The influence of the gas flow rate during methane biofiltration on an inorganic packing material

The influence of the gas flow rate (GFR), when varied between 1 and 5.5 L/min, on the conversion, the elimination capacity (EC) and the carbon dioxide production , during the biofiltration of methane using a biofilter charged with an inorganic packing material, has been investigated. The methane concentrations considered for this purpose were selected from the operating range of 1300–12 000 ppmv. The experiments involved were conducted, using a nitrogen minimal salt nutrient solution, for the biofilter periodic irrigation, in which the nitrogen concentration was maintained at 0.75 g/L, and the phosphorus concentration was of 0.3 or 1.5 g/L. The results obtained from this study have confirmed the view that the GFR is a important parameter, the optimum values found, leading to methane conversions of ≥90%, being ≤2 L/min for inlet loads ≤55 g/m³/h. Based on this result, it was then established that the maximum volumetric load (VL) of methane in the biofilter must be estimated at around 0.075 m³ (methane)/m³ (biofilter)/h, that is, 6.8 m³ (polluted gas)/m³ (biofilter)/h. In addition, when the GFR is selected between 1 and 4.2 L/min, it has an influence on the EC. However, the GFR does not affect the within the biofilter. It has also been established that the high phosphorus level (i.e., 1.5 g/L), present in the nutrient solution, is to be preferred in the biofilter.     

A Study of the Biofiltration of High‐Loads of Toluene in Air: Carbon and Water Balances,Temperature Changes and Nitrogen Effect

Biodegradable atmospheric pollutants, released at low to moderate concentrations, can be removed by biofiltration. In this work, a laboratory‐scale compost‐based biofilter has been evaluated for the removal of high levels of toluene in air (～ 4.0 g.m^?3). By applying a variable nitrogen input in the irrigation solution, it was shown that the biodegradation extent can be controlled through the nutrient supply. The maximum elimination capacity achieved was 135 g.m^?3.h^?1, for a N‐concentration of 3.0 g of N.L^?1. A quantitative analysis of the bioreaction aspects (stoichiometry, temperature) led to the determination of the water flow rates associated with the toluene oxidation. Thus, it was estimated that some 530 to 800 g of water.day^?1 were lost at the bioreactor outlet, but were balanced by the irrigation system.     

Effect of flow rate on temperature in a Bi-P-O catalyst bed: Global enhancement by forced flow rate cycling

Effects of flow rate on reactivity of oxidative coupling of propylene with Bi₂O₃-P₂O₅ were investigated by reaction experiments and by model calculations. Although the conversion is lower at the higher flow rate because of the shorter contact time, there may be a case that when the temperature in the catalyst bed increases and it causes the reaction rate to accelerate. It is thought that the heat was accumulated in the catalyst bed when heat generation rate was much faster than the heat removal rate. The simple calculation based on the assumption of the pseudo-homogeneous phase indicated that the heat was not accumulated at the higher flow rate by the steady-state operation. However, heat wave emerged and accelerated the reaction after the flow rate was changed from the lower flow rate to the higher flow rate. Forced flow rate cycling, an operation where flow rate is changed periodically, was experimentally conducted. The time averaged conversion was slightly enhanced compared with the result from the steady-state operation at the flow rate of . In addition, even in the steady-state operation under the condition where a non-adiabatic reactor packed with only catalyst was used, the conversion and the yield of benzene became higher at the higher flow rate because of the temperature increase in the catalyst bed.     

流速对磁场阻垢效果的影响

利用双道的实时监测系统,通过监测碳酸钙过饱和溶液中的pH和Ca2 浓度在析晶过程中的变化,系统的研究了不同流速下磁场的阻垢效果.准确、可重复的试验数据表明,磁场对碳酸钙过饱和溶液有阻垢效果,并且不同流速下磁场的阻垢效果不同.同时试验结果还表明在磁处理时间恒定的条件下,在0～6 m/s的流速范围内,溶液通过磁场的流速越高磁处理的阻垢效果越强.     

