drying tunnels
Introduction
Solid drying consists of separating small amounts of water or other liquid from a solid in order to reduce the liquid content. Drying is usually the final stage of a series of operations and often the product that is removed from a dryer for packaging.[1].
Drying operations
There are several types of drying operations,[2] that differ from each other due to the methodology followed in the drying procedure; It can be by removing water from a solution through the process of boiling in the absence of air; It can also be by removing water through adsorption of a solid, and by reducing the liquid content in a solid, to a certain value through evaporation in the presence of a gas.
The solids that dry can have different shapes - flakes, granules, crystals, powder, tables or continuous sheets - and have very different properties.
The product being dried can withstand high temperatures or requires gentle treatment at low or moderate temperatures. This gives rise to a large number of types of commercial dryers on the market. The differences lie fundamentally in the way in which the solids move through the drying zone and in the way in which heat is transmitted to the product to be dried.
Drying equipment
Contenido
Las operaciones de secado pueden clasificarse ampliamente según que sean por lotes o continuas. Estos términos pueden aplicarse específicamente desde el punto de vista de la sustancia que está secando.
El equipo de secado, puede ser tan sencillo como un soplador con una resistencia adaptada, o tan complejo como un secador rotatorio.
Tray dryers
The tray dryer, or shelf dryer, consists of a cabinet, large enough to house the materials to be dried, in which a sufficient amount of hot, dry air is blown. In general, the air is heated by steam, but not saturated, so that it can carry enough water for efficient drying.
It is necessary to note an interesting situation of dryer optimization. In this case, when the air is heated with steam, several aspects must be taken into account. If we look at the psychrometric chart, the air to be used must have a high wet bulb temperature, a high enthalpy, but a low relative humidity. Since the drying operation, like any transfer operation, depends on the interfacial contact time (which does not vary noticeably in this type of dryer due to the variation in air speed), the interfacial contact area (which in our case we require to be solids in lumps, or grains, to increase this relationship), the temperature and humidity gradient and the resistance. In general, in this type of dryers, the variables that can be set or varied are the gradients, which is why it is important that the air does not enter cold or humid, since this minimizes the gradient and eliminates the efficiency of the dryer.