煤灰基本特征及其微量元素的分布规律

对兖州矿区煤灰的化学成分、微量元素分布及灰的岩石学特征等方面进行了研究，并对灰产率与微量元素含量分布之间的关系进行了研究，同时对影响煤灰化学成分的因素方面进行了初步探讨。通过对兖州矿煤灰的采样分析可知,研究区煤灰由结晶物质、玻璃状物质和末燃尽有机质组成，其化学成分主要为SiO2,Al2O3,Fe2O3和CaO及少量的O3,P2O5,Na2O和TiO2,煤燃烧过程中微量元素发生了再分布，多数微量元素在煤灰中富集。同时它们在飞灰中富集的浓度明显高于底灰，即随着煤灰粒度的变小，它们在其中富集的浓度越高，其含量与煤灰的粒度成反比。微量元素Th,V,Zn,Cu,Pb与灰产率之间成正相关关系，而Cl与灰产率成负相关关系。     

Characteristics and composition of fly ash from Canadian coal-fired power plants

Fly ashes were collected from the electrostatic precipitator (ESPs) and/or the baghouse of seven coal-fired power plants. The fly ashes were sampled from power plants that use pulverized subbituminous and bituminous feed coals. Fly ash from bituminous coals and limestone feed coals from fluidized-bed power plant were also sampled. The fly ashes were examined for their mineralogies and elemental compositions. The fly ashes from pulverized low sulfur coals are ferrocalsialic, those from high sulfur coals are ferrosialic and the fly ashes from the fluidized bed coals are ferrocalcic. The concentrations of As, Cd, Hg, Mo, Ni, and Pb in fly ash are related to the S content of the coal. Generally, those feed coals with a high S content contain higher concentrations of these elements. The concentrations of these elements are also greater for baghouse fly ash compared to ESP fly ash for the same station. The S content of fly ash from high S coal is 0.1% for pulverized ESP fly ash and 7% for baghouse fly ash from the fluidized bed, indicating that most of the S is captured by fly ash in the fluidized bed. The baghouse fly ash from the fluidized bed has the highest content of Cd, Hg, Mo, Pb, and Se, indicating that CaO, for the most part, captures them. Arsenic is captured by calcium-bearing minerals and hematite, and forms a stable complex of calcium or a transition metal of iron hydroxy arsenate hydrate [(M²⁺)₂Fe₃(AsO₄)₃(OH)₄·10H₂O] in the fly ash. Most elements in fly ash have enrichment indices of greater than 0.7 indicating that they are more enriched in the fly ash than in the feed coal, except for Hg in all ESP ashes. Mercury is an exception; it is more enriched in baghouse fly ash compared to ESP. Fly ash collected from a station equipped with hot side ESP has a lower concentration of Hg compared to stations equipped with cold side ESP using feed coals of similar rank and mercury content. Fly ash particles from fluidized bed coal are angular and subangular with cores of quartz and calcite. The quartz core is encased in layer(s) of calcium-rich aluminosilicates, and/or calcium/iron oxides. The calcite core is usually encased in an anhydrite shell.     

Trace elements (Mn,Cr, Pb,Se, Zn,Cd and Hg) in emissions from a pulverized coal boiler

The concentrations of seven trace elements (Mn, Cr, Pb, Se, Zn, Cd, Hg) in raw coal, bottom ash and fly ash were measured quantitatively in a 220 tons/h pulverized coal boiler. Factors affecting distribution of trace elements were investigated, including fly ash diameter, furnace temperature, oxygen concentration and trace elements' characteristics. Modified enrichment factors show more directly element enrichment in combustion products. The studied elements may be classified into three groups according to their emission features: Group 1: Hg, which is very volatile. Group 2: Pb, Zn, Cd, which are partially volatile. Group 3: Mn, which is hardly volatile. Se may be located between groups 1 and 2. Cr has properties of both Groups 1 and 3. The smaller the diameter of fly ash, the higher is the relative enrichment of trace elements (except Mn). Fly ash shows different adsorption mechanisms of trace elements and the volatilization of trace elements rises with furnace temperature. Relative enrichments of trace elements (except Mn and Cr) in fly ash are larger than that in bottom ash. Low oxygen concentration will not always improve the volatilization of trace elements. Pb forms chloride more easily than Cd during coal combustion.     

