基于非线性屈服准则及主应力判据的圆形巷道围岩岩爆过程的数值模拟

鉴于考虑拉伸截断的线性莫尔-库仑屈服准则不能考虑岩石在高应力条件下的非线性屈服特征,根据虎克-布朗本构模型,将上述屈服准则在受压区的线性屈服函数修改为非线性形式。采用3种岩爆的主应力判据,判别圆形巷道开挖之后围岩中各种级别岩爆的分布及演变规律。计算采用"先加载,后挖洞"的方式,岩石服从弹—脆—塑性本构模型。研究发现,发生高级别岩爆的单元数少于发生低级别岩爆的单元数;轻微岩爆区的形态更接近于塑性区及剪切应变增量的高值区。根据巴顿判据,发生重岩爆的单元数较多,而且主要发生的是拉伸岩爆;根据陶振宇判据,发生轻微及中等岩爆的单元数均多于根据谷明成-陶振宇判据判别的结果。上述两种判据判别的结果均表明,在不考虑拉伸岩爆的条件下,只有位于围岩内部的单元才有可能发生高级别的岩爆,而位于巷道表面的单元一般仅发生轻微岩爆。     

Calculation Of Electric Field Strength Distributions For New Electrostatic Precipitator Discharge Electrode Designs

New collecting and discharge electrode configurations are being used in electrostatic precipitators. In order to mathematically model preclpitators with these arrangements, it is necessary to develop reliable models of the field strength distributions of these electrodeplate geometries. This paper presents the concept of an equivalent wire diameter and attenuation functions, permitting use of the well-known wire-plate calculations. Experimental data presented in this paper shows the approximation techniques are sufficiently accurate.     

An Intelligent Emissions Controller for Fuel Lean Gas Reburn in Coal-Fired Power Plants

ABSTRACT

The application of artificial intelligence techniques for performance optimization of the fuel lean gas reburn (FLGR) system is investigated. A multilayer, feedforward artificial neural network is applied to model static nonlinear relationships between the distribution of injected natural gas into the upper region of the furnace of a coal-fired boiler and the corresponding oxides of nitrogen (NO_x) emissions exiting the furnace. Based on this model, optimal distributions of injected gas are determined such that the largest NO_x reduction is achieved for each value of total injected gas. This optimization is accomplished through the development of a new optimization method based on neural networks. This new optimal control algorithm, which can be used as an alternative generic tool for solving multidimensional nonlinear constrained optimization problems, is described and its results are successfully validated against an off-the-shelf tool for solving mathematical programming problems. Encouraging results obtained using plant data from one of Commonwealth Edison's coal-fired electric power plants demonstrate the feasibility of the overall approach.

Preliminary results show that the use of this intelligent controller will also enable the determination of the most cost-effective operating conditions of the FLGR system by considering, along with the optimal distribution of the injected gas, the cost differential between natural gas and coal and the open-market price of NO_x emission credits. Further study, however, is necessary, including the construction of a more comprehensive database, needed to develop high-fidelity process models and to add carbon monoxide (CO) emissions to the model of the gas reburn system.     

An Assessment of the Emissions Inventory Processing Systems EMS-2001 and SMOKE in Grid-Based Air Quality Models

Abstract

In the United States, emission processing models such as Emissions Modeling System-2001 (EMS-2001), Emissions Preprocessor System-Version 2.5 (EPS2.5), and the Sparse Matrix Operator Kernel Emissions (SMOKE) model are currently being used to generate gridded, hourly, speciated emission inputs for urban and regional-scale photochemical models from aggregated pollutant inventories. In this study, two models, EMS-2001 and SMOKE, were applied with their default internal data sets to process a common inventory database for a high ozone (O₃) episode over the eastern United States using the Carbon Bond IV (CB4) chemical speciation mechanism. A comparison of the emissions processed by these systems shows differences in all three of the major processing steps performed by the two models (i.e., in temporal allocation, spatial allocation, and chemical speciation). Results from a simulation with a photochemical model using these two sets of emissions indicate differences on the order of ±20 ppb in the predicted 1-hr daily maximum O₃ concentrations. It is therefore critical to develop and implement more common and synchronized temporal, spatial, and speciation cross-reference systems such that the processes within each emissions model converge toward reasonably similar results. This would also help to increase confidence in the validity of photochemical grid model results by reducing one aspect of modeling uncertainty.     

