Fuel Processing Technology (v.89, #11)
Editorial Board (IFC).
Natural Gas (I).
Effect of yttrium and praseodymium on properties of Ce0.75Zr0.25O2 solid solution for CH4–CO2 reforming by Qunying Wu; Jixiang Chen; Jiyan Zhang (993-999).
Ce0.75Zr0.25O2 solid solutions doped with Y3+ or Pr4+/Pr3+ were prepared by the co-precipitation method, and their physicochemical properties were characterized by means of N2 adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, FT-Raman, and H2 temperature-programmed reduction and thermogravimetric analysis. Their performance in CH4–CO2 reforming was also tested in an atmospheric fixed-bed reactor. Ce0.75Zr0.25O2 and Y3+ or Pr4+/Pr3+ doped Ce0.75Zr0.25O2 solid solutions are of CaF2 structure, and the thermal stability of Ce0.75Zr0.25O2 is enhanced by doping Y3+ or Pr4+/Pr3+. Comparing with Ce0.75Zr0.25O2, the migration of bulk lattice oxygen species become easier and the content of surface oxygen species is higher in the doped Ce0.75Zr0.25O2, which is due to either oxygen vacancies or/and structural distortion resulted from the doping. The activity of the solid solutions in CH4–CO2 reforming is closely related to the surface oxygen species. Y3+ or Pr4+/Pr3+ doped Ce0.75Zr0.25O2, especially the former, show higher activity than Ce0.75Zr0.25O2, and Y3+ doped Ce0.75Zr0.25O2 possesses better stability. All of the catalysts have good coke resistance. The catalyst deactivation is mainly due to the catalyst sintering.
Keywords: Ce0.75Zr0.25O2 solid solution; Yttrium; Praseodymium; Methane reforming with carbon dioxide; Synthesis gas;
Investigation on pyrolysis of Moroccan oil shale/plastic mixtures by thermogravimetric analysis by A. Aboulkas; K. El harfi; M. Nadifiyine; A. El bouadili (1000-1006).
Thermal degradation processes for a series of mixtures of oil shale/plastic were investigated using thermogravimetric analysis (TGA) at four heating rates of 2, 10, 20 and 50 K min− 1 from ambient temperature to 1273 K. High density polyethylene (HDPE), low density polyethylene (LDPE) and polypropylene (PP) were selected as plastic samples. Based on the results obtained, three thermal stages were identified during the thermal degradation. The first is attributed to the drying of absorbed water; the second was dominated by the overlapping of organic matter and plastic pyrolysis, while the third was linked to the mineral matter pyrolysis, which occurred at much higher temperatures. Discrepancies between the experimental and calculated TG/DTG profiles were considered as a measurement of the extent of interactions occurring on co-pyrolysis. The maximum degradation temperatures of each component in the mixture were higher than those of the individual components; thus an increase in thermal stability was expected. In addition, a kinetic analysis was performed to fit thermogravimetric data. A reasonable fit to the experimental data was obtained for all materials and their mixtures.
Keywords: Pyrolysis; Oil shale; Plastic; Kinetics;
An experimental and numerical analysis of the HCCI auto-ignition process of primary reference fuels, toluene reference fuels and diesel fuel in an engine, varying the engine parameters by Hatim Machrafi; Simeon Cavadias; Philippe Gilbert (1007-1016).
For a future HCCI engine to operate under conditions that adhere to environmental restrictions, reducing fuel consumption and maintaining or increasing at the same time the engine efficiency, the choice of the fuel is crucial. For this purpose, this paper presents an auto-ignition investigation concerning the primary reference fuels, toluene reference fuels and diesel fuel, in order to study the effect of linear alkanes, branched alkanes and aromatics on the auto-ignition. The auto-ignition of these fuels has been studied at inlet temperatures from 25 to 120 °C, at equivalence ratios from 0.18 to 0.53 and at compression ratios from 6 to 13.5, in order to extend the range of investigation and to assess the usability of these parameters to control the auto-ignition. It appeared that both iso-octane and toluene delayed the ignition with respect to n-heptane, while toluene has the strongest effect. This means that aromatics have higher inhibiting effects than branched alkanes. In an increasing order, the inlet temperature, equivalence ratio and compression ratio had a promoting effect on the ignition delays. A previously experimentally validated reduced surrogate mechanism, for mixtures of n-heptane, iso-octane and toluene, has been used to explain observations of the auto-ignition process.
Keywords: Auto-ignition; Diesel fuel; Primary reference fuels; Toluene reference fuels; HCCI; Engine; Inlet temperature; Equivalence ratio; Compression ratio;
Coal char combustion under a CO2-rich atmosphere: Implications for pulverized coal injection in a blast furnace by A.G. Borrego; E. Osório; M.D. Casal; A.C.F. Vilela (1017-1024).
