Multi-Component Migration in the Gas Phase of Soil: Comparison between Results of Experiments and Simulation by Dusty Gas Model

Fick's law has been used to simulate gas systems within soil, although this law can be applied only to binary gas systems and the effect of the Knudsen diffusion is not considered. By contrast, the dusty gas model can be applied to multi-component gas systems with Knudsen diffusion. Blanc's law is a simplified version of the dusty gas model, but it can be used only for gas systems in which the tracer gas is dilute. Although the dusty gas model is superior to other methods for simulating gas systems within soil, it is not generally used because of its complexity. Numerical techniques such as the Eulerian-Lagrangian method for solving the advection-dispersion equation can be used to simulate the migration of chemical substance in the water or gas phases of soil within the range of every Péclet number. We derived the compound diffusion coefficient and compound velocity from the dusty gas model and formulated the advection-diffusion equation with these values by using the characteristic finite element scheme. Results of the model developed here were consistent with the results of column experiments conducted in this study, and the precision of the developed model was verified.     

Formulation of a Dusty Gas Model for Multi-Component Diffusion in the Gas Phase of Soil

Soil vapor extraction and bio-venting have been utilized for purification of contaminated soil or groundwater. It is necessary to predict the movement of gas phase components in soil for the design of soil vapor extraction and bio-venting systems. Though chemical substances migrate with advection and diffusion in gas phase of soil, we investigated multi-component diffusion systems in gas phase of soil. Numerical modeling for multi-component diffusion is useful to the prediction of the movement of components. A dusty gas model for multi-component diffusion systems has not so far been formulated by the Finite Element Method; furthermore it has not been applied for assessing the movement of components in the gas phase of soil. Accordingly, a dusty gas model for three gas phase components was formulated by the Finite Element Method in this study, and the concentrations of components in binary and multi-component gas systems were calculated by numerical methods developed in this study. As a result, it was found that the dusty gas model must be applied for study of diffusion in a multi-component gas system; and the study showed that the difference between molecular weights of gas phase components influenced the movement of components in the gas system.     

呼叫中心在燃气行业中的应用

燃气企业原有的业务服务电话分散,给客户带来诸多不便。如何为客户提供统一的服务电话成了燃气企业急待解决的课题。文章介绍了呼川中心的概念、组成、设计以及在南京港华应用情况。     

城市生活垃圾填埋场气压分布一维稳态分析模型

掌握填埋场气压分布是填埋气灾害控制和资源化利用的基础。提出了分层垃圾填埋体气压分布一维稳态分析模型及求解方法。该模型可分析含有给定抽气压力或给定抽气流量水平导气层的填埋体气压分布。采用该模型探讨了垃圾分层特征、封顶覆盖层下和填埋体内的高渗透性水平导气层、填埋体底部渗沥液导排系统兼作填埋气导排通道对填埋体气压分布的影响规律。通过参数分析得到以下结论：填埋体垃圾不考虑产气速率和固有渗透系数随垃圾埋深增加而减小（产气速率和固有渗透系数按埋深平均）会高估填埋体内气压;封顶覆盖层下和填埋体内设置水平导气层可有效降低填埋体内气压;填埋体底部填埋气导排通道对填埋气气压较大的深部垃圾降压效果较明显。分析结果表明,该模型可指导填埋气收集系统设计,如水平导气层位置和间距布置及抽气功率选择等。     

Re-Entrainment and Dispersion of Exhausts from Indoor Radon Reduction Systems: Analysis of Tracer Gas Data

Tracer gas studies were conducted around four model houses in a wind tunnel, and around one house in the field, to quantify re-entrainment and dispersion of exhaust gases released from residential indoor radon reduction systems. Re-entrainment tests in the field suggest that active soil depressurization systems exhausting at grade level can contribute indoor radon concentrations 3 to 9 times greater than systems exhausting at the eave. With a high exhaust concentration of 37,000 Bq/m³, the indoor contribution from eave exhaust re-entrainment may be only 20% to 70% of the national average ambient level in the U.S. (about 14 Bq/m³), while grade-level exhaust may contribute 1.8 times the ambient average. The grade-level contribution would drop to only 0.18 times ambient if the exhaust were 3,700 Bq/m³. Wind tunnel tests of exhaust dispersion outdoors suggest that grade-level exhaust can contribute mean concentrations beside houses averaging 7 times greater than exhaust at the eave, and 25 to 50 times greater than exhaust midway up the roof slope. With 37,000 Bq/m³ in the exhaust, the highest mean concentrations beside the house could be less than or equal to the ambient background level with eave and mid-roof exhausts, and 2 to 7 times greater than ambient with grade exhausts.     

多气源天然气瓦换性研究中的配气问题

在多气源天然气的互换性试验中,配气是十分关键的准备工作。本文介绍了国标中的相关规定以及配气计算原则,提出了使用管道天然气掺混单一气体、利用AGA指数法和Weaver4~数法来判定配气精度的方法。同时还讨论配气操作中的一些具体问题以及相应的解决措施。     

多气源天然气互换性研究中的配气问题

在多气源天然气的互换性试验中,配气是十分关键的准备工作.本文介绍了国标中的相关规定以及配气计算原则,提出了使用管道天然气掺混单一气体、利用AGA指数法和Weaver指数法来判定配气精度的方法.同时还讨论配气操作中的一些具体问题以及相应的解决措施.     

