Bituminous Coal Combustion Research Articles

E212 INFLUENCE OF TWO-STAGE AIR INJECTION CONDITIONS ON NOx AND UNBURNED CARBON OF SUB-BITUMINOUS COAL COMBUSTION

Because of large recoverable reserves, sub-bituminous coal is an important energy resources. The disadvantage of sub-bituminous coal is that it contains more than 20% moisture. This makes ignition less efficient. And combustion flame became diffused. Both emissions of NOx and unburned carbon in fly ash become high. We have already shown that these emissions can be reduced by adjusting the air injection conditions from the burner to better suit sub-bituminous coal combustion. However, the reduction is insufficient compared with bituminous coal combustion. In this investigation, influence of two-stage air injection conditions on NOx and unburned carbon concentration in fly ash was studied and the optimum air injection conditions necessary in order to reduce those emissions were clarified.

Enhancement of combustion efficiency with mixing ratio during fluidized bed combustion of anthracite and bituminous blended coal

In order to investigate the effect of mixing ratio of bituminous coal to blended coal on the enhancement of combustion efficiency, combustion experiments of blended coal with anthracite and bituminous are done in a laboratory scale fluidized bed combustor (10.8 cm ID and 170 cm height). The gross heating values of anthracite and bituminous coal used in this study are 2,810 cal/g and 6,572 cal/g, respectively. Experimental parameters are fuel feed rate, superficial gas velocity and mixing ratio of bituminous coal to blended coal. The combustion efficiency increases with the mixing ratio of bituminous coal due to the lower unburned carbon losses and higher burning velocity of bituminous coal. The rate of combustion in the combustor was increased with mixing ratio resulted from a higher burning velocity of bituminous coal. The measured combustion efficiency experimentally is about 3.5-12.4% higher than that of the calculated value based on the individual combustion of anthracite and bituminous coal under the same operating conditions. The optimum mixing ratio (MR) of bituminous coal determined is around 0.75 in this study.

The Impact of the Bituminous Coal Combustion from the Thermoelectric Power Plant from Paroseni on the Environment of Jiu Valley

The Jiu Valley Basin is one of the most important coal mining areas in Romania. Other industries, including a power plant, are also well developed in this area. Therefore, pollution is very high. One of the most polluted environmental compounds is the air. High mountains surround the Jiu Valley, which makes difficult the air refreshing. For this reason, it is very important to discuss the air pollution and especially that produced by dust. Since the industrial companies are concentrated in a small area, it is very difficult to identify and prosecute the polluting one. The present paper aims to identify the sources of air pollution, especially among the mining companies, because the power plant is considered the most important polluting agent in this area.

In-situ laser spectroscopy of CO, Ch4, and H2O in a particle laden laboratory-scale fluidized bed combustor

The pyrolysis, devolatilization and char combustion of bituminous coal and biomass (beechwood, firwood) were investigated in a laboratory-scale fluidized bed combustor by tunable diode laser spectroscopy. Individual fuel particles were suspended in the freeboard of the unit. The bed temperature was 800 ?C, the oxygen partial pressure 0 to 20 kPa (0-10 vol.%). Two Fabry Perot type tunable near infrared diode lasers were deployed for quantitative in-situ species concentration measurements. CH4 and CO were measured simultaneously during devolatilization and char combustion in-situ 10 mm above the surface of the fuel particles as well as H2O using laser spectroscopy. Sand particles were passing the probing laser beam path. Besides the resonant absorption of the laser light by CO, CH4 and H2O severe and strongly transient non-resonant attenuation by partial blocking of the beam and beam steering effects occurred. By wavelength tuning the two laser sources, species concentrations could be determined. The measured absorbances had to be corrected for the real temperature measured at the position of the probing laser beam. In addition, CO, CO2 and O2 were determined ex-situ by con ventional methods. A spatial profile inside the FBC of major species (CH4, CO, CO2, O, H, OH) was calculated using a chemical kinetics program for a single fuel particle in a plug flow reactor geometry. The results were compared to the experimental findings. Good agreement was found. Tunable diode laser spectroscopy was found to be an apt method of determining quantitative species concentrations of multiple gases in a high temperature multi phase environment.

The influence of fuel additives on the behaviour of gaseous alkali-metal compounds during pulverised coal combustion.

The alkali-metal vapour release during pulverised hard (bituminous) coal combustion was investigated in a semi-technical drop flow reactor in the temperature range 1100-1400 degrees C. Absolute concentrations of total gas-phase sodium and potassium species were determined using the in situ/on-line excimer laser induced fragmentation fluorescence technique (ELIF). Alkali-metal concentrations measured for the untreated coals were found to be in the range 0.1 to 4.7 ppm, depending on the temperature. As well as observing the temperature dependence, the effect of co-feeding defined amounts of silica and clay minerals was studied. In addition, to assist interpretation of ELIF measurements, ash samples were taken and analysed by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The additives lead to a pronounced binding of the alkali-metal species and suppression of the sharp temperature dependence observed without co-feeding. Therefore, the use of such getter materials can be confirmed as an effective way to remove corrosive alkali-metal species from the flue gas in pulverised coal combustion.

