The dynamic release characteristics of Hg0 during low calorific value coal combustion were investigated in a combining laboratory-scale furnace coupled with atomic fluorescence spectroscopy. The results show that the sulfur has an inhibitory effect on the homogeneous oxidation of Hg0 in flue gas. The instant intensity of Hg0 release increases with increasing temperature while the amount of Hg0 release gradually decreases with increasing temperature. Compared with that under air, the instant intensity of Hg0 release under O2/CO2 atmosphere increases to some extent with a lower decreasing rate of Hg0 release peak. The release ratio of elemental mercury (Hg) from Yuwu (YW) and Qinxin (QX) coal increases while that from Yonghao (YH) coal decreases under O2/CO2 atmosphere. In the range of 800–1100°C, the release rate of Hg reaches more than 96% under the residence time of 50 s.

The thermodynamic properties of impurities in silicon-based solutions are the theoretical basis of silicon purification technology. These properties represent valuable information in regards to impurity removal for solar-grade silicon production by metallurgical methods. The thermodynamic properties of impurity components in silicon solutions obtained by both model calculations and experimental measurements are reviewed in detail in this paper with special focus on the infinite dilute activity coefficient and activity interaction coefficient of impurity components in binary Si-i and ternary Si-i-j systems. A positive or negative activity interaction coefficient value can be used to predict a mutually reinforcing or mutually restrictive relationship among impurity components during silicon purification. This review may provide workable guidance to researchers in selecting suitable refining systems and optimized refining conditions for silicon purification according to the thermodynamic properties of the impurity components therein; further, they may be used to establish a silicon solution thermodynamics database to support silicon purification technology.

The effects of the simultaneous injection of MgO and magnesite powder on the combustion of coals, properties of the primary slag, and softening-melting properties of the burden were investigated. There were four aspects to the results that we obtained. First, MgO showed catalytic activity for dehydrogenation and carboxyl group removal from coal; as a result, with increasing MgO, the combustion ratio and pyrolysis ratio of the coal investigated improved. Notably, when the content of MgO increased from 0% to 3.21%, the combustion ratio increased from 67.75% to 75.73%. Secondly, the MgO distribution in the slag sample was close to that in the standard slag after melting for 10 min. After 50 min, the difference in MgO content between the slag and standard slag samples was less than 1%. Thirdly, with an increase in the content of MgO, the short-slag feature of the slag was obvious, the viscosity fluctuated wildly, and the melting temperature increased significantly. It is proposed that the properties of the primary slag could be improved by decreasing the MgO content. Finally, with the increase in the MgO added to the burden, the softening-melting properties of the burden degraded. When the MgO content was 0.86%, ΔPmax was only 2.04 kpa, and S 59 kPa·°C. However, when the MgO content was 2.61%, ΔPmax was 20.00 kPa, and S 1349 kPa·°C. Therefore, the technology of MgO injection into tuyeres with pulverized coal was beneficial for blast furnace operation.

The continuous flow reactor was used to treat simulated ammonia nitrogen wastewater by inoculating the sludge after filtration and adding a suspended filler. Regulations of free ammonia (FA), free nitrous acid (FNA), and dissolved oxygen (DO) in the reactor were the key to achieving a successful start-up of the pilot scale nitrosation reactor. The results show that the enrichment of ammonium oxidizing bacteria (AOB) and the elimination of nitrite oxidizing bacteria (NOB) are achieved by adjusting the operational mode of high DO, low DO, FA, and FNA in the reactor operation. The nitrite production rate (NPR) in the reactor was 1.27 kg·(m3·d)-1 and the nitrogen accumulation rate (NAR) was stable at 98% at the end of the start-up period. qPCR was used to study the difference in the functional microorganisms (AOB, NOB) between the beginning and the end of the start-up period. The results show that the copy number of microbial AOB grew from 5.3×109 copies·mL-1 to 1.6×1011 copies·mL-1. The copy number of NOB decreased from 1.1×1010 copies·mL-1 to 1.2×109 copies·mL-1, because of the joint regulation of DO, FA, FNA to suppress NOB.

