Fuel Processing Technology

Published by Elsevier
Online ISSN: 0378-3820
Publications
Article
The effects of acidic properties and structural changes of Y zeolite, produced by steaming, on the zeolite cracking activity, coking tendency and distribution of various products during catalytic conversion of bulky 1,3,5-triisopropylbenzene (TIPB) are reported. NaY zeolite with framework Si/Al ratio of 2.4 was synthesized by a hydrothermal method and ammonium exchanged. The zeolite was dealuminated by a temperature-programmed steaming to form USY1 and USY2 zeolites with framework Si/Al ratio of 8.1 and 12.3 respectively. The catalysts were characterized by XRD, XRF, SEM, AAS, NH3–TPD and N2 adsorption–desorption techniques. The samples were in-situ activated at 748 K and evaluated by TIPB cracking at 623 K. The coke content of the catalyst beds was estimated by TPO using an FT-IR gas cell. The results of activity measurements reveal that the dealuminated zeolites lead to lower cracking activity initially; while, they exhibit higher activity at longer times. In addition, a slight modification of the window diameter of Y zeolite, as revealed by pore size distribution analyses, alters the diffusion limitation of the reactant and products through the pores of the zeolite and significantly affects the adsorbent–adsorbate interactions. TPO experiments show that compared to the precursor zeolite, lower amount of coke is formed on the dealuminated catalysts possessing lower density of acid sites. However, the coke formed on USY samples is heavier than that formed on its precursor Y zeolite. This may be attributed to the larger pores shaped in the dealuminated catalysts which in turn provide suitable places for coke formation and growth.
 
Article
The U.S. Department of Energy commissioned the National Renewable Energy Laboratory (NREL) to develop a long-term research plan for commercializing lipid fuels and coproducts, thereby displacing petroleum and establishing a new biobased industry. This article summarizes the findings of a more detailed report: Biomass Oil Analysis: Research Needs and Recommendations, NREL/TP-510-34796. This paper provides a summary of the needs and challenges involved in displacing petroleum with lipid fuels. It identifies research agendas that could support a larger lipid fuel industry and provides guidance for researchers and funding organizations. This analysis found that modest production cost reductions and significant increases in lipid production could be achieved, but only if there are government incentives to promote the use of the high cost lipid fuels. Without the incentives, lipid fuel use will remain modest and there will be little need for research to increase supply. Research that reduces production costs is not sufficient to bring the cost of lipids in line with petroleum fuel.
 
Article
Fixed bed biomass gasification is a promising technology to produce heat and power from a renewable energy source. A twin-fire fixed bed gasifier based CHP plant was realized in the year 2003 in Wr. Neustadt, Austria. Wood chips are used as fuel, which are dried and sieved before being gasified to a low calorific gas of about 5.8 MJ/Nm3dry. Before the clean gas is fed into a gas engine a cyclone and a RME (rapemethylester)/H2O quench system followed by a wet electrostatic precipitator (ESP) is used for gas cleaning. The CHP plant has a fuel power of 2 MWth and an electric output of 550 kWel. As scale up and optimization tool a hot test rig with a capacity of 125 kWth was built. Basic parameters like the type of wood chips, power and air distribution were varied to investigate the effect on gas composition, tar content in the producer gas and carbon content in the ash. Additionally a temperature profile over the height of the 125 kW hot test rig was measured. Furthermore, the results from the hot test rig are discussed and compared with the results from the 2 MWth demonstration plant.
 
Article
Biodiesel was synthesized from rocket seed oil by base-catalyzed transesterification with methanol. The synthesis of biodiesel was confirmed by FT-IR and NMR (1H and 13C) spectroscopy. Various fuel properties of the synthesized biodiesel were determined using ASTM methods and discussed accordingly. A total of eleven fatty acid methyl esters (FAMEs) were identified in rocket seed oil biodiesel (RSOB) by the retention time and the fragmentation pattern data of GC/MS analysis. The identified FAMEs were, methyl 9-hexadecenoate (C16:1), 14-methyl pentadecanoate (C16:0), methyl 9,12-octadecadienoate (C18:2), methyl 9-octadecenoate (C18:1), methyl octadecanoate (C18:0), methyl 11-eicosenoate (C20:1), methyl eicosanoate (C20:0), methyl 13-docosenoate (C22:1), methyl docosanoate (C22:0), methyl 15-tetracosenoate (24:1) and methyl tetracosanoate (C24:0). The percentage conversion of triglycerides to corresponding methyl esters determined by 1H NMR was 88.49%.
 
Article
A 2-year demonstration program is carried out by the Danish utility I/S Midtkraft at a 150-MWe PF-boiler unit reconstructed for co-firing straw and coal. As a part of the demonstration program, a comprehensive in situ measurement campaign was conducted during the spring of 1996 in collaboration with the Technical University of Denmark. Six sample positions have been established between the upper part of the furnace and the economizer. The campaign included in situ sampling of deposits on water/air-cooled probes, sampling of fly ash, flue gas and gas phase alkali metal compounds, and aerosols as well as temperature measurements. Material balance closures were carried out at all operating conditions. The experimental data was evaluated together with researchers from the Technical University of Denmark and the results were stored in a data base program developed under the CHEC-research program to predict deposition propensities and high temperature corrosion during co-combustion of straw and coal in PF-boilers. Danish full scale results from co-firing straw and coal, the test facility and test program, and the potential theoretical support from the Technical University of Denmark are presented in this paper.
 
Amount of sulphur loss after non-isothermal oxidative desulphurisation of feed and Hg-treated coals 
Article
This paper reports a relatively simple low-temperature non-isothermal oxidative desulphurisation of coal organic sulphur by weakening the CS bond using HgCl2 solution to an inorganic sulphur-free high-sulphur Indian coal. When oxidised from 50°C to 150°C in air under normal atmospheric pressure, there is continuous decrease of organic sulphur content in the samples of the feed and Hg-treated coals. Desulphurisation is more in the Hg-treated coal (4.97–14.53 wt.%) than in the feed coal (3.72–10.93 wt.%). Kinetic study reveals that the oxidative desulphurisation process follows pseudo-first order kinetics and the rate constants have been found to be in the range (3.09–5.06)×10−5 s−1 for feed coal and (4.19–6.80)×10−5 s−1 for Hg-treated coal. The activation energies for the sulphur loss reaction in the oxidative desulphurisation process by using the pseudo-first order kinetic (feed coal: 2.21×102 J mol−1; Hg-treated coal: 1.53×102 J mol−1) have been found to be almost similar to those calculated by applying the Coats and Redfern's equation (feed coal: 2.19×102 J mol−1; Hg-treated coal: 1.53×102 J mol−1). However, the value is higher (feed coal: 3.50×102 J mol−1; Hg-treated coal: 2.70×102 J mol−1) when Horowitz and Metzger's equation is applied. The frequency factors computed by the pseudo-first order kinetics are very low and have been found to be 2.66×10−5 s−1 for feed coal and 3.96×10−5 s−1 for Hg-treated coal, suggesting very low rate of successful collisions for the formation of the activated complex. Evaluation of thermodynamic parameters viz., ΔH, ΔU, ΔS and ΔG, reveals that this oxidative desulphurisation process is non-spontaneous in nature and the degree of non-spontaneity of such a process in the feed coal is more relative to that of the Hg-treated coal.
 
