Fuel Processing Technology (v.84, #1-3)
Editorial Board (IFC).
In situ IR studies on the mechanism of methane oxidation over Pd/Al2O3 and Pd/Co3O4 catalysts by Zhenhua Li; Genhui Xu; Gar B Hoflund (1-11).
In situ FTIR spectra of adsorbed O2 and CH4 at different temperatures were obtained from 5 wt.% Pd/Al2O3 and Pd/Co3O4 catalysts. It was found that O2 can be easily adsorbed on these catalysts to form reactive species, which appear at different bands with the change of temperature and the kind of the oxide support. These can explain why the catalytic activities of these Pd-containing catalysts are so dependent on the temperature and the oxide support. For CH4 adsorption, even at the temperature above light-off temperature, no adsorbed species of CH4 were detected by IR. In situ methane oxidation IR spectra proved that the intermediates of HCOO− and CO3 − are formed during reaction, which decompose to form CO and CO2, respectively.
Keywords: In situ IR; The adsorption of O2; The adsorption of CH4; Catalytic methane oxidation;
N2O emission under fluidized bed combustion condition by B.X Shen; T Mi; D.C Liu; B Feng; Q Yao; Franz Winter (13-21).
In this paper, many rules about N2O and NO x emission under fluidized bed combustion conditions were found by experiments. The research results indicate that CaO, CaSO4, Fe2O3 and char have important influence on decomposition of N2O; co-combustion of coal and biomass are effective measures to low N2O and NO x emission.
Keywords: N2O decomposition; Influence of oxide and sulfate; Co-combustion of coal and biomass;
Adsorption of metal ions on humic acids extracted from brown coals by Halina Martyniuk; Jadwiga Więckowska (23-36).
The paper shows results of examination of ion exchange capacity of solid and gel forms of humic acids of brown coals in respect to 17 metal ions. Adsorption of metal ions from single- and multicomponent solutions was carried out in dynamical conditions. The highest affinity to active centers of humic acids proved to have ions of Pb, Ag, Hg, Cu, Ba and Cd. Both types of humic acids selectively adsorbed lead ions, whereas gel forms of humic acids were selective adsorbers of Cr+3 and Al+3. Examination of IR spectra showed that the higher pH solutions, the higher share of the COOH groups in metal ions bonding was involved. The Pb, Ag, Hg and Cu ions are exceptional because even at low pH reaction of the solution (<5) they are bounded with phenolic groups as well. Only these metal ions are able to form complex compounds with carboxylic and phenolic groups of humic acids.
Keywords: Humic acids; Metal ions; Adsorption;
Recovery of sulphur from very high ash fuel and fine distributed pyritic sulphur containing coal using ferric sulphate by Sunil K Srivastava (37-46).
Studies on inorganic sulphur removal from (i) five high sulphur coals, where pyrite is highly disseminated in the organic matrix of coal and cannot be separated by a low-cost, simple and conventional-technology flotation process, from the northeastern (NE) region of India (viz., Ledo, Baragolai, Tipong, Dilli and Jeypore), (ii) two high sulphur coals from Wardha Valley coalfield of Central India (viz., Majri and Bellora), and (iii) five very high sulphur coal rejects from Taroda, Bellora, Rajur and New Majri (U/G) collieries in Wardha Valley coalfield, and recovery of sulphur in the form of ferric sulphate were carried out using aqueous ferric sulphate solution prepared from the ferric sulphate purchased from the market (for the first experiment). This was followed by three to four more similar experiments using the recovered ferric sulphate from the previous experiment. The objective was to see if the results are reproducible when the recovered, re-recovered and ferric sulphate was used for the subsequent experiments. It was found that the results were reproducible. ≥90% of the fine distributed as well as undisseminated (in organic matrix of coal) pyritic and sulphate sulphur were removed with recovery of ferric sulphate. The converted ferric sulphate from pyrite and sulphate sulphur was also recovered. It was established that the highly disseminated pyrite in coal was converted into ferric sulphate, hence removal of pyritic sulphur was achieved, which was otherwise not possible with the flotation technique, and the ferric sulphate recovered was successfully used again and again for the removal of inorganic sulphur from high sulphur coals/rejects. The process shows potential for use in utilizing very high ash and very high sulphur containing coal rejects, which otherwise cannot be used as high ash fuel in fluidized bed combustion unit, by way of recovering sulphur in the form of value-added product.
