Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Direct vs. Indirect Rotary Kilns

741 views

Published on

Rotary kilns are available in both direct-fired and indirect-fired configurations. Each type offers its own unique advantages and disadvantages. This presentation gives an overview of the two types and the advantages and disadvantages each has to offer.

Published in: Engineering
  • Be the first to comment

Direct vs. Indirect Rotary Kilns

  1. 1. Direct vs. Indirect Rotary Kilns Experts in process design and material processing for over 65 years.
  2. 2. 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.
  3. 3. Rotary kilns are available in two configurations: direct-fired, and indirect-fired.
  4. 4. Rotary kilns are available in two configurations: direct-fired, and indirect-fired. Each type offers distinct advantages and disadvantages. And while there can be some overlap in applications, in general, each type is better suited for different applications.
  5. 5. The following will give an overview on each type of configuration, as well as their advantages and disadvantages.
  6. 6. Direct-Fired Kilns
  7. 7. DIRECT-FIRED KILN
  8. 8. Direct-fired kilns rely on direct contact between the material and process gas to process the material.
  9. 9. Combustion gas is pushed through the drum in either a co-current or counter-current fashion, efficiently processing the material inside the drum.
  10. 10. The main advantage to the direct-fired kiln is that it is highly efficient.
  11. 11. The main advantage to the direct-fired kiln is that it is highly efficient. The direct contact between the material and process gas allows for optimal heat transfer.
  12. 12. The main advantage to the direct-fired kiln is that it is highly efficient. The direct contact between the material and process gas allows for optimal heat transfer. However, a few disadvantages to working with this type of kiln do exist…
  13. 13. More Off-Gases Because a process gas is used to heat the material, direct-fired kilns produce more off-gases that will require treatment than their indirect-fired counterparts.
  14. 14. Risk of Entrainment Similarly, the direct contact with the process gas can be a problem when working with fine materials. The process gas could potentially pick up and entrain the material, carrying it out through the exhaust system.
  15. 15. Risk of Entrainment Similarly, the direct contact with the process gas can be a problem when working with fine materials. The process gas could potentially pick up and entrain the material, carrying it out through the exhaust system. The degree of entrainment depends on a variety of factors, including gas velocity, gas density, particle density, and shape.
  16. 16. In situations such as this, the design of the kiln must center around permissible gas velocities instead of heat transfer requirements.
  17. 17. In situations such as this, the design of the kiln must center around permissible gas velocities instead of heat transfer requirements. For this reason, when working with fine materials, an indirect kiln may be a more suitable option.
  18. 18. Applications Direct-fired kilns are the most common equipment of choice when it comes to thermal processing, because of the efficiency they offer. They are commonly used to process a variety of materials, including:
  19. 19. Applications Direct-fired kilns are the most common equipment of choice when it comes to thermal processing, because of the efficiency they offer. They are commonly used to process a variety of materials, including: •  Proppants
  20. 20. Applications Direct-fired kilns are the most common equipment of choice when it comes to thermal processing, because of the efficiency they offer. They are commonly used to process a variety of materials, including: •  Proppants •  Minerals (Bauxite, Gypsum, Phosphates)
  21. 21. Applications Direct-fired kilns are the most common equipment of choice when it comes to thermal processing, because of the efficiency they offer. They are commonly used to process a variety of materials, including: •  Proppants •  Minerals (Bauxite, Gypsum, Phosphates) •  Specialty Ceramics and Clays
  22. 22. Applications Direct-fired kilns are the most common equipment of choice when it comes to thermal processing, because of the efficiency they offer. They are commonly used to process a variety of materials, including: •  Proppants •  Minerals (Bauxite, Gypsum, Phosphates) •  Specialty Ceramics and Clays •  Iron Ore
  23. 23. Applications Direct-fired kilns are the most common equipment of choice when it comes to thermal processing, because of the efficiency they offer. They are commonly used to process a variety of materials, including: •  Proppants •  Minerals (Bauxite, Gypsum, Phosphates) •  Specialty Ceramics and Clays •  Iron Ore •  And more…
  24. 24. Indirect-Fired Kilns
  25. 25. INDIRECT-FIRED KILN
  26. 26. Unlike direct-fired kilns, indirect kilns do not utilize direct contact between the material and process gas to process material.
  27. 27. Unlike direct-fired kilns, indirect kilns do not utilize direct contact between the material and process gas to process material. Instead, the drum is enclosed in a heat shroud, which is externally heated. This heats the drum itself, and the material is processed through direct contact with the shell of the drum.
  28. 28. The disadvantage to an indirect kiln is that it is much less efficient than a direct kiln.
  29. 29. The disadvantage to an indirect kiln is that it is much less efficient than a direct kiln. However, processing with an indirect kiln offers many advantages…
  30. 30. Inert Processing Environment Indirect processing is beneficial because it allows for the processing environment inside the drum to be tightly controlled. This is necessary when processing materials that may form an undesirable compound with nitrogen or oxygen at high temperatures.
  31. 31. Inert Processing Environment Indirect processing is beneficial because it allows for the processing environment inside the drum to be tightly controlled. This is necessary when processing materials that may form an undesirable compound with nitrogen or oxygen at high temperatures. An indirect kiln allows for the processing to occur in an inert environment.
  32. 32. Temperature Control Indirect kilns also allow for the temperature along the length of the kiln to be tightly controlled as well.
  33. 33. Temperature Control Indirect kilns also allow for the temperature along the length of the kiln to be tightly controlled as well. This is beneficial when a material needs to be brought up to temperature and then held there for a specific amount of time.
  34. 34. No Risk of Entrainment In addition to these advantages, indirect kilns are also beneficial because they avoid the risk of entrainment when processing fine materials, which can be an issue when processing in a direct kiln.
  35. 35. Applications Indirect kilns are used throughout a variety industries to process many different materials. Commonly processed materials include:
  36. 36. Applications Indirect kilns are used throughout a variety industries to process many different materials. Commonly processed materials include: •  Carbon Black
  37. 37. Applications Indirect kilns are used throughout a variety industries to process many different materials. Commonly processed materials include: •  Carbon Black •  Chemical Precipitates
  38. 38. Applications Indirect kilns are used throughout a variety industries to process many different materials. Commonly processed materials include: •  Carbon Black •  Chemical Precipitates •  Filter Cakes
  39. 39. Applications Indirect kilns are used throughout a variety industries to process many different materials. Commonly processed materials include: •  Carbon Black •  Chemical Precipitates •  Filter Cakes •  Finely Ground Solids
  40. 40. Applications Indirect kilns are used throughout a variety industries to process many different materials. Commonly processed materials include: •  Carbon Black •  Chemical Precipitates •  Filter Cakes •  Finely Ground Solids •  And more…
  41. 41. Conclusion Both direct and indirect rotary kilns provide a highly engineered solution to thermal processing needs, each offering distinct advantages and disadvantages that make them better suited to different processes.
  42. 42. has been a leader in the thermal processing industry since the 1950s, providing process & product development, feasibility testing, maintenance services, and high-quality, custom rotary kilns.
  43. 43. Want to learn more? Download our Rotary Kiln Handbook The Rotary Kiln Handbook Rotary Kiln Sizing & Design Processing Challenges Service & Maintenance And more… Download Now

×