High efficiency convection oven

Abstract

Processes and systems for improvements on the efficiencies of convection ovens utilizing exhaust heat recuperation in the form of heat exchangers and premixed combustion systems, and a combination thereof. The heat exchangers and premixed combustion systems allow for increased efficiency of use of fuel and gaseous mixtures within convection oven cavities for improved heating capabilities and decreased efficiency losses.

1 . A method of operating a convection oven, the method comprising the steps of:
 integrating a first heat exchanger with an oven cavity to increase an operating efficiency of the oven cavity;   pulling a combustion gas into the oven cavity through at least one side of the oven cavity via a constant-speed or variable-speed inducer blower;   pushing the combustion gas out of a flue in the form of flue gases from the oven cavity; and   recovering useful heat from the flue gases upon exiting the cavity with a second, recuperative heat exchanger integrated with the oven cavity, resulting in preheating of combustion air entering a combustion cavity via the inducer blower.   
     
     
         2 . The method of operating a convection oven according to  claim 1  wherein the recuperative heat exchanger is external to the oven cavity. 
     
     
         3 . The method of operating a convection oven according to  claim 2  further comprising guiding the combustion air through the recuperative heat exchanger with a combustion air intake manifold heating the combustion air; and
 delivering the preheated combustion air to the combustion cavity to mix with a fuel for combustion. 
 
     
     
         4 . The method of operating a convection oven according to  claim 3 , further comprising recycling a portion of an exhaust energy back to the combustion cavity as incoming combustion air. 
     
     
         5 . The method of operating a convection oven according to  claim 4 , wherein the incoming combustion air absorbs a portion of exhaust heat that is normally rejected as waste heat. 
     
     
         6 . An apparatus for the practice of the method of  claim 1 , the apparatus comprising:
 an oven cavity;   at least one heat exchanger configured to physically integrate with the oven cavity;   an exit flue gas exhaust path;   an entry combustion air path, wherein the exit flue gas and combustion air communicate via heat transfer; and   a blower positioned with respect to an exit of the oven cavity, the blower adapted to maintain a suitable pressurization in the oven cavity.   
     
     
         7 . The apparatus of  claim 6  wherein the at least one heat exchanger comprises a flue-to-air heat exchanger. 
     
     
         8 . The apparatus of  claim 6  wherein the blower is further adapted to maintain internal circulation in the oven cavity for improved temperature control. 
     
     
         9 . The apparatus of  claim 6  wherein the exit further comprises a secondary inducer adapted to necessitate an intake manifold of the combustion air with the at least one heat exchanger. 
     
     
         10 . A method of operating a convection oven, the method comprising the steps of:
 integrating a high-efficiency premix burner with an oven cavity to increase an operating efficiency of the oven cavity;   utilizing a premixed combustion system with the high-efficiency burner by premixing a fuel supply and an air supply resulting in flue gases; and   introducing the flue gases into the oven cavity with a blower.   
     
     
         11 . The method of operating a convection oven according to  claim 10 , the premixed combustion system further comprising:
 pushing the fuel supply and the air supply into the oven cavity with the blower, the blower operating at constant or variable speeds; and   permitting variable heating rates independent of a combustion gas recirculating within the oven cavity with a fuel and air mixer and the premix burner.   
     
     
         12 . The method of operating a convection oven according to  claim 10  wherein the premixed combustion system operates with a desired, reduced level of excess air. 
     
     
         13 . An apparatus for the practice of the method of  claim 10 , the apparatus comprising:
 an oven cavity;   a high-efficiency premix burner adapted to provide a controlled hot stream of flue gases to the oven cavity;   an electronically-controlled blower configured to feed an air or a fuel and air mixture into the high-efficiency burner;   the electronically-controlled blower further comprising a fuel and air mixer and the premix burner;   a fuel supply provided to the oven cavity; and   an air supply provided to the oven cavity, wherein the fuel supply and air supply are provided to the oven cavity via the blower, fuel and air mixer and premix burner.   
     
     
         14 . The apparatus of  claim 13  wherein the electronically-controlled blower is adapted to operate at variable speeds. 
     
     
         15 . The apparatus of  claim 13  wherein the blower balances pressure in a combustion cavity of the oven via a differential pressure sensor between the oven cavity and an installation space. 
     
     
         16 . The apparatus of  claim 13  wherein the burner comprises a flame holder, the flame holder composed of porous, high-temperature resistant material. 
     
     
         17 . The apparatus of  claim 16  wherein the high-temperature resistant material is a metal. 
     
     
         18 . The apparatus of  claim 13  further comprising an operational lock on a door of the oven cavity adapted to prevent opening of the oven cavity. 
     
     
         19 . A method of operating a convection oven, the method comprising the steps of:
 integrating an exhaust heat recuperator with an oven cavity to increase an operating efficiency of the oven cavity;   pulling combustion gases through a side of the oven cavity via a downstream blower;   pushing the combustion gas out of a flue from the oven cavity;   cooling the combustion gases exiting the flue resulting in preheating of the combustion gases entering the oven cavity via the downstream blower;   recovering useful heat from gases upon exiting the oven cavity with a recuperative heat exchanger integrated with or separate from the oven cavity, resulting in preheating of the combustion gases entering a combustion cavity, wherein the combustion gases are drawn in by the downstream blower; and   wherein the heat exchanger utilizes a premixed combustion system by premixing fuel and air, employing a combustion blower upstream of ignition and introducing the combustion gases into the oven cavity.   
     
     
         20 . The method of operating a convection oven according to  claim 19 , further comprising controlling the pressure or temperature increase in the oven cavity by limiting the volume of the combustion gases flowing through the exhaust heat recuperator through utilizing a bypass to a flue exit;
 independently controlling the combustion heating rate and combustion gas recirculation by stabilizing temperatures in the oven cavity; and   improving cooking by reducing a boundary layer thickness on a product inside the oven cavity through independent control of the downstream blower versus the upstream combustion blower.