Incorporating empirical knowledge into data-driven variable selection for quantitative analysis of coal ash content by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy(LIBS)has become a widely used atomic spectroscopic technique for rapid coal analysis.However,the vast amount of spectral information in LIBS contains signal uncertainty,which can affect its quantification performance.In this work,we propose a hybrid variable selection method to improve the performance of LIBS quantification.Important variables are first identified using Pearson's correlation coefficient,mutual information,least absolute shrinkage and selection operator(LASSO)and random forest,and then filtered and combined with empirical variables related to fingerprint elements of coal ash content.Subsequently,these variables are fed into a partial least squares regression(PLSR).Additionally,in some models,certain variables unrelated to ash content are removed manually to study the impact of variable deselection on model performance.The proposed hybrid strategy was tested on three LIBS datasets for quantitative analysis of coal ash content and compared with the corresponding data-driven baseline method.It is significantly better than the variable selection only method based on empirical knowledge and in most cases outperforms the baseline method.The results showed that on all three datasets the hybrid strategy for variable selection combining empirical knowledge and data-driven algorithms achieved the lowest root mean square error of prediction(RMSEP)values of 1.605,3.478 and 1.647,respectively,which were significantly lower than those obtained from multiple linear regression using only 12 empirical variables,which are 1.959,3.718 and 2.181,respectively.The LASSO-PLSR model with empirical support and 20 selected variables exhibited a significantly improved performance after variable deselection,with RMSEP values dropping from 1.635,3.962 and 1.647 to 1.483,3.086 and 1.567,respectively.Such results demonstrate that using empirical knowledge as a support for datadriven variable selection can be a viable approach to improve the accuracy and reliability of LIBS quantification.

Recovering germanium from coal ash by chlorination with ammonium chloride

A new process of enriching germanium from coal ash was developed. The processinvolves in mixing the coal ash and ammonium chloride and then roasting the mixture to producegermanium chloride that is then absorbed by dilute hydrochloric acid and hydrolyzed to germaniumoxide. The germanium recovery reached to 80.2% at the optimum condition: mass ratio of NH_4Cl/coalash is 0.15, roasting temperature 400℃ and roasting time 90 min.

Valency Study of Vanadium in Stone Coal Ash of Jiangxi Province

Vanadium-bearing stone coal is a new vanadium resource; recovery of V2O5 from the coal has been investigated. It has been found that a satisfactory extraction of V2O5 depends on both the oxidation of V and its reaction with sodium salt. V in the coal ash of Yushan mainly exists in two oxidation states; 98% V (Ⅲ) and 2% V(Ⅳ). The distribution of valency of V shows that organic matter determines V valency at low temperatures, at about 470℃ , V(Ⅲ) is completely oxidized to V (Ⅳ); above 500 ℃, the temperature is the most important factor for the oxidation of V At higher temperatures no more V is oxidized to V(Ⅴ); an equilibrium is established after 92% of V is oxidized to V(Ⅴ). The roles of NaCl in the recovery of V2O5 from the coal ash were discussed. The best conditions for roasting are temperature 750-800℃ for 1 h. under the oxidation-chlorination atmosphere. When the ore : NaCl = 100 :10 by weight, ηroast reaches 85.5%. According to the results, a flowsheet for V2O5 extraction from coal ash has been proposed.

Pozzolanic Reaction Kinetics of Coal Ashes

The pozzolanic reactivity was determined by the hydration kinetics of pozzolanic reaction based on the fact that the hydration products of active SiO2 and Al2O3 with lime were soluble in dilute hydrochloric acid. The results show that the pozzolanic reaction of active SiO2 and Al2O3 of coal ashes follows apparent first-order kinetics. The reaction rate constant of FBC ashes is greater than that of PC ashes, while the activation energy of the former is lower than that of the latter. It is confirmed that the pozzolanic activity of fluidized bed combustion（FBC） ashes is significantly higher than that of PC ashes, and the reaction barrier of the former is lower than that of the latter, because the microstructures of FBC ashes, such as mineralogical composition, morphology and polymerization degree of [SiO4] and [AlO6] are more favorable to the pozzolanic activity development than those of PC ashes.