Highly crystalline zeolite — a from flyash of bituminous and lignite coal combustion

Flyash is being generated in voluminous amounts by large scale coal combustion process. It poses a serious threat to thermal power industries specifically, in India, wherein the percent of utilisation of flyash is very poor (3–5%). In view of this problem, newer methods of its disposal and utilisation are being explored. The synthesis of zeolite from flyash appears to be one of the most promising alternatives as it has emphasis on value addition to waste material. Flyashes originating from different sources of coal differ in their characteristics and have implications in this work on Zeolite-A production. These factors have been thoroughly investigated and the conditions favourable for formation of Zeolite-A have been delineated. The reactivity of flyash towards zeolite formation is directly dependent on the SiO 2/Al 2O 3 ratio, Fe 2O 3 and CaO content. Amongst the flyashes investigated, so far the sub-bituminous coal based flyash with SiO 2/Al 2O 3 ratio of 3.47 appears to be a suitable substrate for Zeolite-A synthesis. These zeolites have been characterised with respect to XRD crystallinity, calcium binding capacity (CBC) and sorption capacity, wherein the crystallinity ranges from 50 to 100%, the CBC ranges from 290 to 560 meq/100 g and sorption capacity ranges from 16.6 to 23.8%.

Effect of boiler output on trace element partitioning during coal combustion in two fluidised-bed power stations

The main aim of this study was a detailed comparison of trace element partitioning during combustion of bituminous coal and lignite in two circulating fluidised-bed units at 40 and 100% boiler output. The elements considered here are: S, Cl, Br, V, Cr, Co, Ni, Cu, Zn, Ge, As, Se, Sn, Sb, W, Hg, and Pb. The trace element concentrations in combustion products show enrichment of most of the elements in fly ash related to bottom ash as well as the slight element enrichment in fly ash at 40% boiler output compared with the 100% output. Using an element balance calculation the proportion of each element in bottom ash, fly ash and emissions was determined. Results showed that at both boiler outputs the highest relative percentages of elements that entered into emissions were Hg and Cl.

Characterization of Carbon Concentrates from Coal-Combustion Fly Ash

A study of carbon concentrates separated by a number of different commercial and laboratory methods from various coal-combustion fly ashes was undertaken to determine what common and unique chemical and physical properties can be expected in such concentrates. The properties were determined using a variety of physical and spectroscopic characterization methods and then were compared among the carbon concentrates and in two cases with the properties of the unprocessed fly ashes. The class F fly ashes originated from a total of seven different utilities burning bituminous coals and underwent one of six different processing methods to produce the carbon concentrates, which contained from 24% to 76% carbon. Three different configurations of triboelectrostatic separators were used to produce the carbon concentrates in addition to two different flotation methods plus a proprietary carbon recovery process. The results showed that unburned carbon concentrates from fly ash have properties similar to most carbon blacks and would be poor replacements for activated carbon in adsorption processes unless they are activated in a separate step. The untreated carbon may have applications as a substitute for carbon black provided it could be obtained in sufficient purity. The results have implications for those who wish to use carbon concentrates from coal-combustion fly ashes in secondary markets, especially as sorbents and fillers.

The effects of ammonia on SO2 emissions in a fluidized bed combustor under pseudo-staged combustion.

The reduction of SO2 by ammonia gas addition during staged combustion of bituminous coal has been studied in a 2 m high fluidized bed combustor of 30 cm static bed height and a freeboard height of 100 cm. The coal was introduced to the combustor at 42 cm above the distributor and the ammonia gas was injected at 52 cm above the distributor by an uncooled stainless steel injector. Experiments were carried out to investigate effects of ammonia gas injection on SO2 emissions of (i) air staged levels, (ii) excess air levels, (iii) primary air factor

Legislative and environmental issues on the use of ash from coal and municipal sewage sludge co-firing as construction material

