八钢煤粉灰分影响燃烧性能的试验研究

在高炉喷吹煤粉的生产中 ,煤粉灰分是影响煤粉燃烧率主要因素之一。目前 ,八钢高炉喷煤比虽已达到15 0 kg/t的喷煤水平 ,但由于煤粉灰份含量一直偏高 (Aadmax=16 % ) ,这对煤粉的充分燃烧 ,进一步提高喷煤量有较大的影响。通过对煤粉灰分的试验研究 ,定量分析了煤粉灰分对煤粉返回火焰长度及粉尘云最低着火温度的影响 ,从而找出煤粉灰份的经济控制点。

BOND PERFORMANCE EXPERIMENT FOR FLY ASH CONCRETE AND STEEL BAR

The impact of fly ash content on bond performance of steel bars and their surrounding concrete is studied by means of sticking strain gauges on steel bars. The average bond stress-slip curves, the steel strain-anchor location curves, and the bond stress-anchor position curves of the pullout specimens with various fly ash contents are obtained. Results indicate that the bond performance of concrete and steel bars can be improved and the distribution of steel strain along the anchorage length tends to be more uniform by adding fly ash in concrete specimens, and both ultimate bond stress and ultimate slip deformation increase the most when 20% of specimens′ content is fly ash.

Dry coal fly ash cleaning using rotary triboelectrostatic separator

More than 80 million metric tons of fly ash is produced annually in the U.S. as coal combustion by-product. Coal fly ash can be converted to value-added products if unburned carbon is reduced to less than 2.5%. However, most of fly ash is currently landfilled as waste due to lack of efficient purification technologies to separate unburned carbon from fly ash. A rotary triboelectrostatic separator has been developed and patented recently at the University of Kentucky with unique features. Several fly ash samples have been used to understand the effects of major process parameters on the separation performance. The results show that compared to existing triboelectrostatic separators, the rotary triboelectrostatic separator has significant advantages in particle charging efficiency, solids throughput, separation efficiency, applicable particle size range.

Heavy metals distribution in fly ash from gangue power plant

To make assessment on its environmental security, fly ash samples were collected from the gangue power plant. Total content of heavy metals in sieved fly ash were analytically determined. We also carried out Tessier extractive experiments to check the chemical species of heavy metals. Experiment results show that the content of Cu, Zn, Pb and Cd ascend when particle size is smaller. Cu, Zn, Pb and Cd obviously enrich in particulate fly ash. The chemical species of heavy metal distribution ranking sequence generally is residual〉organic combinative〉Fe-Mn oxide combinative〉carbonate combinative〉ion-exchangeable. Lead＇s amiable-move species were high in proportion, amounted to 35%. Total content of Cadmium is at low level, but its ion-exchangeable species is relatively high in proportion. Nickel and zinc is mainly distributed in residue. Cu is mainly distributed in residue and organic combinative form. The content of manganese is relatively high in fly ash, and the carbonate combinative iron-manganese oxide combinative species are main chemical form. Cr is mainly distributed in residue, and its other chemical species are at low level. Compared with the soil background value of study area and Shandong Province, the content of Cu, Ni, Zn, Mn and Cr in fly ash of gangue power plant is lower. While contents of Pb and Cd were higher than background value, and amiable-move species is relatively high in proportion. They are more apt to cause heavy metal pollution.

Kinetics of decomposition of mullite and corundum in coal fly ash under highly alkaline condition

Decomposition kinetics of mullite and corundum in coal fly ash with highly alkaline solution was studied.The effects of the reaction temperature and reaction time on decomposition rates of mullite and corundum and alumina extraction efficiency were investigated.The results show that increasing reaction temperature and reaction time increases the decomposition rates of mullite and corundum and alumina extraction efficiency,with the decomposition temperature of mullite lower than that of corundum.After 90 min reaction at 220℃,more than 100 g alumina was extracted when recycling 1 L of alkaline solution.The decomposition processes of mullite and corundum corresponded with the shrinking unreacted core model,and the reaction rate was under chemical reaction control,with the activation energies of mullite and corundum being 67.46 and 161.82 kJ/mol,respectively.