Pulverized coal injection (PCI) is employed in blast furnace tuyeres attempting to maximize the injection rate without increasing the amount of unburned char inside the stack of the blast furnace. When coal is injected with air through the injection lance, the resolidified char will burn in an atmosphere with a progressively lower oxygen content and higher CO2 concentration. In this study an experimental approach was followed to separate the combustion process into two distinct devolatilization and combustion steps. Initially coal was injected into a drop tube furnace (DTF) operating at 1300 °C in an atmosphere with a low oxygen concentration to ensure the combustion of volatiles and prevent the formation of soot. Then the char was refired into the DTF at the same temperature under two different atmospheres O2/N2 (typical combustion) and O2/CO2 (oxy-combustion) with the same oxygen concentration. Coal injection was also performed under a higher oxygen concentration in atmospheres typical for both combustion and oxy-combustion. The fuels tested comprised a petroleum coke and coals currently used for PCI injection ranging from high volatile to low volatile bituminous rank. Thermogravimetric analyses and microscopy techniques were used to establish the reactivity and appearance of the chars.Overall similar burnouts were achieved with N2 and CO2 for similar oxygen concentrations and therefore no loss in burnout should be expected as a result of enrichment in CO2 in the blast furnace gas. The advantage of increasing the amount of oxygen in a reacting atmosphere during burnout was found to be greater, the higher the rank of the coal.
Keywords: Combustion; Oxy-combustion; Coal char; Blast furnace; Reactivity; PCI;
A model for performance optimization of wet flue gas desulfurization systems of power plants by Yi Zhong; Xiang Gao; Wang Huo; Zhong-yang Luo; Ming-jiang Ni; Ke-fa Cen (1025-1032).
In this paper, a model of limestone/gypsum wet flue gas desulfurization (WFGD) system was developed based on unsteady theory. The models of processes of absorption section and oxidation section were developed and incorporated into the WFGD integral model. The sub-model of motion of slurry drops, absorption of SO2, dissolution of limestone and crystallization of gypsum were included in the model of absorption section, while the model of oxidation section was developed by the population balance theory. The calculation results of the desulfurization system for 300 MW utility in China by this model was compared to that of corresponding measured results. The simulation results agreed with the measurement results very well. The operation mode of boilers of power plant in China is different to that of other countries since variable coal property and unstable loads of boilers. The differences of operation mode lead to the variation of process parameters of WFGD system. The influences of liquid-to-gas ratio, SO2 concentration of inlet flue gas, and combination mode of different spray levels to the desulfurization efficiency were analyzed. Based on the analysis, some advices of performance optimization of flue gas desulfurization systems in China were suggested.
Keywords: Wet flue gas desulfurization; Unsteady theory; Spray scrubber; Numerical calculation; Optimization;
Mercury emissions from six coal-fired power plants in China by Liang Zhang; Yuqun Zhuo; Lei Chen; Xuchang Xu; Changhe Chen (1033-1040).
Mercury emission field measurements based on the Ontario Hydro Method (OHM) were conducted for six coal-fired power plants in China. The mercury mass balances for the six power plants varied from 100.3% to 139.5% of the input coal mercury for the whole system. About 0.02%–1.2% of the mercury remained in the bottom ash. In the first five power plants equipped with pulverized coal boiler, most of the mercury was emitted from the stack to the atmosphere. The plants with Electrostatic Precipitator (ESP) system emitted more Hg0 than Hg2+, while the plants with the Fabric Filter (FF) emitted less Hg0 than Hg2+. Virtually all of the HgP enter the ESP or the FF was removed. The FF systems had better Hg0 and Hg2+ removal efficiencies than the ESP systems. The flue gas desulfurization (FGD) system removed up to 78.0% of Hg2+ and only 3.14% of Hg0 in the flue gas, while 8.94% of the original mercury in the coal was removed by the FGD system. The average mercury removal efficiencies of the ESP systems was 11.5%, that of the FF systems was 52.3% and that of the combined ESP + FGD system was 13.7%, much lower than the average removal efficiencies of pollution control device systems in US plants which have been used in previous studies of Chinese mercury emission inventory. Hg0, rather than Hg2+ as assumed in previous estimates, has been found to be the dominant species emitted in the atmosphere. The average emission factor was found to be 4.70 g/TJ (10.92 bl/Tbtu), which is much higher than for US plants burning bituminous coals due to the high mercury content in the Chinese coal and the low mercury removal efficiency of air pollution control devices of power plants.
Keywords: Field measurement; Mass balance; Partition of mercury; Removal efficiency; Mercury speciation; Emission factor;
A study on the carbonization of grapeseed and chestnut shell by Didem Özçimen; Ayşegül Ersoy-Meriçboyu (1041-1046).
Carbonization experiments of grapeseed and chestnut shell samples having the average particle size of 0.657 mm and 0.377 mm, respectively, were performed to determine the effect of temperature, sweep gas flow rate and heating rate on the biochar yield. A statistical design technique was applied by the use of a two-level factorial design matrix to interpret experimental results. Carbonization conditions were selected according to a two-level factorial design matrix considering the following variables: temperature (723 K and 823 K), nitrogen gas flow rate (0 and 1000 cm3/min) and heating rate (5 and 20 K/min). Empirical relations between the biochar yield and the carbonization conditions were developed. To comment on the effect of parameters between the superior and inferior levels and to prove the accuracy of design equations from statistical design technique, biochar yields obtained at different conditions were also presented in the graphical way. It was found that temperature has the strongest effect on the biochar yields in comparison with nitrogen gas flow rate and heating rate. Biochar yields of grapeseed and chestnut shell were decreased with the increasing temperature, heating rate and sweep gas flow rate. A comparison between the fuel properties of waste materials and biochar products was also done.
