•The impact of CWSP droplets coagulation and splitting on their ignition was shown.•Ignition delay of coagulating droplets is shorter than that of double-volume droplet.•Ignition delays of split ...droplets are far shorter than those of pre-collision droplets.•Limit ignition temperature of droplet is between those of split and coagulated droplets.•Coagulation and splitting have essential impact on low-temperature ignition of CWSP.
The coal-water slurries based on different types of coals and waste petrochemicals or other combustible liquids (CWSP) are very attractive for creation of cheap energetic fuel (for replacement of the coal and gas). Together with evident economic effect, the CWSP is perspective from ecological point of view. It contains a lot of water and therefore the air pollution by nitrogen and sulphur oxides is low. However, the energetic parameters of combustion of such slurry are enough far from excellence. Numerous publications were done during last years about development of new CWSP compositions as well as about improvements of its ignition and combustion techniques. The actual task is stable ignition of the slurry composition at low (critical) temperatures. In this work, we have investigated for a first time the influence of coagulation and splitting of fuel droplets onto the integral parameters of the ignition (using high-speed video-recording technique). These results clearly show the differences of ignition processes of single CWPS droplets and the aerosol flow ignition in combustion chamber. Our experiments gave the understanding of scales of co-influence of fuel droplets onto the ignition parameters. We have used the fuel compositions based on milled (particle size ∼100μm) lignite and bituminous coal, coal-processing wastes, waste industrial oils and mazut. The investigations were done for two-body system where droplet sizes were the same (0.5–1.5mm) at every experiment. The temperature in the combustion chamber was in range from 600K to 1200K. Some sequences of coagulation/splitting were observed: coagulation/splitting inside the combustion chamber; droplet coagulation before injection into the combustion volume. The influence of these processes on the ignition delay time and critical ignition temperature was defined. It was shown that splitting of the CWSP droplets leads to essential (for some times) decrease of the heating stage duration and faster ignition. Otherwise, the coagulation leads to deceleration of fuel heating and therefore to deceleration of gas-phase and heterogeneous ignition. It was shown for a first time that ignition delay time of coagulating droplets can be determined as average value between ignition delays of separate initial droplet and the droplet with the twice bigger volume. The critical ignition temperatures of separate fuel droplets are in range between temperature conditions of the splitting and coagulation. The ignition delay times of fuel fragments which appear after splitting are much lower than for initial droplets. At low temperature ignition the conditions of droplets coagulation and splitting are very important because the ignition delays durations can differ for some times. The influence of the coagulation and splitting effects becomes vanishingly small at oxidant flow temperature more than 1000K. The obtained in this paper results should be accounted for combustion chambers working in low-temperature regime of the CWSP combustion that looks attractive from ecological, technical, economical and fire-safe points of view.
In Romania, as well as worldwide, lignite for the production of electrical energy is mainly extracted in quarry conditions. At the present time and for the near future at least, extracting lignite ...will be done with the help of continuous action excavators, especially with rotary headed excavators with radial digging, that undertake the cutting and the evacuation of the rocks from the baric step and of the lignite. On the mechanized operation lines, the excavator is the leading equipment. The growth in work efficiency of the excavator is conditioned by choosing it according to the concrete conditions of exploitation and in correlation with the other equipments on the operation lines for extracting lignite and mine waste from the coating of the lignite strata, rational intensive and extensive exploitation, adopting a modern and efficient system for doing maintenance, as well as undergoing rehabilitation and modernization processes for maintaining their technical condition at a suitable level. Estimating the duration of safe functioning of an equipment that has a certain degree of risk is a requirement of current legislation. This paper undertakes to present one of the calculus methods that is at the basis of the objective estimation of the remnant life duration of an excavator.
The character of indigenous lignite was measured by proximate analysis, ultimate analysis, coal ash analysis, coal true relative density, specific area.et al. The results showed that the internal ...moisture content is 8-9%, volat ile matter content is more than 45%, the oxygen content is above 20% while the sulphur content less than 0.5%.The main ash content is SiO2 and Al2O3, ash fusion point is above 1200 degree centigrade. The calorific value is between 12∼19MJ/kg. Macropore and mesopore is the pattern in the lignite.
