摘要
煤炭高效清洁利用中,煤气化为基础的多联产技术是其发展的必然趋势。但煤气化过程中,煤中的硫主要以硫化氢的形式存在于粗煤气中,其对设备存在腐蚀作用、并会使催化剂中毒,因此气体中的硫含量必须进行严格的控制。煤气脱硫净化已成为大规模煤气化技术中非常重要的一部分
中高温煤气脱硫主要是借助于可再生的单一或复合金属氧化物与H2S反应生成金属硫化物,经再生过程重新转化成金属氧化物并副产单质硫等,从而达到气体净化的目的。脱硫剂的制备方法主要通过脱硫剂的形态和结构的变化,影响其脱硫效率。改善脱硫剂的制备方法提高其机械强度和硫容、化学稳定性等物化性能,以满足不同的硫化条件,是许多学者的研究重点之一。
本论文采用超(亚)临界水浸渍法制备锰基负载型中温煤气脱硫剂。实验考察了锰的不同前驱体溶液制备的脱硫剂的脱硫活性,并通过原子吸收分光光度计(AAS)、扫描电镜(SEM)、氮气物理吸附仪、X射线光电子能谱仪(XPS)等表征仪器对制备的脱硫剂进行表征分析,探究其脱硫活性存在差异的原因;考察了多组份复合金属氧化物脱硫剂的脱硫性能,并对锰铜双组份复合脱硫剂的制备温度、制备时间等操作条件进行了优化;制备的脱硫剂在含C02和H20的模拟煤气中进行硫化实验,对硫化后脱硫剂进行了再生性能的研究;并对实验用氧化铝载体的改性进行了初步探讨。主要实验结论如下:
(1)以醋酸锰溶液为前驱体时制备的中高温煤气脱硫剂具有最优的脱硫活性,其穿透时间高达400min,穿透硫容为2.07g硫/100g脱硫剂;而以硝酸锰、硫酸锰和氯化锰为前驱体时制备的脱硫剂的穿透时间不足100min,穿透硫容不足醋酸锰为前驱体制备的脱硫剂的硫容的25%.AAS, SEM,TPR和XPS等表征结果表明,醋酸锰溶液为前驱体时制备的脱硫剂中活性金属氧化物的粒径小且分散均匀,上载量高达91.8%。
(2)经铜改性的锰基脱硫剂的机械强度和脱硫性能较好,制备温度为350℃、制备时间30min、活性组分锰铜摩尔比为7:3时,制备的锰铜复合脱硫剂具有最优的脱硫性能;制备温度过高(≥410℃)或制备时间过长(≥45min),都会导致制得的脱硫剂的机械强度大大降低;锰、铜、铁三组分复合金属脱硫剂的活性比铜锰双金属组份脱硫剂有一定程度的提高,脱硫精度和硫容较好。
(3)制得的脱硫剂气氛效应显著,气体中CO2和H2O的存在降低了脱硫剂的脱硫活性,穿透时间减少了近250min。
(4)超(亚)临界浸渍法制得的脱硫剂的再生性能良好,经三次硫化-再生循环实验后仍保持较好的脱硫性能;超(亚)临界水浸渍后的氧化铝载体表面性质发生了明显改变,载体中的Al与水中的OH-1结合形成了新的化合物。硫化后脱硫剂的机械强度高于未硫化或再生后的脱硫剂的机械强度。
(5)液体石蜡对吸水性的氧化铝载体进行改性,可使活性金属氧化物在载体表面的分散性能得到改善,硫化氢与载体表面的活性金属氧化物的有效接触面积增大,脱硫活性提高。
Poly-generation technology based on coal gasification is the inevitable trend of technology development to efficiently and cleanly use coal. In the coal gasification process, the sulfur in coal can be released and mainly present in the form of hydrogen sulfide in coal gas. The content of H2S in coal gas must be limited in order to obviate its poisoning catalyst and corrosive facilities in the subsequent use. The desulfurization purification of coal gas is one of the key technologies of the large-scale application of coal gasification.
Desulfurization from hot coal gas is mainly performed with the help of the renewable single or composite metal oxides reacting with H2S to generate metal sulfides, and then the metal sulfides in the regeneration process being eventually converted to elemental sulfur. The preparation method has the direct effect on the morphology and structure of desulfurizer, which further affects their desulfurization efficiency. By adjusting the desulfurizer preparation method, the mechanical strength, sulfur capacity, physical and chemical properties (including the chemical stability and et al.) of desulfurizer can be improved to meet the needs of different working conditions, which has been the focus of many scholars.
The manganese based desulfurizers were prepared by the super (sub) critical water impregnation method for removing H2S from hot coal-based gas at medium temperature in this paper. Desulfurization efficiency of desulfurizers prepared with different precursor solution of manganese was explored, and the properties of desulfurizers were tested by atomic absorption spectrophotometer (AAS), scanning electron microscope (SEM), nitrogen physical adsorption instrument, X-ray photoelectron spectrometer (XPS) techniques. Study of desulfurization performance of desulfurizers prepared with multi-component composite metal oxide was performed, and the preparation temperature, preparation time and other operation conditions of Mn-Cu desulfurizer were optimized. The desulfurizers were evaluated in the simulated coal-based gas containing CO2and H2O and their regeneration performances were also studied. The main results are shown as follows.
(1) The Mn-based desulfurizer prepared with acetate solution as precursor has the best desulfurization activity, in which the penetrating time reaches400min and the sulfur capacity is about2.07g sulfur/100g sorbent. In comparison, other desulfurizers prepared from the nitrate, sulfate and chloride solution used as precursors perform rather poor desulfurization activity. Their penetrating time is below100min and the sulfur capacity is only about25%of acetate precursor desulfurizer. The results from AAS, SEM, BET, XPS characterization show that the active metal oxide of desulfurizer prepared with manganese acetate solution as precursor presents the properties of small particle size, uniform dispersion and high uploading rate (the maximum of91.8%).
(2) The Mn-based desulfurizer modified by copper has the best desulfurization efficiency and mechanical strength. The optimal preparing conditions of Mn-Cu bi-metal oxides desulfurizer are350℃,30min and Mn:Cu mole ratio of7:3. The preparing temperature of above410℃or time of above45min can make the mechanical strength of desulfurizer greatly decrease. The desulfurization efficiency and sulfur capacity of Mn-Cu-Fe desulfurizer is improved comparing with Mn-Cu based desulfurizer.
(3) The atmosphere effect of desulfurizer is obvious. CO2and H2O in inlet gas causes the decrease of desulfurization activity of desulfurizer, its penetration time is reduced by nearly250min.
(4) The desulfurizer prepared by the super (sub) critical water impregnation method has the good regeneration performance, which still keeps good desulfurizing properties after three times of continuous sulfidation and regeneration cycle experiments. The surface properties of alumina earrier after impregnated by super (sub) critical water are obviously changed and the new compound may be formed by A1and OH-1. The mechanical strengths of desulfurizer after sulfidation are higher than the fresh and regenerated desulfurizers.
(5) Alumina carrier can be improved by impregnating liquid paraffin and then the active components are well dispersed on the surface of carrier, which increases the effective contact between H2S and carrier.
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