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1.
A theoretical model of air and steam co-injection to prevent the downward migration of DNAPLs during steam-enhanced extraction 总被引:1,自引:0,他引:1
When steam is injected into soil containing a dense volatile non-aqueous phase liquid contaminant the DNAPL vaporized within the heated soil region condenses and accumulates ahead of the steam condensation front. If enough DNAPL accumulates, gravitational forces can overcome trapping forces allowing the liquid contaminant to flow downward. By injecting air with steam, a portion of the DNAPL vapor remains suspended in equilibrium with the air, decreasing liquid contaminant accumulation ahead of the steam condensation front, and thus reducing the possibility of downward migration. In this work, a one-dimensional theoretical model is developed to predict the injection ratio of air to steam that will prevent the accumulation of volatile DNAPLs. The contaminated region is modeled as a one-dimensional homogeneous porous medium with an initially uniform distribution of a single component contaminant. Mass and energy balances are combined to determine the injection ratio of air to steam that eliminates accumulation of the contaminant ahead of the steam condensation front, and hence reduces the possibility of downward migration. The minimum injection ratio that eliminates accumulation is defined as the optimum injection ratio. Example calculations are presented for three DNAPLs, carbon tetrachloride (CCl4), trichloroethylene (TCE), and perchloroethylene (PCE). The optimum injection ratio of air to steam is shown to depend on the initial saturation and the volatility of the liquid contaminant. Numerical simulation results are presented to validate the model, and to illustrate downward migration for ratios less than optimum. Optimum injection ratios determined from numerical simulations are shown to be in good agreement with the theoretical model. 相似文献
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After a short update of the current more accepted definition of BLEVE, the special features of water BLEVEs are analyzed. The stronger overpressure wave generated in the case of water as compared to that of other substances is justified in terms of volume change. Through a comparison with liquefied pressurized propane, three possibilities are analyzed: the simultaneous contribution of both the liquid and the preexisting vapor, the contribution of the liquid flash vaporization, and the contribution of the pre-existing vapor. Also a historical survey on a set of 202 BLEVE accidents –the largest sample of BLEVE accidents surveyed until now– is presented. LPG was the most common substances in this set of accidents. However, water and LNG (11% of water and 4% of LNG in the studied cases) have also been involved. Impact failure (44.8%) and human factor (30.3%) were the most common causes of BLEVEs. Transport, storage, process plants, and transfer were the activities in which more accidents occurred. 相似文献
3.
When steam is injected into soil containing a dense volatile non-aqueous phase liquid contaminant, the DNAPL vaporized within the heated soil region condenses and accumulates ahead of the steam condensation front. If enough DNAPL accumulates, gravitational forces can overcome trapping forces allowing the liquid contaminant to flow downward. By injecting air with steam, a portion of the DNAPL vapor remains suspended in equilibrium with the air, decreasing liquid contaminant accumulation ahead of the steam condensation front, and thus reducing the possibility of downward migration. In a previous work, a theoretical model was developed to predict the optimum injection ratio of air to steam that would eliminate accumulation of DNAPL ahead of the temperature front and thus minimize the potential for downward migration. In this work, the theoretical model is summarized, and an experiment is presented in order to evaluate the optimum injection ratio prediction. In the experiment, a two-dimensional water saturated sand pack is contaminated with a known mass of TCE (DNAPL). The system is then remediated by co-injecting air and steam at the predicted optimum injection ratio, calculated based on the average contaminant soil concentration in the sand pack. Results for the co-injection of air and steam are compared to results for the injection of pure steam or pure air. Injection at the predicted optimum injection ratio for a volumetric average NAPL saturation, reduced accumulation of the contaminant ahead of the condensation front by over 90%, as compared to steam injection alone. This indicates that the optimum injection ratio prediction is a valuable tool for limiting the spreading of DNAPL during steam-enhanced extraction. Injection at the optimum injection ratio resulted in earlier recovery of contaminant than for steam injection alone. Co-injection of steam and air is also shown to result in much higher recovery rates than air injection alone. 相似文献
4.