Carbon dots (CDs) finds applications in the field of optoelectronics, energy conversion, energy storage, etc. In this work, the electrochemical properties of CDs (obtained from a green source, ...lignite) were established to employ them for supercapacitor application. CDs-modified carbon felt working electrode was fabricated and its electrochemical properties were studied and compared with lignite-modified carbon felt working electrode. The CDs-modified electrode showed a superior capacitance compared with lignite-modified electrode which was evidenced from their cyclic voltammograms, electron impedance spectroscopy, and charge/discharge studies. The highest observed specific capacitance value for CDs-based electrode is 30.5 F g
−1
which is 14 times higher than that of lignite-modified electrode.
In the work, we successfully fabricate mesoporous N- and O-enriched carbon (NOC) with adjustable porosity and specific surface area (SSA) by using low-cost lignite as a precursor coupled with general ...KOH or ZnCl
2
activation for electrochemical capacitors (ECs). Physicochemical and electrochemical characterizations reveal that chemical activating agents influence significantly upon the specific morphology, pore structure, and electrochemical performance of the resultant products. Strikingly, KOH-activated NOC (NOC-K) sheets are endowed with high SSA of ∼1257 m
2
g
−1
, large pore volume of 1.3 cm
3
g
−1
, and optimized pore size of ∼3 nm, rendering its electrochemical capacitance superior to those of NOC and ZnCl
2
-activated NOC (NOC-Z) in 6 M KOH. Thanks to its rich mesoporosity coupled with large electroactive SSA and heteroatom doping (N of ∼4.8 at.% and O of ∼23.3 at.%) effect, the NOC-K electrode yields even better electrochemical behaviors in 1 M H
2
SO
4
than those in 6 M KOH.
An alternative approach to biowaste management involves the application of an innovative household dryer for the dehydration of biowaste at source, in order to significantly reduce its mass and ...volume, and subsequently the collection frequency.
The main objective of this work is to assess the potential impacts of the system under examination, which involves the household dryer use and kerbside collection of the dehydrated residues (biomass), by conducting a Life Cycle Assessment study. The stages considered in the present study include the following: (a) the construction of the household biowaste dryer; (b) the use of the dryer and the collection of dehydrated residues; (c) the end-of-life treatment of the dryer. The results revealed that emissions coming from kerbside collection account for the vast majority of the total emissions from each category examined, apart from Terrestrial Ecotoxicity, where lignite, heavy fuel oil and diesel combustion during electricity production affect mainly this category. The potential impact in Global Warming over 100 years was estimated to be 8.87 kg CO2 eq / t biowaste. The Human Toxicity Potential was 1.86 kg 1,4-DB eq / t biowaste, Terrestrial Ecotoxicity Potential was 0.027 kg 1,4-DB eq / t biowaste, Freshwater Aquatic Ecotoxicity Potential was 0.0126 kg 1,4-DB eq / t biowaste and Marine Aquatic Ecotoxicity Potential was 521.85 kg 1,4-DB eq / t biowaste. Acidification Potential was estimated at 0.035 kg SO2 eq / t biowaste, while Eutrophication Potential was 0.0065 kg PO4— eq / t biowaste. Finally, Photochemical Oxidation Potential was 0.0014 kg C2H4 eq / t biowaste.
Investigations were done on two former open-cast lignite mining sites under reclamation, an artificial sand dune in Welzow Süd, and a forest plantation in Schlabendorf Süd (Brandenburg, Germany). The ...aim was to associate the topsoil hydrological characteristics of green algae dominated as well as moss and soil lichen dominated biological soil crusts during crustal succession with their water retention and the repellency index on sandy soils under temperate climate and different reliefs. The investigation of the repellency index showed on the one hand an increase due to the cross-linking of sand particles by green algae which resulted in clogging of pores. On the other hand, the occurrence of moss plants led to a decrease of the repellency index due to absorption caused by bryophytes. The determination of the water retention curves showed an increase of the water holding capacity, especially in conjunction with the growth of green algae layer. The pore-related van Genuchten parameter indicate a clay-like behaviour of the developed soil crusts. Because of the inhomogeneous distribution of lichens and mosses as well as the varying thickness of green algae layers, the water retention differed between the study sites and between samples of similar developmental stages. However, similar tendencies of water retention and water repellency related to the soil crust formation were observed. Biological soil crusts should be considered after disturbances in the context of reclamation measures, because the initial development of green algae biocrusts lead to an increasing repellency index, while the occurrence of mosses and a gain in organic matter enhance the water holding capacity. Thus, the succession of biocrusts and their small-scale succession promote the development of soil and ecosystem.