The use of a venturi tube to sustain the pipeline pressure in the dense-phase pneumatic conveying of pulverized coal system is promising for its application to the pressurized entrained-flow coal gasification process, in spite of the limited knowledge of the fundamentals of the gas-solid flow through the venturi tubes at high-pressure and dense-phase pneumatic transport conditions. In this paper, a series of experiments were carried out and the geometry parameters of the venturi tube, including the convergent angle, the throat diameter, the throat length and the diffuser angle were varied at constant flow conditions to evaluate their effect on the conveying properties and on the pressure reduction effects in the flow of gas-solid mixtures through the venturi tube. The optimum values or ranges of the above mentioned venturi geometrical parameters in the application of venturi tubes to dense-phase pneumatic conveying of pulverized coal are determined in this work. These values will provide a useful reference for the design of feeding systems in the pressurized entrained-flow coal gasification process. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

In the present study, the activities of components and formation enthalpies of binary Si-Al and Si-B solutions are calculated by a molecular interaction volume model (MIVM). Contributing to investigating deeply the removal of impurities B and Al from silicon solutions, the Wagner self-interaction parameters of B, Al in dilute silicon solutions at 1693-1873 K were tried by the use of the MIVM. The predicted activities and formation enthalpies were compared to the reported experiment data from the literature, which show that thermodynamics properties of binary silicon solutions can be accurately predicted and this model can provide effective verification and forecast for experiment.

The volatilization of the impurities (Zn,Sb,Mg,Mn,Cu and Sn),in binary Si-based solutions in vacuum refining of metallurgical grade Si,was mathematically formulated with molecular interaction volume model (MIVM),theoretically analyzed in thermodynamics and experimentally investigated.The separation coefficient,volatilization rate and gas-liquid equilibrium diagram of silicon-based binary alloy in vacuum distillation of Si were derived in terms of the pair interaction potential B and activities calculated with MIVM model.The calculated results show that the evaporation of impurity significantly depends on the distillation temperature and its activity.After most Sb,Zn and Mg impurities were removed from the molten silicon,the contents of Mn,Cu and Sn decreased but slowly because of the low evaporation rates.The measured and predicted results were found to be in good agreement.We suggest that the calculation be of some basic interest in vacuum refining of metallurgical grade silicon.

In the near future, biogas is a promising alternative to fossil fuels to provide energy and heat. MILD oxy-fuel combustion is a recently proposed idea to utilize biogas more efficiently. So far there have been two possible ways to establish MILD oxy-fuel combustion: the reactants are diluted by CO2 or H2O, respectively. Although until now there have been a number of studies to compare reaction characteristics of biogas under these moderation operations, further investigation on this topic is still required. Especially, comparison from the viewpoint of the second law of thermodynamics has not received much attention. In this work, through changing the preheated temperature of oxidant and concentration of oxygen in oxidizer mixture, we carry out a comprehensive comparison on the performance of biogas MILD oxy-fuel combustion organized in O-2/CO2 or O-2/H2O atmosphere, respectively. The results show that, although H2O moderation has some advantages that summarized in previous publications, such operation also has a number of disadvantages, for example being high sensitive to oxygen concentration and existing large obvious temperature fluctuation, as compared with its CO2 counterpart. Some shortcomings of H2O moderation operation (e.g. worse performance due to more entropy generation), which have been neglected by previous research, can be more easily illustrated from the viewpoint of the second law of thermodynamics. Through the present analysis, it indicates that further comparison is necessary for other fuels to determine a suitable moderation approach to organize MILD combustion regime. (C) 2015 Elsevier Ltd. All rights reserved.

The present work details the flow characteristics and pressure drop of the gas–coal mixture through venturi under high pressure and concentration. A series of experiments of both single-phase gas and gas–coal mixture flows through the venturi were carried out, and the distribution of pressure, volumetric loading ratio and superficial gas velocity were obtained and compared. The results show that a sharp decrease in static pressure and volumetric loading ratio was observed inside the venturi. The degree of the decrease of pressure in the diffuser section is the lowest (≤20%). When keeping the average throat gas velocity same, the inlet gas velocity of gas–coal mixture flows is lower than that of single-phase gas flow, while the outlet gas velocity is higher. In addition, the variation of throat gas velocity is more remarkable. It may indicate a greater energy transfer with the presence of particles. The pressure drop of the gas–coal mixture increases with the increase of superficial gas velocity, volumetric loading ratio and gas density. Further, the pressure drop models of single-phase gas flow and gas–solid flows through the venturi have been established by adopting the Farbar's approach based on the mathematical regression analysis. The models contribute to predict the pressure drop of venturi with deviations below 25%.

