Freeze Drying Shelf Temperature Control via Pressure Feedback
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Solution Overview
Problem
Current freeze-drying control systems lack precise optimization and feedback control, leading to inefficient processes and potential product damage due to inadequate temperature control during the primary drying phase, especially in pharmaceutical applications where sterility and quality are critical.
Innovation Solution
A method and system utilizing a Dynamic Parameters Estimation (DPE) algorithm to calculate real-time product temperature and process variables, allowing for continuous adjustment of shelf temperatures to minimize drying time while maintaining product safety, suitable for sterile and aseptic processes, and capable of handling automatic loading/unloading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional freeze-drying control systems are used, then the process is simple to operate, but the drying time is extended and product quality is compromised due to lack of precise temperature control
Solution Approach 1:
The patent implements a feedback control system that continuously monitors chamber pressure and calculates sublimation front temperature in real-time. The controller adjusts shelf temperature based on feedback from pressure sensors and thermal models, creating a closed-loop control system that optimizes drying time while maintaining product quality without requiring complex hardware modifications.
Solution Approach 2:
The system dynamically changes the shelf temperature parameter throughout the drying process based on real-time calculations of sublimation front temperature. The controller adjusts temperature setpoints according to the drying stage and product moisture content, transitioning from higher temperatures during primary drying to lower temperatures during secondary drying, thereby optimizing both speed and quality.
2Productivity
If higher shelf temperatures are applied to reduce drying time, then productivity increases, but product damage occurs due to excessive temperature
Solution Approach 1:
The feedback mechanism continuously monitors chamber pressure and uses thermal models to calculate the actual sublimation front temperature. When the calculated temperature approaches the product damage threshold, the controller automatically reduces the shelf temperature setpoint, preventing product damage while maximizing drying speed within safe temperature limits.
Solution Approach 2:
The system employs dynamic temperature adjustment rather than static temperature settings. The shelf temperature is continuously modified based on real-time process conditions, allowing the system to operate at higher temperatures when safe and reduce temperatures when approaching product damage thresholds, thereby optimizing the balance between productivity and product safety.
3Reliability
If precise temperature control is implemented to protect product quality, then product integrity is maintained, but the control system complexity increases
Solution Approach 1:
The patent replaces complex physical measurement systems with a computational approach. Instead of installing multiple temperature sensors throughout the product, the system uses pressure sensor data combined with thermal conduction models to calculate sublimation front temperature, substituting mechanical sensing with mathematical modeling to achieve precise temperature control with minimal hardware complexity.
Solution Approach 2:
The system introduces a thermal model as an intermediary between the simple pressure measurement and the complex temperature control objective. The model translates easily measurable chamber pressure into estimates of sublimation front temperature, serving as a computational mediator that enables precise temperature control without requiring direct temperature measurement hardware.
4Measurement precision
If invasive measurement methods are used to monitor product temperature, then measurement precision improves, but sterility is compromised
Solution Approach 1:
The patent uses chamber pressure as an intermediary parameter to infer product temperature without direct contact. Pressure measurements taken by non-invasive sensors are combined with thermal models to calculate sublimation front temperature, eliminating the need for invasive temperature probes that would compromise sterility while maintaining measurement precision through computational methods.
Solution Approach 2:
The system substitutes direct temperature measurement hardware with a computational modeling approach. Instead of inserting temperature sensors into the product (which would breach sterility), the system uses pressure sensor data and thermal conduction equations to calculate temperature, replacing mechanical sensing with mathematical modeling to preserve both sterility and measurement accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves optimal freeze-drying conditions by accurately estimating product temperature and process parameters, reducing drying time while ensuring product integrity and quality, even in the presence of uncertainties and disturbances, and is non-invasive, making it suitable for sterile processes.
Implementation Method 1
said method comprising the steps of: measuring with said pressure sensor placed inside said drying chamber an inner pressure of the drying chamber during said primary drying phase
Implementation Method 2
calculating with said controller an evolution of a product temperature of a product to be dried and of a plurality of process/product related parameters by means of a Dynamic Parameters Estimation (DPE) algorithm, which implements an unsteady state model for mass transfer in said drying chamber and for heat transfer in the product
Implementation Method 3
The heat is transferred from the shelf to a product surface and from the latter to a sublimating or ice front interface that is a boundary or interface between frozen portion and dried portion of product
Implementation Method 4
The condenser chamber is also connected to one or more vacuum pumps sucking air so as to achieve high vacuum value inside both chambers
Implementation Method 5
the pressure inside the drying chamber is lowered below 1-5 mbar so as to allow the frozen water and/or solvents in the product to sublime directly from solid phase to gas phase
Implementation Method 6
The condenser chamber includes condenser plates or coils having surfaces maintained at very low temperature, i.e. −50° C., by means of a refrigerant or freezing device
Implementation Method 7
wherein the vapour can be re-solidified or frozen
Data Source
AI summary
A method for monitoring and/or controlling and a freeze drying process in a freeze dryer apparatus provided with a drying chamber having a temperature-controlled shelf supporting containers of a product to be dried, comprises during a primary drying phase of the freeze drying process the steps of:isolating the drying chamber closing an isolating valve thereof and sensing and collecting pressure values inside the drying chamber for a defined pressure collecting time and a shelf temperature of the temperature-controlled shelf (Step 1);calculating a product temperature of product and a plurality of process/product related parameters (Step 2);calculating a new shelf temperature and a sequence of shelf temperatures up to the end of the primary drying phase, that maximizes a sublimation rate of the product maintaining the product temperature below a maximum allowable product temperature.