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561.
为研究注CO2增产煤层气过程中注气温度对煤层渗透特性变化的影响,利用自主研发的CO2置换驱替CH4实验系统,在注气温度为40,50,60 ℃条件下进行CO2置换驱替CH4实验,定量分析置换驱替过程中出口气体流量、孔隙压力以及煤层渗透率等变化规律。研究结果表明:在实验测试的40~60 ℃范围内,提高CO2注入温度有助于产出更多的CH4及封存CO2,CO2注入温度越高,出口混合气体流量和CH4气体流量越大,呈现出先升高后降低并趋于稳定的变化趋势,实验结束时置换体积比分别为2.704,2.741和2.595,注气温度为60 ℃时驱替效果较好,每产出单位体积的CH4注入的CO2量最少;煤层孔隙压力随注气时间呈现先逐渐上升后趋于平稳的变化趋势,逐渐趋近注气压力0.8 MPa;注CO2置换驱替CH4及提高CO2注入温度会降低煤层的渗透性,注气温度恒定时,渗透率随注气时间增加呈现先逐渐降低后趋于平稳的变化规律,注气温度由40 ℃升至60 ℃时,渗透率从0.017 1×10-15 m2下降至0.009 8×10-15 m2,降低幅度为34.50%~42.69%。 相似文献
562.
A full probabilistic Explosion Risk Analysis (ERA) is commonly used to establish overpressure exceedance curves for offshore facilities. This involves modelling a large number of gas dispersion and explosion scenarios. Capturing the time dependant build up and decay of a flammable gas cloud size along with its shape and location are important parameters that can govern the results of an ERA. Dispersion simulations using Computational Fluid Dynamics (CFD) are generally carried out in detailed ERA studies to obtain these pieces of information. However, these dispersion simulations are typically modelled with constant release rates leading to steady state results. The basic assumption used here is that the flammable gas cloud build up rate from these constant release rate dispersion simulations would mimic the actual transient cloud build up rate from a time varying release rate. This assumption does not correctly capture the physical phenomena of transient gas releases and their subsequent dispersion and may lead to very conservative results. This in turn results in potential over design of facilities with implications on time, materials and cost of a project.In the current work, an ERA methodology is proposed that uses time varying release rates as an input in the CFD dispersion simulations to obtain the fully transient flammable gas cloud build-up and decay, while ensuring the total time required to perform the ERA study is also reduced. It was found that the proposed ERA methodology leads to improved accuracy in dispersion results, steeper overpressure exceedance curves and a significant reduction in the Design Accidental Load (DAL) values whilst still maintaining some conservatism and also reducing the total time required to perform an ERA study. 相似文献
563.
564.
Ona LF Alberto AM Prudente JA Sigua GC 《Environmental science and pollution research international》2006,13(3):177-183
Background Aims, and Scope. Lead (Pb) is a naturally occurring element that poses environmental hazards when present at elevated concentration.
It is being released into the environment because of industrial uses and from the combustion of fossil fuels. Hence, Pb is
ubiquitous throughout global ecosystems. The existence of potentially harmful concentrations of Pb in the environment must
be given full attention. Emissions from vehicles are major source of environmental contamination by Pb. Thus, it becomes imperative
that concentrations of Pb and other hazardous materials in the environment not only in the Philippines, but elsewhere in the
world be adequately examined in order that development of regulations and standards to minimize risk associated with these
materials in urban areas is continued. The objectives of this study were: (1) to determine the levels of Pb in soil from selected
urbanized cities in central region of the Philippines; (2) to identify areas with soil Pb concentration values that exceed
estimated natural concentrations and allowable limits; and (3) to determine the possible sources that contribute to elevated
soil Pb concentration (if any) in the study area.
Methods This study was limited to the determination of Pb levels in soils of selected urbanized cities located in central region
in the Philippines, namely: Site 1 – Tarlac City in Tarlac; Site 2 – Cabanatuan City in Nueva Ecija; Site 3 – Malolos City
in Bulacan; Site 4 – San Fernando City in Pampanga; Site 5 – Balanga City in Bataan; and Site 6 – Olongapo City in Zambales.
Soil samples were collected from areas along major thoroughfares regularly traversed by tricycles, passenger jeepneys, cars,
vans, trucks, buses, and other motor vehicles. Soil samples were collected from five sampling sites in each of the study areas.
Samples from the selected sampling sites were obtained approximately 2 to 3 meters from the road. Analysis of the soil samples
for Pb content was conducted using an atomic absorption spectrophotometer. This study was conducted from 2003 to 2004. Since
this study assumed that vehicular emission is the major source of Pb contamination in urban soil, other information which
the researchers deemed to have bearing on the study were obtained such as relative quantity of each gasoline type disposed
of in each city within a given period and volume of traffic in each sampling site. A survey questionnaire for gasoline station
managers was prepared to determine the relative quantity of each fuel type (diesel, regular gasoline, premium gasoline, and
unleaded gasoline) disposed of or sold within a given period in each study area.
Results and Discussion Analysis of soil samples for Pb content showed the presence of Pb in all the soil samples collected from the 30 sampling
sites in the six cities at varying concentrations ranging from 1.5 to 251 mg kg–1. Elevated levels of Pb in soil (i.e. greater
than 25 mg kg–1 Pb) were detected in five out of the six cities investigated. Site 4 recorded the highest Pb concentration
(73.9 ± 94.4 mg kg–1), followed by Site 6 (56.3 ± 17.1 mg kg–1), Site 3 (52.0 ± 33.1 mg kg–1), Site 5 (39.3 ± 19.0 mg kg–1),
and Site 2 (38.4 ± 33.2 mg kg–1). Soil Pb concentration in Site 1 (16.8 ± 12.2 mg kg–1) was found to be within the estimated
natural concentration range of 5 to 25 mg kg–1. Site 1 registered the least Pb concentration. Nonetheless, the average Pb
concentration in the soil samples from the six cities studied were all found to be below the maximum tolerable limit according
to World Health Organization (WHO) standards. The high Pb concentration in Site 4 may be attributed mainly to vehicular emission.
