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Effect of pressure on gasification reactivity of three Chinese coals with different ranks
Chunyu LI, Jiantao ZHAO, Yitian FANG, Yang WANG
Front Chem Eng Chin. 2010, 4 (4): 385-393.
https://doi.org/10.1007/s11705-010-0501-1
The gasification reactivities of three kinds of different coal ranks (Huolinhe lignite, Shenmu bituminous coal, and Jincheng anthracite) with CO2 and H2O was carried out on a self-made pressurized fixed-bed reactor at increased pressures (up to 1.0 MPa). The physicochemical characteristics of the chars at various levels of carbon conversion were studied via scanning electron microscopy (SEM), X-ray diffraction (XRD), and BET surface area. Results show that the char gasification reactivity increases with increasing partial pressure. The gasification reaction is controlled by pore diffusion, the rate decreases with increasing total system pressure, and under chemical kinetic control there is no pressure dependence. In general, gasification rates decrease for coals of progressively higher rank. The experimental results could be well described by the shrinking core model for three chars during steam and CO2 gasification. The values of reaction order n with steam were 0.49, 0.46, 0.43, respectively. Meanwhile, the values of reaction order n with CO2 were 0.31, 0.28, 0.26, respectively. With the coal rank increasing, the pressure order m is higher, the activation energies increase slightly with steam, and the activation energy with CO2 increases noticeably. As the carbon conversion increases, the degree of graphitization is enhanced. The surface area of the gasified char increases rapidly with the progress of gasification and peaks at about 40% of char gasification.
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Experiments on the effect of the pressure on the mineral transformation of coal ash under the different reaction atmosphere
Nijie JING, Qinhui WANG, Zhongyang LUO, Tao JIE, Xiaomin LI, Kefa CEN
Front Chem Eng Chin. 2010, 4 (4): 394-399.
https://doi.org/10.1007/s11705-010-0505-x
This paper investigated the effect of the pressures, reaction atmospheres and coal ash species on the ash fusibility with high-pressure thermogravimetric analysis (PTGA) apparatus and X-ray diffraction (XRD) analysis. Each specimen analyzed by XRD was observed for the mineral conversion and formation of new minerals with the pressures under different atmospheres. These results indicate that the pressure restrains the transformation and decomposition of minerals. Many low-temperature minerals are still present under the elevated pressure. The different reaction atmospheres have different effects on the formation of coal ash minerals. Under the N2 atmosphere, the present microcline may decrease the melting temperature of coal ash. And later, it transforms into sanidine at high pressure; thus, the melting temperature of coal ash may increase. Under the CO2 atmosphere, the minerals such as microcline, lomonitite, geothite and illite are still present with the increase in pressure; this may reduce the melting temperature. While under the H2O atmosphere, there are magnetite and anorthoclase, which may produce the low-temperature eutectics decreasing the melting temperature. The coal ash abundance in basic oxides or higher SiO2, Fe2O3, K2O and Na2O has lower melting temperature. While the ash sample with more SiO2 and Al2O3 and less Fe2O3 and basic oxides may lead to higher melting temperature.
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Experimental investigations on combustion characteristics of syngas composed of CH4, CO, and H2
Qingwei FAN, Shien HUI, Qulan ZHOU, Qinxin ZHAO, Tongmo XU
Front Chem Eng Chin. 2010, 4 (4): 404-410.
https://doi.org/10.1007/s11705-010-0513-x
The residual gas and remained raw gas in dual gas resources polygeneration system are quite complex in components (mainly CH4, CO, and H2), and these results to the distinguished differences in combustion reaction. Experimental investigations on basic combustion characteristics of syngas referred above are conducted on a laboratory-scale combustor with flame temperature and flue gas composition measured and analyzed. Primary air coefficient (PA), total air coefficient (TA), and components of the syngas (CS) are selected as key factors, and it is found that PA dominates mostly the ignition of syngas and NOx formation, while TA affects the flue gas temperature after high temperature region and NOx formation trend to be positive as H2/CO components increase. The results provide references for industrial utilization.
