TechNews

You probably know it bit or two about spray drying already. However, spray drying is not just spray drying. There are several factors that are important if one wants to ensure the maximum output. This is just a quick guide.

Avoid surface tension
Depending on the hydrophobic / hydrophilic characteristics of your wet material you should always use a carrier that neutralizes the interactions or the material and the slurry. Usually some kind of amphipathic carrier is sued.

Temperature
If the quality of the end product is too low it is highly possible that the evaporator gas was too high. Usually, just lowering the temperature 10-20 degrees can have substantial impact on the quality.

Duration of the drying process
Sometimes the time span of the drying process is simply too long. Although most drying plants cant simple chance that try sending some of your material to a flash drying plant and measure the impact.

Molecular weight
Lighter molecules can easily boil of. One way to avoid this is by having a taller tower. The scientific explanation is a bit complicated but water ten to leave the micelles and go into the air phase.

Fluidization is a term used for industrial processes where granular material (like sand or rice) is forced into a liquid state in fluid beds by using either a gas or a liquid.

Imagine a pile of sand lying in the bottom of a tower. Then you start blowing a gas gently through the sand from below. First “nothing” happens because gravitational force keeps the sand at the bottom of the tower. However, if you continuously increase the gas blow the sand grains will eventually start to fly.

This happens when physical force (read: pressure) from the gas or liquid is higher than the gravity. What happens at this point is that the sand grains will start to float around in the tower as if they were liquid themselves, and therefore the name fluidization. If the gas blowing force and the force of gravity is equal, we would see a typical steady state.

However, if the gas blowing force is greater than the gravity the granular material will rise upwards.

Industrial applications of fluid beds
The clever thing about fluidization is that the method is brilliant for separating and also drying wet material like grains and powder. You can even handle solid material like calcium or clay by first grinding the material and then sending it through fluid bed drying.

We want to corrode a granular material
Let us say we have a granular material able to corrode at high temperature. First, we would have to fluidize the material in our tower. Then, think about what happens if you start increasing the temperature. Here is what happens.

As the granular material corrodes (cracks down) the weight of each particle is decreased and thereby gravity pulls each particle with less force, which results in an upwards force (by the gas).

This means that any material up to a maximum weight will rise to the top of the tower and thereby the uprising material can be separated from the granular material that has not yet corroded. This means that you basically have a bullet proof separation of a material having a certain weight.

We want to separate and dry a granular material
Usually this is what goes on at a dairy processing plant. The procedure is the same as above but by heating the material, water will typically separate from the granular material. Then, all you need is some way of excluding the water.

This can be done by adding membrane inside the tower, which only water can penetrate. As the water concentration is greater inside the tower than outside the simple rule physical / chemical equality will result in water leaving the tower through the membrane.

There are several industrial ways to dry a wet material. However, depending on the kind of material different techniques can be applied. Flash dryers are obviously very fast. It only takes a few seconds to dry the wet material in the drying plants.

The name comes from the fast moisture flashing off the wet material. Basically any kind of wet material that you wish to have in powder formula can be dryid.

When wanting to remove moisture (usually water) the wet material is dispersed into a stream of heated gas (usually air or nitrogen). The product is separated by generating cyclones within the drying chamber.

Also, filters can be applied for separating unwanted components. Actually, there are so many possibilities for refined the drying system that they can not all b explained here. The highly elevated temperatures in the evaporators ensure a fast drying process. Then, after the material has been heated and separated it is conveyed into a drying duct.

Big machinery
Some of the largest drying plants can dry more than 20 ton of wet material each hour. However, must smaller plants are more common. The temperature of the hot gas can easily be up to 1400 °F or 650 °C.

There are several ways of drying wet material, removing moisture and producing fine powders. They all resemble one another which mean that choosing which kind of drying plants to install can be tricky.

Here is a list of some ways to dry compounds:

• thermal
• freeze
• chemical
• spray
• flash

How to choose the right technique is matter of many factors. For instance what kind of material do you want to dry and how big loads are we talking about? Also is time an important factor or is it important for your company to save on energy expenses?

In the pharmaceutical business the drying system should be applicable for GMP production. In waste handling plant separation of the dry material demands for high technology filters. Sensitive material might demand for low temperature and thus needs specialized tools for evaporation. Typically this are products which should be freeze dried and but other products or even the same products might benefit from being spray dried at very high temperatures. Maybe chemical drying is more preferred for your compound?

Choosing the right technique
The best way to choose the right plant is to pinpoint every critical factor and the contact the major drying plant companies and hear want kind of solutions they can offer.

Suitable product to dry
Basically any wet material can be dried, these products being either of high viscosity or pastes. The important point is to select a proper speed and temperature among other factors.

Fast and cheap
Flash dryers and spin flash dryers are time efficient and therefore often also energy efficient. However, time is very often the most important factor in the preservation of products, because the longer the drying process takes the greater impact it has on the quality of the end product.

Additional features
As for any other spray dryer there are several additional features which can be incorporated onto the spin dryer. Most commonly a variety of filter can be applied for ensuring a finer end product. Also the filter enables a higher production percentage as particles being to big a left in the drying chamber for additional drying and powdering.

There are several techniques within the field of spray drying and some of them are might be called different terms by various companies. However, here are some of the most important techniques in alphabetic order:

aseptic spray drying
This technique is used for removing any biological life form present in the food product. Often this technique is used for products meant for long term storage.

ddgs drying
ddgs drying stand for Distillers Dried Grains with Solubles and refers to the product you get after you remove the ethyl alcohol during fermentation using yeast.

disc dryers
This technique is based upon rotating or circulating a product within a double walled disc which are locked inside a central tube. The disc dryers technique is used for preventing that any product from being lost during conservation by scraping the inside of the bundle dryers.

Fluid bed drying
Here the product is fluidized by sending a gas through the product. This is a cheap form of spray drying and it is an ideal technique for products not being sensitive to heat.

Ring dryers
The ring dryers are almost identical to flash type dryers. However, a centrifugal classifier is used. This technique is worth using for wet or very large quantum of material. The ring dryers filter out the fine and dry material which is why grinders or disintegrators often are used at the same ting.  

Spent grain dryers
Spent grain dryers have one purpose in the industry of brewery and that is to prevent spent grains from being lost.

Tube Bundle Dryers
By drying the product within a firm housing one prevents the product from coming into contact with the drying steam. Usually used for wet products like drinking products.

There are several techniques within the field of spray drying and some of them are might be called different terms by various companies. However, here are some of the most important techniques in alphabetic order:

aseptic spray drying
This technique is used for removing any biological life form present in the food product. Often this technique is used for products meant for long term storage.

ddgs drying
ddgs drying stand for Distillers Dried Grains with Solubles and refers to the product you get after you remove the ethyl alcohol during fermentation using yeast.

disc dryers
This technique is based upon rotating or circulating a product within a double walled disc which are locked inside a central tube. The disc dryers technique is used for preventing that any product from being lost during conservation by scraping the inside of the bundle dryers.

Fluid bed drying
Here the product is fluidized by sending a gas through the product. This is a cheap form of spray drying and it is an ideal technique for products not being sensitive to heat.

Ring dryers
The ring dryers are almost identical to flash type dryers. However, a centrifugal classifier is used. This technique is worth using for wet or very large quantum of material. The ring dryers filter out the fine and dry material which is why grinders or disintegrators often are used at the same ting.  

Spent grain dryers
Spent grain dryers have one purpose in the industry of brewery and that is to prevent spent grains from being lost.

Tube Bundle Dryers
By drying the product within a firm housing one prevents the product from coming into contact with the drying steam. Usually used for wet products like drinking products.