Providing Pure Gas and Air to BioProcess Units: Part OneNovember 30, 2018 by Karl Lutkewitte
*The author made a units error in the original post. In the bullet point underneath the second paragraph, the bolded 21 L/min has been corrected from the original 21 psig.
Providing Pure Gas and Air to upstream and downstream BioProcess units is critical business. Here are a couple of things we have learned over the years that might help.
Determine Available Valve Cv before Completing Piping Design
PRVs (and BPRVs) have a flow operating range. Like any pressure/flow valve or instrument, there is a pressure and flow operating range associated with the device. They won’t operate well outside of that operating range. Design for that before finishing the piping design because it can come back and bite you.
Let’s assume we need a PRV to handle the blanketing requirement for 8, 10 L Single Use Bioreactors (SUB). Let’s also assume that the regulator inlet supply pressure is 3.5 barg (50.8 psig), and that the outlet set pressure is .1 barg (1.45 psig). Further, for simplicity sake, assume a blanketing gas change of once a minute for an average head space volume at the top of the SUB bags of 3 Liters.
- If all 8 bioreactors are operating at the same time, the max flow rate requirement would be 24 L/min (3 L/min x 8). If only one bioreactor were being used, the flow rate through the valve would be 3 L/min, if two, 6 L/min and so on. Using the many charts from one of our LP series data sheets (Figure 1 below), you can see that 24 L/min exceeds the max flow capacity of the valve if our inlet pressure is 50 psig (3.5 barg). Looking at the chart, we can see that we can really only effectively regulate flows between 2 psig and 21 L/min. In other words, this single regulator could handle pressure regulation for 7 or less SUB’s. If I were designing this system I would probably select 2 of these valves, with each valve handling 4 SUB’s.
In the same vein, don’t select a PRV to handle 2, 10 L SUB’s and expect that same regulator to work 1 ½ years later when Phase 2 of the project is funded, and you need the capacity to add 6 or more SUB’s. It’s not going to work. The PRV’s chosen for the example above, would have the capacity to feed six more SUB’s, three more off each regulator. To accommodate phase 2, Install clamped Tee’s upstream and/or downstream of the current regulators so as to easily add that capacity later.
Finally, an interesting side note: notice on the chart below (and all of our other Direct Acting Clean Gas Point of Use regulators, that as inlet pressure increases, so does the operating range, and offset decreases. In the example above, if our inlet pressure were 100 psi, we could easily handle the gas requirements for all 8 of the SUB’s.
Karl Lutkewitte, Steriflow Valve Product and Sales Manager