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Experimental study on the laminar flame speed of hydrogen/natural gas/air mixtures
Chen DONG, Qulan ZHOU, Xiaoguang ZHANG, Qinxin ZHAO, Tongmo XU, Shi’en HUI
Front Chem Eng Chin. 2010, 4 (4): 417-422.
https://doi.org/10.1007/s11705-010-0515-8
Laminar flame speeds of hydrogen/natural gas/air mixtures have been measured over a full range of fuel compositions (0–100% volumetric fraction of H2) and a wide range of equivalence ratio using Bunsen burner. High sensitivity scientific CCD camera is use to capture the image of laminar flame. The reaction zone area is employed to calculate the laminar flame speed. The initial temperature and pressure of fuel air mixtures are 293 K and 1 atm. The laminar flame speeds of hydrogen/air mixture and natural gas/air mixture reach their maximum values 2.933 and 0.374 m/s when equivalence ratios equal to 1.7 and 1.1, respectively. The laminar flame speeds of hydrogen/natural gas/air mixtures rise with the increase of volumetric fraction of hydrogen. Moreover, the increase in laminar flame speed as the volumetric fraction of hydrogen increases presents an exponential increasing trend versus volumetric fraction of hydrogen. Empirical formulas to calculate the laminar flame speeds of hydrogen, natural gas, and hydrogen/natural gas mixtures are also given. Using these formulas, the laminar flame speed at different hydrogen fractions and equivalence ratios can be calculated.
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Regeneration of Fe2O3-based high-temperature coal gas desulfurization sorbent in atmosphere with sulfur dioxide
Ruizhuang ZHAO, Ju SHANGGUAN, Yanru LOU, Jin SONG, Jie MI, Huiling FAN
Front Chem Eng Chin. 2010, 4 (4): 423-428.
https://doi.org/10.1007/s11705-010-0503-z
Regeneration of a high-temperature coal gas desulfurization sorbent is a key technology in its industrial applications. A Fe2O3-based high-temperature coal gas desulfurizer was prepared using red mud from steel factory. The influences of regeneration temperature, space velocity and regeneration gas concentration in SO2 atmosphere on regeneration performances of the desulfurization sorbent were tested in a fixed bed reactor. The changes of phase and the composition of the Fe2O3-based high-temperature coal gas desulfurization sorbent before and after regeneration were examined by X-ray diffraction(XRD) and X-ray Photoelectron spectroscopy(XPS), and the changes of pore structure were characterized by the mercury intrusion method. The results show that the major products are Fe3O4 and elemental sulfur; the influences of regeneration temperature, space velocity and SO2 concentration in inlet on regeneration performances and the changes of pore structure of the desulfurization sorbent before and after regeneration are visible. The desulfurization sorbent cannot be regenerated at 500°C in SO2 atmosphere. Within the range of 600°C – 800°C, the time of regeneration becomes shorter, and the regeneration conversion increases as the temperature rises. The time of regeneration also becomes shorter, and the elemental sulfur content of tail gas increases as the SO2 concentration in inlet is increased. The increase in space velocity enhances the reactive course; the best VSP is 6000 h-1 for regeneration conversion. At 800°C, 20 vol-% SO2 and 6000 h-1, the regeneration conversion can reach nearly to 90%.
