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Inorganic acids (sulfuric acid (H2SO4) or phosphoric acid (H3PO4)) are generally employed as depressants in the reverse flotation of collophanite to separate apatite from dolomite. In this study, t...

In sensorless control, sliding mode observer is widely used because of its insensitivity to parameter changes and strong robustness. For unnecessary high frequency chattering and the lack of accuracy in calculation of rotor position and machine speed in the conventional sliding mode observer, a new sliding mode observer based on the new constant velocity reaching law is used to suppress the high frequency chattering of the machine system. A new constant speed reaching law is designed to replace the conventional constant speed reaching law and it is introduced into new sliding mode observer. This method improves the approaching speed of sliding mode and reduces the high frequency chattering of conventional sliding mode observer. In addition, the arctangent function is used to estimate the position of the machine rotor, and the phase compensation for the Angle position error of the machine rotor is carried out. The simulation results show that compared with the Conventional sliding mode observer, the proposed new sliding mode observer is more stable and has better control performance.

The exploitation of natural gas hydrate is always hindered by the migration of water and sands due to gas production. Depressurization combined with thermal stimulation is an effective method for hydrate dissociation. This paper reported the influence of gas-liquid-solid migration on morphological change of hydrate sediments in natural gas production using visualization method. Different backpressures combined with thermal stimulation methods were applied to simulate natural gas hydrate exploitation. Pressure compensation was first employed to study sediment recovery features. The expansion rate of a porous medium layer under combined dissociation and different backpressure (4.5, 3.5, 2.5, 1.5, and 0.1 MPa) was discussed. A 176% hydrate sediment expansion rate was found after the combined dissociation at 0.1 MPa. In addition, it was observed that the height of the water layer above the porous media after pressure compensation was gradually reduced with a decrease in backpressure and eventually disappeared at 0.1 MPa. It was also found that the disappearing water layer caused an anomalous memory effect phenomenon. Expansion and subsidence of sediments provide a better reference for hydrate exploitation and geological safety.

Natural gas hydrate (NGH) has been widely considered as an alternative form of energy with huge potential, due to its tremendous reserves, cleanness and high energy density. Several countries involving Japan, Canada, India and China have launched national projects on the exploration and exploitation of gas hydrate resources. At the beginning of this century, an early trial production of hydrate resources was carried out in Mallik permafrost region, Canada. Japan has conducted the first field test from marine hydrates in 2013, followed by another trial in 2017. China also made its first trial production from marine hydrate sediments in 2017. Yet the low production efficiency, ice/hydrate regeneration, and sand problems are still commonly encountered; the worldwide progress is far before commercialization. Up to now, many gas production techniques have been proposed, and a few of them have been adopted in the field production tests. Nevertheless, hardly any method appears really promising; each of them shows limitations at certain conditions. Therefore, further efforts should be made on the economic efficiency as well as sustainability and environmental impacts. In this paper, the investigations on NGH exploitation techniques are comprehensively reviewed, involving depressurization, thermal stimulation, chemical inhibitor injection, CO2–CH4 exchange, their combinations, and some novel techniques. The behavior of each method and its further potential in the field test are discussed. The advantages and limitations of laboratory studies are also analyzed. The work could give some guidance in the future formulation of exploitation scheme and evaluation of gas production behavior from hydrate reservoirs.

In this study, the effects of various characteristics of artificial and natural magnetite concentrates on their pelletizing behaviors were elucidated through batch pelletizing experiments. The resu...

In order to improve the dynamic performance of the traditional proportional integral-differential (PID) vector control system, a control method with improved exponential reaching law and proportional resonance is proposed. First, a sliding mode controller based on the improved exponential reaching law is designed and introduced into the motor control system. The exponential reaching law does not add new parameters. But can achieve the goal of reducing chattering and improving anti-disturbance performance. Then, a current controller based on improved proportional resonance is proposed. It can track the ac signal quickly and reduce the number of coordinate rotation transformation of motor system. The simulation results show that this method can effectively improve the dynamic performance and robustness of the control system.

