Hi, I am writing this blog on behalf of KERONE a 40 year young (#40yearsyoung) organization has emerged as an quality manufacturer of technically advanced and challenging heating and drying system, to introduce its reads about the some aspects of the Indirect dryers. The word indirect itself defines that these types of the dryers in which the heater and the subject material under the drying process are separate. The formal definition given by the Hall (1980) that “the indirect dryers are dryers in which the heating medium does not come into contact with the product being dried”.
Unlike direct contact dryers in the indirect dryers the wet material to be dried is heated by means of contacting the material to heater surface i.e. heater heats contacted surface (heat exchanger) and wet materials in placed on such heated surface, this process is known as conduction. The greatest concern points while selecting the dryers are 1) Material to be dried 2) Product quality that is required; hence these points are always required to be taken in to consideration before selecting best fit for of the indirect dryers. The temperature and heating source also largely get influenced by the residence time (time for which the material will reside within the heater) of subject material, as to have lower residence time the high heat source is required to get higher temperature and lower temperature is required for the longer residential time.
Advantages of the Indirect Dryers:
- The indirect dryer offer higher energy efficiency as compared to direct dryer
- The loss of the energy through exhaust gas stream as minimum
- Waste heat can also be utilized for the drying
- Being closed loop the vapor produced while drying are also utilized to increase the temperature
- Indirect dryers need minimum cleaning of the exhaust gas as the exhaust flow is low
- Suitable for the toxic and active materials as low emission of fines and particles from the dryer
- Vacuum drying can also be easily achieved
- Ideal for heat sensitive materials
- Risk of fire and explosion hazards is reduced to greater extend as drying is from conduction
Limitation of the Indirect Dryers:
- Limitation of rate of heat transfer and availability of the heat transfer areas for large scale equipments
- Indirect dryers also have reduce upper limit of drying temperature and maximum throughput when compared to direct dryers
- Indirect dryers have typically higher capital costs due to the need for heat exchange surfaces
Application of Indirect Dryers:
Indirect dryers have proven their successful usage in drying of following applications:
- Food and dairy products
- Baby Food
- Milk and buttermilk
- Potato flakes
- Black Carbon and Etc.
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