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Sulfidation/regeneration multicycle testing of nickel-modified ZnFe2O4 desulphurization sorbent
Wei LI, Jinju GUO, Jiejie HUANG, Jiaotao ZHAO
Front Chem Eng Chin. 2010, 4 (4): 435-440.
https://doi.org/10.1007/s11705-010-0506-9
A commercial metal oxide sorbent for the desulphurization of coal-derived gas requires high desulphurization reactivity, mechanical strength, ability to regenerate, and stability to endure many sulfidation-regeneration cycles. In this paper, the sulfur capacity and multiple cycles of a nickel-modified ZnFe2O4 sorbent prepared by the sol-gel auto-combustion method were measured in a fixed-bed reactor at middle temperature of 300°C (sulfidation temperature) and 500°C (regeneration temperature). Also, the BET surface area, pore volume, average pore diameter and X-ray diffraction (XRD) patterns of the sorbent through multicycles were studied. Multicycle runs indicate that the sulfidation reactivity decreases slightly during the second cycle and keeps steady in the following cycles. The results indicate that the nickel-modified ZnFe2O4 keeps high reactivity and structural stability in the multicycle testing of sulfidation/regeneration.
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Preparation and selection of Fe-Cu sorbent for COS removal in syngas
Bowu CHENG, Zhaofei CAO, Yong BAI, Dexiang ZHANG
Front Chem Eng Chin. 2010, 4 (4): 441-444.
https://doi.org/10.1007/s11705-010-0507-8
A series of iron-based sorbents prepared with iron trioxide hydrate, cupric oxide by a novel method was studied in a fixed-bed reactor for COS removal from syngas at moderate temperature. In addition, the sorbents mixed with various additives in different ratios were tested. The effects of additive type and ratio on the breakthrough capacity and desulfurization performance, as well as the influence of operating conditions on sulfidation behavior of the sorbent, were investigated. The simulate gas contained 1% COS, 5% CO2, 20%–30% CO and 60%–70% H2. The outlet gases from the fixed-bed reactor were automatically analyzed by on-line mass spectrometry, and the COS concentration before breakthrough can be kept steady at 1 ppmv. The result shows that the breakthrough sulfur capacity of the sorbent is as high as 25 g-S/100 g. At 700 K and space velocity of 1000 h-1, the efficiency of sulfur removal and breakthrough sulfur capacity of the sorbent increase with the increase of copper oxide with an optimum value. The result shows that the species and content of additives also affect desulfurization performance of the sorbent.
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A study on the catalytic performance of Pd/γ-Al2O3, prepared by microwave calcination, in the direct synthesis of dimethylether
Ruizhi CHU, Xianyong WEI, Zhimin ZONG, Wenjia ZHAO
Front Chem Eng Chin. 2010, 4 (4): 452-456.
https://doi.org/10.1007/s11705-010-0522-9
A series of Pd/γ-Al2O3 hybrid catalysts were prepared by impregnation and subsequent calcination under microwave irradiation. The catalysts were used for direct synthesis of dimethylether (DME) from syngas. The results show that calcination under microwave irradiation improved both the activity and selectivity of the catalysts for DME synthesis. The optimum power of the microwave was determined to be 420 W. Under such optimum conditions, CO conversion, DME selectivity and time space yield of DME were 60.1%, 67.0%, and 21.5 mmol·mL-1·h-1, respectively. Based on various characterizations such as nitrogen physisorption, X-ray diffraction, CO-temperature-programmed desorption, and Fourier transform infrared spectral analysis, the promotional effect of the microwave irradiation on the catalytic property was mainly attributed to both the higher dispersion of Pd and the significant increase in the adsorption on the CO-bridge of Pd. Microwave irradiation with very high power led to the increase in CO-bridge adsorption and thereby decreased the catalytic activity, whereas the coverage by metallic Pd of the active sites on acidic γ-Al2O3 significantly occurred under microwave irradiation with very low power, resulting in a decrease in the selectivity to DME.