Behaviour of elements and minerals during preparation and combustion of the Pernik coal,Bulgaria

The chemical and mineral composition, including major (Al, Ca, Fe, K, Mg, S, Si, Ti), minor (Na, P) and trace (Br, Cl, Co, Cr, Cu, Li, Mn, Ni, Pb, Rb, Sr, Zn) elements and different minerals, of the Pernik subbituminous coals and their preparation and combustion solid waste products were studied. Feed coals, upgraded coals (high-grade and low-grade coals) and their waste products, namely coal slimes and host rocks generated from the Pernik coal preparation plant, as well as combustion waste products such as bottom ashes, fly ashes and lagooned ashes resulted from the Republica coal-fired thermoelectric power station were characterized. The occurrence and behaviour (partitioning, volatilization, condensation, capture and retention) of the above-mentioned elements and various minerals during coal preparation and combustion are described. The results indicate some technological problems and possible environmental pollution of the air, water, soil and vegetation with certain elements in the areas surrounding both thermoelectric power station and coal preparation plant.     

Prediction of trace element volatility during co-combustion processes

The behaviour of some selected trace metals (Hg, Cd, As, Pb, Sb, Cr, Co, Cu, Mn, Ni and V) during co-combustion processes of bio-waste materials (sewage sludge, waste wood, refused derived fuel) and coal has been predicted by thermodynamic equilibrium calculations using the HSC-Chemistry 4.0 software. The influence of temperature, flue gas composition, trace element concentration and minor fly ash components on equilibrium composition was evaluated. For most of the elements, an increase in the HCl concentration favours the formation of gaseous species while increasing concentration of SO₂ in the gas composition enhances the formation of condensed species. Trace element interactions with minor fly ash components were predicted. From results obtained in this study it may be concluded that, from a thermodynamical point of view, the addition of a secondary fuel in combustion processes does not produce an increase in trace element emissions to the environment. Generally, trace elements are captured in ashes avoiding that these elements reach the stack.     

Volatility and chemistry of trace elements in a coal combustor

The volatility of 16 trace elements (TEs) (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sb, Se, Sn, Te, Tl, V, Zn) during coal combustion has been studied depending on the combustion conditions (reducing or oxidizing) and type of coal (high- or low-ash coal), together with their affinities for several active gaseous atoms: Cl, F, H, O, and S.

The elements can be divided into three groups according to their tendencies to appear either in the flue gases or in the fly ashes from a coal combustor:

Group 1: Hg and Tl, which are volatile and emitted almost totally in the vapor phase.

Group 2: As, Cd, Cu, Pb and Zn, which are vaporized at intermediate temperature and are emitted mostly in fly ashes.

Group 3: Co, Cr, Mn and V, which are hardly vaporized and so are equally distributed between bottom ashes and fly ashes. In addition, Sb, Sn, Se and Te may be located between Groups 1 and 2, and Ni between 2 and 3.

At 400 and 1200 K, the 16 TEs behave differently in competitive reactions with Cl, F, H, O and S in a coal combustor.     

Characterization of unburned carbon from ash after bituminous coal and lignite combustion in CFBs

This paper deals with the characterisation of carbon (UC) from bottom ash (BA) and fly ash (FA) samples from two fluidised-bed power stations burning bituminous coal and lignite. The laboratory results for the carbon determinations and its mass balances are evaluated. Chemical and mineral analyses and textural characteristics (specific surface area and pore-size distribution) are presented. Depletion/enrichment of selected elements (S, Cl, V, Cr, Ni, Cu, Zn, As, Se, Sb, Hg, and Pb) in carbon from the bottom ash are compared with both ash compostions. The strong positive relationships between the concentrations of some trace element contents (Hg, Se, As, Cu, Ni, V and Cl) in fly ash with the content of carbon and the specific surface area of FA are presented and expressed by regression equations with very high correlation coefficients. Laser ablation-ICP-MS has been used to obtain an insight into element distributions within carbon grains from the bottom ash.     

The characteristics of inorganic elements in ashes from a 1 MW CFB biomass gasification power generation plant

This paper investigated the characteristics of inorganic elements in ashes from biomass gasification power generation (BGPG) plant. The ash samples of the gasifier ash, separator ash and wet scrubber ash were collected in a 1 MW circulating fluidized bed (CFB) wood gasification power generation plant. Particle size distribution of ashes was determined by gravimetric measurement and super probe analyzer. The concentrations of trace elements and major ash-forming elements, such as As, Al, Ca, Cd, Cr, Cu, K, Mg, Na, Ni, Pb, Ti in different ashes as a function of particle size were determined by Inductive Coupled Plasma Spectrometer. The concentrations and distribution coefficient and enrichment factors of the inorganic elements in ashes were studied. X-ray fluorescence spectrometer and X-ray powder diffraction were used to provide information on the characteristics of the ashes. The results showed that most of the trace elements had an enrichment tendency in the finer size particles. A considerable amount of the ashes was residual carbon. Most of the volatile e.g. halogen elements and alkali elements existed mainly in wet scrubber ash and enriched in fly ash. Most of the Si, Ni, Pb, Zn, Cr, Cd were found in separator ash, indicating an enrichment of heavy metal elements in separator ash. K, S, Mn, Cu mainly existed in gasifier ash.     

