Radiation-chemical treatment of flue gases from thermal power stations for the removal of mercury vapor

The efficiency of radiation-chemical treatment of flue gases from thermal power stations for removing nitrogen and sulfur oxides was examined as applied to the removal of mercury vapor from the gases. A kinetic scheme of the process was developed. It involves the liquid-phase oxidation of Hg by O₃ molecules formed under the action of ionizing radiation on the gas macrocomponents followed by adsorption of the oxidation products at soot particles. It was found that almost complete removal of mercury vapor is attained at typical radiation doses and soot concentrations in the flue gases.     

On the mechanism of soot particle formation

The results of experiments on the isothermic pyrolysis of acetylene, benzene, and diacetylene in a flow reactor near a low-temperature threshold of soot formation are presented. Diacetylene showed a much higher ability to form soot, coke, and tar than the other hydrocarbons. The threshold temperature of soot formation from diacetylene (800 K) was found to be lower than the threshold temperatures for benzene (1230 K) and acetylene (1200 K) for the same pyrolysis time (0.17 s) and equal hydrocarbon concentrations (on the basis of C atoms). The induction periods of soot formation for acetylene and benzene at 1100–1200 K, which were estimated from experiments, correlated well with literature data extrapolated from the high-temperature region. Invisible soot particles (0.3-0.5 Μm) and particles at different steps of carbonization were found among the products of low-temperature pyrolysis. Experimental data were analyzed and compared within the framework of two soot formation theories presented in the literature (the “acetylene” and “aromatic” theories). The contribution of the process of polyyne polymerization in a gas phase to the formation of a soot aerosol is discussed.     

Simulation of the Radiation-Chemical Conversion of Mercury Vapor in Power-Plant Flue Gases in the Presence of Hydrogen Chloride

The effect of HCl on the conversion of mercury vapor in the electron-beam treatment of power-plant flue gases for removing nitrogen and sulfur oxides was investigated. A kinetic scheme for the process consists of the liquid-phase oxidation of Hg by O₃molecules and OH radicals followed by the adsorption of liquid-phase oxidation products on soot particles, which are removed from the gas flow using filters. It was found that almost complete removal of mercury vapor is attained at typical radiation doses and process temperatures at soot concentrations higher than 100 g/m³(STP). At a soot concentration lower than 100 g/m³(STP) and an HCl concentration higher than 50 mg/m³(STP) in the gas phase, biologically active HgCl₂is formed in considerable amounts.     

Water interaction with hydrophobic and hydrophilic soot particles

The interaction of water with laboratory soots possessing a range of properties relevant for atmospheric studies is examined by two complementary methods: gravimetrical measurement of water uptake coupled with chemical composition and porosity analysis and HTDMA (humidified tandem differential mobility analyzer) inference of water uptake accompanied by separate TEM (transmission electron microscopy) analysis of single particles. The first method clarifies the mechanism of water uptake for bulk soot and allows the classification of soot with respect to its hygroscopicity. The second method highlights the dependence of the soot aerosol growth factor on relative humidity (RH) for quasi-monodisperse particles. Hydrophobic and hydrophilic soot are qualitatively defined by their water uptake and surface polarity: laboratory soot particles are thus classified from very hydrophobic to very hydrophilic. Thermal soot particles produced from natural gas combustion are classified as hydrophobic with a surface of low polarity since water is found to cover only half of the surface. Graphitized thermal soot particles are proposed for comparison as extremely hydrophobic and of very low surface polarity. Soot particles produced from laboratory flame of TC1 aviation kerosene are less hydrophobic, with their entire surface being available for statistical monolayer water coverage at RH approximately 10%. Porosity measurements suggest that, initially, much of this surface water resides within micropores. Consequently, the growth factor increase of these particles to 1.07 at RH > 80% is attributed to irreversible swelling that accompanies water uptake. Hysteresis of adsorption/desorption cycles strongly supports this conclusion. In contrast, aircraft engine soot, produced from burning TC1 kerosene in a gas turbine engine combustor, has an extremely hydrophilic surface of high polarity. Due to the presence of water soluble organic and inorganic material it can be covered by many water layers even below water saturation conditions. This soot demonstrates a gradual diameter growth factor (D(wet)/D(dry)) increase up to 1.22 at 93% relative humidity, most likely due to the presence of single particles with water soluble material heterogeneously distributed over their surface.     

