Small‐b and Fixed‐b Asymptotics for Weighted Covariance Estimation in Fractional Cointegration

In a standard cointegrating framework, Phillips (1991) introduced the weighted covariance (WC) estimator of cointegrating parameters. Later, Marinucci (2000) applied this estimator to fractional circumstances and, like Phillips (1991), analysed the so‐called small‐b asymptotic approximation to its sampling distribution. Recently, an alternative limiting theory (fixed‐b asymptotics) has been successfully employed to approximate sampling distributions. With the purpose of comparing both approaches, we derive here the fixed‐b limit of WC estimators in a fractional setting, filling also some gaps in the traditional (small‐b) theory. We also provide some Monte Carlo evidence that suggests that the fixed‐b limit is more accurate.     

某立式可燃液体储罐区消防灭火及冷却用水系统的设计

根据相关规范和业主要求,某立式可燃液体罐区采用固定式消防冷却水系统和低倍数泡沫灭火系统相结合的灭火系统。本设计通过对市场上实际灭火设备参数的选取,确定了泡沫比例混合装置的参数：并通过对罐区环状消防冷却水管分区布管的比较,选择最优的布管方式,该布管方式不仅避免了因设计取值较小造成消防储水量的不足而且减少了消防用水量。     

安全阀整定压力的探讨

探讨了固定式压力容器直接荷载弹簧式安全阀整定压力的确定方法,分析了整定压力与排放压力、回座压力和密封试验压力之间的关系.     

Single and Multicomponent Sorption of CO2, CH4 and N2 in a Microporous Metal-Organic Framework

Abstract

Single and multicomponent fixed-bed adsorption of CO₂, N₂, and CH₄ on crystals of MOF-508b has been studied in this work. Adsorption equilibrium was measured at temperatures ranging from 303 to 343 K and partial pressures up to 4.5 bar. MOF-508b is very selective for CO₂ and the loadings of CH₄ and N₂ are practically temperature independent. The Langmuir isotherm model provides a good representation of the equilibrium data. A dynamic model based on the LDF approximation for the mass transfer has been used to describe with good accuracy the adsorption kinetics of single, binary and ternary breakthrough curves. It was found that the intra-crystalline diffusivity for CO₂ is one order of magnitude faster than for CH₄ and N₂.     

Adsorption of Gallic Acid from Aqueous Solution Using Fixed Bed Activated Carbon Columns

Naturally occuring matter (NOM), a heterogeneous mixture of complex organic compounds, is invariably present in all surface and ground waters. These materials act as substrate for the growth of bacteria in the distribution system. The disinfection of such water by chlorination produces disinfection by products consisting of several halogenated compounds which are toxic and carcinogenic. As gallic acid is the building block of most NOM, its adsorptive removal from water has been studied using activated carbon columns. The operating variables studied are the hydraulic loading rate (HLR), bed depth (Z), and the feed concentration (C_o). The breakthrough curves are S-shaped and the breakthrough time increases with increasing Z and decreases with increasing HLR and C_o. The adsorption increases with increasing HLR and is maximum around HLR = 8 m³/hr/m². The column design parameters such as the critical bed depth and the depth of the mass transfer zone (MTZ) as calculated using the bed depth service time (BDST) approach are found to agree fairly closely with the experimental values. MTZ is smaller for the carbon cloth indicating its better adsorption characteristics. The adsorption column parameters such as the treated volume and the mass of the carbon required for a desired effluent concentration have been determined from the column data.     

环形分布器内变质量流动的CFD模拟研究

环形分布器是实现导热介质在列管式固定床反应器壳程均匀流动的关键部件,文中采用计算流体力学方法(CFD)对环形分布器内的变质量流动进行了模拟研究。首先计算了环形通道内的速度和静压力分布,在此基础上研究了穿孔阻力系数随开孔几何结构以及入口流体流速的变化规律。模拟结果表明:环形通道内存在较明显的速度梯度和压力梯度;随着流体不断分流,在流道内的流动速度不断减小,静压力逐渐增大。因此,需要沿流动方向将开孔直径逐渐减小,以增大穿孔阻力,从而实现流体的均布。对穿孔阻力系数变化规律的研究结果表明:穿孔阻力系数ξ与出口和主流道的流速比ui/u、厚径比δ/di和入口雷诺数Re0有关。在模拟范围内,ξ先随ui/u的增大而减小,到达一个临界值后,ξ不再随ui/u的增大而变化;δ/di对ξ影响不太明显;当Re0属于湍流范围时,ξ随Re0的变化不太明显,但是总体随Re0的增大而减小。     

常压固定层间歇气化技术的优劣

简单介绍了常压固定层间歇气化技术发展的现状和技术概况,并对常压固定层间歇气化技术优劣进行了分析。说明了该技术虽然落后,但是通过各种技术改造仍然在小合成氨企业中得到广泛的应用。     

煤制合成天然气项目工艺方案与技术经济比较

介绍了煤制天然气（SNG）典型工艺流程;论述了KBR工艺（流化床）、BGL工艺（固定床）、Shell上行水激冷工艺（气流床粉煤气化）的技术方案、工艺装置和公用工程配置;对比了3种不同类型煤气化工艺的主要原料、公用工程消耗和技术经济测算。结果表明,煤气化技术的选择,不仅要考虑煤质特点、原料煤来源和价格以及产品的经济性,而且要从技术的成熟可靠、环境影响和社会效益等多方面因素进行综合评价和对比。     

富氧连续气化和空气间歇增氧气化技术应用情况调查

介绍富氧连续气化的进展,应用中存在的问题,以及富氧气化技术目前的改进情况。     

Effect of particle shape on methanol partial oxidation in a fixed bed using CFD reactor modeling

Particle shape is one of the most important parameters in the design and optimization of fixed-bed processes. To address the impact of particle shape on methanol partial oxidation to formaldehyde over molybdate catalyst, packings of spheres, cylinders, rings, and trilobes are numerically generated. The generated packings are used to carry out resolved particle Computational Fluid Dynamics (CFD) simulations under industrial conditions. Pressure drop, voidage and velocity profiles, radial heat transfer, and local and overall conversion and selectivity results are presented. Despite their lower particle surface area, lower particle effectiveness and more uneven flow distribution than trilobes, and lower overall heat transfer coefficient than cylinders, rings had the best conversion and selectivity due to their balance between the factors. Three longer tubes of rings, rings and cylinders, and rings and trilobes are simulated and show a small gain in selectivity for the rings and trilobes.