METHOD FOR VAPORISING AND REFORMING LIQUID FUELS

Abstract

The invention relates to a method for vaporising and reforming liquid fuels, in particular the catalytic and non-catalytic partial oxidation and the autothermal reforming of liquid fuels with the addition of air- or air-vapour mixtures or air-water mixtures. The invention thereby solves the problems of the mixture formation, soot formation and conversion into low hydrocarbons and hydrogen in conjunction with reforming methods known from the state of the art.

Description

BACKGROUND OF THE INVENTION

The invention relates to a method for vaporising and reforming liquid fuels, in particular the catalytic and non-catalytic partial oxidation and the autothermal reforming of liquid fuels with addition of air- or air-vapour mixtures or air-water mixtures. The invention thereby solves the problems of the mixture formation, soot formation and conversion into low hydrocarbons and hydrogen in conjunction with reforming methods known from the state of the art.

An important object of each system for mixture preparation for reforming liquid fuels is to ensure homogeneous mixing of fuel and oxidants before the actual reforming under all operating conditions. In order to achieve this, a spatial separation of the vaporising and the mixing zone from the actual reforming zone is advantageous. For this purpose, numerous methods from the state of the art are known.

In DE 199 51 585 A1, a reforming device is described in which a hydrocarbon-air-vapour mixture is converted catalytically into a hydrogen-rich product gas. The fuel is thereby injected in liquid form by means of a nozzle into the educt mixture preparation chamber with droplet formation. The method described here cannot ensure over a large range of load states that the educts are mixed homogeneously since, as a result of the nature of the nozzle (also two-material nozzle or three-material nozzle), the droplet size varies greatly with the fuel throughput through the nozzle. As a result, the educts are mixed according to the operating state and hence the droplet size is variably homogeneous.

In EP 0 199 587 B1, an autothermal reforming reactor is described which likewise introduces liquid fuels into a reactor with the help of a nozzle, the atomised fuel being partially oxidised after mixing with oxygen and water vapour directly in a catalyst-lined reaction chamber before the vapour reforming begins in a second likewise catalyst-lined reaction chamber. This method also involves the disadvantage that the droplet size varies as a function of the throughput through the reactor so greatly that homogeneous mixing of all educt flows is at present not ensured.

In EP 0 716 225, a method is described for vaporising liquid fuels by partial catalytic oxidation and heat supply to the liquid by heat radiation. This method cannot be used directly for reforming since the conversion of the fuel into low-chain hydrocarbons and hydrogen is inadequate.

A further method is based on the phenomenon of the so-called cold flame for mixture formation. This thereby involves exothermal prereactions which partially convert and vaporise the fuel with heat release. The reaction is restricted to a characteristic temperature because of the kinetic self-limitation, said characteristic temperature being specific for each fuel. Below this characteristic temperature, the self-ignition of the fuel-oxidant mixture can be avoided reliably (see e.g. A. Naidja, C. R. Krishna, T. Butcher, D. Mahajan, Progr. Energy Combustion Science, 29 (2003) 155-191).

Another, frequently pursued way for mixture formation is to introduce the liquid fuel into liquid water or superheated water vapour, to vaporise this mixture in the first case and subsequently to bring into contact with (air) oxygen.

The methods of so-called cold flames, known from the state of the art, and the introduction of water or water vapour have the disadvantage that they are based either on methods which are very complex with respect to apparatus and control technology or else operate with water or water vapour in order to convert the liquid fuel into the gas phase, which excludes partial oxidation as reforming method. In the case of partial oxidation for diesel reforming, the soot formation represents a problem which is not reliably overcome (F. Joensen, J. R. Rostrup-Nielsen, J. Power Sources, 105 (2002) 195-201). And even with water addition, as with autothermal reforming, the problem of soot formation is not automatically resolved (D.-J. Liu, T. D. Kaun, H.-K. Liao, S. Ahmed, Int. J. Hydrogen Energy, 29 (2004) 1035-1046).

Starting herefrom, it was the object of the present invention to provide a method for reforming liquid fuels, which method eliminates the disadvantages known from the state of the art and enables as homogeneous as possible a mixture of fuel and oxidants.

This object is achieved by the method having the features of claim 1. The further dependent claims reveal advantageous developments.

SUMMARY OF THE INVENTION

According to the invention, a method is provided for vaporising and reforming liquid fuels, in which, in a first reaction chamber, the fuel is vaporised with the supply of air with the help of a first catalyst and is partially oxidised (as disclosed in EP 0 716 225) and, in a second reaction chamber, the vaporised fuel is mixed with additionally supplied air and subsequently is reformed. A ratio of the air volume supplied in the first reaction chamber to the air volume supplied in the second reaction chamber is hereby adjusted between 30:70 and 70:30.

The ratio of the air volume supplied in the first reaction chamber to the air volume supplied in the second reaction chamber is preferably adjusted via distributor structures. A hereby preferred variant provides that the air is supplied via pipelines, the pipelines having opening and/or nozzles and the latter being dimensioned such that the ratio of the air volume supplied in the first reaction chamber to the air volume supplied in the second reaction chamber can be adjusted. Another preferred variant provides that nozzles of porous structures, such as e.g. porous sintered metal bodies, are used as distributor structures.

A preferred variant provides that a second catalyst is used in the second reaction chamber during the reforming. As catalyst, catalytically active noble metals or nickel are used preferably here on ceramic carriers (e.g. honeycomb bodies or packing). A further preferred variant provides that corresponding carriers made of metal structures, e.g. honeycomb bodies, are used. However it is also possible likewise that the reforming is effected without a catalyst.

