Erosion–Oxidation Behavior of Chromized–Aluminized 9% Chromium Steel under Fluidized-Bed Conditions at Elevated Temperature

An investigation into the erosion–oxidation behavior of chromized–aluminized 9% chromium steel has been carried out in a fluidized-bed erosion–oxidation rig in air at temperatures of 550 °C to 700 °C for particle impact angles of 30° and 90°, at speeds of 7.0–9.2 m s⁻¹. After exposure for 200 h, the mean-thickness changes were determined, and the specimens were examined and analyzed by scanning electron microscopy and X-ray diffraction. The results show that the chromized–aluminized specimens experience only relatively small amounts of material loss for 30° particle impacts but greater amounts for 90° particle impacts; such angle dependence is typical of a brittle erosion process. Under both impact angles, the thickness losses increase with increase in speed, and also, in temperature up to 650 °C, but then decrease with further increase in temperature. This change in the behavior between 650 and 700 °C is due to an increase in ductility of the coating and a greater contribution from oxidation. The two coating layers (an outer Al₁₃Cr₂ and an inner α-chromium layer) show similar behavior, i.e., have lower material loss rates under 30° impacts than under 90° impacts. As the oxidation rate of the α-chromium layer is greater than that of the outer layer, the oxide scale plays a greater role in the erosion process for the former, particularly under 30° impacts. These observations are discussed in terms of the thickness changes and the morphologies of the damaged surfaces, with the emphasis being put on the relative roles of growth of the oxide scales and removal of such scales (and the underlying coating) by the impacting particles.     

Emissions of gaseous pollutants,polychlorinated dibenzo-p-dioxins,and polychlorinated dibenzo-furans from medical waste combustion in a batch fluidized-bed incinerator

The quantities of pollutants emitted during the incineration of medical waste using a batch fluidized-bed system have not yet been well characterized. In this study, the CO, NO, and SO₂ in the gaseous emissions of a pilot scale vortexing fluidized-bed incinerator (VFBI) and the toxic polychlorinated dibenzo-p-dioxins and polychlorinated dibenzo-furans (PCDD/Fs) in the fly ash collected from the baghouse were examined. Four kinds of simulated medical wastes with different chlorine contents were used. The effects of the feeding interval, chlorine content, and the addition of calcium carbonate were experimentally evaluated. The results showed that increasing the feeding interval decreased the amount of all pollutants due to the decreased bed temperature and prolonged residence time in the incinerator. The addition of calcium carbonate decreased the emissions of the three gaseous pollutants; however, the concentrations of PCDD/Fs of the fly ash increased while calcium carbonate was added. The concentration of NO and SO₂ decreased while CO concentration increased with the increasing of chlorine content in the simulated medical waste. The magnitude of the effects of the operating parameters on the PCDD/F congeners formed followed the order: chlorine content > feeding interval > Ca/Cl ratio. Based on the experimental results, we extrapolate that the threshold value of the chlorine content was about 1% for PCDD/Fs generation. At a lower chlorine content, the PCDDs formation rate is higher than that at a higher chlorine content, especially for 1,2,3,4,6,7,8-HpCDD and OCDD. When the chlorine content exceeds the threshold value of 1%, the formation rate of PCDFs exceeds that of PCDDs.     

丙烯氨氧化合成丙烯腈流化床反应器的模型拟合

基于反应动力学实验结果,分析考察了丙烯氨氧化反应的动力学行为,提出了关于反应转化率与目的产物收率的幂函数形式的拟合模型,藉此对某厂丙烯腈工业流化床反应器的操作数据进行了关联,在考虑反应器中气－固流动影响的前提下,建立了丙烯腈反应器的下述宏观数学模型：反应转化率Ｘ＝０．８３２５ｕ－０．１０５８Ｒ－０．０１６４ＮＨ３Ｒ０．２５０９Ｏ２ｅｘｐ（－０．７４５９＋３５９．７９／Ｔ）丙烯腈单收ＹＡＮ＝０．０８９６ｕ０．０３４２Ｒ０．２３３３ＮＨ３（５．８２４５ｅｘｐＲ１．１３３７Ｏ２－Ｒ４．７４４５Ｏ２）ｅｘｐ（－２．０６５１＋５２２．９８／Ｔ）模型拟合的相对误差小于１０％．     

循环流化床技术在化工企业电站锅炉的应用

简要介绍了循环流化床燃烧技术,并结合抚顺石化洗涤剂化工厂锅炉改造后运行的实际情况,总结了循环流化床锅炉应用于现代化工企业的特点与优势,尤其是其掺烧三泥的特性,并通过与原有链条锅炉技术指标的比较,证明循环流化床锅炉确实更加适合现代化工企业发展的需要.     

Stability of pore-plated membranes for hydrogen production in fluidized-bed membrane reactors

Pd-based membranes prepared by pore-plating technique have been investigated for the first time under fluidization conditions. A palladium thickness around 20 μm was achieved onto an oxidized porous stainless steel support. The stability of the membranes has been assessed for more than 1300 h in gas separation mode (no catalyst) and other additional 200 h to continuous fluidization conditions. Permeances in the order of 5·10⁻⁷ mol s⁻¹ m⁻² Pa⁻¹ have been obtained for temperatures in a range between 375 and 500 °C. During fluidization, a small decrease in permeance is observed, as consequence of the increased external (bed-to-wall) mass transfer resistances. Moreover, water gas shift (WGS) reaction cases have been carried out in a fluidized bed membrane reactor. It has been confirmed that the selective H₂ separation through the membranes resulted in CO conversions beyond the thermodynamic equilibrium (of conventional systems), showing the benefits of membrane reactors in chemical conversions.     

