Experimental Study On Pellets Preparation From Bamboo And Characteristics Of Hydrochar Obtained From Biomass

Moso bamboo was used as the raw material.Firstly,the influences of the process parameters including the grain size,the moisture content,the preheating temperature,and the applied forces of the raw materials on the loose density and durability of bamboo pellets were studied by using the orthogonal experiments in this paper.The optimum factors were as follows,the grain size of raw materials was 0.38 mm;the moisture content was 15%;the preheating temperature was 125 ?;and the pressure was 20 MPa.Under this condition,the loose density reached 1.110 g/cm3 and the durability reached 0.955.Secondly,hydrothermal carbonization was employed to pretreat moso bamboo for hydrochar preparation in this study.Thermal gravimetric curves were measured for the raw bamboo and hydrochars at different heating rates(10?20?40 K/min).The combustion kinetics parameters were calculated by the model-free methods,of which Flynn-Wall-Ozawa(FWO)was the most appropriate for the calculation of activated energy and has similar values with Kissinger-Akahira-Sunose(KAS).The activation energy increased first and then decreased with the increase of the mass conversion.Both the first and second peaks in DTG curves shifted to the higher temperature and meanwhile the ignition performances of hydrochars decreased and the burnout temperatures increased when the heating rate increased.The higher the hydrothermal temperature,the greater the calorific value and the lower the energy yield were.Taking the calorific value,the energy yield and the comprehensive combustion characteristic index into considering,hydrochar prepared at 260 ? for 30 mins was suitable for use as fuel.Eventually,influences of feedwater pH(3–11)were studied for hydrothermal carbonization(HTC)of microcrystalline cellulose(MC)at 220 ?,4 h.Sodium hydroxide,sodium bicarbonate and citric acid were used to prepare solutions of different pH values,respectively.Elemental and scanning electron microscopy(SEM)analyses were used to investigate the influences of the pH values of solutions from 3 to 11 on physical,chemical,thermal and structural characteristics of hydro-chars.The van Krevelen diagram was also used to analyze the influences of the pH values of solutions on the hydrothermal carbonization process.Results showed that mass yield and carbon fixed ration(FC)decreased with increased acidity.Hydro-char yield and FC were only 35.5% and 41.82% under the pH of 3,and the hydro-char possessed the best aromaticity.Whereas at pH of 11,the hydro-char yield and FC reached as high as 46.5% and 48.91%,and the hydro-char had the best hydrophilic respectively.Dehydration was the main reaction during the HTC process.SEM images showed that the microsphere size of HCA(hydro-chars from acidic condition)decreased with increased acidity while HCB(hydro-chars from basic condition)had uniform microsphere size and good sphericity.