Catalytic burner arrangement

Abstract

A catalytic burner arrangement including at least a catalytic burner unit with a housing having a reaction chamber in which a catalyst is arranged is provided wherein the catalyst is adapted to react a fuel, particularly a hydrogen containing fluid, with an oxidant, particularly air, for producing heat, the housing having a fluid inlet for supplying a fluid stream into the housing and a fluid outlet for exiting a fluid stream from the housing, and the catalytic burner arrangement further includes a mixing unit forming a mixing chamber in which fuel and oxidant are mixed, wherein the mixing device includes a fuel inlet, an oxidant inlet and an fuel-oxidant-mixture outlet, and wherein the fluid inlet of the catalytic burner unit merges with the fuel-oxidant-outlet of the mixing unit for transferring the fuel-oxidant-mixture from the mixing chamber to the reaction chamber of the catalytic burner unit wherein the fuel inlet of the mixing chamber is arranged upstream of the oxidant inlet of the mixing unit.

Claims

1. Catalytic burner arrangement comprising a catalytic burner unit with a housing having a reaction chamber in which a catalyst is arranged, wherein the catalyst is adapted to react a fuel with an oxidant for producing heat, the housing having a fluid inlet for supplying a fluid stream into the housing and a fluid outlet for exiting a fluid stream from the housing, a mixing unit forming a mixing chamber in which fuel and oxidant are mixed, wherein the mixing unit comprises a fuel inlet, an oxidant inlet and a fuel-oxidant-mixture outlet, and wherein the fluid inlet merges with the fuel-oxidant-mixture outlet of the mixing unit in a main fluid flow direction for transferring the fuel-oxidant-mixture from the mixing chamber to the reaction chamber of the catalytic burner unit, wherein the fuel inlet is arranged upstream of the oxidant inlet with regard to the main fluid flow direction, the main fluid flow direction extends in a straight line from the fluid inlet to the reaction chamber, and the fuel-oxidant-mixture outlet is an opening in a basis plate of the mixing unit, and wherein the fuel inlet and the oxidant inlet are arranged angled to a direction of a main fluid stream streaming through the fuel-oxidant-mixture outlet to the reaction chamber.

2. Catalytic burner arrangement according to claim 1, wherein the mixing chamber has two basis plates which are connected by at least one side face, wherein the fuel-oxidant-mixture outlet is arranged at one of the basis plates and the oxidant inlet is arranged at the side face.

3. Catalytic burner arrangement according to claim 2, wherein a length of the pipe-shaped fuel-oxidant-mixture outlet extends over at least the oxidant inlet.

4. Catalytic burner arrangement according to claim 1, wherein the fuel inlet and/or the oxidant inlet is designed as at least one pipe having a longitudinal axis, whereby a directed fluid stream of fuel and/or oxidant is introduced into the mixing chamber.

5. Catalytic burner arrangement according to claim 4, wherein the mixing chamber is prismatically or cylindrically shaped, having two basis plates and at least three side surfaces sides or a mantel side, wherein the fuel inlet and the oxidant inlet are arranged at the side surfaces or the mantel side, and the fuel-oxidant-mixture outlet is arranged at one of the basis plates, and wherein the directed fluid streams are offset from a longitudinal axis of the mixing chamber, thereby providing at least one tangential fluid stream.

6. Catalytic burner arrangement according to claim 4, wherein the longitudinal axis of the fuel inlet and/or the oxidant inlet is inclined to a cross sectional plane of the mixing chamber.

7. Catalytic burner arrangement according to claim 1, wherein the mixing chamber is prismatically or cylindrically shaped, having two basis plates and at least three side surfaces sides or a mantel side, wherein the fuel inlet and the oxidant inlet are arranged at the side surfaces or the mantel side, wherein the fuel-oxidant-mixture outlet is arranged at one of the basis plates.

8. Catalytic burner arrangement according to claim 1, wherein the oxidant inlet and the fuel inlet are arranged substantially rectangular to each other.

9. Catalytic burner arrangement according to claim 1, wherein the fuel is a hydrogen containing fuel and the oxidant is air.

10. Auxiliary power assembly based on fuel cell technology comprising at least a fuel processing assembly which is adapted to convert hydrocarbon fuels into a hydrogen rich gas for fuel cells by using at least hydrocarbon fuel and steam; downstream of the fuel processor assembly, at least one fuel cell or fuel cell stack for providing auxiliary power; and downstream of the at least one fuel cell or fuel cell stack, a catalytic burner unit which is adapted to burn unused hydrogen exiting from the at least one fuel cell or fuel cell stack by using an oxidant and a catalyst for reacting oxidant and hydrogen to heat, wherein the heat is used to produce steam used in the fuel processing assembly, wherein a catalytic burner arrangement according to claim 1 is used.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following the invention will be described by means embodiments shown in the figures. Thereby, the embodiments are exemplarily only and are not intended to limit the scope of the protection. The scope of protection is solely defined by the attached claims.