Keywords: Sulphur recovery; Desulphurization; Fine distributed pyritic sulphur; High ash fuel;
Modifications of coking coal and metallurgical coke properties induced by coal weathering by M.D. Casal; A.I. González; C.S. Canga; C. Barriocanal; J.J. Pis; R. Alvarez; M.A. Dı́ez (47-62).
Chemical changes in the structure of organic matter of coking coals during storage modify their thermoplastic properties and behaviour during carbonization. As a result, the anisotropic carbon structure of the metallurgical cokes produced and their physical properties are altered. In this work, the weathering behaviour of 10 bituminous coals of different geographic origin, rank and thermoplastic properties, used as components in the preparation of industrial coking blends for coke manufacture, was studied by means of Gieseler plastometry and Fourier transform infrared (FTIR) spectroscopy. These coking coals were stored in piles at the Instituto Nacional del Carbón (INCAR) open stockyard for a period of time of up to 7 months. Special attention was paid to the relationship between the relative amount and type of aliphatic hydrogen (semi-quantitatively evaluated by FTIR), and thermoplastic properties. Depending on the nature of the coking coal, a different response to natural weathering can be expected. Thus, the results showed that there is a direct link between a decrease in methylene groups and a loss of fluidity in the weathered coals, resulting in a decrease in anisotropic carbon of the resultant cokes with weathering time. In addition, the rate of anisotropic carbon loss induced by weathering could be associated with the rank parameters of the initial coals.
Keywords: Bituminous coal; Weathering; Plastic properties; FTIR spectroscopy; Metallurgical coke; Anisotropy;
Relationship between chemical composition and pyrolysis behaviour of a medium temperature pitch (or Lurgi-gasifier pitch) by L Sima; C Blanco; R Santamarı́a; M Granda; H Slaghuis; R Menéndez (63-77).
This paper studies the chemical composition and pyrolysis behaviour of a medium temperature pitch produced in the SASOL–Lurgi coal gasification process. The results are compared to a commercial petroleum pitch and a commercial binder coal-tar pitch. The SASOL pitch had a high content in oxygen, mainly forming phenols, which make it very reactive at temperatures between 410 and 430 °C, temperatures at which the commercial pitches do not react in a great extent. Despite the high reactivity shown by the SASOL pitch, anisotropic structures, of peculiar shapes, where developed on pyrolysis. Also noticeable is the low polyaromatic hydrocarbon (PAH) content of this pitch, which is of significant interest from a safety and environmental point of view. On the light of these results, possible applications for the SASOL pitch are pointed out.
Keywords: Medium temperature pitch; Chemical composition; Thermal analysis; Mesophase;
Numerical simulation on three-dimensional nonlinear and unstable seepage of fluid in underground coal gasification by Lanhe Yang (79-93).
Nonlinear seepage movement characteristics of fluid in underground coal gasification (UCG) are studied in this paper. On the basis of a model experiment, via the analysis of seepage field distribution and its change patterns in the process of coal gasification in the gasifier, the mathematical models of three-dimensional unstable and nonlinear seepage are established. The selection method of choosing major model parameters is illustrated. Solution to the mathematical models is made through the finite element method. This paper also analyzes and discusses the simulated calculation results. The gas pressure declines along the slope of the coal bed gradually, whose range of drop varies greatly. In the combustion cavity zone, the pressure changes slightly; in the burning zone, the fluid pressure drops sharply; and when it comes to the loosening zone, the value of the pressure stands at the minimum. The simulated results indicate that the relative differentiations among all the measuring points in the gasifier range from 10% to 18%. The calculated results agree virtually with measured ones, which supports that the numerical simulation of seepage field in the gasifier is reliable.
Keywords: Underground coal gasification; Three-dimensional unstable; Nonlinear; Seepage field; Numerical simulation;
Preparation of activated mesocarbon microbeads with high mesopore content by Zengmin Shen; Ruisheng Xue (95-103).
In this study, activated mesocarbon microbeads (AMCMBs) with high mesopore content were prepared from the chemical activation of mesocarbon microbeads (MCMBs) with KOH. The resulting activated mesocarbon microbeads possess well-developed pore structure. The maximum value of the total pore volume is 2.45 cm3/g, and BET surface area can reach 3182 m2/g. Especially, the resulting mesoporous activated microbeads also have mesopore content ranging from 56.1% to 65.7%. It can be seen from the isotherms of N2 at −196 °C that the resulting activated mesocarbon microbeads have high adsorption capacity.