The Fe3O4 and Fe2SiO4 in copper slag were successfully reduced to metallic iron by coal-based direct reduction. Under the best reduction conditions of 1300 &deg, C reduction temperature, 30 min reduction time, 35 wt.% coal dosage, and 20 wt.% CaO dosage (0.75 binary basicity), the Fe grade of obtained iron concentration achieved 91.55%, and the Fe recovery was 98.13%. The kinetic studies on reduction indicated that the reduction of copper slag was controlled by the interfacial reaction and carbon gasification at 1050 &deg, C. When at a higher reduction temperature, the copper slag reduction was controlled by the diffusion of the gas. The integral kinetics model research illustrated that the reaction activation energy increased as the reduction of copper slag proceeded. The early reduction of Fe3O4 needed a low reaction activation energy. The subsequent reduction of Fe2SiO4 needed higher reaction activation energy compared with that of Fe3O4 reduction.

Cu2+ and Fe3+ are generally inevitable in the flotation of molybdenite. In this work, the effect of Cu2+ and Fe3+ on the flotation of molybdenite was investigated through flotation tests. The influence mechanism was studied by Zeta potential measurement, scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) analysis. The results showed that the flotation of molybdenite was strongly depressed by Cu2+ and Fe3+, and the depression of Fe3+ was more powerful than that of Cu2+. The depression performance of molybdenite was significantly influenced by pH in the presence of Cu2+ and Fe3+, which was due to the adsorption of different hydrolyzed species as pH varied. The depression mechanism involved two different models in Cu2+ solution. In acid media, the depression was mainly contributed to the coverage of less hydrophobic CuS, as well as a small amount of hydrophilic Cu(OH)2 and Cu2+ on molybdenite surface. While in alkaline condition, the adsorption of Cu(OH)2 precipitate was the main reason for the depression. In Fe3+ solution, Fe(OH)3 precipitate was the main component adsorbed on molybdenite surface to make the surface of molybdenite hydrophilic.

In order to establish the kinetics of oxidation of artificial magnetite pellets, we comprehensively studied kinetics of the oxidation of artificial magnetite pellets from low temperature to high temperature using chemical analysis. The results show that when the oxidation temperature is below 1 073 K (800 °C), the reaction is controlled by the step of internal diffusion, and the model function is 2 G(a) = 1−3(1−x)2/3 + 2(1−x) (α, reaction degree). When the temperature is above 1 073 K (800 °C), the reaction mechanism was chemical reaction, and the model function is 1 G(a) = 1−(1−x)1/3. The apparent activation energy for the oxidation of artificial magnetite pellets was also determined, which was 8.90 kJ/mol for the low temperature and 67.79 kJ/mol for the high temperature. Based on the derived kinetic equation for the oxidation of artificial magnetite pellets, the calculated value is consistent with the experimental data. Compared with that of nature magnetite pellets, the apparent activation energy is decreased obviously, which indicates that the artificial magnetite pellets are oxidized more easily than nature magnetite pellets.

Fe–P separation and the behaviors of Fe and P in separation process of high-phosphorus oolitic hematite ore from western Hubei province in China were studied. Various parameters, including reducing...

Phosphate concentrates are widely used as primary sources in the production of fertilizers worldwide, but the efficient removal of dolomite from apatite in flotation relies heavily on selective depressants. Conventional apatite depressants such as sulfuric and phosphoric acid inevitably cause serious environmental pollution. It is urgent to explore green and efficient depressants to substitute conventional ones for the clean production of phosphate concentrate. In this work, iminodisuccinic acid (IDS) was explored as an efficient and environmental-friendly dolomite depressant in the direct flotation of apatite from dolomite. The depression performances were evaluated by micro-flotation and the interaction mechanism was revealed through adsorption capacity, Microcalorimetry, Zeta potential, Fourier Transform Infrared (FTIR), X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) measurements. Mico-flotation results showed that IDS selectively depressed dolomite but hardly affected apatite flotation, improving the separation efficiency and upgrading the quality of apatite concentrates successfully. Mechanism study demonstrated that IDS preferentially adsorbed on dolomite due to its higher affinity to Mg sites on dolomite. IDS was dominantly chelated with Mg sites to form octahedral complexing structure via the coordination of COO− with Mg sites. While IDS was weakly adsorbed on apatite thought weak hydrogen bond between F sits of apatite with carboxyl within IDS. The pre-adsorption of IDS impeded NaOL adsorption on dolomite, but didn’t influence the NaOL adsorption on apatite. The work proved that IDS could be used as a green and selective dolomite depressant for the clean flotation of apatite from dolomite, which is of great importance for the sustainable production of fertilizer.

