Direct Drying and Indirect Drying
Bulk solids require fast processing and high throughput making rotary dryers the perfect choice. With heavy-duty wear-resistant construction coupled with their versatility in terms of feedstock variety, rotary dryers are perfectly fitted for working with various bulk solids.
Direct fired rotary dryers are way more common than their indirect fired counterparts. Nearly all modern industrial production lines prefer employing direct fired setups. However, indirect setups can be a better choice in specific situation and depending on technological requirements. Choosing the right setup is incredibly important for the quality of the end product.
Direct and Indirect Dryers. Pros and Cons.
One of the most obvious similarities between two setups is that they both employ rotating drum as a vessel where drying is being conducted. However, these two setups approach the process from different angles.
In a direct fired setup, the material intimately contacts with hot gases. Such close contact ensures high efficiency of the drying process. At the same time, the interior of the vessel is usually decorated with lifters that enhance the process further increasing energy efficiency. Lifters drastically improve the process by equalizing the heat distribution across the material evenly and constantly shuffling the material.
Indirect setups do not allow the material to interact with hot gases directly. This allows for advantageous processing of specific materials and for specific purposes. We will highlight two important benefits of indirect setups.
1. The air-flow does not entrain the material or affect its distribution and movement which is beneficial for production processes involving various fine and delicate materials.
2. Indirect fired rotary dryers completely prevent inflammation or undesired combustion inside the vessel which is more than important when processing various combustible materials. Having a complete control over the conditions of processing is also important when working with various foods and pharmaceutical materials that require careful processing.
Indirect dryers heat up the drum and its walls start emitting heat as well effectively transferring it to the material inside. The radiation ensures even heat distribution and renders lifters useless since there is no air flow inside the vessel. Lifters are completely unnecessary in such setups. Another benefit is that you do not have to worry about exit gases since all burning happens externally.
The Material Of the Dryer
The vast majority of industrial direct fired dryers are made of carbon steel. However, this material is not suited for high temperatures and we use special alloys to build indirect fired equipment. This helps in constructing reliable and durable rotary dryers that can withstand continuous heating.
Direct fired rotary dryers are widely used in various industries. They are mostly used to process bulk solids. Direct fired setups are most commonly incorporated in production lines related to agriculture, mining, chemistry, etc. Direct fired dryers are used to work with minerals, ores, and other heavy materials.
Indirect fired rotary dryers have less applications and occupy niche positions in production lines. These setups are employed by various food and pharmaceutical companies and useful for processing fine materials, sensitive chemicals, combustible materials, etc. Indirect dryers enable manageable drying environment and perfectly fit in specific production cycles.
Strommashina offers a wide array of direct and indirect rotary dryers for various applications. Depending on your requirements, we can equip them with add-ons and enhancements of all sorts. Please, contact us today and receive complete information about our products!