In the Lectures where the necessary heat transfer area for the production of aspirin was being discussed, we had calculated (a) the volume of the scaled up version of the tank and the agitation rate (V = 1500 Litres and N = 630 rpm). We had also calculated (b) the heat transfer required from the steam jacket in the scaled up version to heat from 70^{o}C to 80^{o}C. (Heat Transferred = 76107.6 kJ/h). We now have to consider the necessary tank volume if the agitation intensity is unchanged , we are adding 200kg/h of crystals and we have heat transfer sufficient to keep the solution at 75^{o}C.
The following guidance notes are given to extend the lecture notes:
The case study brief said that heating and dissolution of the crystals required 460 kJ/kg. Thus the energy needed is 460x200 = 92000kJ/h. This indicates that we need more heat transfer area then calculated in Part (b) of the study, thus we will have to increase the volume of the dissolution tank. If we ay that the new heat requirement is Q_{2}:
If we take the ratio of the heat transfer coefficients:
We had shown:
If this is substituted into equation (1)
This can be written as
Now we can write:
If we go back to our Pilot Plant where Q_{1} is 7290 kJ/h then we can calculate an adjusted volume - this is the task in CASE 3.