【作者】 杨懿；

【导师】 蔡宁生；

【作者基本信息】 清华大学 ， 动力工程及工程热物理， 2017， 博士

【摘要】 以煤气化为核心的煤基多联产系统是煤炭清洁利用的重要途径,而煤合成气脱除H₂S是其中的关键环节。本文以稀土元素改性SnO₂为脱硫剂,针对还原性气氛下的还原行为,水蒸气条件下的硫化行为,水蒸气和SO₂再生气氛下的再生行为,和COS水解转化及共脱等四个方面进行了深入的研究。首先,针对SnO₂脱硫剂避免还原生成单质锡的关键问题,从脱硫剂制备和合成气气氛两个角度出发,研究了稀土元素改性和不同H₂O/H₂比等影响因素。稀土元素改性SnO₂脱硫剂Sn2Y-700经过700oC以上高温煅烧后,生成了烧绿石结构的Y₂Sn₂O₇,提高了SnO₂的还原温度,从而提高了脱硫剂的使用温度。在同一还原温度下,水蒸气浓度增加会抑制SnO₂的还原过程。对于SnO₂,避免单质锡生成时的最小H₂O/H₂比和还原温度之间的关系遵循SnO₂还原反应在平衡状态时的H₂O/H₂比和温度的关系。其次,针对合成气含有水蒸气的条件下SnO₂脱硫剂硫化性能下降的现象,采用稀土元素改性SnO₂脱硫剂,通过抑制晶粒生长和改善孔隙结构,提高了改性脱硫剂的硫化性能。La2Sn脱硫剂在400oC、30 vol.%H₂和10 vol.%H₂O下的突破硫容为102.8 mg/g。研究了不同水蒸气浓度、硫化温度等因素的影响规律,提出了水蒸气条件下的硫化反应过程需要考虑水蒸气和硫化产物的再生反应,并建立了固定床反应器硫化模型。然后,在水蒸气条件下和SO₂条件下分别得到了400-600oC下SnO₂脱硫剂再生过程中的H₂S浓度曲线和单质硫回收率曲线。再生后,SnO₂脱硫剂发生了烧结现象,导致循环初始阶段的硫化性能下降。对改性脱硫剂Sn2Y-700和La2Sn/Al₂O₃进行了连续硫化-再生实验表明,改性脱硫剂的循环性能稳定。根据两种再生方式的优缺点分析,提出了两阶段再生工艺。最后,针对合成气中的COS和H₂S共脱过程,研究了300-400oC下SnO₂脱硫剂的COS水解转化脱除过程,发现硫化产物SnS是导致COS水解转化率下降的原因。而稀土元素改性脱硫剂可以提高COS水解转化率,并通过同步脱除H₂S,实现COS的水解增强过程。在模拟煤制合成气条件下,改性脱硫剂可以连续稳定实现COS和H₂S共脱。更多还原

【Abstract】 Coal polygeneration system based on gasification is an important way for the clean coal utilization,while H₂S removal from coal syngas is one of the key technologies.Based on the rare earth metal oxide modified SnO₂ sorbent,the dissertation aimed to study the following four aspects,including the reduction behavior of the sorbent under the reducing atmosphere,sulfidation reaction with high concentration steam,regeneration characteristics under steam regenenration and SO₂ regeneration,and COS hydrolysis and co-removal with H₂S.In order to avoid the formation of metallic tin during the reduction of SnO₂ sorbent,rare earth metal oxide modification in the preparation and the influence of H₂O/H₂ ratio in the syngas were studied.For Y modified sorbent,after calcination under at least 700oC,there was pyrochlore Y₂Sn₂O₇ in the Sn2Y-700 sorbent.Y₂Sn₂O₇ increased the reduction temperature of SnO₂ and made it possible to improve the working temperature.At the same reduction temperature,increasing the steam content inhibited the reduction of SnO₂.When there was no metallic tin in the sorbent,the relationship between the minimum H₂O/H₂ ratio and temperature followed the relationship in the equilibrium state of SnO₂ reduction reaction.Under the syngas with high steam content,there was degradation in the sulfidation of SnO₂ sorbent.For La and Y modified sorbent,the sulfidation performance improved by inhibiting SnO₂ grain growth and improving pore structure.At 400oC,30 vol.%H₂and 10 vol.%H₂O,La2Sn sorbent had the breakthrough sulfur capacity of 102.8 mg/g.Based on the study of the influence of steam content and sulfidation temperature,the sulfidation process with steam regeneration was proposed and a fixed-bed reactor sulfidation model was built.The regeneration of SnO₂ sorbent was tested under the steam regeneration and SO₂regeneration at 400-600oC.The H₂S concentration curves and elemental sulfur recovery curves were obtained,respectively.After regeneration,the sintering of SnO₂sorbent resulted in the decrease of cyclic desulfurization performance in the initial cycles.The rare earth metal oxide modified sorbent maintained a stable cyclic desulfurization performance with steam regeneration.Based on the pros and cons of steam regeneration and SO₂ regeneration,a two stage regeneration process was proposed.In the COS and H₂S co-removal process,the COS hydrolysis catalyzed by SnO₂sorbent was studied at 300-400oC and found that the formation of SnS caused the degradation of COS conversion.The La and Y modifide SnO₂ sorbent improved the COS hydrolysis conversion and achieved a COS enhanced hydrolysis by H₂S co-removal.A cyclic desulfurization test of modified SnO₂ was carried out under the simulated coal syngas atmosphere and realized a continuous co-removal of COS and H₂S.更多还原