Abstract:
The method for the reformation of fuels, in particular of heating oil ( 20 ′) and of another liquid fuel is carried out using an oxygen containing gas ( 5   a   , 5   b   , 21′, 22′ ). The method includes the following steps:
       formation of a fuel/gas mixture by dispersing of the fuel in a jet of the oxygen containing gas ( 21 ′);   additionally an admixture of gas of a return flow ( 3   b ) and vaporization of the dispersed fuel;   generation of synthesized gas from the gas mixture by means of partial oxidation and also reformation processes by heterogeneous catalysis;   branching off of the produced synthesized gas into a product flow ( 3   a ) and the return flow ( 3   b ) for a recirculation; and   a regulated extraction of heat from the return flow for the setting of a predetermined temperature of a catalyst support ( 10 ) on which the heterogeneous catalysis takes place.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method for the reformation of fuels, in particular of heating oil or another liquid fuel, preferably for the purpose of obtaining electrical and thermal energy by means of high temperature fuel cells. The invention also relates to apparatuses for carrying out the method and also to a plant with fuel cells in which the method of the invention is used. 
     The reformation of hydrocarbons, which are for example present in the form of fuel gas or vaporized heating oil, can be carried out catalytically at around 800° C. with the admixture of water in vapor form and a supply of heat. During the reformation, carbon monoxide and hydrogen arise which, as educts, can be used for electrochemical processes in high temperature fuel cells, for example in the battery of fuel cells as is known from EP-A-0 780 917. This battery contains a cell block with fuel cells which is surrounded by a heat insulating sleeve. An afterburning space is located between the sleeve and the cell block. A reformer (also termed a pre-reformer) which is suitable only for the preparation of a gaseous fuel is arranged in the sleeve. It is connected to a heat exchanger by means of which the heat required for the reformation processes can be supplied to it from exhaust gases. 
     When air or another oxygen containing gas which is composed of an inert component and of a component consisting of molecular oxygen O 2  is admixed to the hydrocarbons a partial oxidation takes place in parallel to the endothermic reformation processes, the partial oxidation is exothermic and water arises as a reaction product. The water formed by the partial oxidation serves as an educt of the reformation. An admixture of water is thus no longer required or only partly required, which is advantageous since water is expensive having regard to the demands made on its purity. However a problem arises when the reformation is carried out together with a partial oxidation, as the following explanations show: 
     The reformation processes are carried out by a heterogeneous catalysis in a catalytic converter with a uniform structure. The catalytic converter consists of a catalyst support, on the surface of which the catalytically active material, namely a platinum material (in particular platinum, rhodium or palladium), nickel or a mixture of such metals, is applied. The oxidation which takes place simultaneously does so much more quickly then the endothermic reformation reaction; it thus takes place in an inlet region of the catalytic converter in which high temperatures arise as a result of the heat output through the oxidation. These temperatures can result in a deactivation of catalytically active metals, for example by vaporization, and thus damage to the catalytic converter. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a method for the reformation of a fuel, in particular heating oil or another liquid fuel, in which a partial oxidation is carried out simultaneously with the reformation but in which a damaging effect of the exothermic processes on the catalytic converter is avoided. This object is attained in that with a return of synthesized gas the temperature in the inlet region of the catalytic converter can be reduced so far that thermal damage is prevented. 
     The method for the reformation of fuels, in particular heating oil or another liquid fuel, is carried out using an oxygen containing gas. The method comprises the following steps:
     formation of a fuel/gas mixture by dispersing of the fuel in a jet of the oxygen containing gas;   additionally an admixture of gas of a return flow and vaporization of the dispersed fuel;   generation of synthesized gas from the gas mixture by means of partial oxidation and also reformation processes by heterogeneous catalysis;   branching off of the produced synthesized gas into a product flow and the return flow for a recirculation; and   a regulated extraction of heat from the return flow for the setting of a predetermined temperature of a catalyst support on which the heterogeneous catalysis takes place.   