The Kinetics of Catalytic Incineration of Dimethyl Sulfide and Dimethyl Disulfide over an MnO/Fe2O3 Catalyst

ABSTRACT

The catalytic incineration of dimethyl sulfide and dimethyl disulfide [(CH₃)₂S and (CH₃)₂S₂] over an MnO/Fe₂O₃ catalyst was carried out in a bench-scale catalytic incinerator. Three kinetic models (i.e., the power-rate law, the Mars and Van Krevelen model, and the Langmuir-Hinshelwood model) were used to analyze the results. A differential reactor design was used for best fit of kinetic models in this study. The results show that the Langmuir-Hinshelwood model may be feasible to describe the catalytic incineration of (CH₃)₂S and (CH₃)₂S₂. This suggests that the chemical adsorption of O₂ molecules is important in this incineration.     

Absorption and Reaction Kinetics of Amines and Ammonia Solutions with Carbon Dioxide in Flue Gas

Abstract

The removal system for the absorption of CO₂ with amines and NH₃ is an advanced air pollution control device to reduce greenhouse gas emissions. Absorption of CO₂ by amines and NH₃ solutions was performed in this study to derive the reaction kinetics. The absorption of CO₂ as encountered in flue gases into aqueous solutions of monoethanolamine (MEA), diethanolamine (DEA), and NH₃ was carried out using a stirred vessel with a plane gas-liquid interface at 50 °C. Various operating parameters were tested to determine the effect of these variables on the absorption kinetics of the reactants in both gas and liquid phases and the effect of competitions between various reactants on the mass-transfer rate.

The observed absorption rate increases with increasing gas-liquid concentration, solvent concentration, temperature, and gas flow rate, but changes with the O₂ concentration and pH value. The absorption efficiency of MEA is better than that of NH₃ and DEA, but the absorption capacity of NH₃ is the best. The active energies of the MEA and NH₃ with CO₂ are 33.19 and 40.09 kJ/mol, respectively.     

Anthropogenic impacts on suspended sediment load in the Upper Yangtze river

Climate change and human disturbance drive catchment erosion and increase riverine sediment load sensitively in small and medium-sized watersheds. This is not always true in large basins, where aggregation and buffering effects have dampen the ability to determine the driving forces of sedimentation. Even though there are significant responses to sedimentation in large river basins, it is difficult to get a precise quantitative assessment of specific drivers. This paper develops a methodology to identify driving forces that change suspended sediment load in the Upper Yangtze river. Annual runoff and sediment load data from 1954 to 2005 at the Yichang gauging station in the Upper Yangtze basin, daily precipitation data from 60 meteorological stations, and survey data on reservoir sediment were collected for the study. Sediment load/rainfall erosivity (S/R), is a new proxy indicator introduced to reflect human activities. Since the mid-1980s, S/R in the Upper Yangtze has dramatically declined from 0.21 to 0.03 (×10¹⁰ t ha h MJ⁻¹ mm⁻¹), indicating that human activity has played a key role in the decline of the suspended sediment load. Before the mid-1980s, a higher average S/R is attributed to large-scale deforestation and land reclamation. A significant sediment decrease occurred from 1959 to 1961 during an extreme drought condition, and an increase in sedimentation in 1998 coincided with an extreme flood event, which was well recorded in the S/R curve. This indicates that the S/R proxy is able to distinguish anthropogenic from climate impacts on suspended sediment load, but is not necessarily indicatory in extreme climate events. In addition, typical drivers of riverine sediment load variation including soil conservation projects, reservoirs construction, and land use/cover change are discussed.     

