1,721,079 research outputs found
An understanding of lump coal physical property behaviour (density and particle size effects) impacting on a commercial-scale Sasol-Lurgi FBDB gasifier
No full textThermal processes which utilize coarse coal, such as fixed-bed gasification and chain grate stoker boilers, are dependant on a stable particle size for stable operation. During coarse coal utilization, thermal fragmentation of lump coal (upon heating) produces hydrodynamic effects (pressure drop fluctuations) manifesting itself in a variety of ways, and include: channel-burning and solids elutriation. Primary thermal fragmentation occurring in the drying zone of a fixed-bed reactor is primarily a function of moisture content release with ensuing particle size reduction. Large particles tend to fragment more than finer particles, thus leading to hydrodynamic problems. From fragmentation studies it was elucidated that a thermal “stable size” is reached through the process of thermal fragmentation for optimum heat transfer and utilization during the drying and pyrolysis zone regions of the coarse coal utilization process.
In this paper, the Sasol-Lurgi MK IV FBDB gasifier turn-out physical property profiles (bulk density and particle size distribution) results will be discussed. It was found that these profiles provided significant insight into the complex heterogeneous nature of the coal transformation processes occurring within the fixed-bed reactor. In the case of the bulk density profile, a shrinking core and flaking mechanism was proposed to explain the increase in density occurring in the bottom half of the gasifier.
The +25 mm size fraction distribution profile was found to clearly show the fragmentation effects occurring within the reactor. Primary fragmentation was inferred as the mechanism responsible for causing breakage of this size fraction down to a remaining ca. 15% +25 mm fraction. The significant breakage of the coarse +25 mm fraction is expected to influence unstable gasifier conditions in the top part of the gasifier, due to pressure drop fluctuations caused by void packing. A good correlation was obtained for the relationship between bulk density versus the −25 mm + 6.3 mm size fraction content, indicating that the bed-packing density is highly dependent on the relative abundance of this intermediate size fraction. The −6.3 mm size fraction distribution profile was found to not be significantly different between the four reaction zones identified in the gasifier. Breakage of the coarser +6.3 mm sizes occurred continuously, and could possibly be related to breakage caused by the ash-grate when sampling.
The Ergun Index was successfully used to profile the fragmentation zones identified and to show areas within the gasifier where pressure drop and resultant instability occurs. This is the first-ever identification of this phenomenon occurring within a fixed-bed gasifier and is expected to lead to significant optimization challenges to ensure better stabilit
Mössbauer and other spectroscopic analyses of North-East Indian coals and tailings products
No full textThe South African industry use of Mössbauer spectroscopy to solve operational problems
No full textSouth Africa is a country that is very rich in mineral resources but the use of Mössbauer spectroscopy to solve operational industrial problems is however very limited. In the Bushveld Igneous Complex the main minerals extracted from the ore are the platinum group metals and chromium, but secondary recovery of base metals such as nickel, copper and cobalt forms an integral part of the process. Losses of nickel in the slag can amount to about 4 % and subsequent a slag cleaning furnace is used to reduce the loss to less than 0.5 % nickel oxide. The Fe2+/Fe3+ ratio and mineralogy was used to determine the partial oxygen pressure in the furnaces and also the efficiency of the nickel recovery. From the Mössbauer results, augmented with XRD, SEM, EMP-WDX and MLA analyses, optimum conditions were determined to ensure minimum metal losses. The use of Mössbauer spectroscopy in the coal industry, to investigate mineral changes that occur during its use, is also of importance. The main minerals present in coal were determined with the aid of various techniques, such as Mössbauer, XRD, SEM and HR-TEM, with the major iron minerals found to be pyrite, illite, ankerite and jarosite. A large quantity of coal is used to produce syngas via gasification plants for the production of synthetic fuels. The change of the mineral matter during gasification was studied and the changes occurring during the gasification process were followed. The syngas produced, is further treated by means of the Fischer–Tropsch process where an iron catalyst is incorporated in the process. The usefulness and fouling of the catalyst is being studied with the aid of Mössbauer spectroscopy. The calibration of equipment to determine work hardening in mining equipment was also investigated and found to be a useful tool in industry. From the above few examples it is evident that, although used on a limited base, Mössbauer spectroscopy, augmented by various other spectroscopic tools, still ensures optimal recovery and production of the vast resource base of South Afric
Electron beam and Mössbauer techniques combined to optimise base metal partitioning in the furnace
No full textFurnace slag and matte samples from Anglo Platinum smelters were analysed using a combination of electron microbeam and Mössbauer techniques. The object of the investigation was to establish the distribution of the base metals (nickel, copper and cobalt) in slag, and to predict their recovery by milling and flotation. In addition, the data was used to assess the viability of process optimisation using a modelling program. Slag samples were analysed quantitatively by EPMA, employing longer counting times for trace elements, and correcting for Fe-Kβ peak interference on Co-Kα An automated software program was used to run phase specific analysis of entrained matte inclusions in slag. The technique allows simultaneous measurement of inclusion size, and correlation of size with composition. The results were combined with EPMA data to determine maximum theoretical base metal recovery from slag.
