Cooking appliance with heat exchanger

Abstract

The invention relates to a cooking appliance (10) with a cooking chamber (14) in which food can be cooked in a cooking chamber atmosphere, a gas burner (20), a combustion air supply channel (28), an exhaust gas discharge channel (24) and a heat exchanger (22) with which combustion heat of the gas burner (20) can be transferred to a cooking chamber atmosphere, wherein a heat exchanger (34) is associated with the exhaust gas discharge channel (24) with which waste heat of the exhaust gas can be transferred to gas that is supplied to the cooking appliance (10).

Description

[0001] The invention relates to a cooking appliance with a cooking chamber in which food can be cooked in a cooking chamber atmosphere, a gas burner, a combustion air supply duct, an exhaust gas discharge duct and a heat exchanger with which the combustion heat of the gas burner can be transferred to a cooking chamber atmosphere or a steam generation system.

[0002] Such a cooking appliance is a professional cooking appliance such as is used in restaurants, canteens and large catering establishments. The gas burner is used to heat the atmosphere in the cooking space. In addition, a steam generator can be provided with which water vapor is generated, which is also introduced into the cooking chamber. A gas burner can also be used as the heat source of the steam generator.

[0003] With such a cooking appliance it is possible to cook food in the cooking chamber either in hot air, in a pure steam atmosphere or in a mixed atmosphere, ie a cooking chamber atmosphere that has a moisture content of >0% and <100%.

[0004] As part of the general further development of these cooking appliances, the invention is based on the object of increasing the efficiency of the cooking appliance and reducing energy consumption.

[0005] To solve this problem, a cooking appliance of the type mentioned at the outset provides for the exhaust gas discharge duct to be assigned a heat exchanger, with which the waste heat of the exhaust gas can be transferred to gas that is supplied to the cooking appliance. The basic idea of ​​the invention is to use the heat that is still contained in the exhaust gas from the gas burner after it has left the heat exchanger.

[0006] The gas to which the heat contained in the exhaust gas is supplied can be the combustion air that is supplied to the gas burner. This increases the exhaust gas temperature of the gas burner, so that there is a greater driving temperature difference in the heat exchanger, with which heat is transferred to the cooking chamber atmosphere or the steam generation system.

[0007] The gas that is heated in the heat exchanger can also be the fuel gas that is supplied to the gas burner. This also generally leads to a higher temperature at the inlet of the gas burner and thus also to a higher exhaust gas temperature.

[0008] The gas that is heated in the heat exchanger can also be a mixture of combustion air and fuel gas that is fed to the gas burner. This results in the greatest increase in temperature at the inlet of the gas burner.

[0009] It is preferably provided here that the heat exchanger is arranged downstream of a mixing chamber in which the combustion air is mixed with fuel gas. This has the advantage that the mixing chamber and the components contained in it are at a rather low temperature level, so that the components do not have to be designed for high thermal stresses.

[0010] The gas heated in the heat exchanger can also be fresh air that is supplied to the cooking chamber. As a result, when fresh air is supplied, the temperature of the cooking chamber atmosphere is reduced to a lesser extent and, accordingly, less energy is required to heat the cooking chamber atmosphere back to the desired temperature.

[0011] According to one embodiment of the invention, it is provided that the heat exchanger is a tube-in-tube heat exchanger. Such a heat exchanger is characterized by a small space requirement.

[0012] It is preferably provided here that the exhaust gas discharge channel is the internal pipe. With this design, the exhaust gas pipe does not have to be expensively insulated, at least in the area of ​​the heat exchanger, since the pipe lying on the outside represents insulation.

[0013] According to one embodiment of the invention, it is provided that the heat exchanger is arranged in a technical space of the cooking appliance. This is possible because the heat exchanger reduces the exhaust gas temperature to such an extent that the heat input into the technical room is acceptable.

[0014] Alternatively, it is provided that the heat exchanger is arranged in a pressure chamber of the cooking appliance that is assigned to the cooking chamber. This keeps the heat input away from the technical room. In this case, the exhaust gas discharge duct is preferably the external pipe, since heat dissipation to the pressure chamber is desired.