Although Site 4 only ranked 3rd in total volume of vehicles, it has the greatest number of Type B and Type C vehicles combined.
Included in these categories are diesel trucks, buses, and jeepneys which are considered the largest contributors of TSP (total
suspended particles) and PM10 (particulate matter less than 10 microns) emissions.
Conclusion Only one (San Juan in Site 4) of the thirty sampling sites recorded a Pb concentration beyond the WHO permissible limit of
100 mg kg–1. San Juan in Site 4 had a Pb concentration of >250 mg kg–1. On the average, elevated Pb concentration was evident
in the soil samples from San Fernando, Olongapo, Malolos, Balanga, and Cabanatuan. The average soil Pb concentrations in these
cities exceeded the maximum estimated natural soil Pb concentration of 25 mg kg–1. Average soil Pb concentration in Site 1
(16.8 mg kg–1) was well within the estimated natural concentration range of 5 to 25 mg kg–1. Data gathered from the study
areas showed that elevated levels of Pb in soil were due primarily to vehicular emissions and partly to igneous activity.
Recommendation and Outlook The findings of this study presented a preliminary survey on the extent of Pb contamination of soils in urban cities in central
region of Philippines Island. With this kind of information on hand, government should develop a comprehensive environmental
management strategy to address vehicular air pollution in urban areas, which shows as one of the most pressing environmental
problems in the country. Basic to this is the continuous monitoring of Pb levels and other pollutants in air, soil, and water.
Further studies should be conducted to monitor soil Pb levels in the six cities studied particularly in areas with elevated
Pb concentration. The potential for harm from Pb exposure cannot be understated. Of particular concern are children who are
more predisposed to Pb toxicity than adults. Phytoremediation of Pb-contaminated sites is strongly recommended to reduce Pb
concentration in soil. Several studies have confirmed that plants are capable of absorbing extra Pb from soil and that some
plants, grass species in particular, and can naturally absorb far more Pb than others. 相似文献
565.
566.
长兴岛沿岸海域海冰融化水水质状况 总被引:10,自引:3,他引:10
在长兴岛北岸,采集平整冰、堆积冰和搁浅冰。作了26项水质分析,采用三种行业标准评价,结果表明全盐量、氯化物和硫酸盐指标不合格,平整冰全盐量按非盐碱地区标准评价超标7.7倍,按盐碱地区标准评价超标3.8倍。氯化物超标16.6倍,硫酸盐超标2.3芦。堆积冰全盐量按非盐碱地区标准评价超标6.7倍,按盐碱地区标准评价超标2.3倍。氯化物超标15.6倍,硫酸盐超标1.5倍。搁浅冰全盐量按非盐碱地区标准评价超标3.7倍,按盐碱地区标准评价超标1.8倍。氯化物超标10.4倍,硫酸盐超标1.4倍。其余23项合格。 相似文献
567.
568.
渤海和黄海北部地区负积温资源的时空分布特征 总被引:26,自引:0,他引:26
论文以日平均气温≤-4℃的累积值和日数作为与海冰有关的气候指标,统计了渤海和黄海北部沿岸及其邻近地区52个气象站≤-4℃积温和日数的逐年资料,并根据52个气象站的气候指标值与经度、纬度、海拔高度的相关关系,建立空间分布方程,推算无资料海区中214个网格点的≤-4℃积温和日数,绘制渤海和黄海北部地区≤-4℃积温和日数分布图。研究结果表明:≤-4℃积温的空间分布呈现南北差异大、东西变化小的特征,-100℃等值线与渤海和黄海北部常年冰情分布范围大致相当;冰情较重的偏重低温年、严重低温年的≤-4℃积温保证率在黄海北部和辽东湾不超过40%,在渤海湾和莱州湾只有20%以下。 相似文献
569.
土石混合体是一类较为复杂的宏观二元介质不连续岩土体,不同的块体分布情况及不同的试件尺度导致其具有不同的等效强度特性。基于随机集合体构造(RA S)方法构建了土石混合体的随机模型,编制程序实现了随机模型的输出和数值模型的生成。以西南某大型堆积体滑坡中的典型土石混合体为例,考虑含石量和不同粒径分布规律,建立多组不同尺寸随机模型,进行了大量的数值试验,得到了强度表征单元体积(REV)尺度,在此基础上得到了等效强度参数,并分析了土石混合体受力性能和渐进破坏模式。研究结果表明,土石混合体存在REV尺度,案例所得的REV尺度为1.0 m×1.0 m,不同尺度数值计算结果有一定差别,基于REV尺度的力学参数才符合工程意义。 相似文献
570.
污泥膨胀是活性污泥工艺运行中经常遇到的最棘手的问题之一。本实验以人工合成污水为底物,采用序机式活性污泥法(SBR);研究投加无机混凝剂氯化钙控制污泥膨胀的情况,同时研究丝状菌和菌胶团的变化。研究发现,投加氯化钙后,丝状菌数量明显减少;形成较多大而密实规则的菌胶团,污泥膨胀得到控制。污泥容积指数(SVI)由最初的309.5 mL/g降到67.1 mL/g,污泥沉降性能改善。停止投加氯化钙后又运行了18周期,活性污泥没有发生再次膨胀。投加氯化钙对COD去除率没有明显影响。研究结果表明,投加氯化钙是一种有效的污泥膨胀应急控制措施。 相似文献