Effect of CaO and hydrothermal carbonization conditions on the fuel characteristics of rice husk hydrochars

The effects of hydrothermal temperature and catalyst concentration on the basic elements and combustion characteristics and kinetic parameters of hydrochars were investigated using ultimate analyzer and thermogravimetric method with rice husk as the research object and CaO as the additives. The results showed that: (1) the fixed carbon content of hydrochars gradually increased with the increase of hydrothermal temperature, whereas the volatile content gradually decreased. When CaO was added, the changes of fixed carbon and volatile fraction gradually decreased with the increase of hydrothermal temperature, and H/C atomic ratio increased to different degrees, which had a certain inhibitory effect on the degree of hydrothermal carbonization of rice husk. (2) The peak of the volatile fraction combustion section of hydrochars combustion derivative thermogravimetric curve was higher than that of the fixed carbon combustion section. CaO concentration has less effect on the volatile combustion section, and the combustion peak of the fixed carbon section is significantly reduced. (3) When the heating rate of the combustion test is accelerated, the ignition and burnout temperatures of the sample increase and the overall combustion curve shifts to the high temperature region. (4) The comprehensive combustion index S-N decreases with the increase in hydrothermal temperature. When the hydrothermal temperature is certain, the CaO concentration causes the S-N to increase and then decrease, which finally reduces the combustion performance of hydrochars. (5) The activation energy of the fixed carbon combustion section of hydrochars is lower than that of the volatile combustion section, and the activation energy of both volatile and fixed carbon combustion sections gradually decreases after adding CaO. The primary reaction kinetic model was used to describe the combustion kinetics of hydrochars, and the correlation coefficients (R-2) were all above 0.92, and the results were reliable.