Assessment of the Radiological Impact on the Environment near a Storage Site of Coal Ashes in a Thermal Power Plant

The radiological impact of coal ashes, with enhanced natural radioactivity in the storage site, is due to the presence of naturally occurring radionuclides. Some of these radionuclides have a radioactive period of several million years and will, therefore, have time to migrate to the soil, atmospheric air, surface water, and groundwater. This impact depends mainly on the activity of these coal ashes, the duration of exposure to such waste, transfers to the air, and the leaching phenomenon by rainwater. In this study, and so as to assess the radiological impact of coal ashes of the storage site of the JLEC-Morocco thermal power plant on environment, some analyses are performed by alpha dosimetry and a digital dosimeter on samples of coal ashes, soil, atmospheric air, surface water and groundwater belonging to a perimeter of 10 km around that site. The obtained results show that, within the studied area, the radiological impact on the soil of the coal ashes of the storage site is insignificant even though the concentrations of radon in the near vicinity (1 to 2 km) are moderately important, and remain below 200 Bq/m3. In the atmospheric air, this impact remains medium for the neighborhoods of the storage site (2 to 3 km) with radon activities superior to 10 Bq/m3. These results also show that there may be a water contamination of wells located at the storage site without any transfer of radioactivity into the groundwater of the area studied where the concentrations of radon are less than 11.1 Bq/l.

Characteristics of Coal Ashes in Yanzhou Mining District and Distribution of Trace Elements in Them

In the process of combustion of coal organic and inorganic materials in it will undergo a complex variation. Part of them will become volatiles and, together with coal smoke, enter into atmosphere, some will remain in micro-particulates such as ash and dust and find their way into atmosphere in the form of solid particles, and the rest will be retained in ash and slag. Coal ashes are the residues of organic and inorganic substances in coal left after coal combustion and the composition of coal ashes is dependent on that of minerals and organic matter in coal. This paper deals with the chemical composition of coal ashes, the distribution of trace elements in them and their petrological characteristics, and also studies the relationship between the yield of coal ashes and the distribution of trace elements. In addition, a preliminary study is also undertaken on the factors that affect the chemical composition of coal ashes. As viewed from the analyses of coal ash samples collected from the Yanzhou mining district, it can be seen clearly that coal ashes from the region studied are composed chiefly of crystalline materials, glassy materials and uncombusted organic matter and the major chemical compositions are SiO 2, Al 2O 3, Fe 2O 3, and CaO, as well as minor amounts of SO 3, P 2O 5, Na 2O, K 2O and TiO 2. During the combustion of coal, its trace elements will be redistributed and most of them are enriched in coal ashes. At the same time, the concentrations of the trace elements in flying ash are much higher than those of bottom ash, i.e., with decreasing particle-size of coal ashes their concentrations will become higher and higher. So the contents of trace elements are negatively proportional to the particle-size of coal ashes. There has been found a positive correlation between the trace elements Th, V, Zn, Cu and Pb and the yield of coal ashes while a negative correlation between Cl and the yield of coal ashes.

Simultaneous Measurements of Coal Ash Composition by Laser-induced Breakdown Spectroscopy in Different Optical Collection

针对燃煤组分分布不均匀的特性，研究不同收光模式对激光诱导击穿光谱技术同步测量灰成分的影响。选用具有不同灰成分含量梯度的燃煤样品作为检测对象，对比分析同向收光和侧向收光下灰成分组成元素谱线信号探测的强度和稳定性及SiO2、Al2O3、Fe2O3、CaO、MgO和TiO2含量定量分析的精确度。研究结果表明，相同实验条件下同向收光模式的光谱信号稳定性和定量分析精确度更好，检验样品中各灰成分的预测值和参考值之间的拟合度均在0．986以上。而侧向收光模式下探测到的光谱信号强度更强，光谱探测下限可以达到190nm。