Keywords: MCMB; Activated mesocarbon microbeads; Activation; Mesoporocity; KOH; High surface area;
Catalytic conversion of palm oil over mesoporous aluminosilicate MCM-41 for the production of liquid hydrocarbon fuels by Farouq A. Twaiq; Noor Asmawati M. Zabidi; Abdul Rahman Mohamed; Subhash Bhatia (105-120).
The catalytic cracking of palm oil to liquid hydrocarbon fuels was studied in a fixed bed micro-reactor operated at atmospheric pressure, reaction temperature of 723 K and weight hourly space velocity (WHSV) of 2.5 h−1 over the synthesized mesoporous molecular sieve MCM-41 materials. Mesoporous aluminosilicate with Si/Al ratio of 50 was synthesized using the hydrothermal method. Different pore sizes were obtained by changing the type of template and organic directing agent (ODA) used. The synthesized materials were characterized using various analytical methods such as X-ray powder diffraction (XRD), BET surface area, inductive coupled plasma (ICP), MAS NMR, FTIR and temperature-programmed desorption (TPD). The materials exhibit a crystalline structure of MCM-41 mesoporous molecular sieves with surface area varyng from 550 to 1200 m2/g and an average pore size (APS) ranging from 1.8 to 2.8 nm. The synthesized MCM-41 catalysts show high activity for palm oil cracking. The conversion of palm kernel oil, lower-molecular-weight oil, was higher as compared to higher-molecular-weight, palm olein oil. MCM-41 materials were selective for the formation of linear hydrocarbons, particularly, C13 when palm kernel oil was used and C17 when palm olein oil was fed. The yield of liquid product decreased with the increase of surface area of the catalyst. The gasoline selectivity increased whereas diesel selectivity decreased with the conversion of palm oil.
Keywords: Catalytic cracking; Hydrothermal synthesis; Palm oil; Mesoporous molecular sieve catalyst;
The release of the hazardous elements from coal in the initial stage of combustion process by Jun Zhang; Chun-Li Han; Yi-Qian Xu (121-133).
The studies on the behavior of the accessory elements during coal combustion are helpful to control the emission of the hazardous air pollutant (HAP) emissions. In this paper, the release of the hazardous accessory elements, As, Cd, Co, Cr, Mn, Ni, P, Pb, Sb, Se, and V in the initial stage of coal combustion was studied. Three sequential extraction agents, including the water, the ammonium acetate solution (AAS) and the hydrochloric acid solution (HAS) as indicated order, were employed to determine the occurrence of each element. The results showed that there were obvious differences in the volatility performance among the elements in this stage, almost nonvolatile capacity for elements Mn, Ni and P; low volatile capacity for elements As, Co and V; volatile capacity for elements Cd, Cr and Pb; and high volatile capacity for elements Sb and Se. The experimental results also showed that the volatility of the element is depended on the occurrence modes of element, the type of the coals, and the operating conditions. During the initial stage of coal combustion, there was also some transformation among the different occurrence modes of element defined as the water soluble (WS), the ammonium acetate soluble, the acid soluble and the acid insoluble (AI).
Keywords: Release; Hazardous element; Coal; Combustion;
Catalytic activity of silica supported sulfated zirconia catalysts for liquid phase etherification of C6 olefins with alcohols by Shaobin Wang; James A. Guin (135-146).
Etherification of certain C6 olefins with alcohols over a commercial ion-exchange resin and some supported sulfated zirconia catalysts was investigated. The commercial resin catalyst Amberlyst 15 shows nonselective to ether production. Silica-supported sulfated zirconia shows a comparable and even higher ether yield than the commercial resin while the catalytic activity is dependent on zirconium precursors, preparation technique, calcination temperature, ratio of SZ on silica, and reaction temperature. Addition of promoters, transition metal oxides, will also influence the catalytic activity while depending on the nature of promoter. Ni and Pt increase the catalytic activity and Fe shows no significant influence on olefin conversion whereas Mn reduces the catalytic activity. However, these promoters reduce the ether selectivity and ether yield. Silica-supported SZ catalysts also exhibit varying activities for etherification of different olefins and alcohols.
Keywords: Etherification; C6 olefins; Alcohols; Silica;
The advantages of vacuum-treatment in the thermal upgrading of low-rank coals on the improvement of dewatering and devolatilization by Mahidin; Yuji Ogaki; Hiromoto Usui; Osamu Okuma (147-160).