For the economy of any co-firing process, it is important that the common waste management options of ash remain practical. Ash from bituminous coal combustion is typically handed to the construction industry. This paper describes the current European legislation on use of ash for construction purposes. Also, it presents an experimental study on the suitability of fly ash from combustion of mixtures of bituminous coal and municipal sewage sludge as additive to cement and concrete, and for use in open-air construction works, based on the ash chemical composition and the characteristics of the extract of the ash. Presently, two European standards forbid the use of ash from co-firing as additive to cement or concrete. This study shows that ash derived from coal and sewage sludge co-firing contains generally less unburned carbon, alkali, magnesium oxide, chlorine, and sulfate than coal ash. Only the concentration of free lime in mixed ash is higher than in coal, even though, at least up to 25% of the thermal input, still below the requirements of the standards. This ash also meets the requirements for the use of fly ash in open-air construction works — concentration and mobility of few elements — although this management option is forbidden to ash from co-firing. The leaching of Cd, Cr, Cu, Ni, Pb and Zn was investigated with three leaching tests. The concentration of these metals in the extracts was below the detection limit in most cases. The concentration of Cu and Zn in the extract from fly ash was found to increase with increasing share of sewage sludge in the fuel mixture. However, the concentration of these two metals in the extract is not regulated. This study indicates that excluding a priori the use of ash from co-firing as a suitable additive for construction material could cause an unnecessary burden on the environment, since probably ash would have to be disposed of in landfill. However, allowing this requires the modification of current European standards to include limitations on all elements and compounds, absent in coal but which might be present in other fuels, that are deleterious for the quality of construction materials.

00/03587 Study on metal species partitioning along the flue gas path in combustion of bituminous coal and dry sewage sludge

00/03587 Study on metal species partitioning along the flue gas path in combustion of bituminous coal and dry sewage sludge

Controlling Powdered Fuel Combustion at Low Temperature in a New Entrained Flow Reactor

If low temperatures of 800-1000°C are used for the combustion of powdered solid fuels (coal or waste) energy can be produced while at the same time emissions of atmospheric pollutants are minimised. We have developed and precisely characterised an apparatus to determine the kinetic parameters of the potentially limiting reactions (devolatilisation and solid residue oxidation) involved during high heating-rate combustion. The gas phase chemical composition, and structural changes in particles accompanying the combustion can also be followed. Calculation of characteristic time constants and simulation by Computational Fluid Dynamics were necessary to establish heat and mass transfer conditions in which intrinsic kinetic parameters can be assessed with a maximum accuracy. An experimental parametric study of a bituminous coal combustion then demonstrates the accuracy that could be reached. The individual effects of devolatilisation temperature, of atmosphere oxygen content and of particles diameter on the combustion progress are quantitatively characterised.

Determination of Sulfite in Oriental Herbal Medicines

Sulfite was detected in 7 varieties of Oriental herbal medicines (Pueraria radix, Zingiberis rhizoma, Platycodon radix, Adenophora radix, Pinellia tuber, Astragalus radix, and Paeonia radix) on the Korean market. Sulfiting of commercial Oriental herbal medicines by fumigation with burning bituminous coal was simulated, and the accumulation of sulfite was investigated by using fresh Platycodon radix roots obtained from a growing field. The sulfite level reached a plateau in 9 h, and the maximum sulfite level found by the Monier-Williams (MW) method (AOAC 990.28) was 1020 ppm. The sulfite content in the simulated Platycodon radix sample determined by alkali extraction followed by ion-exclusion chromatography with electrochemical detection (AOAC 990.31) was approximately 17% lower on average than the MW results. Free-sulfite levels determined by acid extraction and ion-exclusion chromatography with electrochemical detection were between 19 and 49% of the MW results. The advantages of different methods for sulfite determination and the significance of the results are discussed.

Measurement of soot and char in pulverized coal fly ash

The unburned carbon in the fly ash produced by low-NOx pulverized coal combustion has been shown by electron microscopy to be a mixture of porous coal char particles and aggregates of submicron particles, which are thought to be soot. The carbon is bimodally distributed with large soot aggregates mixed with the char in the particles larger than 10μm and dispersed soot found with the submicron particles. A method for determining the mass of soot and char by liquid-suspension gravity separation was used with both laboratory-scale and power plant fly ash samples. For low-NOx, staged, pilot-scale combustion of bituminous coal the soot in the furnace exit ash was estimated to be 0.2–0.6% of the fuel carbon, which was about 35% of the total unburned carbon.

Characterization of mullite in silicoaluminous fly ash by XRD, TEM, and 29Si MAS NMR

Mullite contained in a silicoaluminous fly ash (originating from power plant of La Maxe, near Metz in the east of France) issue from bituminous coal combustion has been studied by X-ray diffraction, nuclear magnetic resonance of 29Si spinning at magic angle, and transmission electron microscopy linked with energy-dispersive spectroscopy. By using results from X-ray diffraction [1] and nuclear magnetic resonance spectroscopy [2], an average value of 0.35 for x, the oxygen holes rate in mullite Al 4+ 2 x Si 2− 2 x O 10− x , could be determined. Thus, Al 2O 3 content is only slightly higher than those corresponding to the classical formula (Al 2O 3) 3 · (SiO 2) 2. It is shown also that the composition is heterogeneous and depends on the crystallites; Ti and Fe are impurities substituting for Al in the structure. The average chemical formula of the mullite determined here is Al 4.61Fe 0.05Ti 0.02O 9.65.

