Coal Combustion (coal + combustion)

Distribution by Scientific Domains


Selected Abstracts


Special Issue on Coal Combustion and Pollutant Control

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2007
Minghou Xu
[source]


Mechanisms of Submicron and Residual Ash Particle Formation during Pulverised Coal Combustion: A Comprehensive Review

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2005
D. Yu
Coal fly ash has been a traditional concern of utilities since coal was used to generate electricity because it may bring about a number of technical and economic problems such as slagging, fouling, corrosion, erosion, waste disposal and overall boiler efficiency reduction. Moreover, fine particulates that escape the combustion system are recognized to have a negative impact on health and the environment due to the enrichment of the toxic trace elements and being readily inhaled. This work gives a brief review of the studies carried out in the past decades and tries to elucidate those processes that contribute to ash formation. They include the mechanisms that control submicron ash formation and those that are related to residual ash formation. The mechanism of vaporization and condensation is believed to be the major source of submicron ash particles and is discussed in detail in this review. Residual ash formation is the consequence of the competition between ash coalescence and char fragmentation. Moreover, fragmentation of excluded minerals and rotationally induced shedding may also contribute to the residual ash formation. Our literature review has provided a number of experimental and theoretical results describing how the submicron ash and residual ash are formed, Finally we present some recommendations for possible future research topics, including sampling techniques, measurement techniques, experimental studies and modelling efforts. [source]


Special Theme Issue: 4th International Symposium on Coal Combustion

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2001
Associate Professor Dr. -Ing.
No abstract is available for this article. [source]


The Partitioning of Arsenic, Selenium, Cadmium, and Cesium during Pulverized Coal Combustion in a 17 kW Downflow Combustor

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2001
Wayne S. Seames
The combustion of coal liberates arsenic, selenium, cadmium, and cesium into the environment. These toxic metals, which are discharged with the flue gas or collected with fly ash, may vaporize in the hot portions of the combustor then return to the solid phase in cooler zones of the process downstream. Understanding the mechanisms by which toxic metals partition between the vapor and solid phases is an important step for predicting and mitigating the effect of these metals upon the environment. An investigation of these partitioning mechanisms was performed. The results suggest that the dominant heterogeneous partitioning mechanism for transformation to the solid phase in the post-combustion zone is the reaction of metal vapor on the surface or within the pores of a supermicron ash particle for the Pittsburgh seam and Illinois #6 coals but not for the Ohio blend coal. A relationship between the concentration of supermicron phase arsenic, selenium, and cadmium to calcium was also observed, suggesting the formation of As-Ca, Se-Ca, and Cd-Ca reaction products. Selenium appears to be more reactive than arsenic for the formation of these calcium-based complexes. [source]


Investigation and Application of "Bluff-body in Cavity" Burner for Pulverized Coal Combustion

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2001
Gang Chen
Abstract The flow and combustion process of a new type of pulverized coal burner, the "bluff-body in cavity", is studied in this paper. This is an improvement on the basic principle of the ordinary bluff-body burner. Mean and fluctuating velocity components and turbulence characteristics of the flow in the outlet of the "bluff-body in cavity" burner were measured using a three-dimensional laser particle dynamics anemometer (3D-PDA). Combustion tests showed that this burner is better than an ordinary burner with only a bluff-body regarding the ignition and flame stability. Application of this new burner in several power plant boilers (65-670 t/h) showed that the temperature in the flame zone is high, the combustion process is very stable, and the boiler efficiency is increased. These improvements indicate a promising future for the burner. [source]


Incidence and impact of axial malformations in larval bullfrogs (Rana catesbeiana) developing in sites polluted by a coal-burning power plant

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2000
William A. Hopkins
Abstract Amphibian malformations have recently received much attention from the scientific community, but few studies have provided evidence linking environmental pollution to larval amphibian malformations in the field. We document an increased incidence of axial malformations in bullfrog larvae (Rana catesbeiana) inhabiting two sites contaminated with coal combustion wastes. In the polluted sites, 18 and 37% of larvae exhibited lateral curvatures of the spine, whereas zero and 4% of larvae from two reference sites had similar malformations. Larvae from the most heavily polluted site had significantly higher tissue concentrations of potentially toxic trace elements, including As, Cd, Se, Cu, Cr, and V, compared with conspecifics from the reference sites. In addition, malformed larvae from the most contaminated site had decreased swimming speeds compared with those of normal larvae from the same site. We hypothesize that the complex mixture of contaminants produced by coal combustion is responsible for the high incidence of malformations and associated effects on swimming performance. [source]


