16 replies to this topic

[Orzelgorskiego]

Dear Engineers,

 

I have to design the dryer for running 24hr per day. By using saturated steam it can be a little bit expensive to use this machine.

I am wondering whether there is another option to heat the material inside? The temperature needed inside the drying chamber is max.70degC.

We would like to make heated jacket and rotor. Please help with some ideas.

 

Thank you a lot.

Tomasz 

[breizh]

Hi,

You may want to share with us more information about your product (liquid, slurry, solid). Consider the technologies used in food industries. How big should be the unit? capacity?

Underneath a link with technologies and examples.

Unit Operations in Food Processing - R. L. Earle (nzifst.org.nz)

It could be hot air powered by electricity instead of steam, microwaves.

Edit:

Another way could be a wiped film evaporator powered with hot oil for liquid.

https://www.ablazegl...d-applications/

 

One more technology I used for drying chemicals:

https://www.andritz....ouda-drum-dryer

 

More information, better answer.

 

Breizh

[Orzelgorskiego]

Hello,

 

Thank you for fast feedback. Material is stabilized sewage sludge. Please see below mass balance.

 

 

https://www.dropbox....tytułu.jpg?dl=0

Edited by Orzelgorskiego, 22 June 2023 - 05:50 AM.

[Orzelgorskiego]

Do you know maybe where I can find comparison of energy consumption/running cost per hr. of  steam rotary dryers and hot air dryers?

Edited by Orzelgorskiego, 22 June 2023 - 07:17 AM.

[breizh]

Hi ,

Why don't you use a press filter or a centrifuge to dewater your sludge?

If needed, then you can consider a dryer.

Breizh

[Orzelgorskiego]

We are using a filter press before feeding to the Digester.

They have a limit of pressing to approx. 75% moisture.

 

Tomasz

[breizh]

Hi,

I don't understand what you try to achieve. Let you draw a blocks diagram or a simple PFD to explain your current process.

In any case you cannot feed a dryer with a slurry with 75 % liquid, you need an intermediate step where you get a wet cake, the less wet the better, to feed a dryer, the reason why I mentioned the use of press filter or centrifuge.

 

I assume your liquid is water, why do you want to operate under vacuum, or I misunderstand the temperature set point of 70C?

 

On the market you can find batch filter dryer, Nutsche type. Google should be your ultimate resource.

 

Good luck

Breizh

[Orzelgorskiego]

Dear Breizh,

 

Thank you a lot of help. We do not have any P&ID yet.

We are looking for alternative heating source for drying of stabilized sludge with moisture of 75%.

We cannot dewater the sludge more because the process required this moisture at level approx. 75%.
70degC is the maximum drying temp which can last for 24hr. Drying cannot be performed faster. We cannot exceed 70degC temp. It is under normal atmospheric conditions, not under vacuum.

 

We are considering saturated steam heating and water heating so far by heat exchanger. Heat calculatons are attached.From this it turned out that we need surface around 50m2.

 

https://www.dropbox....ations.png?dl=0

 

Tomasz

[breizh]

Hi,

Sorry but still unclear how you want to evaporate water @ 70C under atmospheric pressure. 

Regarding your process data I see inconstancies, initial mass balance you are thinking to get a dry cake about 10% residual water and in your last post you mention 25%.

Did you check with suppliers of dewatering machines the possibility to perform a test with your product? This should be the first step prior to "size" any dryers.

Share with us a simple Blocks diagram or simple PFD.It won't take long to draw one.

 

Breizh

[Orzelgorskiego]

Dear Breizh,

 

We have to choose between the saturated steam heating or hot water heating.

As I wrote before the maximum drying temp can be 70degC. There is no vacuum drying,but normal atmospheric system.

We have to find what is more efficient at this temp water or saturated steam?

 

 

Could you check whether we have made the correct calculation for energy from steam and from hot water?

