Engineering R&D: The small freeze
A smaller footprint is a clear improvement in the newest generation of cryogenic freezers, and incremental improvements in heat transfer rates are making them affordable options.
Incorporating cryogenic freezing in place of mechanical freezing gave way in the last decade to an appreciation of the ROI cryogenic systems provide in terms of reduced yield loss, improved product quality, throughput and a focus on safety and sanitation. Continuous refinement of the underlying technology has strengthened the economic argument, resulting in applications beyond high-margin food products.
Linde developed cryogenic impingement freezers for food a dozen years ago and enhanced its market position in 2006 with the acquisition of BOC Gases. As a result, Linde inherited BOC’s cryogenic impingement system with atomized liquid nitrogen, which significantly shrank the footprint of high-volume machinery (see “Cryogenic impingement boosts freezer efficiency,” Food Engineering). Technical development has continued, resulting in increasingly compact designs and more efficient heat transfer. An example is Linde’s Cryoline XF cross-flow spiral freezer, which received a US patent in December.
Ed Cordiano guides the marketing and sales strategy and manages the technology portfolio within some of Linde’s food manufacturing sectors. He was named program manager-bakery & prepared foods for Linde’s food and beverage team last year. Cordiano has more than 12 years of experience in the industrial gas business, including six years as segment manager for modified atmosphere packaging. Cordiano holds a BS in mechanical engineering from Case Western Reserve University and an MBA from Northwestern University.
FE: What notable improvements are occurring in cryogenic freezing?
Cordiano: Spraying the cryogen onto the product for conductive heat transfer has been done forever. However, over the years, improvements have been made to increase the convective heat transfer to accelerate freezing rates, boost throughput and improve efficiency. Our new cross-flow spiral freezer exemplifies this. Conventional spirals have a boxy design and an inefficient airstream within the freezer. The new units have a cylindrical shape and create even airflow across the entire belt width. The result is at least a 10 percent efficiency gain and a 33 percent smaller footprint.
FE: How has the airflow been improved and what does that mean to the end user?
Cordiano: The stainless steel enclosure wraps itself around the belt, leaving no gap between the belt’s outer edge and the freezer wall. With conventional units, there is higher airflow on the outside of the belt than the inside, resulting in temperature gradients across the belt. Because users have to meet a freezing spec, they end up over-freezing product on the outside of the belt, resulting in an increased freezing cost. The new cross-flow design evenly distributes airflow across the belt, resulting in more efficient use of the gas and better consistency and quality in the final product.
FE: How large is the new Cryoline XF unit?
Cordiano: With a 30-inch belt, the cross-flow spiral freezer measures 10 ½ feet high, 13 feet wide and a little over 21 feet long. A larger unit with a 40-inch mesh belt is also available.
FE: Was the velocity of the air flow increased, as well?
Cordiano: More than the velocity, the system creates a unified airstream across the entire belt width. This is a value to food manufacturers as it drives down freezing cost and leads to a consistent freeze and higher quality product.
FE: Linde also is touting the hygienic design of its new IQF freezer. In what way has hygiene been improved?
Cordiano: Cleanability for improved product safety is paramount today, and there is constant concern about the drip, drain and draw of any freezer, with proper sloping to ensure there is no pooling of water after the sanitation cycle. Fifteen years ago, IQF freezers were essentially sealed boxes around a conveyor belt. Today, systems provide complete access to all food contact surfaces, are CIP capable, and meet the American Meat Institute’s principles of sanitary design.
FE: What is unique about the Cryowave IQF Tunnel freezer?
Cordiano: Traditionally, IQF products were frozen in flighted freezers. The new Cryowave freezer does away with the flighted design traditionally used with CO2 freezers. With flighted systems, product goes up an incline, then drops to another belt to prevent sticking. CO2 snow build-up is common, requiring frequent stopping of the production line for cleaning. The flighted freezer has been around for decades, but there were significant challenges with the snow build up, yield loss of product and overall inefficiency of these units.
The new Cryowave design employs proprietary “rolling wave” action. A series of bars are positioned under the stainless-steel mesh belt along the length of the unit. The bars lift the belt in a sequenced pattern, creating a rolling effect that prevents product from sticking to each other or the belt and expose the entire surface area of product for efficient heat transfer and freezing. Either nitrogen or carbon dioxide can be used as the cryogen.
FE: What cryogen options exist for rapid freezing of food?
Cordiano: While there are several cryogenic gases, there are only two options with food: nitrogen or carbon dioxide. It comes down to the type of product, the freezing requirements and the value to the customer.
FE: Which is the most cost effective?
Cordiano: It’s really a value issue in terms of yield gain, production throughput increase, etc. and the utilization of available BTUs associated with each type of cryogen.
The choice of cryogen ultimately comes down to the application. For example, nitrogen remains in a liquid state at atmospheric pressure, making it the only element that can be used in immersion freezers. Optimizing the heat transfer rate is a continuous improvement effort in order to provide our customers with the most efficient and cost-effective solution.
FE: What contribution has controls technology made to efficiency?
Cordiano: Over the years, machines have gone from push buttons and relays to HMIs to make them not only more user friendly but also to optimize the freezing rate. Both off-the-shelf and customized controls architecture has been developed to make outcomes more repeatable. For example, operating parameters for specific food products or recipes can be programmed to reduce the time required for switch outs and to eliminate guesswork by the operator.
FE: Are there new applications for cryogenic freezing?
Cordiano: Linde has recently introduced the Cryoline PE freezer which freezes sauce pellets in a consistent weight and shape using liquid nitrogen. Wet, sticky products traditionally have been very difficult to IQF efficiently, and an even bigger challenge has been developing a solution that fits the customer’s space. Both the cross-flow design and the hygienic Cryowave freezer are designed to address those issues.
Cryogenic freezing is a very strong application in all food segments from large protein manufacturers to bakeries. It’s low capital cost and simple installation provides easy entry for small and large processors. Cryogenics is used on par-baked and fully baked goods, and in pizza crust and pizzas with toppings. The ability to lock in moisture is key, both for improving yield for protein foods and increasing product quality.