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Study on direct alcohol/ether fuel synthesis process in bubble column slurry reactor
Zhen CHEN, Haitao ZHANG, Weiyong YING, Dingye FANG
Front Chem Eng Chin. 2010, 4 (4): 461-471.
https://doi.org/10.1007/s11705-010-0517-6
The recent studies of direct alcohol/ether synthesis process in slurry reactors were reviewed, and the research work in our laboratory was carried out in this paper. a global kinetics model for direct dimethyl ether (DME) synthesis from syngas over a novel Cu-Zn-Al-Zr slurry catalyst was established according to the total of 25 experimental data, and a steady-state one-dimensional mathematical model was further developed in bubble column slurry reactor (BCSR), which was assumed that the bubble phase was plug flow, and the liquid phase was fully mixed flow. The numerical simulations of reactor design of 100000 t/a dimethyl ether pilot plant indicate that higher pressure and lower temperature were favorable to the increase of CO conversion, selectivity of dimethyl ether, product yield and height of slurry bed. The optimal operating conditions for DME synthesis process were obtained: reaction temperature at 240°C, reactor pressure at 5 MPa and reactor diameter of 2.5 m.
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Ni-Co bimetallic catalyst for CH4 reforming with CO2
Xiaohong LI, Jun AI, Wenying LI, Dongxiong LI
Front Chem Eng Chin. 2010, 4 (4): 476-480.
https://doi.org/10.1007/s11705-010-0512-y
A co-precipitation method was employed to prepare Ni/Al2O3-ZrO2, Co/Al2O3-ZrO2 and Ni-Co/Al2O3-ZrO2 catalysts. Their properties were characterized by N2 adsorption (BET), thermogravimetric analysis (TGA), temperature-programmed reduction (TPR), temperature-programmed desorption (CO2-TPD), and temperature-programmed surface reaction (CH4-TPSR and CO2-TPSR). Ni-Co/Al2O3-ZrO2 bimetallic catalyst has good performance in the reduction of active components Ni, Co and CO2 adsorption. Compared with mono-metallic catalyst, bimetallic catalyst could provide more active sites and CO2 adsorption sites (C+ CO2 = 2CO) for the methane-reforming reaction, and a more appropriate force formed between active components and composite support (SMSI) for the catalytic reaction. According to the CH4-CO2-TPSR, there were 80.9% and 81.5% higher CH4 and CO2 conversion over Ni-Co/Al2O3-ZrO2 catalyst, and its better resistance to carbon deposition, less than 0.5% of coke after 4 h reaction, was found by TGA. The high activity and excellent anti-coking of the Ni-Co/Al2O3-ZrO2 catalyst were closely related to the synergy between Ni and Co active metal, the strong metal-support interaction and the use of composite support.
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Sensitivity analysis of a methanol and power polygeneration system fueled with coke oven gas and coal gas
Guoqiang ZHANG, Lin GAO, Hongguang JIN, Rumou LIN, Sheng LI
Front Chem Eng Chin. 2010, 4 (4): 491-497.
https://doi.org/10.1007/s11705-010-0511-z
The sensitivity analysis of a polygeneration energy system fueled with duo fuel of coke oven gas and coal gas is performed in the study, and the focus is put on the relations among syngas composition, conversation rate and performance. The impacts of the system configuration together with the fuel composition on the performance are investigated and discussed from the point of cascading utilization of fuel chemical energy. First, the main parameters affecting the performance are derived along with the analysis of the system configuration and the syngas composition. After the performance is being simulated by means of the Aspen Plus process simulator of version 11.1, the variation of the performance due to the composition of syngas and the conversion rate of chemical subsystem is obtained and discussed. It is obtained from the result that the proper conversion rate of the chemical subsystem according to the specific syngas composition results in better performance. And the syngas composition affects the optimal conversion rate of the chemical subsystem, the optimal point of which is around the stoichiometric composition for methanol production (CO/H2 = 0.5). In all, the polygeneration system fueled with coke oven gas and coal gas, which can realize the reasonable conversion of syngas to power and chemical product according to the syngas composition, is a promising method for coal energy conversion and utilization.