Partitioning behaviour of elements between slag and matte depends on many parameters such as temperature, slag and matte composition, and oxygen partial pressure (pO2). Initially, predicted base metal distributions as calculated using the FactSage modelling program did not agree well with measured levels. Later, the use of Mössbauer Fe3+/Fe2+ ratios, which defined pO2 as more oxidising than previously assumed, and entrained matte composition results, allowed more accurate predictions to be made
Selective adsorption of heavy and light metals by natural zeolites
Get PDFRecent studies have shown that zeolite can be applied through an ion-exchange process to remove metals from solutions. In this paper the potential of two zeolites to perform as sorbents for treatment of multi-metal system is investigated. Parameters such as initial metal concentration, contact time, zeolite type and affinity for heavy versus light metals are taken into consideration. All the samples were prepared and characterized by XRD, XRF and FTIR.
Evaluating suitable model for the determination of binding affinity, the results showed that the pseudo second order kinetic model was adequate for such prediction. The binding affinity followed the order Co>Cu>Ca>Mg which was mainly correlated to the electronegativity of the metals. The FT-IR spectra revealed that the functional group –OH was mostly responsible for the binding of metals on the two zeolites.
The zeolites studied have shown preferential binding of heavy metals and can therefore be used to mitigate the level of such pollutant in multi-metal water syste
Bentonitc clay adsorption affinity for anionic and cationic dyes
No full textThe incidence of dye pollution in South Africa is quite alarming, requesting effective and affordable techniques to curb further degradation of the limited water resource. Adsorption is an attractive technique due to a better removal efficiency of contaminants. Bentonite also known as montmorillonite clay, has a very large surface area, suitable for adsorption; however the availability of binding sites on the clay is dependent on the geochemical transformation undergone during the genesis, making the geographical source of the clay an important parameter determining his adsorption potential. This consideration has motivated the need to test the adsorption potential of local bentonite clay for the removal of anionic and cationic dye from solution. The clay was characterized using XRD, XRF and FTIR. The adsorption affinity was tested using isotherm and kinetic models. According to the FTIR spectroscopy profile, dyes attached to the clay through interaction between the cetonyl group of the clay and the amines-primary and -secondary functional groups of methyl orange (MO) and methylene blue (MB) respectively. The adsorption capacity values obtained from the pseudo-second order kinetic model indicate that our bentonite clay has higher affinity for MB (qe = 147.06 mg/g) than MO (qe = 11.82 mg/g). It therefore ensues that our clay is suitable for the removal of MB from polluted water, but will require activation to improve the affinity for M
Mobility potential of metals in acid mine drainage occurring in the Highveld area of Mpumalanga Province in South Africa: implication of sediments and efflorescent crusts
No full textPrediction of the dispersion of pollutants from the acid mine drainage is an important step toward the development of remediation strategy and mitigation of environmental impact. Geochemical studies are often carried out to determine the speciation and mobility of metal pollutants in sediments and water. In the present study sequential leaching and humidity cell tests were carried out on the sediments from acid mine drainage (AMD) basin for the determination of the susceptibility of metal release. The X-ray diffraction (XRD) and Mössbauer analyses were carried on the efflorescent salts from the stream bank to determine the secondary minerals that could further contribute to AMD pollution impact; while speciation of metals in AMD solution was done using the geochemical model PHREEQC. The results show that metals such as Fe, Ni and U are bioavailable from the exchangeable fraction F1 of the sediments in the range of 1.1–81%; while secondary minerals contribute to higher release of Fe and SO42− in solution. The sediments studied were found to have a relatively higher acidity potential (36 and 73) versus a negligible neutralization potential. Species prediction of dissolved metals showed dominance of free metal ion species in water. Secondary minerals such as goethite and iron sulfate which have been reported to contribute to further acidification of water were found in the efflorescent crusts. The findings in this study therefore predict higher mobility and sustainable occurrence of metals in the effluent considered, prompting intervention for preservation of the environment and scarce water resource
A multi-analytical study on the sulphur components in some high sulphur Indian Tertiary coals