Dechlorination of PCBs in the simulative transformer oil by microwave-hydrothermal reaction with zero-valent iron involved

The conventional hydrothermal reaction with iron powder, NaOH and H₂O as reactants was reported to occur at temperature above 423 K, and iron oxides (Fe₃O₄ and NaFeO₂) and hydrogen were produced. In this study, microwave heating was adopted to take the place of conventional heating to induce the hydrothermal reaction. Under microwave irradiation, NaOH and H₂O absorbed microwave energy by space charge polarization and dipolar polarization and instantly converted it into thermal energy, which initiated the hydrothermal reaction that involved with zero-valent iron. X-ray diffraction (XRD) analysis found Fe₃O₄/NaFeO₂ and confirmed the occurrence of microwave-induced hydrothermal reaction. The developed microwave-hydrothermal reaction was employed for the dechlorination of PCBs. Hexadecane containing 100 mg L⁻¹ of Aroclor1254 was used as simulative transformer oil, and the dechlorination of PCBs was evaluated by GC/ECD, GC/MS and ion chromatography. For PCBs in 10 mL simulative transformer oil, almost complete dechlorination was achieved by 750 W microwave irradiation for 10 min, with 0.3 g iron powder, 0.3 g NaOH and 0.6 mL H₂O added. The effects of important factors including microwave power and the amounts of reactants added, on the dechlorination degree were investigated, moreover, the dechlorination mechanism was suggested. Microwave irradiation combined with the common and cheap materials, iron powder, NaOH and H₂O, might provide a fast and cost-effective method for the treatment of PCBs-containing wastes.     

The dissipation rates of trichlorfon and its degradation product dichlorvos in cabbage and soil

The residual levels and dissipation rate of trichlorfon, and its degradation product, dichlorvos, in cabbage crops and the soil in which these were grown, were determined by gas chromatography at two geographically distant experimental sites, one in Kunming and one in Beijing, China. Trichlorfon was applied at two dosages (900 g ai ha⁻¹ and 1350 g ai ha⁻¹). Maximum final residues of trichlorfon in soil and cabbage were 1.23 mg kg⁻¹ and 1.81 mg kg⁻¹ respectively at Kunming, and 0.35 mg kg⁻¹ and 0.70 mg kg⁻¹ respectively at Beijing. However, the final residues of dichlorvos in both cabbage and soil was only 0.04 mg kg⁻¹ at Kunming, and only 0.03 mg kg⁻¹, or “not detectable”, at Beijing. The mean half-life of trichlorfon in cabbage was 1.80 d with a dissipation rate of 90% over 5 d, while that in soil was 3.05 d with a dissipation rate of 90% over 14 d at one experimental site. The dissipation rates of trichlorfon and its degradation product dichlorvos at the two experimental sites were different, suggesting that degradation of these pesticides was affected by local soil characteristics and climate. When applied at both the recommended dosage and at 1.5 times this, no detectable residues of either trichlorfon or dichlorvos were found in soil or cabbage at harvest. Although trichlorfon can easily degrade into dichlorvos, which is highly toxic to humans and other animals, the observed low residual levels of dichlorvos suggest that trichlorfon is safe when applied at the recommended dosage.     

湖北省"两圈"生物资源生态足迹动态分析

本文对1998-2008年湖北省武汉城市圈和鄂西生态文化旅游圈的生物资源生态足迹及其组成、人均生物资源生态足迹、生物资源生态承载量和生物资源生态赤字(盈余)进行了动态分析.研究表明,武汉城市圈生物资源生态足迹组成以耕地为主,其他生态生产性用地的足迹比例较小,各市州生物资源生态足迹整体呈现逐年增加的趋势,人均生物资源生态足迹小于省均值,生物资源生态承载量先升高后降低,各市州生物资源生态承载量由大到小排序为:黄冈、孝感、武汉、咸宁、天门、黄石、仙桃、鄂州、潜江,生态赤字呈增大趋势;鄂西生态圈除神农架外其他各市州的生物资源生态足迹均较大,林地足迹占主要地位,其总量对全省的贡献较大;人均生物资源生态足迹大于省均值,生物资源生态承载量呈增高趋势,各市州由大到小排序为:宜昌、十堰、襄樊、荆州、恩施、随州、荆门、神农架,该圈一直保持很高的生物资源生态盈余,但盈余值有减小的趋势.