Article
Wood pellets have become an important renewable energy fuel. Nowadays the main raw materials used for their production are wood wastes from wood industries. However, these wood wastes have other uses in Spain and it is necessary to look for other possible raw materials. In this work, vine shoots and industrial cork residue were studied as raw materials. The results showed that pelletisation of vine shoots presented a high energy demand. This energy requirement was reduced with the addition of industrial cork residue. Moreover, industrial cork residue decreased the ash content of pellets and increased their heating value, although it decreased their physical properties at the same time. Regarding combustion, the addition of industrial cork residue decreased the accumulation of ash in the pellet burner and its sintering tendency. The major conclusion of the work is that the most appropriate blend to improve pelletisation and combustion processes is 30% wt. of vine shoots and 70% wt. of industrial cork residue.
 
Article
Cofiring of biomass with coal has been conducted using all kinds of combustion technologies which include cyclone boilers, wall-fired and tangentially-fired pulverized coal boilers, fluidized-bed boilers and stoker-fired boilers. Fundamental studies and experiments were also performed on biofuel safety issues, blended biofuel/coal storage and transport and fuel chemistries. The cofiring programs has led to the development of a database concerning biofuel properties which was coupled with computer programs to evaluate certain issues associated with blending.
 
Article
The current volume presents 19 papers that advance research and technology in C1 chemistry and fuel science technology. This introductory paper contains a brief outline of the material presented in those papers.
 
Article
The total and size fractionated concentrations of As, Cd, Cr, Cu, Ni, Pb and Zn in bottom ash and two fly ash fractions from a large-sized (246 MW) fluidized bed boiler were compared to Finnish statutory limit values for forest fertilizers, which came into force in March 2007. Fly ashes were sampled from the different fields (i.e. electrodes) of the electrostatic precipitator (ESP) unit treating the stack gases. The bottom ash and the fly ash from the first ESP field are suitable for use a forest fertilizer. Due to the elevated As concentration (40 mg/kg; d.w.), which exceeded its Finnish limit value of 30 mg/kg (d.w.), the fly ash from the second ESP field is not suitable as a forest fertilizer alone. The results of ash sieving indicated that an As concentration of 40 mg/kg (d.w.) for particle size less than 0.125 mm for fly ash 2 from the second ESP electrode field exceeded the As limit value of 30 mg/kg (d.w.). In addition, a Pb concentration of 170 mg/kg (d.w.) for fly ash 1 from the first ESP electrode field for particle size 0.5–2.0 mm exceeded the Pb limit value of 150 mg/kg (d.w.). These two specific fractions are therefore not suitable for used as a forest fertilizer alone.
 
Article
Experiments with a small-scale cyclone burner used for burner enrichment in a down-fired pulverized-coal 300 MWe utility have been conducted on an air/particle test facility. Particle separating efficiency was obtained with different positions of an adjustable vane. Industrial experiments were performed on a full-scale boiler. The gas temperature distribution along the primary air and coal mixture flow, gas temperature distribution of the furnace, and gas components such as O2, CO, CO2 and NOX in the near-wall region were measured for the first time. The influence of the adjustable vane position on coal combustion in the furnace was determined. With the adjustable vanes at the nozzle, ignition of the primary air and pulverized-coal mixture was delayed and the gas temperature peak was above the burner arch, with high NOX emission. Raising the vanes can bring forward the ignition point but results in the fuel-rich flow being up ahead of time, leading to a rise in carbon content in fly ash and NOX emission.
 
Article
In June 2005, the U.S. Environmental Protection Agency (EPA) finalized the Clean Air Mercury Rule (CAMR). As part of the rule, all coal-fired power plants were required to do continuous mercury measurements. Although CAMR has now been vacated by the courts, based on discussion with the EPA, it is expected that the mercury measurement requirements as written will be part of any future mercury regulations. This paper focuses on the process for certifying a continuous mercury monitor and conducting a relative accuracy test audit using EPA Method 30B. Based on the experience gained at the Energy & Environmental Research Center, a number of recommendations for conducting a RATA are provided.
 
Article
In this study, the physical and chemical properties of bottom ash and fly ash originating from the co-combustion of biomass-derived fuels (i.e. wood chips, sawdust, bark, and peat) from a 32 MW fluidized bed boiler at a municipal district heating plant were investigated. Silicate minerals were predominant in the bottom ash and calcium minerals in the fly ash, with most of the inorganic nutrients and heavy metals being enriched in the fly ash. The enrichment factors for heavy metals in the fly ash varied between 0.2 for silicon and 16.3 for lead, and for plant nutrients, between 1.5 for phosphorous and 108 for potassium. However, all heavy metal concentrations in both the bottom ash and fly ash were significantly lower than the current Finnish limit for maximum allowable heavy metal concentrations for forest fertilizers, which came into force in March 2007. According to the particle size distribution, the mass loadings of heavy metals in the fly ash were more than 90% contributed by the smallest particle size fraction lower than 0.074 mm. In the bottom ash, between 83.6 and 91.9% of the mass loadings of heavy metals were contributed by the particle size fraction between 0.5 and 2.0 mm.
 
Article
In this work, a CFD numerical study of co-firing coal and cynara in a 350 MWe utility boiler is presented. The most influent operational factors related to the biomass feeding conditions such as biomass mean particle size, level of substitution of coal by biomass and feeding location in the furnace, are analyzed, determining their influence in the combustion process. Validation of the simulations is performed using measurements gathered at the plant. Results from the study show interesting conclusions for their implementation in the power plant, suggesting recommendable limits in the maximum biomass substitution level and particle size in order to keep a reasonable boiler efficiency, and pointing out the outstanding influence of the biomass injection location discussing thermal and fluid-dynamic implications and the possibility of introducing retrofitted or specific biomass burners.
 