[0015] The invention is described below with reference to various embodiments which are illustrated in the accompanying drawings. In these show:

[0016] figure 1 schematically shows a cooking appliance according to a first embodiment of the invention;

[0017] figure 2 schematically shows a cooking appliance according to a second embodiment of the invention;

[0018] figure 3 schematically shows a cooking appliance according to a third embodiment of the invention; and

[0019] figure 4 schematically shows a cooking appliance according to a fourth embodiment.

[0020] In figure 1 is a schematic of a cooking appliance 10 shown the one housing 12 has, in which a cooking chamber 14 is provided. The cooking room 14 can with a door 16 be locked.

[0021] In the cooking room 14 food can be cooked in a cooking chamber atmosphere. The atmosphere in the cooking chamber can be hot air, steam or a mixture of hot air and steam. In addition, it can be provided that microwave radiation is used for cooking.

[0022] In order to generate steam, a steam generator (not shown here) is provided, in which water can be evaporated if required. The resulting water vapor is then released into the cooking chamber 14 brought in.

[0023] It's a gas burner 20 provided, which serves to heat the cooking chamber atmosphere. A heat exchanger is used to heat the air 22 used, simplified here as the outer surface of an exhaust gas discharge duct 24 is shown. With the exhaust gas discharge duct 24 becomes the exhaust gas of the gas burner 20 discharged from the cooking appliance to the outside.

[0024] In the simplified representation of figure 1 is the heat exchanger 22 like that in the cooking room 14 arranged that the cooking chamber atmosphere when using a fan wheel 26 in the cooking chamber 14 is circulated, also the outer surface of the exhaust gas discharge duct 24 immediately downstream of the gas burner 20 flows around, so that heat from the exhaust gas over the wall of the exhaust gas discharge duct 24 and those as heat exchangers 22 serving outer surface of the exhaust gas discharge channel 24 transferred to the cooking chamber atmosphere.

[0025] Around the gas burner 20 to operate, this is supplied with a mixture of combustion air V and fuel gas B. The combustion air V and the fuel gas B via suitable channels 28 , 30 a mixing chamber shown here schematically 32 fed. The control flaps, valves and other components used are not shown for the sake of clarity.

[0026] Starting from the mixing chamber 32 is the mixture of combustion air V and fuel gas B through a heat exchanger 34 routed downstream of the heat exchanger 22 located and the exhaust gas discharge duct 24 assigned. From the heat exchanger 34 the mixture of combustion air V and fuel gas B flows through another channel 36 into the gas burner 20 .

[0027] The heat exchanger 34 serves to heat the mixture of combustion air V and fuel gas B. The energy required for this is provided by the exhaust gas from the gas burner 20 withdrawn through the exhaust gas discharge duct 24 flows.

[0028] The heat exchanger 34 preferably works on the countercurrent principle in order to increase efficiency.

[0029] In the embodiment shown, the heat exchanger 34 designed as a tube-in-tube heat exchanger, with the exhaust gas discharge channel 24 is the inner tube surrounded by a tube through which the mixture of combustion air V and fuel gas B flows.

[0030] Inside the heat exchanger 34 Heat transfer structures can be provided, for example ribs on the outside of the exhaust gas discharge channel 24 .

[0031] When operating the gas burner 20 the exhaust gas leaves the heat exchanger 22 usually with a temperature above 400 °C. The temperature is usually in the range of 450 °C to 500 °C. This waste heat, which would otherwise be discharged unused from the cooking appliance, is used according to the invention to preheat the mixture of combustion air V and fuel gas B before it enters the gas burner 20 entry. This compared to the prior art higher temperature of the mixture when it enters the gas burner 20 occurs, leads to a corresponding increase in the temperature of the exhaust gas. Accordingly, the driving temperature difference, which is necessary for heating the atmosphere in the cooking chamber in the heat exchanger, increases 22 can be used. Accordingly, there is a lower overall volume throughput through the gas burner 20 (and thus a reduced supply of fuel gas B) is necessary to transfer the same amount of heat to the cooking chamber atmosphere.

[0032] Since the combustion air V and fuel gas B have a much lower temperature than the cooking chamber atmosphere when entering the device, the heat exchanger according to the invention in principle allows a significantly higher efficiency than would be achievable, for example, by a corresponding increase in the heat exchanger surface between the gas burner and the cooking chamber atmosphere.

