Looking for Suggestions Regarding How to Melt Solid Raw Materials Fast

[rafadan]

Hello All,

I am looking into a designing a process involving a heated batch mixer of 30m^3 volume. All the raw materials are solid granules. The process involves melting the material and then processing it further. I want to minimize the melting time of the material. Normally, the first choice is to use a outer jacket with oil heating in the mixer. However the surface area is quite limiting for the heat transfer even though i use a 3/1 height to diameter ratio in the tank. The other option is to use internal coils which can provide a very high heating surface, but it might create difficulties with cleaning. The materials all melt around 110 degree Celsius and the target temperature is 140 Celsius. Maximum temperature allowed for the heating medium is also limited to ~170 degree Celsius. The viscosity of the material will be quite low around 0.2-0.3 Pas when melted.

What I am planning is to have a premelting mixer feeding the processing mixer and take advantage of the processing time in the second mixer while melting the material. Another thing I could think of is to heat the material in the mixer while it is melted, and then pump it through a heat exchanger to heat it up faster from 110 to 140.

I am looking for any suggestions that might show me a new perspective. For example, would it be possible to use a lobe pump to pump the half melted material through a tube heat exchanger? Are there any commonly used applications for fast melting of solid granules? Any suggestions, or ideas are more than welcome

 

[Compositepro]

It all depends on the reactivity or stability of your material. If your material is stable in its molten state, then the best approach is to pre-melt it in drums placed in a forced air oven. This will take many hours so it is usually done overnight, so that it is ready to use in the morning. A lower cost solution are drum warmers. Keep in mind that convection currents are usually a very important aspect in how materials melt. So heat applied to the bottom of a container is much more effective than anywhere else. But you still have to maintain the heat at higher levels.

Rapid melting of reactive materials requires some very expensive equipment that looks like an extruder.

 

[SuperSalad]

A scraped wall heat exchanger might do the trick to reduce insulation by the phase change.

Andrew H.

http://www.mototribology.com

 

[rafadan]

@Compositepro

Thank you for the reply. That is a good advice, but stability could be an issue, as well as there are many different material and they would need to be premixed in advance to be put in drums. Maybe it could make sense to pre-melt the 2-3 main components of the mix in advance and use it in a liquid phase. It could speed the process up a lot.

I was also thinking about extruders, but what is commonly a "large" extruder is about 2-4 T/h which is still not very fast for filling a 30m^3 reactor. Can you send a link if there is a specific type of machine similar to an extruder that you were thinking about?

@SuperSalad

Thank you for the reply. First time I heard about the scraped wall heat exchanger and it looks like it could do the trick! I will definitely look into it in more detail.

 

[EdStainless]

It sounds like you need a combined method.
The material could be pre-heated (but not melted).
Then it could be fed through an extruder like machine to just provide the energy for the phase change, just barely melt it.
Then into a vessel that is jacketed with 150C heat transfer fluid.
By doing it in stages you might have better luck with sizing.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[MortenA]

I was thinking the same thing as Ed, may be fluid bed with warm air e.g. 100ºC and then final melting

Best regards, Morten

 

[georgeverghese]

Induction heating come to mind when you ask for rapid heating if this material is an electrical conductor.

 

[rafadan]

Hi @georgeverghese,

thank you for the suggestion, I actually stumbled upon a company who made induction heaters, but it seemed to me that the wall of the mixer would get much hotter than desired. We don't want any part of the material to be warmer than 170ºC. Do you think it be possible with induction heating if the material is conductive, but considerably less than metal?

Hi @MortenA,

I am also thinking it is best to have 2 stages and my idea is to have two almost identical mixers feeding each other. The first one will be for heating and pre-melting and the second is for the actual process. I will also look into the fluid bed heating which could speed up the initial heating.

 

[georgeverghese]

Maybe change the material of construction of this mixing vessel to be non conducting? Vendors you could reach out to from Google may help :

https://www.interpowerinduction.com/batch-reactors-vessels/