Enrichment of carbon recovery of high ash coal fines using air fluidized vibratory deck separator

Coal is primarily beneficiated by wet gravity methods. The wet processing of coal is an efficient practice. However, it introduces the moisture in the range of 6%-15%, depending upon the size of coal which is as detrimental as ash content to the heating value of coal. Dry beneficiation of coal fines was carried out using an air fluidized vibrating table in which the coal particles get separated from the heavier mineral particles as a result of horizontal and vertical stratification. Two level factorial design matrix was used to optimize and assess the interactive effects of the operational parameters of a pneumatic table viz. deck eccentric, side tilt and air flow rate on the clean coal yield and its ash content. Double stage processing was found to be more effective for reducing the ash content of the clean coal. Initial stage of processing at a higher ash level generates a reject of high ash with low combustibles. Cleaning of the rougher concentrate at 34%-35% ash level shows significant improvement in the organic efficiency （88.6%） and useful heat value of clean coal （15690 kJ/kg）. The performance of air fluidized vibrating deck was measured by Ep value which is 0.18.

Electrical properties of fly ash and its decarbonization by electrostatic separation

The basic principle of fly ash triboelectrification is analysed. The mineral electrical index and test method are introduced. The electric difference of different mineral composition of fly ash is discussed by analysis of chemical and mineral composition of fly ash in Xinwen power plant. The dielectric constant and charge-mass ratio of carbon and ash of fly ash are tested. Combined with the experimental study on rotary triboelectrostatic separation, the charged characteristic of fly ash particles with different size is gained. The results show that the dielectric constant of fly ash with different grain size decreased with the decrease of particle size, which lead to the poor electrical conductivity, Thus it can be seen that par- ticle size plays a leading role in conductivity, The charge of carbon and ash with each size increased with the decreased of particle size; and the charge-mass ratio between carbon and ash with the same size lar- ger with the decrease of size, which indicated that the finer particle size, the more favorable for triboelec- trification separation. In the same conditions, the best decarburization effect is realized when the particle size ranges from 0.038 to 0.074 ram, whose decarbonization rate and efficiency index reached 38.93% and 120.83% respectively.

Improved Sorting Scheme of Microstructure of Fly Ash

Aiming at the problem of the existing sorting for microstructure of fly ash, an improved scheme was put forward in this paper. First, fly ash particles are divided into four groups as low calcium, iron, high calcium and char particle according to the substance components of fly ash. Then fly ash particles are divided into 14 sub groups, for example: cenospheres, plerospheres, solid spheres, porous char and dense char based on their chemical composition, shape and the characteristics of inner structure of fly ash. It has a distinct difference in granule configuration, inner structure and substance components. Some disadvantages of the existing scheme such as unilateralism and imprecision have been overcome in the advanced schemes.

Consolidation analysis of composite foundation with partially penetrated cement fly-ash gravel(CFG) piles under changing permeable boundary conditions

Based on the double-layered foundation theory, the composite ground with partially penetrated cement fly-ash gravel(CFG) piles was regarded as a double-layered foundation including the surface reinforced area and the underlying untreated stratum. Due to the changing permeability property of CFG piles, the whole consolidation process of the composite ground with CFG piles was divided into two stages, i.e., the early stage(permeable CFG pile bodies) and the later stage(impermeable pile bodies). Then, the consolidation equation of the composite foundation with CFG piles was established by using the Terzaghi one-dimensional consolidation theory. Consequently, the unified formula to calculate the excess pore water pressure was derived with the specific solutions for the consolidation degree of composite ground, reinforced area and underlying stratum under instant load obtained respectively. Finally, combined with a numerical example, influencing rules by main factors(including the replacement rate m, the treatment depth h1, the permeability coefficient Ks1, Kv2 and compression modulus Es1, Es2 of reinforced area and underlying stratum) on the consolidation property of composite ground with CFG piles were discussed in detail. The result shows that the consolidation velocity of underlying stratum is slower than that of the reinforced area. However, the consolidation velocity of underlying stratum is slow at first then fast as a result of the transferring of effective stress to the underlying stratum during the dissipating process of excess pore water pressure.

