模拟烟气中汞吸附形态与脱附特性研究
发布时间：2019-07-03 20:37
【摘要】：我国是煤炭资源丰富的能源消费大国,燃煤电厂已成为最大的固定汞排放源,因此汞污染和排放控制已成为研究热点。活性炭喷射(ACI)应用来脱除燃煤烟气中的汞是目前认为最具商业化应用前景,但成本昂贵。燃煤飞灰价格低廉,来源广泛,且具有潜在脱汞能力,成为研究热点。有关飞灰吸附烟气汞的影响研究已有报道,但汞在吸附剂表面的形态研究甚少。本课题旨在研究廉价高效的脱汞吸附剂,首先对溴素改性后的活性炭和飞灰在模拟烟气中进行汞吸附的影响因素实验,然后采用程序升温脱附(Temperature Programmed Desorption,TPD)方法,研究不同烟气组分及模拟烟气条件下,汞在改性活性炭及飞灰表面的吸附形态与脱附特性,深入探讨汞吸附的机理。首先,选取四种燃煤电厂ESP飞灰(FA)作为汞吸附剂,利用NH4Br溶液浸渍搅拌改性(NH4Br-FA,NBFA)。采用N2吸附/脱附、X射线荧光光谱法(XRF)、扫描电子显微镜(SEM)等手段对样品进行表征。在固定床汞吸附实验装置上,对改性前后飞灰样进行模拟烟气条件下Hg0吸附实验研究。结果表明:负载到飞灰中未燃碳(UBC)表面的溴元素,会增加其邻位的活性,使其更容易吸附Hg0，促进了飞灰对Hg0的吸附及氧化作用,使飞灰吸附Hg0能力大大增强。烟气中酸性气体的存在能极大地促进Hg0氧化,被氧化的Hg0中有75%的气态Hg2+,其余的Hg0被氧化吸附在飞灰表面。UBC含量对改性飞灰脱除Hg0的影响很大,含量越高,吸附氧化作用越强;含量越低,催化氧化作用越强。低UBC含量的飞灰表面结构形态对Hg0的催化氧化作用具有一定促进作用。其次,在固定床进行了烟气组分O2,SO2,NO对两种溴素改性飞灰的汞吸附和汞氧化能力的影响研究。选取飞灰中主要的无机金属氧化物,利用NH4Br溶液进行浸渍改性,研究飞灰的无机组分在模拟烟气气氛下对Hg0脱除的影响。利用TPD方法对飞灰吸附样表面的汞形态进行探究,获得了单烟气组分与无机金属氧化物对飞灰吸附Hg0的反应机理。结果表明:溴素对飞灰中Fe2O3和TiO2的影响主要在于增加它们的晶格氧量,同时烟气中的O2不断补充消耗的晶格氧,促进了它们对Hg0Ur催化氧化。烟气组分NO对NBFA吸附氧化Hg0起着重要作用,在飞灰表面形成Hg2(NO3)2和HgBr2,部分Hg2(NO3)2在150℃反应温度下分解生成Hg(NO3)2和HgO。UBC含量低的飞灰活性位点少,表面分解的物质会脱离飞灰表面活性位点,促进Hg2+比例的增加;SO2对飞灰脱除Hg0起抑制作用,主要原因在于Hg0对碳质材料活性位点形成竞争吸附。UBC成分对Hg0的吸附氧化机制主要遵循Langmuir-Hinshelwood机理,而有溴素存在的无机金属氧化物对Hg0的作用机制主要遵循Mars-Masessen机理。因此飞灰对汞吸附氧化脱除的过程伴随着多种机理的协同作用。最后,考察了一种原始活性炭(Fresh Activated Carbon,FAC)在N2气氛,溴素改性活性炭(NH4Br-AC,NBAC)分别在N2,O2,SO2,NO及模拟烟气气氛下,对气态汞的吸附性能。利用N2吸附/脱附、傅里叶变换红外光谱(FTIR)和扫描电子显微镜/X射线能谱仪(SEM-EDX)对活性炭进行表征。对纯汞化合物与Si02的混合物、FAC以及NBAC吸附Hg0后的产物分别进行TPD实验,研究其表面的汞吸附形态。结果表明,AC脱除Hg0机理是AC表面的有机物与Hg0反应生成Hg-OM(Hg Organic Matter),部分含氧官能团与元素汞结合生成HgO,但是效率很低,穿透率高达94%。溴素对FAC的改性增加了活性炭表面溴素邻位点的活性,极大地促进了对Hg0的吸附能力,且在表面形成了 HgBr2。单组分O2与NO可促进NBAC对Hg0的吸附,而S02起抑制作用。02主要在NBAC表面促进Hg0氧化生成HgO。NO效果最为显著,在活性炭表面生成了Hg2(N03)2。SO2与Hg0对活性炭表面的酯基存在竞争吸附,降低了对Hg0的吸附率。溴素浸渍改性活性炭对Hg0脱除的机理与溴素改性飞灰中的UBC对Hg0脱除的机理相似,且受烟气组分中的NO的影响较大,都遵循Langmuir-Hinshelwood机理。
[Abstract]:The coal-fired power plant has become the largest source of fixed mercury emission, so the pollution and emission control of mercury has become a hot spot. The application of activated carbon injection (ACI) to remove mercury from coal-fired flue gas is the most commercial application, but it is expensive. The coal-fired fly ash has the advantages of low price, wide source and potential mercury removal capability, thus being a hot spot for research. The study of the effect of mercury on the adsorption of flue gas from fly ash has been reported, but the form of mercury on the surface of the adsorbent is very low. The purpose of this study is to study the influence factors of the mercury adsorption on the activated carbon and fly ash modified by the bromine in the simulated flue gas, and then the temperature programmed Desorption (TPD) method is used to study the different smoke components and the simulated flue gas conditions. The adsorption and desorption characteristics of mercury on the surface of modified activated carbon and fly ash were studied, and the mechanism of mercury adsorption was discussed. First, four kinds of coal-fired power plant ESP fly ash (FA) are selected as the mercury adsorbent, and the NH4Br solution is used for dipping and stirring modification (NH4Br-FA, NBFA). The samples were characterized by N2 adsorption/ desorption, X-ray fluorescence spectroscopy (XRF), and scanning electron microscopy (SEM). In the fixed-bed mercury adsorption experiment device, the experimental study on the adsorption of Hg0 under simulated flue gas conditions was carried out on the fly ash samples before and after modification. The results show that the bromine element