双循环旋风分离器分离性能的实验研究

双循环旋风分离器采用筒锥结构,有2个切向进气口,即主进气口和回流口,分别位于筒体的中部和顶端。排灰口底部设有稳流锥,灰仓侧壁设置了抽气口。通过实验研究了进口位置、进口气速、稳流锥和抽气操作对此新设备分离性能的影响。实验设备直径为0.250 m,实验物料采用粒径0.1—36μm,平均粒径为8.72μm的石英砂。结果表明:主进口进料,风速在12—19 m/s变化时,总分离效率为98.5%—99.17%,可以基本去除大于3μm的颗粒。主进口进料比回流口进料总分离效率大1.5%—3.5%。采用主进气口进料时,稳流锥可以提高总分离效率0.15%—0.2%,抽气操作可以提高总分离效率0.3%—0.4%;回流口进料时,分别提高1.5%—2%和0.6%—1%。     

双循环旋风分离器阻力性能的实验研究

双循环旋风分离器通过将主进气口设于简体中部,将顶部进气口设为回流口,消除了传统旋风分离器顶部进气口存在的二次流和短路流,进而使大于3μm颗粒的分离效率接近100%.基于工程设计理论的需求,研究了该新设备的阻力性能.利用直径为0.250 m的实验设备,测定了其压降与进口气速的关系,考察了不同结构和操作条件对其阻力性能的影...     

多效旋风分离器性能的实验研究

多效旋风分离器通过采用2级螺旋管预分离含尘气体、螺旋形顶盖板导流、筒体中心稳流锥稳流和吸气回流系统防止粉尘返混等措施,解决了在旋风流场中分离微米及亚微米级颗粒的难题。文中通过实验研究了直径为0.25 m的多效旋风分离器的压降、分离效率和进口风速的关系,实验物料粒径范围为0.1—23μm,平均粒径为7.59μm。结果表明:在10—14 m/s入口风速时,对0.1—3μm颗粒的分离效率大于90%,对大于5μm颗粒的分离效率接近100%,压降在500—1 000 Pa。风速大于16 m/s时,对0.1—2μm颗粒的分离效率大于75%。     

双循环旋风分离器除尘机理的数值模拟

双循环旋风分离器通过将主进口设置在筒体中部,将顶部进气口设置为回流口,消除了进气口附近的二次流,避免了短路流,将大于3μm颗粒的分离效率提高至接近100%,并避免了少量11—15μm颗粒的短路逃逸。为了探索该设备的除尘机理,借助CFD软件,通过数值模拟研究的方式,辅助分析了2种进气口在分离性能上不同,传统旋风分离器不能完全分离3—8μm和11—15μm颗粒的机理,以及消除二次流的方法。计算结果表明:当回流气速低于主进气速时,会产生类似于顶端进气口的现象,即二次流、灰环和短路流,降低了小于6μm颗粒的分离效率。当回流气速略大于主进气速时,可以完全消除主进气口附近的二次流,使得所有粒径颗粒的分离效率都较高。模拟结果与实验结果从定性的角度符合较好。     

Cyclone Washer Adapted from an American‐Type Cyclone Separator

A modified cyclone washer was designed, fabricated, and its collection efficiency evaluated. This equipment consists of an American‐type cyclone separator with a triple cone and a spray nozzle was introduced into its cylindrical body. The study consisted of an experimental evaluation of the operating conditions at ambient and higher than ambient temperatures, varying chimney height and water flow rate, with the purpose of humidifying the dust. The collection efficiency of the cyclone washer was evaluated particles of micronized quartz with an average diameter of 7.48 μm and a density of 2.650 g/cm³. The amount of particles varied from 20–100 mg/m³ of air. An average efficiency of 97.07 ± 1.03 % was obtained with four spray nozzles, a chimney height of 0.645 m and 0.358 m³/s of gas.     

