Biodiesel as a renewable collector for coal flotation in the future

Biodiesel is a renewable and clean energy which is being developed day by day. However, oil and coal reserves are decreasing due to an increase in energy demand for the development of social economy. Additionally, fine coal is usually beneficiated by flotation using diesel or kerosene as collectors, which may be a waste of energy. Therefore, using biodiesel as a collector for coal flotation has its potential value. In this investigation, biodiesel was used as a collector for coal flotation. Three bituminous coal samples with different coal ranks were selected, that is, gas coal, coking coal, and lean coal. FTIR results showed that biodiesel contained much more abundant unsaturated fatty acids than diesel. Flotation results showed that the flotation performances of three coal samples using biodiesel as collector were similar to that using diesel as collector. Even better, the concentrate yields of three coal samples using biodiesel as collector were a little higher than that using diesel as collector, while their concentrate ash contents were similar. Throughout this paper, it was proved that biodiesel could have a potential application in coal flotation.     

Effects of flotation on the release behavior of sulfur and nitrogen during coal pyrolysis

Two Chinese coals were selected to investigate the effects of flotation on the release behavior of sulfur and nitrogen during pyrolysis. The results show that the removal rate of minerals and sulfur-containing compounds from raw coal by flotation are closely related to coal properties. The significant alterations of sulfur and nitrogen forms on coal surface are mainly presented in the decrease of sulfidic-S, thiophenic-S, and pyridinic-N, the increase of sulfones-S and quaternary-N after flotation. The release of sulfur- and nitrogen-containing gases during pyrolysis of raw and clean coals has evident differences, which are mainly caused by the change of the relative proportions of different sulfur and nitrogen forms in the process of flotation.     

Effects of calcium chloride and sodium chloride on the flotation removal of unburned carbon from coal fly ash

The effects of calcium chloride and sodium chloride on the coal fly ash flotation were investigated by studying the surface properties of coal fly ash. X-ray photoelectron spectroscopy and scanning electron microscopy showed the presence of many lime particles in the coal fly ash, which, together with Ca(OH)₂(s), could be adsorbed on the rough surface of unburned carbon particles. The flotation results indicated that calcium chloride reduced the performance of unburned carbon removal from the coal fly ash, whereas sodium chloride increased froth stability thereby improving the flotation performance.     

Effects on enrichment characteristics of trace elements in fly ash by adding halide salts into the coal during CFB combustion

The effects on enrichment characteristics of trace elements (TEs) in fly ash by adding halide salts into the coal during coal combustion were conducted on a 6 kW_th circulating fluidized bed (CFB) experimental device. Results show that unburn carbon content in fly ash has little relationship with the concentration of TEs namely Hg, As, Pb, Cr and Mn. All the TEs are enriched in fly ash for the raw coal CFB combustion. Concentration of Hg and Mn increases with increasing the addition amount of CaCl₂, NH₄Cl and NH₄Br. As, Pb and Cr enrich in fly ash more strongly when adding more CaCl₂ into the coal while more addition of NH₄Cl and NH₄Br leads to the decrease of their enrichment compared to addition amount of 0.1 wt%. On the whole, putting halide salts into the coal results in the TEs enriched in fly ash, which benefits for TEs removal during the coal combustion. Combining this method with the chemical sequential extraction or thermal treatment of the fly ash will be a promising way to realize the TEs removal and their recovery.     

Investigation of the effectiveness of desliming and flotation in cleaning Malatya-Arguvan lignite

This study investigated the possibility of cleaning Malatya-Arguvan lignite using the flotation method. Because preliminary flotation studies suggested that desliming affects flotation performance, an attempt was made to quantify the effects of the major influencing parameters on the effectiveness of desliming and flotation. Because the optimum collector dosage was found to be very high, the effects of addition of sodium oleate and Aero 3477 were also investigated, to reduce the collector dosage. However, flotation results showed that the addition of sodium oleate and Aero 3477 does not alter the collector dosage significantly. Despite all the aforementioned efforts, only 20% of feed ash could be removed.     

A new process based on a combination of gravity and flotation for the recovery of clean coal from flotation tailings

Beneficiation of clean coal from flotation tailings with a high intergrown ash content is gaining popularity in China. It not only improves the utilization rate of coal resources but also reduces environmental pollution. In this paper, a novel gravity–flotation process is proposed to concentrate low-ash fine coal and includes the disposal of tailings via gravity, grinding liberation, and froth flotation. The experimental results show that the clean coal had an ash content of 12.33% and the yield from the flotation tailings was 32.24% with an ash content of 46.39%, which has economic value in the current market.     