Keywords: Biomass; Carbonization; Factorial design; Biochar; Grapeseed; Chestnut shell;
Copyrolysis of oils/waxes of individual and mixed polyalkenes cracking products with petroleum fraction by Božena Mlynková; Elena Hájeková; Martin Bajus (1047-1055).
Copyrolysis of 10 mass% solutions (oils/waxes from individual or mixed polymers with heavy naphtha) is a route for treatment of plastic waste. Linear low-density polyethylene (LLDPE), mixture of high-density polyethylene/low-density polyethylene/linear low-density polyethylene/polypropylene (HDPE/LDPE/LLDPE/PP = 1:1:1:1mass) and linear low-density polyethylene/low-density polyethylene/polypropylene/high-density polyethylene/polyvinyl chloride/polyethylene terepthalate/polystyrene (LLDPE/LDPE/PP/HDPE/PVC/PET/PS = 1:1:2:2:0.05:0.05:0.156 mass) were converted to oils/waxes, gases and solid residues by thermal decomposition in batch reactor at 450 °C. Oils/waxes were dissolved in virgin heavy naphtha to create the feedstock. The influence of residence time from 0.08 to 0.51 s at temperatures 780 °C and 820 °C on product distribution during the copyrolysis was studied. The yields obtained from gaseous and liquid products of solutions are compared to the yields obtained from virgin heavy naphtha. It was studied how addition of the oil/wax influences formation of C2 and C3 hydrocarbons (mainly ethene and propene) and aromatics in comparison to the virgin heavy naphtha. The ethene and propene yields from copyrolysis of solutions are comparable or higher than from virgin heavy naphtha. Copyrolysis of solution LLDPE/LDPE/PP/HDPE/PVC/PET/PS gives the maximum yields of propene from all studied oils/waxes. The result suggests that oils/waxes from polymers are suitable feedstocks for copyrolysis with virgin heavy naphtha.
Keywords: Copyrolysis; Recycling; LLDPE; Polymer mixtures; Naphtha; Oils/waxes;
Ethanol production by solid state fermentation of sweet sorghum using thermotolerant yeast strain by Jianliang Yu; XuZhang; Tianwei Tan (1056-1059).
Solid state fermentation of chopped sweet sorghum particles to produce ethanol was studied statically using thermotolerant yeast. The influence of various process parameters, such as yeast cell concentration, particle size and moisture content, on the ethanol yield was investigated. Optimal values of these parameters were 4 × 106 cells/g raw sorghum, Dp = 1.5 mm and 75%, respectively. Addition of reducing agent H2SO3 into the fermentation medium provided anaerobic condition, and obtained the maximum ethanol yield of 7.9 g ethanol per 100 g fresh stalks or 0.46 g ethanol/g total sugar, which was 91% of the theoretic yield.
Keywords: Sweet sorghum; Ethanol; Solid state fermentation;
Experimental measurement of gas concentration distribution in an impinging entrained-flow gasifier by Miaoren Niu; Zhuoyong Yan; Qinghua Guo; Qinfeng Liang; Guangsuo Yu; Fuchen Wang; Zunhong Yu (1060-1068).
On a laboratory-scale testing platform of impinging entrained-flow gasifier with two opposed burners, the detailed measurements of gas concentration distribution have been performed for carbonaceous compound (diesel oil) at atmospheric pressure. Under the condition of 1.48–2.36 O/C ratios (kg/kg), radial gas samples are collected at three axial positions and the syngas exit position with stainless steel water-cooled probes, the concentration distribution of the major gases (H2, CO, CO2, CH4 and O2) under stable operating state was determined with a mass spectrometry. These data are used to clarify mixing and reaction characteristics within the reactor, to give insight into the combustion process and provide a database for evaluating predictive mathematical models.
Keywords: Gasification; Entrained-flow gasifier; Gas concentration distribution;
Possibility of obtaining hydrogen from coal/waste–tyre mixture by V. Kříž; Z. Brožová; O. Přibyl; I. Sýkorová (1069-1075).
Technically applicable gas with a high hydrogen content (ca 78%) was obtained through a two-stage pyrolysis of the mixture of Lazy bituminous coal with 15% waste tyre-rubber. The experiments were carried out in a laboratory pyrolysis unit with a 100 g charge. The incorporation of a thermal-degradation module in the stream of steam–gas mixture at the output of the pyrolysis reactor induced the decomposition of volatile products and significantly increased the yield of hydrogen. The influence of temperature of the cracking module (in the range between 900 and 1200 °C) on the amount of hydrogen in the pyrolysis gas was monitored. The solid by-product (carbonaceous residue) may be used as smokeless fuel or a sorbent precursor.
Keywords: Hydrogen; Coal; Tyres; Two-stage pyrolysis;
Effect of biomass particle size and air superficial velocity on the gasification process in a downdraft fixed bed gasifier. An experimental and modelling study by Francisco V. Tinaut; Andrés Melgar; Juan F. Pérez; Alfonso Horrillo (1076-1089).
