Abstract
A Kentucky coal sample treated by microwave irradiation (MI) combined with sodium hydroxide solution was performed using a thermo-gravimetric analyzer (TGA) coupled to a Fourier transform infrared spectrometer (FTIR). The combustion properties and structural changes of coal under different conditions were investigated and compared. The results show that the desulfurization efficiency of coal samples increases with the increase of sodium hydroxide solution concentration. Microwave irradiation can significantly improve the desulfurization efficiency. The whole combustion process of the treated coal sample becomes longer; the combustion performance becomes worse. The total mass loss of coal treated samples is significantly reduced, and the temperature corresponding to the maximum weight loss rate decreases with the increase of sodium hydroxide concentration. The infrared spectra of the coal samples treated with microwave and 5% sodium hydroxide solution were basically unchanged, while the O containing groups and aromatic C-H groups increased in the coal samples treated with 20% sodium hydroxide solution.
Highlights
Compared with the raw coal, the ignition temperature values of the coal sample treated with sodium hydroxide solution was shifted to lower temperatures, and the burnout temperature was shifted to higher temperatures, so the whole combustion range became longer (See Figure 2d)
It can be to seen compared with raw coal, the combustion characteristic indexby of increases due thethat removal of inflammable substances in the coal samples treated coal samples treated by microwave combined with sodium hydroxide solution decreases alkali solution and microwave irradiation
AsAs thethe concentration of of sodium hydroxide solution used in in thethe experiment increases, the temperature corresponding to the maximum weight loss rate experiment increases, the temperature corresponding to the maximum weight loss rate of of treated coal sample decreases
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Various methods have been used for coal desulfurization before combustion by physical, chemical, and biological ways. Each of these processes can remove sulfur from coal to a certain extent, but they all have limitations. Research confirmed that microwaves combined with chemical reagents efficiently and safely remove sulfur from coal under lower temperature conditions [10,11,12]. The present research focuses on the changes of (1) sulfur forms and (2) organic functional groups in coal samples before and after microwave combined reagent desulfurization. The above studies confirmed that microwave combined auxiliary desulfurization has different effects on the organic structure and sulfur type of coal samples. TGA and FTIR were applied to explore the effects of coal combustion characteristics by microwave irradiation combined with sodium hydroxide solution
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