In this work, 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) was explored as a novel sphalerite depressant in the selective flotation of galena from sphalerite. The separation performances were investigated by single and synthetic flotation tests. The depression mechanism was examined by Fourier Transform Infrared spectroscopy (FTIR), zeta potential and X-ray Photoelectron Spectroscopy (XPS) analysis. The flotation test results showed that PBTCA was an effective sphalerite depressant with good selectivity at broad pH range, which could achieve satisfactory separation results. Zeta potential and FTIR results indicated that PBTCA was more prone to adsorb on sphalerite surface than that of galena. In addition, SIBX could replace adsorbed PBTCA on the galena surface while it was impossible to substitute that on the sphalerite surface, which rendered sphalerite surface hydrophilic and enlarged the floatability difference. XPS analysis manifested that PBTCA was adsorbed on sphalerite surface through the strong complexation between carboxyl, phosphonic acid groups and Zn sites on sphalerite surface, forming C-O-Zn or P-O-Zn bond.

More than 65% of the worldwide natural gas is transported through pipelines. Gas hydrate formation and blockage in the pipeline are commonly encountered, causing significant problems in safe and efficient transportation. Yet the instrument simulating the high-pressure multiphase flow and demonstrating the hydrate blocking behavior at flowing conditions is not available. In this work, a high-pressure visual flow loop is developed to detect and observe the hydrate nucleation, growth, and deposition during the multiphase flow. The pressure limit is designed to be 8 MPa, and the temperature can go down to −20 °C. This device allows a direct observation of the gas-liquid flow regime during transportation; investigations on the initiation and evolution of hydrate blockage in the dead-leg section, U-shaped region, and rising pipes are now possible. Sensors are distributed along the pipelines to detect the pressure and temperature change; the differential pressure is used to effectively detect the degree of hydrate blockage, which increases upon hydrate formation. The visual flow loop could also help examine the effect of shut-down and restart of the pump on the flow behavior. The system has been verified feasible demonstrating the flow behavior and predict hydrate blockage. The developed device would help understand the mechanism of hydrate blockage in the transportation pipelines and provide guidance to efficiently avoid such problems.More than 65% of the worldwide natural gas is transported through pipelines. Gas hydrate formation and blockage in the pipeline are commonly encountered, causing significant problems in safe and efficient transportation. Yet the instrument simulating the high-pressure multiphase flow and demonstrating the hydrate blocking behavior at flowing conditions is not available. In this work, a high-pressure visual flow loop is developed to detect and observe the hydrate nucleation, growth, and deposition during the multiphase flow. The pressure limit is designed to be 8 MPa, and the temperature can go down to −20 °C. This device allows a direct observation of the gas-liquid flow regime during transportation; investigations on the initiation and evolution of hydrate blockage in the dead-leg section, U-shaped region, and rising pipes are now possible. Sensors are distributed along the pipelines to detect the pressure and temperature change; the differential pressure is used to effectively detect the degree of hydra...

For the detection of deep-sea natural gas hydrates, it is very important to accurately detect the 13CO2/12CO2 isotope ratio of dissolved gas in seawater. In this paper, a 13CO2/12CO2 isotope ratio sensor is investigated, which uses a tunable diode laser absorption spectroscopy (TDLAS) technique at 4.3 &mu, m. The proposed sensor consists of a mid-infrared interband cascade laser (ICL) operating in continuous wave mode, a long optical path multi-pass gas cell (MPGC) of 24 m, and a mid-infrared mercury cadmium telluride (MCT) detector. Aiming at the problem of the strong absorption intensity of the two absorption lines of 13CO2 and 12CO2 being affected by temperature, a high-precision temperature control system for the MPGC was fabricated. Five different concentrations of CO2 gas were configured to calibrate the sensor, and the response linearity could reach 0.9992 for 12CO2 and 0.9996 for 13CO2. The data show that the carbon isotope measurement precision was assessed to be 0.0139&permil, when the integration time was 92 s and the optical path length was 24 m. The sensor is combined with a gas&ndash, liquid separator to detect the 13CO2/12CO2 isotope ratio of CO2 gas extracted from water. Results validate the reported sensor system&rsquo, s potential application in deep-sea natural gas hydrate exploration.

