Mechanism and Kinetic Study on Elemental Mercury Oxidation in Flue Gas by Ozone Injection

The mechanism and kinetics of the elemental Hg oxidation in flue gas by ozone injection are investigated in detail by using quantum chemistry, kinetic simulation and experimental research. The reaction processes, activation energies and kinetic parameters are calculated and analyzed by quantum chemistry. From the comparison of activation energies, the Hg⁰ oxidation ability of oxidizing radicals is that: NO₃>O₃>NO₂. The calculated results are in good agreement with literature experimental results. The calculated kinetic parameters are employed for kinetic simulation. The results of kinetic simulation are in good agreement with the experimental results. Results show that, the Hg⁰ oxidization increases linearly when the mole ratio of O₃/NO becomes larger or the reaction temperature becomes higher. The reaction Hg+NO₃ = NO₂+HgO is the key elemental reaction and the concentration of NO₃ is the most important factor for affecting Hg⁰ oxidation.     

城市煤气多气种掺混技术的应用

介绍了多气种掺混的气质持性及符合7R气质特性的“三气”掺混最佳比；提出了以烟道气替代两段炉贫煤气进行掺混的思路，并对原商品煤气中两种“三气”掺混技术的经济效巢进行了比较。     

Technology Optimization of Wet Flue Gas Desulfurization Process

Optimization of the wet limestone (calcite) flue gas desulfurization (FGD) process is described, with the focus on the layout of subprocesses and equipment. The aim of optimization was to check the effectiveness and reliability of alternative layouts, involving intermediate product (gypsum) storage in the absorber make‐up tank, instant production of limestone slurry from powder in a wet screw conveyer and automatic gypsum dewatering line operation. Three alternatives, standard layout, optimized layout and optimized layout without reheating of treated gas, were designed and tested in a small industrial FGD plant. The comparison included evaluation of desulfurization efficiency, economical feasibility (considering a 125 MW power plant) and reliability of operation. The efficiency of the system was not affected by the layouts. Investment costs were reduced by 5 and 15 % for alternatives 1 and 2, respectively, compared to standard offers on the market. With respect to operating costs, variable operating and maintenance costs could be decreased by 0.5 up to 2.5 %, respectively. As shown by risk and reliability analysis, the availability of the system in both alternative layouts remained unchanged or was better with regard to the standard layout.     

Mercury speciation and its emissions from a 220 MW pulverized coal-fired boiler power plant in flue gas

Distributions of mercury speciation of Hg⁰, Hg²⁺ and Hg ^P in flue gas and fly ash were sampled by using the Ontario Hydro Method in a 220 MW pulverized coal-fired boiler power plant in China. The mercury speciation was varied greatly when flue gas going through the electrostatic precipitator (ESP). The mercury adsorbed on fly ashes was found strongly dependent on unburnt carbon content in fly ash and slightly on the particle sizes, which implies that the physical and chemical features of some elemental substances enriched to fly ash surface also have a non-ignored effect on the mercury adsorption. The concentration of chlorine in coal, oxyge nand NO _x in flue gas has a positive correlation with the formation of the oxidized mercury, but the sulfur in coal has a positive influence on the formation of elemental mercury. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Mercury release from FGD

The release of mercury from flue gas desulfurization (FGD) gypsum in the manufacture of 100% FGD wallboard was studied. Calcination, with product temperatures ranging from 150 to 180 °C, appears to be the most likely process to release mercury from the FGD. Two samples evaluated in trials conducted to simulate the calcining of FGD in flash calcining and kettle processes showed that the potential of mercury release exists. The differing amounts of mercury released by the two processes could be separated by orders of magnitude. Measurements in real production facilities are essential to developing a valid answer to the question of mercury release during FGD gypsum wallboard production.     