loaded into the surface of the unburned carbon (UBC) in the fly ash can increase its vicinal activity, make it easier to adsorb Hg0, promote the adsorption and oxidation of the fly ash to the Hg0, and greatly enhance the ability of the fly ash to adsorb the Hg0. The presence of the acid gas in the flue gas can greatly promote the Hg0 oxidation, the oxidized Hg0 has 75% of the gaseous Hg2 +, and the rest of the Hg0 is oxidized and adsorbed on the surface of the fly ash. The higher the content of UBC on the removal of Hg0 from the modified fly ash, the higher the content, the stronger the adsorption oxidation, the lower the content and the stronger the catalytic oxidation. The surface structure of fly ash with low UBC content can promote the catalytic oxidation of Hg0. Secondly, the influence of flue gas component O2, SO2 and NO on the mercury adsorption and the mercury oxidation capacity of two kinds of bromine-modified fly ash was studied in the fixed bed. The main inorganic metal oxides in fly ash were selected, and the effects of the inorganic components of fly ash on the removal of Hg0 under simulated flue gas atmosphere were studied by using the solution of NH4Br. The mercury form of fly ash adsorption-like surface was studied by TPD method, and the reaction mechanism of single-flue gas component and inorganic metal oxide on the adsorption of Hg0 to fly ash was obtained. The results show that the effect of the bromine on the Fe2O3 and TiO2 in the fly ash is mainly to increase their lattice oxygen content, and the O2 in the flue gas constantly replenish the consumed lattice oxygen and promote their catalytic oxidation to Hg0Ur. The flue gas component NO plays an important role in the adsorption and oxidation of the NBFA, and the Hg2 (NO3)2 and the HgBr2 are formed on the surface of the fly ash, and the partial Hg2 (NO3)2 is decomposed to generate Hg (NO3)2 and HgO under the reaction temperature of 150 DEG C. The effect of SO2 on the removal of Hg0 from fly ash is mainly due to the competitive adsorption of Hg0 on the active site of the carbonaceous material. The mechanism of the adsorption and oxidation of the UBC component to the Hg0 mainly follows the Langmuir-Hinshelwood mechanism, and the mechanism of the inorganic metal oxide with the bromine in the Hg0 mainly follows the mechanism of Mars-Masessen. Therefore, the process of adsorption and oxidation of mercury by fly ash is accompanied by a variety of mechanisms. In the end, an original activated carbon (FAC) was investigated in the atmosphere of N2, the modified activated carbon (NH4Br-AC, and NBAC) in N2, O2, SO2, NO and the simulated flue gas atmosphere, and the adsorption properties of the gaseous mercury were investigated. The activated carbon was characterized by N2 adsorption/ desorption, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope/ X-ray energy spectrometer (SEM-EDX). TPD experiments were carried out on the mixture of pure mercury compound and Si02, FAC, and NBAC to study the mercury adsorption in the surface. The results show that the mechanism of the removal of Hg0 from the AC surface is the Hg-OM (Hg Organic Matter) generated by the reaction of the organic substance of the AC surface with the Hg0, the partial oxygen-containing functional group and the elemental mercury are combined to form the HgO, but the efficiency is very low and the penetration rate is as high as 94%. The modification of the FAC increases the activity of the bromine-adjacent site on the surface of the activated carbon, greatly