Effect of different milling processes on the mineral distribution in a coal powder

Coal samples obtained from Wanbei(WB),Pingxiang(PX),Liupanshui(LP),and Datong(DT) mines were pulverized,using either a vibration mill or a ball mill,to different degrees of fineness.The effect of the different grinding methods on the mineral distribution within the pulverized coal was investigated by using proximate analysis,particle size analysis,and float-sink tests.The results show that the ash content in WB,PX,and DT coal increases with increasing particle size overall,while the ash content of the LP coal remain almost the same within each size fraction.In that case the ash in each fraction is similar to that of the raw coal.The ash versus size distributions for the same coal sample milled with the same grinding method to different degrees of fineness are similar.The ash versus size distribution of the coal powder with a 15% screen residue that was prepared with the vibration mill is different from the distribution of a similar sample prepared with a ball mill.The curves also vary between different coal samples.The grinding method has a great influence on the distribution of minerals across the various particle sizes.The float-sink tests and the laser particle size analysis results on PX and DT coal samples show that fines dominate the higher density fractions although the large +2.0 g/cm3 fraction was dominated by coarse particles.The size distribution of the low density fraction and +2.0 g/cm3 density fraction is bimodal.The size distribution of the intermediate density fraction is multimodal.

Separating Performance of Fly Ash in Water Media

The stress state and floating sinking reqularity of various particles in fly ash in water were analyzed. The formula for calculating the floating sinking rate was given. And the formula for calculating the magnetic force needed to separate magnetic beads from magnetic separator was also obtained.

M■ssbauer spectroscopic studies the characterization of three China coal and the corresponding fly-ashes and bottom ashes

Three fresh China coals （lignitie, bituminite and anthracite） from different geological origin and the corresponding fly and bottom ashes were studied by room temperature（RT） Mossbauer spectroscopy（MS）. The iron-bearing minerals were characterized to be mainly pyrite in all coal samples by the hyperfine parameters.Suphate（FeSO4·nH2O） was found in bituminite and anthracite coal.The MSssbauer spectra of the fly and bottom ashes as a result of pulverised coal combustion（PCC） in Xiaolongtan,Shuicheng and Luohuang Power Plants are comprised of superimposed sextets and doulets of oxides includes maghemite（γ-Fe2O3）, magnitite（Fe3O4）, haematite（α-Fe2O3）, magnesioferite （MgFe2O4）, Fe^3＋/Fe^2＋ -mullite, Fe^3＋ -glass silicate and metallic iron. The studies also show that iron-bearing minerals in coals are largely dependant on geological regions and coal rank, the composition of the corresponding fly and bottom ashes will not only depend on the type and mineralogy of the feed coal but also on the local nature of combustion.

Kinetics Analysis on Mixing Calcination Process of Fly Ash and Ammonium Sulfate

The further development of the extraction of alumina that is produced in the calcination process of ammonium sulfate mixed with fly ash was limited because of the lack of systematic theoretical study. In order to aggrandize the research of the calcination process, the kinetics and reaction mechanism of the calcinations were studied. The result suggests that there are two stages in the calcination process, and the alumina extraction rate increases swiftly in the initial stage, but slows down increasing in the later stage. The apparent activation energy of the initial and later stages equals to 13.31 and 35.65 kJ·mol-1, respectively. In the initial stage, ammonium sulfate reacts directly with mullite in the fly ash to form ammonium aluminum sulfate, while in the later stage, aluminum sulfate is formed by the reaction between ammonium aluminum sulfate and ammonium sulfate.

COMPARATIVE RESEARCH ON THE CHARACTERISTICS OF THE FLYASH FROM COAL REFUSE-FIRED AND COAL-FIRED POWER PLANTS

The physical,chemical and mineral facies properties of the flyash from Xiezhuang Coal Refuse Fired Power Plant have been studied by means of naked eyes,microscope,chemical composition analysis and XRD analysis,and compared with that of the flyash from Taian Coal Fired Power Plant.The result shows that the flyash from coal refuse fired power plant is of better quality in making construction items,for being brighter in color,fine and high activity.Some ways of comprehensive utilization of the ash have been suggested in this paper.

