Drying

Definition

Drying is defined by removing or reducing liquid components (moisture) from or in bulk solids by thermal processing. The moisture is evaporated and removed.

Fields of application

Lodige dryers can process any product which in its dry form is a bulk solid. The consistency of the wet product ranges from liquid to pasty to free flowing.

Operation Principle

The Lodige dryer was developed from the Lödige Ploughshare® Mixer. It consists of horizontal, cylindrical drum with heating jacket. The product is heated by the jacket and the product moisture is thereby evaporated. A horizontal shaft along the longitudinal axis of the dryer drum is equipped with shovels for mixing the drying product according to the fluid bed principle. This ensures that the product is heated evenly (no local hot spots) and moist material is brought continuously in contact with the heated wall. The intensity of the product movement increases during the drying process while moisture and therefore viscosity decrease. Use of choppers at the right time produces a bigger heat transfer area and therefore leads to increased drying speed. The dryer is heated by the jacket operated with hot water, steam or thermal oil. Molten salt or an electric heating can also be used to achieve higher temperatures.

 

Drying Processes

1. Vacuum Drying

Lowering the system pressure (vacuum) reduces the drying temperature of products with moisture bound on the particle surface to the evaporation temperature of the liquid. The reduced product temperature leads to a big temperature gradient between jacket and product and therefore to increased heat transfer and drying capacity. In addition it is a very gentle process for temperature sensitive materials. Vacuum drying is carried out in a closed system. Evaporated product moisture is recuperated in a condenser. This ensures safe handling of products containing flammable or toxic liquids.

2. Convection/Contact Drying

This drying process also uses for the most part heat transfer from the jacket into the product. However the product moisture is removed by a hot gas (typically air or nitrogen) which is blown through the dryer. The drying process can be generally carried out at standard pressure. Due to the excellent mixing and intense heat transfer through the drum wall relatively low amount of gas are required.

This drying process is carried out batch wise in mixers (FKM) or continuously in dryers (CGT).

3. Stripping

This process is mostly applied to remove solvents from bulk solids. Steam is injected into the product bed. The steam condenses on the particle surface and replaces the lower boiling solvent. Simultaneously the product is heated up as the steam releases its thermal energy. The solvent is then recuperated in a condenser downstream of the dryer. The now water moist product can be dried using the vacuum or convection/contact drying. This process is ideal for the removal of flammable liquids as the steam injection provides an inert atmosphere. This process is carried out batch wise in mixers (FM, FKM ) or dryers (VT, VTA) or continuously in dryers (CGT).

4. Fluid Bed Drying

Unlike the processes described above, drying in a fluid bed results from convection. The inlet air is headed prior to inflow into the Fluid Bed Processor. It homogeneously flows through the special designed Conidur® bottom and fluidizes the product. This ensures an excellent heat transfer and high drying rate.

Machines for drying

Lödige offers dryers in different configurations. These are especially adapted to the product and processes of our customers. Please find the appropriate machines for drying processes below:

Lödige DRUVATHERM® VT Laboratory Shovel Dryer

DRUVATHERM® Vacuum Shovel Dryer

DRUVATHERM® Reactor DVT

Continuous CGT Granulator Dryer DRUVATHERM

 

Fluid Bed System 

Fluid Bed Processor LFP

Granucon® Continuous drying with defined retention time

Brochure

Always the right mix

Always the right mix

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