Pollution of the territory of Chelyabinsk and the suburbs with arsenic upon coal combustion

The pollution of the territory of Chelyabinsk and the suburbs with arsenic upon coal combustion is evaluated. The found concentrations of arsenic as a carcinogenic substance in the soils of this territory are higher than the maximum permissible concentration (2 mg/kg) by a factor of 7–19.     

Heavy metal characterization of CFB-derived coal fly ash

The present study investigates the heavy metal content of coal fly ash (FA) samples coming from three different sampling points (secondary cyclone, cooler and filter) of a pilot plant combustion facility. The combustion experiments were carried out in a 0.1 MW Circulated Fluidized Bed (CFB) boiler using South African coal, with the addition of limestone for sulfur capture. FA was tested for the presence of selected heavy metals using inductively coupled plasma optical emission spectrometry (ICP-OES); batch leaching tests were conducted as well. The samples were also characterized in terms of their microstructure, chemical and mineralogical composition, total surface area and particle size distribution. Most of the studied metals (Cd, Cr, Cu, Ni, Mn, Zn) showed enrichment in the fine, filter FA particles, while Pb was mostly concentrated in the cooler sample. Regarding leaching characteristics of the examined samples, Cr was found to occur in considerable amounts. Although the use of CFB technology for the combustion of solid fuels steadily gets bigger worldwide, only a very limited number of studies have environmentally assessed CFB-coal FAs to date. Thus, the current study aims to contribute toward building a more integrated knowledge on the environmental impact of this abundant power production by-product.     

Mechanisms of fine particulates formation with alkali metal compounds during coal combustion

Two types of coals with different sodium (Na) and potassium (K) concentrations were burned in an electrically heated drop tube furnace, to study the formation of particulates in association to alkali metal compounds from the coals. The particulates formed from these coals during combustion were separated by a low pressure impactor (LPI). The particulates collected in each stage of the LPI were analyzed, using an atomic adsorption spectrometer (AAS). The results obtained show that ash particles have bimodal particle size distribution for both coal types. This tendency could be due to the difference of the inherent minerals in raw coals. It was further observed that Na and K were enriched in the fine particulates for both types of coal. There was a dependence of the Na enrichment on the fine particles on concentration of excluded mineral in the raw coals. This work, therefore, showed that the appearance of alkali metal in the ash particles related to the nature of Na and K concentrations in raw coals.     

Organic emissions in coal combustion in relation to coal structure and combustion temperature

The pulsed combustion of coal has been studied in a small fluidized-bed reactor. The effect of combustion temperature and coal rank on the organic composition of the off-gas was investigated. Results are presented for the combustion of an anthracite, a medium-volatile bituminous coal and a high-volatile bituminous coal at 700, 800 and 900°C. The analytical techniques used include on-line FT-i.r., O₂ monitoring, FID and off-line g.c.-m.s. using Tenax as adsorbent. About 120 hydrocarbons were found, of which over 80% have been identified. Overall combustion characteristics such as oxygen consumption, total amount of unburned hydrocarbons and swelling properties of the coal have been related to the composition of the organic substances in the off-gas. The distribution of the polycyclic aromatics, from benzene to chrysene, and of alkylated derivatives is discussed in detail. Oxygen-containing compounds have also been analysed, although detailed discussion would be premature.     

RSP分解炉SC室湍流流动特性对煤粉燃烧的影响

本文对RSP分解炉SC室的湍流动力特性.特别是湍流度、旋流强度等方面进行了研究,通过数值模拟的方法探讨了其对SC室煤粉燃烧的影响,为今后RSP分解炉的技术改造提供了借鉴.     

Detonation combustion of coal

Results of an experimental study of continuous spin detonation of a coal-air mixture with addition of a certain amount of hydrogen in a plane-radial vortex chamber 500 mm in diameter are presented. The tested substance is fine-grained cannel coal from Kuzbass, which has a particle size of 1–7 μm and contains 24.7% of volatiles, 14.2% of ashes, and 5.1% of moisture. Stable regimes of continuous spin detonation with transverse detonation waves having velocities of 1.86–1.1 km/s with respect to the cylindrical wall of the combustor are obtained for the first time. The mass fraction of hydrogen is 1.5–0.88% of the air flow rate and 50–3.4% of the coal consumption rate. The maximum specific coal consumption rate of 106 kg/(s · m²) is obtained.     