Article
The dielectric properties of 4,6-dimethyldibenzothiophene (DMDBT), hexadecane (HD), quinoline (QL), and HD/QL mixtures were investigated at six microwave frequencies (0.4, 0.9, 1.4, 1.9, 2.5 and 3.0 GHz) and temperatures ranging from 297 K to 624 K. While both DMDBT and HD exhibited limited response under these conditions, QL demonstrated high dielectric loss with a penetration depth comparable to that of water. Through the use of the Debye relationship and solvent mixing rules, a model is proposed to predict the dielectric constant and loss factor for HD/QL mixtures. Based on the observed dielectric behaviour of QL, microwave-assisted separation/conversion may be effective during upgrading of light cycle oil (LCO) for similar, difficult-to-remove nitrogen compounds.Research Highlights► Hexadecane, quinoline and 4,6-DMDBT as model compounds in LCO upgrading. ► Temperatures of 297 to 624 K, microwave freq.: 0.4, 0.9, 1.4, 1.9, 2.5 and 3.0 GHz. ► Both Hexadecane and 4,6-DMDBT nearly transparent to microwave radiation. ► Quinoline exhibits high dielectric loss, with a penetration depth comparable to water. ► Debye relationship and solvent mixing rules accurately described mixture properties.
 
Average corrosion loss from the probe experiments. Maximum measured values are indicated.
SEM-micrograph of Sanicro28 (left) and 15Mo3 (right), MSW period.
SEM-mapping pictures of Sanicro28 (left) and 15Mo3 (right), MSW period.
Article
Incineration of municipal solid waste is often associated with high temperature corrosion problems. This paper presents results of full-scale corrosion tests in a 65 MW waste fired combined heat and power plant. A failure case indicated alarmingly high corrosion rate of the superheater tubes. Corrosion tests with five different alloys were carried out within this work in order to determine plant specific corrosion rates on different superheater materials. Additional tests were done to determine the effect on the corrosion rate from adding chlorine containing polyvinyl chloride to the ordinary fuel mix. A corrosion probe with metal temperatures ranging from 320 °C to 460 °C was used to estimate corrosion loss and to collect deposits. The sampling was performed at a flue gas temperature of 470 °C for 10 days. The probe rings were analysed using scanning electron microscope and micrometer measurements to determine the deposit chemistry and corrosion rates. The results showed significant differences in corrosion rates depending on tube material. Chlorine was shown to have a key role in the corrosion process, even at these relatively low temperatures. The results indicated a chlorine induced corrosion mechanism involving volatile iron chloride with a high corrosion rate on the superheater materials typically used. Addition of extra polyvinyl chloride to the fuel mix had an increasing effect on the corrosion.
 
Article
The fundamental natures of the interaction between thiophene and ionic liquids of 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]+[PF6]−) and 1-n-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]+[BF4]−) were investigated using ab initio calculations and correlated with previous experimental results. The optimized structures show that the anions of the ionic liquids are situated outside the ring plane of the thiophene, with the fluorine atoms interacting with the hydrogen atoms of the thiophene, and the cation of the ionic liquids approaches the thiophene with its positively charged atoms approaching the negatively charged atoms of TS. It is concluded that thiophene molecules interact with the ionic liquids mainly via Coulombian attraction. Further analysis explained the results obtained from an absorption experiment that the molar ratios of the absorbed thiophene to the ionic liquids were approximately 3.5/1 and 2.4/1 for [BMIM]+[PF6]− and [BMIM]+[BF4]−, respectively. The strong electron donation of the phosphorus atom to the fluorine atoms in the PF6− cluster is believed to be the major factor resulting in the higher molar ratio of thiophene/[BMIM]+[PF6]−. The other factor is the difference of the compactness between the cation and the anion in the two ionic liquids.
 
Article
This paper presents the results of a study carried out on a small-scale 10 kW fixed-bed combustor fired by blended pellet fuels burning on a thin depth fuel-bed. The use of the thin fuel-bed may contribute to major advances in the introduction of low-cost, fully automated small-scale combustors by eliminating de-ashing mechanisms, and improving operating conditions. The pellets were made by pressing the mixture of finely ground lignite or its by-product (xylite) with wood chips. The xylite (woody lignite) and the wood chips are wastes produced during the production of lignite fuel and timber, respectively. Therefore, using these materials to produce the high quality pellet fuel contributes to environmental conservation. Water and calcium hydroxide suspensions were used as pelletising agents playing the role of binders. The major objective was to study the improvement of the quality of the blended pellet fuels in regard to their combustion and emission behaviours when burned on the thin fuel-bed. The ignition and combustion behaviour of the pellets were compared to those of conventional lignite briquettes. The study proved that the pellets on the thin fuel-bed ignited faster and had steady burnout. The emissions of NOx, SO2, CO and hydrocarbon compounds were comparatively lower than those from burning of lignite briquettes in a domestic combustor. The addition of calcium hydroxide suspensions played not only the role of binding together the raw material blends, but also provided favourable Ca/S molar ratio optimum for considerable reduction of the SO2 emissions. The need to reduce further the specific emissions of SO2 leads to exceeding the proportional value of Ca/S molar ratio, which lowers the calorific value of the pellets. Thermogravimetric studies helped in establishing the comparative pyrolysis behaviours of the lignite and wood chips.
 
Article
Modeling mercury speciation is an important requirement for estimating harmful emissions from coal-fired power plants and developing strategies to reduce them. First-principle models based on chemical, kinetic, and thermodynamic aspects exist, but these are complex and difficult to develop. The use of modern data-based machine learning techniques has been recently introduced, including neural networks. Here we propose an alternative approach using abductive networks based on the group method of data handling (GMDH) algorithm, with the advantages of simplified and more automated model synthesis, automatic selection of significant inputs, and more transparent input–output model relationships. Models were developed for predicting three types of mercury speciation (elemental, oxidized, and particulate) using a small dataset containing six inputs parameters on the composition of the coal used and boiler operating conditions. Prediction performance compares favourably with neural network models developed using the same dataset, with correlation coefficients as high as 0.97 for training data. Network committees (ensembles) are proposed as a means of improving prediction accuracy, and suggestions are made for future work to further improve performance.
 
