Abstract:
A system for reacting fuel and oxidizer into reformate employing a reformer having a first reaction zone to which the fuel and oxidizer are supplied, and a second reaction zone to which the product gas emerging from the first reaction zone and an oxidizer are supplied. The reformer further includes on or more heat dissipators for removing reaction heat produced in the first reaction zone before entry of the product gas into the second reaction zone.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a system for reacting fuel and oxidizer into reformate, employing a reformer which has a first reaction zone, to which the fuel and oxidizer can be supplied, and a second reaction zone to which the product gas, emerging from the first reaction zone, and an oxidizer can be supplied.  
         [0003]     2. Description of Related Art  
         [0004]     The use of fuel cells in the motor vehicle domain to produce electrical energy is becoming increasingly important. In particular, the continued development of auxiliary power units (APU) is being pursued in order to provide electrical energy to the vehicle electrical system and thereby enable supply of current to the electrical devices located in the motor vehicle so that the supply is independent of the operation of the internal combustion engine.  
         [0005]     To produce the electrical energy, SOFC (Solid Oxide Fuel Cell) fuel cells are often used, to which a product gas emerging from the reformer is supplied for purposes of producing electrical energy. Partial oxidation (POX) is often used as the type of reforming performed in the reformer. This process can be carried out thermally (TPOX, Thermal Partial Oxidation) or using a catalyst (CPOX, Catalytic Partial Oxidation). In any situation, in the partial oxidation reaction heat is formed which must be considered in the design of the reformer and other components. Close monitoring of the resulting temperatures is necessary to ensure that the temperatures are below the upper temperature boundaries established for the reformer, components and materials.  
         [0006]     One approach to consideration of these upper temperature boundaries is thermal decoupling of the product gas from the reformer after emergence of the product gas from the reformer, as is indicated in, for example, U.S. Pat. No. 6,562,496. In this way, components which are downstream of the reformer can be protected against high temperatures; however, the danger of damage to the catalyst or the reformer materials cannot be completely prevented by this approach.  
       SUMMARY OF THE INVENTION  
       [0007]     A primary object of the present invention is to develop generic systems and processes such that the problems of the prior art are at least partially overcome and, in particular, the danger of damage to system components is minimized.  
         [0008]     The invention is based on a generic system in which there are means for dissipating the reaction heat which has been produced in the first reaction zone before entry of the product gas into the second reaction zone. Generally, the net heat production in the first reaction zone is higher than in the following second reaction zone. It is therefore advisable that the temperature increase which occurs due to the net heat production be limited by dissipating the heat which forms in the first reaction zone. In particular, a gas for further reaction is supplied to the second reaction zone, from which gas the reaction heat from the first reaction zone has been removed so that a further reaction of the gas in the second reaction zone can be easily accomplished with respect to a further temperature increase.  
         [0009]     It is particularly useful for the means for dissipating the reaction heat include a heat exchanger for removing heat from the first reaction zone. In this way, the components which are assigned to the first reaction zone can be protected against excess temperatures.  
         [0010]     Specifically, this embodiment of the invention would include a means for dissipating the reaction heat utilizing a heat exchanger for removing heat from the product gas which has emerged from the first reaction zone. This measure alone can reduce the temperature load of the components which are downstream of the first reaction zone, i.e., the temperature load of the second reaction zone.  
         [0011]     The invention has an advantage in that the means for dissipating the reaction heat can use cathode air of a fuel cell assigned to the system as a cooling medium. In this manner, reaction heat is advantageously dissipated, on the one hand, and on the other hand, the cathode air is heated so that the high temperatures, which are necessary for the operation of a SOFC fuel cell, are reached.  
         [0012]     Furthermore, the invention preferably includes a means for dissipating the reaction heat via the use of a cooling medium from a cooling circuit. For example, the cooking circuit of an internal combustion engine. When the system is used in a motor vehicle, the meshing of the system of the invention with other motor vehicle systems can be used.  