The Mineral Transformation of Huainan Coal Ashes in Reducing Atmospheres

By using the advanced instrumentation of a Computer Controlled Scanning Electron Microscope (CCSEM), X-ray diffraction (XRD) and X-ray fluorescence (XRF), the ash composition and the mineral components of six typical Huainan coals of different origins were studied. The transformation of mineral matter at high temperatures was tracked by XRD in reducing conditions. The quartz phase decreased sharply and the anorthite content tended to increase at first and then decreased with increasing temperatures. The formed mullite phase reached a maximum at 1250 ℃ but showed a tendency of slow decline when the temperature was over 1250 ℃ . The mullite formed in the heating process was the main reason of the high ash melting temperature of Huainan coals. Differences in peak intensity of mullite and anorthite reflected differences in phase concentration of the quenched slag fractions, which contributed to the differences in ash melting temperatures. The differences in the location of an amorphous hump maximum indicated differences of glass types which may affect ash melting temperatures. For Huainan coal samples with relatively high ash melting tempera- tures, the intensity of the diffraction lines for mullite under reducing condition is high while for the samples with rela- tively low ash melting temperature the intensity for anorthite is high.

Study on Inorganic Flocculant Prepared from Powdered Coal Ashes

The feasibility of preparing flocculant from powdered coal ashes is studied in detail. By means of orthogonal tests, the influence of various factors, such as the activation temperature, the activation time, the ratio of CaO to Al2O3, the hydrochloric acid concentration, the reaction time and the reaction temperature, on preparation is investigated, and the hest operating condition is determined.

Research on municipal solid waste composting with coal ash

Considering the fact that there is much coal ash in the municipal solid waste (MSW) in some cities of China, the feasibility of composting in this situation was studied and the effect of content of the coal ash on the composting process and some basic relative technological parameters were investigated. The values of the moisture, the total organic matter, the content of coal ash, the C/N ratio and the ventilation were suggested to be 50%60%, 40%60%, 40%60%, (25∶1)(35∶1) and 0.050.20 m 3/(min·m 3), respectively.

Slagging characteristics of molten coal ash on silicon-aluminum combustion liners of boiler

In order to study the slagging characteristics of boiler combustion liners during pulverized coal stream combustion, the slag samples on the surface of combustion liner were investigated by X-ray diffractometry, scan electron microscopy and energy dispersive X-ray analysis, and the transformation characteristics of the compositions and crystal phases were studied. The results show that the size of slag granules decreases as the slagging temperature increases; the crystallinity of coal ashⅠreduces to about 48.6% when the temperature is increased up to 1 350 ℃, and that of the coal ash Ⅱ reduces to about 65% when the temperature is increased up to 1 500 ℃; the encroachment of molten coal ash to the combustion liner is strengthened. At the same time, the diffusion and the segregation of the compositions in combustion liners have selectivity, which is in favor of enhancing the content of crystal phases, weakening the conglutination among molten slag compositions and combustion liner, and avoiding yielding big clinkers. But the diffusion of the compositions in combustion liners increases the porosity and decreases the mechanical intensity of combustion liner, and makes the slag encroachment to the liner become more serious.

Utilization of Coal Ash as a Barrier Material for Radioactive Waste Disposal

About 10% of total electricity (386 MkW) was generated by nuclear power plants in the world (2014) and about 58,400 tons of uranium has been mined in uranium mines annually. A plenty of radioactive waste material is produced from uranium mines and nuclear power plants. The wastes must be disposed or stored safely for a long term. Because if they leak and/or move from disposal or storage sites due to air/groundwater flow, then a serious environmental pollution can occur. Hence, multi-layer system has been proposed and employed in order to seal off these radioactive waste materials from biosphere. Basically, bentonite is now used for establishing one of absorbing and sealing layers in this system. However, the amount of high quality bentonite is very limited and in some cases it is hard to be obtained. On the other hand, a great deal of refuse from coal burning plants is produced every year and the amount of it is expected to be higher each year especially in developing countries. More than half of coal ash is utilized and the remaining is disposed at the disposal sites. However, the life of the disposal site is limited and it is difficult to find a new disposal site. It is requested that the percentage of the utilization of the coal ash be increased in every field. From the above two points of view, a fly ash-based barrier system is considered in this research and this paper discusses the applicability of fly ash as a content of barrier material. Based on the results of a series of laboratory tests, it can be concluded that fly ash has a potential for use in the buffer material as the bentonite is substituted.