Emission of trace toxic metals during pulverized fuel combustion of Czech coals

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2003
P. Danihelka
Abstract A study of the trace elements emission (As, Se, Cd, Co, Cr, Cu, Zn, Hg, Tl, Pb, Ni, Sn, Sb, V, Mn and Fe) from pulverized coal combustion has been made at six heating and power stations situated in the Czech Republic. The amount of chlorine in coal has considerable influence on volatilization of some elements such as Zn, Cu, Pb, Hg and Tl, which is explained by the formation of thermodynamically stable compounds of these elements with chlorine. Generally, the affinities for Cl follows the order Tl > Cu > Zn > Pb > Co > Mn > Sn > Hg. The experimental data indicates enrichment of some of the trace toxic elements in the emissions (Cu, Zn, As, Se, Cd, Sn, Sb, Hg and Pb) and good agreement was obtained by thermodynamic equilibrium calculations with a few exceptions. In the case of Fe, Mn, Co, Cr and Sn calculated values are overestimated in the bottom ash and there are zero predicted amounts of these elements in the fly ash. In comparison, the results from experiments show up to 80% of these elements retained in fly ash. This implies that there exist additional steps leading to the enrichment by Fe, Mn, Co, Cr and Sn of small particles. Such mechanisms could include the ejection during devolatilization of small inorganic particles from the coal of bottom ash particles, or disintegration of the char containing these metals to small particles of fly ash. On the other hand, there are slightly overestimated or similar values of relative enrichment factors for As, V, Cu, Cd, Sb, Tl and Pb in the fly ashes and zero predicted values for bottom ashes. Our experimental results show about 5% or less of these elements are retained in bottom ashes, so they probably remain in the bottom ash inside unburned parts of coal. Copyright © 2003 John Wiley & Sons, Ltd. [source]


The effects of solid absorbents on the emission of trace elements, SO2, and NOx during coal combustion

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2001
J. F. Cheng
Abstract The emission of toxic metals from the combustion of fossil fuels is an important global environmental issue. Solid absorbents can be used to control the emission of toxic trace elements from coal combustion. In this paper, limestone, CaSO4, bauxite, kaolinite and CaO are employed for this purpose and experiments are carried out in an electrically heated drop-tube furnace. The trace elements investigated are Pb, Cd, Cr and As. It is observed that the absorptive capacity is related to the qualities of the absorbents (type, amount and particle size) and the combustion temperature. The results also show that some absorbents can reduce SO2 emission simultaneously, but no influence on NOx emission. Copyright © 2001 John Wiley & Sons, Ltd. [source]


A Novel Device for Single Particle Light Scattering Size Analysis and Concentration Measurement at High Pressures and Temperatures

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 2 2008
Heinz Umhauer
Abstract Based on the findings of previous work, a novel instrument was developed for the size analysis and concentration measurement of particles dispersed in gases at high temperatures (600,°C) and pressures (16 bar). The main motivation for the construction of this device was a measurement requirement at the conditions of a pressurized pulverized coal combustion (PPCC) test installation in Dorsten, Germany. The development of a high efficiency (>,50,%), coal based, combined cycle process, and specifically, the development of efficient gas cleaning technology for gas combustion under demanding conditions (1400,°C and 16 bar) was the main target. A suitable measurement technique was required for the determination of particle size and concentration downstream of the gas cleaning equipment, which is able to operate close to the given conditions. The performance of the novel device was tested in several measurement series with various monodisperse aerosols at ambient conditions as well as in high pressure, high temperature situations with very satisfactory results, i.e., the lower detection limit (50,% counting efficiency at ca. 0.3 ,m) and resolution of the novel device are comparable to state of the art instruments (of the same principle) intended for room temperature operation. [source]


Methods for measuring the concentrations of SO2, and of gaseous reduced sulphur compounds in the combustion chamber of a circulating fluidized bed boiler

