Environmental safety on recycling process using pyrolysis gasification and reforming technology

本研究的目的是阐明目前正在发展的气化和重整过程中可能对环境和天然气利用设备造成负面影响的物质，特别是二恶英和多环芳烃(PAHs)的排放特征。实验采用了两种测试设备：小型设备(原料处理能力：~2 kg/h)和小规模设备(~15 kg/h)。结果表明，即使在缺氧条件下，废旧木材、城市生活垃圾衍生燃料和废纸塑料燃料(RPF)也会产生二恶英。测量的气体浓度范围为0.1~几ng-TEQ/m^3N。这种形成是在650℃左右的低温下形成的，在700℃以上降至较低水平。结果还表明，在气化和重整过程中，生成的二恶英被分解，这可能是由于催化剂的作用和气体停留时间的增加。不同原料的二恶英含量不同，木质生物质的二恶英含量低于RPF的二恶英含量，在1 mg/m~3~数百mg/m·3N的高浓度范围内，PAHs的生成量显著增加。其中，苯的生成浓度一般在100~5000 mg/m^3N之间。为此，重点研究了苯废气减排技术的发展。几种催化剂用于该化合物的还原，发现一种镍催化剂在300℃时对苯高转化率甲烷是有效的。水分和乙烯等碳氢化合物的共存对反应没有影响。结果表明，即使在重整后的较低温度下，也可以采用催化剂工艺来开发一种有效的气体净化技术。

The aim of this study is to clarify emission characteristics of substances, especially dioxins and poly-aromatic hydrocarbons (PAHs) that may cause negative effects to the environment and gas utilization equipment after the gasification and reforming process currently developing. The experiments employed two kinds of test equipments, which are a small-scale equipment (Process capacity for raw materials: 〜2 kg/h) and a bench-scale equipment (〜15kg/h).The results showed that dioxins were generated from waste woods, refuse derived fuel made from municipal solid waste and refuse paper and plastic fuel (RPF) even under oxygen deficient conditions. The measured concentrations were in the range of 0.1〜several ng-TEQ/m^3N in gas. The formation occurred at low temperatures around 650 -C and it decreased to low level over 700℃. The result also suggested that the formed dioxins were decomposed during the gasification and reforming processes probably because of the effect of catalyst and of the increase of gas residence time. The concentrations were differed between the kinds of raw material, and the amount of dioxins from woody biomass was smaller than that of from RPF.PAHs were significantly generated in high concentrations in the range of 1 mg/m^3〜several hundred mg/m^3N. Among those, benzene formed in the concentration range of typically 100〜5000mg/m^3N. Therefore, investigation was concentrated on the development of reduction technology of benzene exhaust. Several catalysts were applied for the reduction of the compound and a nickel catalyst was found to be effective on high benzene conversion to methane at 300℃. The coexistence of moisture and hydrocarbons such as ethylene did not affect on the reaction. The results suggested that an effective gas cleaning technology could be developed by using catalyst process even at low temperatures after the reforming process.