Formation and Growth Behavior Analysis of Slagging Rings in Rotary Kiln-Type Hazardous Waste Incineration Systems

Rotary kiln incineration technology has the advantages of strong material adaptability and a simple treatment process and has been widely used in hazardous waste treatment. However, the actual incineration process has caused problems such as ring formation in the treatment system due to the lack of research on the slagging mechanisms. In this paper, slagging phenomena occurring in the second half of the rotary kiln, the exit flue of the secondary combustion chamber, and the wall of the quench tower are analyzed and discussed in detail through characterization methods. The results indicate that the adhesion of low-melting alkali metal salts on the refractory surface in the second half of the rotary kiln is the key factor in forming the initial slagging layer. In the growth process of the slagging ring, the formed liquid phase can bond incineration residues of different sizes together and form a dense embryo body through liquid phase sintering. The deposition and solidification of molten/semi-molten fly ashes cause slagging formation in the exit flue of the secondary combustion chamber. The slagging phenomenon occurring in the inner wall of the quench tower belongs to the “crystalline-coalesce-hardening” process of the inorganic salts precipitating out of the high-salt wastewater.

Thermodynamic Refractory Corrosion Model for Ferronickel Manufacturing

A thermodynamic model, based on SimuSage, was developed to simulate refractory corrosion between a magnesia-based refractory material and ferronickel (FeNi) slags. The model considers a theoretical cross-section of a refractory material to simulate a ferronickel smelter application. The current model is structured into 10 zones, which characterize different sectors in the brick (hot to cold side) perpendicular to the refractory surface with an underlying temperature gradient. In each zone, the model calculates the equilibrium between the slag and a specified amount of refractory material. The emerging liquid phases are transferred to subsequent zones. Meanwhile, all solids remain in the calculated zone. This computational process repeats until a steady state is reached in each zone. The simulation results show that when FeNi slag infiltrates into the refractory material, the melt dissolves the magnesia-based refractory and forms silicates (Mg,Fe,Ca)2SiO4 and Al spinel ((Mg,Fe)Al2O4). Furthermore, it was observed that iron oxide from the slag reacts with the refractory and generates magnesiowustite (Mg,Fe)O. Practical lab-scale tests and scanning electron microscopy (SEM)/Energy Dispersive X-ray Spectroscopy (EDS) characterization confirmed the formation of these minerals. Finally, the refractory corrosion model (RCM) ultimately provides a pathway for improving refractory lifetimes and performance.

COMBUSTION RESEARCH OF IMPINGING GAS JETS AT STABILIZATION OF THE FLAME FRONT ON A VERTICAL SURFACE

The conditions of stabilization of combustion of detached gas jets on the vertical surface of the range of nozzle diameters d0 = 1.6–3.0 mm are investigated. The mechanism of flame stabilization of a detached gas jet on a vertical surface is shown, which allows to increase the gas flow rate through one nozzle by 3 or more times with stable combustion, compared to diffusion combustion of a free gas jet, which is not stabilized. The optimal distance to the vertical refractory surface in the nozzle calibers for the creation of slot bottom burner devices has been established. The necessity of using the minimum angles of attack till failure of combustion, which were experimentally founded, for the construction of slot bottom burner devices, is substantiated. It is experimentally established that starting from the gas pressure in the collector-pipe near 500 mmwg and, accordingly, the speed of its flow through the nozzle is more than near 100 m/s at a distance to the vertical surface on which the flame is stabilized 15 < L/d0 <= 30, for the range of nozzle diameters d0 = 1.6–3.0 mm, dimensionless area base sg/s0 of the elliptical cylinder Eb, less than 2–2.5 times of the maximum observed at a distance L/d0 near 40. Bibl. 15, Fig. 6.

Surface activity of humic substances depending on their origin

Humic substances are a general category of naturally occurring, biogenic, heterogeneousorganic substances that can be characterised as being yellow to black in colour, of highmolecular weight and refractory. Surface tension measurement defined humic substances assurface active substances. Unless micellar structural model of humic substances has beensuggested, in the same time there are only a few studies about the factors that affect thesurface activity of humic solutions. The objective of this study was to study changes insurface activity depending on the origin and properties of humic substances.The surface tension-pH curves of humic substances featured a minimum for all solutions,declining steeply from higher and lower pH values. The decrease in surface tension withdecreasing pH reflects the gradual neutralization of acidic sites, which created amphiphilicspecies that migrated to the surface. Surface tension of solutions of humic substancesdecreased with increasing concentration, as well as in presence of metal salts. Manyindustrially produced humic materials demonstrated no or insignificant impact on surfacetension of their solutions, but humic substances isolated from natural environments (water,soil, peat, sediments) demonstrated significant impact of surface tension of their solutions.Thus there exist direct links between origin, structure of humic substances and their ability toinfluence surface tension of aquatic solutions.

