保温时间与粒度对稻秆和棉秆热解产物组成及能量转化影响

热解炭化技术的开发对秸秆的能源化利用具有重要意义。试验研究了保温时间与粒度对水稻和棉花秸秆热解产物理化特性及能源转化的影响。结果表明,保温时间从0到120 min中,秸秆生物炭产率先降低后略增加,热解气中CH_4、C_nH_m和H_2百分含量增加,其高位热值和能量转化率增加,而生物炭的pH值、电导率、灰分、固定碳、C、高位热值增加,保温时间为90 min的生物炭的炭化程度最好。秸秆中能量有1.5%~5.4%保留在热解气中,有50%~57%保留在生物炭中。不同粒度相比,粗粉秸秆的生物炭的炭产率、挥发分、H、O、N及碳转化率最高,细粉秸秆热解气中CO和CH_4百分含量、高位热值和能量转化率最高,而超微秸秆生物炭的pH值、灰分、C最高。棉花秸秆生物炭的挥发分、固定碳、C、H、碳转化率、高位热值和能量转化率高于水稻秸秆生物炭。

Effects of holding time and particle size on physicochemical properties and energy conversion of pyrolysis product conponent of rice straw and cotton stalk

The development of pyrolysis technology has great significances for using crop residue resources and relieving energy crisis. Physicochemical properties and energy conversion of gases and biochar obtained from the pyrolysis with different particle sizes of rice straw and cotton stalk were investigated under different holding time. The results showed that the biochar yields firstly decreased from 0 to 90 min and then slightly increased, and the gas yields gradually increased. With the increase of holding time, the proportions of CO2 and CO in bio-gas decreased, while the proportions of CH4, CnHm and H2 in bio-gas increased. With the increase of holding time, the contents of the ash, fixed carbon, C, pH value and electrical conductivity with different particle sizes of biochar increased from 0 to 120 min, while the contents of volatile matter, H, O and N of the biochar decreased. The higher heating values of gases and biochar with different particle sizes of crop residues gradually increased with the increasing holding time, and the energy conversion efficiency in the gas increased, however, the energy conversion efficiency in the biochar decreased. The carbon conversion efficiency in the biochar was significantly higher than that in gas (P<0.05). 1.5%-5.4% energy of crop residue was remained in the bio-gas, and 50%-57% energy of crop residue was remained in the biochar. The biochar produced at the holding time of 90 min had good carbonization degree and can be used as fuels. Different crop residues and different particle sizes had great significant influences on the physicochemical properties of pyrolysis gases and biochar (P<0.05). Comparing the three different particle sizes of crop residues, the biochar yield of the coarse grinding crop residue was the highest and the tar yield was the lowest, while the biochar yield and gas yield of the ultrafine grinding crop residue were the lowest and the tar yield was the highest. The proportions of CO and CH4, higher heating value and the energy conversion efficiency of the pyrolysis gases of the fine grinding crop residue were the highest. The contents of volatile matter, H, O, N and the carbon conversion efficiency of the coarse grinding crop residue biochar were the highest, and the contents of S, electrical conductivity and energy conversion efficiency of the fine grinding crop residue biochar were the highest, while the contents of ash, C, pH value of the ultrafine power crop residue biochar were the highest. Comparing the different types of crop residues, the gas yield, carbon conversion efficiency, higher heating value and energy conversion efficiency of the pyrolysis gases of rice straw were higher than those of cotton stalk, while the proportions of CO2, CH4, CnHm and H2 produced by the pyrolysis of cotton stalk were higher than those of rice straw. The ash content and electrical conductivity of rice straw biochar were higher than those of cotton stalk biochar, while the volatile matter, fixed carbon, pH value, C, H, N, S, carbon conversion efficiency, higher heating value and energy conversion efficiency of the cotton stalk were higher than those of rice straw biochar. The maximum higher heating values of gases and biochar of rice straw and cotton stalk were 7.33, 6.62 MJ/m3 and 20.22, 23.58 MJ/kg, respectively. Cotton stalk is more suitable for pyrolysis carbonization, and the biochar of cotton stalk is more suitable to be applied as fuels.