Refrigeration & Equipment Engineering

Unit 6 - Ice Plant

6.4.1.Block ice
The traditional block ice maker forms the ice in cans which are submerged in a tank containing circulating sodium or calcium chloride brine. The dimension of the can to make block ice is usually selected to give a freezing period between 8 to 24 hours. Too rapid freezing result in brittle ice. The block weight can vary from 12 to 150 kg depending on the requirements, 150 kg is considered as the largest size of blocks one can conveniently handle. Thicker the block, longer is the freezing time. Blocks less then 150mm thick can easily be broken and a thickness of 150 to 170mm is preferable, to prevent the block toppling. The size of the tank required is related to the daily production. A traveling crane lifts a row of cans and transports them to thawing tanks at the end of the freezing tank. When they are submerged in water the ice release from the moulds. The cans are tipped to remove the blocks. Once ice is removed the cans are filled with fresh water and replaced in the brine tank for further cycle. This type of Plant often requires continuous attention and shift system is operated by the labor force which may be 10 to 15 workers for 100t/ day plant. Block ice plants require a good deal of space and labor for handling the ice. The later factor has been the main reason for the development of modern automatic ice making equipments. Blocks ice still has a use, and sometime an advantage, over other forms of ice in tropical countries, storage, handling and transport can all be simplified if the ice is in the forms of large blocks, simplification is often obligatory in small scale fisheries and in relativity remote situations. With an appropriate ice crushing machine block ice can be reduced to any particular size but the uniformity of size will not be as good as that achieved with some other toms of ice. In some situation block ice may also be reduced in size by a manual crushing method.