Corrosion-resistant Refractory Linings for Hazardous Waste Treatment in Rotary Kilns

With the rapid development of modern society, hazardous wastes are increasing rapidly. According to recent studies, plasma gasification technology is currently considered the best solution for treating such waste under proper regulatory frameworks, offering advantages such as minimal residue and energy recovery. This paper focuses on a combined rotary kiln and plasma gasifier for hazardous waste. Based on Ansys Fluent software for numerical simulation of the input material. Analysis of the equal-diameter rotary kiln, the variable-diameter rotary kiln, and the conical rotary kiln found that the conical rotary kiln demonstrated superior efficiency compared to the equal-diameter rotary kiln. Using CFD simulation technology, the rotary kiln with different diameters was analyzed in terms of the temperature field and concentration field in this numerical simulation study to compare and analyze the product components (CO, CO2, H2O, H2) distribution. The analysis of the temperature field and concentration field demonstrates that the conical rotary kiln achieves a more rational distribution of product concentrations.

Hazardous waste output in the world is increasing every year. To achieve higher efficiency and lower pollution, the incineration technology for hazardous waste needs to be studied further. This study mainly reviews the research progress in incineration, slagging, and pollutant emission in the rotary kiln in China and abroad in the last 10 years, and conducts a comprehensive analysis and evaluation of the research. Considering that there are many variables involved in the incineration process, the incineration law cannot be validated in a limited timeframe by experiments. Researchers often use computer simulations to predict and verify the incineration process through experiments and to provide reference opinions for commercial operations. Through the analysis of the research progress in rotary kilns, it is observed that the basic research in rotary kilns is becoming mature. The latest research trend in rotary kilns is interdisciplinary and mixed research. From a new perspective, further research should be focused on a comparative analysis of the rotary kiln and the cement kiln, full life cycle assessment of the impact factors of rotary kiln on the environment, the impact of the factory treatment process on the workers’ health, etc. The research direction of rotary kiln in China and abroad for the future has been predicted reasonably.

Digital twin model for solid waste treatment in rotary kiln

More than 50 million tons per year of zinc-bearing dust with large amounts of zinc and iron resources is produced by iron and steel smelting in China, which is classified as hazardous solid waste. The zinc-bearing dust is an important secondary resource, in which the zinc and iron can be recycled as raw materials for the iron and zinc industries after separating them. Rotary kiln reduction is one of the main methods for separating zinc and iron from zinc-bearing dust. In this study, the 5 mm composite pellets containing zinc-bearing dust is prepared by forced disturbed pelleting as reduction charge. The rotary kiln system with controllable temperature field and atmosphere field by multi-point quantitative air suppling is used as the main equipment of reduction. This technology can realize the treatment of raw materials with high iron and zinc content in rotary kiln, but also can effectively improve the production efficiency and the quality of zinc oxide powder, reduce the kiln-ringing. Compared with the conventional rotary kiln method, the processing capacity of zinc-bearing dust increase by 30%. The zinc removal ratio reaches 95% and the ZnO content of zinc oxide powder is 53.93 wt.%. The TFe content and ZnO content of reduction product are 60.56 wt.% and 0.25%, respectively. The annual operation ratio of zinc-iron separation by rotary kiln with zinc-bearing dust is 92%. The metallization rate of reduction product is controllable. The reduction product with metallization rate of 65.97% can be used as a sintering raw material, and the comprehensive energy consumption is 187kgce/t. The reduction product with metallization rate of 88% can 1 be used as a converter steelmaking raw material, and the comprehensive energy consumption is 253.1kgce/t.

1 - The Rotary Kiln Evolution and Phenomenon

Development of refractory materials for the high-temperature zone of the rotary kilns used in the cement industry that is the second-largest user of refractory materials is given in the article. It is shown that the history of refractory materials used in this rotary kiln high-temperature zone commenced with alumina-silicate materials and ended with specially developed periclase-based materials used currently. Advantages and drawbacks of these materials are considered. Basic information is provided about the manufacture of cement for consideration of possible chemical reactions between cement kiln raw material and refractory material components.

