生物质作为可再生能源，具有资源丰富、着火容易、污染物排放低等优点，但存在能量密度低、水分高等缺点。煤粉则具有能量密度高的优点和着火困难、污染物排放高等缺点。将生物质高比例掺混入煤粉（生物质/煤粉质量比大于5∶5），可有效解决生物质利用率低、能量密度低、煤粉着火较难和污染物排放高等问题，提高能源利用率，实现节能减排，该方法已成为一种新型能源利用技术。目前学者研究主要集中低掺混比例（小于5∶5），国内常见生物质与煤粉在高掺混比例下的混燃特性尚有待深入研究。采用热重分析法研究了不同生物质（玉米秸秆、稻杆、玉米芯、棉花及杨木屑）与煤粉在高掺混比例下（0∶10、5∶5、6∶4、7∶3、8∶2、10∶0）的燃烧特性和动力学特性，分析了不同生物质种类及掺混比例对燃料热失重特性、特征温度、反应动力学、燃尽特性及燃烧特性指数等影响，并确定不同生物质的最佳掺混比例。结果表明：混合样品的失重曲线表现为失水、挥发分燃烧、固定碳燃烧3个阶段。最大失重速率在第1阶段变小，第2阶段变大，燃烧整体前移。混合样品的着火温度和燃尽温度分别比煤粉下降约100和40 ℃，在协同作用下，掺混后杨木屑的着火温度随掺混比例的增加而增大；掺混后玉米秸秆、稻杆和棉花随掺混比例的增加先减小后增大，在7∶3时最小；掺混后玉米芯则随掺混比例的增加而减小；所有种类生物质掺混后的燃尽温度均下降。单一生物质的活化能均小于煤粉，其排序为稻杆＞杨木屑＞玉米秸秆＞棉花＞玉米芯（第1阶段），杨木屑＞棉花＞玉米芯＞稻杆＞玉米秸秆（第2阶段）。随掺混比例增大，第1阶段掺混后棉花和杨木屑活化能先增大后减小，玉米芯和稻杆逐渐减小，且均在8∶2时最小；掺混后玉米秸秆先减小后增大，6∶4时最小。第2阶段掺混后玉米芯、杨木屑和棉花活化能逐渐减小，8∶2时最小；玉米秸秆和稻杆先减小后增大，分别在6∶4和7∶3时最小。燃尽特性指数变化规律不同，掺混后棉花在7∶3时抑制作用最强，玉米秸秆、稻杆、玉米芯、杨木屑分别在8∶2、6∶4、6∶4和8∶2时促进作用最强。单一生物质的综合燃烧特性指数为玉米芯＞棉花＞玉米秸秆＞稻杆＞杨木屑，约分别为煤粉的10.0倍、7.7倍、7.0倍、6.5倍和6.2倍；且玉米芯和棉花在8∶2时、稻杆和玉米秸秆在7∶3时综合燃烧特性指数最大，小范围改变掺混比例，燃烧特性指数几乎无变化。

Biomass, as a renewable energy source, has the advantages of abundant content, easy ignition and low pollutant emission, but has the disadvantages of low energy density and high moisture. Coal powder has the advantages of high energy density and disadvantages of difficult ignition and high pollutant emission. Combining firing carbon neutral energy biomass to pulverized coal at a high blending ratio (the mass ratio of biomass to coal is greater than 5∶5) can effectively solve the problems of the low utilization rate and low energy density of biomass, and the difficult ignition and high pollutant emissions of coal, improve energy utilization rate, achieve the goal of energy conservation and emission reduction, which has become a new energy utilization technology. At present, scholars merely investigate the co-combustion characteristics at low blending ratio (less than 5∶5), deeper insight into the co-combustion characteristics of biomass and coal at high blending ratio is required. The combustion characteristics and kinetic characteristics of coal powder and different biomasses (corn stalk, rice stalk, corn cob, cotton and poplar sawdust) at distinct blending ratios (0∶10, 5∶5, 6∶4, 7∶3, 8∶2 and 10∶0) were studied by thermogravimetric analysis. The effects of biomass species and blending ratio on fuel heat loss characteristics, characteristic temperature, reaction kinetics, burnout characteristics and combustion characteristic index of mixed samples were analyzed, and the optimal blending ratio of different biomass was determined. The results show that the weight loss curve of the mixing samples show three stages: water-loss stage, volatile-combustion stage and fixed carbon-combustion stage. The maximum weight-loss rate decreases in the first stage and increases in the second stage, and the combustion process advances. The ignition temperature and burnout temperature decrease by about 100 ℃ and 40 ℃, respectively, compared with that of pulverized coal. Under the synergistic effect of promotion and inhibition, the ignition temperature of poplar sawdust increases gradually with the increase of mixing proportion. Corn straw, rice stalk and cotton decrease firstly and then increase, and the minimum is at 7∶3,while corn cob gradually decreases. And the burnout temperature of all species decreases. The activation energy of single biomass is lower than that of pulverized coal. In the first stage, the rankingis rice stalk, poplar sawdust, corn stalk, cotton and corn cob from the largest to the smallest, while in the second stage, the ranking is poplar sawdust, cotton, corn cob, rice stalk and corn stalk. With the increase of blending ratio, cotton and poplar sawdust increases first and then decreasesin the first stage, while corn cob and rice stalk decrease gradually, and both of them are minimum at 8∶2. Corn stalk decreases first and then increases after blending, and the minimum is at 6∶4. In the second stage, corn cob, poplar sawdust and cotton gradually decrease, and the minimum at is 8∶2. Corn straw and rice stalk decrease first and then increase, and the minimum value is at 6∶4 and 7∶3, respectively. The changes of burnout characteristic index are different. Cotton has the strongest inhibition effect at 7∶3, while corn straw, rice stalk, corn cob and poplar sawdust have the strongest promotion effect at 8∶2, 6∶4, 6∶4 and 8∶2, respectively. The comprehensive combustion characteristic indexes of single biomass from the largest to the smallest are corn cob, cotton, corn stalk, rice stalk and poplar sawdust, which are about 10.0 times, 7.7 times, 7.0 times, 6.5 times and 6.2 times of coal powder. Corn cob and cotton reach the maximum value at 8∶2, and rice stalk and corn straw reach the maximum value at 7∶3. The combustion characteristic index has almost no change when the mixing proportion is changed in a small scope. 

0 引言

1 试验

   1.1 试验装置

   1.2 试验方法

2 结果与讨论

   2.1 热失重特性分析

   2.2 特征温度分析

   2.3 反应动力学分析

   2.4 燃尽特性指数分析

   2.5 综合燃烧特性指数分析

3 结论