Spray Drying is one of the most widely applied unit operations in the dairy and food industries. Ranging in size to produce either a few kilos or high tonnages of powder per hour, SiccaDania offers single, two and three-stage dryer designs incorporating wide body and tower- form shaped drying chambers. The chamber design selection is closely tied to the desired dryer performance and powder requirements. Spray drying not only allows the transformation of liquids into powders. It is a most effective means of achieving specific powder properties of particle size, residual moisture content, degree of agglomeration, bulk density etc. and this is irrespective of capacity. SiccaDania supplies the latest designs of spray dryers due to extensive in-house technology know-how in this exact discipline.
A spray drying system consists of the following main parts:
The feed system controls the supply of the feed in liquid form to the atomizer. In order to achieve low energy consumption, the feed is very often pre-heated before entering the high pressure feed pump and afterwards pumped to the atomizer. There are two ways of atomizing the feed into the top of the drying chamber, centrifugal or nozzle atomization. The end powder product specifications determines the type of atomization system.
Main air heating system
The main air heating system supplies the drying chamber with the designed amount of air. The air rate is calculated with SiccaDania’s process calculation program and is based on actual ambient conditions in the actual place where the dryer system will be installed. Ambient conditions such as humidity and temperature as well as ground level has a huge influence of the air amount required to dry the feed into powder. The main air system consist of air filters, pre-heating systems, air heater, supply fan and from time to time dehumidification system. The main air system is built up acc. To actual requirements of product and ambient conditions.
The drying chamber is where the evaporation of the water from the product takes place. The design of the drying chamber is dependent on which type of product to be dried. The chamber is designed to provide a sufficient residence time of the product in the chamber in order to obtain the correct evaporation and at the same time make sure that the product is not kept too long in the hot air zone and thereby coursing degradation of the product. The shape of the chamber is also a parameter when looking for specific particle sizes and product
Internal fluid bed
The internal fluid bed is an integrated part of the drying chamber. The internal fluid bed is often used as secondary drying at lower temperatures and also to prevent deposits on the conical sides of the chamber. The thermal efficiency of the dryer is also improved by this 2. stage drying. The internal fluid bed is widely used within the dairy and food industry where products are often heat sensitive.
External fluid bed
The external fluid bed can be divided into several sections, depending on the application. The external fluid bed is either a standalone unit for specific functionality powders or it is an integrated part of the spray drying system which will apply the final drying and cooling of the product. SiccaDania will calculate the correct design and drying cooling parameters for the application. Fluidization velocities and applied air temperatures in relation to design of the fluidization plate gives the final product quality.
Secondary air systems
The secondary air system supplies all fluid beds, fines return, atomizer cooling and CIP nozzle purge air systems. Each system is individually regulated to the correct temperature, filter grade and flow and can also be combined with dehumidification systems where necessary. This makes the complete drying system very flexible and combining the main air system to the secondary system with manifolds eliminates the risk of leakage from additional heat exchangers.
Fines and air filtration system
The fines coming out of the drying chamber and external fluid bed together with the exhaust air will be separated from the exhaust air before let to the atmosphere. Cyclones and bag filters are the most common ways of filtrating the fines from the air. Cyclones are seldom to stand alone as the emission will often violate the environmental requirements in terms of the permitted mg of powder per m3/air. Therefore a bag filter is necessary. A bag filter can be a standalone solution as this technology is able to remove the required powder fines before outlet to the atmosphere. The fines are collected in a fines return system, thereby the powder loss is reduced to a minimum. The fines can be re-entered to the top of the dryer to achieve agglomeration of the powder or it can be sent to the internal or external fluid bed. Again the required powder specifications will decide the design of the fines system.
The final step of the drying system is the powder sifter. The powder sifter will separate the large powder particles from the powder, size is determined for the separation. The off-size is bagged off and the powder can be either directly packed into big bags or conveyed to silo system for other packing systems.
SiccaDania engineers turnkey projects where spray dryers are involved since the company possesses the know-how regarding the upstream and downstream processes e.g. feed pre-treatment (mixing, concentration, homogenization, heat treatment) and powder handling (agglomeration, cooling, conveying and packaging).