Determination of volatile polynuclear aromatic hydrocarbons in air from particulate profiles by means of partial least-squares regression

The possibility of estimating the total (particulate and gaseous) concentrations of volatile polynuclear aromatic hydrocarbons (PAH's) in air on the basis of measured concentrations of PAH's in particles by means of partial least-squares regression (PLS), is discussed. The results show that the estimation can be good for samples exposed to the same source and collected under similar weather conditions.     

高岭土对焚烧烟气中Pb、Cd排放的控制特性研究

采用流化床焚烧炉进行焚烧实验,研究了烟气中颗粒物形态Pb和Cd的排放规律以及炉内添加高岭土粉末对Pb、Cd排放的影响。用低压冲击器分级采集颗粒物,原子吸收分光光度计检测Pb、Cd浓度,用扫描电镜/X射线衍射/能谱仪观察高岭土吸附重金属前后表面形貌和反应物的种类并检测表面元素分布。结果表明,PM10中90%以上的Pb和85%以上的Cd分布在亚微米颗粒物中;在焚烧炉内,Pb比Cd更易于向PM10中迁移。高温下高岭土与重金属Pb、Cd蒸气反应而产生共晶融化,随温度升高融化量逐渐增加。共晶融化可以促使颗粒相互黏附,促进亚微米重金属向粗颗粒中迁移。添加高岭土可以有效控制亚微米Pb、Cd排放,对亚微米Pb的最高吸附效率达83%,对亚微米Cd的最高效率达50%。高岭土对Pb吸附效率顺序为950℃1000℃850℃900℃;高岭土与Cd反应所需的温度较高,直至1000℃时才具有明显吸附效果。     

Analysis of Mechanisms at the Plasma–Liquid Interface in a Gas–Liquid Discharge Reactor Used for Treatment of Polluted Water

Aqueous solutions polluted by contaminants different from those generally studied (phenol and chlorophenols) were treated in a falling film gas–liquid dielectric barrier discharge reactor. The lower was the Henry’s law constant of a molecule, the better was its removal percentage, regardless of its other chemical properties. In the case of saturated molecules, the removal mechanism is the transfer of pollutants from the liquid phase to the gas phase where they react with the active species of the discharge. For phenol, the reaction with ozone in the liquid phase was estimated to be responsible of about 30% of the removal. A computational fluid dynamic modelling provided a better understanding of the phenomena, indicating that mass transfer of pollutants from liquid to gas is accelerated due to (1) the intense mixing in the liquid film and (2) the reaction of the pollutant with the active species in the gaseous phase.     

Pretreatment of landfill leachate by chemical oxidation processes

Kinetics and efficiency of Fenton’s and ozonation processes for the pretreatment of two landfill leachates (fresh and mature) resulting from municipal waste disposal were studied. Both samples presented high organic load, high toxicity and low biodegradability. These were the reasons why oxidative treatment was proposed. Fresh and mature leachate showed different behaviors in the oxidation experiments. The final extents of removal were attained in comparable time intervals in both oxidation systems. Maximal removal of organics by the Fenton’s oxidation reached more than 50 % according to COD. Zero or first order kinetics were found the best to describe the organic components (in terms of COD and DOC) removal by the Fenton’s oxidation for both landfill leachates. Higher reaction rate values of the Fenton’s oxidation were achieved with fresh leachate samples. The efficiency of initial organics removal with ozone was about 70 % for mature leachate, while in case of the fresh one only 41 % of COD were removed. The best fits of COD and DOC experimental data from oxidation of fresh and mature leachates were obtained by a combined kinetic model. No significant improvement of the biodegradability of landfill leachates was achieved using these treatment procedures. Regarding toxicity, ozonation showed to be more effective than the Fenton’s oxidation. Advanced oxidation experiments confirmed that the Fenton’s oxidation and ozonation are comparable oxidative treatment techniques for the reduction of organic pollution in the investigated municipal landfill leachates. However, neither of them is effective enough to be used as a pretreatment method followed by biological treatment.     