希腊国家天然气输气系统介绍及其启示

本文介绍了希腊国家天然气输气系统的管理运营公司、系统组成、气源布置、输气管网和LNG接收站,对照分析了重庆地区的天然气供应系统值得改进和完善之处。     

地暖对单层大空间火灾烟气运动的影响

为研究地暖采暖对单层大空间火灾烟气上升过程的影响,设计建立了小规模实验装置进行实验,并利用FDS 软件模拟实验工况,通过对比实验值和模拟值证实了FDS 软件模拟的可靠性。利用FDS 软件,对真实采暖单层大空间的火灾烟气上升规律进行数值模拟,提出该环境中影响烟气运动的主要因素及控制措施。研究结果表明：地暖采暖环境中的火灾烟气处于不稳定状态;在地暖采暖空间中,烟气上升和顶棚射流的速度都将有所提高,从而总体加速了烟气的发展进度。     

液化气混空气燃气与天然气的互换性

燃气互换性问题存在于城市燃气供应的始终，在供气气源的性质发生较大变化时问题尤为突出。在液化气混空气为主要气源的城市燃气供气系统中，将来引进天然气时，所遇到的问题中最重要的就是液化气混空气燃气与天然气之间的互换性问题。作者采用美国燃气协会(A．G．A．)互换性判定方法，对这两种燃气的互换性进行了判定分析，并根据燃气用具的运行特性，分析了以液化气混空气燃气作为基准气设计和进行初调整的燃气用具，使用天然气后可能出现的问题。为将来天然气能顺利地与液化气混空气置换提出了合适的液化气混空气比例。     

信息技术在天然气转换中的应用

信息技术在工程技术中的应用越来越广泛,将其应用于天然气转换工作中,提高了效率、安全性,降低了差错率.文章介绍了上海燃气市北销售公司所采用的GIS系统、客户帐务信息系统、客户转换数据信息系统、转换现场联网指挥系统.     

油气田建设水土保持措施体系研究

文章对西南地区典型油气田建设工程水土保持措施的类型、工程量进行数理统计,监测评估水土保持措施体系的实施效果,对不同的工程单元分区利用多元相关分析方法,研究水土保持措施与实施效果之间的线性关系,进一步提出不同类型水土保持措施的优先等级。结果表明：当前油气田建设过程中,工程措施使用频率最高,植物措施与临时措施对水土保持效果最为显著。为西南油气田建设工程水土保持措施制定和实施提出指导性建议。     

China's fuel gas sector: History,current status,and future prospects

China has a unique urban pipeline network of three types of fuel gases: manufactured gas (coal gas), Liquefied Petroleum Gas (LPG), and natural gas. Manufactured gas, which is often seen as an outdated technology in the western world, is still widely used in Chinese cities. LPG is distributed through community-based pipelines in many Chinese cities, in addition to its distribution in cylinders and canisters in rural areas. Natural gas consumption is increasing throughout China, particularly as a cooking fuel. Expanding the production and supply of natural gas in China faces many challenges. In particular, China's controls on natural gas prices have deterred investment in exploration and natural gas imports. However, recent price decontrols of unconventional natural gas (defined in Chinas as shale gas, coal-bed methane, and coal-to-natural-gas), and recent pricing reforms, appear likely to increase natural gas use. The prospect for increased exploration is promising but will still depend greatly on the future of institutional reforms. In the near term, regulatory reforms toward a more market-driven system will be the most critical issue in the development of China's fuel gas sector.     

Geothermal ground gas emissions and indoor air pollution in Rotorua, New Zealand

The emission of toxic gases from the soil is a hazard in geothermal regions that are also urbanized because buildings constructed on geothermal ground may be subject to the ingress of gases from the soil directly into the structure. The Rotorua geothermal field, New Zealand, is extensively urbanized but to date no studies have evaluated the extent of the ground gas hazard. The main gases emitted are hydrogen sulphide (H2S) and carbon dioxide (CO2), both of which are highly toxic and denser than air. This paper reports preliminary findings from a study of selected buildings constructed in the gas anomaly area. Properties were investigated for evidence of ingress by H2S, CO2, and 222Rn, with a view to determine the means and rates of gas entry and the nature of any consequent hazard. H2S and CO2 were investigated using infrared active gas analysers and passive detector tubes left in place for 10-48 h. 222Rn was measured over a period of 3 months by poly-allyl diglycol carbonate sensors. Eight of the nine buildings studied were found to suffer problems with soil gases entering the indoor air through the structure. The primary means of gas entry was directly from the ground through the floors, walls, and subsurface pipes. Indoor vents were located and found emitting up to approximately 200 ppm H2S and approximately 15% CO2, concentrations high enough to present an acute respiratory hazard to persons close to the vent (e.g., children playing at floor level). In some properties, gas problems occurred despite preventative measures having been made during construction or during later renovations. Typically, these measures include the under-laying of concrete floors with a gas-proof butanol seal, under-floor ventilation systems or the installation of positive-pressure air conditioning. Recently constructed buildings (<10 years) with butanol seals were nevertheless affected by ground gas emissions, and we conclude that such measures are not always effective in the long term.     

