联合CO2捕集的生物质化学链气化制备合成气系统分析

本文提出以Fe₂O₃为载氧体、以CaO捕集CO₂的生物质化学链气化系统,利用Aspen Plus软件对该系统进行了模拟,以合成气组成（干基）、合成气氢碳比、含碳产物的碳摩尔分布、冷气效率及收率等为系统性能评价指标,重点分析了燃料反应器温度（T_FR）、载氧体Fe₂O₃与生物质碳摩尔比（Fe₂O₃/C）、水蒸气与生物质碳摩尔比（Steam/C）、CaO与生物质碳摩尔比（CaO/C）等系统参数对固体生物质化学链气化系统的影响。结果表明,在T_FR = 825℃、Fe₂O₃/C = 0.5、Steam/C = 0.71和CaO/C = 0.26条件下,合成气制备系统性能较优,合成气中H₂和CO₂含量分别为55.2%和15.4%,氢碳比为1.93,冷气效率为78.2%,被CaCO₃捕集的生物质碳为18.2%,收率（湿气基）为1.95 Nm³/kg_biomass,其中合成气中H₂和CO收率为1.24 Nm³/kg_biomass。     

Thermo-neutral production of metals and hydrogen or methanol by the combined reduction of the oxides of zinc or iron with partial oxidation of hydrocarbons

Stoichiometry and temperature requirements are determined for combining the endothermic reduction of metal oxides (ZnO, Fe₂O₃, and MgO) with the exothermic partial oxidation of hydrocarbons (CH₄, n-butane, n-octane, and n-dodecane) in order to co-produce simultaneously metals and syngas in thermo-neutral reactions. Thermogravimetric and GC measurements on the combined reduction of ZnO and Fe₂O₃ with the partial oxidation of CH₄ were conducted at 1400 K to experimentally verify the products predicted by equilibrium computations, and resulted in the complete reduction to Zn and Fe, respectively, while producing high quality syngas. A preliminary economic assessment that assumes a natural gas price of 11.9 US$/MWh and credit for zinc sale at 750 US$/metric ton, indicates a competitive cost of hydrogen production at 6.0 US$/MWh, based on its high heating value. The proposed combined process offers the possibility of co-producing metals and syngas in autothermal non-catalytic reactors, with significant avoidance of CO₂ emission.     

Electrochemical characteristics of iron carbide as an active material in alkaline batteries

Electrochemical properties of iron carbide (Fe₃C) for use as an alkaline battery anode were investigated during charge–discharge cycles. Results of electrochemical measurements and Mössbauer spectroscopy suggested that Fe₃C is oxidized irreversibly to Fe₃O₄ during discharge processes and that the produced Fe₃O₄ is subsequently changed to Fe(OH)₂ and Fe during the charging process, raising the discharge/charge capacity in further galvanostatic cycles. In addition, the electrode particles were observed to be less than 100 nm in diameter and to be highly dispersed on the surface of carbon black. These phenomena seems to be caused by dissolution and deposition of Fe(OH)₂ and Fe via intermediate iron species, leading to exposure of a fresh Fe₃C surface to the electrolyte after the second discharge.     

Fuel saving, carbon dioxide emission avoidance, and syngas production by tri-reforming of flue gases from coal- and gas-fired power stations, and by the carbothermic reduction of iron oxide

Flue gases from coal, gas, or oil-fired power stations, as well as from several heavy industries, such as the production of iron, lime and cement, are major anthropogenic sources of global CO₂ emissions. The newly proposed process for syngas production based on the tri-reforming of such flue gases with natural gas could be an important route for CO₂ emission avoidance. In addition, by combining the carbothermic reduction of iron oxide with the partial oxidation of the carbon source, an overall thermoneutral process can be designed for the co-production of iron and syngas rich in CO. Water-gas shift (WGS) of CO to H₂ enables the production of useful syngas. The reaction process heat, or the conditions for thermoneutrality, are derived by thermochemical equilibrium calculations. The thermodynamic constraints are determined for the production of syngas suitable for methanol, hydrogen, or ammonia synthesis. The environmental and economic consequences are assessed for large-scale commercial production of these chemical commodities. Preliminary evaluations with natural gas, coke, or coal as carbon source indicate that such combined processes should be economically competitive, as well as promising significant fuel saving and CO₂ emission avoidance. The production of ammonia in the above processes seems particularly attractive, as it consumes the nitrogen in the flue gases.     