脱硫废水蒸发增强电除尘脱除PM2.5和SO3实验研究

搭建燃煤热态实验系统,研究脱硫废水蒸发对电除尘和脱硫系统的影响;考察脱硫废水蒸发前后细颗粒粒径的变化、电除尘出口PM_2.5和SO₃浓度变化;分析增强电除尘脱除PM_2.5和SO₃机理。结果表明,脱硫废水蒸发后,蒸发室出口细颗粒粒径峰值由0.1 μm增大到1.1 μm,观察脱硫废水蒸发前后扫描电镜,明显观察到废水蒸发后颗粒团聚长大,颗粒间存在絮状物;采用脱硫废水烟道蒸发后,电除尘细颗粒脱除效率提高5%左右,PM_2.5数量浓度脱除效率提高25%左右;SO₃脱除效率为60%-80%,烟气中SO₃浓度对增强电除尘脱除PM_2.5和SO₃均有影响;脱硫废水蒸发对脱硫系统的效率和脱硫浆液的pH值没有影响。     

应用水汽相变促进湿法脱硫净烟气中PM_(2.5)和SO_3酸雾脱除的研究

在石灰石-石膏法脱硫净烟气中分别采用添加适量蒸汽和湿空气方式建立PM_(2.5)和SO_3酸雾凝结长大所需的过饱和水汽环境,在测试分析湿法脱硫净烟气中PM_(2.5)及SO_3酸雾物性的基础上,考察了蒸汽及湿空气添加量、脱硫净烟气温度等的影响。结果表明,湿法脱硫净烟气中PM2.5除含有燃煤飞灰外,含Ca SO_4、Ca SO_3及未反应的Ca CO_3等组分;由于SO_3酸雾基本处于亚微米级粒径范围,湿法烟气脱硫(WFGD)系统对SO_3酸雾的脱除率仅为35%-55%;添加适量蒸汽及湿空气方式均可促进湿法脱硫净烟气中PM_(2.5)和SO_3酸雾脱除,最终排放浓度随蒸汽或湿空气添加量的增加而降低,其中,添加蒸汽方式适合于脱硫净烟气温度较低(≤50-55℃)的场合,在脱硫净烟气温度较高(≥55-60℃)时,利用添加湿空气方式替代添加蒸汽更具技术经济优势。     

Investigation of Soot Deposition and Composition in a Radio Frequency Plasma of Benzene

A radio frequency (rf) discharge has been utilized to study the decomposition of benzene. SEM inspection has shown that the size of soot particles ranged from 0.5 to several μm. The soot deposited on silicon wafers was analyzed by gas chromatography/mass spectrometry (GC/MS). It was shown that the main components of the soot are polyphenyls (biphenyl and terphenyls) and a trace amount of polycyclic aromatic hydrocarbons (PAHs). Acetylene and hydrogen have been detected by plasma diagnostics techniques using Fourier transform infrared (FTIR) and optical emission spectroscopic techniques. However, GC/MS analysis has shown that the relative yields of PAHs are much less than those of polyphenyls, which indicates that the conventional hydrogen abstraction-acetylene addition (HACA) model for soot formation is not applicable to the benzene plasma due to the reason of temperature. The rf power, the carrier gas flow-rate, the relative yields of polyphenyls, and plasma temperatures were correlated. The reaction pathways of benzene elimination and soot formation in plasma are discussed. This study has provided a new route to control the contamination due to PAHs.     