     In the following the invention will be explained with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an apparatus for carrying out the method of the invention, 
         FIG. 2  is a diagram with a temperature profile which results with partial oxidation and simultaneous reformation in a catalytic converter, 
         FIG. 3  shows a plant with a battery of high temperature fuel cells and an apparatus in accordance with the invention for the reformation of heating oil, 
         FIG. 4  shows a particular two-material nozzle, and 
         FIG. 5  shows a second embodiment of the apparatus of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The method of the invention can be carried out with the apparatus shown in  FIG. 1. A  heating oil/gas mixture is sprayed into the apparatus  1  by means of a two-material nozzle  2  which has a central infeed  20  for heating oil  20 ′, a lateral infeed  21  for an oxygen containing gas  21 ′ and a nozzle tip  23 . In this connection a further part flow  22 ′ of the oxygen containing gas is united with the heating oil/gas mixture via an infeed  22  and a ring-like nozzle  13 . (The method of the invention can also be carried out without this part flow.) At the outlet of the nozzle  13  the emerging jet brings about a depression by which the gas of a hot return flow  3   b  is sucked in. Heat is supplied to the dispersed heating oil, which can be fed cold into the two-material nozzle  2 , by mixing of this hot gas with the jet of the nozzle  13  so that the heating oil is vaporized. A radiation of heat through the hot catalytic converter  10  contributes to heating of the dispersed heating oil so that the heat required for the vaporization does not have to be supplied solely by the return flow  3   b.    
     The two-material nozzle  2  is arranged at a distance remote from the catalytic converter  10 , with the distance to an entry surface  100  being sufficiently large that an adequately long dwell time exists for the vaporization of the heating oil prior to the inlet and that the mixture enters into the catalytic converter  10  distributed over the full entry surface  100 . The catalytic converter  10  is located in a first cylindrical tube  11 . A second cylindrical tube  12  forms part of an outer wall of the apparatus  1 . The catalytically produced synthesized gas is branched off below an outlet surface into a product flow  3   a  and the return flow  3   b . The product flow  3   a  leaves the apparatus  1  through an outlet tube  29 . The return flow  3   b , driven by a pressure drop which arises as a result of the depression at the nozzle  13 , is guided upwardly through a recirculation gap, which is a ring space between the two tubes  11  and  12 . Heat is extracted from the return flow  3   b  by means of a heat exchanger  6 . With a regulated extraction of heat the temperature T K  of the catalytic converter  10  can be influenced so that, for example, the average temperature adopts a predetermined value. 
     The temperature T K  has a profile as is qualitatively illustrated in the diagram of FIG.  2 . The x-axis, the direction of which is drawn in in  FIG. 1 , extends in the main flow direction of the catalytic converter  10 . The left-hand line  100 ′ of the diagram corresponds to the inlet surface  100 , the right-hand line  101 ′ corresponds to the outlet surface. As already mentioned the temperature has a maximum in the inlet region as a result of the exothermic processes. The endothermic processes of the reformation bring about a gradual reduction of the temperature after the maximum. The temperature interval ΔT quoted must lie within an interval, the limits of which are given by a required minimum temperature of around 700° C. and a maximum permissible temperature of around 1000° C. This condition cannot be satisfied without the measure of the invention. 
     Due to the return flow  3   b  the temperature interval ΔT of the temperature profile is smaller and the average temperature can be set lower. The reduction of ΔT results for two reasons: a) The partial pressure of the heated oil vapor is reduced by the returned gas (increase of the proportion of inert gas); and b) Water is already made available in the inlet region of the catalytic converter (water which arises in the process) for the reformation processes and thus produces a heat sink. These two reasons also have the advantageous effect that soot formation in the catalytic converter  10  is suppressed. 
     With regard to the recirculation, the packing should have a structure which produces the smallest possible flow resistance. An ordered packing is of advantage, the structure of which is a honeycomb structure with parallel flow passages or a structure with wave-shaped foils and open, crossing, flow passages (“crossed channel structure”). A reticular foam structure or a structure of a three-dimensional braid is also possible. 