Influence of Hydrothermal Pre-Treatment of Coal Fly on the Synthesis of Belite Phase

In this paper, the results of an extensive investigation of hydrothermal pre-treatment for synthesizing belite phase from reactive mixtures （CaO/SiO2 molar ratio of 2） consisting of one waste kinds （bottom ash-BA or fly ash-FA） from fluidised brown coal combustion in Slovakian power plant and CaO （analytical grade reagent） addition are summarized. Changes in structure and phase composition of hydrothermally synthesized belite precursors and subsequent calcinated products were compared with those of starting mixtures. Based on XRD diffraction patterns, the formation of the new profiles corresponding to CSH phases with low degree of ordering as belite precursors after hydrothermal treatment was confirmed. Calcination of hydrotermally treated products at 900℃ led to transformation of CSH phases to wollastonite, belite and gehlenite phase. Differences in phase composition of products before and after calcination depend upon waste quality and precursor＇s synthesis conditions. Bottom ash isn＇t suitable as raw material for synthesizing belite phase because of high CaO content fixed in anhydrite form （44.1%）. Coal fly ash with low CaO content in anhydrite form （4.2%） and its hydrothermal treatment in combination with subsequent heating offer opportunities for the utilization of coal fly ash as raw material for belite production.

STUDY ON THE SEPARATION AND UTILIZATION TECHNOLOGY OF MAGNETIC BEAD IN FLY ASH

On the basis of study on physical and chemical properties of magnetic bead (MB) in fly ash (FA), the paper gives out the separation methods of MB and results of three separating process. The result of comparative test in size, density, stability, magnetic material content, specific magnetic susceptibility (SMS), medium recovery oxidation resistance and wear resistance between MB and magnetic fines currently used in dense medium separation leads to that using MB recovered from fly ash is used as medium solids in coal cleaning in stead of magnetic fines not only have no influence upon taryests of separation, but can bring good economic and social benefits.

Adsorption of acid fuchsin onto LTA-type zeolite derived from fly ash

A facile strategy without organic template was developed for the conversion of fly ash to LTA-type zeolite(LTA-Z),which could be used as a good adsorbent for the removal of acid fuchsin(AF).XRD results indicated that the pure crystalline product was obtained with the structure of LTA-type zeolite.SEM investigations showed that the well-defined LTA-Z crystals exhibited uniform size with the same cubic shape.The maximum AF adsorption amount was observed at pH=5,slightly lower than pHPZC of LTA-Z.Higher temperature favored AF adsorption onto LTA-Z and it was an endothermic process.Furthermore,AF adsorption amount increased with initial AF concentration increasing and LTA-Z dosage decreasing.Surface sorption governed this process at the initial 120 min period,followed by the internal diffusion of AF molecules between porous sites.The Langmuir model was determined as the adsorption isothermal,suggesting that the monolayer coverage of AF on LTA-Z surface was involved.

A 3D numerical simulation of laser-induced incandescence of soot particles in coal combustion products

Laser-induced incandescence (LII) has received increasing attention as a potentially powerful technique for in-situ measuring of the volume fraction and primary size of soot particles in combustion systems. In this study, a 3D Monte Carlo simulation combined with a Mie equation was developed to analyze the influence of spectral absorption and scattering on the measured LII flux emitted by soot particles. This paper represents a first attempt to analyze soot measurement using the LII technique in coal combustion products. The combustion products of gases (CO2, N2), soot, and fly-ash particles, present between the location of laser-excited soot and the LII flux receiver. The simulation results indicated that an almost Beer-Lambert exponential decrease in LII flux occurred with an increase in the volume fraction of soot particles, while a nearly linear decrease occurred with an increase in the volume fraction of fly-ash particles. The results also showed that scattering effects of both soot and fly-ash particles on the LII flux could be neglected. Compared with the absorption of gases, a decrease of 20% of LII flux was observed with soot particles, and a decrease of 10% with fly-ash particles.