Rotary kiln is a kind of large scale sintering device widely used in metallurgical, cement, refractory materials, chemical and environment protection industries. Its complicated working mechanism includes physical change and chemical reaction of material, procedure of combustion, thermal transmission among gaseous fluid, solid material fluid and the liner. The automation problem of such processes remains unsolved because of the following inherent complexities. A rotary kiln is a typical distributed parameter system with correlative temperature distribution of gaseous phase and solid phase along its axis direction. Limited by device rotation and technical design, sensors and actuators can be installed only at the kiln head and kiln tail, and lumped parameter control strategies are employed to deal with distributed parameter problems. Thus the rotary kiln process is a multivariable nonlinear system with strong coupling, large lag and uncertain disturbances. Moreover, the key controlled variable of burning zone temperature is measured with serious disturbances. Most of rotary kilns are still under manual control with human operator observing the burning status. As a result, the product quality is hard to be kept consistent and energy consumption remains high, kiln liner is easy to wear out, the kiln running rate and yield is low. Although several advanced control strategies including fuzzy control (Holmblad & Ostergaard, 1995) , intelligent control (Jarvensivu et al., 2001a; Jarvensivu et al., 2001b) and predictive control (Zanovello & Budman, 1999) have been introduced into process control of rotary kiln, all these researches focused on stabilizing some key controlled variables but are valid only for cases that boundary conditions do not change frequently. As a matter of fact, the boundary conditions of a rotary kiln often change. For example, the material load, water content and components of the raw material slurry vary frequently and severely. Moreover, the offline analysis data of components of raw material slurry reach the operator with large time delay. Thus conventional control strategy cannot reach automatic control and keep the product quality consistent. To deal with the complexity of operation conditions, the authors have proposed an intelligent control system based on human-machine interaction for an alumina rotary kiln in (Zhou et al., 2004; Zhou et al., 2006), in which human intervention function was design so that, if the operation condition changed largely, the human operator observing burning status can intervene the control actions when the system is in the automatic control mode to enhance the adaptability of the control system. Source: Reinforcement Learning: Theory and Applications, Book edited by Cornelius Weber, Mark Elshaw and Norbert Michael Mayer ISBN 978-3-902613-14-1, pp.424, January 2008, I-Tech Education and Publishing, Vienna, Austria O pe n A cc es s D at ab as e w w w .ite ch on lin e. co m

Numerical investigation of the impact of coating layers on RDF combustion and clinker properties in rotary cement kilns

Thermal co-treatment of combustible hazardous waste and waste incineration fly ash in a rotary kiln

Rotary kilns are central equipment in material processing operations such as oxide ore reduction, clinker manufacturing, and hazardous waste incineration. This work focuses on an industrial-scale rotary kiln for Ferronickel production via the Rotary Kiln-Electric Furnace (RKEF) process. Rotary kilns are prone to mechanical failure exacerbated by thermal effects, mainly during transient operation, such as preheating and cooling. However, few studies have tackled the impact of the transient operation on the stress state in the rotary kiln wall. Therefore, we evaluate the thermal and mechanical behavior of the rotary kiln wall during preheating. Actual operation data and a thermal model enable to obtain the temperature distribution along the kiln length. This temperature distribution is the starting point for calculating the stress state of the shell and refractory. The maximal thermal gradient occurs at 10 m from the hot end, with temperatures at the outer and inner surfaces of 200 °C and 820 °C, respectively. The von Mises stress shows a maximum of 121 MPa at the wheel position in the hot region of the refractory and a range of 30–60 MPa in the shell. In addition, the compressive stress is higher than the ultimate compressive strength of the refractory. However, it does not necessarily represent refractory detachment due to the plastic deformation undergone by the refractory under high temperatures. This work paves the way towards developing a tool for accurately predicting rotary kiln mechanical failure, which can help optimize operating conditions and assist in programming maintenance.

