Pre-Rinse and Intermediate Rinse - The Processes Of Cleaning

Pre-rinse cycles often utilize recovered ‘water’ from the intermediate rinse stage. This serves two purposes: first, to reduce total water consumption (and effluent generation); and second, to utilize any heat energy and possible residual detergent solution carried into the recovered rinse tank during the rinse recovery stage. It is not uncommon to find heated pre-rinse systems in certain applications, such as cream production, where the hot pre-rinse solution provides a greatly enhanced method of product residue removal.

The pre-rinse stage is important because it is not desirable to introduce excessive soiling into the dilute detergent tank. This stage is generally controlled via a timer, sometimes split between product recovery and drain, and these timers are often set at excessive levels to ensure maximum product removal. However, this may not be cost-effective in circumstances where water and effluent costs are high. In general, the pre-rinse cycle for tanks, silos or vessels consists of several ‘burst’ or ‘pulsed’ rinses, as this both improves rinsing efficiency and can reduce water consumption significantly.

The intermediate rinse serves to remove all traces of detergent and entrained soil from the plant being cleaned and, in a partial recovery situation, to recover as much detergent (and thermal energy) back to the dilute detergent tank as possible; it also may need to be sufficient to cool the plant down ready for disinfection and/or refilling. The intermediate rinse should use potable water, and is normally cold, although – if a warm secondary detergent step is being incorporated – it may be desirable to use hot water (if available from sources such as recovered and suitably treated condensate). The intermediate rinse is often recovered and reused as the pre-rinse for the next cleaning cycle.