Adsorption technology for direct recovery of compressed,pure CO<Subscript>2</Subscript> from a flue gas without pre-compression or pre-drying

The effects of the sorption and the regeneration temperatures on the performance of a novel rapid thermal swing chemisorption (RTSC) process (Lee and Sircar in AIChE J. 54:2293–2302, 2008) for removal and recovery of CO₂ from an industrial flue gas without pre-compression, pre-drying, or pre-cooling of the gas were mathematically simulated. The process directly produced a nearly pure, compressed CO₂ by-product stream which will facilitate its subsequent sequestration. Na₂O promoted alumina was used as the CO₂ selective chemisorbent, and the preferred temperatures were found to be, respectively, 150 and 450 °C for the sorption and regeneration steps of the process. The specific cyclic CO₂ production capacity of the process and the pressure of the by-product CO₂ gas were substantially increased over those previously achieved by using the sorption and regeneration temperature of, respectively, 200 and 500 °C (Lee and Sircar in AIChE J. 54:2293–2302, 2008). The net compressed CO₂ recovery from the flue gas (∼92%) did not change. However, substantially different amounts of high and low pressure steam purges were necessary for comparable degree of desorption of CO₂. A first pass estimation of the capital and the operating costs of the RTSC process was carried out for a relatively moderate size application (flue gas clean up and CO₂ recovery from a ∼80 MW coal fired power plant). Both costs were substantially lower than those for a conventional absorption process using MEA as the CO₂ solvent (Desideri and Paolucci in Energy Convers. Manag. 40:1899–1915, 1999).     

410t/h煤粉锅炉的汞排放及其NID系统除汞特性研究

对配备有NID系统的410t/h燃煤电站锅炉的煤、底渣、飞灰进行取样,测定了样品中汞的含量。采用Ontario Hydro方法测定了NID前和ESP后烟气中汞的形态。实验结果表明,汞主要以飞灰形式排放,占总汞量的90%,烟气汞占10%。NID前和ESP后的烟气中,汞的浓度分别为21.3μg/m3~22.4μg/m3和1.93μg/m3~3.67μg/m3,说明该NID系统对烟气中汞具有相当高的脱除效率,达到83.6%~90.9%。对汞的化学形态研究表明,NID前烟气汞主要以Hg2+形式存在,占气态汞量的67%;ESP后烟气中Hg2+占气态汞量的71.8%~85.1%,Hg0的含量为零,说明烟气中Hg0在NID系统中经历一系列的氧化还原反应后,被氧化成Hg2+并吸附脱除。     

LIFAC烟气脱硫中应用蒸汽相变促进细颗粒物脱除的实验研究

在炉内喷钙尾部增湿活化(LIFAC)脱硫后的低温高湿烟气中添加适量蒸汽建立蒸汽相变所需的过饱和环境,促进水汽在细颗粒物表面凝结,进而由高效除雾器脱除凝结长大的含尘液滴.采用电称低压冲击器(ELPI)实时测定细颗粒物数量浓度及粒径分布,维萨拉温湿度变送器测试烟气温度和湿度.考察了活化水添加量、蒸汽添加量、细颗粒物数量浓度...     

复合聚并协同脱除燃煤颗粒物及颗粒态重金属的中试研究

燃煤颗粒物和其上富集的As、Se、Pb等重金属排入大气后危害环境和人体健康。本研究开发以湍流聚并、壁面回流吸附为原理的复合聚并器，研究了聚并前后对颗粒物和颗粒态重金属的聚并效果。首先采用数值模拟方法综合考虑压力损失、速度均匀性和颗粒物聚并效果，优选了折叶片作为复合聚并器的叶片类型。随后进行了不同流量的颗粒物聚并中试研究，发现复合聚并器对PM₁的聚并率可达32.84%，随着流量从11.1 m/s增加到17.6 m/s，PM_2.5聚并率呈现一定下降趋势，说明了流量增加导致颗粒停留时间缩短和颗粒物聚并率的下降。通过对比聚并前后颗粒物中As、Se、Pb的浓度变化，发现聚并过程增强了对气态重金属的吸附，也会聚集富含重金属的纳米级颗粒物，从而造成PM₁中重金属浓度的增加。聚并后PM₁内的As、Se、Pb绝对浓度的降低，显示了复合聚并器对颗粒物和颗粒态重金属的协同脱除效果。     

