Delivering technology solutions for spray coating systems and applications...

 

 

THERMOControl -- True "PAT" Control System

Thermodynamics Background

Considerable work was done to improve the understanding of thermodynamics of coating systems in the past.  This led to the use of thermodynamics analyses in reducing the number of variables for design of experiments, reducing variables during troubleshooting, and bridging processes for scale up and tech transfer.  However, most thermodynamics analyses have been done by only a handful of scientists using spreadsheet programs that are often tedious and error-prone.  It is believed that the main reason for the lack of use of thermodynamics science is due to industry still lacking cost-effective and easy-to-use tools that can provide precise analysis of thermodynamics. 

Current Methods for Process Control
The pharmaceutical industry commonly uses the conventional proportional-integral-derivative (PID) feedback control system.  The set-points are sent down from the main control station to individual programmable logic controllers (PLC’s) for the control of each process variable using pre-optimized PID loop-tuning variables.  Complex control systems are not used and not needed since most control variables are inlet variables that do not have dead time or are significantly coupled with other variables. 
Limitations of Current Methods and Drivers for  THERMOControl

More complex control systems are needed if the bed or exhaust conditions (i.e., temperature and humidity) are controlled directly.  Although most recent control systems can deliver stable controls of exhaust temperature using the appropriate control loop tuning variables, there have been some reports of control instability as well.  It is believed that no exhaust humidity controls exist in the pharmaceutical industry.

Some limitations of current control methods (i.e., controlling the inlet variables) are that

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Heat loss is not directly controlled, resulting in variable bed and exhaust temperatures from day to day, season to season, and equipment to equipment

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Humidity is often not controlled therefore the coating condition is not controlled (having a desiccant system does not mean that humidity is controlled)

 The difficulties in controlling exhaust conditions using simple control systems and in controlling external variables that impact the heat loss make control of the coating environment very difficult. 

Capabilities of THERMOControl

ThermoControl calculates real-time coating environment information, which may be used for various applications.  Coating solution information (solvent type and solids content), and measured inlet and outlet air temperatures, inlet air flow rate and humidity, spray rate, and atomizing air flow rate are used to calculate in real time exhaust humidity, heat loss in the system, and proximity to the lower explosion limit.  The potential uses of these real-time process information include:

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Bridging humidity and temperature information during development, scale up and tech transfer, and troubleshooting atypical processes. 

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Determining the feasibility of manufacturing based on the forecasted humidity for the day.  If the forecasted humidity exceeds process robustness range and no humidity control exists in the system, the process should not be run on that day.

bulletMapping heat loss variation from day-to-day and equipment-to-equipment for establishing robustness ranges for equipment.  

Its advantage over the conventional control systems include

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Elimination of instability associated with direct exhaust temperature control

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Guarantee of process equivalency against variances in heat loss resulting from day-to-day and equipment-to-equipment

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Application to systems with and without humidity control