A tunnel freezer provides a very effective solution for cooling and freezing hot baked products, such as biscuits and bread loafs, as well as a wide range of other foods. It is easy to integrate into existing production lines and requires a lower capital investment than many other types of freezing systems. It also delivers high quality, reliable results and is very fast to install.
The basic design of a tunnel freezer is similar to that used in a cold box, except that the product is frozen by an air current driven by fans located mainly at the end of the tunnel. This allows for rapid cooling or freezing of the product without any dehydration or thermal shock. The cold air is delivered to the products either by direct spraying of liquid nitrogen or carbon dioxide or by indirect circulation of vapor from the freezer’s refrigeration system.
Liquid Nitrogen (LN2) or Carbon Dioxide (CO2) are the cryogens of choice in most tunnel freezers. The cost of these gases varies significantly and can affect the economics of a particular project. A key variable is the total refrigeration value, or BTUs, available to the freezer. A large portion of the BTUs in CO2 and LN2 are consumed to convert them from a solid to a gas (Latent Heat of Vaporization, 86 BTUs per pound). The remaining refrigeration is then available to the freezer and its product.
When compared with other forms of refrigeration, liquid nitrogen has several advantages over both CO2 and ice. At very low temperatures, liquid nitrogen has greater heat transfer efficiency than either CO2 or ice. This translates into lower refrigeration costs, particularly at the extremes of temperature. Liquid nitrogen also retains color more effectively than either CO2 or ice, resulting in a product that looks fresher.
Depending on the application, a tunnel freezer can be configured in various ways. IQF (Belt) Tunnel Freezers are cascade, inline positive-conveying freezers engineered and built for your production requirements. They incorporate a pre-cool zone where moisture is sealed in and separated, a core freezing zone that removes latent heat through continuous fluidized agitation, and a product recovery zone for quick return to the production line.
The Linde CRYOLINE UPT ultra performance tunnel freezer takes this concept to a new level by improving the distribution control of the liquid cryogen that directly contacts the product. This, in combination with vapor circulation, extracts additional refrigeration potential that would otherwise go underutilized. The result is higher cooling efficiency, increased productivity, and a lower overall cost of ownership than traditional tunnel freezers. Contact us to learn more about the possibilities of this innovative freezing system.