A one-dimensional stationary model of biomass gasification in a fixed bed downdraft gasifier is presented in this paper. The model is based on the mass and energy conservation equations and includes the energy exchange between solid and gaseous phases, and the heat transfer by radiation from the solid particles. Different gasification sub-processes are incorporated: biomass drying, pyrolysis, oxidation of char and volatile matter, chemical reduction of H2, CO2 and H2O by char, and hydrocarbon reforming. The model was validated experimentally in a small-scale gasifier by comparing the experimental temperature fields, biomass burning rates and fuel/air equivalence ratios with predicted results. A good agreement between experimental and estimated results was achieved. The model can be used as a tool to study the influence of process parameters, such as biomass particle mean diameter, air flow velocity, gasifier geometry, composition and inlet temperature of the gasifying agent and biomass type, on the process propagation velocity (flame front velocity) and its efficiency. The maximum efficiency was obtained with the smaller particle size and lower air velocity. It was a consequence of the higher fuel/air ratio in the gasifier and so the production of a gas with a higher calorific value.
Keywords: Biomass; Gasification; Downdraft; Propagation velocity;
Approach for promoting liquid yield in direct liquefaction of Shenhua coal by Xian Li; Haoquan Hu; Lijun Jin; Shuxun Hu; Bo Wu (1090-1095).
Single and multi-stage liquefaction of Shenhua (SH) bituminous coal and re-liquefaction of its liquefaction residue (SHLR) were carried out in an autoclave reactor to investigate the essential approach for promoting oil yield and conversion in SH coal direct liquefaction (SHDL). The multi-stage liquefaction includes pretreatment, keeping the reactor at 250 °C for 40 min before heating up to the reaction temperature, and two-stage liquefaction processes consisting of low temperature stage, 400 °C, and high temperature stage, 460 °C. The results show that the pretreatment has slight effect on oil yield and conversion of SHDL, especially for liquefaction at 460 °C. There is a positive function of two-stage liquefaction in shortening reaction time at high temperature. Increasing ratio of solvent to SHLR can promote the oil yield and abate reaction condition in SHLR re-liquefaction, that is, it can promote the conversion from preasphaltene and asphaltene to oil. The primary factor to inhibit coal liquefaction is the consumption of hydrogen free radical (H·) from solvent or H2 and condensation of free radicals from coal pyrolysis after a period of reaction. So the essential approach for increasing oil yield and conversion of SHDL is to provide enough H· to stabilize the free radicals from coal pyrolysis.
Keywords: Coal liquefaction; Multi-stage; Residue;
Characterization of char from rapid pyrolysis of rice husk by Song Hu; Jun Xiang; Lushi Sun; Minhou Xu; Jianrong Qiu; Peng Fu (1096-1105).
In the present study, one process was selected for a fundamental study of structural evolution during rapid pyrolysis, as well as for the study of the influence of such evolution on char reactivity. Chars were prepared at different situations from rice husk. The reactivity of resultant chars was measured using non-isothermal thermogravimetric analysis. The structure of fresh and partly reacted chars was characterized using proximate and ultimate analyses, physical adsorption/desorption measurements of N2 (− 196 °C), mercury intrusion porosimetry (414 MPa), FTIR, Helium pycnometer as well as samples visualization by scanning electronic microscopy (SEM). Appreciable differences in the physical characteristics, depending markedly on the pyrolysis stage, were observed.SEM observation showed that surface of pore in char particle became increasingly rough in the middle of pyrolysis. Micropore characteristics obtained from adsorption/desorption measurement were complex. Release of volatile material led to the development of pores with different changing trends. The surface area of char increased with pyrolysis process to a maximum value of 56.95 m2/g at pyrolysis reaction ratio (R p = 0.90). Macropores in char particles which were evaluated by mercury intrusion porosimetry indicated that the porosity increases continually. Combined the analysis result of density with porosity data, it was showed that particle shrinkage happened at the first stage of rapid pyrolysis. The H/C, O/C and N/C ratios of the char changed with different trends when the pyrolysis reaction ratio increased. Furthermore, FTIR studies indicated a gradual decrease in the intensities of OH, C–H and C–O stretches with pyrolysis process. At the end of reaction, most bands disappeared, resulting in a char that was mainly an aromatic polymer of carbon atoms.
Keywords: Rice husk; TG/SEM/FTIR; Adsorption/desorption; Mercury intrusion porosimetry; Helium pycnometer;
Catalytic decomposition of ammonia over fly ash supported Ru catalysts by Li Li; Shaobin Wang; Zhonghua Zhu; Xiangdong Yao; Zifeng Yan (1106-1112).
Fly ash (FA), an industrial waste material, has been treated by physical and chemical methods. These materials were then employed as supports for preparation of Ru-based catalysts for H2 generation from ammonia decomposition. The physicochemical properties of the supports and Ru-based catalysts were characterised using several techniques. The results revealed that the surface area of FA could be enhanced and thus improved the dispersion of Ru particles, resulting in higher catalytic activity. Ru/FA-800 exhibits the highest conversion due to higher surface loading of Ru, stronger NH3 adsorption and least acid sites.
Keywords: Fly ash; Ru catalyst; NH3 decomposition; H2 production;
Effects of methanol co-feeding in F–T synthesis on a silica supported Co-catalyst by Wei Zhou; Zhongyi Ma; Kegong Fang; Jian-gang Chen; Yu-han Sun (1113-1120).