STUDY ON THE FUNCTION OF REINFORCED RUBBER OF MODIFIED POWDERED COAL ASH

The powdered coal ash (PCA) was classified, then the ash particle (- 45μm) was modified by a surface active agent and obtained modified powder coal ash (MPCA). The character of the MPC was investigated, when it was used as a new type reinforced filler of rubber.The results show that MPCA can replace or party replace carbon black or silica as reinforced fillers of rubbers.

Experimental study on the activation of coal gasification fly ash from industrial CFB gasifiers

Coal gasification fly ash(CGFA)is an industrial solid waste from the coal circulating fluidized bed(CFB)gasification process,and it needs to be effectively disposed to achieve sustainable development of the environment.To realize the application of CGFA as a precursor of porous carbon materials,the physicochemical properties of three kinds of CGFA from industrial CFB gasifiers are analyzed.Then,the activation potential of CGFA is acquired via steam activation experiments in a tube furnace reactor.Finally,the fluidization activation technology of CGFA is practiced in a bench-scale CFB test rig,and its advantages are highlighted.The results show that CGFA is characterized by a high carbon content in the range of 54.06%–74.09%,an ultrafine particle size(d50:16.3–26.1 μm),and a relatively developed pore structure(specific surface area SSA:139.29–551.97 m^(2)·g^(-1)).The proportion of micropores in CGFA increases gradually with the coal rank.Steam activation experiments show that the pore development of CGFA mainly includes three stages:initial pore development,dynamic equilibrium between micropores and mesopores and pore collapse.The SSA of lignite fly ash(LFA),subbituminous fly ash(SBFA)and anthracite fly ash(AFA)is maximally increased by 105%,13%and 72%after steam activation;the order of the largest carbon reaction rate and decomposition ratio of steam among the three kinds of CGFA is SBFA>LFA>AFA.As the ratio of oxygen to carbon during the fluidization activation of LFA is from 0.09 to 0.19,the carbon conversion ratio increases from 14.4%to 26.8%and the cold gas efficiency increases from 6.8%to 10.2%.The SSA of LFA increases by up to 53.9%during the fluidization activation process,which is mainly due to the mesoporous development.Relative to steam activation in a tube furnace reactor,fluidization activation takes an extremely short time(seconds)to achieve the same activation effect.It is expected to further improve the activation effect of LFA by regulating the carbon conversion ratio range of 27%–35%to create pores in the initial development stage.

Corrosion Behavior of the Ni-Cr-Fe Base Superalloy GH984G in a Synthetic Coal Ash and Flue Gas Environment

The corrosion behavior of the new Ni-Cr-Fe base superalloy GH984G in a synthetic coal ash and flue gas environments was studied at 700 ℃. The results showed that the corrosion rate was slow during the initial corrosion stage, then followed by a stage of faster mass loss. During the corrosion test, the scale trended to spall slightly, resulting in the formation of corrosion pits on the sample surfaces. The main corrosion products were identified as NiFeCrO4 and a small amount of Cr2O3. The scale microstructure involved the presence of three corrosion layers. The outer layer contained Cr, Ni, Fe, O and a small amount of S. Many micro-cracks were detected in the Cr-rich intermediate oxide layer. The inner corrosion layer was thin and rich in S. Internal sulfidation and internal oxidation occurred in the substrate. Because of its relatively high Cr content, the GH984G superalloy exhibited a good corrosion resistance under the test conditions.

The application of molecular simulation in ash chemistry of coal

One of the crucial issues in modern ash chemistry is the realization of efficient and clean coal conversion.Industrially,large-scale coal gasification technology is well known as the foundation to improve the atom economy.In practice,the coal ash fusibility is a critical factor to determine steady operation standards of the gasifier,which is also the significant criterion to coal species selection for gasification.Since coal behaviors are resultant from various evolutions in different scales,the multi-scale understanding of the ash chemistry is of significance to guide the fusibility adjustment for coal gasification.Considering important roles of molecular simulation in exploring ash chemistry,this paper reviews the recent studies and developments on modeling of molecular systems for fusibility related ash chemistry for the first time.The discussions are emphasized on those performed by quantum mechanics and molecular mechanics,the two major simulation methods for microscopic systems,which may provide various insights into fusibility mechanism.This review article is expected to present comprehensive information for recent molecular simulations of coal chemistry so that new clues to find strategies controlling the ash fusion behavior can be obtained.