颗粒床-旋流耦合分离器不同操作模式下的性能分析

通过实验分别考察了满床/空床操作模式对内置颗粒床-旋流耦合分离器分离性能的影响,获得了两种操作模式下的设备压降和捕集效率。通过改变入口粉尘浓度、入口气速和粉尘颗粒种类,发现满床操作条件下的分离效率比空床操作条件下的分离效率高,且前者压降较低。通过对出口粉尘粒径的分析,含有捕集颗粒的内置颗粒床可有效提高5 μm以下的粉尘颗粒的捕集效率,弥补了离心分离的短板。引入性能指数对不同操作模式进行定量分析,验证了满床操作条件下的耦合分离设备具有更好的综合分离性能。     

防返混锥对双循环旋风器性能的影响研究

前面的研究表明,双循环旋风分离器的设计使得大于3μm颗粒的分离效率接近100%。本文通过CFD模拟软件Fluent 6.2对带有防返混锥的双循环旋风分离器内的压力场和颗粒轨迹进行了数值模拟,并与实验结果进行了比较,模拟结果和实验结果基本一致。模拟得出防返混锥可使分离器的阻力系数增加12%,并减小灰仓内3μm以下颗粒的返混量。实验结果表明,进口气速在8～21m/s时,防返混锥可使主进口和回流口的阻力系数分别增加14.6%和11.8%;当进口平均气速在15～19m/s时,若采用主进口进料,防返混锥可使总分离效率提高0.15%～0.2%;若采用回流口进料,可提高1.5%～2%。     

Analysis of particle trajectories in a quick-contact cyclone reactor using a discrete phase model

The Eulerian–Lagrangian approach with a discrete phase model (DPM) is used to investigate the motion trajectories of the particles at the range of 1–50 μm in the quick-contact cyclone reactor, in which the cracking reactions and the separations of catalysts and products can occur respectively and simultaneously. The results show that the typical motion trajectories of the particles in the quick-contact cyclone reactor can be described as three types: trapping, escaping and dust ring. The first typical motion of particles corresponds to the particles successfully separated from the gas flow, while the other two types can lead to more coking and erosion in the reactor. Moreover, a pre-vortex flow is observed in the mixing-reaction chamber. Additionally, the grade separation efficiency of each particle size is also obtained by counting the numbers of escaping and capturing particles. The particles with diameter larger than 10 μm are separated completely from the gas. The reactor also has a strong capability to trap the particles of small diameters (5 μm <d_p<10 μm). Both results indicate that the separation efficiency of the reactor has met the requirement as a primary separator. Compared with the experimental results, the separation efficiency in the simulated method is higher than 98% with errors of no more than 1.31%. It is illustrated that separation efficiency of the reactor can be predicted by CFD simulation.     

Hydrodesulfurization of athabasca fluid coke — conversion and mechanism

Hydrodesulfurization of Athabasca (Syncrude) fluid coke was studied for particle sizes of ?74 + 53, ?53 + 44 and ?44 μm using a quartz reactor. Five flow rates of hydrogen from 1.2 × 10^?6 to 2.5 × 10^?6 m³/s were investigated with from 0.45 to 1.0 g of coke. Gas production — time profiles for H₂S and CH₄ were obtained at temperatures from 973 to 1073 K for each particle size range. Desulfurization rates were functions of particle size and temperature. Results agree with predictions of the shrinking core model, the rate being controlled initially by the gas film and chemical reaction resistances followed by control due to diffusion of hydrogen through the increasing ash layer. Below 998 K, the apparent activation energy was determined to be 293 kJ/mol · K, while at temperatures between 998 and 1073 K it was 29 kJ/mol · K.     

旋风分离器内颗粒质量浓度分布数值模拟

采用颗粒随机轨道模型和单元内颗粒源法,对旋风分离器内不同粒径颗粒质量浓度分布进行了数值模拟。结果表明,粒径较小的颗粒(dp≤4μm)大部分在旋风分离器分离空间锥段进行分离,而较大颗粒(dp>4μm)大部分在环形空间与分离空间筒段即被分离。随着颗粒粒径增加,分离器外壁的颗粒质量浓度逐渐呈螺旋灰带分布,内旋流夹带减小,环形空间顶板下方出现顶灰环。升气管入口0.25D(筒体直径)附近的短路流对小颗粒的影响较大。在分离空间下部排尘口附近0.5D有明显的颗粒返混,返混量随着颗粒粒径增大而减少。     

