Fuel Processing Technology (v.91, #12)

Dimensional analysis for assessing the performance of electrostatic precipitators by F.J. Gutiérrez Ortiz; B. Navarrete; L. Cañadas (1783-1793).
Electrostatic precipitators (ESP) are widely used in industry today and much research has been carried out during the last decades. Dimensional analysis (DA) allows to reduce the number of parameters necessary for defining the ESP performance and provides a reliable scaling-up of the desired operating conditions from the pilot-scale to full-scale plant (based on the invariance of the pi-space). Likewise, DA gives a consistent extrapolation within the range covered by dimensionless number and a greater flexibility in choice of parameters. DA together with similarity analysis is presented in this work in order to obtain a functional dependence between a target number and a set of few dimensionless numbers. The target selected has been the penetration, i.e., the ratio of particle dust concentration at the outlet of the ESP (C o) and that at the inlet of the ESP (C i). The results can be valuable to assess the data from ESP of different operating characteristics, under geometric, electrical, fluid dynamics and electro-hydrodynamics similarity. Thus, as a consequence of these analyses, several quite reduced models have been formulated theoretically and later tested and validated with experimental data obtained in a pilot ESP in order to show an application of the study. Four models have been fitted by linear regression, resulting unsatisfactory. However, two additional models fitted by non-linear regression predict values of particle removal efficiency that agrees well with the experimental data. Thus, this paper is focused towards dimensional analysis in ESP model building, showing both the reduction in effort and more effective modeling that can result.
Keywords: Electrostatic precipitator; Dimensional analysis; Similarity; Scale-up; Pilot plant; Modeling;

Simulation of the operation of an industrial wet flue gas desulfurization system by L.E. Kallinikos; E.I. Farsari; D.N. Spartinos; N.G. Papayannakos (1794-1802).
In this work the simulation of a wet flue gas desulfurization (FGD) unit with spray tower of a power plant is presented, aiming at an efficient follow-up and the optimization of the FGD system operation. The dynamic model developed to simulate the performance of the system has been validated with operation data collected over a long period of time. All the partaking physical and chemical processes like the limestone dissolution, the crystallization of calcium sulfite and gypsum and the oxidation of sulfite ions have been taken into account for the development of the simulation model while the gas absorption by the liquid droplets was based on the two-film theory. The effect of the mean diameter of the slurry droplets on the performance of the system was examined, as it was used as an index factor of the normal operation of the system. The operation limits of the system were investigated on the basis of the model developed. It is concluded that the model is capable of simulating the system for significantly different SO2 loads and that the absorption rate of SO2 is strongly affected by the liquid dispersion in the tower.
Keywords: Wet flue gas desulfurization; Oxidation; Absorption; Mass transfer; Interfacial area; Dynamic model;

Oxidation desulfurization of fuel using pyridinium-based ionic liquids as phase-transfer catalysts by Dishun Zhao; Yanan Wang; Erhong Duan; Juan Zhang (1803-1806).
In this work, several ionic liquids based on pyridinium cations are prepared. The ionic liquids are employed as phase-transfer catalysts (PTCs) for phase-transfer catalytic oxidation of dibenzothiophene (DBT) dissolved in n-octane. The partition coefficients of DBT between ionic liquids and n-octane are investigated. Then H2O2–formic acid is used as an oxidant and ionic liquids are used as PTCs. The reaction turns to be heterogeneous and desulfurization rate of DBT increased apparently. When IL ([BPy]HSO4) is used as PTC, and the condition are: temperature is 60 °C, time is 60 min, H2O2/sulfur molar ratio (O/S) is 4, the desulfurization rate reaches the maximum (93.3%), and the desulfurization of the real gasoline is also investigated, 87.7% of sulfur contents are removed under optima reaction conditions. The PTC [BPy]HSO4 can be recycled for five times without significant decrease in activity.
Keywords: Desulfurization; Phase-transfer catalysts; Oxidation; Ionic liquids;

