Perchlorate: Problems,Detection, and Solutions

The perchlorate anion (ClO 4 m ) is produced when the solid salts of ammonium, potassium, and sodium perchlorate, and perchloric acid dissolve in water. Ammonium perchlorate, used in solid rocket engine fuels, has a limited shelf life and must periodically be replaced. Before 1997, perchlorate could not be readily detected in groundwater at concentrations below 100 µg/L, until the California Department of Health Services developed an acceptable analytical method that lowered the detection limit to 4 µg/L. Subsequently, groundwater containing perchlorate were soon encountered in several western states, and contamination became apparent in Colorado River water. Most perchlorate salts have high water solubilities; concentrated solutions have densities greater than water. Once dissolved, perchlorate is extremely mobile, requiring decades to degrade. Health effects from ingesting low dosage perchlorate-contaminated water are not well known: it interferes with the body's iodine intake, causing an inhibition of human thyroid production. Contaminated surface and groundwater treatment may require bio- and/or phytoremediation technologies. Perchlorate in groundwater is relatively unretarded; it probably travels by advection. Therefore, it may be used as a tracer for hydrocarbon and metal contaminants that are significantly more retarded. Possible forensic techniques include chlorine isotopes for defining multiple or commingled perchlorate plumes.     

杉木人工林生态系统可燃物空间分布规律研究

在国家野外科学观测研究站-会同生态站的集水区中设置固定标准地,利用标准地和生物量调查数据,对杉木人工林的可燃物负荷量空间分布规律进行了研究,结果表明:杉木人工林生态系统的自然整枝能力较差,细小可燃物的空间分布均匀,易燃可燃物连续性好;含水率以近地面的最小;11年生的杉木人工林生态系统的枯死枝叶的总负荷量高达0.198 t.hm-2,分布于0～1.5 m的空间层中,这种均匀的空间分布规律为树冠火的发生创造了条件,从而加大了杉木人工林生态系统的火险性.建议在杉木人工林生态系统的经营过程中,要加强人工整枝,改变可燃物的空间分布;减少易燃可燃物的数量,降低森林的燃烧性;对于枯死枝叶可采取人工和计划烧除的措施进行清理.     

影响飞机燃油箱惰化系统参数的数值研究

选取单个飞机燃油箱,运用CFD方法模拟了燃油箱惰化系统的惰化过程。CFD方法的模拟结果与文献中的理想混合模型及经验公式吻合较好。通过模拟,发现增加富氮气体的流量、提高富氮气体中的氮气含量可以缩短惰化时间,而增加富氮气体喷嘴直径和燃油箱的体积则会延长惰化时间。其他参数如燃油箱的形状和富氮气体喷嘴位置对惰化时间没有明显的影...     

Fugitive Gas Emissions from Fuel Tanks

Many fuel installations and industrial operations often are associated with the release, whether deliberately or inadvertently, of fuel vapors into the surrounding atmosphere. Most of these releases may be considered to be relatively small on a thermal basis, but they do represent collectively a serious source of unburned hydrocarbon emissions into the atmosphere. Moreover, the emissions of methane from various sources of natural gas contribute significantly to green house gas emissions.

The paper presents computed results of the transient dissipation of a fixed mass of methane when released within vertical cylindrical vessels containing air, which are open to the outside atmosphere under ambient conditions. Particular attention is given to the rates of emission of gas into the outside atmosphere and how it is affected by the composition and mass of the fuel released and the size and configuration of the fuel retaining cylindrical tank. The corresponding transient formation, growth and subsidence of flammable zones within such a vessel are also described. Some guidelines for reducing the hazards associated with such releases are presented.     

