High humidity steam cooker with continuously running conveyor
TECHNICAL FIELD 
     This invention relates to cookers and more particularly it relates to cookers through which are transported food products on a continuously moving conveyor belt. 
     BACKGROUND ART 
     In the field of industrial cooking requiring the rapid cooking and throughput of large quantities of food it has been customary to pass the food through a cooker on a conveyor belt. Typical examples of such prior art are as follows: 
     U.S. Pat. No. 3,982,481--E. T. Console et al. This shows a chamber through which a conveyor belt passes to carry produce for blanching in a steam spray. 
     Certified Manufacturing, Inc., Lynwood, Calif. 90262 has marketed gas fired broilers with a conveyor belt transport therethrough. 
     U.S. Pat. No. 1,491,958--J. F. Logan et al., uses a spiral conveyor to transport food in cans through a dry heat chamber. 
     However, in this type of prior art there are many unsolved problems relating to the cooking, the efficiency and the sanitation of conveyor type cooking systems. 
     Thus, particularly with rapid cooking techniques, the juices, essences and moisture is withdrawn from food products changing the appearance, flavor and texture thereof. 
     Also the cooking may not be uniform to the center of such products as meat which needs be cooked at the inner bone structure. 
     In general the food products present an interface to the heating medium that does not efficiently transfer heat, such as the fat skin layer of a piece of fowl. Also, such residue as fat drippings can significantly decrease heating efficiency. 
     Whenever a continuously running conveyor is used it tends to carry heat out of the cooker and cool air into it. This wastes energy and establishes an uncomfortable working environment for loading the conveyor. 
     Also the amount of energy carried out of a hood or exhaust system is significant, and in the case of steam heat for example, there can be significant heat loss by condensation of the steam into droplets. 
     The conveyor belts are difficult to sanitize, particularly in those systems that pass the belt back through the cooker to bake on residue. Other movable and irregularly shaped parts in or near cookers are apt to accumulate contaminating residue and breed bacteria. Also accessibility of the systems is in many cases difficult for takedown and entry into interior compartments for cleaning and sanitation. 
     Accordingly, it is an object of this invention to provide an improved, efficient, sanitary conveyor type cooker for food products that resolves the foregoing problems, and provides other features and advantages which will be found throughout the following text. 
     BRIEF DISCLOSURE OF THE INVENTION 
     Food products such as fish, meat, fowl or produce are carried on a conveyor belt in a spiral path through a steam cooking chamber. The chamber is kept near 100° C. and 100% humidity by two steam sources both supplied with pure water and at a pressure above atmospheric in order to produce efficient rapid cooking without loss of humidity and with protection to appearance and flavor. 
     One steam source comprises a heat exchange surface in a pool of water on the floor of the chamber stirred to create heating efficiency and to skim off fat drippings from chicken or meat products. The other externally located steam generator has steam piped into the chamber. 
     The continuously running conveyor belt is passed on a return path outside the cooker through a continuously run spray detergent cleaning and sanitizing bath, and the internal parts of the cooker are all accessible by doors on all sides thereof. Driving machinery and elements requiring lubrication are all located outside the cooker to present simple sanitary surfaces for cleaning and sanitation. An internal cleaning spray system is also provided. 
     Other features are found hereinafter in the more detailed description of the preferred embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a system schematic diagram showing the various features of the invention; 
     FIG. 2 is a side elevation sketch of the cooker cabinet afforded by the invention; 
     FIG. 3 is a diagrammatic view, partly broken away, of a continuous conveyor belt spray cleaner afforded by the invention; 
     FIG. 4 is a diagrammatic view in perspective, partly broken away, showing the spiral conveyor path within the cooker as afforded by this invention; 
     FIG. 5 is a diagrammatic view in perspective, partly broken away, showing the steam supply means for the cooker as afforded by this invention; and 
     FIG. 6 is a perspective view of the cooker cabinet array as provided by this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The overall system and combinational aspects of the cooking system provided by this invention are set forth in FIG. 1. Thus, it is seen that food products 10 to be cooked are loaded on a conveyor belt 11 at the loading station 12 outside the cooker room wall 13. Preferably the food products are substantially uniform in size and weight such as chicken legs, sized fish filets, steaks, etc. The products thus are loaded on the conveyor belt 11 at atmospheric pressure at loading station 12 outside the cooker room 14 which is kept at a pressure above atmospheric. This not only keeps the working conditions more comfortable but improves the cooking efficiency as hereinafter shown. 
