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1.
Liang Kong Yanjun Ding Yi Zhang Lichuan Yuan Zhansong Wu 《Korean Journal of Chemical Engineering》2009,26(2):534-541
A hierarchical gain scheduling (HGS) approach is proposed to model the nonlinear dynamics of NO
x
emissions of a utility boiler. At the lower level of HGS, a nonlinear static model is used to schedule the static parameters
of local linear dynamic models (LDMs), such as static gains and static operating conditions. According to upper level scheduling
variables, a multi-model method is used to calculate the predictive output based on lower-level LDMs. Both static and dynamic
experiments are carried out at a 360 MW pulverized coal-fired boiler. Based on these data, a nonlinear static model using
artificial neural network (ANN) and a series of linear dynamic models are obtained. Then, the performance of the HGS model
is compared to the common multi-model in predicting NO
x
emissions, and experimental results indicate that the proposed HGS model is much better than the multi-model in predicting
NO
x
emissions in the dynamic process.
This paper was presented at the 7
th
China-Korea Workshop on Clean Energy Technology held at Taiyuan, Shanxi, China, June 25–28, 2008. 相似文献
2.
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. 相似文献
3.
Flavio H. Oliveira Marly E. Osugi Fabiana M. M. Paschoal Demetrius Profeti Paulo Olivi Maria Valnice Boldrin Zanoni 《Journal of Applied Electrochemistry》2007,37(5):583-592
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/Sn0.99Ir0.01O2 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. 相似文献
4.
Hiu Liu Nana Xin Qingxi Cao Long Sha Dezhi Sun Shaohua Wu 《Korean Journal of Chemical Engineering》2009,26(4):1137-1143
The Computational fluid dynamics (CFD) code PHOENICS is applied to simulate and evaluate the combustion process within the
furnace of a 1,000 MW dual circle tangential firing single furnace lignite-fired ultra supercritical (USC) boiler. The dependence
on overfire air (OFA) positioning on the combustion process is studied. The results show that the highest temperature appears
on the upside of the burner zone close to the front wall, and the high temperature zone rises with elevated OFA positions.
However, the temperature field distributions are similar despite differing OFA positions. The char content near the rear wall
is higher than that near the front wall, and below the furnace arch, coal particles concentrate towards the front wall. Also
with elevated OFA positions, nitrogen oxide (NO
x
) concentrations at the outlet fall, but char content increases. In regard to NO
x
emission and char burnout, the suggested optimal distance from the OFA center to the center of the uppermost primary air
nozzle should be 6 meters.
This work was presented at the 7
th
China -Korea Workshop on Clean Energy Technology held at Taiyuan, Shanxi, China, June 26–28, 2008. 相似文献
5.
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. 相似文献
6.
Vadim Yu. Plaksin Heon-Ju Lee Valentin A. Riaby Young Sun Mok Sang Hoon Lim Ji Hun Kim 《Korean Journal of Chemical Engineering》2008,25(1):84-88
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. 相似文献
7.
Luis I. Díez 《Fuel》2008,87(7):1259-1269
A CFD investigation has been carried out about the performance of a 600 MWe tangentially coal-fired boiler, focusing on the reduction of NOx attainable by using overfire air. To this purpose, a comprehensive combination of NOx chemistry models has been used, coupled with the numerical simulation of fluid and particle flow, solid fuel combustion and heat and mass transfer. Predicted values of gas temperature and species concentration have been adopted to validate the model against actual measurements from the full-scale boiler, under conventional and overfire air arrangements. A reasonable agreement has been attained in most cases. Additionally, modelling sensitivity has been evaluated against variations in some fuel-dependent parameters hard to measure or estimate (devolatilisation rates, nitrogen content in volatiles and char, reburning rates). As a result, an analysis tool is available to study the response of this kind of boilers to a variety of coal feedstock and combustion conditions, in a feasible and economic manner. 相似文献
8.
