Anyone who has ever run Vertical Plate Freezers before will always agree that defrosting is the single most important thing to good product quality & throughput. Ensuring the blocks are released with a minimum of heat input means overall higher product quality (less handling damage) and higher throughput (no waiting for the edges to re-freeze)
Despite its importance in the overall production process – defrosting tends to be commonly misunderstood by production staff & refrigeration engineers alike.
The Freezertech defrosting process is a proven method which offers both the highest possible capacity (fastest defrost time) and the lowest possible temperature (less heat input into the product). Each & every freeze comes ready to work with this method, all the diagrams & control logic are supplied with every freeze. Detailed assistance on capacity calculations & customized installations are also available with every order.
Based on Ammonia (R717) -40°C Evaporating / +25°C Condensing
Typical defrost time - under 2 minutes
The photo here shows an MDM Salmon block when defrosted with the Freezertech high capacity method. This product actually defrosted around -7°C due to the high oil content – which is 7° lower than the visible melting of excess ice on the front of the plates which most people use to indicate a complete defrost.
Here the defrosting took around 100 to 120s (2 minutes) and a temperature sensor in each plate indicates the completion, so there was no need to rely on the operator guessing if it had finished or not. Our plate freezer controller system handles both the freezer & valve operation so the users know everything is working together at its best.
Since the defrost is carried out in the shortest possible time with the minimum of heat input into the product, the product is frozen solid by the time it is lifted from the freezer, which meant no waiting period before handling the blocks (in this case, a crane system which relies on the product being completely solid)
The photo here shows the results of a poor defrost – here the customer had to wait in excess of 20 minutes for the freezer to finish defrosting so the product could safely be ejected. This excess time meant that the product itself gained most of the heat load, leading to nearly 5mm of unfrozen volume on the edges of each block (which is nearly 10% of the total frozen volume).
This leads to longer waiting times for the product to solidify before handling, possible product damage from handling too soon, production delays & excess load in the cold storage areas.
The defrosting methods we use where originally developed for our CO2 plate freezers and quickly integrated into other refrigerants – the examples here being used on Ammonia.