     The products first undergo an optional pure water spray mist process at station 15 to wet the surface of the products for better heat interface exchange with the steam inside cooker housing 16. It should be recognized that particularly in the case of meat products which are covered by a fat, this wetting step is important to reduce the insulation characteristics and to achieve more efficient and rapid cooking. 
     The products are then passed through a duct 17 or . opening in upper part of the cooker housing and through a spiral conveyor path 18 to assure the proper dwell time within the cooker at the chosen conveyor speed. The conveyor belt is of stainless steel for sanitary purposes and is not lubricated, since that would introduce contamination for food products. 
     The conveyor exits the cooker housing 16 at a lower duct 19 which is in the form of a trap reducing the steam and heat energy leaving the cooker on the conveyor belt 11. Thus baffles 20 resist flow of hot air or steam out of the cooker housing 16 and fan 21 creates a counter flow of air at least sufficient to prevent any significant unnecessary outward flow of heat energy by way of gases carried outwardly by conveyor 11. This fan can control the rate of fresh air flow into cooker housing 16 as later discussed. 
     The cooked food products 10&#39; are then conveyed to unloading station 22 outside cooker room 14 on the outside of wall 23. The conveyor belt is typically wide enough for several side-by-side pieces of meat, produce, fish or poultry, for example, and a typical throughput is over a ton of raw products per hour with typical cooking times of 20 minutes between input loading station 12 and output unloading station 22. The cooked product temperature is uniformly in the order of 97° C. 
     The cooking is solely with water droplet free steam near 100° C. and 100% humidity at a pressure above atmospheric. The high humidity atmosphere prevents losses of humidity of the product as it passes through the cooker and helps retain juices, essences and flavor of the product. Also it improves the heating steam interface heat exchange at the product surface for more efficient cooking. 
     The higher pressure not only produces a pressure-cooker like cooking efficiency to the cooking process, but is critical in connection with the flavor and conveyor type product flow as well. Thus, consider products loaded at the conveyor loading station 12 at atmospheric pressure when introduced into the cooking chamber will then tend to draw the steam internally within the cellular structure of the product for faster more intimate contact and quicker more uniform cooking throughout. This action also resists the leaking and removal of juices and essences of the product for better flavor control. 
     Part of the steam, typically 25%, is provided by an external steam generator 30 with filter to remove water droplets as supplied with pure water 31 to prevent contamination. This is piped to various locations 32, 33 within the cooker to assure a constant circulating flow of steam near 100% humidity 100° C. atmosphere about the products being carried on belt spiral 18. Also, for example, a jet 33 may flow steam in a direction counter the belt flow path to create a circulation path preventing undesired loss of steam out of duct 19 as the belt leaves the cooker, and together with fan 21 can create a desired ratio of input of outside air for circulation. 
     For this purpose an outlet stack 35 will let out of the cooking housing 16 an amount of steam flow controlled by valve means 36. 
     The remaining steam is provided by an internal boiler having the pool of water 40 on the floor of the cooking chamber as heated by the heat exchange element 41. To assure the right amount of steam and pressure within the cooking chamber, the power is controlled as a function of the temperature at the gas discharge stack 35 as sensed by temperature sensor 43. 
     For better steam producing efficiency the water in pool 40 is circulated by means such as paddle wheel 45 and electric motor 46. This is additionally used to improve steam production efficiency by creating a wave flow 47 travelling toward fat skimmer 48 which receives the crest of the waves on which the fat rides and removes the fat in the manner of a swimming pool skimmer mechanism. This prevents any accumulation of an insulating fat film on the pool 40 that prevents or reduces steam output, and further it removes a substance which could cause both sanitation and flavor problems if resident long in the cooker chamber. The fat is not thus broken down into a residue gas which would flavor the product adversely nor a scum which would not be easily sanitized. Also the fat may constitute a useable by-product. 
     To further improve sanitation, those elements which require lubrication or access for maintenance are located outside the cooking chamber, as exemplified by motor 46 and belt conveyor drive mechanism 49. Also the belt 11 is returned from unloading to the loading station outside the cooking chamber as shown by the view of FIG. 2 where there is a niche 50 in the cooker housing 16 to permit a short return path through a conveyor duct 51. The access doors 52 are supplied on all sides of the housing for accessibility for maintenance and sanitation. 