Inert coal macerals in combustion

Pilot-scale pulverized-coal combustion experiments with two western Canadian coals have shown that the combustion efficiencies of the coals were inversely related to the inert contents of the coals, i.e. semi-fusinite, fusinite and oxidized vitrinite. These macerals were found to persist through the flame in a partially reacted form. The burn-out of a coal with an inert maceral content over 50% was unaffected by normal changes in combustion conditions; the same changes were successful in improving the burn-out of a coal containing less than 40% inert macerals. Coals with high inert maceral contents produce fly-ash with high levels of unburnt carbon and will require a combination of higher temperatures and higher excess-air levels and longer residence times to achieve combustion efficiencies similar to those of coals with higher reactive-maceral contents. The association of resinitic and bituminous materials with the mineral matter in the Canadian sub-bituminous coal indicated that macerals which contribute significantly to ignition and flame stability are discarded as a washery reject.     

煤粉燃烧室改烧混合煤的技术措施

我厂窑外分解窑和立波尔窑采用烟煤与无烟煤比例为３０％∶７０％的混合煤，这种煤的挥发分为８％～１２％、灰分为２０％～２４％、细度为２％～５％、水分＜３．５％、着火温度约６００℃。３台Φ３．５m×１０m中卸烘干生料磨配套的３个煤粉燃烧室仍然只能烧烟煤，每天２号煤磨（Φ２．２m×４．４m）要为此专门开机４h左右。如果燃烧室也烧混合煤，既可以节省每吨烟煤与无烟煤近９０元的差价，也可以停开２号煤磨。燃烧室所用煤计划与立波尔窑所用混合煤一样，由１号风扫煤磨（Φ２．８m×８m）磨制。本着尽可能节省投资的原则，我们采…     

Fluidized bed combustion of coal

To conserve oil an alternative start-up procedure for the fluidized-bed combustor has been established which uses charcoal. The elutriated carbon loss has been measured for different grades of coal, and the variation of carbon loss with fluidization velocity is also reported. The results could be useful in the design of fluidized-bed combustion systems.     

Microwave plasma combustion of coal

Microwave plasma is studied as an alternative to oil or gas fuel for ignition and stabilisation of burning of lean coal. The study is performed on an experimental set-up, which includes a burner with a microwave plasma generator, coal and air supply systems, and measurement equipment. Power and thermochemical characteristics of the coal-plasma interaction have been measured and analysed. The obtained results indicate an essential intensification of ignition and combustion processes in the microwave burner compared to those in conventional burners. In particular, it has been demonstrated that the microwave energy consumption is only about 10% of the required expenditure of oil or gas, measured in heat equivalent. A design of an industrial microwave-plasma burner is proposed. Prospects of such burner for applications at industrial boilers of power plants are discussed.     

DEM-LES simulation of coal combustion in a bubbling fluidized bed Part II: coal combustion at the particle level

The discrete element method-large eddy simulation (DEM-LES) is used to model coal combustion at the particle level in a bubbling fluidized bed. The gas phase is modelled as a continuum and the solid phase is modeled by DEM. Chemical reactions consist in the heterogeneous reactions of char with O₂, CO, CO₂, NO, and N₂O, and in the homogeneous reactions involving CO, O₂, NO, and N₂O. The colliding particle-particle heat transfer is based on the analysis of the elastic deformation of the spheres during their contact. The model predicts the effects of the particle heterogeneous flow structure on the thermal characteristics of coal particles when heating and burning, and the gaseous emissions from a fluidized sand-coal binary mixture. The heating rates are 1627 and for, respectively, 0.8 and diameter coal particles fed into the fluidized bed. The instantaneous contribution of the collision heat transfer is weak, less than 5.0% of the total power exchanges (coal combustion, radiation, convection and collision) during the heating and 1.5% during the combustion. The temperature of the coal particles exceeds the bed temperature, which is in qualitative agreement with experimental data from literature. The effects of the diameter of coal particles, of the bed temperature, and of the inlet gas velocity on the thermal characteristics are also studied.     

DTGA combustion of coals in the Exxon coal library

Coal combustion experiments were carried out over the temperature range 25–900 °C using air at atmospheric pressure in a derivative thermogravimetric analysis system. Sixty-six coals high in vitrinite (> 80% mineral-matter-free basis) and low in inorganics (all but 12 samples < 10%) were examined as part of a coal characterization programme. The coals varied in rank from lignites (69% carbon on a dry, mineral-matter-free basis) to low-volatile bituminous (91% carbon). Combustion rates increased progressively with increasing temperature, passed through maxima and then declined. The rate data were fitted to an Arrhenius equation and plots showed four distinct regions of combustion. Apparent activation energies were calculated for each region and varied from ≈4 kJ mol^?1 in the high-temperature, diffusion-controlled region to 290 kJ mol^?1 in the chemical-reaction controlled, low-temperature region. The temperatures at which 50% of the sample had burned away ($\text{sol1}\text{2}\text{-}\text{life}$) were rectilinearly related to oxygen and carbon contents (correlation coefficient squared values of 0.88 and 0.86, respectively).     