A new upgrading method for low-rank coals by a combined process of vacuum drying and tar coating has been developed, and some advantages have been observed. This upgrading technique is able to produce upgraded coals comparable to a bituminous coal; the surface of the coals can be effectively coated in order to suppress low-temperature oxidation and spontaneous combustion. The dewatering rate in the vacuum drying stage at 200 °C reached up to 93.81%, and degree of devolatilization significantly increased with elevation of upgrading temperature, from 15.7% at 200 °C to 35.9% at 300 °C. Furthermore, the specific surface area and susceptibility toward the low-temperature oxidation of coals were influenced by the upgrading treatment.
Keywords: Upgrading; Vacuum drying; Devolatilization; Low-rank coals;
Tar removal from biomass-derived fuel gas by pulsed corona discharges by S.A. Nair; A.J.M. Pemen; K. Yan; F.M. van Gompel; H.E.M. van Leuken; E.J.M. van Heesch; K.J. Ptasinski; A.A.H. Drinkenburg (161-173).
Tar removal from fuel gas obtained from biomass gasification offers a significant challenge in its deployment for power generation as well as for other applications such as production of chemicals by processes such as Fischer–Tropsch. The present investigation focuses on pulsed corona discharges for the mentioned objective. The paper is meant to give an overview of our developments in the area of pulsed power development for large-scale plasma processing. In addition, lab-scale results as well as pilot-scale results for tar removal on an actual gasifier are presented.
Keywords: Pulsed corona; Plasma; Tar; Biomass; Pulse power; Non-thermal plasma;
Fluidized-bed gasification of waste tire powders by D.Y.C Leung; C.L Wang (175-196).
A laboratory-scale fluidized-bed gasifier was used to investigate the characteristics of tire powder gasification. Granulated tire powders were gasified with air at a temperature range of 350–900 °C. Results showed that the operational parameters [i.e., equivalence ratio (ER) and tire feed rate] and tire particle size have significant effects on various gasification results, including the bed temperature, secondary reaction temperature, product gas composition, gas yield, gas heating value, product (i.e., gas, tar, and char) distribution, volatile release ratio, fixed carbon conversion ratio, and energy recovery ratio. An optimum ER may exist for a fixed tire feed rate and tire particle size at which higher product gas yield, gas heating value, and energy recovery ratio can be achieved. A gaseous product, mainly containing CO, H2, CH4, C2H6, and longer-chain hydrocarbon with a calorific value of about 6 MJ/Nm3, can be generated at the highest yield rate of 11 Nm3/h under the optimum operation conditions achieved in this study. The char and oil yields were found to lie in the range of 24–37% and 0–37%, respectively, corresponding to over 90% and 18% of the volatile release and fixed carbon conversion. Under these conditions, the energy recovery was between 15% and 38%.
Keywords: Waste tire; Gasification; Gases production; Energy recovery;
Gas-phase mercury removal by carbon-based sorbents by Si-Hyun Lee; Young-Ok Park (197-206).
To develop carbon-based sorbents to be used in gas-phase mercury removal, the performance of virgin activated carbons (AC) with that of sulfur-impregnated activated carbons was compared. Virgin AC with increased oxygen functional groups was superior in mercury adsorption performance. The adsorption performance of sulfur-impregnated AC depended on the pore characteristics of virgin AC used as raw material and the types of sulfur, rather than on the amount of sulfur impregnated. AC that impregnates sulfur should have a large pore diameter (average pore diameter above 20 Å). A method of reactive sulfur impregnation has been developed. With the method, the utilization efficiency of sulfur to mercury adsorption was maximized.
Keywords: Carbon-based sorbents; Gas-phase mercury removal; Mercury adsorption; Sulfur-impregnated activated carbons;
Supercritical desulfurization of low rank coal with ethanol/KOH by Krittika Charutawai; Somkiat Ngamprasertsith; Pattarapan Prasassarakich (207-216).
Desulfurization of Mae Moh coal with supercritical ethanol/potassium hydroxide in a semicontinuous reactor was studied. A two-level factorial experimental design was applied to study the main effects on sulfur reduction. The variables investigated in this work were temperature, pressure, time and potassium hydroxide concentration. The measured responses in the experimental design were coal yield, sulfur reduction and ash reduction. The analysis of the results from the design showed that two variables, temperature and KOH concentration, can be considered to have a significant effect on the pyritic sulfur and total sulfur reduction.
Keywords: Desulfurization; Coal; Supercritical fluid; Ethanol; Potassium hydroxide;
A study on regeneration of Mn–Fe–Zn–O supported upon γ-Al2O3 sorbents for hot gas desulfurization by Jinchang Zhang; Yanhui Wang; Runyu Ma; Diyong Wu (217-227).
