![]() ![]() Continuous sterilization systems typically are pre-sterilized with steam by direct injection and/or with hot water. ![]() Cooling HEXs can use cooling tower/chilled water, but also may use vacuum to reduce temperature and draw off any accumulated water from direct steam injection. Heating is accomplished indirectly using steam or hot water via a heat exchanger (HEX) or directly by mixing steam with incoming medium (steam injection). This circulation tank can be pressurized or non-pressurized with the non-pressurized design approach requiring a second “flash” cooler before returning flow to the recycle tank to avoid flashing. Medium is recycled back to a circulation tank (also called a surge or recycle tank) or diverted to the sewer during start up or process upsets (such as a decrease in sterilization temperature or an increase in system flowrate). The residence time that medium is held at sterilization temperature, t R (min), is varied by adjusting flowrate and/or length of the holding loop.Įnergy is recovered by pre-heating incoming cold medium from 15☌ (worst case) to 120☌ with outgoing sterilized medium that is cooled from its sterilization temperature of 150 to 45☌ prior to entering the process cooler where it is cooled further to 35☌. A continuous sterilizer heats non-sterile (raw) medium to the desired sterilization hold temperature (typically 135–150☌), maintains it at constant temperature in an adiabatic holding loop (consisting of a long length of insulated stacked piping connected with U-bends for compactness), then cools it to 35–60☌ before transferring flow to a fermenter that has been previously sterilized empty or with a minimal amount of water. Differences between design and observed temperature, pressure, and other profiles were quantified and investigated.Ĭontinuous sterilization also is known as high-temperature, short-time (HTST) sterilization. Sterilizer performance also was characterized over the expected range of operating conditions. Examples of enhancements adopted include sanitary heat exchanger (HEX) design, incorporation of a “flash” cooling HEX, on-line calculation of F o and R o, and use of field I/O modules located near the vessel to permit low-cost addition of new instrumentation. In addition, the reasoning behind selection of some of these improved features has been incorporated. Design strategies of this new continuous sterilizer system and the expanded control system are described and compared with the literature (including dairy and bio-waste inactivation applications) and the weaknesses of the prior installation for expected effectiveness. This new equipment was retrofitted into an industrial research fermentation pilot plant, designed and constructed in the early 1980s. An existing Honeywell Total Distributed Control 3000-based control system was extended using redundant High performance Process Manager controllers for 98 I/O (input/output) points. A new continuous sterilization system was designed, constructed, started up, and qualified for media sterilization for secondary metabolite cultivations, bioconversions, and enzyme production.
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