Intensification of degradation of aqueous solutions of rhodamine B using sonochemical reactors at operating capacity of 7 L

In the present work, degradation of rhodamine B, a typical dye effluent commonly observed in chemical processing wastewaters has been investigated using a sonochemical reactor with capacity of 7 L. The reactor consists of an ultrasonic bath equipped with a single large transducer having longitudinal vibrations with operating frequency of 25 kHz and rated power output of 1 kW. The effect of operational conditions such as the rhodamine B initial concentration, operating pH and use of additives such as H(2)O(2), CCl(4) and TiO(2) has been investigated initially. A mathematical model has also been fitted to estimate the rate constant for rhodamine B removal under different operating conditions. Intensification studies have been carried by combining sonochemical oxidation with photocatalytic oxidation under optimized conditions. In all the investigated systems, complete removal of rhodamine B (10 ppm initial concentration) was obtained using a combination of sonochemical reactor and CCl(4). Sonocatalysis (in the presence of TiO(2)) of rhodamine B showed 92% degradation, while sonophotocatalysis gave degradation of 93%. TOC analysis at various optimum conditions was also performed to quantify the extent of mineralization and it was observed that the extent of mineralization is always lower than the extent of removal of parent compound.     

Application of the TNO multi-energy and Baker-Strehlow-Tang methods to predict hydrogen explosion effects from small-scale experiments

Analytical models or abacus are of importance to predict explosion effects in open and congested areas for industrial safety reasons. The goal of this work is to compare overpressure and flame speed values of small-scale deflagration experiments to predicted values from the TNO multi-energy (TNO ME) method and the Baker-Strehlow-Tang (BST) method. Experiments were performed in cylindrical congested volumes of hydrogen – air mixtures varying from 1.77 L to 7.07 L. The reactivity was controlled by the equivalence ratio of hydrogen-air mixtures, ranging from 0.5 to 2.5. The congestion was realized with varying numbers of grid layers and configurations. The influence of the obstacle density and the importance of the mixture reactivity to choose the strength index in order to predict the effects of an explosion has been highlighted for the TNO ME method. Predictive flame speed values from the BST method are in accordance with almost half of the experimental results and the method is conservative in most tested configurations. The use of the TNO ME method has been validated on a small-scale experiment to predict maximal overpressures generated by the deflagration of medium and large-scale H₂/air clouds.     

Medium-scale experiments on vented hydrogen deflagration

A series of medium-scale experiments on vented hydrogen deflagration was carried out at the KIT test side in a chamber of 1 × 1 × 1 m³ size with different vent areas. The experimental program was divided in three series: (1) uniform hydrogen–air mixtures; (2) stratified hydrogen–air mixtures within the enclosure; (3) a layer deflagration of uniform mixture. Different uniform hydrogen–air mixtures from 7 to 18% hydrogen were tested with variable vent areas 0.01–1.0 m². One test was done for rich mixture with 50% H₂. To vary a gradient of concentration, all the experiments with a stratified hydrogen–air mixtures had about 4%H₂ at the bottom and 10 to 25% H₂ at the top of the enclosure. Measurement system consisted of a set of pressure sensors and thermocouples inside and outside the enclosure. Four cameras combined with a schlieren system (BOS) for visual observation of combustion process through transparent sidewalls were used. Four experiments were selected as benchmark experiments to compare them with four times larger scale FM Global tests (Bauwens et al., 2011) and to provide experimental data for further CFD modelling. The nature of external explosion leading to the multiple pressure peak structure was investigated in details. Current work addresses knowledge gaps regarding indoor hydrogen accumulations and vented deflagrations. The experiments carried out within this work attend to contribute the data for improved criteria for hydrogen–air mixture and enclosure parameters to avoid unacceptable explosion overpressure. Based on theoretical analysis and current experimental data a further vent sizing technology for hydrogen deflagrations in confined spaces should be developed, taking into account the peculiarities of hydrogen–air mixture deflagrations in presence of obstacles, concentration gradients of hydrogen–air mixtures, dimensions of a layer of flammable cloud, vent inertia, etc.     

Gas leakage consequence modeling for buried gas pipelines

One of conservation transfer methods for such widely-used gases as natural gas and hydrogen is buried pipelines. Safety of these pipelines is of great importance due to potential risks posed by inefficiencies of the pipelines. Therefore, an accurate understanding of release and movement characteristics of the leaked gas, i.e. distribution and speed within soil, the release to the ground surface, the movement of hydrogen gas through the ground, gas underground diffusion, gas dispersion in atmosphere, and following consequences, are very important in order to determine underground dispersion risks. In the present study, consequences of gas leakage within soil were evaluated in two sub-models, i.e. near-field and far-field, and a comprehensive model was proposed in order to ensure safety of buried gas supply pipelines. Near-field model which is related to soil and ground and its output is the gas released at different points and times from ground surface and it was adopted as input of far-field sub-model which is dispersion model in atmosphere or an open space under the surface. Validation of near-field sub-model was performed by the experimental data obtained by Okamoto et al. (2014) on full-scale hydrogen leakage and then, possible scenarios for far-field sub-model were determined.     

新型聚乙烯填料生物滴滤床净化硫化氢气体运行特性

研究高密度聚乙烯改良型拉西环填料按其不同规格分层填充后生物滴滤床去除硫化氢气体的运行特性.126d的长期运行试验结果表明,该反应器具有压降低、负荷沿塔高分布均匀的显著优点.在去除率90%时,气体停留时间最短为12s,入口负荷最大为110g/(m3·h),反应器最大去除负荷为84g/(m3·h).底层去除比率在37%～55%之间,负荷在2层填料间分布均匀.整个长期运行期间反应器压降一直低于280Pa/m,反冲周期大于2个月,长期运行底层未发生生物量积累,稳定运行时压降的变化可以作为反应器反冲的监控指标.故障恢复试验表明,反应器在停止供应气相基质6d后,去除率恢复到95%仅需1d,喷淋液pH的剧烈变化对于反应器具有明显的不良影响.     