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2000
Maríaa Joséa Fernández
Abstract The present work was aimed at developing and improving methods for measurement of gaseous sulphur compounds in the combustion chamber of a fluidized bed boiler (FBB). The sampling of SO2 was improved by removing NH3 and H2O with a sorbent immediately after the probe. The concentration of reduced sulphur species was determined by means of two conventional SO2 analyzers and an intermediate converter, where the reduced species are oxidized to SO2. Gas phase sulphides were also sampled with a gas quenching probe by means of a basic solution which was subsequently analysed by wet chemistry. The methods were tested during coal combustion in a 12 MW circulating FBB without limestone for two cases of air-staging. Le but de ce travail était de développer et d'améliorer les méthodes de mesure des composés gazeux du soufre dam la chambre de combustion d'une chaudière à lit fluidisé. On a amélioré la prise d'échantillons de SO2 en retirant le NH3 et le H2O avec un sorbant tout de suite après la sonde. La concentration d'espéces réduites de soufre a été déterminée à l'aide de deux analyseurs de SO2 classiques et un convertisseur d'intermédiaires, où les espèces réduites sont oxydées en SO2. Des échantil-Ions de sulfures gazeux ont également été prélevés à l'aide d'une sonde de trempe du gaz en utilisant une solution basique qui a été analysée par la suite en chimie humide. Ces méthodes ont été testées lors de la combustion de charbon dans une chaudière à lit fluidisé circulant de 12 MW sans calcaire pour deux cas d'étagement de l'air. [source]


Advanced coal combustion and utilization part II,fundamentals and new technology

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2010
Zhenghe Xu
No abstract is available for this article. [source]


Effects of bias combustion on volatile nitrogen transformation

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2010
Xiaohui Zhang
Abstract Nitrogen oxides (NOx) are among the principal pollutants from coal combustion, which have caused serious environmental issues around the world. Many advanced combustion systems have been developed to reduce NOx emissions. Technologies that combine low NOx burners (LNB) and air staging systems have been widely used as they can control the formation of volatile NOx effectively. In this paper, the process of volatile nitrogen release was simulated using the FG,DVC pyrolysis model, in order to provide reliable reference for designing LNBs and air staging combustion systems. The mechanism of NOx emission from volatile N in a combustion system was studied with CHEMKIN 4.1 package, which demonstrated that noticeable reduction of NOx could be obtained at an equivalence ratio (ER) of 1.22, which was 3,4% and 10,15% higher than that at an ER of 0.77 and 0.39, respectively. Sensitivity study of all basic reactions indicated that NH2 and HCNO radicals are the major inter-compounds which can reduce NO at bias combustion conditions. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]


Influence of oil-atomized air on flow and combustion characteristics in a 300 MWe down-fired boiler

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2010
Zhengqi Li
Abstract A method of admitting oil-atomized air into a furnace to adjust coal combustion in a down-fired boiler is described. Experiments with a small-scale furnace simulating a down-fired, pulverized-coal, 300-MWe utility boiler were carried out at a single-phase test facility to investigate the influence of oil-atomized air on the aerodynamic field in the furnace. With the acceleration of oil by secondary air, the primary air/fuel can reach a more distant position with respect to the burner nozzle and the volume of the recirculation zone shrinks. Industrial experiments were also performed in a 300-MWe full-scale boiler. The gas temperature distribution along the primary air/fuel flow in the furnace and the gas components in the near-wall region were measured with the dampers of the oil-atomized air box open and closed. When open, the oil-atomized air does not impede the ignition of the primary air/fuel and can carry the primary air/fuel to a position much deeper in the furnace, resulting in a lowered carbon content in the fly ash. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]


Advanced coal combustion and utilization part I,emission and control

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2010
Minghou Xu
No abstract is available for this article. [source]


Partitioning behavior of mercury during coal combustion: the influence of low-NOx burners and operation load of boiler