Chemical waste salt is a hazardous waste generated during chemical production, and it is crucial to complete the recycling of the waste salt in a practical way. In the case of waste salt recycling by rotary kiln pyrolysis carbonization, ringing affects the pyrolysis efficiency and process running, thus a study on waste salt ringing was conducted. The results showed that the particle size is the key to the ring formation in rotary kiln, and pyrolysis temperature, pyrolysis time and temperature distribution in the rotary kiln also affect the material discharge rate during pyrolysis of waste salt in the rotary kiln. Thermogravimetric analysis and SEM images revealed that the volatilization of organic matter in the material due to pyrolysis caused a decrease in the abrasion resistance of the waste salt particle, which was the factor behind the ringing during pyrolysis in the rotary kiln. This study may provide a reference for the implementation of similar waste salt pyrolysis carbonization processes.

Rotary kiln has been widely used in hazardous waste treatment because of its strong adaptability to raw materials, high productivity, and simple processing technology. However, the formation of deposits reduces its performance period and profitability. This study characterized the deposit mineralogy and thermodynamically and experimentally investigated its formation mechanism. The results show that the main phases of the deposit are magnetite, monolithic iron, olivine, and yellow feldspar. They indicate that the deposit formation process was accompanied by the participation of alkaline and iron oxides. The intermediate product Ca2SiO4 can promote the generation of low melting point phases, such as CaFeSiO4 and Ca2Al2SiO7, which are the main phases of deposit materials. Additionally, the reduction intermediate product FeO facilitated the generation of a liquid ferrous mixture (Fe3O4-FeO and Fe3O4-FeO-Fe mixture), which in turn further promoted the growth of the initial deposit phase. The solid deposit formed and attached to the kiln inner wall, along with a decrease in temperature. These results are expected to provide an idea or approach for fundamentally solving the problem of deposits in the rotary kiln.

The treatment of numerous hazardous wastes like filter residues, dusts, metal scrap or heavily polluted waste water takes place at elevated temperatures. In current technologies the energy demand is delivered by the energetic content of the wastes, fossil fuels or electricity. Especially, at high concentration of inorganic components many hazardous wastes do not have a sufficient calorific value to cover the heat demand of the high temperature processes. The use of concentrated solar radiation for heat supply to the waste treatment would allow to substitute fossil fuels and to reduce the exhaust gas flow. Basing on the theoretical results of design studies of a solar waste treatment process a mini-plant rotary kiln was constructed for the solar furnace in Cologne. The applicability of the rotary kiln mini-plant was verified by melting experiments. Also process simulations of exhaust gas cleaning plants are carried out for different layouts for selected waste materials in technical scale.

The motion of input material in a rotary kiln is an important aspect of its operation. This can be observed especially in the case of the implementation of the hazardous waste incineration process in this device. The values of the flow parameters, mainly the residence time and the degree of mixing, can determine the proper and safe treatment of waste. The relationships that occur in the layer of solid material in a rotary kiln have not been completely recognized. This article presents a research method that involves an experiment on a laboratory stand simulating a rotary kiln in association with a dedicated algorithm. Multi-criteria tests were carried out. The adopted research method was the tracer method. It used a tracer which, subject to the same transport conditions as other material particles, provided information on the characteristic of the motion of tested materials in the rotating cylinder. The application based on the residence time distribution (RTD) algorithm returned information about the characteristics of the motion of the material in the rotary cylinder in terms of residence time distribution and the degree of mixing. This tracer method, together with stimulus impulses on the grate and a dedicated RTD algorithm, was used here as a sensor method to examine the characteristics of material motion on various grate systems. The data obtained as a result of this research may include, among others, the boundary conditions for numerical simulations of processes carried out in a rotary kiln.

Erosion behaviour of rotary kiln refractory and its effects on ringing during steel-rolling oily sludge incineration