Case Study

Nitrogen Freezing System Helps Seafood Business Grow

Back in December, R.A. Lesso Seafood Company installed a new freezing system at their processing plant in Biloxi, Miss. The system was needed to replace a carbon dioxide system that the processor had outgrown when its production requirement more than doubled.

The new system, which uses liquid nitrogen as the refrigerant, combines an Air Products 10-foot long Cryo-QuickCrust Plus Immersion Freezer with a Cryo-QuickTunnel Freezer extension. The combined system allows the customer to individually quick-freeze over three and a half tons of shrimp per hour for sale to R.A. Lesso Seafood Company's U.S. markets.

At the Biloxi site, the shrimp pass through a bath of liquid nitrogen (-320°F) and are instantly crust frozen. The shrimp then tumble onto two separate and stacked conveyor belts where cold nitrogen gas generated by the liquid nitrogen bath further freezes the shrimp. The freezing is completed in the tunnel extension to achieve maximum efficiency.

Cryo-QuickCrust Plus Immersion Freezer
The immersion freezer is capable of freezing a wide variety of non-bulky, quick-frozen products - but is particularly suited for freezing smaller products that tend to clump, such as diced meats, seafood, and fruits. Requiring only 10 feet of floor space, compared with a normal freezer that can take up 30 to 50 feet, the unit allowed Lesso to add production capacity without investing in a major plant expansion. Using the liquid nitrogen immersion technology in a multi-tiered system, the Crust Plus unit alone can freeze 3000 to 4000 pounds per hour of individually quick-frozen product. By using an Air Products tunnel with the Crust Plus unit, belt speeds can be increased without reducing the overall time the product is exposed to the liquid nitrogen refrigerant. This allows Lesso to achieve an extra 2000 to 3000 pounds per hour of production.

Lesso Seafood found that because the system used liquid nitrogen as the refrigerant, a significantly lower capital investment was required than for mechanical freezers. While the variable cost of freezing with liquid nitrogen is higher than mechanical costs, there was virtually no capital cost for the liquid nitrogen system. Likewise, products with a high water content, such as shrimp, are difficult to individually quick freeze with a mechanical system. The slower freezing rate of the mechanical system can cause the shrimp to clump and dehydrate. These clumping and dehydration problems, in turn, can cause significant quality concerns.

It was also Lesso's experience that the immersion system was extremely efficient and easy to clean and maintain because of its simple design, construction, and few moving parts. Also, the snow buildup typically associated with carbon dioxide freezing was eliminated.

Cryo-Quick Tunnel Freezer
The freezing system at Lesso combines the small footprint and immersion technology of the Crust Plus unit with the efficiency of a more traditional tunnel. In the Crust Plus unit, the product moves through the liquid nitrogen bath and then tumbles to a second and third belt located directly below the immersion bath. Once the product completes the two passes on the belts, it is conveyed onto the belt of the tunnel freezer, which is end to end with the Crust Plus unit. The tunnel freezer quick-freezes or chills product as it is carried along a mesh conveyor. All surfaces of the product are exposed to cold nitrogen gas throughout the tunnel as well as a liquid nitrogen spray at the exit. The tunnel freezer is designed to work in conjunction with the immersion unit, using the re-circulated nitrogen gas to increase efficiency. In effect, the two freezers operate as one.

The tunnel unit incorporates gullwing doors that open up for fast and thorough cleaning, which typically takes less than one hour. And like the immersion unit, simple design, construction and few moving parts make the freezer easy to maintain and use.

Commenting on the new installation, Rudy Lesso, III, vice president of Lesso Seafood Company said, "Air Products was able to custom-tailor a freezing system to meet our specific production requirements. The freezers have helped us double our throughput, improve product quality, and lower operating costs."

By Pam Ahlberg

For more information contact: Air Products and Chemicals, Inc., 7201 Hamilton Blvd., Allentown, PA 18195. Tel: 800-654-4567; Fax: 800-880-5204.