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2009
Guang-Qian Luo
Abstract Two 200 MW, pulverized bituminous coal-fired electric utility boilers each equipped with a five-field cold-side electrostatic precipitator (ESP) as the only air pollution control device (APCD) were investigated on mercury distribution and speciation under various conditions. With the same fuel consumption, both facilities are the same but with different burners, low-NOx type and conventional type. Sampling points of gaseous mercury and chlorine species were at the inlet and outlet of the ESP. The mercury concentrations in various solids, including parent coal, bottom slag, economizer bottom ash and fly ash in different hoppers of ESP, were sampled and analyzed. The Ontario Hydro Method was employed to detect mercury in flue gas, and HCl and Cl2 were detected by the EPA method 26. A series of tests were conducted on the boiler with low-NOx burners under various loads (70, 85 and 100% of full load) and on the other boiler with conventional burners under full load. Results showed that small amount of mercury remained in the solid combustion products and most of mercury was released into the atmosphere. The majority of the released mercury was in oxidized form. Burner types and load variation had effects on Cl species concentration in flue gas. Furthermore, particle diameter and carbon content and specific surface area of fly ash affected speciation and distribution of mercury and mercury removal efficiency of ESP. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]


CFD modeling of rotary cement kilns

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2008
Kaustubh S. Mujumdar
Abstract Rotary cement kilns are widely used to convert calcineous raw meal into cement clinker, and are key components in the cement industry. In this article, we report a comprehensive computational fluid dynamics (CFD)-based model to capture key transport processes in rotary cement kilns. Separate but coupled computational models were developed for the bed and the freeboard regions of the rotary kiln. The complex swirling airflow produced by kiln burners, coal combustion, gas-phase combustion of volatile matter and radiative heat transfer in the freeboard region were modeled. The clinkerization reactions in the bed region were modeled assuming solids as pseudo fluids. Coating formation in cement kilns (for both bed and freeboard regions) was considered. Appropriate source and sink terms were developed to model transfer of CO2 from the bed to the freeboard region due to calcination reaction in the bed region. The developed bed and freeboard models were coupled by mass and energy communication through common interface. These coupled computational models were able to quite satisfactorily predict the available data from industrial kilns and previously published results. The computational models were also able to capture the intricacies of the burning zones of rotary cement kilns for changing burner-operational parameters like axial to swirl ratio and oxygen enrichment. The developed approach, computational models and simulation results will not only help in developing better understanding of cement kilns but also provide quantitative information about influence of burner design and other design parameters on kiln performance. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source]


The Oxidation Kinetics of Mercury in Hg/O/H/Cl System

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2005
Y. Qiao
The potential for regulation of mercury emission from coal-fired boilers is a concern for the electric utility industry. Field data show a wide variation in the fraction of mercury that is emitted as a vapor versus that retained in the solid products. The reason for this variation is not well understood. Near the end of the flue gas path, mercury exists as a combination of elemental vapor and HgCl2 vapor. The data show that HCl2 is more likely to be removed form the flue gas. The need to describe accurately mercury reaction products and their concentration-time correlation prompted investigation of mercury chemical kinetic mechanisms and their application to real combustion systems. This paper uses chemical equilibrium analysis to study the speciation of mercury in flue gases during coal combustion and gasification. The paper presents a simple kinetic model of mercury oxidation in the Hg/O/H/Cl system. The results porn the model calculation are in reasonable agreement with the Mamani-Paco and Heleble [1] experimental data [source]


Aggregation Experiments on Fine Fly Ash Particles in a Gradient Magnetic Field

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 8 2007
W. Li
Abstract Aggregation experiments were conducted on two kinds of fly ash particles in the size range of 0.023,9.314,,m in a gradient magnetic field produced by permanent magnetic rings. The two types of fly ash particles were obtained from Dongsheng and Datong coal combustion. The effect of particle size, total particle mass concentration, particle residence time in the magnetic field and gas velocity were examined. Experimental results showed that the removal efficiencies in a gradient magnetic field are much higher than those in a uniform magnetic field. The total and single-sized particle removal efficiencies can be improved by increasing the total particle mass concentrations and the particle residence time in the magnetic field or reducing the gas velocity. Mid-sized particle removal efficiencies are higher than those of the larger and smaller ones. With the increase in total particle removal efficiencies, the particle size corresponding to the maximum values of single-sized particle removal efficiencies and the particle number median diameters both decrease. Both the single-sized and total removal efficiencies for the particles from the Dongsheng coal combustion are higher than those from the Datong coal combustion. [source]