Ignition of wood and coal particle mixtures in conditions of steam and water boiler furnaces

The results of experimental studies of the ignition processes of a large set of particles (from 100 to 500) of wood-coal composite fuels under conditions of high-temperature radiation-convective heating are presented. The ignition of wood-coal fuel mixture fuel particles was studied under the conditions of their free fall along the quill ceramic cylinder passage in a high-temperature oxidizing medium (air). Such a configuration provides the conditions that most closely match the heating conditions of actual furnaces of heat generating installations.The experiments have been carried out on the mixtures of particles of subbituminous coal (that is quite typical of coal-fired power industry) with the particles of woody biomass of three types: birch, pine and larch, which are widely spread in the territory of many states of the northern part of the Earth hemisphere. The recording of the heating and ignition processes of the fuel mixture particles was carried out with a high-speed Photron FASTCAM CA45 (500 fps) camera. The air temperature in the passage along which the particles moved varied in experiments from 873 K to 1273 K. The purpose of the experiments performed was the ignition delay time (t_ign). The main variable factors are the ambient temperature and the concentration of woody components. The consistent errors in determining the main characteristics of the process did not exceed 5%, the random ones did not exceed 13%. The size of coal particles in the experiments did not exceed 60 μm, and of the wood - 5 mm.It has been established that in such a fuel system one of the fuel components of the coal particle is “conducting” (or leading), and the second is “conducted” in the reaction of the thermochemical response of the fuel mixture with air oxygen. According to the results of experimental studies, the ignition delay times for the wood-coal particle mixtures have been stated. The increase in the concentration of small-sized coal particles in fuel mixtures from 0% to 100% leads to the decrease in the entire induction period (up to 20%) at the relatively cold temperatures.It was also found that with typical sizes of coal particles up to 60 μm, stable ignition of sufficiently large wood particles (up to 5 mm), present in the mixture, is provided. The conditions and characteristics of ignition of wood-coal mixtures hardly depend on the type of wood, which is the second component of the mixture.According to the results of the research conducted and following the requirements for optimizing the processes of fuel combustion, the use of mixed coal- and wood-based fuels in boilers of large and small power plants is justified.     

The reactions of zinc,zinc chloride and zinc oxide with coal. An x-ray diffraction study

The reactions of zinc chloride and zinc oxide with coal have been studied using X-ray diffraction to monitor the 002 graphite line. It was observed that reaction of either reagent causes this diffraction line to disappear. Furthermore, addition of zinc metal reduces the weight of zinc chloride or zinc oxide needed to remove this 002 diffraction. Experiments with magnesium compounds indicate that the results with zinc compounds and coal cannot be extended to the analogous magnesium species. Thus it appears that zinc chloride or zinc oxide are capable of breaking up some of the regularity of the coal structure. This effect is enhanced by zinc metal indicating the possibility of a reaction in which zinc is switching between the elemental and oxidized forms.     

Characteristics and conditions for ignition of bio-coal mixtures based on coal and forest combustible material

The results of the experimental studies of the ignition process of a pulverized fuel mixture based on coal and biomass — forest combustible material (FCM) have been given. As the second component of the fuel the wastes of various deciduous or coniferous species of trees have been used.The experiments have been carried out on the equipment that provides a fairly low level of error when registering the main characteristics (ignition delay time of the fuel particles _tign, ambient temperature T_g) of heat and mass transfer processes occurring together during ignition of bio-coal fuel during thermal preparation. It has been established that the addition of biomass to coal leads to a significant reduction (up to 30%) of the entire ignition period of the fuel mixture. The video recording of the ignition processes has allowed to identify the main stages of thermal preparation and ignition of the bio-coal fuel particles. It has been established that the particles of biomass (leaf or fir needles) ignite faster than coal.A mathematical model has been developed based on the results of a detailed analysis of the videograms of the ignition process of the bio-coal mixtures describing the joint flow of the main processes of heat and mass transfer under conditions of the intense phase and thermochemical transformations. A numerical simulation of the ignition process has been carried out and the ignition delay times have been established. A comparative analysis of the theoretical and experimental values of t_ign has shown their good conformance.     

Co-combustion characteristics study of bagasse,coal and their blends by thermogravimetric analysis

Co-combustion technology was used to investigate the combustion of bagasse and bagasse blending with coal at different ratios (20%, 50%, and 70% bagasse in weight) using thermogravimetric analysis (TGA). The results show that three stages were observed during bagasse combustion and the main combustion process occurred at the second stage. Compared with combustion of coal, the co-combustion of bagasse blending with coal has lower first peak temperature (T_p1), slightly lower average reaction rate (R_v), and higher reaction rate at the first peak (R_p1). The best blend ratio of bagasse/coal is 20%/80%, and the inhibitory effect is found during the co-combustion.     

