One type of ice plant that is very suitable for use in fishing boats is the water ice machine that produces chilled ice crystals. When mixed with water, the crystals allow the slurry to be easily pumped anywhere on the boat with flexible hoses. This ice acts in the form of a slurry, similar to CSW, and therefore can be used in CSW tanks or fish holds. It can also be used in slightly less liquid form to pack fish in tote boxes. Figure 2.5 shows schematically how this type of installation can be mounted on appropriately sized fishing boats.
Slush ice is a mixture of ice crystals in water and water slurry. Ice is created by freezing ice crystals from a weak saline solution in an in-tube tube heat exchanger, also called an etched surface heat exchanger. Water is frozen on the inner tube surface as small round/ellipsoid crystals (about 0.2 to 1.3 mm in diameter) and a rotary screw conveyor transports the ice crystals from the heat exchanger to the water in a storage tank. The resulting ice and water mixture (water ice) can be pumped from the storage tanks through pipes or hoses to the fish cooling area or directly to a sealed container. The density and fluidity of the slush ice can be adjusted by regulating the amount of water added so they can be adapted to different applications.
The advantages requested for aqueous ice for cooling fish are as follows (see also Table 2.6):
It provides faster and even cooling of fish to 0 ° C or lower due to improved heat transfer.
It provides better contact with the fish surface without caries or pressure damage.
It is claimed that ice pollution is significantly reduced due to the closed system design and storage of the ice maker.
Ice can be pumped directly to where it is needed, so there is no need for storage.
Typical features for twin-tube ice machine
Note: Currently, 2.5 to 24 tons slush snow ice machine models with 24-hour capacity have separate cooling systems for built-in installation, as stand-alone units or remote units.
Since the “raw material” for ice production is a brine solution (3-5 percent NaCl), seawater can be used for ice water production. This allows the units to be mounted on fishing boats. The commercial application of aqueous ice in industrial purse boats has been tested with good results for cooling small pelagics. Ice has been used to improve the traditional RSW system on a conventional purse-ship and to improve cooling by significantly shortening the cooling time from 7-20 hours to about one hour in regular RSW. As can be seen in Figure 2.6, the cooling time of fish in ice is quite short compared to leaf ice and can be compared with the cooling times encountered with CSW.