A. Field of the Invention
This invention relates generally to industrial and commercial freezing systems for comestibles such as meat, seafood, vegetables and baked products. In particular, the invention relates to a blast freezer system designed for continuous production and which achieves a high throughput of product with a minimum of labor. The freezer system can be either fixed or portable. Some embodiments described below are particularly suited for installation on fishing boats or in remote processing locations, but the invention is applicable to freezing systems in general.
B. Description of Related Art
Many methods are commonly used for preserving foodstuffs, including canning, salting, drying, retort pouching, smoking and freezing. However, all of these methods substantially alter the taste and texture of the preserved foodstuff that typify freshness, except freezing. Freezing can maintain the freshness of food, medical specimens and other items for extended periods of time and can be considered the preferred method of long term preservation for almost all foodstuffs, particularly seafood, meat, fruit and vegetables as well as baked goods. Blast freezing systems are known which are designed for freezing large quantities of comestibles such as meats, seafood, vegetables and bakery products, in a relatively short amount of time. Such systems work by subjecting the comestibles to air chilled to very low temperatures, such as xe2x88x9240 degrees F., for a period of time sufficient to completely freeze the product.
The process of freezing unavoidably changes the food product chemically, biologically and physically. The magnitude of these changes, and the resulting quality of the frozen food product, is greatly affected by many factors, including the rate, method and temperature of the freezing process, and the temperature and air quality during freezing and storage. Generally speaking, it is accepted that fast freezing rates and low consistent storage temperatures are necessary for high quality in most frozen food products. Fast freezing rates create smaller ice crystal formation and less migration of compounds that remain soluble during the freezing process, which greatly affects the taste and texture of the resulting frozen product. Depending on the type of foodstuff, some compounds continue to migrate after the product is considered frozen, further altering the taste and texture. Although recommended storage temperature very for different products, consistent low temperatures of xe2x88x9220xc2x0 F. to xe2x88x9240xc2x0 F. or lower reduce this migration to nil and are considered necessary for the high quality long term storage of most frozen food. So-called blast freezing systems have been developed to freeze foodstuffs at these temperatures quickly.
Another factor that greatly affects the quality of frozen foodstuff and other items is the elapsed time between harvesting and freezing. Most products, particularly seafood, begin to deteriorate rapidly after harvest, resulting in altered taste and texture making them less desirable in the market place. Fishing vessels, in order to sell to more particular markets and to stay on the fishing ground until full, must have suitable production equipment on board for freezing while at sea. Likewise, agricultural organizations must have production freezing equipment nearby, reducing the time between harvest and processing making the resulting product suitable for the more desirable markets that expect high quality frozen foods.
Freezing methods and systems are described in U.S. Pat. Nos. 6,235,332, 4,164,129, 5,452,588 and 3,696,631. The ""332 patent describes a freezer system for freezing delicate fish filets and other items of food in a freezing tunnel. This device alternates product in-feed onto two or more freezing conveyors, where product is solidified enough to be gravity dropped onto a lower core freezing conveyor without product damage. This freezer uses less space than most for its capacity, however the space occupied by the belt returning on the underside of each conveyor to the end where it is reloaded is non-productive space inside the expensive low temperature freezing area. In contrast, the present inventive system distributes the freezing air more efficiently throughout the freezer and to the product in a more controlled manner, increasing overall efficiency and enabling more frozen product to be produced per hour as compared to the ""332 patent. This prior system, as well as other systems, have often required more units of space per units of capacity than those presented herein. Additionally, this freezer is impractical for freezing larger items that require longer dwell times or are too heavy or delicate to drop onto the core-freezing conveyor without damage.
Another substantial advantage of the certain embodiments of the present invention over this and other prior art is a novel trolley design for comestibles which has the ability to configure the freezing area for a very wide variety of product on trays, belts or hanging structures. Additionally, the product density in the freezer is high, but the product remains in contact with the air or a freezing surface (e.g., product tray) on all sides. Additionally, the freezing surface upon which the product is carried through the ""332 patent remains fixed within the freezer, resulting in a shut down of the entire freezer for cleaning at more frequent intervals then the present invention. Another advantage of certain embodiments of the present invention over the ""332 patent is that is the present freezer design has the ability to provide consistent low temperature refrigeration to an adjacent storage facility, without requiring an additional refrigeration system.
Another prior art freezer is described in U.S. Pat. No. 4,164,129. This system provides for spiral, belt and trolley modes of freezing with various duct configurations, allowing their individual use with one refrigeration source. The system of the ""129 patent uses a great deal more space for a given capacity than the present invention, making it impractical for shipboard or remote site installation. Furthermore, the spiral belt freezer, although providing similar continual throughput benefits as provided by the present invention, does not allow for variation in product gap, the space between the belts as it rotates around the center axis, thus limiting product versatility. Space is also not efficiently utilized in the ""129 patent, as the entire center core area around which the belt rotates is not utilized. Additionally, the freezing system of the ""129 patent would likely have to be shut down for more frequent cleaning, and uses a belt which is limited to a very narrow range of small products such as peas or diced vegetables. The trolley mode of operation in the ""129 patent is a batch approach to freezing, which requires more labor and scheduling than continual throughput systems and does not provide the benefits of auto loading or variable spacing and hanging configurations.
A ship-board freezing system is set forth in U.S. Pat. No. 3,696,631. This patent relates to brine freezing onboard a fishing vessel, specifically a deck mounted brine freezing apparatus and integral hold refrigeration system. Brine freezing is often used for shrimp and other similar product and is accomplished at warmer temperatures than desirable for many other freezing applications. While the system of the ""631 patent may be well suited for its intended purpose of brine freezing shrimp, it is not suited for broad use on a variety of different comestibles.