Yi Zhang Yanjun Ding Zhansong Wu Liang Kong Tao Chou 《Korean Journal of Chemical Engineering》2007,24(6):1118-1123
An empirical model to predict the boiler efficiency and pollutant emissions was developed with artificial neural networks
based on the experimental data on a 360 MW W-flame coal fired boiler. The temperature of the furnace was selected as an intermediate
variable in the hybrid model so that the predictive precision of NO
x
emissions was enhanced. The predictive precision of the hybrid model was improved compared with the direct model. Three optimal
operational objects were proposed in order to minimize the fuel and environmental costs. Based on the neural network model
and optimal objects, a genetic algorithm was employed to seek real-time solution every 30 seconds. Optimum manipulated variables
such as excess air, primary air and secondary air were obtained under different optimal objects. The above algorithm interconnected
with a distributed control system (DCS) formed the supervisory control and achieved real-time coordinated optimization control
of utility boilers.
This work was presented at the 6
th
Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006. 相似文献
9.
Ramesh Pratibha Nalini Larysa Khomenkova Olivier Debieu Julien Cardin Christian Dufour Marzia Carrada Fabrice Gourbilleau 《Nanoscale research letters》2012,7(1):124
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. 相似文献
10.
The advanced reburning process for NOx emission control was studied in a down-fired 20 kW combustor by evaluating the performance of 15 pulverised coals as reburning fuels. The proximate volatile matter contents of the coals selected ranged from around 4 to 40 wt% (as received) with elemental nitrogen contents from around 0.6 to 2.0 wt%. The effects of reburn fuel fraction, reburning zone residence time, ammonia agent injection delay time (relative to the reburn fuel and burnout air injection points) and the nitrogen stoichiometric ratio are reported in detail and the optimum configurations for advanced reburning, established as a function of operating condition and coal type. The experimental results show that advanced reburning can reduce NOx emissions up to 85%. The maximum benefits of advanced reburning over conventional reburning were observed at the lower reburn fuel fractions (around 10%). The results demonstrate that under advanced reburning conditions equivalent or higher levels of NOx reduction can be achieved while operating the reburn zone closer to stoichiometric conditions compared with conventional reburning operating at high reburn fuel fractions (20-25%). Thus the practical problems associated with fuel-rich staged operation can be reduced. The effect of coal properties on the advanced reburning performance was also investigated. As with conventional reburning, the fuel nitrogen content of the coal used was found to have little influence on the NOx reduction efficiency except at the highest reburn fuel fractions. There was, however, a strong correlation between the effectiveness of advanced reburning and the volatile content of the reburning fuels, which not only depended on the reburn fuel fraction, but also the mode (rich or lean) of advanced reburning operation. These parameters are mapped out experimentally to enable the best operating mode to be selected for advanced reburning as a function of the reburning fuel fraction and volatile content. 相似文献
11.
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 mmolcu gcat
-1 possessed high surface areas (230–430 m2gcat
-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. 相似文献
12.
Ryan Zarnitz 《Fuel》2007,86(4):554-559
In this study, computational fluid dynamic (CFD) and kinetic models were used to investigate the relative performances of coal volatiles and natural gas reburning. This modeling approach considers fluid dynamic and non-isothermal effects, which were not considered in past laboratory flow reactor studies. The commercial CFD code FLUENT 6.1 was used to predict the residence times and temperatures for reburning tests in the down-fired combustor (DFC), a 0.5 MMBTU/h research combustor at The Pennsylvania State University. To predict NOx concentrations within the combustor, this data was then applied to an advanced reburning kinetic model used in past studies. For equal firing rates and stoichiometric ratios, reburning using methane yielded lower concentrations of NOx (and, therefore, better NOx reduction performance) than reburning using coal volatiles. The coal volatiles give increased flame temperature over natural gas, which apparently offsets the increased reburn zone hydrocarbon radical yield of coal volatiles over natural gas. 相似文献
13.
