Interactions of CO, HCl, and Sox in Pulverised Coal Flames

The effect of HCl and SO_2 on CO oxidation in pulverised coal flames was investigated experimentally and kinetically in an entrained flow combustion reactor. Two bituminous coals (German 'Goettelborn' and a Polish coal) were used as fuels with a feeding rate of 1 or 1.5 kg/h. HCl or SO_2 is introduced into the reactor premixed with the primary air. Experimental results indicate that HCl addition may inhibit CO oxidation in coal flames and increases CO emission. Reducing temperature in the reactor will enhance the inhibitory effect of HCl on CO oxidation. The measured CO profiles along the reactor height clearly show that the addition of HCl may inhibit CO oxidation. In the experimental range of SO_2 addition. The inhibiting effect of SO_2 on CO oxidation is less significant than HCl. A detailed kinetic mechanism is used to model the reactions. And the controlling reactions are analysed.

Coflow jets with large velocity difference - a new aerodynamic principle of flame stabilization and combustion intensification

A new aerodynamic principle of flame stabilization and combustion intensification, the coflow jets with large velocity difference, is described. One or more small high-velocity jets of air or steam, injected off the axis and in the same direction as the low-velocity main fuel-air flow into the combustor, create a large recirculation zone of high turbulence intensity in which the combustibles and high temperature gases are effectively mixed, so that stable and intensive combustion can be maintained even for fuels with poor ignition. A pulverized coal combustor based on the principle mentioned above is shown to be characteristic of excellent combustoom and a simple structure. A number of precombustors of this type are in operation at some power stations and industrial boilers of China. Using such precombustor, successtul startups and part-load operation of the boilers have become available under conditions of unpreheated air and low-grade coal with volatiles as low as 15% and ash content as high as 30%. This principle shows good promise as an attractive new technology of combustion.

Release of Sulfur and Chlorine During Cofiring Rdf and Coal In An Internally Circulating Fluidized Bed

An internally circulating fluidized bed (ICFB) was applied to investigate the behavior of chlorine and sulfur during cofiring RDF and coal. The pollutant emissions in the flue gas were measured by Fourier transform infrared (FTIR) spectrometry (Gasmet DX-3000). In the tests, the concentrations of the species CO, CO2, HCl, and SO2 were measured online. Results indicated when cofiring RDF and char, due to the higher content of chlorine in RDF, the formation of HCl significantly increases. The concentration Of SO2 is relatively low because alkaline metal in the fuel ash can absorb SO2. The concentration of CO emission during firing pure RDF is relatively higher and fluctuates sharply. With the CaO addition, the sulfur absorption by calcium quickly increases, and the desulfuration ratio is bigger than the dechlorination ratio. The chemical equilibrium method is applied to predict the behavior of chlorine. Results show that gaseous HCl emission increases with increasing RDF fraction, and gaseous KCl and NaCl formation might occur.

Optimization of Air Staging In A 1 Mw Tangentially Fired Pulverized Coal Furnace

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. NO, 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. (C) 2008 Elsevier B.V. All rights reserved.

Effect of coal-over-coal reburn on furnace temperature and heat flux distributions in 1 MW tangentially fired furnace

The furnace temperature and heat flux distributions of 1 MW tangentially fired furnace were studied during coal-over-coal reburn, and the influences of the position of reburn nozzle and reburn fuel fraction on furnace temperature and heat flux distributions were investigated. Compared with the baseline, the flue gas temperature is 70–90 C lower in primary combustion and 130–150 C higher at furnace exit, and the variations of the flue gas temperature distributions along furnace height are slower. The temperature distribution along the width of furnace wall decreases with the increase of the relative furnace height. In the primary combustion zone and the reburn zone, the temperature and heat flux distributions of furnace wall are much non-uniform and asymmetric along the width of furnace wall, those of furnace wall in the burnout zone are relatively uniform, and the temperature non-uniformity coefficients of the primary combustion zone, the reburn zone and the burnout zone are 0.290, 0.100 and 0.031, respectively.

