草本生質物與柳杉-生物污泥顆粒燃料製粒性質研究

Abstract

本研究以環模造粒機對草本生質物與生物污泥等原料進行造粒並評估其性質，以解決國內生物污泥與草本生質物處理之問題，以利後續之應用；如做為鍋爐燃料或替代部份化石燃料，以達到減碳的目的。 其中草本生質物分別為芒草、稻桿、培地茅、狼尾草與玉米桿。而污泥除單獨造粒外亦可混合不同比例柳杉進行造粒，使原料整體含水率調整成較易造粒之條件。本研究使用污泥與柳杉造粒的比例，分別為30：70，50：50，70：30，以S3W7、S5W5與S7W3代表。並測量草本、污泥（100：0）、柳杉（0：100）與混合顆粒如熱值、灰分、整體密度、顆粒堅牢度等基本性質。 結果顯示草本生質物熱值以芒草﹙17.98 MJ/kg﹚最高，且灰分﹙5.33％﹚最低，為五種草本生質物最具優勢之原料。而污泥顆粒熱值依係為S3W7﹙17.89 MJ/kg﹚＞W5S5﹙17.18 MJ/kg﹚＞S7W3﹙15.83 MJ/kg﹚；灰分為S3W7﹙15.79％﹚﹤W5S5﹙22.59％﹚﹤S7W3﹙29.39％﹚，可看出隨柳杉混合比例增加顆粒成品熱值上升，灰份下降。此外，在混合造粒上，生物污泥造粒順利，而單純柳杉木質造粒則不易造粒，兩者混合後可降低問題發生。因此在造粒前可視需求混成不同比例之原料，以達最佳效益。 整體密度中除污泥之原料﹙570 kg/m3﹚與顆粒﹙580 kg/m3﹚差異不大外，其餘原料經過造粒可大幅增加其密度。如五種草本生質物原料整體密度範圍約為50 －70 kg/m3，製成顆粒後密度範圍約為565－600 kg/m3，利於降低運送成本。顆粒堅牢度範圍約為70﹙狼尾草﹚－90％﹙污泥﹚，在實驗造粒上尚未達到顆粒燃料標準中可用於商業化之標準，因此對於提升堅牢度之方法，尚須進一步探討。

The purpose of the study was to measure the properties of pellets made from sludge and grass biomass in order to understand its performance, to solve excess domestic sludge, and to substitute fossil fuel for reductions of carbon emission. Five species of grass biomass were used in this study. They were silvergrass (Miscanthus floridulus), rice straw (Oryza sativa), vetiver (Vetiveria zizanioides), Chinese pennisetum (Pennisetum alopecuroides), and starchy corn (Zea mays). Ring- die pellet mill was used for pelletizing. Besides using mono species materials, sludge was mixed with woody biomass in different ratio to adjust its moisture content. Five different proportions of sludge to woody biomass were mixed and tested, they were 100：0(S10), 30：70(S3W7), 50：50(S5W5), 70：30(S7W3), and 0：100(W100). The heat value, ash content, bulk density, and pellet durability index (PDI) were also tested to evaluate the basic characteristics of these pellets. Compared to other grass biomass, silvergrass has the advantage of the highest heat value (17.98 MJ/kg) and the lowest ash content (5.33%) among the five grass biomass. Regarding the sludge- wood pellet, the heat value of mixed pellet was 17.89 MJ/kg, 17.18 MJ/kg, and 15.83 MJ /kg, for S3W7, S5W5, and S7W3 type pellets, respectively. Ash contents were 15.79%, 22.59%, and 29.39 for S3W7, S5W5, and S7W3, respectively. It was found, as increasing of woody biomass portion, the heat value increased while ash content decreased. Hence, mixing sludge with woody biomass as pellet fuel can reach a desirable ratio to reduce sludge problem after combustion. The bulk density of biomass increased largely after pelletized except the sludge. There is no significant bulk density difference between sludge (570kg/m3) and pelletized sludge (580kg/m3). The bulk densities of the five grass biomass were about 50 kg/m3 to 70 kg/m3 before pelletizing. However, the bulk densities were ranged from 565 to 600 kg/m3after pelletizing. Hence, volume of biomass was reduced significantly. Pellet durability index(PDI) was ranged from 70% (Chinese pennisetum) to 90％(sludge). These values were lower than that of commercial product. Further study is necessary for improving this property.