The removal of impurities from metallurgical grade silicon using the O-2 and H2O-O-2 gas blowing techniques was firstly studied by thermodynamics. The relationships between the boron content in refined silicon and the equilibrium partial pressures of gaseous boride species were established, which shows a theoretical limitation for boron removal from metallurgical grade silicon using the H2O-O-2 gas blowing technique. The data also showed that the impurity boron in silicon was mainly volatilized in the form of B3H3O6, BHO2 and BO and the volatilization of boric hydrate species was much more than that of the oxide species. The impurities removal from metallurgical grade silicon including Fe, Al, Ca, Ti, B, P and C was studied using an O-2 gas blowing in a ladle and in succession a mixed Ar-H2O-O-2 gas blowing was operated in a DC arc furnace for boron removal. It showed a removal efficiency higher than 90 % for Al, Ca and 50 % for B using the O-2 gas blowing technique in the ladle. Impurity boron was reduced from 35 ppmw to 18 ppmw in the ladle and it was once again reduced to 0.6 ppmw using an Ar-H2O-O-2 gas blowing technique in the DC arc furnace for a systematic pressure of 5 Pa when the ratio of H2O to O-2 and the refining times are 2:1 and 12 min, respectively.

运用分子相互作用体积模型并结合Si、Al二元系的无限稀活度系数γSi、γAl,利用牛顿迭代法计算出对势能相互作用参数Bsi,Al和BAl,si,然后再利用Bsi,A1和BAl,si计算Al-Si二元系中Si和Al的活度系数γsi、γAl和活度aSi、aAl,进一步利用γsi、γAl计算出Al的分离系数βAl和蒸馏过程中Al的挥发速率,同时根据γSi、γAl绘制出Al-Si合金蒸馏过程中的气液相平衡图.研究结果表明:活度计算值与实验值吻合较好,由βAl＞ ＞1可预测,通过真空蒸馏能很好地实现Si和Al的分离.此研究为真空蒸馏分离铝硅合金提供了可靠的理论依据及预测模型,对于研究铝硅合金中铝的分离限度具有重要参考作用.

Flow instability is a key question which needs to be solved for the development of dense-phase pneumatic conveying. Flow patterns are closely related with flow instability. There is a gap in our knowledge of gas–solid flow patterns in the dense-phase pneumatic conveying due to the lack of advanced measure technology and analysis methods. Electrical Capacitance Tomography (ECT) is an effective and advanced measure method which was used to research flow patterns in pulverized coal dense-phase pneumatic conveying with solid–gas ration of 60–560 kg/kg. With stack of ECT images in order of time, different flow patterns were defined and classified in the horizontal and vertical pneumatic conveying systems. Plug flow, fluidized flow, slug flow and stratified flow were observed in the horizontal pneumatic conveying; there were plug flow, fluidized flow, slug flow and annular flow in the vertical pneumatic conveying. The relationship between Reynolds number and Archimedes number was used to predict transition of these flow patterns. The prediction is in good agreement with experimental results in the experimental range. In addition, some analysis methods were introduced to research the flow patterns, such as the Standard Deviation (SD), Power Spectrum Density (PSD) and wavelet analysis. We found that flow stability can be represented with SD and PSD. PSD is preferred to SD for its higher resolution ratio and noise immunity. The wavelet analysis can reflect flow characteristics and energy distributions in the different scales for different flow patterns.

Research on flow patterns can provide a better understanding Of particle dynamics in dense phase pneumatic conveying of pulverized coal. In this paper, electrical capacitance tomography (ECT) has been employed to study flow patterns in, the 20 mm diameter vertical riser. Three flow patterns were identified.. on the basis of ECT image analysis, and their characteristics and formation mechanisms were discussed. The flow patterns at high solid concentration were more asymmetrical than those at low solid concentration. Solid concentration signals obtained from ECT were analyzed by different signal analysis methods including relative standard deviation (RSD), probability density function (PDF), and power spectral density function (PSD), Which were verified to be effective enough to identify the characteristics of the different how patterns. Additionally, the Bi model (Bi, H. T.; Grace, J. R. Int J. Multiphase Flow 1995, 21, 1229-1239) was modified to effectively predict chocking velocity in the vertical dense-phase pneumatic conveying of pulverized coal.

The influence of gas type (air and CO2) and hopper pressure (0-400 kPa) on the discharge of the pulverized coal was investigated. For aerated discharge, fluidization in the hopper is the initial state of the discharge process; the state of gas-solid fluidization affects the subsequent hopper discharging significantly. Compared to air, CO2 showed a weaker ability to fluidize the pulverized coal, and thus it was more difficult to improve the hopper discharge at atmospheric pressure. On the other hand, increasing the hopper pressure did not affect the basic discharge law but increased the discharge rate to a certain degree. In addition, with the increase of the hopper pressure, the discharge differences between the air and CO2 aeration series reduced, because the discharge rate had a larger promotion from atmospheric pressure to 400 kPa for the CO2 case.