The effects of methanol on the performance of Co/SiO2 catalyst for Fischer–Tropsch synthesis were studied in a fixed-bed reactor at 210 °C and 2.0 MPa. It was found that external addition of methanol brought about an increase in the selectivity of methane, water and CO2 and a decrease in the activity of the catalyst. FTIR and TPSR characterizations proved that methanol first converted to the methoxy groups and water and then the methoxy groups reacted with hydrogen to produce methane, which led to the increase of the selectivity of methane and water. And the increase of the selectivity of CO2 was ascribed to the water–gas shift reaction. The decline of the activity might result from the instantaneous oxidation of the metallic cobalt due to the sudden addition of methanol and the formation of cobalt silicates and/or hydrosilicates species. More methanol introduction into the feeding gas would result in the formation of larger amount of silicates species, which led to the more serious deactivation of the catalyst. In addition, the hydrogen was found necessary for the chain propagation whereas CO was not. The methanol might substitute for CO to perform the chain initiation.
Keywords: Fischer–Tropsch synthesis; Co/SiO2 catalyst; Methanol; Performance;
Fragmentation of wood char in a laboratory scale fluidized bed combustor by D. Ruben Sudhakar; K. Srinivas Reddy; Ajit Kumar Kolar; Bo Leckner (1121-1134).
Casuarina equisetifolia, a hard wood, and a popular energy crop in many tropical countries, was investigated experimentally for its char fragmentation in a laboratory scale atmospheric bubbling fluidized bed combustor. The effect of fuel shape and size on wood char fragmentation was studied. Wood particles of spherical, cylindrical (aspect ratio of 1), and cubical shapes of different sizes ranging from 10 to 25 mm were used in the experiments. Fragmentation of wood char was quantified in terms of various parameters, such as Number of Fragments (NF), Percentage of Fragmentation Events, Frequency of Fragmentation, Timing interval of Fragmentation, Size distribution of char and Fragmentation Index (FI). Also, qualitative observations on the evolution of char in terms of deformation, cracks and surface texture are discussed. It was observed that Casuarina equisetifolia wood of sizes greater than 15 mm, of all shapes undergoes primary fragmentation during the devolatilization phase. Furthermore, chars fragment at the early stages (1st or 2nd quarter) of the char combustion phase, underscoring the significance of the phenomenon in fluidized bed combustion. For all the shapes of wood considered, there appears to be a cut-off size of the initial wood, below which its char certainly undergoes fragmentation. It was observed that the average char particle size at any instance during its combustion falls in a narrow range of 3.7–6.9 mm, 3–6.6 mm and 3–9.5 mm for spherical, cylindrical and cubical wood particles, respectively. Wood of initially cylindrical shape undergoes extensive fragmentation when compared with spherical and cubical shapes.
Keywords: Char fragmentation; Fluidized bed; Combustion; Experiments; Wood;
Olefins alkylation thiophenic sulfur of the real gasoline over the fluorinated Hbeta zeolite catalyst by Zekai Zhang; Xiaoye Guo; Shenglin Liu; Xiangxue Zhu; Longya Xu (1135-1141).
The efficiency of the catalytic alkylation, the first step of the olefins alkylation thiophenic sulfur (OATS) process was investigated in three typical gasoline samples with different olefins contents over a fluorinated Hβ zeolite catalyst. Under the reaction conditions of 120 °C, 1.5 MPa and WHSV 0.5 h− 1, over 95% light sulfur compounds in the feeds could be transformed to be heavier than the heptyl-thiophenes within a period of time-on-stream. The lifetime of the catalyst could prolong from 10 h to 26 h when the olefins content in the gasoline feed decreased from 40.87 wt.% to 9.20 wt.%. It was also found that the olefins content decrease was favorable for keeping and promoting the octane number by redistributing the components of the treated gasoline. In addition, the influence of the reaction conditions such as the temperature and WHSV on the efficiency of the catalytic alkylation was investigated.
Keywords: Thiophenes; Alkylation; Gasoline; Olefins content; Hβ-F;
Effects of hydrogen addition on methane combustion by Ke Zhao; Dawei Cui; Tongmo Xu; Qulan Zhou; Shien Hui; Hongli Hu (1142-1147).
In this study, the effect of hydrogen on methane combustion characteristic was tested. The ignition temperature (T 10) and burn off temperature (T 90) was carried out in a quartz reactor at atmospheric pressure with the mixture flow rate of 800 mL/min. The compositions of outlet gas were measured online by Gasmet DX4000 FTIR gas analyzer. The results showed that hydrogen enhanced the activity of methane. For all methane concentration range, the T 10 of methane could decrease 50 °C–70 °C with the H2/CH4 mole ratio at 0.1. For 1 vol.% methane combustion, when the H2/CH4 was equal to 0.05, the T 10 and T 90 could decrease 45 °C and 42 °C, respectively. When the H2/CH4 was 2.5, the T 10 and T 90 could decrease about 170 °C and 180 °C, respectively. Further more, CO generated in a wider temperature range when the hydrogen was added.
