Calculations for Drying of Solids in Batch Process

[ChemRat]

I need guidance on how to calculate the impact of a change inteh material of construction of a vessel on the drying rate of a solid in a batch process. I have the following on exisitng system:
1. 1000 gal carbon steel horizontal vessel.
2. 20% propylene glycol circulates through the jacket vessel at 75 deg C and at 100 gpm.
3. I'm trying to dry the solid from 20% water to below 5%.
4. The 1000 gal drum is under vacuum of 10 PSIA
5. This is a batch process so the next wet cake does not drop into the dryer until the existing wet cake has reached the 5% (it takes about 10 hrs to dry).


We are considering purchase a new vessel that's 316 stainless steel. How can I calculate how the impact of the change in material of construction on the drying rate?

 

[m777182]

You do not say anything about your material and construction of your dryer so that presumingly all mechanical design details are kept unchanged then the heat flow through the wall of the dryer will be changed only due to different heat conductivity of SS 316.
m777182

 

[ChemRat]

The only difference between the old dryer and the new is the material of construction of the dryer. we do not change the dimensions of the dryer nor the material we are drying, So How would I link the difference in the thermal heat conductivity between carbon steel and stainless steel to dtermine the change in the drying time?

 

[m777182]

You are supposed to calculate thermal resistances on propylene glycol side, throuhg the wall and on the inner side wall. Only the second term changes approx. by a factor 4 and in the sum of all three resistances the second term will be 4 times higher. As an approximation the second term contributes about 5% of the resistance, now it is going to be ~5%*4=20%. If you calculate new sum you get 0,95+0,20=1,15 so your resistance will be very roughly about 15% higher or your heat flow ~13% lower. Actually SS is very likely more smooth so that heat resistance on the inner and the outer side of the wall wiill be slightly changed in such a sense that the increased thermal resistance of the SS wall will be partly compensated.
m777182