Thermochemical hydrogen production from a two-step solar-driven water-splitting cycle based on cerium oxides

A new thermochemical cycle for H₂ production based on CeO₂/Ce₂O₃ oxides has been successfully demonstrated. It consists of two chemical steps: (1) reduction, 2CeO₂ → Ce₂O₃ + 0.5O₂; (2) hydrolysis, Ce₂O₃ + H₂O → 2CeO₂ + H₂. The thermal reduction of Ce(IV) to Ce(III) (endothermic step) is performed in a solar reactor featuring a controlled inert atmosphere. The feasibility of this first step has been demonstrated and the operating conditions have been defined (T = 2000 °C, P = 100–200 mbar). The hydrogen generation step (water-splitting with Ce(III) oxide) is studied in a fixed bed reactor and the reaction is complete with a fast kinetic in the studied temperature range 400–600 °C. The recovered Ce(IV) oxide is then recycled in first step. In this process, water is the only material input and heat is the only energy input. The only outputs are hydrogen and oxygen, and these two gases are obtained in different steps avoiding a high temperature energy consuming gas-phase separation. Furthermore, pure hydrogen is produced (it is not contaminated by carbon products like CO, CO₂), thus it can be used directly in fuel cells. The results have shown that the cerium oxide two-step thermochemical cycle is a promising process for hydrogen production.     

Carbothermal reduction of alumina: Thermochemical equilibrium calculations and experimental investigation

The production of aluminum by the electrolytic Hall–Héroult process suffers from high energy requirements, the release of perfluorocarbons, and vast greenhouse gas emissions. The alternative carbothermic reduction of alumina, while significantly less energy-intensive, is complicated by the formation of aluminum carbide and oxycarbides. In the present work, the formation of Al, as well as Al₂OC, Al₄O₄C, and Al₄C₃ was proven by experiments on mixtures of Al₂O₃ and activated carbon in an Ar atmosphere submitted to heat pulses by an induction furnace. Thermochemical equilibrium calculations indicate that the Al₂O₃-reduction using carbon as reducing agent is favored in the presence of limited amounts of oxygen. The temperature threshold for the onset of aluminum production is lowered, the formation of Al₄C₃ is decreased, and the yield of aluminum is improved. Significant further enhancement in the carbothermic reduction of Al₂O₃ is predicted by using CH₄ as the reducing agent, again in the presence of limited amounts of oxygen. In this case, an important by-product is syngas, with a H₂/CO molar ratio of about 2, suitable for methanol or Fischer–Tropsch syntheses. Under appropriate temperature and stoichiometry of reactants, the process can be designed to be thermo-neutral. Using alumina, methane, and oxygen as reagents, the co-production of aluminum with syngas, to be converted to methanol, predicts fuel savings of about 68% and CO₂ emission avoidance of about 91%, vis-à-vis the conventional production of Al by electrolysis and of methanol by steam reforming of CH₄. When using carbon (such as coke or petcoke) as reducing agent, fuel savings of 66% and CO₂ emission avoidance of 15% are predicted. Preliminary evaluation for the proposed process indicates favorable economics, and the required high temperatures process heat is readily attainable using concentrated solar energy.     