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Modeling the gas flow in a cyclone separator at different temperature and pressure
Gujun WAN, Guogang SUN, Cuizhi GAO, Ruiqian DONG, Ying ZHENG, Mingxian SHI
Front Chem Eng Chin. 2010, 4 (4): 498-505.
https://doi.org/10.1007/s11705-010-0502-0
The gas flow field in a cyclone separator, operated within a temperature range of 293 K – 1373 K and a pressure range of 0.1 – 6.5 MPa, has been simulated using a modified Reynolds-stress model (RSM) on commercial software platform FLUENT 6.1. The computational results show that the temperature and pressure significantly influence the gas velocity vectors, especially on their tangential component, in the cyclone. The tangential velocity decreases with an increase in temperature and increases with an increase in pressure. This tendency of the decrease or increase, however, reduces gradually when the temperature is above 1000 K or the pressure goes beyond 1.0 MPa. The temperature and pressure have a relatively weak influence on the axial velocity profiles. The outer downward flow rate increases with a temperature increase, whereas it decreases with a pressure increase. The centripetal radial velocity is strong in the region of 0 – 0.25D below the vortex finder entrance, which is named as a short-cut flow zone in this study. Based on the simulation results, a set of correlations was developed to calculate the combined effects of temperature and pressure on the tangential velocity, the downward flow rate in the cyclone and the centripetal radial velocity in the short-cut flow region underneath the vortex finder.
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Numerical simulation of fluid dynamics in the stirred tank by the SSG Reynolds Stress Model
Nana QI, Hui WANG, Kai ZHANG, Hu ZHANG
Front Chem Eng Chin. 2010, 4 (4): 506-514.
https://doi.org/10.1007/s11705-010-0508-7
The Speziale, Sarkar and Gatski Reynolds Stress Model (SSG RSM) is utilized to simulate the fluid dynamics in a full baffled stirred tank with a Rushton turbine impeller. Four levels of grid resolutions are chosen to determine an optimised number of grids for further simulations. CFD model data in terms of the flow field, trailing vortex, and the power number are compared with published experimental results. The comparison shows that the global fluid dynamics throughout the stirred tank and the local characteristics of trailing vortices near the blade tips can be captured by the SSG RSM. The predicted mean velocity components in axial, radial and tangential direction are also in good agreement with experiment data. The power number predicted is quite close to the designed value, which demonstrates that this model can accurately calculate the power number in the stirred tank. Therefore, the simulation by using a combination of SSG RSM and MRF impeller rotational model can accurately model turbulent fluid flow in the stirred tank, and it offers an alternative method for design and optimisation of stirred tanks.
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Experimental study on bubble behavior and CFD simulation of large-scale slurry bubble column reactor
Haoyi SUN, Tao LI, Weiyong YING, Dingye FANG
Front Chem Eng Chin. 2010, 4 (4): 515-522.
https://doi.org/10.1007/s11705-010-0516-7
Slurry bubble column reactors (SBCR) is a three-phase fluidized reactor with outstanding advantages compared with other reactors and is difficult to scale-up due to lack of information on hydrodynamics and mass transfer over a wide range of operating conditions of commercial interest. In this paper, an experiment was conducted to investigate the bubble behavior in SBCR with a height of 5600 mm and an interior diameter of 480 mm. Bubble rise velocity, bubble diameter, and gas holdup in different radial and axial positions are measured in SBCR using four-channel conductivity probe. Tap water, air, and glass beads (mean diameter 75–150 μm) are used as liquid, gas, and solid phases, respectively. It shows that hydrodynamic parameters have good regularity in SBCR. Moreover, a commercial computational fluid dynamics (CFD) package, Fluent, was used to simulate the process in SBCR. The simulations were carried out using axi-symmetric 2-D grids. Data obtained from experiment and CFD simulation are compared, and results show that the tendency of simulation is almost uniform with the experiment, which can help to obtain further understanding about multiphase flow process and establish a model about the synthesis of alcohol ether fuel in SBCR.
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