Numerical investigation of effects on premixed hydrogen/air flame propagation in pipes with different contraction or expansion angles

Numerical simulations of premixed hydrogen-air flame propagation in a pipe with different contraction or expansion angles are carried out in this study. The effects on the flame propagation characteristics are investigated, including flame shape, the speed of flame front and overpressure. Results show that the flame propagation at different contraction angles experiences 6 flame stages: spherical flame stage, finger-shaped flame stage, stage of flame front touching the sidewalls, classic tulip flame stage, dissipation stage of tulip flame and its re-formation stage. The formation of tulip flame and the following stages are promoted by the contraction structure. Meanwhile, the development of the flow and pressure fields near the contraction are analyzed and it is found that the paraclinical effects induced by the contraction angle enhance the tulip re-formation. In the sudden expansion pipes, a triple flame stage appears in the pipes. The flame front remains relatively static for a period of time. However, the flame would continue to propagate when the expansion angle becomes larger and the flame propagation distance in the ducts increased obviously with the larger expansion angle. Baroclinic effect can inhibit the intensity of the vortex in the flow field, and hence weaken the forward transport of fuel. This inhibit effects decrease with the expansion angle becomes larger. The results of this study have implications concerning designs for pipe geometry of hydrogen and may help get better hydrogen transportation.     

Gasification of waste plastics by steam reforming in a fluidized bed

The process of producing synthetic gas from waste plastics by steam reforming was investigated. To evaluate this process, the steam reforming of the oils derived from low-density polyethylene and polystyrene were carried out using a laboratory-scale fluidized bed of Ni-Al₂O₃ catalysts. The performance of gasification in terms of carbon conversion, gas yield, and gas compositions was examined. Although oils derived from plastics contain many kinds of heavy hydrocarbons and aromatics, they were well gasified at temperatures above 1023 K with a steam/carbon ratio of 3.5 and a weight hourly space velocity of 1 h⁻¹. The hydrogen content of the product gas was very high at approximately 72 vol% for polyethylene-derived oil and 68 vol% for polystyrene-derived oil. These compositions agreed well with the values calculated from chemical equilibrium.     

Effect of ignition position on the run-up distance to DDT for hydrogen-air explosions

The method described in this paper enabled reliable and accurate positioning of an overdriven detonation by calculation of shock wave velocities (detonation and retonation) for hydrogen explosions in a closed 18 m long horizontal DN150 pipe. This enabled an empirical correlation between the ignition position and the run-up distance to DDT to be determined. It was shown that the initial ability of the flame to expand unobstructed and the piston-like effect of burnt gas expanding against the closed end of the tube contributed to initial flame acceleration and hence were able to affect the run-up distance to overdriven detonation. Flame speeds and rates of initial pressure rise were also used to explain how these two competing effects were able to produce a minimum in the run-up distance to DDT. The shortest run-up distance to DDT, relative to the ignition position, for this pipe and gas configuration was found when the ignition position was placed 5.6 pipe diameters (or 0.9 m) from the closed pipe end. The shortest run-up distance to DDT relative to the end of the pipe was recorded when the ignition source was placed 4.4 pipe diameters or 0.7 m from the pipe end.     

Nanoparticles in mitigating gaseous emissions from liquid dairy manure stored under anaerobic condition

A number of mitigation techniques exist to reduce the emissions of pollutant gases and greenhouse gases(GHGs) from anaerobic storage of livestock manure. Nanoparticle(NP)application is a promising mitigating treatment option for pollutant gases, but limited research is available on the mode of NP application and their effectiveness in gaseous emission reduction. In this study, zinc silica nanogel(ZnSNL), copper silica nanogel(CuSNL), and N-acetyl cysteine(NACL) coated zinc oxide quantum dot(Qdot) NPs were compared to a control lacking NPs. All three NPs tested significantly reduced gas production and concentrations compared to non-treated manure. Overall, cumulative gas volumes were reduced by 92.73%–95.83%, and concentrations reduced by 48.98%–99.75% for H_2S, and 20.24%–99.82% for GHGs. Thus, application of NPs is a potential treatment option for mitigating pollutant and GHG emissions from anaerobically stored manure.     

Evaluation of alternative landfill cover soils for attenuating hydrogen sulfide from construction and demolition (C&D) debris landfills

Hydrogen sulfide (H(2)S) generated from C&D debris landfills has emerged as a major environmental concern due to odor problems and possible health impacts to landfill employees and surrounding residents. Research was performed to evaluate the performance of various cover materials as control measures for H(2)S emissions from C&D debris landfills. Twelve laboratory-scale simulated landfill columns containing gypsum drywall were operated under anaerobic conditions to promote H(2)S production. Five different cover materials were placed on top of the waste inside duplicate columns: (1) sandy soil, (2) sandy soil amended with lime, (3) clayey soil, (4) fine concrete (particle size less than 2.5 cm), and (5) coarse concrete (particle size greater than 2.5 cm). No cover was placed on two of the columns, which were used as controls. H(2)S concentrations measured from the middle of the waste layer ranged from 50,000 to 150,000 ppm. The different cover materials demonstrated varying H(2)S removal efficiencies. The sandy soil amended with lime and the fine concrete were the most effective for the control of H(2)S emissions. Both materials exhibited reduction efficiencies greater than 99%. The clayey and sandy soils exhibited lower reduction efficiencies, with average removal efficiencies of 65% and 30%, respectively. The coarse concrete was found to be the least efficient material as a result of its large particle size.