Design of the CIP circuit

In traditional CIP systems, solutions were circulated via numerous supply and return lines, separate from process lines; however, as previously mentioned (Section 14.3.2.6), it is desirable, for economic and practical reasons, that a major portion of the tubing, fitting and valves be shared between the CIP, SIP and process circuits. CIP circuits have thus evolved towards a higher integration level with that of the process, as reviewed in Seiberling (1992); manual and ring transfer panels are particularly useful for this purpose (see Section 14.3.2.6). An example of shared CIP and SIP piping is illustrated in Figure 14.7.

A vessel is best cleaned using one or several 'spray balls' or 'spray heads', generally mounted on its upper internal part. The cleaning solution can thus reach and flow on internal surfaces without the need to fill up the vessel, which would take a very long time and be costly. Spray balls are typically sized for a flow rate of 3-5 m3/h each, and a pressure drop of 1-2 bar (Greene 2003). Above 2.5 bar, aerosols can form, which should be absolutely avoided. Spray balls can be either static or dynamic; in this latter type, the head rotates during cleaning, thanks to a mechanical or hydraulic drive. Dynamic spray balls are typically more efficient, covering larger surface areas, but they are also more expensive and more prone to failure. Static spray balls have a smoother and

CtP-Aufarbeitungsanlage /CIP-system Produktionsanlage / production plant

CtP-Aufarbeitungsanlage /CIP-system Produktionsanlage / production plant

Cip Layout

Zlrkulalion CIP-AuftJBreitung circulation CiP preparation

- Zlrkulalion CIP-Relnigung circulation CIP cleaning

Zlrkulalion CIP-AuftJBreitung circulation CiP preparation

- Zlrkulalion CIP-Relnigung circulation CIP cleaning

Figure 14.6 Example of a CIP system with one multiple-tank recirculating unit for the cleaning of a group of process tanks (e.g. bioreactors). The CIP unit consists of four tanks, for fresh water, two cleaning solutions and recycled water, as well as of three small containers for concentrated cleaning agents. The CIP circuit is designed in such a way that equipment can be cleaned in separate groups. This is illustrated here with the cleaning of tank R3 and part of the transfer line from tank R2; the thick lines show the circulation path of the CIP solutions (courtesy of Bioengineering).

smaller surface area and thus tend to be easier to sterilize. Design, selection criteria and operating conditions of various types are discussed in detail elsewhere (Adams & Agarwal 1990; Greene 2003; Haga et al. 1997). In large tanks (>1000 litres), additional spray balls or valves may be required in the central and lower parts of the tank to clean the stirrer, baffles, spargers and other side-mounted nozzles. Alternatively, the gas sparger itself may be used to spray the cleaning solution. The distribution efficiency of spray balls can be enhanced by operating the stirrer during cleaning operations. In some cases, nonetheless, it may be necessary to fill the vessel partially in order to immerse the impeller in the cleaning solution. Examples of spray devices for tank cleaning are shown in Figure 14.8.

The tank outlet valve should be carefully sized, as an undersized line might lead to a 'bathtub-bing' effect, causing residues to accumulate on the sides of the tank; with an oversized line, the minimum velocity required for efficient cleaning might not be reached. For a proper control of the outlet flow rate, the use of a return pump is thus recommended (Greene 2003). To avoid excessive air incorporation in the return line, a removable flat-plate vortex breaker, 1 inch above the tank bottom, can be used (Seiberling 1992).

Multi-element filter housings, which were traditionally washed manually after dismantling, can now also be cleaned in place (Graf & Bernsley 2002). For this purpose, the solutions are circulated simultaneously through a spray-ball installed at the top of the housing and through the inlet and outlet piping while air pressure prevents the housing from filling (Figure 14.9).

Steam

Steam Steam

Steam

Steam Steam

Bioreactor With Sip

air out media 1 media 2

media 3

Figure 14.7 Example of a valve and piping configuration for the combined CIP and SIP of a bioreactor. The main steam inlets for the bioreactor are the spray ball and sparger; the various inlets (air, media) and outlet (air) can be sterilized separately. The figure also illustrates the high integration of process, SIP and CIP piping thanks to ring transfer panels (see Figure 14.5) (courtesy of Bioengineering).

air out media 1 media 2

media 3

Figure 14.7 Example of a valve and piping configuration for the combined CIP and SIP of a bioreactor. The main steam inlets for the bioreactor are the spray ball and sparger; the various inlets (air, media) and outlet (air) can be sterilized separately. The figure also illustrates the high integration of process, SIP and CIP piping thanks to ring transfer panels (see Figure 14.5) (courtesy of Bioengineering).

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Figure 14.8 Examples of spray devices for the CIP of a tank. @ Static spray ball with action radius of 360 °C; one or several of these balls (depending on the size of the tank) are typically installed in the upper part of the tank, as shown schematically in Figure 14.6. ® Static spray valve ('e' shows the inlet of the cleaning and rinse solutions, as well as of steam, during SIP (as discussed in Section 14.4.2.2); 'c' shows the outlet of condensed water during SIP). © Location of spray valves to clean a stirred tank (courtesy of Bioengineering).

In piping, the general recommendation for the velocity of the cleaning and rinse solutions is about 1.5 m/s (Greene 2003). When the solution flows through pipes of different diameters in series this rule should be applied to the largest diameter, in the case of several diameter changes, it is recommended the circuit be split to accommodate the different flow rates needed to reach the desired velocity. Lines should be cleaned individually or in series rather than in parallel, since in this latter case it would be difficult to attain the desired velocity in each path, and it might be possible for one path to back up into another and impede cleaning. Haga et al. (1997) have shown that if dead legs have a length/diameter (L/D) ratio above 2-3 (which is however not recommended, see Section 14.2.4), increasing the velocity up to 2-3 m/s may be beneficial in reducing the cleaning time. Above a L/D ratio of 6, however, the dead leg becomes practically uncleanable, no matter how fast the solution is circulated.

For mobile equipment, such as portable tanks, stand-alone CIP stations have been developed. They work on the same principles as above, except that the equipment to be cleaned has to be moved manually to the station and connected to the supply and return lines. Our recommendation is to use such stations even for bioreactors as small as 25-30 litres, since the weight (typically above 50 kg) makes their handling and transport into a washer very tedious.

Figure 14.9 CIP of a filter housing. The housing is cleaned by the simultaneous circulation of solutions through a spray ball at the top and through the inlet and outlet process piping (reproduced with permission from Graf and Bernsley 2002).

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