Please see the attached file with steam properties.

https://www.dropbox....ljbh2e80r5&dl=0

 

Water energy at 70degC (0.3 bar) = 289 kJ/kg

Energy of 1m3 = 1000L of water at 70degC =   289kJ/kg * 1000kg = 289 000 kJ

Vapor energy at 70degC (0.3 bar) = 2336 kJ/kg

Specific volume of steam = 5.2m3/kg

 

1KG of vapour = 5,2m3

xKG            -         1m3

 

xKG = (1KG * 1m3)/5,2m3 = 0,192KG

Energy of vapour in 1m3 = 0,192KG * 2336 kJ/kg = 448 kJ

 

Comparing energy in 1m3 from water we have 289 000 kJ and from vapor 448 kJ

Please tell me whether we made correct calculations for above.

[breizh]

Hi,

So far you did not share with us a full picture of your process. 

Regarding your last post, it does not make any sense to compare energy content of hot water and steam based on volume.

To better understand your needs, tell us about your role in your organization and your background.

 

This link underneath together with the calculator may help you in your work.

https://www.spiraxsa...arn-about-steam

 

Good luck.

 

Breizh 

 

 

[Orzelgorskiego]

Dear Breizh,

 

Thank you for help.

 

P&ID is not necessary. There will be horizontal shell diameter 2m, length 10m and we need to heat the material which will be inside from outside, we have to decide whether by water or steam. Drying do not have to be performed at 100 degC, drying process is slow and will last 24hr.

 

Here you can see the movie of such dryer.

https://www.youtube....G9zdCBiaW8tdGVj

 

Regarding the evaporation:

Evaporation occurs at any temperature, but only at the boiling point does the liquid evaporate in its entire volume.

 

I am mechanical engineer and I work under such dryer design where we cannot exceed 70degC of material in drying chamber

 

Only thing which I need is to compare the heat from water vs steam. Whether we made correct calculations.

 

Tomasz

[breizh]

Hi,

Your equipment is called a paddle mixer, quite similar to the one from Andritz,Gouda , except that yours has no heating source within the shaft and paddles.  Not a big deal.

You seem not understand that 0.3 bar steam, is a pressure below atmospheric pressure (1 bar Absolute). 

Do you have such heat source? 

Regarding liquid state and vapor state, you need to take into account the latent heat.

Using saturated steam, we consider that the vapor will condensate and transfer the latent heat to the product.

In other words, the quantity transferred will be the mass of steam time the mass of steam : Q=mass steam *latent heat steam (T,P) (kg/h*kcal/kg)

If you use hot water, you may see a Delta T between (inlet - outlet) about 20 to 30 C at max thus the quantity transferred will be: 

Q=mass water *cp water*Delta T.

 

Note: expecting no losses from the lid.

 

Good luck

Breizh 

[Orzelgorskiego]

Dear Breizh,

 

Thank you for explanation. The more efficient and cheaper is saturated steam.

I do not have such a heat source. I do not know whether is it possible to buy such a device?

 

When we have normal drying process with steam at 6bar for example we decrease the pressure in the drying chamber by using vacuum pump. Then boiling point can be at level 70degC. 

 

Do you think that if I will buy for instance 1bar steam generator, could I heat the rotor inside by this heating source? Not going to the boiling point but heat the product within 70 - 90degC.?

 

Tomasz

[breizh]

Hi,

Using vacuum pump means the risk of carry over solid (dust) together with moisture with risk for clogging. Not that simple, be aware of.

Better for you to consult equipment supplier and or contract a third party for the engineering study.

Because you are located in Europe you may want to contact these companies Andritz (link above) and or Buettner, link underneath:

https://www.buettner...-dryer-systems/

 

Good luck anyway.

Breizh

[horatorres]

First, reducing 75 % water  by steam or hot air is too expensive.

 

The logical way is reduced to 10 - 15 % by a centrifugation machine or filter press, later dried in a horizontal drum with hot air..

 

Horacio

 

 

First, reducing 75 % water  by steam or hot air is too expensive.

 

The logical way is reduced to 10 - 15 % by a centrifugation machine or filter press, later dried in a horizontal drum with hot air..

 

Horacio

[Orzelgorskiego]

Dear All,

 

Thank you all for a lot of help.

 

Tomasz