Hydrothermal carbonization of forest waste into solid fuel: Mechanism and combustion behavior

Abstract

The structural characteristics and fuel performance of hydrochars prepared by hydrothermal carbonization (HTC) of forestry waste (FW) were studied. Proximate analysis and ultimate analysis were used to characterize the chemical composition of the samples, scanning electron microscopy and specific surface area analysis were used to characterize the microscopic results of the samples, Fourier transform infrared spectroscopy and Raman spectroscopy were used to characterize the microcrystalline structure, and non-isothermal thermogravimetry was used to characterize the combustion properties of the HTC products. The results show that with the increase of the HTC temperature, the mass yield of hydrochar decreases, and the content of gas products and liquid products increases. With the increase of HTC temperature, the volatile content of hydrochar gradually decreases, and the fixed carbon content gradually increases. The high heating value (HHV) of FW-280 sample is 1.46 times that of the FW. The porosity and specific surface area increase first and then decrease with the increase of the HTC temperature, and reach the maximum value at 240 °C. With the increase of HTC temperature, the IG/IAll value of the sample increased from 0.282 to 0.346, and the order degree of the carbonaceous structure gradually increased. The combustion process of hydrochars can be divided into two stages: volatile matter removal and carbon combustion. FW-280 has better combustion performance due to its higher carbon content and Rmax2 value of 0.002616. Therefore, the comprehensive research on the physicochemical properties and combustion performance of FW hydrochar will facilitate the expansion of the application of FW resources.