     Additionally a detergent spray system provides for continuous cleaning of the belt at 55 and for a spraying of the cooking chamber as depicted at spray outlet 56 with a sanitary detergent solution. 
     The belt cleaning spray mechanism is shown in detail in FIG. 3, which with all succeeding figures uses similar reference characters for common features to facilitate comparison. 
     Installed in the return duct 51&#39; about the stainless steel conveyor belt 11 is a spray wash unit 55 powered by continuously running motor-pump 57. The belt has interconnected stainless steel segments which permit travel around guide rollers 58, 59 and other flow paths within the system. The conveyor belt 11 has a central open grating upon which the products rest which permits steam and detergent spray solution 60 to flow through the belt into sump 61 for recirculation by motor-pump 57. 
     Sufficient spray nozzle arms 62 are provided with nozzle construction and spray pressure such as to dislodge any crumbs or drippings of the product remaining on the belt after cooking and unloading. A sanitary detergent solution is used to provide a sanitary belt for receiving a new loading of products at station 12 without contamination from the continuously running belt. Because the belt 11 does not return through the cooker, there is less tendency to bake on any residue and the cleaning function is simplified. Brushes may be used if desired and the brush 64 removes moisture from the roller 58 to keep the belt drier. It dries rapidly because it is warm after leaving the cooker and the reduced atmospheric pressure outside wall 13 permits quick evaporation of residue moisture. The solution in sump 61 is filtered for removing residue before recirculation by the pump, and the detergent solution can be changed as often as necessary to maintain strict sanitary conditions without possibility of introducing bacteria or retaining contaminating residue. Note all mechanisms such as pump 57 are kept outside the sanitary cooking compartment and ductwork 17&#39;, 51&#39; keeping any foreign substances off the belt 11. 
     Features shown in FIG. 4 include the spiral path 18 taken by the belt 11 through the cooker chamber, access doors 52, etc. for internal access, maintenance and sanitation and the placement of drive means such as chain sprocket 68 for driving the conveyor belt through the spiral path 18 and its associated drive mechanisms. The catwalk array 69 gives a size perspective of the cooker housing 16, and provides access to top entry panels and the mechanism 68 for maintenance. The spiral belt path may have as many convolutions as necessary to retain particular specialty products within the cooking chamber a desired dwell time for the desired belt travel speed. 
     Details of the heating mechanisms are shown in FIG. 5. For sanitary purposes stainless steel is used wherever possible and the interior walls of the housing 16 are smooth to avoid any surfaces that could cause dripping or collect contamination. The interior 70 of the housing walls is insulated to preserve heat and to produce a safe and lower temperature outside wall environment around operational personnel. 
     The steam generator unit 30 could be any standard commercially available steam generator unit and is preferably made of stainless steel. It is coupled to a boiler for a supply of sanitary steam from pure water by means of piping 71. Approved pure water make-up is entered from source 31 to assure sanitary steam. All piping is stainless steel sanitary steam pipe with pipe insulation having sanitary jacketing. 
     The floor water may be pumped out by pump 75 through drain 76 when sanitizing by detergents from piping 56. 
     The fat skimmer duct 48 has internal baffling to reduce the loss of hot water and it leads to a settling tank (not shown) for segregation of fats. 
     The external steam is preferably disposed through piping 78 to the four corners of the cooking chamber and steam is released at nozzles 32&#39;, 33&#39; or along the length of the piping such as shown at 79 to provide proper mixture and saturation along the spiral conveyor path with the steam evaporated from the lower water pool. 
     Externally the cooking cabinet 16 is shown in FIG. 6. The top housing 80 encloses the mechanisms for driving the spiral conveyor system within housing 16 and the top access door 81 permits entry for maintenance, inspection, sanitation and the like. 
     It is therefore evident that the steam cooking system provided by this invention has advanced the state of the art and provided many improved features. Those novel features believed descriptive of the spirit and nature of the invention are set forth with particularity in the appended claims. 
     INDUSTRIAL APPLICATION 
     Large volumes of food products are processed on a continuously running conveyor belt passing through an energy efficient steam cooker which preserves product humidity, flavor and appearance. Thus, fish, meat, poultry, produce and like food products can be cooked. There are self-cleaning and apparatus features for meeting the strictest of sanitation requirements.