Article
Dry catalytic hydrogenation, using an impregnated molybdenum catalyst, has been used to explore the processes of coal liquefaction and their relation to coal structure. It was found that for high activity the molybdenum must be present as MoS2 and that the conditions used for impregnation can strongly influence catalyst dispersion and activity. At temperatures of 400°C and lower, a subbituminous coal was more readily converted to liquid products and gases, than a coal of bituminous rank. The low-rank coal products were comparatively richer in hydrogen, possessed higher oil to asphaltene ratios and were more aliphatic than the bituminous coal liquids.It is considered that the higher reactivity of the low-rank coal is attributable to the initial reactions being conducted under conditions which promote hydrogenation while minimizing condensation and cracking reactions.Examination of reacted coals by reflected fluorescent light microscopy showed a close correlation between the yield of extractable liquids and the maximum intensity of vitrinite fluorescence. The fluorescence appears to be directly related to the liberation of relatively low molecular weight species within the coal structure. Coal pretreatment by low-temperature dry hydrogenation, prior to higher temperature liquefaction in the presence of solvent, improved the overall conversion and product selectivity of both bituminous and subbituminous coals. It is suggested that subtle control of the initial conversion reactions can lead to more efficient liquefaction of coals of different rank.
 
Article
Landfill gas (LFG) was upgraded to pure methane using the adsorption and absorption processes. Different toxic compounds like aromatics and chlorinated compounds were removed using granular activated carbon. The activated carbon adsorbed toxic trace components in the following order: carbon tetrachloride > toluene > chloroform > xylene > ethylbenzene > benzene > trichloroethylene ≈ tetrachloroethylene. After removing all trace components, the gas was fed to absorption apparatus for the removal of carbon dioxide (CO2). Two alkanolamines, monoethanol amine (MEA) and diethanol amine (DEA) were used for the removal of CO2 from LFG. The maximum CO2 loading is obtained for 30 wt.% MEA which is around 2.9 mol L− 1 of absorbent solution whereas for same concentration of DEA it is around 1.66 mol L − 1 of solution. 30 wt% MEA displayed a higher absorption rate of around 6.64 × 10− 5 mol L− 1 min− 1. DEA displayed a higher desorption rate and a better cyclic capacity as compared to MEA. Methane obtained from this process can be further used in the natural gas network for city.
 
Article
Carbon dioxide transfer capacities of aqueous ammonia solution and monoethanolamine (MEA) solution were compared. The ammonia process for CO2 capture was simulated using a semibatch reactor, where the flow of gas is continuous. The CO2 carrying capacity in g CO2 per g of NH3 solution (8 wt.%) circulated is 0.07 as compared with 0.036 g CO2 per g MEA solution (20 wt.%). The energy requirement for liquid mass circulation of ammonia solution is approximately 50% of MEA solution for equal weight of CO2 carried. In another comparison, the thermal energy required to regenerate CO2 from the rich solution is substantially less as compared to the MEA process. A 3-cycle absorption–regeneration test was conducted in the semibatch reactor to simulate an approach-to-steady state in a flow system. pH values of the absorbent solution was found to oscillate between 9.6 (CO2-lean) and 8.8 (CO2-rich) under the test conditions. Thermodynamics study shows that ammonium bicarbonate required the least thermal energy among the ammonium compounds for CO2 regeneration.
 
Article
The steam gasification of solid biomass by means of the absorption enhanced reforming process (AER process) yields a high quality product gas with increased hydrogen content. The product gas can be used for a wide range of applications which covers the conventional combined heat and power production as well as the operation of fuel cells, the conversion into liquid fuels or the generation of synthetic natural gas and hydrogen. On the basis of a dual fluidized bed system, steam gasification of biomass is coupled with in situ CO2 absorption to enhance the formation of hydrogen. The reactive bed material (limestone) used in the dual fluidized bed system realizes the continuous CO2 removal by cyclic carbonation of CaO and calcination of CaCO3. Biomass gasification with in situ CO2 absorption has been substantially proven in pilot plant scale of 100 kW fuel input. The present paper outlines the basic principles of steam gasification combined with the AER process the investigations in reactive bed materials, and concentrates further on the first time application of the AER process on industrial scale. The first time application has been carried out within an experimental campaign at a combined heat and power plant of 8 MW fuel input. The results are outlined with regard to the process conditions and achieved product gas composition. Furthermore, the results are compared with standard steam gasification of biomass as well as with application of absorption enhanced reforming process at pilot plant scale.
 
Article
Naphtha is a volatile petroleum fraction containing C4–C15 hydrocarbon compounds used as feedstock for petrochemical processes which are seriously affected by trace metals. Simple methods for copper, iron, lead and silicon determination in naphtha using graphite furnace atomic absorption spectrometry (GFAAS) have been developed. Two different approaches are presented: direct injection of the sample and oil-in-water microemulsion formation using a mixture of the sample, propan-1-ol and nitric acid aqueous solution. The calibration curves showed linear response for each concentration range with correlation coefficients ranging from 0.9728 to 0.9998. Precision figures of 1.7–20%, reported as the relative standard deviation, were calculated from at least twenty consecutive measurements of solutions containing the metal in a concentration level below 100 μg L−1. The characteristic masses varied from 8.5 to 44 pg and the limit of detection, defined as the metal concentration that gives a response equivalent to three times the standard deviation of the blank (n = 10), was found to be within the range 0.01–26 μg L−1. A critical analysis is presented by the authors emphasizing the advantages and limitations of both approaches. The proposed procedures have been used for copper, iron, lead and silicon determination in naphtha feeds processed in Braskem S.A. (Camacari, Bahia, Brazil).
 
Article
A two-step process capable of removing NOx and SO2 simultaneously was proposed, which was made up of an ozonizing chamber and an absorber containing a reducing agent solution. Nitrogen oxides (NO plus NO2) in most practical exhaust gases consist chiefly of NO. The injection of ozone into the exhaust gas gives rise to a rapid oxidation of NO to NO2. Compared to NO, NO2 has relatively high solubility in water, and it can readily be reduced to N2 when the NO2-rich exhaust gas is brought into contact with the reducing agent solution. Sodium sulfide (Na2S) used as the reducing agent in this study can also remove SO2, effectively. As the exhaust gas passed through the ozonizing chamber and the absorber sequentially, NOx removal efficiency of about 95% and SO2 removal efficiency of 100% were obtained. The formation of H2S from sodium sulfide could be suppressed by using a basic reagent, together with the reducing agent. The rate of depletion of the reducing agent during the treatment of the exhaust gas was much faster than expected by reaction stoichiometry, obviously due to the oxygen in the exhaust gas. The amount of sodium sulfide required was found to be about four times the amount of NOx and SO2 removed.
 
