Tank 4 is a surge tank for the operation of the sterilizer. Pump 1 (or 2) from the batching tanks must fill Tank 4 faster than Pump 3 (or 4) feeds the sterilizer. Figure 3 illustrates the piping and instrumentation of the surge tank. It is filled from the batching tanks sequentially so that there is a minimum mixing of the segregated raw materials before sterilizing.

The hot water from Tank 5 also supplies Tank 4 and Pump 3 (or 4). This is necessary to start and finish a batch through the sterilizer. For example, to start, the sterilizer is first steam sterilized (no liquid). At the end of this cycle, hot water from Tank 5 is started through the sterilizer to set or balance the instrumentation. When this is achieved, media is fed to Pump 3 (or 4) by remote operating valves. Similarly, after all the media has been pumped, it is necessary to pump water through the sterilizer until the fermenter volume is correct. If another fermenter is to be filled immediately, the sterile water is diverted to the awaiting empty (and sterile) fermenter, and then the new media for the second fermenter is pumped into the sterilizer.

The control room for the operation of a continuous sterilizer should be close to Tank 4, Pumps 3 and 4, the main steam valves and the valves of the sterilizer itself. This location is essential to sterilize the empty sterilizer and control the pumping of water and/or media.

Figure 4 is a block flow diagram of a sterilizer that is suitable for fermenter volumes of 20,000 to 60,000 gallons capacity. It is based on pumping 150 gpm of non-sterile media to the steam injector. Energy savings could be about 45% if the hot water storage capacity (Tank 5) were equal in volume to a fermenter. Additional energy savings can be made by using the excess hot water for other purposes in the plant, e.g., in crystallizers, vacuum evaporators, space heaters, cleaning, etc.

Notice that the pressure in the sterilizer during operation is greater than the pressure of the cooling water. If any leak should occur in the inner pipe, media will pass into the non-sterile cooling water. In addition, the pressure maintained in the sterilizer is greater than the equilibrium boiling point in the heating section. This reduces the noise and hammering. Proper selection of the steam control valve will reduce noise also. However, there remains considerable noise at the steam injector, and it is good to locate it (and all the sterilizer) outdoors. The injector can be enclosed in an insulated "box" to reduce noise levels still further. One final remark: if the steam supply is directly from a boiler, non-volatile additives must be used. Biotech companies have chosen to use clean steam generators.

Figures 5 and 6 show more details of the piping and instrumentation of the sterilizer.


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