Trace elements in combustion residues from a UK power station

Trace element analyses of combustion residues from Eggborough Power Station (UK) are re-examined and augmented with new data, which has enabled original conclusions [Fuel Process Technol 47 (1996) 79] to be extended in two areas and developed in a third. These are: (a) potential emissions through mass closure with the conclusion that of the elements analysed only As appears to have been lost from the system (mass closures for Se and Hg were not determined but these elements are also probably lost); (b) volatility of elements based on ratios of element concentrations in fly ash to furnace bottom ash and element concentrations in a fine ash fraction to a coarse fraction with the latter appearing to be the more sensitive indicator and (c) the percentage surface association based on trace element analyses of size-fractionated fly ash. From the latter it is concluded that As and Mo are predominantly surface associated with little contained within the glass or other phases, Cu, Zn and Pb have a surface association of about 50%, V, Cr and Ni a lower surface association of between 30 and 20% and Ba and Sr a minor association of about 10%. The same conclusion was also reached for As, Mo and Pb using LA-ICP-MS [Fuel 2004] with, in addition, a similar association suggested for U, Tl and Se.     

Comparison of leachable trace element levels in coal gasifier ash with levels in power plant ash

The levels of 14 trace elements in leachates from three types of ash of a common origin coal were compared. The study was conducted over a one year period at the Kosovo plant in Obilic, Yugoslavia comparing coal gasifier ash with fly ash and bottom ash from a coal-fired power plant using lignite from the Dobro Solo mine. Results obtained indicate that levels of Sb, As, Be, Cr, Cu, Pb, Mo, Ni and Zn in gasifier ash leachate were similar to those in fly ash leachate. Barium levels in gasifier ash leachate averaged 2.7 times that in fly ash and selenium levels averaged 0.33 times. The average ratio for the total set was 0.99. The set average, relative to bottom ash, was 2.1 with the nickel ratio (R_{Ni = 0.31}) differing significantly from the average. Metal oxides, CaO, MgO, Na₂O, K₂O and MgO, in the Kosovo gasifier ash were found at levels similar to those in Kosovo fly ash, and except for K₂O, were approximately twice those in bottom ash. Concentration levels of all components showed relatively small variations averaging 50% of their mean annual concentration over the test period.     

Leaching characteristics of selected Korean fly ashes and its implications for the groundwater composition near the ash disposal mound

Currently only 20% of the fly ash produced in Korea is utilised for industry, and the remainder is disposed as waste in landfill sites. Both anthracite and sub-bituminous coals are burnt in Korea. Fly ash and coal samples were collected from five different coal-fired power stations in Korea and analysed for their chemistry and mineralogy. Batch leaching tests were also carried out to investigate the leaching behaviour of selected fly ashes. The fly ash leachate chemistry was compared with the groundwater taken directly from the monitoring well installed in one of the power stations. The anthracite coals contain illite, pyrophyllite and kaolinite whereas kaolinite is the representative clay mineral for the sub-bituminous coals. Anthracite coals were higher in Si, Al and K than the sub-bituminous coals, reflecting higher mineral matter contents in the anthracite coals. Mullite and quartz are the main mineral phases for two different types of the fly ashes, with some iron oxides. The chemical compositions of the anthracite and sub-bituminous fly ashes are comparable with each other, except for extraordinary high concentrations of Cr for one anthracite fly ash. Most of the trace elements in the ash were enriched in the finer fraction, indicating surface associations. Although, some elements including Na, K, Ca and Cu were released rapidly in the initial stage of leaching, measurable amounts of metals were still detectable in the fly ash leachate treated several times with distilled water. Such leaching behaviour indicates slow and long-term leaching of elements associated with the glass fractions of the ash particle. This was confirmed by leaching of weathered fly ash, which had been disposed of for several years. Comparison of the ash leachate, treated with 0.1N-HCl, fly ash slurry in the ash pond and the groundwater indicate the influence of the ash leachate from the ash disposal mound on the groundwater composition.     