(2) The figures show:

(3) FIG. 1: a schematic illustration of the APU system;

(4) FIG. 2: a schematic view of a first preferred embodiment of the catalytic burner;

(5) FIG. 3: a schematic detailed spatial view of the mixing unit shown in FIG. 2;

(6) FIG. 4: a schematic view of a second preferred embodiment of the catalytic burner;

(7) FIG. 5: a schematic detailed spatial view of the mixing unit shown in FIG. 4;

(8) FIG. 6: a schematic top view of the mixing unit shown in FIG. 3 and FIG. 5

(9) FIG. 7: schematic side views of the mixing unit of FIG. 6.

(10) In the following same or similarly functioning elements are indicated with the same reference signs.

DETAILED DESCRIPTION

(11) FIG. 1 shows a schematic illustration of an auxiliary power unit, APU, system 100 based on fuel technology for providing electric power. The APU system 100 comprises a fuel reformer 102 which is adapted to produce a hydrogen rich gas 104 from a hydrocarbon fuel 105. The hydrogen rich gas 104 is introduced into a fuel cell stack 106 arranged downstream of the fuel reformer 102. In the fuel cell stack electric energy 107 is produced by guiding hydrogen to an anode side of a proton electron membrane and an oxidant to a cathode side. Excess hydrogen 108, which is not used in the fuel cell stack may then be transferred to a catalytic burner assembly 110, where the excess hydrogen 108 is reacted with air to produce heat 112. The heat 112 is then used for producing steam 114 which in turn is used in the fuel reformer 102 for the conversion of hydrocarbon fuel 105 to hydrogen rich gas 108. Byproducts from the fuel reforming process and the catalytic burning, such as carbon dioxide and nitrogen oxides, may leave the catalytic burner 110 as exhaust 116.

(12) FIG. 2 and FIG. 4 show schematic illustrations of two alternative embodiments of the catalytic burner assembly 110. As can be seen from FIGS. 2 and 4, the burner assembly 110 comprises at least two units, namely a burner unit 10 and a mixing unit 20. The burner unit 10 comprises a housing 12 defining a reaction chamber 13 in which a catalyst 14 is incorporated. Further the housing 12 comprises a fluid inlet 16 and a fluid outlet 18. The mixing unit 20 is arranged in close vicinity to the burning unit 10 and adapted to provide a homogenous mixture of air and hydrogen, which is fed through the fluid inlet 16 into the housing 12 and to the catalyst 14. The mixing unit 20 itself comprises a fuel inlet 22 and an oxidant inlet 24, wherein fuel and oxidant are mixed in a mixing chamber 26 and may exit the mixing unit 20 through a fuel-oxidant mixture outlet 28. FIGS. 2 and 4 further depict that the fuel inlet 22 and the oxidant inlet 24 are angled to a fluid flow direction 30 from the mixing unit 20 to the burner unit 10.

(13) Further, the mixing unit 20 may be cylindrically shaped having a mantel side 32 and two base plates 34 and 36. Instead of the cylindrically shape also any other prismatic shape is possible, wherein two base plates 34 and 36 are connected by at least three side surfaces 32.

(14) As can be seen from the first embodiment depicted in FIG. 2, the fuel-oxidant-outlet 28 is a pipe-shaped hollow element and its length L extends at least over one of the inlets 22; 24 in the mixing chamber 26. By extending the pipe-shaped fuel-oxidant outlet 28 over at least one of the inlets 22; 24, the risk of oxidant entering the fuel inlet, which may cause uncontrolled combustions, is significantly reduced. Additionally, the fuel inlet may be arranged upstream of the oxidant inlet 24, whereby the risk of uncontrolled combustions is further reduced. The pipe-shaped fuel-oxidant outlet 28 further comprises a first opening 28-1 arranged in the mixing chamber 26 and a second opening 28-2 which is provided in a bottom plate 34 of the mixing unit 20. Thereby it should be noted that more than one opening may be provided as first and/or second opening 28-1, 28-2.

(15) As illustrated in the second embodiment shown in FIG. 4, the fuel inlet 22 is arranged upstream of the oxidant inlet 24, whereby an entering of the oxidant into the fuel inlet 22 is avoided. Thereby an unwanted ignition of oxidant and fuel inside the fuel inlet 22 is avoided. In contrast to the illustrated embodiment of FIG. 2, the fuel-oxidant outlet 28 is not pipe-shaped but designed as simple opening in the bottom plate 34.

