Insulations jackets on shell of furnace

[henriquebm]

Hi!.
My name is henrique and i´m from Brazil. We work on melting aluminium industry and we would like to Know if it possible put insulations cover jacket on shell of us melting furnace. We have some doubt about dilatation of shell and ceramic insulation inside of the furnace.Our furnace has 1045 steel on shell.

Following information.

working temperature about 1100ºc inside of furnace. On roof area.
Shell temperatures closer 180ºc
I would like to put 1" of jacket insulation´s to achieve temperatures closer 85ºc
First all i need to know some informations ,about dilatation of shell and work temperature of the refractories inside of furnace. Is it possible some damage for furnace?


Henrique B Matos

 

[IRstuff]

Where do you think this dilatation is occuring now?

And what value of thermal conductivity is your insulation? One inch might be a bit light.

TTFN

FAQ731-376

 

[henriquebm]

following the thermal conductivity of insulation jacket 1"
at:
100ºC 0,03 w/mºC

150ºC 0,05 w/mºC

200ºc 0,07 w/mºC

250ºc 0,08 w/mºc

300º 0,09 w/mºc

I don´t put insulation yet. I would like to Know if it possible same damages for my furnace.

Diameter of furnace is 2,4 meter at 180ºc.If i put that jacket the temperatures is gonna higher,but how much? and dilatation? 350 mm of Refractories castables inside of furnace.

 

[IRstuff]

"100ºC 0,03 w/mºC"

And that's my point, 0.03 W/m-K is essentially air; most insulator run in the 0.05 to 0.1 range

Why is the temperature changing? The heat input remains the same, so the heat flux is the same, so the temperature drop is the same.

TTFN

FAQ731-376

 

[henriquebm]

i would like to put some point´s of curve of conductivity.I think on 100ºc air is below 0,03 W/mºC at 100ºc.The material of the jacket is fiber ceramics.I got it that´s point´s on data sheet.The temperatures isn´t changing,i show only one the point´s. By the way, we don´t Know yet which one temperature of the shell after put on the cover jacket.

 

[henriquebm]

sorry! you are absolutely right. Following attached the data sheet with curve of conductivity.
sorry. I has that datasheet only on portugues.

 

[unclesyd]

If the metal shell skin temperature is 180°C without insulation due to temperature reduction from radiation and convection it will be higher with an insulation covering. The insulation company should be able to give you the temperature increase expected.

We have two cases where we use an air gap with an insulated a metal shield to give contact surface below 50°C. The hot side skin temperature is around 200°C.

 

[henriquebm]

sure, but what about heat flux? Convection and radiation on the sheel> Is that amount of heat flux are smaller or bigger/ I need reduce my budjet of fluel. That insulation jacket of 25,4 mm give me one great insulation.I am worried about refractories inside of furnace. I need it something to brake that heat flux. i saw one of these jackets and one rotary kilns and i think it that´s gonna work.

 

[ione]

henriquebm,

you are dealing with multilayer wall. Each layer has got its own thermal resistance (characterized by thermal conductivity and thickness). The thermal resistances are in series (electric analogy) and to get the overall thermal resistance of the multilayer wall you have to sum up the thermal resistance of each layer. Each layer you add acts as a barrier to the heat flux.

 

[henriquebm]

I don´t have Flux of heat and neither temperatures of outer layer. That´s why i am asking.

 

[corus]

The insulating jacket you're intending to use may well crush as the refractory expands. Putting that to one side you can easily work out the outer temperature by summing up the thermal resistance of the layers of material and assume that the hot face is at 1100C. Use forced convection with h=10 W/m K, on the outer steel shell to represent radiation and natural convection. You can then calculate the outer shell temperature. Check your result by using the materials and thicknesses you have now and see if you get 180C now. What is wrong with a shell temperature of 180C anyway? Many steel making operations run with shell temperatures close to 300C.

Hoping to say Tata

 

[MikeHalloran]

Most 'marine exhaust' shops can fabricate flexible insulating jackets comprising ceramic fiber batting sandwiched between stainless mesh and coated fabric, to be wrapped and wired around odd shaped objects. To a limited extent they are removable and reusable.





Mike Halloran
Pembroke Pines, FL, USA

 

[henriquebm]

corus,

I make it like you wrote and your post and i´m found 140ºc.I think i gonna put another values until the result match.
By the way, I don´t have afraid of the temperatures of steel shell. I have afraid if diference of dilatation between the shell and ceramics castables.

thank´s

 

[corus]

You do find sometimes that the manufacturers conductivities are a little out. 140C to 180C isn't too bad a difference that could be explained by either incorrect conductivity or perhaps too large a value of the outer heat transfer coefficient. If you have the result on a spreadsheet then play about with the numbers to see if little changes here and there give you a better results.

As far as the dilatation, or expansion of the ceramic castable, then a thermal blanket will tend to cushion the expansion of the castable. Reducing the shell temperature will be a secondary effect. Calculating the stresses in the outer shell due to the thermal expansion of the castable is a little difficult unless you know the temperature dependent properties of the castable. I have seen a simpler method used in american Ladle design standards but you still need to know the elastic modulus of the materials.

Hoping to say Tata