promotes the adsorption capacity of the Hg0, and forms the HgBr2 on the surface. One-component O2 and NO can promote the adsorption of NBAC to Hg0, while S02 has an inhibitory effect.02 mainly promotes the oxidation of HgO on the surface of the NBAC to produce HgO. The effect of NO is the most significant, and Hg2 (N03)2 is generated on the surface of the activated carbon. The ester group on the surface of the activated carbon has a competitive adsorption on the surface of the activated carbon, and the adsorption rate to the Hg0 is reduced. The mechanism of the removal of the Hg0 by the bromine-impregnated modified activated carbon is similar to that of the UBC in the bromine-modified fly ash, and the effect of NO in the flue gas component is large, and the mechanism of the Langmuir-Hinshelwood is followed.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X701
[Abstract]:The coal-fired power plant has become the largest source of fixed mercury emission, so the pollution and emission control of mercury has become a hot spot. The application of activated carbon injection (ACI) to remove mercury from coal-fired flue gas is the most commercial application, but it is expensive. The coal-fired fly ash has the advantages of low price, wide source and potential mercury removal capability, thus being a hot spot for research. The study of the effect of mercury on the adsorption of flue gas from fly ash has been reported, but the form of mercury on the surface of the adsorbent is very low. The purpose of this study is to study the influence factors of the mercury adsorption on the activated carbon and fly ash modified by the bromine in the simulated flue gas, and then the temperature programmed Desorption (TPD) method is used to study the different smoke components and the simulated flue gas conditions. The adsorption and desorption characteristics of mercury on the surface of modified activated carbon and fly ash were studied, and the mechanism of mercury adsorption was discussed. First, four kinds of coal-fired power plant ESP fly ash (FA) are selected as the mercury adsorbent, and the NH4Br solution is used for dipping and stirring modification (NH4Br-FA, NBFA). The samples were characterized by N2 adsorption/ desorption, X-ray fluorescence spectroscopy (XRF), and scanning electron microscopy (SEM). In the fixed-bed mercury adsorption experiment device, the experimental study on the adsorption of Hg0 under simulated flue gas conditions was carried out on the fly ash samples before and after modification. The results show that the bromine element loaded into the surface of the unburned carbon (UBC) in the fly ash can increase its vicinal activity, make it easier to adsorb Hg0, promote the adsorption and oxidation of the fly ash to the Hg0, and greatly enhance the ability of the fly ash to adsorb the Hg0. The presence of the acid gas in the flue gas can greatly promote the Hg0 oxidation, the oxidized Hg0 has 75% of the gaseous Hg2 +, and the rest of the Hg0 is oxidized and adsorbed on the surface of the fly ash. The higher the content of UBC on the removal of Hg0 from the modified fly ash, the higher the content, the stronger the adsorption oxidation, the lower the content and the stronger the catalytic oxidation. The surface structure of fly ash with low UBC content can promote the catalytic oxidation of Hg0. Secondly, the influence of flue gas component O2, SO2 and NO on the mercury adsorption and the mercury oxidation capacity of two kinds of bromine-modified fly