Mercury emission control in coal-fired plants: The role of wet scrubbers

When coal is combusted, the combination of the elevated temperature and the volatility of mercury and its compounds results in the presence of gaseous elemental mercury and mercury compounds in the combustion flue gas. In January 2005, the European Commission adopted a mercury strategy that envisages a number of measures to reduce mercury levels in the environment and human exposure. A number of options for mercury removal from coal-fired power plants have been investigated. However, more effort is needed to achieve an efficient and cost-effective technology. The main objective of this work is to investigate the influence of scrubber parameters on mercury removal efficiency to establish effective measures for mercury control. In order to attain these objectives, theoretical predictions based on thermodynamical equilibrium data and lab-scale experimental tests were carried out. The results obtained point to pH and slurry concentration as the most critical parameters for converting FGD (Flue Gas Desulphurization unit) into a multipollutant control technology.     

Prediction of the Removal Efficiency of a Novel Two‐Stage Hybrid Scrubber for Flue Gas Desulfurization

Emission of SO₂ from various industrial sources occurs in varying concentrations and quantities. The operation of scrubbers as SO₂ control devices is getting more and more attention as pollution control regulations are tightened. Experimental investigations on the scrubbing of SO₂ in a novel two‐stage hybrid (spray‐cum‐bubble column) scrubber using water and dilute sodium alkali are reported. Empirical and semi‐empirical correlations are developed for the prediction of the performances of the bubble and the spray sections in terms of various pertinent variables of the system for water and alkaline scrubbing, respectively. The contribution of the mass transfer enhancement factor towards the removal of SO₂ has been exploited while developing the semi‐empirical correlation for the prediction of performance in alkaline scrubbing. The predicted values are in excellent agreement with the experimental values. Finally, the operating features of the scrubber and design aspects are discussed in order to develop our understanding for practical applications.     

Catalytic Flue Gas Treatment from Nitriding Processes

Efficient control and minimization of emissions from technical processes is of major concern in industrial development and process operation. The technical process in the focus of the present contribution is the nitriding process of metallic specimen. The ammonia content in nitriding process flue gases reaches up to 618 g·m^–3 (80 vol.‐%) and needs to be reduced to less than 30 mg·m^–3 (40 ppm) to fulfill present regulations. Exhaust gases from nitriding processes today are burnt in flares without emission control where fuels need to be added that produce additional exhaust gas components. The objective of this investigation is to develop an alternative gas cleaning route for nitriding processes based on catalytic dissociation of ammonia. The decomposition was studied for different catalysts at varying process conditions. With these results a dissociation pilot plant was successfully tested in a technical‐scale nitriding process.     

Application of Water‐Swollen Thin‐Film Composite Membrane in Flue Gas Purification

A water‐swollen thin‐film composite membrane, which was a reverse osmosis membrane with a thin polyamide layer, was used to separate a model mixture of N₂, CO₂, and SO₂. The polyamide swells with water, and thus, becomes more permeable to polar gases. The flue gas contains water vapor, which must be removed before it is subjected to SO₂ removal. Here moisture is employed to keep the membrane swollen. Using the model mixture, the humidified feed stream is brought to the membrane, where it is cooled below the dew point, so that water condenses on the membrane to keep the polyamide swollen. The membrane showed high CO₂ and SO₂ permeance, but low selectivity, so it could be applied to separate these two gases from N₂, and thus, is suitable for flue gas purification.     

Column Dust Scrubber Based on an Orifice Plate to Intensify Gas‐Liquid Mixing

A column dust scrubber based on an orifice plate is developed for small and medium‐sized enterprises in China, which urgently need small‐volume, large‐flow scrubbers. The scrubber uses an orifice plate to evenly distribute the gas flow, which forms a uniform and stable impact on the liquid phase. As a result, dust removal via intensified gas‐liquid mixing can be achieved. A laboratory orifice plate scrubber model is developed, prototyped, and preliminarily studied considering the working process of the scrubber (mixed gas‐liquid flow pattern), liquid level, gas flow rate, pressure drop characteristics, dust removal efficiency, etc. The scrubber can achieve a good gas‐liquid mixing state when it is in a stable liquid column flow pattern. The drag coefficient of the scrubber is affected by the discharge of the gas stream to the liquid phase.     