     The plant  9  shown in  FIG. 3  comprises a battery  9 ′ in the form of a stack of planar ring-line high temperature fuel cells  90  and an apparatus  1  in accordance with the invention for the reformation of heating oil. Apart from the fuel cells  90  the following components can be seen: a sleeve  93  which has a non-illustrated internal construction by means of which environmental air  50  (inlet  92 ) is preheated during operation and uniformly distributed to the cell stack; an afterburning space  94  between cell stack  9 ′ and sleeve  93  from which waste heat is led away via a heat exchanger  95  (transfer of heat Q to a water circuit, for example); a fan  96  with which the exhaust gas is sucked away and conveyed into a chimney  97 ; a pole  98  for the transmission of electrical energy E to a consumer. 
     Oxygen-containing gas forwarded by a pump  4  is fed into the apparatus  1  with the two partial flows  21 ′ and  22 ′. Environmental air  5   a  and/or exhaust gas  5   b  from an afterburning of the fuel cell battery  9 ′ is used as the oxygen containing gas. In a mixing apparatus  5  an ideal ratio of environmental air  5   a  and exhaust gas  5   b  is produced. The product gas for the reformation is fed through the line  29  into a central distributor passage  91  of the battery  9 ′. 
       FIG. 4  shows a special two-material nozzle  2 . This contains a heating cartridge  25  (electrical connections  25   a ) with which the heating oil  20 ′ can be preheated to 400-420° C. to assist the vaporization or to carry it out. 
     A second embodiment of the apparatus of the invention is shown in FIG.  5 . For the return flow  3   b  a second tube  7  is added to the first tube  11  containing the catalytic converter  10 , with the second tube  7  being formed as a jet compressor. The second part flow  22 ′ and the oxygen containing gas are exploited as a driving medium. Synthesized gas is sucked in through a tube  70  by a driving nozzle  71 . A subsequent downstream tube element  72 , in which a momentum transfer takes place from the driving medium to the synthesized gas, is formed as a heat exchanger  76  which corresponds to the heat exchanger  6  in the embodiment of FIG.  1 . In a subsequent diffuser  73 , deionized water  80  can be sprayed by a nozzle  8  into the return flow  3   b  in order to utilize this fed-in water  80  as a reaction component of the reformation processes and for a cooling of the returned synthesized gas. The return flow  3   b  conveyed by means of the jet compressor  7  is distributed in the upper part of the apparatus  1  between an outer wall  11   a  and a truncated cone-like wall  13 ′ around a two-material nozzle  2 . The gas of return flow  3   b  is united through the ring gap at the nozzle tip  23  with the heating oil/gas mixture emerging from the nozzle  2  and supplied to the catalytic converter  10 . The nozzle  2  can also be of the type shown in FIG.  4 . 
     For the complete vaporization of the heating oil the return gas must be sufficiently hot that a temperature of around 250-300° C. is achieved. When gas is recirculated with a temperature of 900° C. then the ratio of the return flow to the product flow must amount to around 1:4. The higher the recirculation ratio is selected, the more uniform is the temperature profile in the catalytic converter. A ratio greater than 1 is however not sensible for economic reasons, since the driving of the recirculation flow becomes expensive due to a high requirement of the momentum input. 
     The momentum required for the recirculation can be made available by means of the reaction air in different ways. The reaction air can be fed in in total via the two-material nozzle, which results in a fine atomization that is associated with a relatively large energy requirement. The reaction air can be fed in subdivided into primary and secondary air, the primary air in the two-material nozzle and the secondary air for example in a jet compressor. This second way is however more expensive apparatus-wise. 
     When carrying out an autotherm reformation in which water is used as a reaction agent in addition to air the water can be exploited for the regulation of the reaction temperature; the water can then be injected into the recirculation gap. 
     The method of the invention can also be carried out with liquid fuels such as methanol, ethanol or “biodiesel” (vegetable oil). Moreover gaseous fuels (natural gas, liquid gas, biogas) can be used when the method of the invention is modified somewhat (no vaporization of the fuel). With these fuels, which have a lower adiabatic temperature increase than heating oil, the conversion or turnover can be improved by a supply of heat—for example into the recirculation gap.