WO2000078669A1

WO2000078669A1 - Fuel processor for producing hydrogen and apparatus suitable for use in such processor

Info

Publication number: WO2000078669A1
Application number: PCT/NL2000/000364
Authority: WO
Inventors: Anton Scholten; Petrus Franciscus Maria Theresia Van Nisselrooij; Walter Ricor De Jongh; Jan Stokman
Original assignee: Plug Power Inc.
Priority date: 1999-05-27
Filing date: 2000-05-26
Publication date: 2000-12-28
Also published as: AU5254900A; NL1013478C2

Abstract

Fuel processor for the production of a gas stream comprising hydrogen. A mixture comprising hydrocarbon, steam and oxygen is reacted in a catalytic partial oxidation (CPO) (11). After the CPO (11), the mixture is passed through a number of high temperature CO-Shift units (16.1-16.3) that are arranged in series. Also described are a fuel processor characterised by the way of saturating hydrocarbon with water and a device for generating a third and a fourth stream from a first and second stream.

Description

Title: Fuel processor for producing hydrogen, and apparatus suitable for use in such processor

The invention relates to a fuel processor for producing a gas stream which comprises hydrogen through catalytic combustion of a mixture which: comprises at least one gaseous hydrocarbon compound, water vapor and oxygen, the fuel processor comprising a gas stream path along which the mixture is passed and a CPO catalyst included in the gas stream path, to which the mixture is supplied for the catalytic combustion. (CPO is understood herein to mean Catalyst Partial Oxidation.)

The invention also relates to an apparatus for generating from a first and second gas stream a third and fourth gas stream. A fuel processor of the type described in the opening paragraph is known per se. The hydrogen generated is often used to be supplied to a fuel cell which burns the hydrogen for generating electric energy and/or heat. In this connection it is important that the hydrogen generated by the fuel processor comprises as less carbon monoxide as possible, because this is detrimental to the proper operation of the fuel cell. The invention has, inter alia, for its object to provide a fuel processor which generates a gas stream with hydrogen which comprises less carbon monoxide than the known fuel processor. Accordingly, the fuel processor according to the invention is characterized in that in the gas stream path downstream of the CPO catalyst a plurality of series connected HT shifts are included through which, in use, the mixture leaving the CPO catalyst respectively flows. Because a plurality of series connected HT shifts are included, it has become possible to regulate per HT shift the temperature of the mixture flowing through the HT shifts. Thus the above amount of CO can be minimized. HT shift is understood herein to mean high-temperature shift catalyst. In particular it holds that in the gas stream pa.th respectively between the CPO catalyst and the nearest HT shift located downstream of the CPO catalyst and between the HT shifts heat exchangers are included which exchange heat between, on the one hand, the mixture supplied to the CPO catalyst and, on the other hand, the mixture flowing through the series connected HT shifts downstream of the CPO catalyst. The effect thus achieved is that the temperature of the mixture leaving a HT shift is higher than the temperature of the mixture flowing into a HT shift located downstream of the above-mentioned HT shifts. Because the temperature, seen in downstream direction, decreases per HT shift, this has the result that the reaction equilibrium is shifted such that the amount of carbon monoxide in the mixture decreases accordingly. According to a practical further elaboration it holds that each HT shift is provided with two opposite sides which form respectively an inlet and an outlet of the HT shift, the HT shifts being arranged with respect to each other in a direction coinciding with the normal of the above sides of the HT shifts, an outlet of a first HT shift being located opposite an inlet of a second HT shift, and the second HT shift being included in a box-shaped chamber having a bottom and upright side walls, the bottom being located between the inlet of the second HT shift and the outlet of the first HT shift, and the gas stream path from the first HT shift to the second HT shift extending respectively along an outer side of the bottom of the box-shaped chamber, between the heat exchanger and an outer side of the upright side wall of the box-shaped chamber, between the second HT shift and an inner side of the upright side wall of the box-shaped chamber to a space located between the inner side of the bottom of the box-shaped chamber and the side of the second HT shift which comprises the inlet. The fuel processor may thus be of very compact design. In particular it holds that each HT shift is included in a box-shaped chamber. This measure, too, realizes that the fuel processor is of very compact design. This particularly holds if each HT shift is of tubular design with two opposite open ends which form respectively the inlet and the outlet of the HT shift, axial axes of the HT shifts coinciding at least substantially with an axial axis of the tubular inner wall of the heat exchanger. Preferably, it holds in that case that the heat exchanger is further provided with a tubular insulating outer wall which has a heat insulating function.

To further improve the efficiency and reduce the amount of carbon monoxide, it holds in particular that, furthermore, an LT shift located downstream of the HT shifts is included in the gas stream path, the fuel processor further being provided with an inlet for, in use, adding water to the mixture supplied to the LT shift for cooling the mixture. LT shift is understood herein to mean low-temperature shift catalyst. The processor may further be provided with means for adding water in the form of steam. It is also possible, however, that the inlet comprises atomizing means for adding the water in atomized condition. This has a very favorable effect on the efficiency.