Keywords: Combustion; Methane; Hydrogen; Ignition temperature; Burn off temperature;
Optimization of the ETBE (ethyl tert-butyl ether) production process by Eliana Weber de Menezes; Renato Cataluña (1148-1152).
The synthesis of ETBE (ethyl tert-butyl ether) from the reaction of ethanol with isobutene is an exothermic reaction of equilibrium. To increase the conversion of isobutene requires operating the reaction system at low temperatures and with excess ethanol in order to displace the equilibrium towards the products. ETBE and ethanol form an azeotropic mixture which hinders the recycling of nonreacted ethanol in the process. The purpose of this work is to optimize the synthesis of ETBE eliminating the introduction of water into the system to break the ETBE/Ethanol azeotrope. The production process model proposed here eliminates the recycling of ethanol and suggests the use of the azeotropic mixture (ETBE/Ethanol) in the formulation of gasolines. The direct use of the azeotrope in the formulation of automotive gasolines reduces the implementation and production costs of ETBE.
Keywords: ETBE; Azeotropic mixture (ETBE/EtOH); Gasoline;
Effect of halogens on mercury conversion in SCR catalysts by Sandhya Eswaran; Harvey G. Stenger (1153-1159).
The effect of halogen acids HCl, HBr and HI on mercury conversion was studied in a laboratory-scale SCR reactor using simulated flue gases, and is presented here. Two types of commercially available SCR catalysts, Honeycomb and Plate type catalysts, were used in these studies. HBr and HI both had shown much stronger effects on mercury conversion than HCl. Both HBr and HI oxidized more than 85% of the gas phase mercury at a low concentration of 2 ppm. The age of the catalyst and the type of catalyst also have an effect on mercury conversion. A larger extent of mercury oxidation was observed in the presence of a Honeycomb catalyst than with the Plate catalyst.
Keywords: Mercury; Oxidation; Hydrogen chloride; Hydrogen bromide; Hydrogen iodide; SCR; Catalyst;
Catalytic combustion of soot. Effects of added alkali metals on CaO–MgO physical mixtures by R. Jiménez; X. García; T. López; A.L. Gordon (1160-1168).
The effect of adding alkali metals (Li, Na, K) to a CaO–MgO mixture, on the catalytic combustion of carbon black (CB), a model compound for soot, was studied. Catalysts were prepared by the Sol–Gel method and characterized by surface (BET surface area, XPS, DRIFTS) and bulk (AAS, XRD and TPR) techniques. Samples with a 4:1 catalyst-CB ratio were subjected to catalytic oxidation in a thermo-gravimetric apparatus and the temperature T m, at which combustion occurs at its maximum rate, was recorded for comparison of catalytic activity. The addition of alkali metals (Li, Na, K) over the CaO–MgO mixture significantly increased the catalytic activity, due to the formation of surface oxygenated species that enhanced the oxidizing properties of the catalyst surface. That activity for CB combustion increases with the atomic number of the alkali metal contained in the catalyst. The presence of alkali metals also diminished the amount and stability of carbonates formed on the catalyst. The K-containing catalyst showed the largest activity for the catalytic CB combustion, because it shows the largest capacity to enrich its surface with α-oxygen type and promotes best the surface dissociation of that oxygen. Furthermore, surface-adsorbed OH and carbonate groups that disable the active sites and prevent the oxygen adsorption and dissociation, were less abundant and desorbed at lower temperatures, showing to be less stable on this K-containing catalyst.
Keywords: Soot; Catalytic combustion; Alkaline metals;
Safe operating conditions determination for stationary SI gas engines by K. Saikaly; S. Rousseau; C. Rahmouni; O. Le Corre; L. Truffet (1169-1179).
Knock is a major problem when running combined heat and power (CHP) gas engines because of the variation in the network natural gas composition. A curative solution is widely applied, using an accelerometer to detect knock when it occurs. The engine load is then reduced until knock disappears. The present paper deals with a knock preventive device. It is based on the knock prediction following the engine operating conditions and the fuel gas methane number, and it acts on the engine load before knock happens. A state of the art about knock prediction models is carried out. The maximum of the knock criterion is selected as knock risk estimator, and a limit value above which knock may occur is defined. The estimator is calculated using a two-zone thermodynamic model. This model is specifically based on existing formulas for the calculation of the combustion progress, modified to integrate the effect of the methane number. A chemical kinetic model with 53 species and 325 equilibrium reactions is used to calculate unburned and burned gases composition. The different parameters of the model are fitted with a least squares method from an experimental data base. Errors less than 8% are achieved. The knock risks predicted for various natural gases and operating conditions are in agreement with previous work. Nevertheless, the knock risk estimator is overestimated for natural gases with high concentrations of inert gases such as nitrogen and carbon dioxide. The definition of a methane number limit based on the engine manufacturer's recommendation is then required to eliminate unwarranted alerts. Safe operating conditions are thus calculated and gathered in the form of a map. This map, combined with the real time measurement of the fuel gas methane number, can be integrated to the control device of the CHP engine in order to guarantee a safe running towards fuel gas quality variation.
