【摘要】：汞是一種具有較強(qiáng)揮發(fā)性、生物累積性及環(huán)境持久性的劇毒污染物,而燃煤是最大的人為汞排放源。因此,燃煤汞排放控制己成為當(dāng)前能源環(huán)境領(lǐng)域重要的研究方向。目前,控制燃煤電廠汞排放最成熟可行的技術(shù)是活性炭噴射技術(shù)(ACI),因?yàn)榛钚蕴繃娚涿摴^程是包含流動(dòng)、傳熱、傳質(zhì)、化學(xué)反應(yīng)在內(nèi)的復(fù)雜兩相流反應(yīng)體系,所以該技術(shù)在燃煤電廠的應(yīng)用還存在較多問題。本文針對(duì)汞在吸附劑表面的吸附形態(tài)與吸附機(jī)理,汞吸附動(dòng)力學(xué)、熱力學(xué)與吸附平衡特性,影響吸附劑噴射脫汞效率的關(guān)鍵參數(shù)及影響機(jī)理,吸附劑噴射脫汞機(jī)理及協(xié)同脫除SO2與NO的潛力,吸附劑噴射脫汞預(yù)測(cè)模型等方面的科學(xué)問題展開研究。制備了原始活性炭(R-AC), NH4Br改性活性炭(NH4Br-AC), NH4Cl改性活性炭(NH4Cl-AC)和飛灰(FA)四種脫汞吸附劑,進(jìn)行了物理化學(xué)表征,在固定床上考察入口Hg0濃度、煙氣溫度、粒徑和煙氣組分等因素對(duì)汞靜態(tài)吸附的影響,利用程序升溫脫附(TPD)方法研究吸附劑表面的汞吸附形態(tài),分析不同吸附劑的汞吸附機(jī)理。結(jié)果表明,NH4Br和NH4Cl改性主要以非晶體形態(tài)存在于活性炭表面與中孔中；吸附劑的靜態(tài)汞吸附性能強(qiáng)弱為NH4Br-ACNH4Cl-ACR-ACFA;R-AC對(duì)Hg0的吸附以物理吸附為主,存在少量化學(xué)吸附,產(chǎn)物為HgO; NH4Br-AC對(duì)Hg0的吸附主要是化學(xué)吸附,產(chǎn)物為HgBr2; O2促進(jìn)了R-AC和NH4Br-AC對(duì)H釅的吸附；SO2對(duì)R-AC和NH4Br-AC的Hg0吸附產(chǎn)生了不同的影響,SO2存在時(shí),NH4Br-AC表面的HgBr2生成量減小,但有少量HgS生成；NO促進(jìn)了R-AC和NH4Br-AC對(duì)Hg0的吸附,因?yàn)樵谖絼┍砻嫔闪薍g(NO3)2。利用動(dòng)力學(xué)模型研究了氣相汞在活性炭和飛灰表面的吸附動(dòng)力學(xué)特性,計(jì)算出汞吸附活化能,初始汞吸附速率,并分析汞在活性炭和飛灰表面的吸附熱力學(xué)及吸附平衡特性。結(jié)果表明,汞吸附過程可分為表面吸附和內(nèi)擴(kuò)散吸附兩個(gè)階段；雖外部傳質(zhì)與內(nèi)擴(kuò)散限制汞吸附過程,但汞在活性位點(diǎn)的化學(xué)吸附是R-AC和NH4Br-AC汞吸附速率控制步；對(duì)于飛灰,外部傳質(zhì)是其汞吸附速率控制步；汞在R-AC和NH4Br-AC表面吸附的活化能分別為-10.06610/mol和-28.068kJ/mol,表明吸附是物理吸附和化學(xué)吸附的共同作用；汞在吸附劑表面的初始汞吸附速率與吸附劑的汞吸附容量呈正相關(guān)關(guān)系；熱力學(xué)分析表明汞在R-AC和NH4Br-AC表面的吸附均為自發(fā)、吸熱過程,吸附以物理吸附為主,化學(xué)吸附為輔,吸附過程增加了氣固界面之間的混亂與復(fù)雜程度；汞在R-AC表面的吸附可用Temkin與Langmuir方程較好地描述,汞在NH4Br-AC和FA表面的吸附可用Freundlich方程較好地描述。建立了國(guó)內(nèi)首套模擬煙氣夾帶流反應(yīng)器噴射脫汞實(shí)驗(yàn)裝置,研究了R-AC、NH4Br-AC、NH4Cl-AC及NH4Br改性飛灰(NH4Br-FA)的噴射脫汞特性,考察了入口Hg0濃度,停留時(shí)間,煙氣溫度,吸附劑粒徑,噴射量等參數(shù)對(duì)噴射脫汞的影響,分析了不同吸附劑的噴射脫汞機(jī)理。結(jié)果表明,提高煙氣汞濃度,增加吸附劑停留時(shí)間,減小吸附劑粒徑,均可提高R-AC和NH4Br-AC的噴射脫汞效率與單位汞吸附量；增加吸附劑的噴射量會(huì)提高脫汞率,但降低了單位汞吸附量；煙溫升高,R-AC的噴射脫汞率降低,NH4Br-AC的噴射脫汞率提高；NH4Br改性對(duì)煙氣Hg0的氧化與吸附強(qiáng)于NH4Cl改性；噴射吸附過程中,NH4Br-AC與NH4Cl-AC表面的Br或C1基團(tuán)均能將煙氣中的Hg0分子氧化成HgBr2或HgCl2, HgBr2與HgCl2相比Hg0更容易被吸附；NH4Br-FA的噴射脫汞率較低,其對(duì)煙氣中Hg0的脫除主要是Hg0的氧化,由于飛灰本身的比表面積與孔隙結(jié)構(gòu)均較差,因而降低了對(duì)Hg0的吸附率。在6 kWth燃煤循環(huán)流化床-夾帶流反應(yīng)器噴射脫汞實(shí)驗(yàn)裝置上,研究了貴州無(wú)煙煤燃燒的汞排放與分布特性,考察了NH4Br-AC在燃煤煙氣中的噴射脫汞特性及協(xié)同脫除SO2與NO的潛力。結(jié)果表明：貴州無(wú)煙煤燃燒后排放的汞主要為顆粒汞,比例為77.34%,氣相總汞為22.65%,其中Hg0為10.27%,Hg2+為12.38%；NH4Br-AC停留時(shí)間從0.59s增加到1.79s,脫汞率從70.7%增加到90.5%；NH4Br-AC表面的Br官能團(tuán)顯著提高了其對(duì)汞的吸附親和力；噴射NH4Br-AC的SO2協(xié)同脫除率達(dá)到了30.6%,主要為SO2在NH4Br-AC表面的化學(xué)吸附、毛細(xì)冷凝及部分SO2被氧化成SO3；噴射NH4Br-AC的NO協(xié)同脫除率達(dá)到了38%,主要為NO在NH4Br-AC表面的化學(xué)吸附及部分NO被氧化成NO2。提出了一個(gè)新的活性炭噴射脫汞預(yù)測(cè)模型,該模型基于外部膜傳質(zhì)與表面吸附過程,考慮了汞質(zhì)量平衡與吸附等溫。結(jié)果表明：該模型能合理地預(yù)測(cè)煙道內(nèi)的活性炭噴射脫汞效率,可利用該模型對(duì)活性炭消耗量進(jìn)行合理評(píng)估；模型參數(shù),包括活性炭濃度,顆粒直徑,平衡常數(shù),外部傳質(zhì)系數(shù)及活性炭停留時(shí)間均對(duì)活性炭噴射脫汞效率有重要的影響。
[Abstract]:Mercury is a highly toxic pollutant with strong volatility, bioaccumulation and environmental durability, and coal is the largest source of anthropogenic mercury. Therefore, the emission control of coal-fired mercury has become an important research direction in the current energy environment. At present, the most mature and feasible technology for controlling the mercury discharge of the coal-fired power plant is the activated carbon injection technology (ACI), because the activated carbon injection and demercuration process is a complex two-phase flow reaction system including flow, heat transfer, mass transfer and chemical reaction, The application of the technology in the coal-fired power plant also has more problems. The adsorption and adsorption mechanism of mercury on the surface of the adsorbent, the adsorption kinetics of