Syngas production through gasification of coal water mixture and power generation on dual-fuel diesel engine

In the present study, a syngas was produced by preparing coal water mixtures of two different concentrations and gasifying the coal water mixtures. An entrained-flow gasifier of 1 ton/day scale was used and, after undergoing a purification process, the produced syngas was applied to a modified diesel engine for power generation. As the gasification temperature increased, the carbon conversion and the cold gas efficiency were found to increase. In the composition of the produced syngas, the content of H₂ remained constant, that of CO increased, and those of CO₂ and CH₄ decreased. The carbon conversion increased with equivalence ratio. A maximum cold gas efficiency of 66.1% was found at the equivalence ratio of 0.43. N₂ was additionally supplied to verify the gasification characteristics depending on the gas feed flow rate. The optimum feed flow rate was verified at different slurry concentrations and equivalence ratio. The produced syngas was supplied to a modified diesel engine and operated depending on the syngas feed flow rate and the engine operation conditions. The brake thermal efficiency of the engine was constant regardless of the syngas feed flow rate. The diesel engine showed high efficiency despite the mixing of the syngas.     

The role of coal in energy production—Consumption and sustainable development of Turkey

Energy is one of the indispensable factors regarding the assurance of social prosperity and economic development of a country. The developing countries struggle to obtain energy sources reliable in the long term to complete their economic development, and the developed countries struggle to get them to keep their present prosperity levels. Coal seems to continue its indispensable position among the other energy sources for many years because of its production in more than 50 countries, the least effect it has from the price fluctuation and its usage lifespan of more than 200 years. The countries that are aware of it have investments in mining fields in the countries rich in coal reserves, and they continue investing considerable amount of money.     

Reversible poisoning of nickel/zirconia solid oxide fuel cell anodes by hydrogen chloride in coal gas

The performance of anode-supported solid oxide fuel cells (SOFC) was evaluated in synthetic coal gas containing HCl in the temperature range 650-850 °C. Exposure to up to 800 ppm HCl resulted in reversible poisoning of the Ni/zirconia anode by chlorine species adsorption, the magnitude of which decreased with increased temperature. Performance losses increased with the concentration of HCl to ∼100 ppm, above which losses were insensitive to HCl concentration. Neither cell potential, nor current density had any effect on the extent of poisoning. No evidence was found for long-term degradation that can be attributed to HCl exposure. Similarly, no evidence of microstructural changes or formation of new solid phases as a result of HCl exposure was found. From thermodynamic calculations, solid nickel chloride phase formation was shown to be highly unlikely in coal gas containing HCl. The presence of HCl at even the highest anticipated concentrations in coal gas would minimally increase the volatility of nickel.     

Comparative study on combustion and oxy-fuel combustion environments using mixtures of coal with sugarcane bagasse and biomass sorghum bagasse by the thermogravimetric analysis

Biomass and coal have different physicochemical properties and thermal behavior. During the co-combustion of coal-biomass mixtures, their thermal behavior varies according to the percentage of each fuel in the mixture. Thereby, this research aims to characterize the thermal behavior of mixtures of coal, sugarcane bagasse, and biomass sorghum bagasse as biomass in simulated combustion (O₂/N₂) and oxy-fuel combustion (O₂/CO₂) environments. Experiments have been performed in duplicate on a thermogravimetric analyzer at heating rate of 10 °C/min. A uniform granulometry was considered for all materials (63 μm) in order to ensure a homogeneous mixture. Four biomass percentages in the mixture (10, 25, 50 and 75%) have been studied. Based on thermogravimetric (TG) and thermogravimetric (DTG) analyses, parameters such as combustion index, synergism, and activation energy have been determined, as well as the combustion environment influence on these parameters. The results indicate that, although sugarcane bagasse has the lowest activation energy, the thermal behavior of both types of biomass is similar. Thus, biomass sorghum bagasse can be used as an alternative biomass to supply the power required during sugarcane off-season. For both mixtures, optimal results were obtained at 25% of biomass. By analyzing the environment influence on combustion behavior, the results indicate that when N₂ is replaced with CO₂, it is observed an increase in reaction reactivity, a higher oxidation rate of materials and an improvement in evaluated parameters.     

