Inhibition characteristics of coal dust explosion at the gasification atmosphere

The risk of coal dust explosion threatens the safety of coal gasification process. To reveal the inhibition of carrageenan dry-water material (CDM) on coal dust explosion, a 20 L spherical explosive device was adopted to compare with SiO₂ and NH₄H₂PO₄ at the atmosphere of coal gasification. The thermal decomposition behavior and chemical structures of the explosion residues were characterized by synchronous thermal analyzer, X-ray photoelectron spectroscopy and FTIR. The results indicate that the CDM showed the optimal inhibiting effect on 300 mesh and the maximum explosion pressure of anthracite coal dust was reduced to 0.02 MPa with the percentage of 97.53%. At the same concentration, the inhibiting effect of CDM on the coal dust explosion was better than that of SiO₂ and weaker than that of NH₄H₂PO₄. Through the residues analysis, the CDM mainly prevented the volatilization of C-H and consumption of oxygen-containing groups and sulfur-containing groups contributing to the inhibition of coal dust explosion.     

煤气化配套空分设备流程的选择

结合煤气化工艺,详细分析了化肥工业、合成甲醇项目、多联产及合成油项目和IGCC发电项目等煤气化装置对空分设备的要求和流程选择,得出了各个项目适用的大型空分设备流程。     

Modeling and simulation of coal gasification on an entrained flow coal gasifier

In this paper, the recent researches and developments on coal gasification modeling and simulation are described. Numerical models for the three chemical processes such as devolatilization, char gasification, and gas-phase reaction are reviewed and discussed for further development to improve accuracy. Recently the devolatilization models to describe the coal chemical structure with a simple expression have been proposed and validated on the laboratory-scale flames. It is essential to precisely model char gasification reaction as a rate-determining step and the formulation of the active sites sharing by the mixture and the pore structure formation are important in the modeling. It will become significant to take the elementary reactions into account in the gas phase reaction model. Large-eddy simulation of coal gasification on the laboratory-scale entrained flow gasifier is performed to demonstrate the numerical procedure. Results show the predicted temperature distribution qualitatively agrees with the experiment. Moreover, the gas-liquid-solid three-phase reacting flow simulation is preliminarily performed to capture the molten slag flow behavior within the gasifier. It is revealed that the three-phase simulation can give insight into the complex multiphase and multiphysics phenomena taking place within the gasifier to assess the design and the operating condition.     

Effect of physicochemical properties of coal gasification fine ash on its wettability

Coal gasification, recognized as one of the most effective coal utilization technologies, will produce a certain amount of fine ash during the high-temperature reaction process. The wettability of gasification fine ash is a critical parameter to characterize the degree of high-temperature reaction and determine the separation efficiency of purification process. In the present work, the effect of physicochemical properties on the wetting behavior of different gasification fine ash is studied. The difference in wettability between particle size and types can be explained by the unique properties of particles (i.e. pore structure, mineral composition, and chemical structure). The results show that with the decrease in particle size, the surface morphology transforms from an irregular shape with a rough surface to a spherical shape with a smooth surface. The pore structure, characterized by fractal surface dimension D_s, presents positive correlations with the contact angle for a single type of fine ash. The mineral composition can just qualitatively assess the hydrophilicity of particles. Only the ratio of hydrophilic chemical structure can be used as a generic parameter to describe the wetting performance. Meanwhile, the wettability of hydrophilic particles can be enhanced by increasing moisture content, but there is no significant effect of moisture content on the wettability of hydrophobic particles.     

Evaluation of engineering properties for the use of leached brown coal ash in soil covers

The need to engineer cover systems for the successful rehabilitation or remediation of a wide variety of solid wastes is increasing. Some common applications include landfills, hazardous waste repositories, or mine tailings dams and waste rock/overburden dumps. The brown coal industry of the Latrobe Valley region of Victoria, Australia, produces significant quantities of coal ash and overburden annually. There are some site-specific acid mine drainage (AMD) issues associated with overburden material. This needs to be addressed both during the operational phase of a project and during rehabilitation. An innovative approach was taken to investigate the potential to use leached brown coal ash in engineered soil covers on this overburden dump. The basis for this is two-fold: first, the ash has favourable physical characteristics for use in cover systems (such as high storage capacity/porosity, moderately low permeability, and an ability to act as a capillary break layer generating minimal leachate or seepage); and second, the leachate from the ash is mildly alkaline (which can help to mitigate and reduce the risk of AMD). This paper will review the engineering issues involved in using leached brown coal ash in designing soil covers for potentially acid-forming overburden dumps. It presents the results of laboratory work investigating the technical feasibility of using leached brown coal ash in engineered solid waste cover systems.     

A statistical approach for the assessment of reliability in ceramic materials from ultrasonic velocity measurement: Cumulative Flaw Length Theory

A primary objective of statistical fracture approach is to predict the probability of failure of a component for an arbitrary stress state when the failure statistics are known. This study introduces the fundamentals and application of a new approach to characterize the mechanical behaviour of high temperature ceramic materials, including refractory materials, by coupling non-destructive methods, in particular ultrasonic velocity measurement, and the Batdorf statistical fracture theory. A new approach, termed Cumulative Flaw Length Theory (CFLT), has been developed for the case of macroscopically homogeneous isotropic materials containing randomly oriented microcracks uniformly distributed in a location subjected to non-uniform multiaxial stresses. A function representing the number of cracks per unit volume is estimated based on the histograms of ultrasonic velocity measurements. This function is used without additional assumptions to determine the probability of fracture under an arbitrary stress condition. Two different cordierite-mullite high temperature ceramic materials were characterized under the assumptions of this theory to provide experimental evidence to support the model.     