Three corn stover hydrolysates, enzymatic hydrolysates prepared from acid and alkaline pretreatments separately and hemicellulosic hydrolysate prepared from acid pretreatment, were evaluated in composition and fermentability. For enzymatic hydrolysate from alkaline pretreatment, ethanol yield on fermentable sugars and fermentation efficiency reached highest among the three hydrolysates; meanwhile, ethanol yield on dry corn stover reached 0.175 g/g, higher than the sum of those of two hydrolysates from acid pretreatment. Fermentation process of the enzymatic hydrolysate from alkaline pretreatment was further investigated using free and immobilized cells of recombinant Saccharomyces cerevisiae ZU-10. Concentrated hydrolysate containing 66.9 g/L glucose and 32.1 g/L xylose was utilized. In the fermentation with free cells, 41.2 g/L ethanol was obtained within 72 h with an ethanol yield on fermentable sugars of 0.416 g/g. Immobilized cells greatly enhanced the ethanol productivity, while the ethanol yield on fermentable sugars of 0.411 g/g could still be reached. Repeated batch fermentation with immobilized cells was further attempted up to six batches. The ethanol yield on fermentable sugars maintained above 0.403 g/g with all glucose and more than 92.83% xylose utilized in each batch. These results demonstrate the feasibility and efficiency of ethanol production from corn stover hydrolysates.
Keywords: Corn stover; Enzymatic hydrolysate; Hemicellulosic hydrolysate; Ethanol; Recombinant yeast; Immobilization;

Hydrogen production by glycerol steam reforming with/without calcium oxide sorbent: A comparative study of thermodynamic and experimental work by Xiaodong Wang; Maoshuai Li; Shuirong Li; Hao Wang; Shengping Wang; Xinbin Ma (1812-1818).
Thermodynamic analysis and experimental tests of glycerol steam reforming with/without calcium oxide (CaO) as a carbon dioxide (CO2) sorbent have been performed and compared in this work. Methanol, ethanol, acetaldehyde, acetone and ethylene do not exist in equilibrium conditions according to the equilibrium calculations. Without CaO present, thermodynamic predictions show that a maximum hydrogen concentration of 67% can be obtained at 925 K, with a water to glycerol ratio (WGR) of 9. In the experiments, the Ni/ZrO2 catalyst fails to catalyze the reactions to thermodynamic equilibrium under the selected conditions as the highest hydrogen concentration obtained is 64%. With the presence of CaO, thermodynamic analysis implies hydrogen purity exceeding 95% can be achieved below 925 K at WGRs of 6 and 9. However, CaCO3 does not exist at temperatures greater than 1025 K. In the experiments, a hydrogen purity of 95% with only 5% CH4 as impurity can be reached at 850 K with a WGR of 9. The Ni/ZrO2 catalyst is not active enough to convert excess CH4 to hydrogen in glycerol steam reforming as CH4 concentrations are usually higher than the equilibrium values. The addition of CaO to this system greatly enhances the hydrogen production while reducing the CO concentration.
Keywords: Hydrogen; Glycerol; Steam reforming; CaO sorbent; Thermodynamic analysis;

Experimental and numerical simulation studies of the fluidization characteristics of a separating gas–solid fluidized bed by Yuemin Zhao; Ligang Tang; Zhenfu Luo; Chuncheng Liang; Hongbo Xing; Wanchang Wu; Chenlong Duan (1819-1825).
Gas–solid fluidized bed separation expands the choices of highly efficient dry coal beneficiation methods. The hydrodynamics of 0.3–0.15 mm large Geldart B magnetite powder were studied using a combination of experimental and numerical methods to optimize the design of the solid medium used in the fluidized bed. The results show that the Syamlal–O'Brien drag model is suitable for simulating the bed and it is verified that simulated and experimental results are consistent with each other. If the static bed height is no more than 300 mm then the bed height has minimal effect on the fluidization characteristics. As the superficial gas velocity increases the bed activity is improved. However, at the same time the uniformity and stability of the bed drop. Therefore, the gas velocity should be adjusted to no more than 2.0U mf. The density of the Geldart B bed is uniform and stable, which indicates a relatively high fluidization quality. Furthermore, compounded medium solids consisting of < 0.3 mm magnetite powder with a 0.3–0.15 mm particle content of 65.25% and < 1 mm fine coal were used in a pilot gas–solid fluidized bed of 5–10 ton/h capacity. The pilot bed was used to separate 50–6 mm coal. This test resulted in the coal ash content being reduced from 23.74% to 11.79% with a probable error, E, of 0.07 g/cm3 and a recovery efficiency of 98.26%. This indicates that the bed has good separating performance. Nevertheless, to increase the applicability of the separating bed a further study emphasizing a decrease in the lower size limit of the magnetite powder should be performed.
Keywords: Separating gas–solid fluidized bed; Medium solids; Fluidization characteristic; Numerical simulation; Dry beneficiation of coal;