Comparative analysis of biomass and coal based co-gasification processes with and without CO2 capture for HT-PEMFCs

With the seasonal availability and low energy density of biomass and the high environmental impact of coal, the co-gasification of biomass and coal is an alternative approach facilitating a trade-off between renewable and non-renewable resources. The aim of this study was to investigate hydrogen production from the co-gasification of biomass and coal integrated by means of the sorption-enhanced water gas shift reactor (G-SEWGS) for a high temperature proton exchange membrane fuel cell (HT-PEMFC). The effects of the gasifier temperature, the steam to fuel ratio (S/F ratio), and the equivalence ratio (ER) on the hydrogen production performance and environmental impact of the G-SEWGS were theoretically analysed and compared with the conventional gasifier integrated with the water gas shift reactor (G-WGS) and the sorption-enhanced gasifier integrated with the water gas shift reactor (SEG-WGS). As compared to the conventional water gas shift reactor, the addition of a CaO sorbent in the modified water gas shift reactor not only reduces the amount of the CO₂ emission but also leads to an increase in the hydrogen concentration and hydrogen content. The G-SEWGS provides better performance in terms of its fuel processor efficiency and CO₂ emission than the G-WGS and the SEG-WGS. Also, the problem of sulphur compound in the hydrogen-rich gas can be reduced by using of the sorption-enhanced water gas shift reactor (SEWGS). The best system exergy efficiency, which was around 22% for the power generation, was determined from the HT-PEMFC integrated with the G-SEWGS. The main exergy destruction of around 70% of the total loss was caused by hydrogen production processes.     

煤锁整体机械加工工艺技术研究

本文主要阐述了在煤锁生产过程中,为保证装配位置的精度而采取的机械加工工艺.     

Comparative Analysis of Some Representative Models of Viscosity Versus Pressure in the Case of Various Hydrocarbons and Their Mixtures

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Deflagrations of localised homogeneous and inhomogeneous hydrogen-air mixtures in enclosures

Two original models for use as novel tools for the design of hydrogen-air deflagration mitigation systems for equipment and enclosures are presented. The first model describes deflagrations of localised hydrogen-air mixtures in a closed space such as a pressure vessel or a well-sealed building while the second model defines safety requirements for vented deflagrations of localised mixtures in an enclosure. Examples of localised mixtures include ‘pockets’ of gas within an enclosure as well as stratified gas distributions which are especially relevant to hydrogen releases. The thermodynamic model for closed spaces is validated against experiments available from the literature. This model is used to estimate the maximum hydrogen inventory in a closed space assuming the closed space can withstand a maximum overpressure of 10 kPa without damage (this is typical of many civil structures). The upper limit for hydrogen inventory in a confined space to prevent damage is found to be equivalent to 7.9% of the closed space being filled with 4% hydrogen. If the hydrogen inventory in a closed space is above this upper limit then the explosion has to be mitigated by the venting technique. For the first time an engineering correlation is presented that accounts for the phenomena affecting the overpressure from localised vented deflagrations, i.e. the turbulence generated by the flame front itself, the preferential diffusion in stretched flames, the fractal behaviour of the turbulent flame front surface, the initial flow turbulence in unburnt mixture, and the increase of the flame surface area due to the shape of an enclosure. Validation of the new vented deflagration model developed at Ulster has been carried out against 25 experiments with lean stratified hydrogen-air mixtures performed by the Health and Safety Executive (UK) and Karlsruhe Institute of Technology (Germany).     

A study on the effect of the CO2/steam mixtures and the addition of natural minerals on the reactivity of Adaro coal gasification

The synergetic effect in reactivity and gas yield on the various ratio of CO₂/steam mixtures was investigated. The isothermal gasification was conducted at three different temperatures. The synergy effect was evaluated on the ratio of CO₂/steam mixtures and reaction temperatures. In order to analyze the synergy quantitively, two reaction indexes were calculated from carbon conversion. The effect of natural minerals like Dolomite and Kaolin was investigated as well. The influence of synergy was varied upon the ratio of CO₂/steam mixtures and the optimal synergy was observed when the ratio of CO₂/steam mixtures was 1:2. The best synergy in reactivity and gas yield was shown at 800 °C and at 900 °C, respectively. By adding Dolomite, the synergetic effect in both reactivity and H₂ yield was promoted at 800 °C. Conclusively, the ratio of CO₂/steam mixtures and Dolomite played an important role to facilitate the synergy in the coal gasification.     

Evaluation of column flotation froth behavior by image analysis: effects of operational factors in desulfurization of iron ore concentrate

Flotation performance is expected to be affected by froth characteristics due to the changes in the operating conditions. However, very little study has been undertaken to investigate how froth behavior responds to the flotation variables. This study presents an experimental program performed to investigate the effects of flotation variables including gas flow rate, froth depth, slurry solids percent, frother/collector dosage, and pH on the froth features such as bubble size, froth velocity, froth color and froth stability during desulfurization of an iron ore. These parameters were varied using a central composite design (CCD). Image analysis methods have been developed and employed successfully to characterize the froth features. Results of the CCD experiments showed that the flotation variables have different effects on the froth features. The effect of pH and its interaction with collector dosage have a significant impact on all froth features. Process condition can be accurately deduced from the froth surface appearance which provides a convenient way to quantify the parameters as the process control function.