Oven and method for generating heat for an oven

Abstract: The invention relates to a convection oven for processing food products, preferably, an oven (1) for baking. This is provided with heat-generating devices (4). According to the invention, the heat-generating device is a catalytic burner (4) that creates at least the main part of the heat, whereby higher efficiency is achieved, less space is needed, controllability is greater, and the process is more environmentally friendly. The invention also relates to a method for generating oven heat by means of catalytic combustion.

Description: The present invention relates to an oven of the type set forth in the preamble to claim 1 and to a method of the type set forth in the preamble to claim 4. The invention is intended primarily for baking bread on an industrial scale, but it is not limited to this field of use. It is thus applicable to all other types of processing of food products in ovens. In baking ovens of the type the invention is primarily intended for, heat is generated either electrically, or, more commonly, by means of a burner of a traditional type, which uses oils or gas as fuel, and in which heat is usually applied via a heat exchanger. Traditional burners have several disadvantages, such as poor efficiency, sluggish control cycles, they require a large space, and they produce polluted exhaust gases. The problem of polluted exhaust gases can be solved in part by using catalytic post-combustion of the exhaust gases. Such procedures are previously known from, for example GB 2 185 420; US 4,944,283; DE 33 46 019; NL 7 005 521 and US-A-4 113 439, all of which show the arrangement of catalytic post-combustion in the out-going air. In this manner, one avoids spreading a foul smell out into the environment since pollution products such as grease, oil and the like are burned but do not exit along with the out-going air. The problem remains, however, that the exhaust gases from the burner reach the food products, in addition to the other disadvantages of a conventinal burner mentioned above. Moreover, FR 2 222 058 discloses an oven in which a catalytic combustion device is used in an oven of the kind that transfers heat by means of radiation, that is, to an oven of a type that differs in principle from a convection oven. The object of the present invention is to provide a convection oven and a method for generating heat in such an oven, such that these problems are overcome. This object is achieved according to the invention by providing the oven with the special features set forth in the characterizing portion of claim 1, and by the method that comprises the special procedural steps set forth in the characterizing portion of claim 4. By using a catalytic burner it has become possible to significantly increase efficiency compared with a conventional burner. By using a catalytic burner it has become possible to eliminate the need for a heat exchanger, which is used in conventional burners. A catalytic burner thus makes possible a compact system with a small mass. For 100 kW of power, the system will not weigh more that 2 kg, whereas a corresponding heat exchanger weighs roughly a 150 kg. By eliminating the large mass that the heat exchanger represents, one also achieves a much faster control cycle. Because of the faster control cycle, it becomes much easier to follow the optimal profile of how the temperature should vary as a function of time. The need for space is also greatly reduced by using a catalytic burner with the aforementioned power. Thanks to the complete combustion of a catalytic burner, the cleanliness of the exhaust gases increases. This allows for greater freedom in the choice of fuel quality. The result of this is lower operational costs, better performance, a more compact oven and, most importantly, less environmental impact. In yet another preferred embodiment, the oven air is recirculated, which is advantageous from the standpoint of efficiency, since all of the combustion gases are applied to the oven air. Using current technology, the energy content of the combustion gases is lost out through the exhaust stack. Only the air that is needed for combustion is applied. The above-mentioned and other advantageous embodiments of the invention are set forth in the following dependent claims. The invention is described further in the following detailed description of a preferred embodiment of the invention, with reference to the accompanying figures, of which: Fig. 1 is a schematic section view of an oven according to the invention. Fig. 2 is a perspective view of a catalytic burner used in the oven in Fig. 1. The oven in Fig. 1 is a convection oven where the air is heated by a heat-generating device 4 which, according to the invention, comprises a catalytic burner. The heated air circulates in the oven through a system of channels and openings, as the arrows show. The air thus flows from the burner 4 downward through the channel 5, from which it is distributed through openings (not shown) in the inner wall 6 of the channel. The openings in the wall are arranged so that a uniform flow is achieved in towards the food products to be processed. In the illustrated example, it is bread that is to be baked. The bread pieces 3 are placed on sheets 7 in a bread rack 2. The air flows through the bread rack 2 and onward through openings in the channel wall 8, from which it is led upward and is mixed with the combustion gases. The combustion gases contain air that is added for combustion. The catalytic burner 4 is shown in greater detail in Fig. 2. It has a mainly cylindrical shape, although other shapes are possible, and its surface is coated with the catalytic material consisting of noble metals or metal oxides. The air-fuel mixture applied to the catalyzer reacts chemically with the catalyst material. Combustion is complete and, since the products of combustion consist solely of carbon dioxide and water, the process is environmentally friendly. Since the combustion occurs at a lower temperature than does combustion using a flame, the formation of poisonous nitrous oxides is avoided.

Claims: An oven (1) with a heat-generating device (4) for processing a food product (3), in which the generated heat is transferred to the food product (3) by convection, characterized by said heat-generating device comprising a catalytic burner device (4) effecting the main part of said heat generation. An oven (1) according to claim 1, in which recirculation devices are provided for recirculating the oven air. An oven (1) according to either of claims 1 or 2, which is arranged as a baking oven. A method for generating heat for an oven for processing food products, characterized by at least the main part of the heat being generated by catalytic combustion and by the heat being transferred to the food products by convection. A method according to claim 4, in which the oven air is recirculated. A method according to either of claims 4 or 5, in which said processing is baking.

Inventors: LARSSON LENNART, PERSSON JONAS, LARSSON, LENNART, PERSSON, JONAS
Applicants: SVEBA DAHLEN AB, SVEBA-DAHLEN AB
Application year: 1997
Main classification: A21B1
IPC codes: F24C3, A21B1