Article
The aim of this work was to develop an experimental design to optimize the direct determination of copper in gasoline by graphite furnace atomic absorption spectrometry. The optimization of the process was carried out firstly by evaluating the variables in the procedure (pyrolysis time and temperature, atomization temperature and sample volume) using a factorial design (24). The response surface was constructed and it presented pyrolysis optimal temperature on 800 °C, sample volume of 30 μL using the atomization temperature of 2500 °C. The amount of copper in the gasoline samples from São Luis City (Brazil) varied from 3.65 to 16.21 μg L− 1, with 0.65 and 1.9 μg L− 1 as detection limit and quantification limit, respectively. Accuracy was evaluated by a comparative procedure and the results proved the viability of copper direct determination in fuel samples.
 
Article
The mineralogy of coal and coal ash samples from a wide variety of deposits worldwide has been studied by X-ray diffractometry, light microscopy, SEM, TEM, and DTA-TGA methods. The common major minerals identified in the crystalline matter of coals are quartz, kaolinite, illite, calcite, pyrite, plagioclase, K-feldspar and gypsum, and occasionally dolomite, ankerite, siderite, Fe oxyhydroxides and sulphates. A number of minor and especially accessory minerals are also present. The modes of occurrence and some genetic peculiarities of the minerals found are described and summarized. Minerals and phases of probable detrital origin include mainly silicates, volcanic glass, oxyhydroxides and phosphates. Authigenic minerals of syngenetic origin may be sulphides, clay minerals, carbonates and rarely sulphates and phosphates. Epigenetic minerals, formed by the infiltration of low-temperature hydrothermal solutions, may include sulphides, carbonates, sulphates, clay minerals, quartz, chlorides, and probably alkaline-earth hydroxides and zeolites. The alteration products of detrital and authigenic minerals may be Fe and Al oxyhydroxides, sulphates, kaolinite, illite, chlorite, muscovite, zeolites and calcite. The behaviour of these minerals and phases during low- and high-temperature ashing is also discussed.
 
SEM-EDAX dot image with an elemental distribution of Pb, Zn, Cl, S, P, Si, Ca, and Fe in the fraction enriched in polymer-based char particles of RDC.
Ž . Element contents determined by AAS in dry water-soluble residue DWSR generated from refuse-derived
Article
The trace elements in refuse-derived char (RDC) generated by thermolysis of municipal solid waste (MSW) were studied to elucidate their occurrence, abundance and source. The content, enrichment factor, concentration trend, distribution, nature and modes of occurrence of major, minor and trace elements in RDC and RDC ash were characterized. It was found that a number of trace elements (Ag, Cd, Cl, Cr, Cu, Ho, I, Pb, Pr, Re, Sb, Sm, Sn, and Zn) in RDC have concentrations significantly higher (enrichment factor ≥10) than the respective Clarke (worldwide averaged) values for coals. The distribution of trace elements such as Cr, Cu, Mn, Ni, Pb, Sb, and Zn, is controlled mostly by the organic matter, clay minerals and Fe oxyhydroxides, and in some cases by carbonates, sulphates, phosphates, chlorides and alloys. Organics, heavier, magnetic, fine and especially accessory minerals and phases in RDC are concentrating phases for these trace elements. Trace elements in RDC may be present, in decreasing order of significance, as: element-organic compounds; impurities in the mineral matter; major components in the mineral matter; major and impurity components in the inorganic amorphous matter; and elements in the fluid constituents. This characterization also reveals those elements that have the greatest potential for environmental impacts or for possible resource recovery. The results show that the effective economic and environmental management of MSW and RDC requires a long-term strategy based on a detailed understanding of the source, formation, behaviour and fate of the modes of trace element occurrences in MSW, RDC and combustion waste residues.
 
Article
An activated carbon-supported copper and cerium catalyst–sorbent (Cu–Ce/AC) is studied for phenol adsorption from a water phase and catalytic oxidation of the adsorbed phenol under dry conditions. The Cu–Ce/AC has high phenol adsorption capacities and high phenol oxidation activities. The phenol saturation adsorption capacity of the fresh Cu–Ce/AC is about 209 mg/g. With increasing adsorption–oxidation cycles (repeat uses), the phenol adsorption capacity decreases consecutively to a stable value of about 78 mg/g when the oxidation is carried out at 250 °C for 2 h, which is better than that of other types of AC-based materials. The initial oxidation temperature for phenol is about 160 °C, which is 150 °C lower than the ignition temperature of the AC. The main oxidation products are CO2 and H2O with a small amount of desorbed phenol. The decrease in phenol adsorption capacity after the oxidation is caused by the formation of phenol polymeric residues, which block the micro-pore and perhaps cover the active sites.
 
Article
γ-Radiolysis of acidic aqueous coal slurries is a novel and effective method for the simultaneous oxidative desulphurisation and demineralisation of high-sulphur coals. This method is capable to selectively remove the inorganic and organic forms of sulphur simultaneously through the in situ-generated H2O2 and other radiolytic products. In effect, there is neither any appreciable degradation of coal matrix nor any loss in the caking property and volatile matter content of the coals after the removal of sulphur. However, significant removals of sulphur and mineral matter are effected at rather high γ-dose (175×104 Gy or so). Therefore, for the process to be economically viable and commercially adaptable, the applied γ-dose needs to be somehow substantially brought down, at which the same level of desulphurisation could be achieved. Catalytically, accelerating the radiolysis process is one such possibility to effect the desulphurisation step at a low γ-dose.Reported in this paper are the results of investigations on the desulphurisation and demineralisation of high-sulphur (sulphur content in the range 3–5.5%) Churphy, Chalang and Bapung coals of Meghalaya by γ-radiolytic process catalysed by MnO2. The maximum removal of total sulphur (15.6%, 30.0% and 29.8%) at 30×104 Gy in the presence of MnO2 and the simultaneous removal of mineral matter (20.0% and 18.5% from Churphy and Chalang coals at 30×104 Gy and 12.0% from Bapung coal at 45×104 Gy) are at par with removals at 175×104 Gy without MnO2, which has been attributed to MnO2 catalytically accelerating the radiolytic process via the formation of highly reactive MnO under the action of γ-rays. All the other features of non-catalysed radiolytic desulphurisation such as stabilisation of the slurry and coal not becoming radioactive during irradiation, increase in the heating value, improvement in the caking property, no appreciable degradation of coal matrix after removal of sulphur from the coals remain the same.
 