[0033] In figure 2 shows a second embodiment. The same reference numerals are used for the components known from the first embodiment, and reference is made to the above explanations in this respect.

[0034] The difference between the first and second embodiment is that in the second embodiment the mixing chamber 32 , in which combustion air V and fuel gas B are mixed, downstream of the heat exchanger 34 is arranged and only the combustion air V through the heat exchanger 34 flows.

[0035] In figure 3 shows a third embodiment. The same reference numerals are used for the components known from the previous embodiments, and reference is made to the above explanations in this respect.

[0036] The difference from the second embodiment is that in the third embodiment, the fuel gas B passes through the heat exchanger 34 is routed before it goes to the mixing chamber 32 reached. The combustion air V enters the mixing chamber 32 without being preheated.

[0037] In figure 4 shows a fourth embodiment. Here, too, the same reference numerals are used for the components that are known from the previous embodiments, and reference is made to the above explanations in this respect.

[0038] In the fourth embodiment, the mixture of combustion air V and fuel gas B enters the mixing chamber 32 and also in the gas burner 20 without being preheated. Instead, the heat exchanger 34 used to preheat air entering the cooking cavity 14 reached. The air can either be fresh air F, which is sucked in from the outside, for example in dehumidification mode, or circulating air U, which is used in the cooking chamber 14 taken and after going through the heat exchanger 34 has flowed, the cooking chamber is fed back as a cooking chamber atmosphere G.

[0039] According to a development not shown, the heat exchanger 34 can also be used in a combination, for example, of the first and the fourth embodiment to preheat both a mixture of combustion air V and fuel gas B and air. For this purpose, the heat exchanger 34 be separated internally, so that in a (relative to the flow direction of the exhaust gas) upstream section, heat is first given off to air that enters the cooking chamber 14 is introduced, and in a downstream section heat to the mixture of combustion air V and fuel gas B.

[0040] Depending on the thermodynamic conditions, the two sections of the heat exchanger can also be arranged in reverse.

Claims

[1] Cooking appliance ( 10 ) with a cooking chamber ( 14 ), in which food can be cooked in a cooking chamber atmosphere, a gas burner ( 20 ), a combustion air supply channel ( 28 ), an exhaust gas discharge duct ( 24 ) and a heat exchanger ( 22 ), with the combustion heat of the gas burner ( 20 ) can be transferred to a cooking chamber atmosphere or to a steam generation system, characterized by that the exhaust gas discharge duct ( 24 ) a heat exchanger ( 34 ) is assigned, which can transfer the waste heat from the exhaust gas to the gas supplied to the cooking appliance ( 10 ) is supplied. [2] Cooking appliance according to claim 1, characterized by that the gas is combustion air (V) supplied to the gas burner ( 20 ) is supplied. [3] Cooking appliance according to claim 1, characterized by that the gas is fuel gas (B) which supplies the gas burner ( 20 ) is supplied. [4] Cooking appliance according to claim 1, characterized bythat the gas is a mixture of combustion air (V) and fuel gas (B) that is supplied to the gas burner ( 20 ) is supplied. [5] Cooking appliance according to claim 4, characterized by that the heat exchanger ( 34 ) downstream of a mixing chamber ( 32 ) is arranged in which combustion air (V) is mixed with fuel gas (B). [6] Cooking appliance according to claim 1, characterized by that the gas is fresh air (F) which enters the cooking chamber ( 14 ) is supplied. [7] Cooking appliance according to any one of the preceding claims, characterized by that the heat exchanger ( 34 ) is a pipe-in-pipe heat exchanger. [8] Cooking appliance according to claim 7, characterized by that the exhaust gas discharge duct ( 24 ) the inner pipe. [9] Cooking appliance according to any one of the preceding claims, characterized by that the heat exchanger ( 34 ) is located in a technical room of the cooking appliance. [10] Cooking appliance according to any one of claims 1 to 8, characterized by that the heat exchanger ( 34 ) in a pressure chamber of the cooking appliance ( 10 ) is arranged, which is the cooking chamber ( 14 ) is assigned.