Keywords: Gas engine; Knock; Knock prediction; Knock prevention;
Experimental design applied to the development of a copper direct determination method in gasoline samples by graphite furnace atomic absorption spectrometry by Janyeid Karla Castro Sousa; Allan Nilson de Sousa Dantas; Aldaléa Lopes Brandes Marques; Gisele Simone Lopes (1180-1185).
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.
Keywords: Experimental design; Atomic absorption spectrometry; Gasoline; Copper;
Pulverized coal combustion and NO x emissions in high temperature air from circulating fluidized bed by Qinggang Lu; Jianguo Zhu; Tianyu Niu; Guoliang Song; Yongjie Na (1186-1192).
A new technique of achieving high temperature air was adopted by combustion in high excess air ratio in a circulating fluidized bed (CFB). Experiments on pulverized coal combustion in high temperature air from the CFB were made in a down-fired combustor with the diameter of 220 mm and the height of 3000 mm. High temperature air with lower oxygen concentrations can be achieved steadily and continuously by combustion in the circulating fluidized bed. Pulverized coal combustion in high temperature air shows a uniform temperature profile along the axis of the down-fired combustor and the combustion efficiency is 99.8%. The NOx emission is 390 mg/m3, 13% lower than the regulation for thermal power plants in China. The HCN and NH3 emissions, as well as N2O, are about zero in the exhaust.
Keywords: Pulverized coal combustion; High temperature air; Circulating fluidized bed; NO x ;
Energetic use of the tomato plant waste by José M. Encinar; Juan F. González; Gloria Martínez (1193-1200).
A study of the conventional pyrolysis of the tomato plant waste has been carried out. The objective of this work was to characterize the solid, liquid and gaseous phases obtained in the process for their possible utilization in energy generation. Also, a study of the influence of operation variables has been performed, determining the optimal conditions in which the process can be accomplished. The operation variables studied were temperature (400–800 °C), the initial sample mass (2.5–10 g of tomato plant waste) and the particle size (0.63–2.00 mm). Under the conditions studied here, an increase in reaction temperature leads to a decrease in solid and liquid yields and to an increase in gas phase yield. However the variation in the initial sample mass and the particle size does not seem to exert a defined influence in the yield of the different phases. The higher heating value (HHV) of solids and liquids was determined; also the immediate analysis of the solid phase was carried out. The gas phase, mainly composed of H2, CO, CH4, CO2 and traces of ethane and ethylene, was analyzed chromatographically. The solid phase is constituted for a charcoal with an average higher heating value of 26 MJ kg− 1, the liquid phase presents a HHV of 7.8 MJ kg− 1 at 400 °C, this value diminishes when the temperature is increased, and the gas phase has an HHV between 0.5 and 8.0 MJ (kg of raw material)− 1. According to their characteristics and energy contents, the solid phase can be used as fuel or precursor for the manufacture of activated carbons. The liquid phase could be used as liquid fuel or as organic-compounds source. The gas phase could be used to heat the pyrolysis reactor or to generate heat and electricity in a gas-turbine/vapour-turbine combined cycle. Finally, as previous step to the design of the industrials equipments, a kinetic study of the process, based in the generation of the principal gases, has been carried out. For this study it has been considered that the gases are formed through parallel independent first-order reactions, with different activation energy. From this model, rate constants for the formation of each gas component and their corresponding activation energies were determined.
Keywords: Pyrolysis; Temperature; Tomato plant waste; Pyrolysis kinetics; Energy evaluation;
The influence of the waste ethylene vinyl acetate copolymer on the thermal degradation of the waste polypropylene by Suat Uçar; Ahmet R. Ozkan; Jale Yanik; Selhan Karagöz (1201-1206).
The pyrolysis of the waste polypropylene (PP), the waste ethylene vinyl acetate copolymer (EVA) and their blends has been carried out in a fixed bed reactor at 500 °C. The effect of different ratios of the waste EVA in the waste PP/EVA blends on the thermal degradation of the waste PP was investigated in terms of both product distributions and liquid fuel properties. The compositions of pyrolysis products were characterized in detail. The liquid products from the pyrolysis of the waste PP, the waste EVA and their blends were analyzed using different analytical techniques and fuel properties of pyrolytic liquids were investigated in comparison with commercial diesel. There were no synergistic effects between products from the waste PP and products from the waste EVA. While the ratio of the waste EVA increased in the waste PP/EVA blends, aromatic content of the pyrolytic liquids increased and subsequently paraffinic content of the pyrolytic liquids decreased. In addition, the boiling point distributions of pyrolytic liquids derived from the waste PP/EVA blends were found to be similar for all tested ratios of the waste PP/EVA blends.
Keywords: Pyrolysis; Polypropylene (PP); Ethylene vinyl acetate copolymer (EVA);
H2 rich syngas by selective CO2 removal from biomass gasification in a dual fluidized bed system — Process modelling approach by Tobias Pröll; Hermann Hofbauer (1207-1217).
A process model of dual fluidized bed gasification is presented based on mass- and energy balances. The model further covers the evaluation of thermodynamic equilibrium states. The gasification is investigated for the special case that CaO/CaCO3 is used as bed material allowing selective transport of CO2 from the gasification reactor to the combustion reactor by repeated carbonation and calcination. Experimental data are used to determine the model parameters. An empirical approach towards the kinetics of fuel conversion allows prediction of process behaviour at varied fuel water content. The selective transport of CO2 results in high H2 contents in the produced syngas. The lower operating temperatures in the gasification reactor increase the efficiency of energy conversion. The results are in agreement with experimental data and show the thermodynamic limitations of the technology.