Method of gasification in IGCC system

A coal gasifier is designed to operate at the temperature range of 1200–1300 °C. The 1200 °C sets the lower limit to the carbon reforming efficiency of the high temperature reformer, and the 1300 °C is the lower limit of the fluid temperature of coal slags, below which they may be collected as non-fluid slag. The gasifier is connected to two syngas burners where a portion of product syngas is combusted with O₂ gas and produce ultra hot H₂O and CO₂ gases, these two gases enter into the gasifier and maintain the gasifier temperature at above 1200 °C and reform carbon into syngas. The temperature of the gasifier is controlled by the flow of O₂ gas into the syngas burner, where O₂ gas is completely consumed and none left to enter into the gasifier. This removes any possibility of forming oxidated products, and compressed CO₂ gas spray coal powder into the gasifier column and non-fluid slag is collected at the bottom. A higher level integration of oxidation–reduction cycle is shown for a IGCC system, wherein the exhaust gas of syngas turbine drives the reduction reaction of coal gasification.

A smooth and uniform temperature control within the gasifier assures high efficiency of carbon reforming and quality of product syngas. Conventional Lurgi gasifier relies on its large heat capacity and accumulating coal slag along the inner walls of the gasifier has made the gasifier bigger, lately as large as a three story building. The gasifier of the present design is constructed much smaller in its size, but with greater reforming efficiency.     

Coal conversion submodels for design applications at elevated pressures. Part II. Char gasification

This paper surveys the database on char gasification at elevated pressures, first, to identify the tendencies that are essential to rational design of coal utilization technology, and second, to validate a gasification mechanism for quantitative design calculations. Four hundred and fifty-three independent tests with 28 different coals characterized pressures from 0.02 to 3.0 MPa, CO₂ and steam mole percentages from 0 to 100%, CO and H₂ levels to 50%, gas temperatures from 800 to 1500 °C, and most of coal rank spectrum. Only a handful of cases characterized inhibition by CO and H₂, and only a single dataset represented the complex mixtures of H₂O, CO₂, CO, and H₂ that arise in practical applications. With uniform gas composition, gasification rates increase for progressively higher pressures, especially at lower pressures. Whereas the pressure effect saturates at the higher pressures with bituminous chars, no saturation is evident with low-rank chars. With fixed partial pressures of the gasification agents, the pressure effect is much weaker. Gasification rates increase for progressively higher gas temperatures. In general, gasification rates diminish for coals of progressively higher rank, but the data exhibit this tendency only for ranks of hv bituminous and higher.

These tendencies are interpreted with CBK/G, a comprehensive gasification mechanism based on the Carbon Burnout Kinetics Model. CBK/G incorporates three surface reactions for char oxidation plus four reactions for gasification by CO₂, H₂O, CO and H₂. Based on a one-point calibration of rate parameters for each coal in the database, CBK/G predicted extents of char conversion within ±11.4 daf wt% and gasification rates within ±22.7%. The predicted pressure, temperature, and concentration dependencies and the predicted inhibiting effects of CO and H₂ were generally confirmed in the data evaluations. The combination of the annealing mechanism and the random pore model imparts the correct form to the predicted rate reductions with conversion. CBK/G in conjunction with equilibrated gas compositions accurately described the lone dataset on complex mixtures with all the most important gasification agents, but many more such datasets are needed for stringent model evaluations.

Practical implications are illustrated with single-particle simulations of various coals, and a 1D gasifier simulation for realistic O₂ and steam stoichiometries. The rank dependence of gasification rates is the determining factor for predicted extents of char conversion at the gasifier outlet. But soot gasification kinetics will determine the unburned carbon emissions for all but the highest rank fuels. Only gasification kinetics for gas mixtures with widely variable levels of H₂O, H₂, and CO are directly relevant to gasifier performance evaluations.     