         [0013]     A particularly advantageous embodiment of the invention occurs when the means for dissipating the reaction heat employs fuel and/or oxidizer as the cooling medium before entry into the reformer. This has the advantage that the substances entering the reformer are preheated and in doing so, at the same time, advantageously dissipates the reaction heat for lowering the temperature.  
         [0014]     The system for reacting fuel and an oxidizer of the invention has been developed such that there is an oxidizer supply which has a flow divider to divide the supplied oxidizer between the first and the second reaction zones. The oxidizer, i.e., generally air, can thus be introduced via uniform delivery, division taking place for the different reaction zones by means of a flow divider. The amount of air which is necessary for the reforming processes can thus be centrally set depending on the desired properties of the reformate and depending on the fuel which has been made available.  
         [0015]     Additionally, there is a benefit provided by the invention in that there is provided a mixture formation zone to which the oxidizer for the first reaction zone and the fuel can be supplied, while the oxidizer can be supplied directly to the second reaction zone. The mixture formation zone has the advantage, as a result of the division of the supplied oxidizer, i.e., the dwell time of the oxidizer and of the fuel in the mixture formation zone is increased. This promotes the vaporization process of liquid fuels in the mixture formation zone.  
         [0016]     Furthermore, the invention relates to a reformer for use in a system of the invention. A reformer, which includes the division of its reaction area into at least two reaction zones and accomplishes the dissipation of the heat which forms in the reaction zone, the aforementioned advantages and particulars of the system of the invention can be implemented.  
         [0017]     The invention is based on a generic process in that the reaction heat which has been produced in the first reaction zone is dissipated before entry of the product gas into the second reaction zone. In this way, the advantages of the system of the invention are realized within the framework of the disclosed process. This also applies to the particularly preferred embodiments of the process of the invention which are given below.  
         [0018]     The process of the invention is executed in a useful manner such that the reaction heat is dissipated directly from the first reaction zone. Further, in addition to or as an alternative to the general process, the process of the invention can also be provided with the feature that the reaction heat is dissipated from the product gas emerging from the first reaction zone. In this embodiment, it is particularly beneficial that the reaction heat is dissipated by the cathode air of a fuel cell in the system. However, the process can also be carried out such that the reaction heat is dissipated by a cooling medium from the cooling circuit of an internal combustion engine.  
         [0019]     Likewise, the invention can be provided with dissipation of reaction heat of the fuel and/or the oxidizer before either enters the reformer.  
         [0020]     It is furthermore useful for the supplied oxidizer to be divided between the first and the second reaction zones.  
         [0021]     The process of the invention is particularly advantageously in that the oxidizer for the first reaction zone and the fuel are supplied to a mixture formation zone while the oxidizer is directly supplied to the second reaction zone.  
         [0022]     In this embodiment, it is particularly beneficial when the amount of oxidizer, which is dictated depending on the desired reforming processes, is used per time, That is, some of the given amount of the oxidizer is supplied depending on the given upper temperature boundaries to the first reaction zone and that the remaining part of the given amount of oxidizer is supplied to the second reaction zone.  
         [0023]     The invention is based on the discovery that by dividing the reaction area of the reformer into at least two reaction zones, the danger of exceeding the upper temperature boundaries is reduced by the reaction heat being dissipated from the first reaction zone or being dissipated from the product gas which has emerged from the first reaction zone. The invention is particularly useful in conjunction with reforming processes for providing reformate for a fuel cell.  
         [0024]     However, the invention is also suited for numerous other applications in which a product gas from a reformer can be used, for example, in conjunction with motor vehicle exhaust catalytic converters and motor vehicle drives. The invention has been described above as using the process of partial oxidation as the type of reforming, but the invention can also be used for other types of reforming with net heat production.  
