Abstract:

The CO₂ adsorption performance of the calcium-based adsorbent cycle plays an important role in continuous and efficient hydrogen production from enhanced biomass gasification. Six kinds of synthetic adsorbent powders (CaMg75, CaAl75, CaLa75, CaY75, CaNd75 and CaSi75) and six kinds of synthetic adsorbent particles (CaMg75p, CaAl75p, CaLa75p, CaY75p, CaNd75p and CaSi75p) were prepared by adding different inert carriers into CaO particles and extrusion-spheronization process , wherein the mass fraction of CaO were 75%. Meanwhile, calcium oxide powder (CaO) obtained by calcination of calcium carbonate and its corresponding calcium oxide particles (CaOp) were prepared. The above seven kinds of powders were tested by X-ray diffraction (XRD). Seven kinds of adsorbent powders and seven kinds of particles were tested by specific surface area and pore size tester. Thermogravimetric analysis (TG) was used to test the carbonation-calcination cycle of the above seven adsorbent powders and their corresponding adsorbent particles. Based on the thermogravimetric test results, the enhanced biomass gasification experiment for hydrogen production under the condition of adsorbent recycling was carried out with smoke bars as the original biomass. The results show that there are MgO, Ca₃Al₂O₆, La₂O₃, Y₂O₃, Nd₂O₃ and Ca₂SiO₄ inert carriers in the powders of the six synthetic adsorbents. The inert carriers can not react with CO₂, but also disperse CaO grains. The thermal stability is good. The sintering of the adsorbents can be delayed and the adsorptive performance of the adsorbents can be improved. They have good thermal stability and they can delay the sintering of adsorbent to improve the adsorptive performance of adsorbent. The extrusion-spheronization process destroys the original pore structure of the adsorbent, and the specific surface area of spherical particles of synthetic CaO adsorbent is lower than that of the same kind of powder, which leads to the decrease of adsorptive performance of adsorbent particles. With the increase of thermogravimetric cycles, the adsorption capacity of CO₂ and conversion rate of CaO of adsorbents CaAl75p, CaY75p and CaSi75p in 25 cycles decreased gradually. However, the adsorption capacity of CO₂ is always above 0.15 g CO₂/g biomass, and the conversion rate of CaO is always above 30% respectively. Both data are much higher than that of CaOp, indicating that three adsorbents, CaSi75p, CaAl75p and CaY75p, have better cycling performance. In the enhanced biomass gasification hydrogen production cycle experiment, the volume fraction of H₂ increases significantly after adding the above three adsorbent particles in five cycles, and the concentration of H₂ increases from 46.2% to more than 60%. Addition of CaAl75p, CaY75p and CaSi75p could significantly increase concentration and yield of H₂ in biomass gasification synthesis gas. The composition and yield of the gas change little during the five cycles, indicating that three kinds of adsorbents have good cyclic adsorption capacity and stability.

Key words: biomass, gasification, hydrogen, calcium-based, adsorbents, cyclic adsorption performance

摘要：

钙基吸附剂循环CO₂吸附性能对增强式生物质气化连续高效制氢起重要作用。采用将CaO颗粒分散在惰性载体中的方法并结合挤压成型技术制备了合成吸附剂颗粒。为了筛选循环吸附性能较好的吸附剂，在热重分析仪上进行了循环吸附性能测试。基于热重测试结果开展了吸附剂循环利用条件下的增强式生物质气化制氢实验。结果表明：添加惰性载体能延缓CaO烧结，提高吸附剂的循环吸附能力；挤压成型过程会破坏吸附剂原有孔隙结构，导致吸附剂颗粒吸附性能不同程度降低，其中CaSi75p、CaAl75p和CaY75p三种吸附剂循环性能较好；添加以上三种吸附剂颗粒均可显著提高生物质气化合成气中H₂浓度及产率，5次循环过程中气体成分和产率变化不大，表明吸附剂循环吸附能力和稳定性较好。

关键词: 生物质, 气化, 氢气, 钙基, 吸附剂, 循环吸附性能