Article
This study examined factors impacting the stability of biodiesel (B100) samples collected as part of a 2004 nationwide fuel quality survey in the United States. Biodiesel is significantly less stable than petroleum diesel, so an understanding of the chemical and environmental factors affecting its degradation is required. The survey included samples produced from soy, waste oils, and tallow. The 27 samples were assessed for stability using the ASTM D2274 test for insoluble formation and the OSI method (via Rancimat apparatus) for induction time. Additionally, the samples were characterized for fatty acid make up, relative antioxidant content, metals content, and total glycerin content (free glycerin plus glycerin bound as mono-, di-, and triglycerides). For the samples examined here the polyunsaturated content (or oxidizability) has the largest impact on both increasing insoluble formation and reducing induction time. However, the formation of insolubles is also measurably decreased by increasing relative antioxidant content and increased by increasing total glycerin content. The OSI or Rancimat induction time is also increased by increasing relative antioxidant content, as expected.
 
Article
Experiments on high volatile bituminous coal extraction at ambient temperature have been carried out by means of 18 solvents having their electron-donor and -acceptor properties quantitatively determined (DN and AN numbers) by Gutmann's method. A model for coal extraction, based on the assumption that donor-acceptor bonds occur in coal and are responsible for binding together macromolecular network and extractable substances filling the pores of a network, has been worked out and verified on the basis of experimental data.The results lead to the conclusion that extraction is in principle, a substitution reaction: pore substances are replaced by a solvent molecule in their Donornetwork → Acceptorpore substance or Donorpore substance → Acceptornetwork bonds. Solvents capable of substitution are characterized by specific DN and AN values.
 
Article
Conventional biodiesel production methods utilize alcohol as acyl acceptor and produces glycerol as side product. Hence, with escalating production of biodiesel throughout the world, it leads to oversupply of glycerol and subsequently causes devaluation in the market. In this study, methyl acetate was employed as acyl acceptor in non-catalytic supercritical methyl acetate (SCMA) process to produce fatty acid methyl esters (FAME) and side product of triacetin, a valuable fuel additive instead of glycerol. Consequently, the properties of biodiesel produced (FAME and triacetin) are superior compared to conventional biodiesel method (FAME only). In this research, the effects of reaction temperature, reaction time and molar ratio of methyl acetate to oil on the yield of biodiesel were investigated. Apart from that, the influence of impurities commonly found in waste oils/fats such as free fatty acids and water were studied as well and compared with methanol-based reactions of supercritical and heterogeneous catalysis. Results show that biodiesel yields in SCMA process could achieve 99 wt.% when the operating conditions were fixed at 400 °C/220 bar for reaction temperature, methyl acetate/oil molar ratio of 30:1 and 60 min of reaction time. Furthermore, SCMA did not suffer from adverse effect with the presence of impurities, proving that SCMA has a high tolerance towards contamination which is crucial to allow the utilization of inexpensive waste oils/fats as biodiesel feedstock.Research highlights► The prospect of supercritical methyl acetate (SCMA) reaction was investigated. ► Effects of reaction temperature and impurities (FFA and water) were examined. ► Results showed SCMA did not suffer adverse effect in the presence of impurities. ► SCMA allows simultaneous production of biodiesel and value-added triacetin.
 
Article
The dolomite modified with acetic acid solution was proposed as a CO2 sorbent for calcination/carbonation cycles. The carbonation conversions for modified and original dolomites in a twin fixed-bed reactor system with increasing the numbers of cycles were investigated. The carbonation temperature in the range of 630 °C–700 °C is beneficial to the carbonation reaction of modified dolomite. The carbonation conversion for modified dolomite is significantly higher than that for original sorbent at the same reaction conditions with increasing numbers of reaction cycles. The modified dolomite exhibits a carbonation conversion of 0.6 after 20 cycles, while the unmodified sorbent shows a conversion of 0.26 at the same reaction conditions, which is calcined at 920 °C and carbonated at 650 °C. At the high calcination temperature over 920 °C modified dolomite can maintain much higher conversion than unmodified sorbent. The mean grain size of CaO derived from modified dolomite is smaller than that from original sorbent with increasing numbers of reaction cycles. The calcined modified dolomite possesses greater surface area and pore volume than calcined original sorbent during the multiple cycles. The pore volume and pore area distributions for calcined modified dolomite are also superior to those for calcined unmodified sorbent during the looping cycle. The modified dolomite is proved as a new and promising type of regenerable CO2 sorbent for industrial applications.
 
Article
The effect of the catalyst precursor formulation on the hydrotreatment of Belayim atmospheric residue was investigated and different Q2[MoxSy] complexes were tested. The effect of the counterion Q and of the y/x ratio were examined; the most interesting results were obtained for S/Mo ⩽ 4 with [Mo3S9]2− as the best precursor and with phosphonium salts as the best counterions. Phosphorus promotion might be related to vanadium demetallation. These results were compared with those obtained by using MoO2(acac)2 (acac = acetylacetonate) as the catalyst precursor. In order to discriminate between thermic and catalytic aspects, the effect of catalyst concentration was carefully examined; the higher the concentration, the higher the removal of heteroatoms from the residue without producing too many light products.
 
Article
A nonaqueous potentiometric titration method for the determination of weak acids using ethylenediamine and sodium aminoethoxide as solvent and titrant respectively is discussed. The use of absolutely dry, carbon-dioxide free reagents is found to be essential to accurately determine endpoints. Refinements in purification and storage techniques as well as in experimental procedure compared with earlier work are described in this paper.By using the improved procedures individual phenolic groups in some dihydric phenols were resolved for the first time and previously undifferentiated dihydric phenols are now easily detected and quantitatively determined. In addition, other weakly acidic phenols with previously undetected endpoints have been titrated successfully. The acidic oxygen content of a wide range of Australian coals and of the solid and liquid coal-derived products has been determined by this potentiometric method.
 