Modeling the vaporization of ash constituents in a coal-fired boiler

Emissions of fine particulate and trace toxic metals are being subjected to increasing regulation. This paper addresses how the emission of these compounds can be influenced by changes in combustion conditions, particularly those selected to minimize NOx emissions. The vaporization and condensation of refractory oxides dominate submicron aerosol formation during the combustion of bituminous coals. The vaporization of these oxides is augmented by the reduction of refractory oxides to suboxides or metals. We used available drop tube furnace data to develop and test models for the vaporization of aluminum and iron. The vaporization of alumina is found to occur primarily via reduction of the alumina to Al2O. Although other paths are recognized to be important, the vaporization of iron is approximated by a mechanism involving FeO reduction. The models for aluminum and iron vaporization, together with previously developed models for the other refractory metals, are incorporated into a computational fluid dynamics code to determine the impact of different oxidation-temperature histories in a utility boiler. The vaporization of refractory oxides is calculated for conditions corresponding to the operation of the boiler before and after retrofitting with low-NOx burners and overfire air ports. The results show that the vaporization of refractory oxides is diminished under low-NOx operating conditions and that the different oxygen-temperature histories of particles lead to significant differences in the vaporization of oxides for particles originating from different burners. The vaporization is found to occur primarily in regimes where temperature and CO concentration are high.

Possible interactions between As, Se, and Hg during coal combustion

A thermodynamic analysis has determined in detail the speciation of Hg, Se, and As, which are the most volatile trace elements in the flue gas from burning bituminous coal, depending on the temperature (400–1800 K), the atmosphere (reducing or oxidizing conditions), and the chlorine content. The amount of chlorine in the system greatly affects the identity of stable species; the relative affinities of the three elements to chlorine are in the order: Se > As > Hg under oxidizing conditions at both high (1100 K) and low (600 K) temperatures. Interactions between the three elements are investigated; AsSe(g) and HgSe(g) are found to be possibly present as the major species in the local CO-enriched zone in a boiler. The competing reactions of these three elements for oxygen, hydrogen, and chlorine are also discussed.

A Simple Two-Reactor Method for Predicting Distribution of Trace Elements in Combustion Systems

Utilization of fossil fuels in energy production results in emissions of pollutants. Development in combustion technology has, however, during recent years focused on decreasing emissions of particulates, sulfur, and nitrogen oxides. In addition, combustion also includes a potential risk for emission of trace metals. Due to the fact that many trace elements have been identified as having a negative effect on human health and the natural environment, they have received special attention from a regulatory point of view. This paper describes a simple method for predicting the fate of eight trace elements (As, Cd, Hg, Ni, Pb, Se, V, and Zn) in combustion processes. Using the fuel composition and power plant operating conditions, the trace element concentrations in various ashes and the flue gas are determined. The method, which is based on a global equilibrium approach, describes the overall behavior of the eight trace elements successfully. Distribution/partitioning of the trace elements between the bottom ash, fly ash, and the flue gases is described and compared to measured data from a full-scale coal-fired power plant burning bituminous coal. The outcome from the prediction is actual concentrations of trace elements in main power plant streams.

Characterization of magnetite in silico-aluminous fly ash by SEM, TEM, XRD, magnetic susceptibility, and Mössbauer spectroscopy

Spinel magnetite contained in a silico-aluminous fly ash (originating from la Maxe's power plant, near Metz in the east of France) issued from bituminous coal combustion has been studied by scanning and transmission electron microscopy linked with energy dispersive spectroscopy, X-ray diffraction, susceptibility measurements, and Mössbauer spectroscopy. The results show that in this magnetite Mg is strongly substituted for Fe and the chemical formula is closer to MgFe 2O 4 than Fe 3O 4. Magnetite also contains Mn, Ca, and Si elements, but at a lower proportion. The results are compatible with the chemical formula Fe 2.08Mg 0.75Mn 0.11Ca 0.04Si 0.02O 4 and crystallochemical formula [Fe 2+ 0.92Ca 2+ 0.06Si 4+ 0.02] tetra[Fe 3+Fe 2+ 0.16Mg 2+ 0.73Mn 2+ 0.11] octaO 4, showing the cation distribution on octahedral and tetrahedral sites of the spinel structure. The reason Mg element is not incorporated in soluble surface salt and in glass composition of the silico-aluminous fly ashes is now understood.

99/03330 Study on trace metal partitioning in pulverized combustion of bituminous coal and dry sewage sludge

99/03330 Study on trace metal partitioning in pulverized combustion of bituminous coal and dry sewage sludge