气提-厌氧-接触氧化-气浮工艺处理聚酯废水 总被引:1,自引:0,他引:1
介绍了气提-厌氧-接触氧化-气浮处理工艺在聚酯废水工程中的实际应用,分析并总结了工程设计及运行的经验。实践表明,运用气提塔先对高浓度聚酯废水进行预处理,可以去除废水中对生化有毒性的醛类物质,保证后续生化处理的稳定运行。经气提-厌氧-接触氧化-气浮处理工艺处理后,废水中COD总的去除效率可达到98.7%以上,能够实现稳定达标排放。并可实现部分回用至生产过程。该工艺具有运行稳定和处理效率高等优点,为企业带来了良好的经济效益和社会效益。 相似文献
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Motoyuki Sugano Akihiro Komatsu Masanori Yamamoto Mika Kumagai Takayuki Shimizu Katsumi Hirano Kiyoshi Mashimo 《Journal of Material Cycles and Waste Management》2009,11(1):27-31
Most landfilled plastic waste is a mixture or is in the form of composites with incombustible wastes such as glass, metals,
and ceramics. After hydrothermal treatment, including a steam-explosion process, the separation of mixed waste (MW) into organic
and inorganic substances becomes easy. However, the effect of hydrothermal pretreatment on the subsequent liquefaction of
organic substances from MW is not obvious. In this study, the effects on the liquefaction of polystyrene and high-density
polyethylene are discussed. Moreover, optimum conditions for the liquefaction of organic substances from hydrothermally treated
MW are identified. By means of this hydrothermal pretreatment, including the steam-explosion process, polystyrene and high-density
polyethylene can be significantly converted to oil by liquefaction at 300°–400°C. In comparison with liquefaction of hydrothermally
pretreated mixed waste (HMW) at 300°–400°C with a batch type reactor, the yield of oil increases significantly on liquefaction
using a semi-batch type reactor. It is considered that the radical chain and termination reactions among the radicals from
HMW were inhibited in the semi-batch type reactor. On liquefaction of HMW in a semi-batch reactor, the conversion of HMW to
oil was enhanced on increasing the liquefaction temperature to 350°C and the holding time to 60 min.
Chemical Feedstock Recycling & Other Innovative Recycling Techniques 6 相似文献
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Tohru Kamo Kanji Takaoka Junichiro Otomo Hiroshi Takahashi 《Journal of Material Cycles and Waste Management》2006,8(2):109-115
Steam gasification of dehydrochlorinated poly(vinyl chloride) (PVC) or activated carbon was carried out in the presence of
various alkali compounds at 3.0 MPa and 560°C–660°C in a batch reactor or in a semi-batch reactor with a flow of nitrogen
and steam. Hydrogen and sodium carbonate were the main products, and methane and carbon dioxide were the minor products. Yields
of hydrogen were high in the presence of sodium hydroxide and potassium hydroxide. The acceleration effect of the alkali compounds
on the gasification reaction was as follows: KOH > NaOH > Ca(OH)2 > Na2CO3. The rate of gasification increased with increasing partial steam pressure and NaOH/C molar ratio. However, the rate became
saturated at a molar ratio of NaOH/C greater than 2.0. 相似文献
9.
《Process Safety and Environmental Protection》2014,92(6):532-544
This paper presents a generic mathematical model for retrofitting the steam power plants in an industrial site. The industrial sector under review consists of one steel mill, one oil refinery, and several petrochemical plants, where only small-scale steam integration has been implemented before this study. The relevant unit models in a typical steam power plant are established, and the steam plant retrofit problem is formulated as a mixed-integer nonlinear program (MINLP). Feasible retrofit alternatives suggested by experienced field engineers are investigated in sequence to examine the revenue of those possible modifications. The first scenario examines operational optimization of existent plants; the second option allows installation of one new turbine and replacement of several boilers and turbines with lower efficiency; the third scenario considers using a steam ejector to upgrade the disqualified import steam in the oil refinery. The significant merits from these three retrofit alternatives show that the proposed MINLP formulation has been a great help to enhance the inter-plant steam integration in an industrial sector. 相似文献
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