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Influence of heating and cooling rate on the stress state of the brick lining in a rotary kiln using finite element simulations
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.ORCID iD: 0000-0002-2825-8543
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.ORCID iD: 0000-0002-3907-0802
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.ORCID iD: 0000-0003-0910-7990
2019 (English)In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 105, p. 98-109Article in journal (Refereed) Published
Abstract [en]

Rotary kilns for iron-ore pellets production are highly dependent on a well-functioned refractory brick lining. To improve the long-term capability of the lining, in-situ observations of the bricks' performance are desired, however, the harsh environment inside the rotary kiln makes it difficult or nearly impossible to study the lining during operation. By using numerical simulations as a tool, some of the problems encountered by the brick lining can be studied without limitation of the extreme conditions.

In this work, stress state of the lining was studied under the influence of different heating and cooling rates, and different brick compaction cases. A finite element model was created for conducting the numerical simulations. The numerical model was calibrated for transient heat transfer. Temperature dependent material properties of the bricks and casing were used as input. The heating and cooling was controlled by temperature prescription on the boundary of the brick lining, while brick lining compaction by defining relative position of the bricks in axial and radial directions.

The conducted numerical simulations showed that considerable tensile stress may appear in a large area of the brick during initial heating stage. The large tensile area corresponds well with the typical circumferential cracks experienced by the bricks. It was demonstrated that the compressive stresses counteract the development of tensile stresses. However, the compressive stresses may become very large in the initial stage of heating. The positive effect of lower heating rate was considerable on the tensile stresses, while influence on the compressive stresses was almost unnoticed. The hypothetical cooling rates showed that very high tensile stresses may occur on the surface of the bricks, potentially leading to surface spalling. Furthermore, it was demonstrated that axial compaction is highly important on the stress development in the lining, which, may not always be followed in practice. As a general conclusion, it is recommended to always achieve a tight compaction of the brick lining and to take measures for lowering the heating and cooling rates.

The conducted work exemplifies behaviour of the brick lining for realistic heat transfer and material properties. The insight into the behaviour gives possibilities to make adjustments and directed investments for lowering risk of brick lining failure.

Place, publisher, year, edition, pages
Elsevier, 2019. Vol. 105, p. 98-109
Keywords [en]
High temperature, Stress state, Refractory brick lining, Rotary kiln, Finite element method
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-68375DOI: 10.1016/j.engfailanal.2019.06.031ISI: 000496188200009OAI: oai:DiVA.org:ltu-68375DiVA, id: diva2:1198125
Note

Validerad;2019;Nivå 2;2019-07-08 (johcin)

Available from: 2018-04-16 Created: 2018-04-16 Last updated: 2019-11-29Bibliographically approved
In thesis
1. An Approach for Evaluation of Brick Lining's Mechanical State in Rotary Kilns
Open this publication in new window or tab >>An Approach for Evaluation of Brick Lining's Mechanical State in Rotary Kilns
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Utvärdering av tegelinfodringensmekaniska tillstånd i roterugnar
Abstract [en]

Production of many materials requires treatment at elevated temperatures. Calcination and sintering are some of the important heat treatment procedures which are typically performed in so-called rotary kilns. These, not very well-known treatment vessels, have a significant impact on our everyday life. Our most common materials have direct con-nection to the use of rotary kilns. Concrete−covering the vast 80 wt% of total material production in the world−consists to a large part of cement produced in a rotary kiln. Steel−by far the most produced metal−frequently starts its journey in a rotary kiln in form of iron-ore pellets. Paper−another everyday life product−is dependent on mineral lime that is typically calcinated in a rotary kiln. The importance of rotary kilns in our society cannot be doubted.

The concept of a rotary kiln is rather simple. It consists of a thick cylinder-formed steel casing that, due to high process temperatures, is insulated by a refractory lining. Service conditions inside the rotary kiln are rough and the refractory lining is continuously degrading, especially pronounced in the hot zone of the rotary kiln. If the lining is significantly deteriorated and can no longer protect the casing from the heat−the production is shut-down−leading to very high production losses.

Despite many improvements of rotary kilns in the past decades, there is still a gap in the knowledge regarding refractory linings during usage. Many assumptions are based on practical knowledge. One explanation to this could be the difficulty to study and observe the lining due to the large sizes of rotary kilns and high operating temperatures. Today, computers are of a great help for studying various issues without causing production delays or risking failures. However, the field of rotary kilns has stagnated on this matter and little documentation can be found regarding numerical simulations of the refractory lining for rotary kilns, especially of the thermomechanical character.

The aim of this thesis work was to create a numerical model of a rotary kiln usedin iron-ore pelletizing for studying the mechanical and thermomechanical behaviour of refractory brick lining. For this, a simplified finite element model (FEM) of a rotary kiln was created and its trustworthiness verified. It was confirmed that the model gives agood response. Different tips and justifications in the creation of the model of the rotary kiln are given. Furthermore, some mechanical material tests were performed for data input into the model. Various fundamental cases were studied in cold and hot states of the rotary kiln. It was shown that critical situations affecting the brick lining could be captured in a satisfactory way. The insight into the behaviour of the brick lining with respect to various parameters opens possibilities for lowering risk of brick lining failure by an improved management of the rotary kiln.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2018
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Mechanical Engineering Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-68376 (URN)978-91-7790-112-9 (ISBN)978-91-7790-113-6 (ISBN)
Public defence
2018-06-13, E632, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2018-04-17 Created: 2018-04-16 Last updated: 2018-06-08Bibliographically approved

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Ramanenka, DmitrijGustafsson, GustafJonsén, Pär

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