No full textThe main source of industrial energy in the world is coal. To better understand the distribution of sulphur containing components in high sulphur Tertiary coals, a multi-analytical analysis was carried out on four industrially important high sulphur northeast region (NER) Indian coals. Some of the relevant information on the distribution and speciation of sulphur functionalities in these Tertiary coals were obtained by using chemical analysis, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and Mössbauer spectroscopy techniques. The study revealed the presence of various sulphur compounds such as pyrite (FeS2), disulphides (S–S), sulphone (−SO2–) and aryl thioether (R1–S–R2) in the coals, which are essential to be removed before the coal could be utilised. Sulphur is present in high amounts in MEG (4.54 %) and NG (4.56 %) coal samples. The lowest amount of sulphur was found in TP coal. In the present study, it is shown that the NER Tertiary coals contain higher amounts (>50 %) of organic sulphur, which may be difficult to remove by conventional methods. X-ray photoelectron spectroscopy (XPS) analysis of these Tertiary coals revealed that sulphur is present in two forms namely inorganic and organic. TPR also provide information on sulphur association in coals as iron pyrite, sulphides, thiophene, thiols, etc. Fe components in NER coals contain typically pyrite and Mössbauer spectroscopy where pyrite, illite, marcasite and hematite were observed, which is in agreement with the results obtained with other technique
Nano-mineralogical investigation of coal and fly ashes from coal-based captive power plant (India): an introduction of occupational health hazards
No full textCoal derived nano-particles has been received much concern recently around the world for their adverse effects on human health and the environment during their utilization. In this investigation the mineral matter present in some industrially important Indian coals and their ash samples are addressed. Coal and fly ash samples from the coal-based captive power plant in Meghalaya (India) were collected for different characterization and nano-mineralogy studies. An integrated application of advanced characterization techniques such as X-ray diffraction (XRD), High Resolution-Transmission Electron microscopy (HR-TEM)/(Energy Dispersive Spectroscopy) EDS/(selected-area diffraction pattern) SAED, Field Emission-Scanning Electron Microscopy (FE-SEM)/EDS analysis, and Mössbauer spectroscopy were used to know their extent of risks to the human health when present in coal and fly ash. The study has revealed that the coals contain mainly clay minerals, whilst glass fragments, spinel, quartz, and other minerals in lesser quantities were found to be present in the coal fly ash. Fly ash carbons were present as chars. Indian coal fly ash also found to contain nanominerals and ultrafine particles. The coal-fired power plants are observed to be the largest anthropogenic source of Hg emitted to the atmosphere and expected to increase its production in near future years. The Multi Walled Carbon Nano-Tubes (MWCNTs) are detected in our fly ashes, which contains residual carbonaceous matter responsible for the Hg capture/encapsulation. This detailed investigation on the inter-relationship between the minerals present in the samples and their ash components will also be useful for fulfilling the clean coal technology principle
Geochemistry of ultra-fine and nano-compounds in coal gasification ashes: a synoptic view
No full textThe nano-mineralogy, petrology, and chemistry of coal gasification products have not been studied as extensively as the products of themorewidely used pulverized-coal combustion. The solid residues from the gasification of a lowto medium-sulfur, inertinite-rich, volatile A bituminous coal, and a high sulfur, vitrinite-rich, volatile C bituminous coal were investigated. Multifaceted chemical characterization by XRD, Raman spectroscopy, petrology, FE-SEM/ EDS, and HR-TEM/SEAD/FFT/EDS provided an in-depth understanding of coal gasification ash-forming processes. Thepetrologyof the residues generallyreflected the rank andmaceral composition of the feed coals, with the higher rank, high-inertinite coal having anisotropic carbons and inertinite in the residue, and the lower rank coal-derived residue containing isotropic carbons. The feed coal chemistry determines the mineralogy of the non-glass, non-carbon portions of the residues, with the proportions of CaCO3 versus Al2O3 determining the tendency towards the neoformation of anorthite versus mullite, respectively. Electron beamstudies showed the presence of a number of potentially hazardous elements in nanoparticles. Some of the neoformed ultra-fine/nano-minerals found in the coal ashes are the same as those commonly associated with oxidation/transformation of sulfides and sulfate
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