Addressing the cleanability of glucose feed lines is a key maintenance issue for many process engineers working with large-scale fed-batch processes with Escherichia coli (E-Coli) fermentation systems. The following solution was developed in response to a client who has on-going cleaning as well as maintenance issues with their systems. The client supplied the following P&ID diagram and provided the following details:
“The glucose is fed from a 2″ header and the actual take-off lines are 3/4″. From the header there is a 4″ dead leg to the shut-off valve. The process requires steaming this line prior to take-off all the way to the trap and waste line. The diagram shows quarter turn ball valves which are an on-going cleaning and maintenance issue. Sugar build-up in the valves prevents sealing as well as leaking through the valve bodies on three piece valves.”
The client has used weir style valves without success. Like the ball valves the weir valves suffer with sugar build-up on the weir. The other issue is that the client reports that the nuts on the weir valves “back-off” after steaming. I will get to that in a moment.
To better understand the “as built” system the original P&ID was sketched out in its real life orientation.
Glucose Feed Proper Orientation
In the sketch above it is easier to visualize the multiple dead legs in the system and the unused portions that trap the glucose prior to steaming.
The following sketch imagines how the same system could be designed using the Rattiinox CAD valves which would eliminate the dead legs in the process.
Pictured below is the proposed Rattiinox engineered solution that would eliminate the problem with sugar build-up from the steaming operation as well as improve cleaning and sterilization by eliminating the dead legs. Note: The system could be further optimized by using CAD valves at the steam and PW drops.
A few things to point out with the Rattiinox engineered system. One important change is the addition of a purified water feed for flushing the system prior to steaming. This will address the cooking of the glucose during steaming. The CAD valves are a better choice in this case because the turbulence in the valves results in better flushing with no chance of glucose building up as in the crevices of the ball valves or at the diaphragm body interface with the weir valves. The image below shows one possibility of the Rattiinox CAD valve take off solution that combines the valve on pipe as well as the rinsing and steam valve machined from one piece. There of course are other options that includes the satellite valve as a stand alone valve.
The image below shows the Rattiinox low point drain assembly. With the pT 100 located at the lowest point, sterilization of all the upstream piping can be easily and quickly validated.
Regarding the customer’s comments about the nuts on the weir valves backing off after steaming, this is likely not the case. It has been well documented that many EPDM elastomer compounds used in our industry are not well suited for steaming applications. What we have seen in many cases is that EPDM compounds that have a high compression set will readily deform under load. So under the pressure of the bolt torque in combination with high temperatures the EPDM backer is becoming thinner which gives the appearance of the nuts backing off when in fact they are losing torque because the diaphragm has failed. Repeated torquing accelerates the process. The Rattiinox CAD valves with the solid PTFE diaphragms do not encounter this problem and can be steamed repeatedly without losing compression which results in lower overall costs associated with valve maintenance.