Partitioning of elements in a entrained flow IGCC plant: Influence of selected operational conditions

The partitioning of trace elements and the influence of the feed conditions (50:50 coal/pet-coke feed blend and limestone addition) was investigated in this study. To this end feed fuel, fly ash and slag samples were collected under different operational conditions at the 335 MW Puertollano IGCC power plant (Spain) and subsequently analysed. The partitioning of elements in this IGCC plant may be summarised as follows: (a) high volatile elements (70->99% in gas phase): Hg, Br, I, Cl and S; (b) moderately volatile elements (up to 40% in gas phase and ?60% in fly ash): As, Sb, Se, B, F, Cd, Tl, Zn and Sn; (c) elements with high condensation potential: (>90% in fly ash): Pb, Ge, Ga and Bi; (d) elements enriched similarly in fly ash and slag 30-60% in fly ash: Cu, W, (P), Mo, Ni and Na; and (e) low volatile elements (>70% in slag): Cs, Rb, Co, K, Cr, V, Nb, Be, Hf, Ta, Fe, U, Ti, Al, Si, Y, Sr, Th, Zr, Mg, Ba, Mn, REEs, Ca and Li. The volatility of As, Sb, and Tl and the slagging of S, B, Cl, Cd and low volatile elements are highly influenced by the fuel geochemistry and limestone dosages, respectively.     

Fine particle and trace element emissions from an anthracite coal-fired power plant equipped with a bag-house in China

Fine particle and trace element emissions from energy production are associated with significant adverse human health effects. In this investigation, the fine particles and trace elements emitted from the combustion of pulverized anthracite coal at a 220 MW power plant were determined experimentally in the size range from 30 nm to 10 μm with 12 channels. The particulate size distributions and morphological characteristics before and after the bag-house were evaluated. The uncontrolled and controlled emission factors of particles are compared with the calculated values from the US Environment Protection Agency, AP-42. Size-classified relative enrichment factors of As, Hg, Se, Cd, Cr, Cu, Al, V, Zn, Mn, Fe were obtained. Relative distributions of trace elements between bottom ash, fly ash and flue gas are determined by mass balance method. The bag-house collection efficiencies of particles and trace elements in the particulate phase are obtained. Finally, the controlled and uncontrolled emission factors of elements of different particulate size fractions are obtained, which will provide useful information for PM_2.5 and PM₁₀ emission inventory development, toxic and hazardous pollutant emission estimates and emission standards established for metal-based pollutants from a pulverized coal-fired boiler.     

燃煤电厂脱硫粉煤灰单颗粒研究及元素组成

研究电厂脱硫粉煤灰以粒径在3～45μm的颗粒为主,数量占80%以上,并多是表面光滑的球形微珠,主要的矿物成分是莫来石和石英,它的排放因子达到了2.45 kg/t。脱硫粉煤灰的元素组成选取了Mn、Zn、Cr、Cu、Pb、Ni、Cd七种元素,其中Mn在脱硫粉煤灰中的含量最高,但Mn元素的相对富集因子则小于Zn元素的相对富集因子,说明元素含量高其相对富集因子不一定大,还需要考虑电厂燃烧的煤种中的元素含量,从而来确定元素的富集行为。     

Ash formation during pulverized coal combustion : 1: Aerodynamic influences

The elemental composition of pulverized fuel boiler deposits often differs markedly from that of the corresponding fly ash and coal ash. Evidence is given here to support the hypothesis that such chemical segregation could be induced by competition between aerodynamic drag and inertial forces on a particle in a curved streamline; this increases the probability of impacting the boiler walls for large particles of high density, leading to preferential deposition. A conventional air classifier was used to separate mono-sized samples of pulverized coal and char particles into aerodynamically different fractions, and to prepare vitrinite-char and inertinite-char concentrates. The relevance of such aerodynamic segregation is considered by comparing the enrichment (or depletion) of non-volatile elements in boiler ashes with that in ashes derived from air-classified char fractions. Common trends, particularly for iron (the major fluxing element) have been identified (i) between the highest density fractions and furnace deposits, and (ii) between the lower density fractions and cyclone ash.     

The composition of size-fractionated pulverised coal and the trace element associations

Major and trace element analyses have been performed on size fractions of a pulverised coal from Eggborough Power Station (UK). Minerals are concentrated in the fractions less than 10 μm in size and there is relative enrichment of pyrite in the fractions greater than 50 μm. Because of the compositional variation with size it is possible to proportion statistically the elements between, in this case, organic matter, silicates and pyrite. Germanium, Br and V are dominantly organic associated and Cr, Cu, Ni, Zn, Sr, Ba and Pb are also present in the organic matter, although concentrations are lower than in other fractions of the coal. These elements are either in the organic structures or contained within pore fluids. Chromium, Ga, Rb, Sr, Y, Zr, Nb, Ba, La, Ce, Sm, Th and U are dominantly associated with the silicate fraction, as are V, Ni and Zn, but other coal fractions contribute more to the total coal composition. Concentrated in pyrite are Mo, Se, As, Pb, Sb, and to a lesser extent Ni, Cu and Zn in that these elements are sufficiently concentrated in other fractions that pyrite is not the major location in the coal. Validation for the method is achieved by summing element concentrations in the three fractions and comparing with the bulk composition. Previous calculations on a related coal have been extended and close agreement observed for the composition of the three fractions. The calculated values for the fractions apply specifically to one coalfield, although some of the values may have more general application.     