去除亚微米粉尘的旋风除尘系统开发

本文开发出了亚微米粉尘的旋风除尘系统——环流循环除尘系统。并通过实验测试了该除尘系统的性能。结果表明 ,亚微米粉尘的旋风除尘系统的分割直径 d50 达到了 0 .5 μm～ 0 .7μm,压降小于 35 0 0 Pa,只比常规旋风除尘器的单台压降略高。该工艺系统可使半密闭和开放式电石炉气达到环保排放标准 ,亦能保证密闭电石炉除尘的需要 ,且可用于水泥立窑、锅炉等窑炉除尘     

Numerical simulation and experimental study of gas cyclone–liquid jet separator for fine particle separation

To address the shortcomings of existing particulate matter trapping technology, especially the low separation efficiency of fine particles, herein, a novel gas cyclone–liquid jet separator was developed to research fine particle trapping. First, numerical simulation methods were used to investigate the flow field characteristics and dust removal efficiency of the separator under different working conditions,and to determined suitable experimental conditions for subsequent dust removal experiment...     

Granular-bed filtration assisted by filter cake formation 3. Penetration of filter cakes by a monodisperse aerosol

For several types of granular solids (sands, silicon carbide and copper shot), penetrations have been measured for a monodisperse aerosol (1.1 μm Dow microspheres) passing through fly ash deposited upon horizontal surfaces of the solids. Fractional penetrations can run as low as 10⁻⁵. Pressure drop data for dust cake/granular medium combinations are also given. The data illustrate significance of dust autohesivitiy and dust/granular solid adhesivity for granular-bed filtration assisted by dust cake formation.     

基于响应曲面法的旋风分离器结构优化

为了优化旋风分离器的分离效率和能量损耗,确定影响旋风分离器性能的主要结构参数,采用响应曲面模型和CFD数值模拟,以排尘口直径（D_d）、排气口直径（D_e）、入口速度（V）为设计变量,以压降和总分离效率为目标函数,进行三因素的优化设计分析。研究结果表明,排尘口直径对压降和分离效率影响不大,排气口直径与速度对压降和分离效率影响显著,且排气口直径与速度的交互作用明显。针对本次0.5～10 μm的颗粒群,推荐最优参数组合是D_e/D=0.35、D_d/D=0.37、V=12 m/s。与实验的结构相比,在相近的分离效率情况下,压降降低了一半,有效地减少了能耗。表明所建立的响应曲面模型能够较精确地表示设计变量与目标函数之间的关系,基于响应曲面模型的优化设计方法可以有效用于旋风分离器的结构优化。同时不同的粒径要求可以采用不同的结构进行除尘,在达到分离要求的前提下,采用最小压降的结构,本次研究为分离0.5～10 μm粒径的结构提供有利的依据。     

Effective conductivity of porous ceramics in a radiative environment

The knowledge of the effective thermal conductivity, taking into account conduction and radiation, is crucial for the accurate prediction of the thermal behavior of porous foams, especially in an environment where radiation is dominating. We present a combined experimental-numerical method for the quantification of the temperature-dependent effective thermal conductivity of porous ceramics. The experiments include transient and spatially-resolved temperature measurements of ceramic foam samples with porosities between 75% and 92%, exposed to high radiative fluxes (peak of 1500 kW.m⁻²). Maximum surface temperatures of 1900K for high purity alumina samples and of 1500K for alumino-silicate (AS) samples were measured, and nonlinear temperature profiles through the sample along the main temperature gradient direction were measured. A 3D numerical model based on an OpenFOAM toolbox was developed and used to determine the thermal conductivity, using the experimental temperature measurements as input. We quantified the effective thermal conductivities (ETCs) in a temperature range of 288–1473K and showed that the ETC of AS samples can significantly increase in the presence of incoming and internal radiation. Alumina with 2 to 5 times smaller typical pore sizes (80 μm vs 190 μm, 230 μm, and 400 μm) exhibited an ETC dominated by conduction and relatively unaffected by radiation. This work illustrates that the ETC of porous materials exposed to radiative fluxes do not only depend on material properties or morphology but also on the operational conditions.     