The aim of this study was to produce renewable energy from exhausted coffee residue, which is a form of biomass. As coffee preference continues to increase, the importation of coffee beans has been ...increasing sharply. However, the amount of coffee that is actually consumed is only about 0.2% of coffee beans, while the spent coffee beans are discarded in the form of exhausted coffee residue. Hydrothermal carbonization is a method of producing an improved fuel from renewable energy sources by changing the physical and chemical properties of biochars. Biochars were obtained from a variety of reaction temperatures during hydrothermal carbonization and analyzed using elemental analysis, ultimate analysis, and calorific value measurement. The atomic C/O and C/H ratios of all obtained biochars decreased and were found to be similar to those of lignite and sub-bituminous coal. The highest energy recovery efficiency of biochar indicates that the optimum reaction temperature for hydrothermal carbonization was between 210 and 240 °C, which produced biochars with calorific value of approximately 26–27 MJ/kg. The spectra of biochars obtained from Fourier transform infrared spectroscopy (FTIR) showed fewer C–O and aliphatic C–H functional groups, but more carbonyl C=O functional groups and aliphatic CH
x
groups. The results of this study indicate that hydrothermal carbonization can be used as an effective means to generate highly energy-efficient renewable fuel resources from coffee residue. The thermogravimetric analysis provided the changing combustion characteristics due to increased fixed carbon content.
The influences of five typical additives (coal fly ash, lignite, quick lime, potassium permanganate, dry sewage sludge), freeze–thaw pretreatment and temperatures (100–180 °C) on isothermal drying ...behavior of municipal sewage sludge were evaluated using a thermal analysis technique. The drying kinetics of the samples was addressed based on two falling rate stages. At the same adding dosage of 10%, the average drying rates for sewage sludge blending with coal fly ash, lignite, lime, dry sludge and potassium permanganate increased by 3.57, 2.81, 2.65, 3.05, 4.80% in comparison with the raw sewage sludge. The average drying rates for the sewage sludge after freeze–thaw pretreatment increased by 7.08%. Apparent activation energies for all sludge/additive blends and freeze–thaw sludge sample were less than those of the raw sewage sludge. Apparent activation energies of sludge/lime in two falling rate periods decreased with increasing the lime dosage from 10% up to 30%. Apparent activation energies of freeze–thaw sludge sample in two falling rate periods were the lowest in comparison with all sludge/additive blends. Coal fly ash, lignite, lime, potassium permanganate and back-mixing additives as well as freeze–thaw pretreatment were available for improving the thermal drying kinetics of the sewage sludge.
The particle size distribution (PSD) of feeding coal affects the solid concentration distribution, combustion fraction distribution and coal combustion behaviors in the circulating fluidized bed ...(CFB) boiler. In engineering, the particle size distributions for different feeding coals are determined empirically, such as the mean particle size of anthracite is smaller, and the mean particle size of lignite is larger. But the specific research on the PSD of different feeding coal is still lacking. In the operation of CFB boiler, the PSD of feeding coal is not adjusted. By optimizing the particle size distribution of feeding coal to adjust the mass ratio of fine particles in the dilute zone and coarse particles in dense zone, it is possible to obtain a good solid concentration distribution in the dilute zone and to improve coal combustion performance. This can assure the output of boiler and reduce the carbon content in ash, as well as reduce the friction of boiler and energy consumption of the fan. In this paper, an optimization model of the PSD of feeding coal of CFB boiler was developed, by setting the solid concentration of the furnace outlet and the mean retention time of coarse feeding coal in the furnace as the optimization goal. This procedure is based on the experimental results of primary fragmentation, burnout and ash formation of coal, using wen-chen hydrodynamic model. The optimized PSD of feeding coal had been calculated in some bed inventory, which results in an optimum solid concentration distribution in furnace and lower carbon content in bottom ash. Before and after optimization results showed that when the bed pressure drop was 11.3 kPa, the carbon content in bottom ash was reduced from 2.14% to 0.77%, and the solid concentration in the furnace outlet increased from 2.6 kg/Nm3 to 2.71 kg/Nm3. The calculation accuracy of the model was validated in a1060 t/h CFB boiler.
•The optimized particle size distribution of feeding coal had been worked out.•The mass ratio of the upper fine particles to lower coarse particles was adjusted.•The solid concentration in dilute zone increased after optimization.•The carbon content in bottom ash decreased after optimization.•The burnout time of the four coals were given by experiments.
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