Biomass for Fuel Cells: A Technical and Economic Assessment

Fuel cells can be highly efficient energy conversion devices. However, the environmental benefit of utilising fuel cells for energy conversion is completely dependent on the source of the fuel. Hydrogen is the ideal fuel for fuel cells but the current most economical methods of producing hydrogen also result in the production of significant amounts of carbon dioxide. Utilising biomass to produce the fuel for fuel cell systems offers an option that is technically feasible, potentially economically attractive and greenhouse gas neutral. High-temperature fuel cells that are able to operate with carbon monoxide in the feed are well suited to these applications. Furthermore, because they do not require noble metal catalysts, the cost of high-temperature fuel cells has the greatest potential to become competitive in the near future compared to other types of fuel cells. It is, however, extremely difficult to assess the economic feasibility of biomass-fuelled fuel cell systems because of a lack of published cost information and uncertainty in the predicted cost per kW of the various types of fuel cells for large volume production methods. From the scant information available it appears that the current cost for fuel-cell systems operating on anaerobic digester gas is about US$2,500 per kW compared to a target price of US$1,200 required to compete with conventional technologies.     

Fuel prices and new vehicle fuel economy—Comparing the United States and Western Europe

Several recent papers have documented an effect of fuel prices on new vehicle fuel economy in the United States. This paper estimates the effect of fuel prices on average new vehicle fuel economy for the eight largest European markets. The analysis spans the years 2002–2007 and uses detailed vehicle registration and specification data to control for policies, consumer preferences, and other potentially confounding factors. We find fuel prices to have a statistically significant effect on average new vehicle fuel economy in Europe. The effect estimated for Europe is much smaller than comparable estimates for the United States.     

Impact of source segregation intensity of solid waste on fuel consumption and collection costs

Fuel consumption and collection costs of solid waste were evaluated by the aid of a simulation model for a given collection area of a medium-sized Italian city. Using the model it is possible to calculate time, collected waste and fuel consumption for a given waste collection route. Starting from the data for the current waste collection scenario with a Source Segregated (SS) intensity of 25%, all the main model error evaluated was ?1.2. SS intensity scenarios of 25%, 30%, 35% and 52% were simulated. Results showed an increase in the average fuel consumed by the collection vehicles that went from about 3.3 L/tonne for 25% SS intensity to about 3.8 L/tonne for a SS intensity of 52%. Direct collection costs, including crews and vehicle purchase, ranged from about 40 €/tonne to about 70 €/tonne, respectively, for 25% and 52% SS intensity. The increase in fuel consumption and collection costs depends on the density of the waste collected, on the collection vehicle compaction ratio and on the waste collection vehicle utilization factor (WCVUF). In particular a reduction of about 50% of the WCVUF can lead to an average increase of about 80% in fuel consumption and 100% in collection costs.     

Analysis of radiation hazards to personnel on marine platforms

The large number of radio frequency (RF) transmitters employed in modern marine platforms requires that they operate in mutual coexistence while posing no danger to operators and equipment despite the limited available physical space. A key to the successful system integration is the control of the electromagnetic environment on the ships’ topsides, which might pose radiation hazards (RADHAZ) to personnel (HERP). HERP are caused by transmitter antenna installations that generate intentional EM radiation in excess of the safe levels in zones of personnel activity. Radiation safety to personnel is achieved when the average radiation power density is below the permissible exposure limits (PEL) for HERP at locations of personnel activity and medical equipment operation. This paper describes the analysis tools and techniques for the evaluation of HERP on marine platforms. The same approaches could be employed in the analysis of land site antenna deployment scenarios.     

Should I stay or should I go? Testing optimality models of stopover decisions in migrating birds

Time-minimizing migrants should leave a stopover site if the instantaneous speed of migration drops to the average speed of migration in the environment. This argument has been used in two different ways: either there is local variation in the fuel deposition rate and a fixed expected speed or there is global variation in the fuel deposition rate, i.e. locally experienced variation represents global variation along the route. The first case leads to a far steeper relationship between departure load and fuel deposition rate than the second case. So far, data on departure loads have mainly been analysed within the concept of local variation of the fuel deposition rate and the result that the observed slopes are much lower than predicted has been explained by changes in the expected speed along the route or by individual differences in the expected speed. We show here that the observed relationships generally fall close to the predictions for global variation. We propose that migrants use a behavioural rule which projects the current experience into the future and therefore interprets local variation as global variation. Received: 3 April 1999 / Received in revised form: 22 April 1999 / Accepted: 26 April 1999