An aerated discharge system was established in this paper to investigate the discharge of pulverized coal from a pressurized aerated hopper. Two opposite effects of aerated gas on solid were first revealed. "Fluidized pressurization", which effectively fluidized the solid and improved the subsequent hopper discharge, was then developed. The effect of hopper pressure on the discharge of pulverized coal was studied. Our experimental results showed that the gas volumetric flow rate increased and the gas superficial velocity decreased with the increase of the hopper pressure in the range of 0-1800 kPa. It was confirmed that more energy was needed; the uncertainty and instability was increased to discharge pulverized coal at higher pressures. Gas momentum flux was defined and used to describe the effect of aeration. The optimum gas momentum flux, which was independent of the hopper pressure, was obtained on the basis of the experimental data. The optimum gas volumetric flow rates and the optimum gas superficial velocities corresponding to the maximum solid discharge rates were further predicted, which agreed well with the experimental data. On the other hand, the hopper pressure also showed a positive effect on the solid discharge, as the maximum solid discharge rate increased gradually with the hopper pressure until a limit value of about 8000 kg/h was reached at 800 kPa.

The pneumatic conveying experiments at the high solid–gas ratio (120–300kg/m3) were carried out to compare their conveying characteristics separately using CO2 and air as carrier gas. The differences between them are found to be related with fluidized state of pulverized coal in the feeding vessel and can be explained with material properties involving particle–gas interactions, permeability. Employing electrical capacitance tomography (ECT), the transition from full pipe flow to annular flow was observed with increasing the superficial gas velocity (3.0–8.5m/s) in the vertical pipe and the flow patterns with CO2 and air are found to be similar. The analysis shows there is a significant association between sharp fluctuations of the pressure signals and gas slug. When gas slug was observed in the pipe, there was a large pressure pulse. The occurrence of gas slug is also found to be higher in the transporting with CO2 as carrier gas. The pressure signals may therefore be used to identify gas slug appearing in the pipe. The energy analysis is presented to find that the energy consumption with CO2 is about 7.5% higher than that with air at the same gas flow rate, but the required energy with CO2 is increased by about 20% than that with air at the same solid mass flow rate.

Experimental studies were performed to describe the physical phenomena occurring in dense phase pneumatic conveying of the pulverize coal with a Laval nozzle installed in the pipeline. The maximal coal mass flow rate decreased from 0.87kg/s to 0.35kg/s and an obvious decrease in the solids loading ratio was revealed after the Laval nozzle was installed. In addition, the Laval nozzle showed a better capacity of resisting disturbance, which made it easier to control the coal mass flow rate precisely and promoted the stable conveying process. These specific physical phenomena were proved to result from the high pressure drop of the Laval nozzle. Thereby, a mathematic model was developed to predict the two-phase pressure drop across the Laval nozzle. The pressure drop model described the experimental data within the 15% deviation. The main influence factors contributing to the pressure drop of the Laval nozzle were discussed using the model. Then the effects of gas mass flow rate, solids loading ratio, convergence angle, throat diameter and throat length were revealed.

Pulverized coal is important for gasification to convert carbonaceous fuel to gaseous products with a usable heating value; it is cohesive with a poor flowability, typical of Group C powders. The fluidization behaviors of pulverized coal in a fluidization column and in a Perspex hopper were investigated. The pulverized coal was extremely hard to be fluidized and its experimental incipient fluidizing velocity was much larger than expected. The discharge of pulverized coal from a carbon steel hopper under several aeration rates was studied. Four flow regions were developed, and the major phenomena that occurred during the discharge were analyzed. The mechanism of aerated discharge was probably the integration of various effects, all of which were confirmed by the experimental data.

Based on electrical capacitance tomography technique,the flow regime of dense-phase pneumatic transportation of pulverized coal was investigated.Typical flow regimes in the horizontal pipe and riser were obtained.The study indicated that the flow regime in the horizontal pipe varied significantly with time and there existed several flow regimes,such as full pipe flow,settled layer flow,suspension flow,etc.Statistical analysis results revealed that there were obvious prevailing flow regimes,which changed with superficial gas velocity.An analysis on solids velocity and pressure signals showed that the flow regime correlated reasonably well with pressure signals,which proved the inherent instability of dense phase pneumatic conveying.On the other hand,the dynamic test result of the riser showed that the flow regime was mainly core-annulus structure.