下吸式固定床的生物质H2O/CO2气化数值模拟研究

利用Aspen Plus 软件建立干桦木屑在下吸式固定床气化炉中的气化模型,模拟值与文献实验值吻合良好。利用Aspen Plus的灵敏度分析模块模拟分别以水蒸气（H₂O）和二氧化碳（CO₂）为气化剂时气化剂/生物质碳比（GC值）对气化结果的影响,并结合H₂O、CO₂各自的特点研究其复合气化。结果表明,H₂O气化时可获得富氢煤气,但其净CO₂排放量较高;CO₂气化时碳转化率及冷煤气效率较低,但净CO₂排放量较低;H₂O、CO₂复合气化使碳转化率及冷煤气效率略有降低,但可有效减少气化系统中的净CO₂排放量。     

Analysis of solar chemical processes for hydrogen production from water splitting thermochemical cycles

This paper presents a process analysis of ZnO/Zn, Fe₃O₄/FeO and Fe₂O₃/Fe₃O₄ thermochemical cycles as potential high efficiency, large scale and environmentally attractive routes to produce hydrogen by concentrated solar energy. Mass and energy balances allowed estimation of the efficiency of solar thermal energy to hydrogen conversion for current process data, accounting for chemical conversion limitations. Then, the process was optimized by taking into account possible improvements in chemical conversion and heat recoveries. Coupling of the thermochemical process with a solar tower plant providing concentrated solar energy was considered to scale up the system. An economic assessment gave a hydrogen production cost of 7.98$ kg⁻¹ and 14.75$ kg⁻¹ of H₂ for, respectively a 55 MW_th and 11 MW_th solar tower plant operating 40 years.     

碳酸盐中CO2气化生物质制合成气

以杉木屑为原料,CO₂为气化剂,熔融碳酸盐Li2CO3-Na2CO3-K2CO3(LNK)为热介质和催化剂进行气化制合成气(H2+CO)的研究,考察气化剂CO₂流量、CO₂通入方式、复合熔盐体系中添加的金属氧化物种类和Cr2O3含量等因素对气体产物组成分布及产率的影响。结果表明:CO₂流量显著影响气化反应的平衡;以鼓泡法通入CO₂时生物质的气化效果优于吹扫法的情况,CO₂流量为99.8 L/h时气化效果较好,合成气含量和产率分别达到61.4%和350.2 mL/g生物质;添加的金属氧化物中Cr₂O₃对生物质气化过程的促进作用优于MgO和Fe₂O₃,随着Cr₂O₃含量的增大,合成气含量先增大后略微减小,在Cr₂O₃含量为10.0%时最高,为67.9%。     

Environmental assessment and extended exergy analysis of a “zero CO2 emission”, high-efficiency steam power plant

Aim of this paper is to analyze the performance of an innovative high-efficiency steam power plant by means of two “life cycle approach” methodologies, the life cycle assessment (LCA) and the “extended exergy analysis” (EEA).

The plant object of the analysis is a hydrogen-fed steam power plant in which the H₂ is produced by a “zero CO₂ emission” coal gasification process (the ZECOTECH^© cycle). The CO₂ capture system is a standard humid-CaO absorbing process and produces CaCO₃ as a by-product, which is then regenerated to CaO releasing the CO₂ for a downstream mineral sequestration process.

The steam power plant is based on an innovative combined-cycle process: the hydrogen is used as a fuel to produce high-temperature, medium-pressure steam that powers the steam turbine in the topping section, whose exhaust is used in a heat recovery boiler to feed a traditional steam power plant.

The environmental performance of the ZECOTECH^© cycle is assessed by comparison with four different processes: power plant fed by H₂ from natural gas steam reforming, two conventional coal- and natural gas power plants and a wind power plant.     

