Thermodynamic method for the prediction of solid CO2 formation from multicomponent mixtures

The increase in GHG concentration has a direct effect on global climate conditions. Among the possible technologies to mitigate GHG emissions, CCS is being accepted to gain emission reduction. Such technology also involves cryogenic CO₂ capture processes based on CO₂ freeze-out or where the formation of solid CO₂ must be avoided. Captured CO₂ is usually transported in pipelines for the reinjection.The risk associated to the release of CO₂ is due to the changing temperatures and pressures the system may experience, which can lead to the deposition of solid CO₂ where it must be avoided. Prolonged exposure to dry ice can cause severe skin damage and its resublimation could pose a danger of hypercapnia. It is, thus, necessary to build up a tool able to predict the conditions in which CO₂ can freeze-out.A thermodynamic methodology based on cubic EoSs has been developed which is able to predict solid–liquid–vapor equilibrium of CO₂ mixtures with n-alkanes or H₂S which are usually found in equipment for acidic gas, mainly natural gas, treatment.The focus is a detailed analysis of the method performances when more than two components are present since, for such a case, literature does not provide significant modeling results.     

Trace Metal Contents (Al, Cu and Zn) of Tea: Tea and Soil from Two Tea Plantations, and Tea Products from Different Provinces of China

The present project aims to investigate the possible contamination of teas with the trace metals: Al, Cu and Zn. Tea bushes sampled from two tea plantations in the northern part of Guangdong Province accumulated higher concentrations of Cu and Zn in young leaves, and of Al in old leaves. The analysis of the three metals in tea produced in different provinces indicated higher Al levels in those obtained from Guangdong and Yunnan Provinces, which may be due to the lower soil pH in these areas. Green tea had the lowest Al concentration among the four types of tea studied, as only the bud and two young leaves are used, whereas older leaves are used for other types of tea (black, Oolong and Puerh tea). The transfer of Al, Cu and Zn from soil to different parts of tea bushes was low in general, except for Zn at Lechang tea plantation which next to a Pb/Zn mine, where a higher transfer was observed from young leaves to tea products, indicating possible metal contamination during tea processing. However, low concentrations of Cu and Zn (less than 0.07 mg Cu L^-1 and 0.17 mg Zn L^-1), and moderate amounts of Al (2.1-2.5 mg L^-1) were obtained in the tea liquor (1% hot water extracts).     

Sizing pressure relief valves in flashing and two-phase service: an alternative procedure

In view of the greater accuracy of the ω HEM correlation and the resulting conservative PR valve sizing (relative to the traditional PR valve sizing methods), the ω HEM-based flow calculations are recommended for all situations where flashing or two-phase flow occurs within the PR valve. However, as with any correlation, the accuracy of the ω HEM correlation results drops as the system to which it is applied diverges from the data used to develop it. Analysis of 15 different systems representative of actual refinery streams indicate that for fluids with a wide boiling range and for very non-ideal systems such as those containing hydrogen, the HEM correlation underpredicts the mass flux significantly (i.e. overpredicts the PR valve size). Since the large deviations are on the conservative side, the procedure will result in excessively large PR valves that may cause problems because of chattering of the PR valves, but would not present potential for vessel failure. The majority of the deviations are a result of the fact that the simplifying assumptions built into the correlation for single component do not truly characterize the actual flashing behaviour of many multicomponent fluids. The alternative approach presented, in which the correlation parameter ω is based on the actual flashing behaviour, eliminates nearly all the deviations and significantly improves the results of the correlation regardless of the system analysed. For trouble systems (those containing more than 0.1 wt% hydrogen and for some multicomponent fluids with a nominal boiling range greater than 80°C (150°F), the alternative approach should be used to define the correlation parameter ω. Use of this alternative approach is valid for any system (and will improve the accuracy of the correlation) but does require an additional flash calculation. However, for other systems the original formulation of ω is adequate and can be used.     

Sustainability of farmers' soil fertility management practices: a case study in the North China Plain

To ensure regional self-sufficiency and adequate rural livelihoods in the North China Plain (NCP), tremendous efforts were made over the last two decades by the Chinese government to raise the productivity of crops, despite increasing pressure on the land caused by a growing population. Emphasis was placed on high external input use, especially for wheat, maize and cotton, ignoring the particularities and limitations of the natural resource base. This study assesses the sustainability of current soil fertility management practices on the basis of selected location-specific indicators, such as fertilizer use, soil pH, soil organic matter content, levels of nitrogen (N), phosphorus (P) and potassium (K) in the soil, and identifies determining factors of the yield and environmental impacts of inputs use. Data used for the analysis were gathered from soil tests, groundwater and chive plant tests, household surveys, and statistical yearbooks. Stepwise multiple regression analysis is applied to determine factors affecting the yields. The study revealed unbalanced use of nutrients. Organic fertilizers (manure, crop residues) and K are insufficiently applied, whereas N and P are considerably overused in comparison with recommended doses. The intensive cropping in the area using high-input technologies -particularly fertilizer- has resulted in a remarkable general enhancement of crop productivity and improvement of soil fertility over the years. The yield of wheat and maize has increased 173 and 180 kg ha(-1) annually from 1982 to 2000, respectively and soil fertility status also improved over the years and the values of the selected indicators are within the borderline for sustainability. Irrigation water, FYM application, and total labor used during the cultivation season (with the exception of cotton and chive) for production are the main factors determining the yields of four major crops under study, while popularly and overly used N did not appear to be a significant factor affecting the yield. Its overuse, however, leads to leaching of nitrate into groundwater and nitrate enrichment of vegetables. Of 20 groundwater samples, 16 showed nitrate levels between 55 and 180 mg l(-1), which exceeds recommendations for drinking water (相似文献   

经验正交函数方法和TRMM数据对长江流域降水模式与极端水文过程的研究

气候变化加剧了极端天气和水文事件的发生,降水是区域干旱与洪水事件最直接驱动因素。以TRMM/PR月累积降水反演遥感数据为基础,利用经验正交函数EOF（Empirical Orthogonal Function）方法对长江流域降水时空变化模式进行提取,并对比分析了主要模式振幅强弱与极端水文事件的对应关系。结果表明在流域尺度上EOF方法及TRMM/PR数据可以较好地识别降水主要模式,通过时空尺度变换成功揭示主要降水模式强弱与流域极端水文事件的对应关系。鉴于日益丰富的巨量水文气象时空数据,EOF方法在模式提取、水文模拟、极端事件预估及灾害适应性研究等方面具有应用潜力