Physicochemical Composition And Energy Potential Of Main Crop Straw And Stalk

Crop straw is one of the main biomass resources with a huge annual output worldwide. Its scientific usage could help to realize the sustainable development of agriculture and improve eco-environment. Therefore, the research on crop straw attaches highly attention by the governments. This work investigated the difference, variability and correlation of the compositions and energy potentials of wheat straw, rice straw, corn stover, rape stalk and cotton stalk, which derive from different maturity stages, different kinds and different areas. Near Infrared Spectroscopy technology was used for rapid analysis of the compositions and higher heating value (HHV) of crop straw. The kinetics and products of the combustion of crop straw were also studied. The main contents and results of this thesis are listed as follows:As wheat straw was maturing, with the growth days from236to263days, its contents of dry matter (DM), cellulose (Cel), hemicelluloses (Hem) and monosaccharidic compositions of hemicelluloses increased significantly. The contents of water soluble carbohydrates (WSC), crude protein (CP), nitrogen (N), phosphorus (P) and copper (Cu) decreased initially and then leveled off. The contents of lignin (Lig), ash, sulfur (S), potassium (K) and sodium (Na) increased firstly and then decreased slightly. The content of volatile matter (VM), fixed carbon (FC), carbon (C), hydrogen (H), oxygen (O), and HHV had little variation. There were extremely strong correlations between DM, Cel, WSC, CP, N, P, Cu and growth days of wheat straw at the maturity stage (P<0.01).Near infrared reflectance (NIR) spectroscopy is a fast and feasible technology to analyze the compositions and HHV of wheat straw. Both partial least square (PLS) and genetic algorithm and partial least square (GA-PLS) models could be used for the estimation of the compositions and HHV of wheat straw, and GA-PLS method provides sensitive spectral variables correlated well with the compositions and HHV. GA-PLS models could successfully detect the contents of WSC, CP, Ash and N. It is also able to quantify the contents of DM, Cel, VM and HHV. The GA-PLS models had moderate accuracy in examining the content of Hem, C, S and H.The compositions contents of crop straw were24.91-52.26%for Cel,8.39-32.74%for Hem,10.40-33.36%for Lig,0.32-19.85%for WSC,1.15-13.98%for CP,1.08-8.94%for Moist,55.82-80.25%for VM,1.81-19.63%for Ash,8.57-27.45%for FC,34.65-52.33%for C,3.17-7.95%for H,30.82-50.35%for O,0.18-2.23%for N,0.15-1.44%for S,0.04-3.57g/kg for P,2.04-49.53g/kg for K,0.01-10.97g/kg for Na,0.03-13.92g/kg for Ca,0.05-5.97g/kg for Mg,0.03-2.37g/kg for Fe. The HHV, ethanol conversion yields, and biomethane yields were12.98-18.58MJ/kg,331.89-630.16g/kg, and156.40-267.79L/kg, respectively. Significant differences were found among five crop straw compositions and energy potentials (P<0.01). The coefficients of variation (CV) were negatively correlated with the means of the composition of crop straws. There were also significant correlations among the crop straw compositions, briefly summarized as Hem/Ash-Cel/Lig/WSC/CP/P, WSC-CP, CP-N-P-Mg-Cu, VM-Ash-FC, C-H-O-N-S, P-K-Na-Ca and Ash-C/H/O/K (P<0.01). The contents of Cel, Hem, VM,O, ethanol conversion yields, and biomethane yields of crop straw in Northwest China (NW), Southwest China (SW) and Central South China (CS) were higher than those in North China (NC), East China (EC) and Northeast China (NE)(P<0.05), while Lig, CP, Ash, FC, N, S, P, K, Ca and Fe of crop straw in NE, NC and EC were higher than those in CS, SW and NW (P<0.05). Cel, Hem, Lig, Moist, VM, O, ethanol conversion yields and biomethane yields of crop straw were significantly negative correlated with the latitude and longitude (P<0.05), while WSC, CP, ash, FC, N, P, K, Na, Ca, Mg, Fe, Cu and HHV of crop straw were significantly positive correlated with the latitude and longitude (P<0.05).The ignition temperature and burnout temperature of crop straw were236.45-268.60and490.51-558.68℃.The combustion characteristics of wheat straw, corn stover and rape stalk based on thermogravimetric analysis were the best, followed by cotton stalk, while that of rice straw was the worst. One stage reaction kinetics model for crop straw burning showed that crop straw had low activation energy. The combustion characteristics parameters and kinetic parameters of crop straw were signifiscantly correlated with the composition contents (P<0.05). A large amount of CO2and H2O generated from the combustion of crop straw, followed by CH4, C2H5and NH3, and a small amount of NO, HCN, NO2, HC1and SO2were also detected. The concentrations of gas products of corn stover, rape stalk and cotton stalk were higher than those of rice straw and wheat straw. The alkaline index of crop straw was higher than0.34. The phase structures of the mineral elements of ash residue of wheat straw, rice straw and corn stover were basically the same, while those in rape stalk and cotton stalk were different.