mercury, the thermodynamic and adsorption equilibrium characteristics, the key parameters and the influencing mechanism of the adsorption and demercuration efficiency of the adsorbent, the mechanism of the demercuration of the adsorbent and the potential of the synergistic removal of SO2 and NO, Research on the scientific problems of the sorbent injection demercuration prediction model and so on. Four demercuration adsorbents of the original activated carbon (R-AC), NH _ 4Br-modified activated carbon (NH4Br-AC), NH4Cl-modified activated carbon (NH4Cl-AC) and fly ash (FA) were prepared. The influence of the factors such as particle size and flue gas composition on the static adsorption of mercury was studied. The adsorption of mercury on the surface of the adsorbent was studied by a program temperature-raising and desorption (TPD) method, and the mercury adsorption mechanism of different adsorbents was analyzed. The results show that the modification of NH _ 4Br and NH _ 4Cl is mainly in the surface of the active carbon and the mesopore in the amorphous form; the static mercury adsorption property of the adsorbent is NH4Br-AC4Cl-ACR-ACFA; the adsorption of the R-AC to the Hg0 is mainly due to the physical adsorption, a small amount of chemical adsorption exists, the product is HgO, and the adsorption of the NH4Br-AC to the Hg0 is mainly chemical adsorption, The product is HgBr2; O2 promotes the adsorption of R-AC and NH 4Br-AC to H-type; SO2 has different effects on the Hg0 adsorption of R-AC and NH _ 4Br-AC; in the presence of SO2, the amount of HgBr2 produced on the surface of the NH4Br-AC is reduced, but a small amount of HgS is generated; and NO promotes the adsorption of the R-AC and the NH4Br-AC to the Hg0, as Hg (NO3)2 is generated on the surface of the adsorbent. The adsorption kinetics of gas-phase mercury on the surface of activated carbon and fly ash were studied by dynamic model. The activation energy, initial mercury adsorption rate and adsorption thermodynamics and adsorption equilibrium of mercury on the surface of activated carbon and fly ash were calculated. The results show that the mercury adsorption process can be divided into two stages: surface adsorption and internal diffusion adsorption; while the external mass transfer and the internal diffusion limit the mercury adsorption process, the chemical adsorption of the mercury in the active site is the control step of the adsorption rate of the R-AC and the NH4Br-AC mercury; for the fly ash, the external mass transfer is the mercury adsorption rate control step; The activation energy of the adsorption of mercury on the surface of R-AC and NH 4Br-AC is-10.06610/ mol and-28.068 kJ/ mol, indicating that the adsorption is a common function of physical adsorption and chemisorption, and the initial mercury adsorption rate of the mercury on the surface of the adsorbent is positively related to the mercury adsorption capacity of the adsorbent; The thermodynamic analysis shows that the adsorption of mercury on the surface of R-AC and NH 4Br-AC is a spontaneous and endothermic process, and the adsorption takes physical adsorption as the main and the chemical adsorption is the auxiliary. The adsorption process increases the confusion and complexity of the gas-solid interface; the adsorption of the mercury on the R-AC surface can be well described by the Temkin and the Langmuir equation, The adsorption of mercury on the surface of the NH4Br-AC and FA can be well described by the Freundlich equation. In this paper, an experimental device for the injection and demercuration of the first simulated flue gas entrained flow reactor in China was