High temperature technology

An attempt has been made to outline the areas where progress in various aspects of high temperature technology would produce significant industrial advantages. The aspects covered range from the possibilities of using the heat lost by conventional industries through to areas of newer technologies, such as fusion reactors and magnetohydrodynamic power generation, where a breakthrough in high temperature technology would encourage their useas viable commercial systems. The advantages of increased temperatures for greater efficiencies and the possibilities of using lower grade or alternate fuels are discussed together with the problems posed both in materials terms and in terms of the technical limitations of process control.     

Science and technology of polymeric ablative materials for thermal protection systems and propulsion devices: A review

Ablative materials are at the base of entire aerospace industry; these sacrificial materials are used to manage the heat shielding of propulsion devices (such as liquid and Solid Rocket Motors (SRMs)) or to protect vehicles and probes during the hypersonic flight through a planetary atmosphere. Accordingly they are also known as Thermal Protection System (TPS) materials. Some non-polymeric materials have been successfully used as ablatives; however, due to their versatility, Polymeric Ablatives (PAs) represent the widest family of sacrificial TPS materials. In fact, when compared to non-polymeric ablatives such as high melting point metals, inorganic polymers (or metal oxides or carbides), PAs have some intrinsic advantages such as: tunable density, lower cost, and higher heat shock resistance. This review covers all main topics related to the science and technology of ablative materials with current and potential applications in the aerospace industry. After a short, yet comprehensive, introduction on non-ablative materials, this review paper summarizes fifty years of research efforts on polymeric ablatives, starting from the state of the art solutions currently used as TPS, up to covering the most recent efforts for nanostructuring their formulations.     

Evaluation of the separation performance of an air dense medium gas-solid fluidized bed for coal cleaning: Effect of the binary dense media

The binary dense media plays a significant role in the air dense medium gas–solid fluidized bed for coal separation. Magnetite powder with a narrow size fraction of ?0.20?+?0.15?mm and ?0.35?+?0.25?mm quartz sand were mixed in proportion to form a binary dense media. The separation performance of ?13?+?6?mm coal was evaluated through the combination of various indicators of the yield and ash content of products, combustible material recovery, relative segregation degree, and probable error. Results suggested that the optimal separation performance was achieved by an adjustment of the appropriate operational gas velocities of the bed and use of the binary dense media with a suitable composition as the separating medium. The proportion of the quartz sand mixed in the binary dense media should be adjusted as 10% or 20% and the fluidization number could be varied from 1.6 to 1.8. The satisfactory ash content and yield of clean coal were 10.12% and 68.29%, respectively, with a combustible material recovery of 92.09%. The largest relative segregation degree was 0.95, and the minimum probable error was 0.085?g/cm³ with a standard deviation of 0.024?g/cm³. These findings indicated efficient coal cleaning.     

Surface Preparation of Aluminum Nitride for Metallization: Effect of Temperature on Surface Reactivity

The current aqueous cleaning step in the surface preparation of aluminum nitride (AlN) prior to metallization causes performance and reliability issues for the substrates used for microelectronic packaging due to surface reactions. These issues limit the use of AlN and its replacing of BeO, an environmentally hazardous material currently used. The aim of this investigation was to determine the effects of different solutions on the surface of AlN substrates under varying conditions at times up to 2419.2 ks (28 days). Concentration of the solutions, temperature, and immersion time were varied for the AlN samples in the solutions. Both elevated temperatures (50°C and 90°C) and low temperatures (5°C) were investigated.

Four general types of behavior were observed: minor changes in average surface roughness and microstructure, linear change in average surface roughness and pitted grains, nonlinear change in average surface roughness and product formation on AlN surface, and miscellaneous change in average surface roughness with surface product formation.

The surface roughening kinetics were very complex due to changes in both the reaction product morphology and reaction mechanism with temperature, solvent, and pH for a specific solvent. Minor changes in average surface roughness and microstructure were observed for HCl pH = 5, H₂ SO₄ pH = 5, NaOH pH = 8, NaOH pH = 10, NaOH pH = 12, deionized water and Alfred tap water at 5°C, HCl pH = 3 and oleic acid at 50°C and citric acid and oleic acid at 90°C. Linear changes in average surface roughness and pitted grains were observed for HCl pH = 2 and H₂SO₄ pH = 3 at 50°C and HCl pH = 2, H₂SO₄ pH = 3, and deionized water at 90°C. Non-linear change in average surface roughness and product formation on AlN surface was observed for HCl pH = 5, NaOH pH = 8 and Alfred tap water at 50°C and HCl pH = 5 and H₂SO₄ pH = 2 at 90°C. Miscellaneous changes in average surface roughness with surface product formation were observed for H₂SO₄ pH = 2, H₂SO₄ pH = 5, NaOH pH = 10, NaOH pH = 12, citric acid, Micro-90 and deionized water at 50°C and HCl pH = 3, H₂SO₄ pH = 5, NaOH pH = 8, NaOH pH = 10, NaOH pH = 12, Micro-90 and Alfred tap water at 90°C.