The influence of a plate vortex limiter on cyclone separator

This article presents the CFD calculations of the efficiency and the pressure drop in the cyclone with a 0.2 m diameter equipped with an obstacle – a flat disk, referred to as the plate. It is located in the lower part of the cyclone cone close to the dust outlet. The influence of three different positions and the diameter of the plate were analysed. The RANS equations with the RSM and DPM for particles motion were used.

The presented study confirms that the use of the plate in the lower part of the cyclone may not improve its performance.     

Emissivity characteristics of boron and boric oxide at high temperatures

The spectral emissivity of boron at wavelengths λ = 0.45–6 μm during ignition and combustion was determined experimentally. The spatial resolution was not lower than 100 μm. Liquid boric oxide, boron filaments 100 μm in diameter, and artificially made agglomerates of amorphous boron particles 2 mm in size and ≈1.22 g/cm³ in density served as radiation objects. It was determined that, as the surface temperature increased from 1 490 to 2 800 K, the emissivity of boron in the examined range of wavelength decreased almost linearly in an interval of 0.35–0.20. At temperatures of 1400–2100 and wavelength of 0.65 μm, the absorption coefficient of liquid boric oxide was 2.2 ± 0.2 cm⁻¹.     

Combustion rate of bituminous coal char in the temperature range 800 to 1700 K

The combustion rates of three different sized fractions of char from a swelling bituminous coal have been measured in the temperature range 800 to 1700 K. The mass-median sizes of the fractions were 70, 35 and 18 μm. For each fraction the combustion rate was less than the limiting rate set by diffusion of oxygen to the particle. The chemical reaction rate coefficient (g/g s atm O₂), calculated from the measured rates and corrected for the external diffusion resistance, varied with temperature in a manner appropriate to an apparent activation energy of approximately 27 kcal/mol for the three fractions. The chemical reaction rate coefficient when expressed on the basis of unit external area of particle (g/cm² s atm O₂) increased with increasing particle size at 800 K: at 1250 K the coefficients for the 35 and 18 μm fractions were equal, and lower than those of the 70 μm fraction by a factor of 4. The densities of the particles did not vary appreciably with burn-off, except the density of the 70 μm fraction which increased sharply for values of burn-off between 0 and 0.01. It is probable that combustion occurred in a rate-control regime which was intermediate between that caused by chemical reaction alone and that caused by the combined effects of pore diffusion and chemical reaction.     

旋风分离器研究及其在半干法旋风除尘方面的应用

比较了国内外常用旋风分离器的结构尺寸和性能,利用干燥尾气中的水分,适当冷却尾气使相对湿度妒〉38％,可促使粉尘团聚成较大颗粒,从而减少了旋风分离器尾气排放中d≤3μm的小颗粒,提高了除尘效率。除尘后的颗粒是干态的。半干法除尘比湿法除尘可节约用水和循环水的电能．同时可以避免循环水中生物质的“发酵”变质。     

Thermoelectric properties of A-site deficient La-doped SrTiO3 at 100–900 °C under reducing conditions

Lanthanum doped strontium titanate is a potential n-type thermoelectric material at moderate and high temperatures. (La_0.12Sr_0.88)_0.95TiO₃ ceramics were prepared by two different routes, conventional sintering at 1500 °C and spark plasma sintering at temperatures between 925 and 1200 °C. Samples with grain size between 40 nm and 1.4 μm were prepared and characterized with respect to their thermoelectric transport properties at temperatures between 100 and 900 °C under reducing conditions (H₂/H₂O-buffer mixtures). The thermal conductivity was significantly reduced with decreasing grain size reaching a value of 1.3 W m^−1. K⁻¹ at 600 °C for grain size of 40 nm and porosity of 19%. Electrical conductivity increased with increasing grain size showing a maximum of 500 S cm⁻¹ at 200 °C for a grain size of 1.4 μm. The highest figure-of-merit (zT) was measured for samples with 1.4 μm average grain size reaching 0.2 at 500 °C.