Mo2C/Al2O3的制备及其催化二甲醚水蒸气重整性能研究

通过浸渍沉淀法结合程序升温碳化法制备了Mo₂C/Al₂O₃复合催化剂,并应用于二甲醚水蒸气重整催化体系的研究。考察了二甲醚水解催化载体、水解功能组分Al₂O₃与重整功能组分Mo₂C的比例、反应物浓度对复合催化剂活性的影响。结果表明,β-Mo₂C与γ-Al₂O₃载体以Mo/Al = 1/1耦合后能够高效催化二甲醚重整制氢,其最佳进料水醚比为5,最适反应温度为400℃。     

Nongray radiation from gas and soot mixtures in planar plates based on statistical narrow-band spectral model

The nongray behavior of combustion products plays an important role in various areas of engineering. Based on the statistical narrow-band (SNB) spectral model with an exponential-tailed inverse intensity distribution and the ray-tracing method, a comprehensive investigation of the influence of soot on nongray radiation from mixtures containing H₂O/N₂+soot, CO₂/N₂+soot, or H₂O/CO₂/N₂+soot was conducted in this paper. In combustion applications, radiation transfer is significantly enhanced by soot due to its spectrally continuous emission. The effect of soot volume fraction up to 1×10^-6 on the source term, the narrow-band radiation intensities along a line-of-sight, and the net wall heat fluxes were investigated for a wide range of temperature. The effect of soot was significant and became increasingly drastic with the increase of soot loading.     

A thermodynamic analysis of biogas partial oxidation to synthesis gas with emphasis on soot formation

A thermodynamic analysis of synthesis gas production via partial oxidation (POX) of biogas is performed in the present article. Chemical equilibrium calculations are conducted for partial oxidation of (CH₄+CO₂) mixtures based on Gibbs free energy minimization method emphasizing soot formation. Regarding precise evaluation of carbon dioxide effects on the reforming characteristics, the obtained results are compared with the experimental data. Furthermore, the effects of steam injection at the inlet of the reformer on the coking behavior and syngas production yield are studied. To investigate the effects of the equivalence ratio (?), temperature and pressure, a broad parametric study is performed. The results reveal that the process temperature plays a pivotal role in enhancing the syngas production and soot abatement. It is also found that the pressure has an impractical effect on the syngas production yield, leading to the soot formation and decrease in both hydrogen and carbon monoxide yields. Furthermore, increasing the inlet CO₂/CH₄ makes the thermal reforming efficiency to rise at an equivalence ratio lower than 3. Meanwhile, increasing the steam to methane (S/C) ratio reduces carbon formation and enhances hydrogen production. Nonetheless, when the S/C ratio is larger than 2 at ? = 2.5 and 1 at ? = 3, the enhancement of hydrogen generation is minimized and even tends to become impractical. Therefore, near adiabatic and atmospheric condition at ? = 2.5–3 with S/C < 1 are recommended as the optimum operating routes for partial oxidation of biogas.     

Nanostructure and reactivity of soot from biofuel 2,5-dimethylfuran pyrolysis with CO2 additions

This paper investigated the nanostructure and oxidation reactivity of soot generated from biofuel 2,5-dimethylfuran pyrolysis with different CO₂ additions and different temperatures in a quartz tube flow reactor. The morphology and nanostructure of soot samples were characterized by a low and a high resolution transmission electron spectroscopy (TEM and HRTEM) and an X-ray diffraction (XRD). The oxidation reactivity of these samples was explored by a thermogravimetric analyzer (TGA). Different soot samples were collected in the tail of the tube. With the increase of temperature, the soot showed a smaller mean particle diameter, a longer fringe length, and a lower fringe tortuosity, as well as a higher degree of graphization. However, the variation of soot nanostructures resulting from different CO₂ additions was not linear. Compared with 0%, 50%, and 100% CO₂ additions at one fixed temperature, the soot collected from the 10% CO₂ addition has the highest degree of graphization and crystallization. At three temperatures of 1173 K, 1223 K, and 1273 K, the mean values of fringe length distribution displayed a ranking of 10% CO₂>100% CO₂>50% CO₂ while the mean particle diameters showed the same order. Furthermore, the oxidation reactivity of different soot samples decreased in the ranking of 50% CO₂ addition>100% CO₂ addition>10% CO₂ addition, which was equal to the ranking of mean values of fringe tortuosity distribution. The result further confirmed the close relationship between soot nanostructure and oxidation reactivity.     

