7 replies to this topic

[ramnathsharma]

Dear Friends / colleagues,

We have commissioned a spray dryer for drying our inorganic chemical solution (35-40%) with
475 kg/hr evaporation rate, and product draw rate of 250 kg/hr.

Our target moisture level in the dried product is 0.15% W/W

So far we have achieved mositure level of 0.3% only.

How to reduce the moisture level further ?

Any suggestions /ideas / links ?

Thanks & Regards

Ramnathsharma

[chenblue]

Reducing the droplet size, raising the temperature and speed of hot air, and using the counter-current configuration, can help you to reduce the moisture level. But maybe you need a big dryer to keep the production needed.

[ramnathsharma]

Reducing the droplet size, raising the temperature and speed of hot air, and using the counter-current configuration, can help you to reduce the moisture level. But maybe you need a big dryer to keep the production needed.

Dear Sir,

Thanks for the reply.

Some points to be discussed :

1. Raising the temperature beyond 350 Deg C is not possible since the hot air generator has been designed for maximum of 350 Deg C.

2. Droplet size - We have provided an Atomizer disc - Pls suggest us to modify the atomizer disc

3. Speed of hot air - you mean the blower size - can you suggest the rule of thumb for sizing the blower for spray dryer - we have provided a blower capacity of 8000 m3/Hr - what is ur view?

4. Do you suggest any vibrating fluid bed dryer after the product has been dried in spray dryer chamber ?

Expecting your reply

ramnathsharma

Reducing the droplet size, raising the temperature and speed of hot air, and using the counter-current configuration, can help you to reduce the moisture level. But maybe you need a big dryer to keep the production needed.

Hello

Drying typically follows a constant then a falling rate drying period. In the falling regime, mass loss rates are typically governed by diffusion through the solid to the surface, where the moisture is evaporated. The falling regime can be characterized as an exponential function.

Depending on your product and process, a case or shell may have developed, reducing mass transfer from the core to the surface (the oil on dried cranberries, raisins and other dried fruits acts this way).

I used to dry fruits commercially, and when drying cranberries (vaccinium ??) I discovered that we could dry the cranberries for hours and hours in the falling rate period, and achieve very little. When we let the cranberries 'rest' for 12 hours (i.e. overnight) a simple 1/2 hour dry the next morning achieved what several hours of drying the night before would not achieve.

My hypothesis is that overnight the moisture equilibriated within the partially dry cranberries, moving from one part of the dried fruit to another, and even from one berry to another. I have seen very dry (6%) blueberries mixed with rather wet (18%) blueberries, and after a day or two the mix was at 12%, not just by arithmetic, but by their appearance, texture and mouth feel. Moisture migrates.

I recommend a small experiment, perhaps as simple as taking some of the material you wish dried further, and complete maybe a dozen trials with a very small quantity, possibly using a microwave oven or a convection oven. measure mass loss with time with 'rest' time as a variable. It may yield some useful data, and provide some clues on how to achieve your goals

Good Luck!

[isotactic]

To reduce the inlet humidity, you can install a dehumidifier.

[Andrei]

ramnathsharma.

You don't specify what kind of inorganic material you are drying. A lot of inorganic materials have a "strange" characteristic to crystallize incorporating a certain number of water molecules in the crystalline structure. As a matter of fact there are very few inorganic compounds in nature that are not crystallized, in an amorphous phase. That crystallization water will come out at the moisture analysis.
To remove that water is very difficult in some cases and energy intensive, requiring elevated temperatures to break the crystalline network. It's like a phase transformation.
You should study if you are not in that situation. Because if you are, it will be very difficult to achieve lower moisture levels. I never saw an atomizer to be able to remove the crystallization water while keeping a decent productivity.
Given the equipment you have, your strategy should include:
1. Decreasing the droplet size by increasing the atomizer disk speed;
2. Decreasing the air circulation speed while reducing the feed, in other words increasing the residence time;
3. Keep inlet air temperature as elevated as possible.

Good Luck

[pawan]

The best way is to send us a list of Design data & Actual Data
so that we can analyse & suggest some improvements.
This should include all design related necessary info.