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Scale Up Case Study

Thermodynamics

Problem

Determine the thermodynamically equivalent process in the new process using the current process as the reference.

Problem Categories

Thermodynamics, scale up, optimization, robustness, Wurster, coating pan, thermocoat, PCTSUni and PCTSWurster
Solution

Duplicate exhaust temperature and humidity (environmental conditions).
Analysis of the Current Process
Enter the process conditions in the thermodynamics screen to determine exhaust temperature and humidity .
Design of the New Process
For Wurster, enter the process air flow rate calculated from the hydrodynamics analysis to determine the spray rate and inlet air temperature.  For coating pans, enter the spray rate calculated from the coating uniformity analysis.  If neither spray rate or process air flow rate is available, one of these variables must be guessed to determine the other.  The example below assumes spray rate of 800 g/min for the new process. 
Results
The process air flow rate and temperature that correspond to the same environmental condition as the current process are 8880 SCFM and 51.2°C, respectively. 
Optimization
If there are no coating integrity, coating uniformity or hydrodynamic limitations, the cycle time of the process may be decreased by increasing the spray rate.  Supposing that the development data indicated the exhaust RH and temperature can be as high as 17% and 55°C, respectively, the thermodynamics analysis can be conducted to maximize the spray rate.  Exhaust humidity and temperature were set to 15% and 52°C accounting for control precision.  It is further assumed that the maximum air flow rate is ~3000 SCFM for the unit.  The analysis below shows that ~1000 g/min is the maximum spray rate.  
Robustness Verification
If the system uses a desiccant wheel to dry the process air, the process air dew point can fluctuate.  Assuming that on a very humid day, the air humidity can be as high as 7°C and the process air flow rate can fluctuate +/- 100 SCFM, what is the likelihood that the environmental conditions would still be below 17% RH and 55°C?  The analysis using the thermodynamics screen is shown below:
At 7°C inlet air dew point, the exhaust RH is still less than 17%.

The results for the air flow fluctuation are shown below:

Air Flow

2983 SCFM

3083 SCFM

3183 SCFM

Exhaust RH

51.3°C

52°C

52.7°C

Exhaust T

15.8%

15%

14.2%