Article
Studies were performed at atmospheric pressure in a fixed-bed microreactor at temperatures of 400 and 500°C over HZSM-5, silicalite, silica, silica-alumina, γ-alumina, calcium oxide and magnesium oxide catalysts to determine the various roles of catalyst acidity, basicity and shape selectivity on canola oil conversion and product distribution. Results showed that the initial decomposition of canola oil to long chain hydrocarbons and oxygenated hydrocarbons was independent of catalyst characteristics. However, subsequent decomposition (secondary cracking) of the resulting heavy molecules into light molecules (gas or liquid) appeared to be greatly enhanced by the amorphous and non-shape selective characteristics of the catalyst (as in silica-alumina, γ-alumina and silica). In contrast, a high shape selectivity in a catalyst (as in HZSM-5 and silicalite catalysts) permitted a mild secondary cracking resulting in a low gas yield and a high organic liquid product yield. On the other hand, it was interesting to observe that the presence of basic sites in a catalyst (as in calcium oxide and magnesium oxide) strongly inhibited secondary cracking. This resulted in the production of high yields of residual oil and low gas yields. The production of C2C4 olefins, n-C4 hydrocarbons and aromatic hydrocarbons of unconstrained sizes, which reflected thermal effects on the overall reaction scheme, were predominant in amorphous and non-shape selective catalysts. On the other hand, the formation of C2C4 paraffins, branched chain and total C4 hydrocarbons as well as aromatic hydrocarbons of constrained sizes (C7C9) which were predominant in the shape selective catalysts showed that, apart from the products formed due to thermal effects, the type, structure and sizes of other products are determined principally by the shape selective characteristic of the catalyst.
 
Article
The mineral matter in an Australian black coal has been isolated using a low-temperature ashing (LTA) procedure. This LTA procedure is a modification of the Australian Standard for LTA at 370°C, and alleviates adverse effects to the minerals caused by the heat of combustion. The leaching behaviour of the mineral matter towards aqueous HCl and hydrofluoric acid (HF) is presented. HCl can dissolve simple compounds such as phosphates and carbonates, yet it cannot completely dissolve the clays. HF reacts with almost every mineral in the mineral matter, except pyrite, and most of the reaction products are water soluble. However, at HF concentrations greater than that required to dissolve the aluminosilicate compounds in the mineral matter, insoluble compounds form. These compounds include CaF2, MgF2 and a compound containing Na, which is believed to be NaAlF4. It is proposed that HF reacts preferentially with the aluminosilicates in the mineral matter to form largely AlF2+, AlF3 and SiF4, and that the concentrations of free fluoride (F−) and AlF4− are not high enough to complex cations such as Ca2+, Mg2+ and Na+. When the mineral matter is treated with HF concentrations greater than that required to dissolve all of the aluminosilicates, AlF3, AlF4− and SiF62− form, the concentration of F− is high enough to complex Ca2+ and Mg2+ and form insoluble CaF2 and MgF2, and the concentration of AlF4− is high enough to complex Na+ and form insoluble NaAlF4. This work has application toward the development of a process for producing Ultra Clean Coal with less than 0.1% by weight mineral matter.
 
Article
The effect of HCl, HNO3 and H2SO4 at different concentrations on demineralization of high sulphur coal from Boragolai and Ledo colliery of Makum Coalfield, Assam, India was investigated at ambient and 95 °C. The acids, depending on type and concentration, can reduce the mineral matter in the range of 22.6–32.0% at ambient temperature and 24.8–40.1% at 95 °C from Boragolai coal. The acids at 10% concentration level can remove 7.6–22.6% and 13.6–38.6% sulphur from Boragolai coal at ambient and 95 °C, respectively. HNO3 leads to maximum and H2SO4 minimum desulphurization of the coal samples. The low desulphurization ability of H2SO4 is attributed to high viscosity of the acid at ambient temperature and sulphonation of the coal samples. The demineralization and desulphurization of Ledo coal with the acids are relatively low and is attributed to its higher hydrophobicity.
 
Article
Low-rank coal derived humic acids were fractionated by ultrafiltration to investigate the effects of various experimental conditions on their apparent ‘molecular weights’. With decreasing pH the apparent molecular weight of the humic acids increased dramatically. Aggregation seems to be the reason for this effect. However, detergents, organic solvents or EDTA had a negligible effect on the fragmentation pattern. Oxidation of the coal with H2O2 before the extraction of the humic acids and also the alkaline strength during the extraction influenced the molecular weight of the extracted humic acids to a remarkable degree. Fractionation obtained by ultrafiltration was compared with data of size exclusion chromatography as another technique to determine the molecular weight distribution.
 
Article
Preparation of activated carbon has been attempted using steam as the activating agent by microwave heating from Jatropha hull. The response surface methodology (RSM) technique is utilized to optimize the process conditions. The influences of the three major parameters, activation temperature, activation time and steam flow rate on the properties of activated carbon are investigated using analysis of variance (ANOVA), to identify the significant parameters. The optimum conditions for the preparation of activated carbon has been identified to be an activation temperature of 900 °C, activation time of 19 min and steam flow rate of 5 g/min. The optimum conditions resulted in an activated carbon with an iodine number of 988 mg/g and a yield of 16.56% respectively, while the BET surface area evaluated using nitrogen adsorption isotherm correspond to 1350 m2/g, with the pore volume of 1.07 cm3/g. The activated carbon is hetero porous with the micropore volume contributing to 40.8%.
 
Article
In this study, potassium hydroxide catalyst supported on palm shell activated carbon was developed for transesterification of palm oil. The Central Composite Design (CCD) of the Response Surface Methodology (RSM) was employed to investigate the effects of reaction temperature, catalyst loading and methanol to oil molar ratio on the production of biodiesel using activated carbon supported catalyst. The highest yield was obtained at 64.1 °C reaction temperature, 30.3 wt.% catalyst loading and 24:1 methanol to oil molar ratio. The physical and chemical properties of the produced biodiesel met the standard specifications. This study proves that activated carbon supported potassium hydroxide is an effective catalyst for transesterification of palm oil.
 
Article
The characteristics of the removal of gaseous elemental mercury using activated carbon injection in a particulate collector with fabric filters were experimentally estimated. The experiments showed that, at given conditions in this research, the removals of elemental mercury converged to a certain level as activated carbon continued to be injected irrelatively to the C/Hg ratio or the types of activated carbon. When the C/Hg ratio was fixed at 7000, the elemental mercury removal by the activated carbon collected on the filter surface was 9.5% of the total elemental mercury removal at 1.1m/min in filtration velocity, and 2.2% at 3.3m/min. These values are much lower than those numerically predicted. It means that the gaseous elemental mercury in a particulate collector was reduced mainly by the activated carbon distributed inside the chamber rather than those collected on the filter surface.
 
