Industrial test on coal re-burning at a 600 MW utility boiler and NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> reduction

This research conducts a series of industrial tests on coal reburning of a 600 MW pulverized coal boiler firing lignite, which is one part of a coal reburning demonstration project. When running steadily under 600 MW load, the boiler has an average NO _x emission of 274 mg/m³ (O₂ content in flue gas is converted to 6%), the NO _x emission is reduced by 65.36%. In the meanwhile, loss of ignition (LOI) under coal reburning rarely increases. Three operation conditions — traditional air feeding, air staging and coal reburning — are realized, respectively, during the industrial tests, and the results indicate that coal reburning has the lowest NO _x emission, while the traditional air feeding has the highest NO _x emission. Under the test conditions, the higher the proportion of the reburning coal, the higher the NO _x control can reach. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Reduction of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> in diesel engine emissions by using a plasmatron fuel reformer

An experimental study of diesel exhaust cleaning by means of the plasma chemical pretreatment of fuel is described. Some portion of the fuel was activated in an arc discharge and turned into hydrogen-rich synthesis gas. Plasma chemical reformation of fuel was carried out by using a DC arc plasmatron that was fabricated to increase the ability of gas activation. The yield of diesel fuel reformation reached about 80−100% when small quantities of fuel (flow rate up to ∼6 ml/min) were reformed. The synthesis gas, containing H₂+CO, was supplied into the engine together with the rest of the fuel-air mixture, and the NO _x content in its emissions reduced up to 23%. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Effects of Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> nanometer particles on biological toxicity during zebrafish embryogenesis

This study investigated the toxicity of Cu (1, 10, 15, and 25 mol%) loaded TiO₂ and pure TiO₂ nanometersized photocatalysts during the development of zebrafish embryogenesis. The hatch rate decreased in the Cu _x TiO _y nanoparticles exposed groups (10, 20 ppt) compared to pure TiO₂ nano-particles (10, 20 ppt) exposed or control groups. These Cu _x TiO _y and TiO₂ nanoparticles led to developing mutated embryos with abnormal notochord formation, no tail, damaged eyes and abnormal heart development. Exposure to Cu _x TiO _y and pure TiO₂ nanoparticles led to glutathione increase, catalase activity increase, GST increase and GSR increase than control. Penetration of the Cu _x TiO _y and pure TiO₂ nanoparticles to the embryo was also tested. It was observed that Cu _x TiO _y and pure TiO₂ nanoparticles penetrated into cells. Moreover Cu _x TiO _y penetrated into the skin, nerve and yolk sac epithelium cells on the zebrafish larvae as aggregated particles, which may induce the direct interaction between nanoparticles and cell to cause adverse biological responses. As a result, the Cu-loaded TiO₂ nanoparticles had the toxicity of zebrafish embryo and larvae in the water environment.     

Deactivation of barium oxide-based NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> storage and reduction catalyst by hydrothermal treatment

The deactivation of a barium oxide-based NO _x storage and reduction (NSR) catalyst with hydrothermal treatment was studied by treating it with 10 vol% water vapor diluted in nitrogen at 850°C. XRD, XPS, SEM, IR of CO adsorption, and the N₂ adsorption was used to investigate the physical and chemical changes of the NSR catalyst caused by the hydrothermal treatment. The 12 h hydrothermal treatment decreased its NO₂ storage capacity by 20%. However, the hydrothermal treatment significantly decreased its ability to reduce the stored NO₂. The formation of an inactive phase consisting of platinum and aluminum is believed to be the cause of the severe deactivation of the NSR catalyst.     

