秸秆厌氧发酵改性制备成型燃料试验

Densified biomass fuels production from crop straw pretreated by anaerobic fermentation

针对秸秆压缩成型存在设备磨损严重和厌氧发酵面临的抗生物降解屏障,提出了一种秸秆厌氧发酵改性制备成型燃料的思路并进行了试验研究。以玉米秸秆为原料,在总固体质量分数12%和中温38℃下对原料分别进行为期10和20d的厌氧发酵,发酵后的沼渣经粉碎和干燥后于100℃、6MPa条件下压缩成直径10mm的颗粒燃料。试验结果表明:经过10和20d的发酵,玉米秸秆所含能量仅有14.49%和32.01%转移到沼气中;沼渣弹筒发热量分别达到18.01和18.05MJ/kg,高于原料的17.02MJ/kg;沼渣挥发物质质量分数为74.08%和72.63%,比原料的81.02%分别下降了8.6%和10.4%;沼渣木质素质量分数为16.98%和17.92%,比原料的13.65%分别增加了24.4%和31.3%;沼渣苯醇抽提物质量分数为5.66%和4.86%,比原料的7.52%分别降低了24.7%和35.4%。成型试验结果表明:沼渣制成的成型燃料松弛密度分别为1.041g/cm3和1.150g/cm3,比未发酵秸秆的1.019g/cm3分别提高了2.2%和12.86%。厌氧发酵改性有助于提高秸秆成型性能、制粒达到相同松弛密度所需的压力较小,有助于降低成型过程设备磨损,且基于上述思路形成的气固二元燃料生产工艺,使秸秆的转化利用不再受制于抗降解屏障,值得深入研究。

Corn straw is one of the major crop straws considered for producing renewable fuels and energy in China. Production of densified biomass fuel （DBF） and biogas from corn straw are two main conversion approaches. One of the major problems associated with the DBF production from corn straw is rapid wear of the briquetting/pelleting unit. The primary technical barrier for anaerobic fermentation of corn straw is its recalcitrance structure. Aiming at these problems, we proposed a process of DBF production from corn straw pretreated by anaerobic fermentation. In this process, corn straw is firstly anaerobicly digested to produce biogas, and then the solid digestate is pressed into DBF. In order to prove the feasibility of this process, the anaerobic fermentation experiments were performed at 38℃ at 12% of total solid （TS）. The experiments were divided into two groups with a digestion period of 10 and 20 days, respectively. After anaerobic digestion, the digestate was shed, dried, and pressed into DBF with a diameter of 10mm in a hydraulic device at pressure up to 6 MPa and a temperature of 100℃ .The anaerobic experimental results showed that after 10 and 20 days of anaerobic fermentation, 14.49% and 32.01% of the energy contained by corn straw was converted to biogas energy, and the characteristics of digestate were beneficial to DBF production in terms of lignin and extract contents. The lignin content of solid digestate was elevated to 16.98% and 17.92%, and increased by 24.4% and 31.3% compared to 13.65% of corn straw. The benzene alcohol extract of solid digestate was lowered to 5.66% and 4.86%, and decreased by 24.7% and 35.4% compared to 7.52% of corn straw. At the same time, the characteristic changes of solid digestate on aspects of heat value and volatile content were in favor of improving DBF quality： the bomb calorific values of solid digestate reached 18.01 and 18.05 MJ/kg, higher than the 17.02 MJ/kg of raw material, and the volatile contents of solid digestate reached 74.08% and 72.63%, decreased by 8.6% and 10.4% than the 81.02% of raw material. The DBF production results illustrated that the relaxation densities were 1.041 and 1.150 g/cm 3 , respectively for DBFs produced with solid digestate obtained from anaerobic fermentation for 10 and 20 days, and increased by 2.2% and 12.86% compared to1.019 g/cm 3 of DBF produced with corn straw. In conclusion, co-production of DBF and biogas from corn straw based on anaerobic fermentation has the potential of helping to reduce the wear of a briquetting/pelleting unit in its densification process, and avoiding a recalcitrance structure obstacle in its anaerobic fermentation.