Mercury removal from coal combustion by Fenton reactions – Part A: Bench-scale tests

This series of papers describes the development of technology to convert Hg(0) to Hg(II) in coal-derived flue gas based on the well-known Fenton reactions so that a Hg control strategy can be implemented in a wet scrubber. This effort consists of both bench-scale and pilot-scale work. This first paper reports on the bench-scale tests. The bench-scale results showed that Hg(0) oxidation can be achieved by the Fenton reactions and the oxidation rate is quantitatively dependent on the residence time of the Hg stream in the solution. An average of 75% oxidation of Hg(0) was achieved. Iron-based Fenton-type additives gave much more promising results compared to Cu-based Fenton-like additives for Hg(0) oxidation. The pH value of the sorbent solution also had a significant effect on the oxidation of Hg(0) and a suitable pH window was found to lie between 1.0 and 3.0 for this application. This may be attributed to the chain reaction mechanisms of Fe³⁺/H₂O₂ for Fenton reactions, i.e., the decomposition of H₂O₂ for the production of OOH radicals in the Fe³⁺/H₂O₂ system which is kinetically favoured under a wide range of conditions at pH values of 3 or less. At higher pH values, H₂O₂ is converted to H₂O instead of OOH radicals in the presence of Fe³⁺.     

Design and Implementation of a Gas Generating System for Complex Gas Mixtures and Calibration Gases

A test gas generation system for complex gas mixtures designed to mimic real industrial gas matrices with traces raging from low pptv to high ppmv level and minor and main components ranging from low to high percentage levels with variable relative humidity levels (0–80 % RH) is presented. It combines different gas generation methods to study fragmentation patterns under controlled conditions by means of a proton transfer reaction time-of-flight mass spectrometer, the application of alternative feedstocks in catalytic processes as well as the performance of gas purification and conditioning processes.     

The effect of chlorine and oxygen concentrations on the removal of mercury at an FGD-batch reactor

A series of laboratory scale experiments were conducted in an FGD-batch reactor. A synthetic flue gas was produced and directed through a CaCO₃ suspension contained in a glass reactor vessel. The suspension temperature was set at 54 °C through a water bath. In order to observe the distribution of mercury species in the system, solid, liquid and gaseous samples were taken and analysed. For gaseous mercury determination, continuous measurements were carried out, up and downstream the reactor. Furthermore, the concentration of chlorine in the scrubber solution of the system was varied from 0 to 62 g/l under different oxidative conditions.In a first approach, a concentration drop of elemental mercury coming out of the system was observed. The latter occurs only when high concentrations of Cl⁻ are present, combined with a high O₂ availability in the scrubber. It was also observed that mercury species distribution in the different phases varies, depending on the available chemical form of chlorine and oxygen concentration.     

Advanced Oxidative Removal of Nitric Oxide from Flue Gas by Homogeneous Photo‐Fenton in a Photochemical Reactor

In this work, advanced oxidation removal of nitric oxide (NO) from flue gas by homogeneous Photo‐Fenton was investigated in a photochemical reactor and the effects of several influencing factors on NO removal were evaluated. The gas‐liquid reaction products were determined. The reaction pathways of NO removal are also preliminarily discussed. It was found that with the increase of Fe²⁺ concentration, NO removal efficiency first increased and then decreased. Increasing H₂O₂ concentration and UV radiation intensity greatly increased NO removal efficiency, but the growth rates gradually became smaller. NO removal efficiency greatly reduced with the increase of gas flow and NO concentration, and only slightly decreased with the increase of solution temperature, but significantly increased with the increase of initial solution pH value. The main anion product in the liquid phase was NO₃^–. With respect to removal of NO using homogeneous Photo‐Fenton, ·OH oxidation was the main reaction pathway, and H₂O₂ oxidation was the secondary reaction pathway.     

