Design and Construction of Pilot Scale Tangential Flow Filtration Unit
AIChE Annual Meeting
Monday, November 14, 2016 - 10:00am to 12:30pm
The goal of this study is to design and build a pilot scale tangential flow filtration (TFF) unit to provide a new experiment for chemical engineering students to perform in their unit operations lab. The unit can be used as both a mass transfer experiment and a process control experiment. In mass transfer mode the student will gain hands-on experience with TFF. In process control mode, students will be challenged to tune two coupled control loops to regulate the transmembrane pressure and flow rate simultaneously.
The unit utilizes a 1.14 m2 10 kDa ultracel membrane filter. The system features two 55 liter holding tanks a 5 horsepower pump controlled with a variable frequency drive and a number of manual on/off valves that allow the user to create different pathways for the system. Three magnetic flow meters are used to measure permeate and retentate streams. Three pressure transmitters are used to measure the transmembrane pressure using the equation: TMP = (Pfeed + Preturn)/2 - Ppermeate.
The TFF unit is connected to and operated via a distributed control system (DeltaV). A local operating station is located next to the unit. A graphical user interface (GUI) provides for intuitive operation in mass transfer mode and controller tuning in process control mode. All process data are recorded and archived in a data historian.
In a typical mass transfer operation mode the feed solution is pumped out of one of the tanks into the membrane. The permeate is collected in the second tank while the retentate is returned to the feed tank. The user can set the TMP and permeate flow rate simultaneously. The TMP is controlled by a control valve in the retentate line. The permeate flow rate is controlled by the pump speed.
In process control mode the operation is similar to the operation in mass transfer mode but the membrane module is bypassed and the flow resistances associated with the membrane are simulated with globe valves.
With the valve and membrane pathways on the TFF unit, students will be able to perform two different experiments in lab. With the valve system, students can understand the effects of coupled control loops. With the ultracel membrane, students can perform bioseparation experiments at various operating conditions and quantify the performance of the membrane. The largest risk with this project is exceeding the pressure limit of the membrane. A safety interlock needed to be developed in order to prevent the TMP from reaching a level high enough to damage the membrane. The interlock was a section of code added to the pump control algorithm and was designed to stop the pump immediately if the TMP exceeded a predetermined value. The safety interlock was tested several times and successfully stopped the pump when a spike in TMP was detected.