Dirty hold time

Finally, the dirty hold time and the clean hold time have to be established [17]. When a vessel is not cleaned immediately after use, the remnants may dry in so the vessel may not be cleanable using the normal procedure. The dirty hold time is the time for the cleaning to be completed to be sure that the validated cleaning procedure is still effective. The clean hold time is the time that the equipment may be considered clean after performing cleaning and sanitisation (if applicable) and can be safely used for the next production. 

Aside from a higher stripping efficiency, a packed column is also characterized by a very short holdup time. This may be sufficient for the stripping of certain volatile components (e.g., FFA, tocopherols, etc.) but not enough for a complete deodorization. Therefore, a holding vessel is usually placed after a packed column to properly deodorize the oil. The steam introduced in the retention vessel can be reused as stripping vapor for the packed column, which reduces overall steam consumption. The reuse of this dirty steam, however, may have a negative effect on the final oil quality. 

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