Keywords: Biomass gasification; Synthesis gas; Hydrogen; Process modelling; Simulation;
An experimental and numerical analysis of the influence of the inlet temperature, equivalence ratio and compression ratio on the HCCI auto-ignition process of Primary Reference Fuels in an engine by Hatim Machrafi; Simeon Cavadiasa (1218-1226).
In order to understand better the auto-ignition process in an HCCI engine, the influence of some important parameters on the auto-ignition is investigated. The inlet temperature, the equivalence ratio and the compression ratio were varied and their influence on the pressure, the heat release and the ignition delays were measured. The inlet temperature was changed from 25 to 70 °C and the equivalence ratio from 0.18 to 0.41, while the compression ratio varied from 6 to 13.5. The fuels that were investigated were PRF40 and n-heptane. These three parameters appeared to decrease the ignition delays, with the inlet temperature having the least influence and the compression ratio the most. A previously experimentally validated reduced surrogate mechanism, for mixtures of n-heptane, iso-octane and toluene, has been used to explain observations of the auto-ignition process. The same kinetic mechanism is used to better understand the underlying chemical and physical phenomena that make the influence of a certain parameter change according to the operating conditions. This can be useful for the control of the auto-ignition process in an HCCI engine.
Keywords: Auto-ignition; HCCI engine; Inlet temperature; Equivalence ratio; Compression ratio; Kinetic mechanism;
The effect of aluminum inhibition on the defluidization behavior and generation of pollutants in fluidized bed incineration by Jia-Hong Kuo; Ming-Yen Wey; Chiou-Liang Lin; Han-Min Chiu (1227-1236).
Agglomeration not only affects fluidization behaviors but also generates secondary pollutants. However, adding Al-related minerals such as clay and kaolin is an efficient way to control the agglomeration. Complex compositions of minerals may influence Al inhibition on agglomeration. Accordingly, this study is carried out to estimate the effect of Al inhibition on defluidization observed in a fluidized bed incinerator by using different Al/Na ratios. Emission of pollutants (organics and heavy metals) during the defluidization process is also considered. Several characterization studies (i.e. XRD, ESCA, and SEM/EDS) are applied to identify the eutectics from the agglomerates after defluidization.The results show that Al extends the defluidization time significantly with Al increasing. At various operating conditions, such as operating temperature, gas velocity, and particle size of bed materials, Al inhibits agglomeration by ten times delay with comparison to previous work. Moreover, concentration of organics emitted increases with operating time at the initial combustion step. After defluidization, the concentration of organics decreases apparently owing to combustion heat accumulated at the surface of the sand bed. The emission concentrations of three volatile heavy metals were similar before defluidization, but they sharply increased after the system formed defluidization. The amount of heavy metals emitted followed the order Pb > Cd > Cr at various operating conditions. Results of experiments in emissions of organics and heavy metals performed different behavior during defluidization processes.
Keywords: Fluidized bed incineration; Defluidization; Agglomeration; Aluminum; Emissions;
Effects of NO x -inhibitor agent on fuel properties of three-phase biodiesel emulsions by Cherng-Yuan Lin; Hsiu-An Lin (1237-1242).
Biodiesel is one of the more promising alternative clean fuels to fossil fuel, which can reduce the emissions of fossil fuel burning, and possibly resolve the energy crisis caused by the exhaustion of petroleum resources in the near future. The burning of biodiesel emits much less gaseous emissions and particulate matter primarily because of its dominant combustion efficiency. However, the high oxygen content in biodiesel not only promotes the burning process but also enhances NO x formation when biodiesel is used as fuel. Biodiesel emulsion and the additive of NO x -inhibitor agent are considered to reduce levels of NO x emissions in this experimental study. The biodiesel was produced by transesterification reaction accompanied with peroxidation process. A three-phase biodiesel emulsion of oil-in water drops-in oil (O/W/O) and an O/W/O biodiesel emulsion containing aqueous ammonia were prepared afterwards. The effect of the existence of NO x -inhibitor agent on the fuel properties and the emulsion characteristics of the O/W/O biodiesel emulsions were investigated. The experimental results show that the burning of the O/W/O biodiesel emulsion and the O/W/O biodiesel emulsion containing aqueous ammonia had larger fraction of fuel burnt and thus larger heat release than the neat biodiesel if water content is not considered for the calculation of heating value. The addition of aqueous ammonia within the dispersed phase of the O/W/O biodiesel emulsion appeared to deteriorate the emulsification characteristics. A smaller quantity of emulsion and greater kinematic viscosity were formed while a larger carbon residue and actual reaction-heat release also appeared for this O/W/O biodiesel emulsion. Aqueous ammonia in the O/W/O biodiesel emulsion produces a higher pH value as well. In addition, the number as well as the volumetric fraction of the dispersed water droplets is reduced for the O/W/O biodiesel emulsion that contains aqueous ammonia.
Keywords: NO x -inhibitor agent; Biodiesel; Fuel properties; Three-phase emulsion;