Mechanistic Investigation of Co Containing NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Traps

Co-containing NO _x storage and reduction catalysts were investigated to identify the mechanism of Co promotion. X-ray diffraction and temperature programmed reduction demonstrated that Co exists in a highly oxidized state (Co₃O₄) and that the surface oxygen could be removed from the catalyst a typical operating conditions around 300 °C. Electron microscopy showed that Co is more uniformly distributed over the catalyst surface, as compared to Pt, with particle sizes ranging between 20 and 80 nm. In situ IR studies illustrated that NO _x storage occurs on Co-containing NSR catalyst via formation of nitrites and nitrates as surface intermediates. Finally, it was found that, similar to Pt, the addition of Co to Ba catalysts enhances the nitrite to nitrate transition rate and also increases the overall formation of nitrates. Therefore, the promotional effect shown by Co is the result of the combination of increased NO to NO₂ oxidation and improved surface area for NO₂ spillover to the Ba storage sites.     

Experimental study of N<Subscript>2</Subscript> dilution on bluff-body stabilized LPG jet diffusion flame

The present paper reports the effects of N₂ addition and preheating of reactants on bluff-body stabilized coaxial LPG jet diffusion flame for two cases, namely, (I) preheated air and (II) preheated air and fuel. Experimental results confirm that N₂ addition to the fuel stream leads to an enhancement in flame length, which may be attributed to the reduction in flame temperature. The soot free length fraction (SFLF) also increases, which might be caused by the decrease in fuel concentration and flame temperature. The flame length and also the SFLF are observed to be reduced with increasing temperature of reactants and lip thickness of the bluff body. The NO _x emission level for all burner configurations are found to be attenuated with nitrogen addition, which can be attributed to the reduction of the residence time of the gas mixture in the flame. The emission index of NO _x (EINO _x ) also becomes enhanced with increasing lip thickness and reactant temperature due to an increased residence time and thermal effect, respectively. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 1, pp. 3–10, January–February, 2009.     

Electrochemical oxidation of an acid dye by active chlorine generated using Ti/Sn<Subscript>(1−<Emphasis Type="Italic">x</Emphasis>)</Subscript>Ir<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> electrodes

The generation of active chlorine on Ti/Sn_(1−x)Ir _x O₂ anodes, with different compositions of Ir (x = 0.01, 0.05, 0.10 and 0.30 ), was investigated by controlled current density electrolysis. Using a low concentration of chloride ions (0.05 mol L⁻¹) and a low current density (5 mA cm⁻²) it was possible to produce up to 60 mg L⁻¹ of active chlorine on a Ti/Sn_0.99Ir_0.01O₂ anode. The feasibility of the discoloration of a textile acid azo dye, acid red 29 dye (C.I. 16570), was also investigated with in situ electrogenerated active chlorine on Ti/Sn_(1−x)Ir _x O₂ anodes. The best conditions for 100% discoloration and maximum degradation (70% TOC reduction) were found to be: NaCl pH 4, 25 mA cm⁻² and 6 h of electrolysis. It is suggested that active chlorine generation and/or powerful oxidants such as chlorine radicals and hydroxyl radicals are responsible for promoting faster dye degradation. Rate constants calculated from color decay versus time reveal a zero order reaction at dye concentrations up to 1.0 × 10⁻⁴ mol L⁻¹. Effects of other electrolytes, dye concentration and applied density currents also have been investigated and are discussed.     

Low Activation Energy Pathway for the Catalyzed Reduction of Nitrogen Oxides to N<Subscript>2</Subscript> by Ammonia

A low activation energy pathway for the catalytic reduction of nitrogen oxides to N₂, with reductants other than ammonia, consists of two sets of reaction steps. In the first set, part of the NO _x is reduced to NH₃; in the second set ammonium nitrite, NH₄NO₂ is formed from this NH₃ and NO + NO₂. The NH₄NO₂ thus formed decomposes at ~100 °C to N₂ + H₂O, even on an inert support, whereas ammonium nitrate, NH₄NO₃, which is also formed from NH₃ and NO₂ + O₂, (or HNO₃), decomposes only at 312 °C yielding mainly N₂O. Upon applying Redhead's equations for a first order desorption to the decomposition of ammonium nitrite, an activation energiy of 22.4 is calculated which is consistent with literature data. For the reaction path via ammonium nitrite a consumption ratio of 1/1 for NO and NO₂ is predicted and confirmed experimentally by injecting NO into a mixture of NH₃ + NO₂ flowing over a BaNa/Y catalyst. This leads to a yield increase of one N₂ molecule per added molecule of NO. Little N₂ is produced from NH₃ + NO in the absence of NO₂.     

