DESIGN OF CONTINUOUS STERILIZATION PROCESSES

INDEX DESIGN TWO WAYS DIRECT HEATING INDIRECT HEATING

INTRODUCTION Continuous system includes: Time period during which media is heated. Holding time. Cooling period. Length of holding period: Length of coil. Flow rate of medium.

Hot medium is cooled using two sequential heat exchangers: Utilizing incoming media. Cooling water. Del factor may be achieved by temperature and holding time. Continuous process involves treating small increments of medium, heating up and cooling down periods are very small.

CONTINUOUS STERLIZER Two types which used for treatment of fermentation media: Indirect heat exchanger Direct (steam injector)

Indirect heat exchanger: Two types Double spiral type Plate heat exchanger Double spiral: Consists of Two sheets of high grade stainless steel which are curved around a central axis to form double spiral. Ends of spiral are sealed by covers. Steam is passed through one spiral and medium through other. Incoming unsterile media is used as cooling agent. Plant is sterlized prior to sterlization of medium by circulating hot water through the plant in a closed circuit. The fermenter and pipe work are steam sterlized.

Advantages There is no cross contamination between the two streams. The spiral route traversed by the medium allows sufficient clearance to be incorporate for the system to cope with suspended solids.

Plate heat exchanger : consist of Alternating plates though which we counter current streams are circulated. The plates are separated by gaskets and faliure of these can cause cross contamination. Its is more adaptable because extra plates can be added to increase its capacity.

Direct heat exchanger : It inject steam directly into the unsterile broth. Injection system is combine with flash cooling. Sterlized medium is cooled by passing it through an expansion valve into a vaccum chamber .

Advantages Disadvantages Used for media containing suspended solid. Low capital cost. Easy cleaning and maintenance. High steam utilization efficiency . Very short heating up times. Disadvantages Forming may occur during heating. It requires clean steam free from anti corrosion additives.

Advantage of continuous process: Temperature may be used as a variable in scaling of continuous process so that the increased the del factor may be acheived maintaining the nutrient quality constant.

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