Combined catalytic partial oxidation and CO2 reforming of methane over ZrO2-modified Ni/SiO2 catalysts using fluidized-bed reactor

Nickel on zirconium-modified silica was prepared and tested as a catalyst for reforming methane with CO₂ and O₂ in a fluidized-bed reactor. A conversion of CH₄ near thermodynamic equilibrium and low H₂/CO ratio (1<H₂/CO<2) were obtained without catalyst deactivation during 10 h, in a most energy efficient and safe manner. A weight loading of 5 wt% zirconium was found to be the optimum. The catalysts were characterized using X-ray diffraction (XRD), H₂-temperature reaction (H₂-TPR), CO₂-temperature desorption (CO₂-TPD) and transmission election microscope (TEM) techniques. Ni sintering was a major reason for the deactivation of pure Ni/SiO₂ catalysts, while Ni dispersed highly on a zirconium-promoted Ni/SiO₂ catalyst. The different kinds of surface Ni species formed on ZrO₂-promoted catalysts might be responsible for its high activity and good resistance to Ni sintering.     

Mechanism of fluidized chlorination reaction of Kenya natural rutile ore

In this paper, the thermodynamics and kinetics of nature rutile carbochlorination in a fluidized-bed were investigated. The thermodynamic calculations of TiO2–C–Cl2system show that when C is excess in the solid phase,titanium tetrachloride and carbon monoxide can exist stably. At high temperature, the reaction with CO as the product is the dominant reaction. The appropriate reaction conditions are as follows: reaction temperature of 950 °C,reaction time of 40 min, carbon ratio of 30 wt% of rutile,natural rutile particle size of-96 lm, petroleum coke size of-150 lm, and chlorine flow of 0.036 m3 h-1. Under the above conditions, the reaction conversion rate of TiO2 can reach about 95 %. This paper proposed a reaction rate model, and got a rutile chlorination rate formula, which is generally consistent with the experimental data. For the TiO2–C–Cl2system, the reaction rate is dependent on the initial radius of rutile particle, density, and the partial pressures of Cl2. From 900 to 1,000 °C, the apparent activation energy is 10.569 kJ mol-1, and the mass diffusion is found to be the main reaction-controlling step. The expression for the chlorine reaction rate in the C–Cl2system is obtained, and it depends on the degree of reaction,the partial pressure of Cl2, and the size of rutile particle.     

Fluidized-bed photocatalytic degradation of airborne styrene

Monomeric styrene, an aromatic compound present in many industries involved in the processing of fiberglass reinforced plastic products, is potentially carcinogenic. Based on current literature, studies on the breakdown of styrene via photocatalysis are limited. This study aims to develop suitable photocatalysts to be used in the mineralization of styrene. In particular, two specific objectives are of interest: first, the development of photocatalysts which are able to work under ultraviolet (UV) radiation and potentially visible/solar light irradiation; secondly, the design of an efficient fluidized-bed photoreactor. Preliminary work done using titania-based catalysts incorporated into a designed bench-scale UV photoreactor indicates that up to 80% of styrene can be degraded to water and carbon dioxide, based on an effective concentration (C₀) of 300 ppm.     

Transformation of arsenic in Yima coal during fluidized-bed pyrolysis

Arsenic is one of the most concerned trace elements in coal because of its toxicity and environmental persistence. Little information about the transformation behavior of arsenic under pyrolysis conditions was reported. In this paper, the volatilization behavior of arsenic and the influence of coexisting mineral matters and additive CaO were investigated during pyrolysis of Yima coal in a fluidized-bed reactor at temperatures ranging from 350 to 900 °C. The modes of occurrence of arsenic in Yima raw coal and its two char samples are determined using four methods including density fractionation, demineralization, X-ray diffraction (XRD) and sequential chemical extraction. It is found that arsenic in Yima coal is mainly associated with pyrite, and changes greatly during coal pyrolysis. Staged volatility behavior of arsenic is observed during Yima coal pyrolysis. From 350 to 500 °C, arsenic volatility increases with increasing temperature, while it changes little from 500 to 800 °C. Arsenic behavior in YimaD (demineralized sample of Yima) and CaO additive reveal that the vaporization of arsenic in Yima coal during pyrolysis is retarded by its coexisting mineral matters or added CaO to form thermally stable forms of arsenic. These forms might be generated through the formation of As-Ca complexes such as calcium arsenate, or through absorption and capture reactions with aluminosilicate mineral matters and trapped into their lattices.     

Evaporation of Distilled Water in a Fluidized Bed of Various Types of Fluidizing Particles Under Reduced Pressure

An objective of this study is to continuously obtain dispersed, dry, fine powders from a dilute suspension of heat-sensitive materials at a low temperature and high drying rate. A fluidized bed under reduced pressure was used in this study and, as a first step, only distilled water (without solid powders) was used as a sample. Drying characteristics were examined for various types of fluidizing particles. The diameter of fluidizing particle varied for inert particles (glass beads). Three kinds of hygroscopic porous particles (silica gel beads; 3A, 4B, and 5D) were also used as fluidizing particles. Under reduced pressures, the maximum drying rate was found to be higher than that at atmospheric pressure, while the bed temperature became lower with an increase in the maximum drying rate (i.e., drying at lower temperature with a higher drying rate is possible under reduced pressures. As diameter of the fluidizing particle was increased, the maximum drying rate became higher, although the amount of gas required for fluidization also increased. The maximum drying rates for silica gel beads were found to be almost equal to those of glass beads, with the exception of 3A silica gel beads (having a smaller pore diameter). The bed temperature was lower for silica gel beads compared to glass beads at the same maximum drying rate (i.e., silica gel beads (hygroscopic porous particles) are superior to glass beads (inert particles) with regard to drying at low temperatures at a high drying rate).