Numerical investigation on the flow, combustion and NOx emission characteristics in a 500 MWe tangentially fired pulverized-coal boiler

The characteristics of the flow, combustion, temperature and NO_x emissions in a 500 MW_e tangentially fired pulverized-coal boiler are numerically studied using comprehensive models, with emphasis on fuel and thermal NO_x formations. The comparison between the measured values and predicted results shows good agreement, which implies that the adopted combustion and NO_x formation models are suitable for correctly predicting characteristics of the boiler. The relations among the predicted temperature, O₂ and CO₂ mass fractions are discussed based on the calculated distributions. The predicted results clearly show that NO_x formation within the boiler highly depends on the combustion processes as well as the temperature and species concentrations. The results obtained from this study have shown that overfire air (OFA) operation is an efficient way to reduce the NO_x emissions of the pulverized-coal fired boiler. Air staging combustion technology (OFA operation) adopted in this boiler has helped reduce fuel NO_x formation as well as thermal NO_x formation under the present simulated conditions. The decrease in the formation of fuel NO_x is due to the decreased contact of the nitrogen from the fuel with the oxygen within the combustion air, while the decrease in thermal NO_x formation is caused by a decrease in temperature. The detailed results presented in this paper may enhance the understanding of complex flow patterns, combustion processes and NO_x emissions in tangentially fired pulverized-coal boilers, and may also provide a useful basis for NO_x reduction and control.     

Preparation and characterization of RuO<Subscript>2</Subscript> · <Emphasis Type="Italic">x</Emphasis>H<Subscript>2</Subscript>O/carbon aerogel composites for supercapacitors

A series of RuO₂ · xH₂O/carbon aerogel (CA) composite electrode materials was prepared by a chemical precipitation method. Ultrasonication was used to accelerate the chemical reaction and improve the dispersion of RuO₂ · xH₂O particles on the surface and the pores of the aerogel. The structure and morphology of the as-prepared composite were characterized by N₂ adsorption isotherm, X-ray diffraction (XRD), and field emission-scanning electron microscopy (FE-SEM). The results showed that the CA had a pearly network structure and the composites had a relatively high specific surface area and mesopore volume. The electrochemical performance of the composite electrodes was studied by cyclic voltammetry, galvanostatic charge/discharge measurements and electrochemical impedance measurements. The results indicated a substantial increase in the specific capacitance of the composite. Moreover, the utilization efficiency of RuO₂ · xH₂O was greatly improved by loading it on the conductive and porous CA due to a significant improvement in the inter-particle electronic conductivity and the extensive mesoporous network of the composites.     

Bulk and Surface Properties of Dispersed CuO Phases in Relation with Activity of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Reduction

Synthesized silicas modified with alumina, titania, and zirconia (about 13% wt) were used as supports for dispersing nanosized CuO phase. All the prepared catalysts, containing about 1 mmol_cu g_cat ^-1 possessed high surface areas (230–430 m²g_cat ^-1) and homogeneous coverage of the relevant support, as revealed by SEM-EDS analysis. The nature of the support and its acidity directed the CuO deposition modifying the dimensions of the CuO aggregates and the ratio between highly and scarcely interacting copper species with support, as revealed by complementary analyses. The redox character of the CuO phase was studied realizing cycles of programmed temperature reduction/oxidation (TPR-TPO) which gave the extent of CuO reduction and CuO re-oxidation. Deconvolution of the reduction profiles permitted identifying different copper species which presence depended on the support nature. Attempts were made to individuate relations between the properties of the CuO species and catalytic activity in NO _x reduction with ethene (HC-SCR process) in highly oxidant atmosphere. The CuO phase deposited on the most acidic supports showed the best activity and selectivity in the NO _x reduction.     