载气流量及升温速率对污染土壤中多氯联苯热脱附的影响

利用小型管式炉进行了载气流量和升温速率对多氯联苯污染土壤的热脱附过程影响的实验研究。结果表明流量的增大对多氯联苯含量和毒性当量的去除效率影响不大,载气流量小于400 ml·min^-1时,气相中的脱附量明显增大,载气流量大于400 ml·min^-1则脱附量变化较小,而多氯联苯的毒性当量则随着载气流量增大呈线性增加趋势。实验结果还表明污染土壤中多氯联苯变化速率与升温速率呈明显的正线性相关,随着升温速率增加,污染土壤中多氯联苯去除效率总体呈上升趋势,毒性当量去除效率降低。总体结果分析可以看到升温速率越大,总体效果也越好。污染土壤经热脱附处理后气固相的二 英毒性当量则有不同程度提升,尤其气相内检测到了大量多氯二苯并呋喃生成。     

Impacts of ratio of asymptotic bubble width to diameter of circular tube and Reynolds number in a gas bubble driven flow

This study investigates the steady-state flow field in a circular tube filled with a viscous fluid expelled by a long gas bubble. We use a finite difference method (FDM) with successive over-relaxation (SOR) in the computation of the viscous fluid flows. An empirical deduced bubble profile is employed to simplify the complex computation of the interface shape between the gas and the viscous fluid. By varying the ratio of the bubble width to the diameter of the circular tube (λ), the numerical simulation shows three fluid flow patterns: the complete bypass flow, the recirculation flow and the transient flow. The first two flow patterns of the viscous fluid are coincident with other researches. The transient flow pattern found in the present study shows a clear transition from the complete bypass flow to the recirculation flow, as well as the migration of the stagnation point. The results also clearly present the effects of the inertia force, which is represented by the Reynolds number (Re), on both the flow patterns and the vorticity distribution on the bubble interface. The flow at the rear part of the bubble with higher Reynolds number (i.e., 0<Re?400) is a novel study in recent researches.     

Strength retention in scheelite coated SiC fibers: Effect of the gas composition and pre-heat treatment

Scheelite coating was deposited on SiC fiber tows from various liquid-phase precursors at 1100℃. Strength degradation of SiC fiber was found after fiber coating which was found to be caused by the stress corrosion as a result of gases generated from the decomposition of by-products remaining in the coating. A new and simple method of low temperature pre-heat treatment was adopted to eliminate the stress corrosion in the fiber coating process and to isolate the effect of different types of gases on the stress corrosion cracking of fibers. The tensile strength and fractography of samples with and without pre-heat treatment were compared. Furthermore, the effect of gas composition on the strength degradation of SiC fiber was also investigated through the control experiments.     

Calculation of the phase separation rate in two-phase flow of non-Newtonian power-law fluid and gas bubbles flowing inside the T- and Y-junctions using random vortex method (RVM)

In this paper, the phase separation rate in a two-phase flow of non-Newtonian power-law fluid and gas bubbles flowing inside T- and Y-junction channels with branch angles of 45° and 135° is numerically investigated. The numerical simulation is carried out using the random vortex method (RVM) for the Reynolds number of liquid phase at the inlet of the channel Re_m = 250 for various power-law indexes (n = 0.2–1.4). The result of this research represents valuable information about the effect of branch angle and also the power-law index on the phase separation. The result shows that when increasing the branch angle, the phase separation is increased, while when increasing the power-law index, the phase separation is decreased. The acceptable conformation between this study and the experimental results shows the capability of the evaluated method.     

From the century of the rate equation to the century of the rate constants: a revolution in catalytic kinetics and assisted catalyst design

In the past, rate constants were extracted from rate equations obtained by fitting kinetic data. In the future, they will be calculated by computational chemistry or measured by surface science techniques. They will be used for the start-up of a microkinetic analysis in a combinatorial iteration for the development of optimized catalysts.     

Study of the influence of vane angle on flow, gas species, temperature, and char burnout in a 200 MWe lignite-fired boiler

We measured various operational parameters of a 200-MW_e, wall-fired, lignite utility boiler under various outer secondary air vane angles. The parameters measured were gas temperature, gas species concentrations, char burnout, and component release rates (C, H and N). Cold air experiments of a single burner were conducted in the laboratory. A double swirl flow pulverized-coal burner has a single ring recirculation zone that forms in the secondary air region in the burner. By decreasing vane angles, maximum values of radial velocity, tangential velocity and turbulence intensity all increase. Moreover, swirl intensity of air flow and recirculation zone size increase. Concomitantly, in the central region of the burner, decreasing the vane angles of outer secondary air increases gas temperatures, CO concentrations, char burnout and component release rates of C, H, and N, while O₂ and NO_x concentrations decrease, and an early ignition of pulverized-coal occurs. Meanwhile, in the secondary air region of the burner, conditions are similar except that NO_x mean concentrations are reversed showing instead an increase. In the side wall region, gas temperatures increase, O₂ and NO_x concentrations decrease, but CO concentrations vary only slightly.