In this study, the regeneration conditions of Mn–Fe–Zn–O supported upon γ-Al2O3 sorbents for high-temperature desulfurization of fuel gases were investigated. Mn–Fe–Zn/γ-Al2O3 sorbents with Mn/Fe/Zn molar ratio of 2:1:0.2, AMFZ0.2, were prepared. Desulfurization and regeneration were carried out in a quartz fixed-bed reactor of 10-mm diameter. Sulfidation tests were performed at 650 °C using the gas mixture containing (mol) 0.3%H2S–11.62%H2–19.34%CO–6.85%CO2–61.84%N2 at SV=3000 h−1. Sulfur capacity of the fresh sorbent was about 5.3 gS/100 gSorbent. Regeneration parameters including temperature, concentration of oxygen, space velocity and steam content have been considered in order to obtain suitable regeneration conditions. The regeneration was performed at the following parameters—pressure: atmosphere, temperature: 600–750 °C, space velocity: 2000–3000 h−1 and gas composition (vol.%): 2–8 O2, 4–10 H2O with N2 balance. Typical properties of the sorbents before and after regeneration were characterized using XRD, SEM, BET and ICP methods. The most suitable regeneration conditions were obtained including 700 °C of regeneration temperature, 6.0% of oxygen content and 8.0% of steam in the gas stream.
Keywords: Desulfurization; Regeneration; Sulfur capacity; Sorbents;
The influence of fine char particles burnout on bed agglomeration during the fluidized bed combustion of a biomass fuel by Fabrizio Scala; Riccardo Chirone; Piero Salatino (229-241).
The combustion of biomass char in a bubbling fluidized bed is hereby addressed, with specific reference to the influence that the combustion of fine char particles may exert on ash deposition and bed agglomeration phenomena. Experiments of steady fluidized bed combustion (FBC) of powdered biomass were carried out with the aim of mimicking the postcombustion of attrited char fines generated in the fluidized bed combustion of coarse char. Experimental results showed that the char elutriation rate is much smaller than expected on the basis of the average size of the biomass powder and of the carbon loading in the combustor. Samples of bed material collected after prolonged operation of the combustor were characterized by scanning electron microscopy (SEM)–EDX analysis and revealed the formation of relatively coarse sand–ash–carbon aggregates. The phenomenology is consistent with the establishment of a char phase attached to the bed material as a consequence of adhesion of char fines onto the sand particles.Combustion under sound-assisted fluidization conditions was also tested. As expected, enhancement of fines adhesion on bed material and further reduction of the elutriation rate were observed.Experimental results are interpreted in the light of a simple model which accounts for elutriation of free fines, adhesion of free fines onto bed material and detachment of attached fines by attrition of char–sand aggregates. Combustion of both free and attached char fines is considered. The parameters of the model are assessed on the basis of the measured carbon loadings and elutriation rates. Model computations are directed to estimate the effective size and the peak temperature of char–sand aggregates. The theoretical estimates of the effective aggregate size match fairly well those observed in the experiments.
Keywords: Fluidized bed combustion; Biomass; Bed agglomeration;
Studies of the release rule of NO x precursors during gasification of coal and its char by Jie Feng; Wen-Ying Li; Ke-Chang Xie; Mei-Rong Liu; Chun-Zhu Li (243-254).
This investigation involved the formation and release of precursors of NO x , which were HCN and NH3, during gasification of coal and its char. Gasification was carried out in a fixed bed reactor at atmospheric pressure. The reactor allowed coal particles to be heated up rapidly and held for a pre-specified period of time at peak temperature. The influence of coal rank and coal particle size on the release of N-containing compounds during coal gasification with CO2 is discussed. Gasification agents and coal gasification temperature were two key factors on the amount of nitrogenous compounds released. Results showed that with an increase of reaction temperature a great amount of NH3 was formed during gasification with steam: The yield of NH3 was highest at 800 °C during gasification with CO2. The volatiles in coal played the key role in the formation of HCN and NH3 during coal gasification under steam atmosphere. Volatiles were the main source of the formation of HCN and NH3, mainly from the nascent char thermal cracking, whose procedure could be promoted by H2O(g): The yield of HCN during coal gasification had no strong relation with gasification agents and increased with an increase in gasification temperature. A reasonable mechanism for the formation of nitrogenous compounds during coal gasification was suggested in this study, which could explain some results in the literature on pyrolysis and gasification of coal.
Keywords: Coal gasification; Char gasification; CO2; Steam; Release rule of NO x precursor;
Author Index (257).
Subject Index (259-260).
Contents of Volume 84 (2003) (261-262).