Heavy metal concentrations in bottom ash and fly ash fractions from a large-sized (246 MW) fluidized bed boiler with respect to their Finnish forest fertilizer limit values

The total and size fractionated concentrations of As, Cd, Cr, Cu, Ni, Pb and Zn in bottom ash and two fly ash fractions from a large-sized (246 MW) fluidized bed boiler were compared to Finnish statutory limit values for forest fertilizers, which came into force in March 2007. Fly ashes were sampled from the different fields (i.e. electrodes) of the electrostatic precipitator (ESP) unit treating the stack gases. The bottom ash and the fly ash from the first ESP field are suitable for use a forest fertilizer. Due to the elevated As concentration (40 mg/kg; d.w.), which exceeded its Finnish limit value of 30 mg/kg (d.w.), the fly ash from the second ESP field is not suitable as a forest fertilizer alone. The results of ash sieving indicated that an As concentration of 40 mg/kg (d.w.) for particle size less than 0.125 mm for fly ash 2 from the second ESP electrode field exceeded the As limit value of 30 mg/kg (d.w.). In addition, a Pb concentration of 170 mg/kg (d.w.) for fly ash 1 from the first ESP electrode field for particle size 0.5-2.0 mm exceeded the Pb limit value of 150 mg/kg (d.w.). These two specific fractions are therefore not suitable for used as a forest fertilizer alone.     

Colour measurement as a proxy method for estimation of changes in phase and chemical composition of fly ash formed by combustion of coal

Influence of technology on colour changes of fly ashes was studied in relationships with their chemical and phase composition. Dry bottom boilers at the Detmarovice Power Plant (the Czech Republic) were selected for this study. Combustion tests were performed using mixture of coal and mineral oil residues at the minimum and maximum output of the power plant. Fly ashes for chemical analysis, phase analysis and colour measurements were sampled from the four sections of electrostatic fly ash precipitator. Colour parameters indicate relationships with concentrations of elements which are preferentially bound in silicate matrix. The maximum output of power plant increases the concentration of glass which has decisive influence on values of colour parameters. The changes of colour parameters can indicate the conditions of the technological process. Relationships between colour and constituents of the fly ash are expressed by CIE Lab colour parameters.     

Heavy metal content of bottom ashes from a fuel oil power plant and oil refinery in Cuba

Fly and bottom ashes from fuel oil power plants and oil refineries may contain hazardous trace elements, such as heavy metals, which have a negative impact on the environment with time due to potential leaching through acid rains and into groundwaters. This study provides levels of As, Cr, Cu, Hg, Mn, Ni, Pb, Ti, V and Zn of bottom ashes from a thermal power plant and an oil refinery placed in Cienfuegos Bay, Cuba. Trace elements were measured using X-ray fluorescence (XRF) with a SPECTOR X-LAB PRO 2000 system. High contents of Cr, Ni, Pb, Ti, V and Zn were found in the ashes, with values significantly higher than those reported in literature. According to Cuban regulations these ashes are classified as hazardous waste. For this reason we discuss some management alternatives.This study represents the first report of heavy metals in bottom ashes from power plants and oil refineries in Cuba.     

Evidence for mineral matter forms in coal liquefaction extracts

High- and low-temperature ashes from feed coal, coal extract solution and filter cake from a two-stage coal liquefaction process have been studied by X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive X-ray fluorescence (SEM/EDX). Hydrocracking experiments using alumina support only, in place of the active Ni/Mo catalyst on alumina, were also carried out, with trace metal analysis of the coal extract solution feed and hydrocracked extracts using atomic absorption and emission spectroscopy. The major mineral transformations occurring were of pyrite to pyrrhotite and the fixation of organic sulphur by calcium carbonate. Mineral particles were not observed in the coal extract solution ashes, even under high magnification, and the study indicated that size alone was not a determining factor as to whether a coal mineral was to be found in a coal-derived liquid. None of the trace metals was deposited on the alumina support under hydrocracking conditions, in marked contrast to the results obtained with the normal Ni/Mo catalyst. These results lead to the conclusion that for the deposition of trace elements to occur a reaction must take place and hence the trace elements must be chemically bound in some form.