established. The mercury-demercuration characteristics of R-AC, NH 4Br-AC, NH4Cl-AC and NH 4Br-modified fly ash (NH4Br-FA) were studied. The concentration of Hg0, the residence time, the temperature of the flue gas and the particle size of the adsorbent were investigated. The effect of injection quantity and other parameters on the injection and demercuration is analyzed, and the mercury removal mechanism of different adsorbents is analyzed. The results show that the mercury concentration of the flue gas is increased, the residence time of the adsorbent is increased, the particle size of the adsorbent is reduced, the mercury absorption efficiency and the unit mercury adsorption capacity of the R-AC and the NH4Br-AC can be improved, the injection amount of the adsorbent can be increased, the mercury removal rate can be improved, the adsorption amount of the unit mercury is reduced, and the smoke temperature is increased, The mercury removal rate of the R-AC is reduced, and the mercury removal rate of the NH4Br-AC is increased; the oxidation and adsorption of the NH 4Br-modified to the flue gas Hg0 are stronger than that of the NH4Cl; during the injection and adsorption process, the Br or C1 groups on the surface of the NH4Br-AC and the NH4Cl-AC can oxidize the Hg0 molecules in the flue gas into HgBr2 or HgCl2, and the Hg0 is more easily absorbed compared with the HgCl2; The mercury removal rate of NH 4Br-FA is low, and the removal of Hg0 in the flue gas is mainly the oxidation of Hg0. Because the specific surface area and the pore structure of the fly ash are both poor, the adsorption rate of Hg0 is reduced. In the 6 kWth coal-fired circulating fluidized-bed-entrained-flow reactor-injection demercuration experiment device, the mercury emission and distribution characteristics of the combustion of anthracite in Guizhou were studied. The mercury-demercuration characteristics of NH _ 4Br-AC in coal-fired flue gas and the potential of co-removal of SO2 and NO were investigated. The results show that the mercury in the burning of the anthracite is mainly granular mercury, the proportion is 77.34%, the total mercury in the gas phase is 22.65%, the Hg0 is 10.27%, the Hg2 + is 12.38%, the residence time of the NH4Br-AC is increased from 0.59s to 1.79s, and the demercuration rate is increased from 70.7% to 90.5%; The Br-functional group of the surface of the NH4Br-AC significantly increased its adsorption affinity to mercury; the synergistic removal rate of the SO2 in the injection of NH4Br-AC reached 30.6%, mainly the chemical adsorption of SO2 on the surface of the NH4Br-AC, the capillary condensation and the partial SO2 being oxidized to SO3; the NO co-removal rate of the sprayed NH4Br-AC reached 38%, The chemical adsorption of NO on the surface of the NH4Br-AC and the partial NO are oxidized to NO2. A new model of activated carbon injection and demercuration is proposed. The model is based on the process of external membrane mass transfer and surface adsorption, and the equilibrium and adsorption of mercury are considered. The results show that the model can reasonably predict the mercury removal efficiency of activated carbon in the flue. The model can be used to evaluate the consumption of activated carbon. The model parameters include the concentration of activated carbon, the particle diameter and the equilibrium constant. The external mass transfer coefficient and the residence time of activated carbon have an important influence on the mercury removal efficiency of activated carbon.
【學(xué)位授予單位】：東南大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：X773

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