(16) In both depicted embodiments, the fuel-oxidant mixture outlet 28 merges with the fluid inlet 16 of the burner unit 10. Of course it is also possible that the pipe-shaped fuel-oxidant outlet 28 is elongated, or that a connection pipe is arranged between the burner unit 10 and the mixing unit 20, which fluidly connects the fuel-oxidant-mixture outlet 28 and the fluid inlet 16.

(17) FIG. 3 and FIG. 5 show detailed spatial views of the mixing unit 20 as shown in FIG. 2 and FIG. 4, respectively. As illustrated in FIG. 3 and FIG. 5, the fuel inlet 22 and the oxidant inlet 24 are arranged at the mantel side 32, wherein the fuel oxidant mixture outlet 28 is arranged at/in the bottom base plate 34. The fuel inlet 22 and the oxidant inlet 24 are pipe-shaped providing longitudinal axes A22, A24, whereby a directed fuel stream 38 respectively oxidant stream 40 are provided. These directed streams 38 and 40 are deviated by the walls 32 of the mixing unit 20 into a circular motion 41, whereby turbulences are introduced in the reaction chamber 26. Thereby a mixing of fuel and oxidant is performed. Besides that the mixed gas stream has to undergo a stream redirection from the circular motion the linear motion through the outlet 28, whereby further perturbations may be caused in the fluid streams and the homogeneity of the mixing may even be further improved. As can be further seen from FIG. 3, the pipe-shaped fuel-oxidant outlet 28 intensifies the induced swirling motion and the redirection of the fluid streams, whereby the mixing is enhanced.

(18) It should be further noted that in case a pipe-shaped fuel-oxidant outlet 28 is used, the fuel inlet 22 and the oxidant inlet 24 may be on the same level. Even if an arrangement at the same level is in principle also possible without a pipe-shaped fuel-oxidant-outlet 28, the risk of oxidant entering the fuel pipe 22 increases. In this case, it is therefore preferred to arrange the fuel inlet 22 upstream of the oxidant inlet 24 in order to hinder the oxidant from entering the fuel inlet 22.

(19) For providing an optimal mixing the fuel inlet 22 and the oxidant inlet 24 are arranged in such a way that the respective fluid streams enter the mixing chamber tangentially as depicted in the top view of FIG. 6. By the tangential interjection the swirling motion in the chamber 26 and thereby the homogeneity of the mixing may be maximized.

(20) FIGS. 7a and 7b show a further optional detail of the mixing device 20. As can be seen from the illustrated side views, the axes A22, A24 of the fuel inlet pipe 22 respectively the oxidant inlet pipe 24 may be inclined by a predetermined angle ; in relation to a cross sectional plane 42 of the mixing unit 20. Usually these angles ; is relatively small, preferably below 10 for ensuring that the fluid streams have a sufficiently long stay time in the mixing chamber 26 for developing the desired homogenous mixture. On the other hand the inclination further ensures that air streaming through the oxidant 24 does not enter the fuel pipe 22. Thereby the angles ; may provide the same or a different inclination.

(21) In general the inventive mixing unit hinders ignition of hydrogen in the pipes. Additionally, the mixing unit also reduces emissions of unwanted byproducts produced during the catalytic burning process since all combustible gases are burned due to the homogenous mixing. Additionally, only little excess air is necessary for reaching complete combustion, and increasing the temperature to the desired temperature suitable for methane combustion performed in the catalyst, which in turn reduces the amount of unwanted byproducts. Consequently, the catalytic burner efficiency may be maximized as the reactor temperature and hence the methane conversion is quickly in the desired range.

REFERENCE SIGNS

(22) 100 auxiliary power unit 102 fuel reformer 104 hydrogen rich gas 105 hydrocarbon fuel 106 fuel cell stack 107 electricity 108 hydrogen 110 catalytic burner 112 heat 114 steam production 10 catalytic burner unit 12 housing 14 catalyst 16 fluid inlet 18 fluid outlet 20 mixing unit 22 fuel inlet 24 oxidant inlet 26 mixing chamber 28 fuel-oxidant mixture outlet 28-1; 28-2 openings 30 fluid stream direction from the mixing chamber to the reaction chamber 32 mantel side 34 bottom base plate 36 top base plate 38 fuel stream direction 40 oxidant stream direction 42 cross sectional plane L length of fuel-oxidant outlet A22 longitudinal axis of fuel inlet A24 longitudinal axis of oxidant inlet