炭化预处理对空心棕榈果壳成型颗粒气化反应特性的影响

Influence of carbonization pretreatment on the gasification reaction characteristics of empty fruit bunch pellets

  • 摘要: 水热炭化和干法烘焙等低温炭化预处理方式可有效改善生物质的燃料特性,实现生物质的高效利用。选取空心棕榈果壳(Empty Fruit Bunch,EFB)为实验原料,在180~220 ℃的温度范围对其进行水热炭化和干法烘焙预处理,研究了炭化预处理方式对生物质理化特性的影响。结果表明:水热炭化和干法烘焙均能提高生物质碳质量分数和热值,降低H/C原子摩尔比和O/C原子摩尔比,且在相同的反应温度下,水热炭化的提质作用更为明显。利用大颗粒热重在800~950 ℃下开展了炭化产物成型颗粒CO2气化反应特性研究,实验结果表明:在60 min内,EFB原料颗粒在800 ℃时碳转化率仅30%,在850~950 ℃时碳转化率可达100%,且颗粒的气化反应速率峰值由800 ℃时的0.007%/min提升至950 ℃时的0.042%/min。当气化温度为950 ℃时,水热炭颗粒的气化反应性R0.5(50%碳转化率对应的反应性)由EFB原料颗粒的0.034 min−1降低至180 ℃水热炭颗粒的0.023 min−1,水热温度由180 ℃提升至220 ℃时,R0.5进一步降低至0.011 min−1;200 ℃烘焙炭颗粒的R0.5最高,为0.039 min−1。通过对950 ℃不同气化阶段颗粒气化半焦的表面形貌与比表面积分析证明,EFB原料与烘焙炭颗粒气化过程中灰渣熔融形成的球团黏附于其表面,在碳转化率由50%提升至80%的过程中,颗粒孔隙出现堵塞,比表面积分别降低了502.40 m2/g和452.44 m2/g;碳转化率由80%提升至98%的过程中,灰渣球团逐渐融合并包覆气化半焦表面,导致颗粒的比表面积均降低至1 m2/g左右,R0.98(98%碳转化率对应的反应性)分别降低至0.017 min−1和0.018 min−1;水热炭颗粒在碳转化率由80%提升至98%的过程中比表面积增大了126.98 m2/g,这是由于水热炭化对碱及碱土金属(AAEMs)的脱除缓解了成型颗粒气化过程中的结渣现象,导致颗粒气化反应性无明显变化。研究炭化预处理方式对生物炭成型颗粒理化特性的影响及半焦结构与气化反应性演变的关联机制对生物炭成型颗粒气化技术的开发应用提供重要理论意义。

     

    Abstract: Low-temperature pretreatment methods such as hydrothermal carbonization and dry terrefaction can effectively improve the fuel characteristics of biomass, achieving an efficient biomass utilization. Empty fruit bunch (EFB) was selected as the experimental raw material, and was pretreated by hydrothermal carbonization and dry terrefaction in the temperature range of 180−220 ℃, to study the effect of carbonization pretreatment on the physicochemical properties of biomass. The results showed that both hydrothermal carbonization and dry terrefaction could increase the carbon content and heating value of the biomass, reduce the H/C and O/C, and the quality enhancement effect of hydrothermal carbonization was more obvious at the same reaction temperature. A study on the CO2 gasification reaction characteristics of carbonization product pellets was carried out at 800−950 ℃ using large pellet thermogravimetry, and the experimental results showed that the carbon conversion rate of EFB feedstock pellets was only 30% at 800 ℃ for 60 min, but could be up to 100% at 850−950 ℃, and the peak gasification reaction rate of the pellets increased from 0.007%/min at 800 ℃ to 0.042%/min at 950 ℃. When the gasification temperature was 950 ℃, the gasification reactivity of hydrothermal carbon particles, R0.5 (reactivity corresponding to 50% carbon conversion), decreased from 0.034 min−1 for raw material particles to 0.023 min−1 for HT-180, and decreased to 0.011 min−1 when the hydrothermal temperature was increased from 180 ℃ to 220 ℃; the R0.5 of 200 ℃ terrefaction particles was the highest at 0.039 min−1. The analysis of the surface morphology and specific surface area of the granular gasification char at different gasification stages at 950 ℃ proved that the pellets formed by the melting of ash during the gasification process of EFB feedstock and terrefaction pellets adhered to their surfaces, and the pellet pores were clogged in the process of increasing the carbon conversion from 50% to 80%, and the specific surface areas were reduced by 502.40 m2/g and 452.44 m2/g respectively. During the process of increasing carbon conversion from 80% to 98%, the ash pellets gradually fused and coated the surface of the gasification char, resulting in the specific surface area of the pellets to reduce to about 1 m2/g, and the R0.98 (reactivity corresponding to 98% carbon conversion) to reduce to 0.017 min−1 and 0.018 min−1, respectively. The specific surface area of hydrothermal carbon pellets increased by 126.98 m2/g during the increase of carbon conversion from 80% to 98%, which was attributed to the fact that the removal of AAEMs by hydrothermal carbonization alleviated the slagging phenomenon during the gasification of pellets, resulting in no significant change in the reactivity of the pellets for gasification.

     

/

返回文章
返回