Transfer systems

For efficient plant utilization, it should be possible to perform cleaning and sterilization operations at the same time on adjacent pieces of equipment, without any risk of cross-mixing. This is actually part of the 3-A Accepted Practices for Permanently Installed Sanitary Pipelines and Cleaning Systems (Stewart & Seiberling 1996). For instance it should be possible to clean a bioreactor together with its transfer line immediately after use, and then to sterilize it in preparation for the next batch, while a culture is running in an adjacent vessel.

A practical solution to prevent cross-mixing is the use of block-and-bleed valve arrangements, which ensure that there are always two valves between incompatible fluids; any leakage through a valve would be diverted to the drain (Thompson 1994). A simple example is illustrated in Figure 14.3.

Figure 14.3 Block-and-bleed valve arrangement. This arrangement ensures that there are always two valves between incompatible fluids. Any leakage through the valve is diverted to drain. The system can be made more secure by appropriate use of automated valves (reproduced with permission from Thompson, 1994).

Product

Figure 14.3 Block-and-bleed valve arrangement. This arrangement ensures that there are always two valves between incompatible fluids. Any leakage through the valve is diverted to drain. The system can be made more secure by appropriate use of automated valves (reproduced with permission from Thompson, 1994).

Drain

Drain

To isolate a sterile area from a non-sterile area efficiently, two valves should be installed where possible, since bacteria can grow between valve membranes. In cases where contamination risks are particularly critical (for economical or biosafety reasons), the use of steam block barriers is recommended, where pressurized steam is fed into the space between two valves (Adey & Pollan 1994).

In large-scale facilities, numerous transfer lines between several bioreactors are needed, all of which must be sterilizable and cleanable; consequently, the number of valves required can increase tremendously, particularly if block-and-bleed arrangements and double valve barriers must be incorporated at each transfer route.

Manual transfer panels represent one practical solution to this challenge and have become very popular in the biotechnology industry (Louie & Williams 2000). A manual transfer panel is composed of a series of stainless steel nozzles or ports welded onto a vertical plate. At the rear of the panel, the ports are connected by hard piping to the inlets and outlets of process vessels and of other process functions. At the front, the panel serves as a 'switchboard': two ports can be connected manually via pivoting elbows or short U- or J-shaped pipes ('jumpers') to select the desired route. Process fluids, as well as utilities such as WFI, CIP supply and return solutions, clean steam, and condensate, can all be circulated via such transfer panels. For sterile transfers, the jumper is installed before sterilizing the whole line; after use, the line is cleaned in place before the jumper is dismantled. Jumpers can be equipped with a safety device called a 'proximity switcher', which communicates the actual position of the jumper to the plant automation system, providing confirmation that the correct route has been selected before the transfer is initiated, thus preventing accidental mistransfers. The design of transfer panels and jumpers is discussed in detail elsewhere (Huang et al. 2000; Louie & Williams 2000). Complex transfer panels can even permit a number of simultaneous transfers, yet ensure that there are no cross connections between any two different streams (Seiberling 1992). A simple example, for the selection of the transfer route between one of three source tanks and one of six receiving tanks, is illustrated in Figure 14.4. The use of transfer panels in a large-scale upstream processing plant is also illustrated in Figure 14.11 (Section 14.5.2).

The advantages of manual transfer panels are many. In brief, they provide a true physical isolation of a transfer route, thereby greatly reducing the risk of cross-mixing; they are both highly flexible and adaptable, since ports and piping can be modified without interfering with basic operations. By centralizing process operations, they make efficient use of process space and operator labour. Maintenance is minimal and can be largely confined to nonclassified areas behind the panel. These transfer panels do, however, have a few minor limitations. First, setting up a process route is a manual operation and may require operator travel or coordination between different process areas. Second, transfer panels must be fabricated with very narrow tolerances on dimensions in order to ensure a perfect fit of the jumper to the ports.

Ring transfer panels offer an alternative to manual transfer panels, with similar functions. They consist of a compact arrangement of T-, Y-, X- and corner-type diaphragm valves installed in a ring configuration (Wilde 1998). Process fluids as well as utilities can thus be transferred from any inlet valve to any outlet valve without pocketing, and independently of any SIP and CIP cycles taking place on adjacent pieces of equipment. The inlet fluid is split to flow through the entire ring before exiting through the outlet valve (Figure 14.5). The main advantage of this system is the possibility of fully automated operation. The main drawbacks, however, are the higher maintenance cost (particularly due to membrane replacement) and the fact that the system, unlike a manual transfer panel, does not guarantee absolute isolation of a flow path in case of membrane leaks or failure of the control system.

Flow Transfer Panel

Tank 2c

Tank 2d

Tank 2b

Tank 2a

Waste water

X

cf

N

*

y—C

b

/

Tank 2f

Tank 1b

Figure 14.4 (a) Example of a manual transfer panel, (b) Diagram of the manual transfer panel shown in (a). The panel is used for the selection of the transfer route between one of three source tanks (la-lc) and one of six receiving tanks (2a-2f). Here jumpers are not equipped with proximity switchers; however, each port has a valve that has to be manually opened, after installation of the jumpers, before transfer can take place. When a port is not connected, it is closed by a cap equipped with a small drain; any residual fluid or pressure can thus be released gradually before the cap is removed. The hard pipe connections at the rear of the panel are represented by dotted lines on the diagram (courtesy of Novartis).

Ring Transfer Panel With Sip And Cip

Figure 14.5 Example of a ring transfer panel. Special T-, Y-, X- and corner-type diaphragm valves allow a ring design without dead space. Any inlet can be connected to any outlet; for instance ports 1 to 5 can be inlets, port 6 can be connected to a drain, port 7 to the CIP return line and port 8 to a steam trap (courtesy of Bioengineering).

Ring Transfer Panel With Sip And Cip

Figure 14.5 Example of a ring transfer panel. Special T-, Y-, X- and corner-type diaphragm valves allow a ring design without dead space. Any inlet can be connected to any outlet; for instance ports 1 to 5 can be inlets, port 6 can be connected to a drain, port 7 to the CIP return line and port 8 to a steam trap (courtesy of Bioengineering).

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