The fragmentation of coal particles during the coal combustion in a fluidized bed

This paper presents an experimental method for studying the fragmentation of coal particles during coal combustion in a fluidized bed and the quantitative fragmentation indexes of 10 typical Chinese coal ranks. The influences of a variety of factors such as the bed temperature, the size of coal particles, the coal rank and the fluidizing medium on the fragmentation index of coal particles are also studied. The research results show that the main reason for the fragmentation of coal particles is the primary fragmentation, and that the volatile matter can drastically influence the degree of fragmentation of coal particles.     

Emissions in the combustion of coal and coal-processing wastes

Power stations based on traditional hydrocarbon fuels—in particular, coal—are characterized by considerable atmospheric emissions. In the light of the annual increase in coal consumption and the ongoing environmental deterioration, significant decrease in atmospheric emissions per unit mass of coal consumed must be regarded as a high priority. In the present work, SO₂, CO₂, CO, NO, and NO₂ emissions from power plants around the world are analyzed. The emissions formed in the combustion of traditional types of Russian coal and their processing wastes (filter cakes) are compared. The benefits of using coal–water slurry containing coal-processing wastes at power plants are outlined.     

Modelling coal combustion: the current position

At the present time, computer models for coal combustion are not sufficiently accurate to enable the design of combustion plant or the selection of a coal based on combustion behaviour. Most comprehensive combustion models can predict with reasonable accuracy flow fields and heat transfer, but usually with a much lesser degree of accuracy than the combustion of the coal particles through to char burnout. Many research programmes are aimed at developing a much more accurate predictive tool for assessing coals specially fired in burners or furnaces employing a range of NO_x abatement technologies. Some of the current developments in CFD coal combustion modelling are outlined here. Particular attention is paid to the first step, where the devolatilisation pre-processor code is used to compute the pyrolysis rate, the yields and the composition of volatiles and char. These parameters are used as inputs to the devolatilisation and volatile combustion sub-models, where various options can be used, and also the char burnout sub-models. The accuracy of the sub-models is examined using data from four well-studied coals, three from the UK and one from the US. The main network devolatilisation codes are compared with experimental data. Two char combustion models have also been investigated in order to compare char burnout predictions and the development of char morphology and surface area during burnout are considered. The applications of these sub-models to two combustion situations were considered. These involve reactions in a drop tube furnace and a low NO_x industrial burner and in both cases, the model predictions were compared with experimental measurements.     

Mercury oxidation by hydrochloric acid over TiO2 supported metal oxide catalysts in coal combustion flue gas

Mercury oxidation by hydrochloric acid over the metal oxides supported by anatase type TiO₂ catalysts, 1 wt.% MO_x/TiO₂ where M = V, Cr, Mn, Fe, Ni, Cu, and Mo, was investigated by the Hg⁰ oxidation and the NO reduction measurements both in the presence and absence of NH₃. The catalysts were characterized by BET surface area measurement and Raman spectroscopy. The metal oxides added to the catalyst were observed to disperse well on the TiO₂ surface. For all catalysts studied, the Hg⁰ oxidation by hydrochloric acid was confirmed to proceed. The activity of the catalysts was found to follow the trend MoO₃ ~ V₂O₅ > Cr₂O₃ > Mn₂O₃ > Fe₂O₃ > CuO > NiO. The Hg⁰ oxidation activity of all catalysts was depressed considerably by adding NH₃ to the reactant stream. This suggests that the metal oxide catalysts undergo the inhibition effect by NH₃. The activity trend of the Hg⁰ oxidation in the presence of NH₃ was different from that observed in its absence. A good correlation was found between the NO reduction and the Hg⁰ oxidation activities in the NH₃ present condition. The catalyst having high NO reduction activity such as V₂O₅/TiO₂ showed high Hg⁰ oxidation activity. The result obtained in this study suggests that the oxidation of Hg⁰ proceeds through the reaction mechanism, in which HCl competes for the active catalyst sites against NH₃. NH₃ adsorption may predominate over the adsorption of HCl in the presence of NH₃.