According to a very advanced embodiment of the fuel processor it holds that the LT shift comprises a tubular insulating outer wall and a tubular insulating inner wall which are arranged concentrically with respect to each other, the mixture, in use, flowing through the space formed between the tubular insulating inner wall and the tubular insulating outer wall, and the HT shifts and the CPO catalyst being included in a space enclosed by the tubular insulating inner wall. As a result, the fuel processor is of very compact design. In that case the heat flows are particularly directed in a radial direction from the inside to the outside, while the flow of the mixture is directed at least substantially in axial direction. In particular it holds that the tubular insulating outer wall of the heat exchanger coincides with the tubular insulating inner wall of the LT shift. To further reduce the amount of CO, it preferably holds that the processor is further provided with a PrOx located in the gas stream path downstream of the LT shift as well as an inlet for adding oxygen to the mixture that has left the LT shift and flows to the PrOx. PrOx is understood herein to mean 'preferential oxidation' = selective CO oxidation catalyst. According to a very advanced embodiment it holds that the processor is further provided with a vessel which is filled with water and/or through which water flows, to which vessel, furthermore, the gaseous hydrocarbon compound and oxygen are supplied to be passed through and/or along the water to generate the above mixture supplied to the CPO catalyst, and means for regulating the temperature of the water to adjust the concentration of the water vapor in the mixture supplied to the CPO catalyst. Because water has been supplied to the mixture, more hydrogen is formed per mole of the gaseous hydrocarbon compound in the mixture than when the mixture would comprise only gaseous hydrocarbon and oxygen (air).

To further minimize the amount of CO, it holds that the processor may further be provided with a heat exchanger for exchanging heat between the mixture which has flown through the PrOx and the water contained in the vessel so that the temperature of the mixture forming the gas stream comprising hydrogen falls.

According to the preferred embodiment it holds that in the gas stream path between the LT shifts and the PrOx a heat exchanger is included to further cool the mixture.

The invention also relates to a fuel processor of the type described in the opening paragraph, which is characterized in that the processor is further provided with a vessel which is filled with water, to which vessel the gaseous hydrocarbon compound and oxygen are supplied to be passed through and/or along the water to generate the above mixture and means for regulating the temperature of the water to adjust the concentration of the water vapor in the mixture.

For the apparatus for generating from a first and second gas stream the third and fourth gas stream it holds according to the mvention that the third gas stream comprises a mixture of the first and second gas stream, the apparatus being provided with a chamber enclosing a space in which a ventilator is included, the chamber being provided with a first and second inflow opening for, in use, supplying the first and second gas stream to respectively the first and second inflow opening and a first and second outflow opening, the first and second gas stream, in use, being sucked in by the ventilator and being supplied, separated from each other in the chamber, to respectively a first and second outflow opening, the first outflow opening discharging directly into a first outlet, and the second outflow opening discharging into the first outlet and a second outlet via a bifurcation, a controllable valve being included in the first and/or second outlet to adjust the ratio of the amount of gas originating from the first and second gas stream in the third gas stream from the first outlet, the fourth gas stream comprising a part of the second gas stream flowing through the second outlet.

Such an apparatus has the advantage that by means of one ventilator two gas streams can be pressurized. Moreover, the size of the two gas streams is regulated (modulated) in a similar ratio through a corresponding regulation (modulation) of the rotational speed of the ventilator. In particular it holds that the chamber comprises a cylindrical outer wall which encloses a cylindrical space, the ventilator being designed as a wheel, of which an axis of rotation coincides with an axial axis of the chamber, the wheel on both sides being provided near its circumferential edge with blades, and the first gas stream extending on a first side of the wheel where the blades are, the second gas stream extending on a second side of the wheel where the blades are. According to a further elaboration it holds that the first and second inflow opening are provided in the cylindrical outer wall of the chamber in axial direction of the chamber in a staggered position, the first inflow opening and the first outflow opening being arranged at least substantially in a similar plane directed perpendicularly to the axial axis of the chamber, and the second inflow opening and the second outflow opening being arranged at least substantially in a similar plane directed perpendicularly to the axial axis of the chamber. According to a further elaboration it holds that the chamber is provided with two opposite side walls directed perpendicularly to the axial axis of the chamber, the first side wall comprising a first circular groove extending around the axial axis, in which the first inflow and outflow opening is included, and the second side wall comprising a second circular groove extending around the axial axis, in which the second inflow and outflow opening is included, and the blades of the wheel extending respectively along the first and second groove.