         [0025]     The invention is now explained by way of example with reference to the accompanying drawings using a preferred embodiment. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]      FIG. 1  is a schematic representation of a system in accordance with the invention, and  
         [0027]      FIG. 2  is a flow chart of a process according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]      FIG. 1  shows a system in accordance with the invention which has a reformer  10  that includes a first reaction zone  12  and a second reaction zone  18 . The reaction zone  12  is surrounded by a housing  34 . The reaction zone  18  is surrounded by a housing  36 . The first reaction zone  12  is in thermal contact with a heat exchanger  22 . Furthermore, between the first reaction zone  12  and the second reaction zone  18 , there is a heat exchanger  24 . Also provided is an oxidizer supply  10  with a flow divider  30 , the part of the oxidizer supply  10  which is downstream of the flow divider discharges into a mixture formation zone  32  and directly into the reaction zone  18 . Furthermore, a fuel supply  38  discharges into the mixture formation zone  32 . The heat exchanger  22  is equipped with a coolant feed  40  and a coolant return  42 . Similarly, the heat exchanger  24  is equipped with a coolant feed  44  and a coolant return  46 .  
         [0029]     The system as shown in  FIG. 1  works as follows. Some of the supplied oxidizer  16  is fed into the mixture formation zone  32  via the oxidizer supply  10  and the flow divider  30 . Furthermore, via the fuel supply  38 , fuel  14 , e.g., gasoline or diesel fuel, is supplied to the mixture formation zone. In the mixture formation zone  32 , vaporization and mixing of the oxidizer  16  with the fuel  14  take place. The oxidizer includes, preferably, air which can optionally be mixed with water-containing or water-releasing media flows. It can be, for example, the product gases from combustion processes which have been produced for example in the anode space of the fuel cell and/or in a burner. Likewise, engine exhaust gases can be used. The mixture is then supplied to the first reaction zone  12  where partial exothermal oxidation of the fuel  14  takes place, the reactions being dependent on the amount of oxidizer  16  which has been made available. The reaction heat produced in the reaction zone  12  is partially dissipated via the heat exchanger  22  by means of a coolant  26 . The coolant  26 , e.g., cathode air, cooling water of the motor vehicle engine or oxidizer or fuel, is supplied via the coolant feed  40  to the heat exchanger  22  and is removed again via the coolant return  42 . The product gas emerging from the reaction zone  12  is supplied to another heat exchanger  24 . The heat present in the product gas is in turn dissipated via a coolant  26 , the coolant being supplied via a coolant feed  44  and being removed via a coolant return  46 . It should be noted that the coolants used for heat exchanger  24  can be the same coolants as are used for the heat exchanger  22 . The cooled product gas  20  is now supplied to the second reaction zone  18 , to which there is supplied the portion of the oxidizer  16  which remains in the flow divider, i.e., that amount which has not be supplied to the mixture formation zone  32 . In the second reaction zone  18 , a further reaction of the product gas  20  with the oxidizer  16  takes place, with the reaction again corresponding to the remaining amount of oxidizer  16 . The finished reformate can then be removed from the second reaction zone  18  and can be supplied to another application, e.g., a fuel cell.  
         [0030]      FIG. 2  shows a flow chart of the process of the invention. In step S 01 , an air flow is divided by a flow divider into a first part and a second part. In step S 02 , the first part of the air flow is supplied to the mixture formation zone. This mixture formation zone is likewise supplied with the fuel which is to be oxidized. The fuel, generally supplied in liquid form, vaporizes in the mixture formation zone and is mixed with air in step S 03 . The mixture is supplied in step S 04  to the first reaction zone in which, according to step S 05 , partial reaction of the fuel with the air takes place. In step S 06 , the reaction heat which has been produced in the first reaction zone is partially dissipated by a heat exchanger. In step S 07 , the product gas is removed from the first reaction zone, and, in step S 08 , additional reaction heat is removed from the product gas. In step S 09 , the product gas and the remaining second part of the air emerging from the flow divider are supplied to a second reaction zone. Here, according to step S 10 , further partial reaction of the product gas with air takes place. In step S 11 , the product gas is removed from the second reaction zone.  
         [0031]     The foregoing specific embodiment of the apparatus, processes, and/or compounds employed in the practice of the present invention are, of course, intended to be illustrative rather than limiting, and it will be apparent that numerous variations and modifications of these specific embodiments may be practiced within the scope of the appended claims.