The periclase-chromite refractory decomposition by the action of the pulverized coal and gas medium in course of copper-sulfide raw materials processing

The investigating results are given for the periclase-chromite refractories' composition and structure which are in contact with the pulverized coal and gas medium in the coppersulfide smelting furnaces. The high-temperature burnt copper concentrate and the sulfur dioxide gas suspensions combined action changes the surface and deep refractories layers chemical composition, with that the impurities content reach the value in weight percent: Fe 54,0, Cu 7,2, Zn 6,4, S 1,8. The refractory's surface layer saturation with the iron and non-ferrous metals oxides decreases the porosity and gives rise to low-melting compositions and eutectics. The refractory decomposition is induced by the shelling of the refractory surface layers with the filled porous taking place in course of the heating-cooling cycling because of the phase's thermal linear expansion coefficients. When the spent refractory disposal, it is feasible to separate mechanically the surface layer for the non-ferrous metals extracting, the rest part can be used for obtaining the refractory powder of various purpose.

Infiltration Velocity and Thickness of Flowing Slag Film on Porous Refractory of Slagging Gasifiers

Two analytical formulations that describe the fluid interactions of slag with the porous refractory linings of gasification reactors have been derived. The first formulation considers the infiltration velocity of molten slag into the porous microstructure of the refractory material that possesses an inherent temperature gradient in the direction of infiltration. Capillary pressures are assumed to be the primary driving force for the infiltration. Considering that the geometry of the pores provides a substantially shorter length scale in the radial direction as compared with the penetration direction, a lubrication approximation was employed to simplify the equation of motion. The assumption of a fully developed flow in the pores is justified based on the extremely small Reynolds numbers of the infiltration slag flow. The second formulation describes the thickness of the slag film that flows down the perimeter of the refractory lining. The thickness of the film was approximated by equating the volumetric slag production rate of the gasification reactor to the integration of the velocity profile with respect to the lateral flow cross-sectional area of the film. These two models demonstrate that both the infiltration velocity into the refractory and the thickness of the film that forms at the refractory surface were sensitive to the viscosity of the fluid slag. The slag thickness model has been applied to predict film thicknesses in a generic slagging gasifier with assumed axial temperature distributions, using slag viscosity from the literature, both for the case of a constant slag volumetric flow rate down the gasifier wall, and for the case of a constant flyash flux distributed uniformly over the entire gasifier wall.

Laboratory Study of Corrosion of an Alumina Refractory by Molten Potassium Salts

The increasing use of biomass and waste derived fuels in combustion challenges the chemical durability of refractories. Durability of an alumina refractory was studied in a chemically aggressive environment. A mixture of potassium chloride and carbonate (molar ratio 1:9) was placed on the sample and heated at 700-1000°C in an electric laboratory furnace in air for one week. Cross-sections of the samples were studied by SEM-EDXA to determine penetration of potassium in the refractory. Potassium was found only in the silicate matrix phase of the alumina refractory. Penetration of potassium decreased steeply from the surface to 1 mm, after which the decrease was linear but varied with temperature. At 700 and 800°C the thickness of the matrix layer that had reacted with potassium was 3 mm, while the layer was thinner at 900 and 1000°C. At the higher temperatures a glassy layer consisting of K2O, Na2O, CaO and SiO2 formed on the refractory surface. At 900°C the thickness of the surface layer was of 10μm, while a 200μm layer was measured at 1000°C. The procedure used in this work can be used to develop a laboratory scale method to be used to study corrosion of refractories in biomass combustion devices.

The Influence of Oxygen Injection Configuration in the Performance of an Aluminum Melting Furnace

In the present work, a numerical simulation of the 100% oxy-firing combustion process inside an industrial Aluminum Remelting Reverb Furnace is presented. A staged combustion oxy-fuel burner is being simulated. The natural gas and oxygen were injected toward the aluminum bath, which was considered as an isotherm wall at melt temperature. Two types of burners are compared. For the first case, the oxygen and natural gas jets at the burner exit are parallel to each other, while for the second burner, a divergent oxygen jet is employed. The furnace heat loss to the ambient is neglected since it is small in relation to the heat liberated by the combustion process. The k-ε model of turbulence was selected to represent the turbulent flow field. The combustion process was determined based on the Arrhenius and Magnussen Laws, and the discrete transfer radiation model was employed to predict the radiation heat transfer. The numerical procedure was based on the Finite Volume Method. This numerical model is utilized to determine the flame pattern, species concentration distribution, and the velocity field. The temperature distribution is very useful in the evaluation of the furnace performance. Further, critical regions associated with high temperature spots at the refractory surface were discovered. The effect of the divergent jet in the heat flux distribution at the aluminum bath is also investigated.