鄂尔多斯电厂湿法烟气脱硫调试存在问题探讨

本文介绍了鄂尔多斯电厂2×300MW#机组石灰石-石膏湿法烟气脱硫系统调试过程中遇到的若干问题,并对问题进行了详细的分析和解决,以便对其它同类型脱硫系统的凋试工怍提供参考。     

添加有机酸强化石灰石-石膏湿法烟气脱硫实验

将甲酸作为添加剂,在工业规模实验装置上,研究了有机酸添加剂对脱硫效果的影响。主要考察了浆液在脱硫过程中,浆液pH值、脱硫率、石灰石利用率随甲酸添加量的变化,及脱硫率和浆液pH值的关系,并分析了添加有机酸后石灰石的溶解过程。结果表明,随有机酸添加量的增加,脱硫率和石灰石利用率逐渐升高到某一极值,但过量添加有机酸不能持续强化脱硫过程。浆液pH值在酸性范围内逐渐增加,脱硫率逐级升高。结果为脱硫过程强化提供了参考。     

新技术在30MW级烟气轮机研制中的应用

基于"可控涡"设计理念,采用ANSYS有限元应力分析及Abquse强度分析软件,完成了30MW级烟气轮机的气动设计,通过Dyrobes及CFD软件建模,分别进行了无阻尼和有阻尼状态下的转子临界转速计算以及流场模拟。针对转子容易产生冲蚀和结垢的问题,进行了转子不平衡敏感性分析。     

Experimental study on mercury transformation and removal in coal-fired boiler flue gases

This paper reported mercury speciation and emissions from five coal-fired power stations in China. The standard Ontario Hydro Method (OHM) was used into the flue gas mercury sampling before and after fabric filter (FF)/electrostatic precipitator (ESP) locations in these coal-fired power stations, and then various mercury speciation such as Hg⁰, Hg²⁺ and Hg^P in flue gas, was analyzed by using EPA method. The solid samples such as coal, bottom ash and ESP ash, were analyzed by DMA 80 based on EPA Method 7473. Through analysis the mercury speciation varied greatly when flue gas went through FF/ESP. Of the total mercury in flue gas, the concentration of Hg²⁺ is in the range of 0.11–14.76 μg/N m³ before FF/ESP and 0.02–21.20 μg/N m³ after FF/ESP; the concentration of Hg⁰ ranges in 1.18–33.63 μg/N m³ before FF/ESP and 0.77–13.57 μg/N m³ after FF/ESP, and that of Hg^P is in the scope of 0–12.11 μg/N m³ before FF/ESP and 0–0.54 μg/N m³ after FF/ESP. The proportion of Hg²⁺ ranges from 4.87%–50.93% before FF/ESP and 2.02%–75.55% after FF/ESP, while that of Hg⁰ is between 13.81% – 94.79% before FF/ESP and 15.69%–98% after FF/ESP, with that of Hg^P is in the range of 0%–45.13% before FF/ESP and 0%–11.03% after FF/ESP. The mercury in flue gas mainly existed in the forms of Hg⁰ and Hg²⁺. The concentrations of chlorine and sulfur in coal and flue gas influence the species of Hg that are formed in the flue gas entering air pollution control devices. The concentrations of chlorine, sulfur and mercury in coal and the compositions of fly ash had significant effects on mercury emissions.     

湿法烟气脱硫技术研究现状及进展

介绍了国内外已工业应用的主要湿法烟气脱硫技术,如石灰石/石灰-石膏湿法、海水烟气脱硫和微生物法等工艺技术的应用现状及研究发展,并对近年来国内外发展的脱硫新工艺进行了评述。由此探讨了湿法烟气脱硫技术现在存在的问题、研究情况和发展前景。