Article
Polystyrene-based activated carbon spheres (PACSK) with high surface area were prepared through KOH activation. Effects of the carbonization temperature and the ratio of KOH to carbon spheres (CS) on the textural structure, hardness and yield of the resultant PACSK were studied, and their adsorption to dibenzothiophene (DBT) were investigated. The as-prepared PACSK exhibited a high surface area (up to 2022 m2/g), large total pore volume (≥ 0.78 cm3/g), superior mechanical hardness and high adsorption capacity (ca. 153 mg/g). With the increase of the KOH/CS ratio from 2:1 to 4:1, the surface area, total pore volume, volume of micropores, and volume of mesopores, increase, whereas the volume of small-micropores (< 0.8 nm) decreases from 0.36 to 0.31 cm3/g. The adsorption capacity has a good linear correlation with the volume of small-micropores rather than the surface area. In addition, the large quantity of acidic oxygen-containing groups of PACSK may also be responsible for their higher adsorption capacity and selectivity of DBT. The PACSK saturated by DBT can be regenerated by a washing process in a shaking bath or using ultrasonic with toluene at 80 °C.
 
Article
The emission of potentially toxic compounds of arsenic and selenium present in flue gases from coal combustion and gasification processes has led to the need for gas cleaning systems capable of reducing their content. This work is focused on the capture of these elements in activated carbons which have proven to have good retention capacities for mercury compounds in gas phase. Two commercial activated carbons (Norit RBHG3 and Norit RB3) and a carbon prepared via activation of a pyrolysed coal (CA) were tested in simulated coal combustion and gasification atmospheres in a laboratory scale reactor. Arsenic and selenium compounds were retained to different extents on these carbons, retention efficiency depending mainly on the speciation of the element, which in turn depends on the gas atmosphere. Arsenic retention was similar in both combustion and gasification atmospheres unlike selenium retention. Moreover the retention of arsenic was lower than that of selenium.
 
Article
The aim of the study is to investigate quantitative relationships to predict the energetic interactions resulting from either adsorption or desorption of volatile organic compounds (VOCs) onto granular activated carbon. For that purpose, an experimental database was first built. Heats of adsorption and desorption were determined onto one activated carbon material for a 40 VOCs panel. The measurements were performed using differential scanning calorimetry coupled to thermogravimetry analysis. Adsorption energies were found to range between 40 and 80 kJ mol−1, whereas the desorption energies appear to be about 16% higher. Multiple linear regressions were afterwards tested in order to relate energies data with VOCs molecular properties. In a first approach, physical and chemical properties of the organic compounds were selected to investigate the best correlations. From the results obtained, the main influence of the ionization potential and of the polarisability were enlightened. In a similar way, connectivity molecular indexes were used. Some additional information were thus provided, which demonstrated the influence of the molecular shape, its branching and the steric hindrance.
 
Article
To avoid the emission of toxic mercury compounds from coal combustion and gasification, efficient gas cleaning systems need to be developed. In this work, the effectiveness of activated carbons for retaining mercury in gases from coal gasification was evaluated and contrasted with the results obtained in a coal combustion atmosphere. The performance of a sulphur-loaded carbon (RBHG3) was compared with that of the same carbon without sulphur (RB3). Minor differences were observed in the two atmospheres studied. The retention of mercury at 120 °C was close to 30% in RB3 and up to 70% in RBHG3.
 
Article
Palm shell based activated carbon prepared by K2CO3 activation is used as precursor in the production of carbon molecular sieve by chemical vapor deposition (CVD) method using benzene as depositing agent. The influences of deposition temperature, time, and flow rate of benzene on pore development of carbon molecular sieve (CMS) and methane (CH4) adsorption capacity were investigated. The parameters that varied are the deposition temperature range of 600 to 1000 °C, time from 5.0 to 60 min, and benzene flow rate from 3.0 to 15 mL/min. The results show that in all cases, increasing the deposition temperature, time, and flow rate of benzene result in a decrease in adsorption capacity of N2, pore volume and pore diameter of CMS. The BET surface area of CMS (approximately 1065 m2/g) and the adsorption capacity of CH4 were at a maximum value at a deposition temperature of 800 °C, time of 20 min and benzene flow rate of 6 mL/min. The product has a good selectivity for separating CH4 from carbon dioxide (CO2), nitrogen (N2), and oxygen (O2).
 
Article
Stadtwerke Düsseldorf AG is the utility company responsible for the energy supply of the City of Düsseldorf. To ensure the supply of power and district heat, it operates power plants with a total capacity of around 1100 MW, 600 MW of which are generated by coal-fired power plants with 13 boiler installations located at three different sites. In addition, it operates the refuse incineration plant of the city of Düsseldorf with a capacity of 450,000 tons per year of municipal refuse and industrial waste. Within the last few years, all of the above plants had to be retrofitted with flue gas cleaning systems for the removal of SO2, HCl, HF, NOx, chlorinated hydrocarbons, vaporous heavy metals, etc. The three-stage semi-dry flue cleaning process “System Düsseldorf” meets these requirements, in addition to the following: simple and space-saving technology; flexible capacity; no waste water, no sewage problems; attractive investment and operating cost; utilization of residual products; adaptability to other flue gas cleaning technologies. As anticipated the dust, SO2, HCl, HF, etc., emissions after the lignite-activated coke filter as the second stage, reach zero or near-zero. However, using the same material as a low temperature catalyst in the downstream third stage, the denitrogenisation resulted in emissions of not lower than 200 mg NOx per m3. Consequently, to achieve lower NOx emissions, without reheating the flue gases, other materials were found, such as endowed synthetic carbon, zeolite, or a type of titanium dioxide, all of which are currently in long-term tests. To date, plants for more than 3 million m3 flue gas per hour have been successfully built, and been proven in operation now for more than three years. The only residue from this type of cleaning system, a kind of gypsum, is reused for fabricating lime sand bricks and filling coal and ironpits.
 
Top-cited authors
Gerhard Knothe
  • USDA / ARS / NCAUR
Larry L. Baxter
  • Brigham Young University - Provo Main Campus
Dennis Y C Leung
  • The University of Hong Kong
Juan F. González
  • Universidad de Extremadura
Spliethoff Hartmut
  • Technische Universität München