Jump in the air gasification rate of potassium-doped cellulosic chars by T.G. Devi; M.P. Kannan; V.P. Abduraheem (1826-1831).
Chars prepared from potassium-exchanged carboxy methyl cellulose at several heat treatment temperatures (HTTs) were gasified in air isothermally at selected gasification temperatures (GTs) in the range 633–893 K to investigate the catalytic effectiveness of potassium species. The chars displayed a noticeable jump in gasification rate at a particular gasification temperature (called jump temperature, T j). The magnitude of jump was much less than that reported for copper and nickel catalysis, but comparable with that for calcium catalysis. Increase in HTT caused a decrease in the jump temperature of chars in contrast with the increase observed in copper, nickel and calcium catalysis; also the magnitude of jump did not decrease, but remained unaltered, on increasing HTT. The different behavior of potassium catalysis is correlated to a change in the chemical state of potassium at higher HTT. The results reveal the dependence of jump phenomenon on chemical state and dispersion of catalyst in the char.
Keywords: Char; Potassium doping; Gasification; Thermal analysis; Reactivity;

Maximum solid concentrations of coal water slurries predicted by neural network models by Jun Cheng; Yanchang Li; Junhu Zhou; Jianzhong Liu; Kefa Cen (1832-1838).
The nonlinear back-propagation (BP) neural network models were developed to predict the maximum solid concentration of coal water slurry (CWS) which is a substitute for oil fuel, based on physicochemical properties of 37 typical Chinese coals. The Levenberg–Marquardt algorithm was used to train five BP neural network models with different input factors. The data pretreatment method, learning rate and hidden neuron number were optimized by training models. It is found that the Hardgrove grindability index (HGI), moisture and coalification degree of parent coal are 3 indispensable factors for the prediction of CWS maximum solid concentration. Each BP neural network model gives a more accurate prediction result than the traditional polynomial regression equation. The BP neural network model with 3 input factors of HGI, moisture and oxygen/carbon ratio gives the smallest mean absolute error of 0.40%, which is much lower than that of 1.15% given by the traditional polynomial regression equation.
Keywords: Coal water slurry; Solid concentration; Neural network model; Back-propagation;

Investigation of Fischer–Tropsch synthesis performance and its intrinsic reaction behavior in a bench scale slurry bubble column reactor by Heon Jung; Jung-Il Yang; Jung Hoon Yang; Ho-Tae Lee; Dong Hyun Chun; Hak-Joo Kim (1839-1844).
A bench scale slurry bubble column reactor (SBCR) with active-Fe based catalyst was developed for the Fischer–Tropsch synthesis (FTS) reaction. Considering the highly exothermic reaction heat generated in the bench scale SBCR, an effective cooling system was devised consisting of a U-type dip tube submerged in the reactor. Also, the physical and chemical properties of the catalyst were controlled so as to achieve high activity for the CO conversion and liquid oil (C5+) production. Firstly, the FTS performance of the FeCuK/SiO2 catalyst in the SBCR under reaction conditions of 265 °C, 2.5 MPa, and H2/CO = 1 was investigated. The CO conversion and liquid oil (C5+) productivity in the reaction were 88.6% and 0.226 g/gcat-h, respectively, corresponding to a liquid oil (C5+) production rate of 0.03 bbl/day. To investigate the FTS reaction behavior in the bench scale SBCR, the effects of the space velocity and superficial velocity of the synthesis gas and reaction temperature were also studied. The liquid oil production rate increased up to 0.057 bbl/day with increasing space velocity from 2.61 to 3.92 SL/h-gFe and it was confirmed that the SBCR bench system developed in this research precisely simulated the FTS reaction behavior reported in the small scale slurry reactor.
Keywords: Fischer–Tropsch synthesis; Bench scale; Slurry bubble column reactor; Space velocity; Superficial velocity; Reaction temperature;

Energy-saving direct ethanol production from viscosity reduction mash of sweet potato at very high gravity (VHG) by Liang Zhang; Qian Chen; Yanlin Jin; Huilin Xue; Jiafa Guan; Zhongyan Wang; Hai Zhao (1845-1850).
Sweet potato is an important dietary and economic material in China (accounting for 85% of global production in 2005) and Southeast Asia. The limitation of using root and tuber of sweet potato mash at high solids content is attributed to its high viscous nature. The aim of this study was to investigate the influence of different viscosity reduction factors and found optimal parameters via a surface response design. The optimal xylanase enzyme dose, pretreatment time and temperature were 1.56 AGU/g, 87.6 min and 44.1 °C, respectively. Using pretreatment sweet potato mash on the optimized condition, the final viscosity 498.1 cp and ethanol yield of 135.1 g/kg was obtained by Saccharomyces cerevisiae, which was equivalent to 90.7% of the theoretical yield.
Keywords: Sweet potato; Simultaneous saccharification and fermentation (SSF); Bioethanol; Very high gravity (VHG); Viscosity reduction; Response surface methodogy (RSM);

Author Index (1851-1855).

Subject Index (1856-1862).

Contents Volume (1863-1872).