300 MW燃煤电厂ESP和WFGD对烟气汞的脱除特性

采用燃煤电厂汞形态浓度取样测试OHM标准方法,对一座300 MW燃煤电厂静电除尘器(ESP)和湿法脱硫装置(WFGD)前后烟气进行了等速取样.使用美国Leeman Labs Hydra AA全自动汞分析仪检测烟气中的汞形态浓度.采集了固体样品,包括入炉煤、底渣、ESP电场灰、脱硫剂石灰石、脱硫产物石膏等,使用意大利Milestone公司生产的DMA80全自动汞分析仪检测固体样品中的汞浓度.计算锅炉系统的汞质量平衡,获得了ESP和WFGD前后烟气的汞形态浓度和分布规律,分析讨论了影响烟气汞形态转化的各种影响因素.结果表明,燃煤烟气中气态单质汞Hg⁰和气态氧化汞Hg²⁺占到总汞量的95%.煤渣中的汞可忽略不计;ESP对颗粒态汞Hg^p的脱除效率达到95%以上,但是对Hg⁰和Hg²⁺脱除率不高.ESP对烟气总汞Hg^T脱除效率为12.77%~17.38%;WFGD对Hg²⁺的脱除率达到79.93%~90.53%,但是对Hg⁰没有脱除效果,其含量不仅没有下降反而有少量上升,说明有部分Hg²⁺在WFGD中被还原成Hg⁰.WFGD对Hg^T脱除效率为9.68%~29.36%;该电厂现有污染控制设备ESP+WFGD可以脱除全部的Hg^p和大部分Hg²⁺,但是由于部分Hg²⁺的还原使得Hg^T的脱除效率在25.38%~38.38%.综合来看,该燃煤电厂的污染物控制设备在进行除尘和脱硫的同时,对汞的脱除率并不高,与燃煤中的氯含量较低有关.     

Experiment and mechanical analysis of flue gas desulphurisation with organic solvent

A novel flue gas desulphurisation (FGD) technology using an organic solvent, dimethyl sulphoxide, has been studied. Process parameters studied included solvent concentration, temperature, flow rate and their role in the removal of SO₂ from flue gas. The mechanism of FGD by the organic solvent method is discussed and should be of assistance in the industrial removal of SO₂ from flue gas.     

Oxidization of SO2 by Reactive Oxygen Species for Flue Gas Desulfurization and H2SO4 Production

A strong ionization dielectric barrier discharge was used to produce a high concentration of reactive oxygen species that were then injected into a simulated flue gas in a duct to remove SO₂ by oxidation. Sulfuric acid (H₂SO₄) was produced through the following two reactions: (1) O₃ oxidation of SO₂–SO₃, which then reacted with H₂O to produce H₂SO₄; and (2) reaction of O₂ ⁺ with H₂O to produce ·OH radicals, which then rapidly and non-selectively oxidized SO₂–H₂SO₄. When the molar ratio of reactive oxygen species to SO₂ was 4:1, the SO₂ removal efficiency was 94.6%, the energy consumption per cubic meter of flue gas was 13.3 Wh/m³, the concentration of recovered H₂SO₄ was 4.53 g/l, and the H₂SO₄ recovery efficiency was 28.8%. The H₂O volume fraction in the simulated flue gas affected the SO₂ removal efficiency, whereas the O₂ and CO₂ volume fractions did not. These results prove that oxidation by reactive oxygen species is a feasible method for flue gas desulfurization.