ash was studied in the fixed bed. The main inorganic metal oxides in fly ash were selected, and the effects of the inorganic components of fly ash on the removal of Hg0 under simulated flue gas atmosphere were studied by using the solution of NH4Br. The mercury form of fly ash adsorption-like surface was studied by TPD method, and the reaction mechanism of single-flue gas component and inorganic metal oxide on the adsorption of Hg0 to fly ash was obtained. The results show that the effect of the bromine on the Fe2O3 and TiO2 in the fly ash is mainly to increase their lattice oxygen content, and the O2 in the flue gas constantly replenish the consumed lattice oxygen and promote their catalytic oxidation to Hg0Ur. The flue gas component NO plays an important role in the adsorption and oxidation of the NBFA, and the Hg2 (NO3)2 and the HgBr2 are formed on the surface of the fly ash, and the partial Hg2 (NO3)2 is decomposed to generate Hg (NO3)2 and HgO under the reaction temperature of 150 DEG C. The effect of SO2 on the removal of Hg0 from fly ash is mainly due to the competitive adsorption of Hg0 on the active site of the carbonaceous material. The mechanism of the adsorption and oxidation of the UBC component to the Hg0 mainly follows the Langmuir-Hinshelwood mechanism, and the mechanism of the inorganic metal oxide with the bromine in the Hg0 mainly follows the mechanism of Mars-Masessen. Therefore, the process of adsorption and oxidation of mercury by fly ash is accompanied by a variety of mechanisms. In the end, an original activated carbon (FAC) was investigated in the atmosphere of N2, the modified activated carbon (NH4Br-AC, and NBAC) in N2, O2, SO2, NO and the simulated flue gas atmosphere, and the adsorption properties of the gaseous mercury were investigated. The activated carbon was characterized by N2 adsorption/ desorption, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope/ X-ray energy spectrometer (SEM-EDX). TPD experiments were carried out on the mixture of pure mercury compound and Si02, FAC, and NBAC to study the mercury adsorption in the surface. The results show that the mechanism of the removal of Hg0 from the AC surface is the Hg-OM (Hg Organic Matter) generated by the reaction of the organic substance of the AC surface with the Hg0, the partial oxygen-containing functional group and the elemental mercury are combined to form the HgO, but the efficiency is very low and the penetration rate is as high as 94%. The modification of the FAC increases the activity of the bromine-adjacent site on the surface of the activated carbon, greatly promotes the adsorption capacity of the Hg0, and forms the HgBr2 on the surface. One-component O2 and NO can promote the adsorption of NBAC to Hg0, while S02 has an inhibitory effect.02 mainly promotes the oxidation of HgO on the surface of the NBAC to produce HgO. The effect of NO is the most significant, and Hg2 (N03)2 is generated on the surface of the activated carbon. The ester group on the surface of the activated carbon has a competitive adsorption on the surface of the activated carbon, and the adsorption rate to the Hg0 is reduced. The mechanism of the removal of the Hg0 by the bromine-impregnated modified activated carbon is similar to that of the UBC in the bromine-modified fly ash, and the effect of NO in the flue gas component is large, and the mechanism of the Langmuir-Hinshelwood is followed.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X701
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