Influence of HCl on CO and NO emissions in combustion

The influence of HCl on CO and NO emissions was experimentally investigated in an entrained flow reactor (EFR) and an internally circulating fluidized bed (ICFB). The results in EFR show the addition of HCl inhibits CO oxidation and NO formation at 1073 K and 1123 K. At the lower temperature (1073 K) the inhibition of HCl becomes more obvious. In ICFB, chlorine-containing plastic (PVC) was added to increase the concentration of HCl during the combustion of coal or coke. Results show that HCl is likely to enhance the reduction of NO and N2O. HCl greatly increases CO and CH4 emission in the flue gas. A detailed mechanism of CO/NO/HCl/SO2 system was used to model the effect of HCl in combustion. The results indicate that HCl not only promotes the recombination of radicals O, H, and OH, but also accelerates the chemical equilibration of radicals. The influence of HCl on the radicals mainly occurs at 800-1200 K. (C) 2009 Elsevier Ltd. All rights reserved.

Inhibition of progesterone receptor activity in recombinant yeast by soot from fossil fuel combustion emissions and air particulate materials

Numerous environmental pollutants have been detected for estrogenic activity by interacting with the estrogen receptor, but little information is available about their interactions with the progesterone receptor. In this study, emission samples generated by fossil fuel combustion (FFC) and air particulate material (APM) collected from an urban location near a traffic line in a big city of China were evaluated to interact with the human progesterone receptor (hPR) signaling pathway by examining their ability to interact with the activity of hPR expressed in yeast. The results showed that the soot of a petroleum-fired vehicle possessed the most potent anti-progesteronic activity, that of coal-fired stove and diesel fired agrimotor emissions took the second place, and soot samples of coal-fired heating work and electric power station had lesser progesterone inhibition activity. The anti-progesteronic activity of APM was between that of soot from petroleum-fired vehicle and soot from coal-fired establishments and diesel fired agrimotor. Since there was no other large pollution source near the APM sampling sites, the endocrine disrupters were most likely from vehicle emissions, tire attrition and house heating sources. The correlation analysis showed that a strong relationship existed between estrogenic activity and anti-progesteronic activity in emissions of fossil fuel combustion. The discoveries that some environmental pollutants with estrogenic activity can also inhibit OR activity indicate that further studies are required to investigate potential mechanisms for the reported estrogenic activities of these pollutants. (c) 2005 Elsevier B.V. All rights reserved.

Presence of estrogenic activity from emission of fossil fuel combustion as detected by a recombinant yeast bioassay

Estrogenic activities of emission samples generated by fossil fuel combustion were investigated with human estrogen receptor (ER) recombinant yeast bioassay. The results showed that there were weak but clear estrogenic activities in combustion emissions of fossil fuels including coal, petroleum, and diesel. The estrogenic relative potency (RP) of fossil fuel combustion was the highest in petroleum-fired car, followed by coal-fired stove, diesel-fired agrimotor, coal-fired electric power station. On the other hand, the estrogenic relative inductive efficiency (RIE) was the highest in coal-fired stove and coal-fired electric power station, followed by petroleum-fired car and diesel-fired agrimotor. The estrogenic activities in the sub-fractions from chromatographic separation of emitted materials were also determined. The results indicated that different chemical fractions in these complex systems have different estrogenic potencies. The GC/MS analysis of the emission showed that there were many aromatic carbonyls, big molecular alcohol, PAHs and derivatives, and substituted phenolic compounds and derivatives which have been reported as environmental estrogens. The existence of estrogenic substances in fossil fuel combustion demands further investigation of their potential adverse effects on human and on the ecosystem. The magnitude of pollution due to global usage of fossil fuels makes it imperative to understand the issue of fossil fuel-derived endocrine activities and the associated health risks, particularly the aggregated risks stemmed from exposure to toxicants of multiple sources. (C) 2003 Elsevier Science Ltd. All rights reserved.

The Deposition and Burning Characteristics During Slagging Co-Firing Coal and Wood: Modeling and Numerical Simulation

Numerical analysis was used to study the deposition and burning characteristics of combining co-combustion with slagging combustion technologies in this paper. The pyrolysis and burning kinetic models of different fuels were implanted into the WBSF-PCC2 (wall burning and slag flow in pulverized co-combustion) computation code, and then the slagging and co-combustion characteristicsespecially the wall burning mechanism of different solid fuels and their effects on the whole burning behavior in the cylindrical combustor at different mixing ratios under the condition of keeping the heat input samewere simulated numerically. The results showed that adding wood powder at 25% mass fraction can increase the temperature at the initial stage of combustion, which is helpful to utilize the front space of the combustor. Adding wood powder at a 25% mass fraction can increase the reaction rate at the initial combustion stage; also, the coal ignitability is improved, and the burnout efficiency is enhanced by about 5% of suspension and deposition particles, which is helpful for coal particles to burn entirely and for combustion devices to minimize their dimensions or sizes. The results also showed that adding wood powder at a proper ratio is helpful to keep the combustion stability, not only because of the enhancement for the burning characteristics, but also because the running slag layer structure can be changed more continuously, which is very important for avoiding the abnormal slag accumulation in the slagging combustor. The theoretic analysis in this paper proves that unification of co-combustion and slagging combustion technologies is feasible, though more comprehensive and rigorous research is needed.