Effect of Bi2O3 content on characteristics of Bi2O3–GDC systems for direct methane oxidation

Ceramic systems of Bi₂O₃ and gadolinia-doped ceria (GDC) solid mixture were prepared as catalysts for direct methane oxidation. These systems were characterized by temperature-programmed reduction using hydrogen and carbon monoxide, temperature-programmed reaction of methane, fixed-temperature direct methane oxidation, and X-ray diffraction analysis. Adding Bi₂O₃ to GDC promotes both hydrogen and CO oxidation activities, because of the presence of surface Bi₂O₃ and the high content of mobile oxygen in Bi₂O₃. The reactivity of CO with surface lattice oxygen is enhanced to a higher extent than that of H₂, and this enhanced extent shows a maximum in Bi₂O₃ content. Such a maximum also exists for the catalytic activity of direct methane oxidation. A synergistic effect occurs due to a combination of the high methane reactivity of GDC and the high content of mobile oxygen in Bi₂O₃. The CO₂ selectivity of direct methane oxidation can be modulated by varying the Bi₂O₃ content. The mixing of Bi₂O₃ with GDC also increases the self-de-coking capability of the catalyst during direct methane oxidation, which stabilizes the activity.     

Catalytic steam reforming of tar for enhancing hydrogen production from biomass gasification: a review

Presently, the global search for alternative renewable energy sources is rising due to the depletion of fossil fuel and rising greenhouse gas (GHG) emissions. Among alternatives, hydrogen (H₂) produced from biomass gasification is considered a green energy sector, due to its environmentally friendly, sustainable, and renewable characteristics. However, tar formation along with syngas is a severe impediment to biomass conversion efficiency, which results in process-related problems. Typically, tar consists of various hydrocarbons (HCs), which are also sources for syngas. Hence, catalytic steam reforming is an effective technique to address tar formation and improve H₂ production from biomass gasification. Of the various classes in existence, supported metal catalysts are considered the most promising. This paper focuses on the current researching status, prospects, and challenges of steam reforming of gasified biomass tar. Besides, it includes recent developments in tar compositional analysis, supported metal catalysts, along with the reactions and process conditions for catalytic steam reforming. Moreover, it discusses alternatives such as dry and autothermal reforming of tar.     

Plasma catalytic reforming of methane

Thermal plasma technology can be efficiently used in the production of hydrogen and hydrogen-rich gases from methane and a variety of fuels. This article describes progress in plasma reforming experiments and calculations of high temperature conversion of methane using heterogeneous processes. The thermal plasma is a highly energetic state of matter that is characterized by extremely high temperatures (several thousand degrees Celsius), and a high degree of dissociation and a substantial degree of ionization. The high temperatures accelerate the reactions involved in the reforming process. Hydrogen-rich gas (40% H₂, 17% CO₂ and 33% N₂, for partial oxidation/water shifting) can be efficiently made in compact plasma reformers. Experiments have been carried out in a small device (2–3 kW) and without the use of efficient heat regeneration. For partial oxidation/water shifting, it was determined that the specific energy consumption in the plasma reforming processes is 16 MJ/kg H₂ with high conversion efficiencies. Larger plasmatrons, better reactor thermal insulation, efficient heat regeneration and improved plasma catalysis could also play a major role in specific energy consumption reduction and increasing the methane conversion. A system has been demonstrated for hydrogen production with low CO content (1.5%) with power densities of 30 kW (H₂ HHV)/l of reactor, or 10 m³/h H₂ per liter of reactor. Power density should further increase with increased power and improved design.     

Syngas composition study

The syngas composition characteristic was investigated in the real slurry-feed gasifier using a detailed gas phase reaction mechanism. The results show that the time for syngas to reach equilibrium is much shorter than the residence time for slurry feed entrained-flow gasifiers, indicating a gas phase species partial equilibrium state. Further calculation shows that the four major species, CO, CO₂, H₂, and H₂O, are in equilibrium via the reaction . Suggestions are provided for future modeling and model validation.