Photoluminescence characteristics of Cd<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te single crystals grown by the vertical Bridgman method

In this paper, we report a systematic investigation of band-edge photoluminescence for Cd_1-x Mn _x Te crystals grown by the vertical Bridgman method. The near-band-edge emissions of neutral acceptor-bound excitons (labeled as L1) were systematically investigated as a function of temperature and of alloy composition. The parameters that describe the temperature variation of the energy were evaluated by the semiempirical Varshni relation. From the temperature dependence of the full width at half maximum of the L1 emission line, the broadening factors Γ(T) were determined from the fit to the data. The activation energies of thermal quenching were obtained for the L1 peak from the temperature dependence of the bound exciton peaks and were found to decrease with increasing Mn concentration.     

Using CFD for NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> emission simulation in a dual fuel boiler

The present work is aimed at reducing NO _x formation in a 250 MW dual fuel boiler by means of air staging and over-fire air. CFD simulations are performed to identify the best locations in the boiler walls to install air and fuel injectors. By installing injectors at these locations, it is possible to reduce NO _x production by more than 70% without increasing the amount of CO. This value is in good agreement with available data reported in the literature. Simulation results (gas species analysis and temperature) have been validated with real data taken at the full-scale boiler.     

Combustion and structure formation in the Ti-Ta-C-Ca<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript> system

Biocompatible composites (Ti, Ta)C _x + Ca₃(PO₄)₂ for deposition of nanofilms onto load-bearing implants by ion-plasma sputtering were prepared from Ti + Ta + C + Ca₃(PO₄)₂ mixtures by forced SHS compaction. The effect of Ta + C addition to green mixtures (characterized by parameter z) on the structure/phase formation in combustion products was explored. The addition of tantalum and carbon was found to have little or no influence on the burning velocity U and combustion temperature T _c. Two thermal spikes exhibited by thermograms were associated with the occurrence of two consecutive reactions leading to formation of titanium and tantalum carbides. With increasing z, the grain size of (Ti, Ta)C was found to diminish, its relative density to decrease, while the hardness to markedly grow.      

SHS quenching as a route to bulk glassy Fe<Subscript>34</Subscript>Co<Subscript>34</Subscript>B<Subscript>10</Subscript>Si<Subscript>14</Subscript>Nb<Subscript>8</Subscript> alloys

The method of SHS quenching combined with dynamic annealing was used to prepare bulk amorphous metallic glass alloys Fe₃₄Co₃₄B₁₀Si₁₄Nb₈ in a two-stage process. The structural properties and microstructure of thus prepared materials were found to be close to those produced by other methods, such as melting-injection-molding and melt spinning.      

Electro-oxidation of methanol on co-deposited Pt-MoO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> prepared by cyclic voltammetry with different scanning potential ranges

Pt-MoO _x supported on glassy carbon was co-deposited by cyclic voltammetry (CV). The lower limit of potential was fixed at −0.25 V (vs. SCE), whereas the upper limit was adjusted to be 0.0, 0.10, 0.40, 0.60 and 1.0 V. The as-prepared catalysts were characterized by X-ray photoelectron microscopy, scanning electron microscopy and transmission electron microscopy. The results show that Pt-MoO _x particles are uniformly dispersed on the substrate and the agglomerated microparticles are composed of numerous nanoparticles with a size of several nanometers. The catalytic capabilities of Pt-MoO _x for methanol oxidation were examined by CV and chronoamperometry. Electrochemical measurements demonstrate that the catalytic activities and stabilities of Pt-MoO _x prepared in the potential ranges from −0.25 to both 0.60 and 1.0 V were higher than the others, which may due to the higher active surface area, more appropriate Pt/Mo ratio and more preferred Pt crystallographic orientation.     

SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/SiN<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> multilayers for photovoltaic and photonic applications

Microstructural, electrical, and optical properties of undoped and Nd³⁺-doped SiO _x /SiN _y multilayers fabricated by reactive radio frequency magnetron co-sputtering have been investigated with regard to thermal treatment. This letter demonstrates the advantages of using SiN _y as the alternating sublayer instead of SiO₂. A high density of silicon nanoclusters of the order 10¹⁹ nc/cm³ is achieved in the SiO _x sublayers. Enhanced conductivity, emission, and absorption are attained at low thermal budget, which are promising for photovoltaic applications. Furthermore, the enhancement of Nd³⁺ emission in these multilayers in comparison with the SiO _x /SiO₂ counterparts offers promising future photonic applications.     

NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> emission from incineration of organic liquid waste in a circulating fluidized bed

An incineration test of a toxic chemical organic waste liquid was conducted on a circulating fluidized bed (CFB) incinerator. The flue gas was measured online with the advanced SAE-19 flue gas analyzer. The effects of several factors, in terms of flow rate of waste liquid, ratio of waste liquid injected into dense bed of the CFB, excess air coefficient, the secondary air fraction and bed temperature on NO _x emissions, were verified. The experimental results show that NO emissions in flue gas increase with increase in the flow rate of the waste liquid injected into the bed or the excess air coefficient or the bed temperature and those decrease with increase in the ratio of waste liquid injected into the dense bed of the CFB or the secondary air fraction. During the test runs, NO _x concentration in flue gas met the national regulation on NO _x emissions due to suppressive effect of low temperature and staged combustion in CFB on NO _x formation. This paper was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Active Catalysts for the NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Reduction in a FCC unit

Additives, without noble metals, based in Ce–Al mixed oxides supported on γ-alumina have been investigated as potential catalysts for the NO _x reduction in the FCCU regenerator. The best results were obtained with clusters of Sn–Cu–Al–O interacting with Ce–Al mixed oxides highly dispersed on the γ-Al₂O₃. The strong interaction between the two complex oxides provides a stable catalyst with high activity at high temperature. These additives would be active in the dense phase of the FCC regenerator, being deactivated at oxygen concentrations higher than 2%, but they would be regenerated in the FCC reactor. A. Uzcátegui is in leave to Laboratorio de cinética y catálisis del Departamento de Química, Facultad de Ciencias, Universidad de los Andes, La Hechicera, Merida, Venezuela.     

Experimental study on effects of operating conditions and fuel quality on thermal efficiency and emission performance of a 300-MW boiler unit firing Thai lignite

This paper presents the results of an experimental study on a 300-MW boiler unit fired with Thai lignite. Effects of operating conditions (excess air ratio and unit load) and fuel quality on the boiler heat losses and thermal efficiency as well as on the gaseous (CO₂, CO, NO_x and SO₂) and particulate matter (PM) emissions from the boiler unit are discussed. The boiler thermal efficiency was weakly affected by the excess air ratio, unit load and fuel lower heating value, varying from 90.3 to 92.3% for wide ranges of the above variables. In all the tests, the NO_x, SO₂ and PM emissions were below the national emission standards for these pollutants. Quite low level of the SO₂ emission was secured by the high-efficiency flue gas desulphurization system. The CO emissions of rather small values were detected only at extremely low excess air ratios. The emission rate and specific emission (i.e. per MWh of electricity produced) for NO_x, SO₂ and CO were quantified using experimental emission concentrations of the pollutants. Meanwhile, the emission characteristics for CO₂ were determined with the use of fuel-C and fuel consumption by the boiler. In addition, the emission rate and specific emission for PM were estimated by taking into account the actual fuel-ash content and fuel consumption by the boiler, as well as the effects of SO₂ adsorption by fly ash in the boiler gas ducts and overall ash-collecting efficiency of the electrostatic precipitators and flue gas desulphurization system. Elevated CO₂ and NO_x emissions from the 300-MW boiler units firing Thai lignite are of great concern.