Modeling of a coal-fired slagging combustor: Development of a slag submodel

In a slagging combustor or furnace, the high combustion temperature makes the molten slag layer cover the wall and capture the particles. If these particles contain combustible matter, they will continue to burn on the running slag. As a result, the total amount of ash deposition will be much greater than that in dry-wall combustors and the total heat flux through the deposition surface will change greatly. Considering the limitations of existing simulation methods for slagging combustion, this paper introduces a new wall burning model and slag flow model from the analysis; of particle deposition phenomena. Combined with a conventional combustion simulation program, the total computational frame is introduced. From comparisons of simulation results from several kinds of methods with experimental data, the conclusion is drawn that the conventional simulation methods are not very suitable for slagging combustion and the wall burning mechanism should be considered more thoroughly.

Characteristics of plasma induced by interaction of a free-oscillated laser pulse with a coal target in air and combustible gas

Plasma in the air is successfully induced by a free-oscillated Nd:YAG laser pulse with a peak power of 10(2-3) W. The initial free electrons for the cascade breakdown process are from the ablated particles from the surface of a heated coal target, likewise induced by the focused laser beam. The laser field compensates the energy loss of the plasma when the corresponding temperature and the images are investigated by fitting the experimental spectra of B-2 Sigma(+) -> X-2 Sigma(+) band of CN radicals in the plasma with the simulated spectra and a 4-frame CCD camera. The electron density is estimated using a simplified Kramer formula. As this interaction occurs in a gas mixture of hydrogen and oxygen, the formation and development of the plasma are weakened or restrained due to the chaining branch reaction in which the OH radicals are accumulated and the laser energy is consumed. Moreover, this laser ignition will initiate the combustion or explosion process of combustible gas and the minimum ignition energy is measured at different initial pressures. The differences in the experimental results compared to those induced by a nanosecond Q-switched laser pulse with a peak power of 10(6-8) W are also discussed. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Ignition of single coal particle in a hot furnace under normal- and micro-gravity condition

An experimental study on ignition and combustion of single particles was conducted at normal gravity (1-g) and microgravity (l-g) for three high volatile coals with initial diameter of 1.5 and 2.0 mm, respectively. The non-intrusive twin-color pyrometry method was used to retrieve the surface temperature of the coal particle through processing the images taken by a color CCD camera. At the same time, a mathematical model considering thermal conduction inside the coal particle was developed to simulate the ignition process. Both experiments and modeling found that ignition occurred homogeneously at the beginning and then heterogeneously for the testing coal particles burning at l-g. Experimental results confirmed that ignition temperature decreased with increasing volatile content and increasing particle size. However, contradicted to previous studies, this study found that for a given coal with certain particle size, ignition temperature was about 50–80 K lower at l-g than that at 1-g. The model predictions agreed well with the l-g experimental data on ignition temperature. The criterion that the temperature gradient in the space away from the particle surface equaled to zero was validated to determine the commence of homogeneous ignition. Thermal conduction inside the particle could have a noticeable effect for determining the ignition temperature. With the consideration of thermal conduction, the critical size for the phase transient from homogeneous to heterogeneous is about 700 lm at ambient temperature 1500 K and oxygen concentration 0.23. 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

CFD study of a sudden-expanding coal combustor using Euler-Euler and Euler-Lagrange models

In this study, the Euler-Euler (E-E) and Euler-Lagrange (E-L) models designed for the same chemical mechanism of heterogeneous reactions were used to predict the performance of a typical sudden-expanding coal combustor. The results showed that the current E-E model underestimated the coal burnout rate because the particle temperature fluctuation on char combustion is not adequately considered. A comparison of the E-E and E-L simulations showed the underestimation of heterogeneous chemical reaction rates by the E-E model. (C) 2010 Elsevier Ltd. All rights reserved.