CFD simulations of gas dispersion around high-rise building in non-isothermal boundary layer

Urban heat island phenomena and air pollution become serious problems in weak wind regions such as behind buildings and within street canyons, where buoyancy effect cannot be neglected. In order to apply CFD techniques for estimation of ventilation and thermal and pollutant dispersion in urban areas, it is important to assess the performance of turbulence models adopted to simulate these phenomena. As the first step of this study, we carried out wind tunnel experiments and CFD simulations of gas and thermal dispersion behind a high-rise building in an unstable non-isothermal turbulent flow. The standard k-ε model and a two-equation heat-transfer model as RANS models, and LES, were used for the CFD simulation. One of the important purposes of this study was to clarify the effect of inflow turbulence (both velocity and temperature) on flow field and gas/thermal dispersion for the LES calculation. Thus, LES calculations with/without inflow turbulence were conducted. The inflow turbulence was generated through a separate precursor simulation. The calculated results showed that both RANS models overestimated the size of the recirculation region behind the building and underestimated the lateral dispersion of the gas. Turbulent flow structures of LES with and without inflow turbulence were completely different. The LES result with inflow turbulence achieved better agreement with the experiment.     

Nonlinear Least-Squares Minimization Applied to Tracer Gas Decay for Determining Airflow Rates in a Two-Zone Building

Abstract We developed a method based on tracer gas decay measurements to quantify the airflow rates, including the interzonal airflows, in a two-zone building: different tracer gases were simultaneously pulse-injected into each of the two zones and the evolution of the gas concentrations in each zone was measured; theoretical concentration profiles obtained by solving dynamic material-balance equations for two coupled, well-mixed zones were fit to the experimental data using nonlinear least-squares minimization; and estimates of the airflow rates were iteratively refined until a best fit was achieved between the model and the data. We conducted experiments validating the method in two full-sized rooms of a test house. Airflows were controlled using blowers, and mixing was ensured by the use of fans. Airflow rates inferred by the tracer gas technique agreed with imposed airflow rates within an average absolute error of 8%. Results are also reported for two experiments conducted in the same structure under uncontrolled conditions. Goodness-of-fit tests revealed no statistically significant differences between measured tracer gas concentrations and theoretical concentration profiles constructed using the least-squares parameter estimates.     

Methane eruptions from landfill final cover soil during rainfall events in laboratory experiments

Landfill sites are significant sources of greenhouse gases, particularly methane. It is believed that methane gas eruptions occur under a surface ponding condition during rainfall events. In this study, based on laboratory column experiments in which mixed gas was applied to variably compacted soil columns (10 cm in diameter and 30.5 cm in height) under different rainfall intensities, the effects of the bulk density of the landfill cover soil, the gas injection rates, and the rainfall intensities on the gas eruption phenomenon were investigated. The gas pressure and the water content were monitored during rainfall events. The main results were that (1) an episodic gas compression and eruption cycle was observed under a surface ponding condition, (2) gas eruptions occurred at a higher gas pressure in the soil with a higher dry bulk density, and (3) a higher gas injection rate resulted in continuous gas eruptions. The monitoring of the gas eruption flux and gas concentration in the soil columns, using oxygen-mixed gas as an injected gas, showed that longer gas compression led to higher gas fluxes during the gas eruptions. The concentration of gas in the soil increased over time because of the upward gas flow in accordance with the eruptions. The calculation of the oxygen mass balance indicated that the eruptions had slightly promoted the emission of gas from that which had been stored in the soil prior to the rainfall events.     

小型燃气公司信息化系统建设思路和方法

针对小型燃气公司的特点,结合燃气行业的信息化实施现状,提出了小型燃气公司信息化建设的思路和方法。文中首先分析小型燃气公司的自身运营特点、需求特点,然后归纳出五大核心业务,最后提出具体的建设思路和实施步骤。本文作者结合自身信息化实施过程的经验总结．给小型燃气公司的信息化发展提供实际参考意义。     

The Trans-Anatolian Pipeline (TANAP) as a unique project in the Eurasian gas network: A comparative analysis

Trans-Anatolian Gas Pipeline (TANAP) as a part of the Southern Gas Corridor has significant implications for the transit security of the European Union and the domestic gas market of Turkey. Among those countries in Eurasia, only Turkey's process of liberalization is a success story, albeit an incomplete one. Surrounded by liberal markets to the West and monopolistic markets to the East, Turkey partially possesses a competitive gas market. TANAP, a unique project among the international pipelines in Eurasia, strengthens Turkey's peculiar position by de facto ending the monopoly of the incumbent BOTAŞ over gas transmission and thus contributes to the liberalization of the domestic market.     

浅谈商业用户燃气工程设计中的若干问题

商业用户是城市燃气用户的重要组成部分。特别在工业项目少的城市,积极发展商业用户是快速提高城市总用气量的首选。文章介绍了南宁市商业用户燃气工程设计的一些经验。