An apparatus for the analysis of pressure cores containing gas hydrates at in situ pressures was designed, and a series of experiments to determine the compressional wave response of hydrate-bearing sands were performed systematically in the laboratory. Considering the difficulties encountered in performing valid laboratory tests and in recovering intact hydrate bearing sediment samples, the laboratory approach enabled closer study than the marine environment due to sample recovery problems. The apparatus was designed to achieve in situ hydrate formation in bearing sediments and synchronous ultrasonic detection. The P-wave velocity measurements enabled quick and successive ultrasonic analysis of pressure cores. The factors influencing P-wave velocity (Vp), including hydrate saturation and formation methodology, were investigated. By controlling the initial water saturation and gas pressure, we conducted separate experiments for different hydrate saturation values ranging from 2% to 60%. The measured P-wave velocity varied from less than 1700 m/s to more than 3100 m/s in this saturation range. The hydrate saturation can be successfully predicted by a linear fitting of the attenuation (Q−1) to the hydrate saturation. This approach provided a new method for acoustic measurement of the hydrate saturation when the arrival time of the first wave cannot be directly distinguished. Our results demonstrated that the specially designed non-embedded ultrasonic detection apparatus could determine the hydrate saturation and occurrence patterns in pressure cores, which could assist further hydrate resource exploration and detailed core analyses.

Research on the memory effect can improve the rate and efficiency of hydrate reformation, which has important applications in gas hydrate technology. Depressurization is the most widely used gas hydrate dissociation method; however, studies on the mechanism of depressurization on memory effect are still lacking. In this study, the memory effects were compared and analyzed after the hydrate sediment was subjected to different dissociation patterns. The different dissociation patterns included depressurization (different backpressures: 4.5, 3.5, 2.5, 1.5, and 0.1 MPa) and single thermal stimulation dissociation pattern (STSP). The effect of depressurization-induced sediment morphology changes on hydrate-memory effect and gas conversion was obtained under different backpressures. The results indicated that the memory effect tended to remain stable in the STSP, but changed with depressurization dissociation. The memory effect after depressurization dissociation gradually weakened with decreasing backpressure. Notably, an anomalous memory effects was observed, wherein the memory effect was not weakened, but significantly enhanced after depressurization dissociation at 0.1 MPa. Furthermore, depressurization may not only change the memory effect but could also increase the stable interval of the memory effect and the supercooling degree. The average gas conversion ratio of stable interval after dissociation at 0.1 MPa decreased by nearly 8%.

Relative contact angle and heat of wetting can be used to provide a measurement of surface wettability of synthetic magnetite. The comparison between synthetic and natural magnetite in terms of surface wettability showed that, using the same kind of wetting liquid, the difference in the relative contact angle was 10° between the concentrate and tailings obtained from reverse flotation of synthetic magnetite, while the difference was more than 20° between the concentrate and tailings obtained from reverse flotation of natural magnetite. As for the concentrate and tailings from reverse flotation of synthetic magnetite with water as wetting liquid, the relative ratio of their wetting heat was 106.21%. In comparison, the relative ratio of wetting heat was 176.59% for concentrate and tailings from reverse flotation of natural magnetite, showing a 70.38% difference.

This paper presents a systematic approach for robust performance analysis of active suspension system. Firstly, the background information on H - μ control methods is briefly described. Secondly, the formula of the structured uncertainties of active suspension are given, and the difference between the maximum singular values and structured singular values of a transfer function matrix is discussed. Then the robust performance of an active suspension system in the presence of assumed parameter variation is analyzed. All the steps are illustrated by means of a numerical example of a railway car with lateral active suspension system.

Grimble and Fairbairn's recently published results on H∞ robust self-tuning control are discussed. It is pointed out that further explanation about the system model is needed, and the identified system model should be revised. Grimble (1987 a, b) and Fairbairn and Grimble (1990) give a new approach to designing self-tuning controllers for SISO discrete-time stochastic systems. There are some points that call for further discussion.