustion experiment, thermogravimetric analysis was performed to investigate the combustion characteristic of the blended fuel. Results indicated that the blended fuel could remedy the defect of each individual component and also promote the combustion. Co-combustion experiments were conducted in a lab-scale vertical tube furnace and the ash samples were analyzed by Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES), X-ray Diffraction (XRD), and Scanning Electron Microscope (SEM). Thermodynamic calculations were also made to study the interactions that occurred. Addition of sludge could raise the melting point of wheat straw ash and reduce the slagging tendency. Co-combustion also restrained the release of K and transferred it into aluminosilicate and phosphate. Transfer of Pb and Zn in the co-combustion was also studied. The release and leaching toxicity of the two heavy metals in the co-combustion were weakened effectively by wheat straw. PbCl2(g) and ZnCl2(g) could be captured by K2SiO3 in wheat straw ash particles and generate silicates. Interactions that possibly occurred between K, Zn, and Pb components were discussed at the end of the paper.
Highlights
Biomass energy is attracting the world’s attention due to its zero CO2 emissions and considerable production worldwide
It could be seen in sludge combustion, Pb mainly existed in the form of PbSiO3 and Pb3 (PO4 )2 at low temperatures, meaning that P and Si in the raw sludge could bind with Pb and restrain its release
The value varied widely from the actual release ratio gained by the experiment, it could reveal the decrease of combining capacity of Zn and Cl in the co-combustion
Summary
Biomass energy is attracting the world’s attention due to its zero CO2 emissions and considerable production worldwide. Cl did not exert a significant effect on Zn release in sludge combustion compared with other heavy metals [19,20]. The chemical equilibrium calculation was used to investigate the existing form of alkali and heavy metals and it was believed that the theoretical conclusion corresponded basically with experimental results [25,26]. Despite the numerous studies concerning the combustion of biomass and sludge before, the mechanisms of co-combustion characteristics and slagging control in the co-combustion remain unclear and require further investigation. Mass fraction of sludge in the co-combustion was set as 30% considering its relatively lower heat value and higher amount of heavy metals, and could be applied to the existing biomass power plants [21,22]
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