Rotary kiln design is a complex process, with a variety of factors and material characteristics influencing the sizing and design. This presentation gives an overview of the sizing and design process, including the many factors that will need to be considered during the design stage.

Rotary Kiln Sizing Design

1. Sizing & Design Experts in process design and material processing for over 65 years. Rotary Kiln
Rotary kilns are an advanced thermal processing tool used to cause a chemical reaction or physical change in a solid material through the application of high temperatures.
Rotary kilns are engineered around the unique characteristics of the material to be processed.
Rotary kilns are engineered around the unique characteristics of the material to be processed. And while the process of sizing and designing a custom rotary kiln is not one easily explained in brief, this presentation offers an introduction to the basics of the sizing and design process.

Material Characteristics that Influence Design

Every material behaves differently in a rotary kiln. Many characteristics will influence how the material will respond, requiring a thorough thermal and chemical analysis before processing can begin.
Every material behaves differently in a rotary kiln. Many characteristics will influence how the material will respond, requiring a thorough thermal and chemical analysis before processing can begin. This will aid in determining how the kiln will need to be engineered around those characteristics in order to produce the desired results.

Particle Size Distribution & Bulk Density The particle size distribution and bulk density of a material can influence some of the physical and mechanical aspects of a kiln.

Particle Size Distribution & Bulk Density The particle size distribution and bulk density of a material can influence some of the physical and mechanical aspects of a kiln. A material with a high bulk density, for example, will likely require more horsepower, and subsequently a more robust drive system.

If the material to be processed is in the form of pellets, or has a larger particle size distribution (as opposed to fines), the kiln diameter can be smaller, because a higher air velocity can be utilized.

Abrasiveness & Corrosiveness A material that is corrosive or abrasive may not have a direct effect on the sizing of the kiln, but it will influence the materials of construction.

Abrasiveness & Corrosiveness A material that is corrosive or abrasive may not have a direct effect on the sizing of the kiln, but it will influence the materials of construction. Corrosive or abrasive materials will often require that parts, or all of the kiln be lined or constructed of a corrosion/abrasion- resistant material.

Specific Heat Specific heat is the amount of energy it takes to raise the temperature of 1 gram of material by 1 degree Celsius.

Specific Heat Specific heat is the amount of energy it takes to raise the temperature of 1 gram of material by 1 degree Celsius. The specific heat of a material determines how much energy the kiln will require to cause the desired reaction.

Specific heat varies considerably among materials, with metals having a low specific heat, and water having a high specific heat.

Thermal Conductivity Similar to specific heat, how a material transfers heat will also influence how the kiln will need to be designed around the material.

Thermal Conductivity Similar to specific heat, how a material transfers heat will also influence how the kiln will need to be designed around the material. Will the material transfer its heat easily, allowing for even distribution and low retention time, or will it hold onto its heat, causing cold pockets and increasing retention time, or even requiring the need for additional accessories such as dams or bed disturbers?

Heat of Reaction In many kiln applications, heat (in addition to energy) is required in order for a reaction to occur.
Heat of Reaction In many kiln applications, heat (in addition to energy) is required in order for a reaction to occur. For example, when performing calcination on limestone to convert it to lime, energy is required to perform the dissociation of CaCO3 into CaO and CO2.

Heat of Reaction In many kiln applications, heat (in addition to energy) is required in order for a reaction to occur. For example, when performing calcination on limestone to convert it to lime, energy is required to perform the dissociation of CaCO3 into CaO and CO2. However, the dissociation will not happen at a temperature lower than 900ÂșC.

The temperature and energy required for a reaction to occur can be found in published data, or by performing a Differential Thermal Analysis (DTA), also known as a Differential Scanning Calorimeter (DSC).
Temperature Profiles Temperature profiles are gathered by performing a Thermal Gravimetric Analysis, or TGA, which describes the temperature ranges at which mass loss occurs.

Temperature Profiles Temperature profiles are gathered by performing a Thermal Gravimetric Analysis, or TGA, which describes the temperature ranges at which mass loss occurs. This helps to show where (in terms of temperature) a reaction begins and ends.

A TGA will also reveal reactions that might occur between the start and end point of the intended reaction.
Chemical Composition The chemical composition of a material is also critical in the kiln design process for many reasons.
Chemical Composition The chemical composition of a material is also critical in the kiln design process for many reasons. One reason is that many materials will combust during processing, requiring the kiln to be designed to accommodate this excess heat.

Furthermore, knowing the chemical composition of a material can help to predict what exhaust gases will result from the process, and ultimately, what type of exhaust gas treatment system will be needed.

Sizing A Rotary Kiln


Once the material has been thermally and chemically analyzed, the actual sizing process can begin.
Once the material has been thermally and chemically analyzed, the actual sizing process can begin. The sizing of a rotary kiln is a highly complex process that combines engineering principles with the thermal and chemical analyses.

The size of a rotary kiln is not just a function of capacity, but also of the amount of heat that can be generated during processing due to combustible and/or volatizing material.

The size of a rotary kiln is not just a function of capacity, but also of the amount of heat that can be generated during processing due to combustible and/or volatizing material. Kiln length and diameter are calculated based on the maximum feed rate, the required retention time, and what the bed profile will need to be (how full of material the kiln will be).

Once a rough design of the kiln is achieved, various computer programs can be used to help predict how the design will work with the material.

Once a rough design of the kiln is achieved, various computer programs can be used to help predict how the design will work with the material. With the preliminary design configured, kiln internals can be considered, such as what type of refractory will work best.

Because kiln sizing and design is such a complex process, it is often recommended that testing be conducted.
Because kiln sizing and design is such a complex process, it is often recommended that testing be conducted. Testing helps to work out process variables, define time and temperature profiles, and provide data for process scale-up, ensuring the most efficient processing solution is achieved.

Conclusion Rotary kiln design is a complex process that must take many factors into account. Material characteristics such as specific heat, bulk density, and more, will all influence how material will behave in the kiln, and subsequently, how the kiln will need to be designed in order to produce desired results.

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