The reforming can hereby be effected, in a preferred variant, by partial oxidation.

A further preferred embodiment concerns the reforming by autothermal reforming. It is necessary for this purpose that water and/or water vapour are supplied in addition in the second reaction chamber.

In particular a packing bed, a honeycomb body or coated metal net is used as catalyst for the reforming.

The mixing of fuel and supplied air after the first and in the second reaction chamber can be assisted preferably by static mixing devices.

A frequently occurring problem during reforming concerns the starting of the method from the cold state. This problem can be resolved in that both reaction chambers and/or both catalysts are preheated to temperatures of 300 to 450° C.

The method according to the invention is intended to be explained in more detail with reference to the subsequent Figures without wishing to restrict said method to the variants shown in the embodiments.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

A first variant for vaporising and reforming liquid fuels is represented in FIG. 1. This is based on a catalytically partial oxidation with the supply of air through a pipe in one step. The method for air supply must thereby be constructed such that the air is introduced in a defined ratio into the first reaction chamber, i.e. the vaporiser, and into the second reaction chamber, i.e. the reformer. The ratio of air introduction into the vaporiser to that into the reformer can be effected by correspondingly dimensioned borings in the pipe. The reactor is divided into the first reaction chamber which has the vaporising catalyst 3 and the reaction chamber with the reforming catalyst 4. Optionally, a heating device 5 can be used to preheat the device. The product gas 6 after the reformer subsequently leaves the reactor. The partial oxidation represented here can also be implemented without a catalyst 4.

The course of the method has the following appearance:

Before starting the device, the catalysts 3 and 4 and the pipe 2 are preheated from the outside for example by a heater. The air supply 1 and the fuel supply 7 are then started. The preheating can be switched off after the beginning of the vaporising and the reforming. In the first reaction chamber, the fuel is vaporised and partially oxidised, in the second reaction chamber, the fuel is subsequently reformed with the additional air supply.

FIG. 2 shows a device with two separate pipes 2 and 8 for the air supply. In this variant, the air flows 1 and 9 can be adjusted independently of each other and hence also the ratio of air flows to the vaporiser and reformer. In this case, water vapour can also be introduced into the second reaction chamber in addition to air through the second pipe. It is possible as a result to convert the fuel by autothermal reforming.

FIG. 3 shows a further variant according to the invention for control of the method. Basically, the location of the air supply in the second reaction chamber, i.e. the reformer, is variable. In the present Figure, the air supply 10 is effected before the second reaction chamber. The air can thereby be introduced through small openings or nozzles in the pipe for the air supply or through porous sintered metal bodies into the reaction chamber. Annular distributor structures are likewise possible. A further possibility is also that the air supply 12 is effected before the second reaction chamber through a supply disposed on one side.

In FIG. 4, a static mixer is provided in addition, relative to FIG. 3, as a supplementary variant. This can be before and/or after the air supply and serves to mix the vaporised, partially oxidised fuel with the remaining air and possibly the water vapour.

FIG. 5 shows a variant in which the second reaction chamber is separate from the first reaction chamber, both reaction chambers being connected by a pipe with a fairly small diameter. In the variant shown here the air supply is likewise effected via a lateral inlet, but it is likewise possible to choose other locations for the air supply.

First measurements have demonstrated the suitability of the new method. A soot-free product gas was thereby produced with an air ratio between 0.38 and 0.46 by means of catalytic partial oxidation. The composition of the product gas and also the average temperatures in the honeycomb catalyst are represented in FIG. 6. The concentrations of the individual gas components correspond very well to the chemical equilibrium. The test apparatus after the experiments shows no soot deposits.

Claims

1. A method for vaporising and reforming liquid fuels, in which, in a first reaction chamber, the fuel is vaporised with the supply of air with the help of a first catalyst and is oxidised greatly substoichiometrically and, in a second reaction chamber, the vaporised fuel is mixed with supplied air and subsequently is reformed, the ratio of the air volume supplied in the first reaction chamber to the air volume supplied in the second reaction chamber being adjusted between 3:70 and 70:30.

2. The method according to claim 1, wherein the ratio of the air volume supplied in the first reaction chamber to the air volume supplied in the second reaction chamber is adjusted via distributor structures.

3. The method according to claim 1, wherein the air is supplied via pipelines with openings and/or nozzles, the openings and/or nozzles being dimensioned such that the ratio of the air volume supplied in the first reaction chamber to the air volume supplied in the second reaction chamber is adjusted.

4. The method according to claim 1, wherein the distributor structure is a nozzle, a boring, a body with other openings, in particular a porous sintered metal body.

5. The method according to claim 1, wherein a second catalyst is used during the reforming.

6. The method according to claim 1, wherein the reforming is effected without a catalyst.

7. The method according to claim 1, wherein the reforming is effected by partial oxidation.

8. The method according to claim 1, wherein the reforming is effected by autothermal reforming, water and/or water vapour being supplied in addition in the second reaction chamber.

9. The method according to claim 1, wherein the catalysts are selected from the group comprising a packing bed, a honeycomb body and a coated metal net.

10. The method according to claim 1, wherein the mixing after the partial oxidation in the vaporiser is assisted by static mixing devices before and after the supply of additional air.

11. The method according to claim 1, wherein the first reaction chamber and/or the first catalyst are preheated to temperatures of 300 to 450° C.

12. The method according to claim 1, wherein the first and the second reaction chamber are connected to each other by a connection channel.

13. The method according to claim 1, wherein the air for the first and the second reaction chamber is supplied via different pipelines.