This paper deals with an experimental study of air staging in a 1 MW (heat input power) tangentially fired pulverized coal furnace. The influences of several variables associated with air staging on NOx reduction efficiency and unburned carbon in fly ash were investigated, and these variables included the air stoichiometric ratio of primary combustion zone (SR1), the locations of over-fire air nozzles along furnace height, and the ratio of coal concentration of the fuel-rich stream to that of the fuel-lean one (RRL) in primary air nozzle. The experimental results indicate that SR1 and RRL have optimum values for NOx reduction, and the two optimum values are 0.85 and 3:1, respectively. NOx reduction efficiency monotonically increases with the increase of OFA nozzle location along furnace height. On the optimized operating conditions of air staging, NOx reduction efficiency can attain 47%. Although air staging can effectively reduce NOx emission, the increase of unburned carbon in fly ash should be noticed. 相似文献
14.
The optimum conditions for synthesizing LiNi1-y
Co
y
O2 (y=0.1, 0.3 and 0.5) by a simplified combustion method, in which the preheating step is omitted, and the electrochemical properties
of these materials were investigated. The optimum condition for synthesizing LiNi0.9Co0.1O2 by the simplified combustion method is calcination at 800 °C for 12 h in air in 3.6 mole ratio of urea to nitrate. The LiNi0.9Co0.1O2 synthesized under these conditions shows the smallest R-factor{(I
006+I
102)/I
101} and the largest I
003/I
104, indicating better hexagonal ordering and less cation mixing, respectively. The LiNi0.7Co0.3O2 synthesized at 800 °C for 12 h in air in 3.6 mole ratio of urea to nitrate has the largest first discharge capacity 156.2 mA h g−1 at 0.5C and shows relatively good cycling performance. This sample shows better hexagonal ordering and less cation mixing
than the other samples. The particle size of the LiNi0.7Co0.3O2 is relatively small and its particles are spherical with uniform particle size. 相似文献
15.
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. 相似文献
16.
Rohit Vijay Hideaki Sakurai Christopher M. Snively Jochen Lauterbach 《Topics in Catalysis》2009,52(10):1388-1399
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. 相似文献
17.
Experiments were carried out on an electrically heated multi-path air inlet one-dimensional furnace to assess NOx emission characteristics of an overall air-staged (also termed air staging along furnace height) combustion of bituminous coal. The impact of main parameters of overall air-staged combustion technology, including burnout air position, air stoichiometric ratio, levels of burnout air (the number of burnout air arranged at different heights of the furnace), and the ratios of the burnout air flow rates and pulverized coal fineness of industrial interest, on NOx emission were simulated to study in the experimental furnace, as well as the impact of air staging on the carbon content of the fly ash produced. These results suggest that air-staged combustion affects a pronounced reduction in NOx emissions from the combustion of bituminous coal. The more deeply the air is staged, the further the NOx emission is reduced. Two-level air staging yields a greater reduction in NOx emission than single-level air staging. For pulverized coal of differing fineness, the best ratio between the burnout air rates in the two-level staging ranges from 0.6 to 0.3. In middle air-staged degree combustion with fM = 0.75, pulverized coal fineness, R90 (%), has a greater influence on NOx emission, whereas R90 has little influence on NOx emission for deep air-staged degree with fM = 0.61. Air-staged combustion with proper burnout air position has little effect on the burnout. For overall air-staged combustion, proper burnout air position and air-staged rate should be considered together in order to achieve high combustion efficiency. 相似文献
18.
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. 相似文献
19.
Combustion simulations were conducted to investigate the parameters controlling the formation of unburned carbon in fly ash from coal reburning in a coal-fired boiler. Unburned carbon (UBC or Loss on ignition, LOI) was generally caused by particles flowing through fuel-rich regions and/or spending insufficient residence time in the furnace. LOI contributions by each individual coal source were identified and quantified. The LOI from the main burners was found to depend mainly on the availability of combustion air in the burner zone. However, the LOI from the reburning jets depended on both the amount of air in the reburning jets and the available over-fire air (OFA) downstream. Moving some air from the lower burners to the upper burners to compensate for the shorter residence time was found to significantly reduce the overall LOI without adverse impacts on the NOx emissions in this study. 相似文献
20.
In this paper, we report a systematic investigation of band-edge photoluminescence for Cd1-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. 相似文献