Advanced Food Processing Equipment, Inc. has developed a drag-through dolly tunnel freezer under the trade mark DRAG TUNNEL(trademark) designed for continuous production. However, the Advanced system is not designed to be moved from one place to another. The location and arrangement of the evaporator configuration in the freezing cell is such that it occupies a considerable volume of space in the cell that could otherwise be devoted to product. Accordingly the capacity of the DRAG TUNNEL(trademark) product is reduced from what it otherwise could be.
Another freezer company, IceBits, has developed a blast freezer using dollies loaded with comestibles. However, the IceBits blast freezer is designed as a batch system, meaning that the freezer is loaded with dollies, the dollies sit in the freezer until the comestibles are frozen, the dollies are removed, and a new batch of dollies are placed in the freezer. The IceBits freezer thus has a relatively low throughput as compared to a freezer designed for continuous production, such as the systems like the Advanced Food Processing Equipment DRAG TUNNEL(trademark) product.
Another company, Seattle Refrigeration, has developed a batch-type blast freezer designed to be housed in a standard shipping container. While the Seattle Refrigeration blast freezer system offers mobility, its use of a batch mode of operation, with three or four batches per day, reduces the productivity of the system as compared to what continuous production systems can provide. This system is also more labor intensive and requires extra equipment. It also has an inefficient evaporator design that is believed to result in uneven freezing rates for product, higher dehydration from the product, and associated frost formation problems.
The world-wide expansion and globalization of food producing entities has greatly increased the need for versatile production freezing equipment that can produce very high quality products, suitable for installation onboard fishing vessels, processing vessels and land based installations in remote areas of the world, as well as more conventional plant locations near industrial centers. Another desirable feature is for the freezing system to provide the refrigeration necessary for the frozen product storage area, thereby eliminating the need for a separate refrigeration system. Another desirable feature is for the freezing system to be containerized and or modular, suitable for manufacturing complete or near complete at the factory enabling easy shipment and commissioning at a remote site. Another desirable feature is for the freezing system to be portable, suitable for moving to new areas as individual fish run seasons are completed, or the harvest of one crop is completed and the freezing capacity is needed elsewhere. Production freezing equipment represents a major investment for most organizations and is therefore important for the equipment to be versatile and suitable for a wide variety of products.
The art has lacked a mobile (i.e., transportable), continuous production blast freezer with a high throughput that meets these needs. Some of the embodiments of present invention meet that need by making high quality continuous production freezing attainable, practical and economical in a wide field of applications, including ship-board freezing, freezing at remote sites, and in other areas where a mobile, high throughput continuous production blast freezer may be desirable.
While some of the features of the preferred embodiment are specifically designed and adapted for use in mobile, i.e., portable freezer application, others features of the disclosed embodiments are capable of employment in freezer systems generally, as will be apparent from the following discussion. For example, the novel evaporator configuration, insulated enclosure designs, trolley designs, and/or automated loading and unloading features can be used with existing freezing systems such as described above.
In one aspect, a freezing system for continuous production of frozen comestibles is provided. The system includes an insulated enclosure having an entrance for receiving comestibles to be frozen and an exit for delivering frozen comestibles. A heat exchanger comprising an evaporator is positioned along one side of said enclosure and extending along the length of the insulated enclosure. One or more fans are provided for blowing air in the insulated enclosure through said evaporator in a manner substantially transverse to the longitudinal axis of said enclosure. In a preferred embodiment, the evaporator has a high capacity to depth ratio. This minimizes frost buildup and moisture removal from the product, as explained below.
In one possible configuration, the system also includes a plurality of trolleys individually moveable within the enclosure between the entrance and the exit. The trolleys are designed for holding comestibles to be frozen, either on trays, on hooks or on mesh supports, or in any other appropriate manner for the comestibles. The trolleys contains adjustment features enabling the placement of the comestibles in the trolleys to be changed depending on the size of comestibles.
The insulated enclosure may take the form of a modified standard shipping container and, as such, can be sized and adapted to be readily transported from one place to another by ship, rail or truck. The container is modified by adding insulation to the walls of the container and installing a refrigeration system, including a heat exchanger in the interior of the container to provide a means for removing heat from the container. The rest of the mechanical equipment for the refrigeration system (condenser, valves, etc) can be placed elsewhere in or on the container itself, in a separate container, or provided exterior of the container in any convenient fashion.
Preferably, the refrigeration system comprises an evaporator placed within the container and one or more fans arranged to blow air over the evaporator and through the trolleys in a direction substantially orthogonal to the direction of movement of the trolleys through the container. A preferred evaporator has a high capacity to depth ratio (where xe2x80x9cdepthxe2x80x9d indicates the distance parallel to the fins in the direction of air flow across the evaporator), and has reduced frost formation characteristics as described below.
The trolleys, in a preferred embodiment, have a solid panel on at least one side thereof to substantially block the longitudinal flow of air in the enclosure. This helps form discrete temperature zones in the container and reduce buildup of frost at the exit location of the enclosure.
In another aspect, a trolley is provided for holding comestibles to be frozen by a freezing system. The trolley comprises a base, and a set of vertical support members extending above the base adapted to receive a plurality of trays holding comestibles to be frozen. The vertical support members having a plurality of closely spaced adjustment features to enable trays to be placed at multitude of different vertical positions in the trolley.
High capacity production freezing systems with continuous throughput may also employ an automated station for removing trays from the trolleys loaded with frozen product, and automatically loading the trolleys with trays loaded with product.
Numerous configurations for the subject freezing system are contemplated. One possible embodiment includes dual insulated containers arranged side by side and separated by a vertically oriented evaporative heat exchanger. Other embodiments will also be described. The subject freezing system of the present invention allows for high capacity continuous throughput freezing that offers portability and transportability that has not been realized in prior art blast freezing systems.