Such an apparatus can be advantageously used in the above-described fuel processor. Here it holds that the first gas stream consists of a mixture of air and a gaseous hydrocarbon compound and the second gas stream consists of air, the third gas consists of a mixture of the first and second gas stream and the fourth gas stream consists of a fraction of the second gas stream, the third gas stream being supplied to the gas stream path and the fourth gas stream being added to the mixture supplied to the PrOx.

The invention will be explained in more detail with reference to the drawings, in which:

Fig. 1 shows a possible embodiment of a fuel processor according to the invention; Fig. 2 shows the temperature curve along the gas stream path through the CPO catalyst, the HT shifts, the LT shift, and the PrOx of the fuel processor of Fig. 1;

Fig 3 shows the temperature curve along the line of Fig. 1;

Fig. 4 shows a part of the apparatus of Fig. 1; Fig. 5A shows a first cross-section of an apparatus according to the invention which can advantageously form part of the fuel processor of Fig. 1;

Fig. 5B shows a second cross-section of the apparatus of Fig. 5A; and

Fig. 6 shows an alternative embodiment of the vessel 6 of Fig. 1.

In Fig. 1 reference numeral 1 denotes a fuel processor for producing a gas stream comprising hydrogen. The fuel processor is of a type which generates hydrogen through catalytic treatment of a mixture which comprises at least one gaseous hydrocarbon compound, water vapor and oxygen. The mixture is passed along a gas stream path for the combustion of the relevant mixture. To obtain the mixture, the apparatus is provided with a vessel 2 filled with water (H₂O). The vessel 2 is provided with an inlet 4, to which the gaseous hydrocarbon, in this example CH , and oxygen, in this example air, is supplied. The gaseous hydrocarbon and oxygen are thus injected at the bottom of the vessel 2 and will bubble up through the water 6 contained in the vessel. Above the water surface in the vessel 2 the gaseous hydrocarbon and oxygen bubbling up in the water 6 form a mixture 8 which also comprises water vapor. The fuel processor is provided with means 10 for regulating the temperature of the water 6. The temperature of the water 6 also determines the temperature of the mixture 8. The temperature of the mixture 8 directly determines the amount of water vapor which is included in the mixture 8. The higher the temperature, the higher the degree of saturation of the mixture with water. The resulting mixture 8 is passed from an outlet 9 of the vessel 2 along a gas stream path for the catalytic combustion. For the catalytic combustion this gas stream path contains, inter alia, a known per se CPO catalyst 11. This CPO catalyst is a catalyst, as also used for automobiles. In the gas stream path downstream of the CPO catalyst are further included a plurality of series connected HT shifts 16.1-16.3. This example relates to three series connected HT shifts. In use, the mixture leaving the CPO catalyst flows through these HT shifts.

The mixture 8 supplied to the CPO catalyst causes the following reactions in the CPO catalyst: CH₄ + x 0₂ → C0₂ + s H₂0 + Q (400 → 900°C) (1) CH₄ + -X H₂0 ^ X CO + 3/2 H₂ - Q (900 → 700°C) (2) k CH₄ + % CO₂ <-> X CO + H₂ - Q (3)

CH₄ + O₂ → CO + 2 H₂ (4) This shows that in addition to hydrogen (H₂) carbon monoxide is also formed (CO). indicates that heat is released. The gas stream which, besides hydrogen, comprises a large amount of carbon monoxide is not suitable for being supplied to a fuel cell for generating electric energy and/or heat. The carbon monoxide results in a less proper operation of the fuel cell. An advantage of the extra water addition is that reaction (2): CH₄ + H₂O -> CO + 3H2 (900 → 700°C) instead of (900 → 800°C) relatively increases and that the amount of carbon monoxide (CO) is reduced with respect to the amount of generated hydrogen (H2). An equivalent of partial CO shift therefore already occurs. The amount of hydrogen which is therefore generated can be regulated by regulating the amount of water contained in the mixture 8. Thus the reaction of formula 4 will occur to a greater or less degree.

In this example the vessel is provided with a water outlet 12 diagrammatically shown in Fig. 1 for supplying the water 6 from the vessel to an electric heating element 10. The resulting heated water is supplied via a line 14 to the vessel again. By means of the heating element 10 the temperature of the water 6 in the vessel 2 can therefore be regulated.

In the gas stream path downstream of the CPO catalyst 11 a plurality of series connected HT shifts 16.1-16.3 are included. This example relates to three series connected, known per se HT shifts. These HT shifts, too, consist of a known per se catalyst of the type also used for automobiles. The mixture leaving the CPO catalyst comprises, as discussed, an amount of carbon monoxide (see formula 2 and formula 3). When this mixture is supplied to the first HT shift 16.1, the following reaction occurs in the HT shift 16.1:

The advantage of the HT shift is therefore that the amount of CO in the mixture is reduced, while as by-product the CO₂ harmless to a fuel cell is generated. To ensure that the reaction equilibrium of the reaction of formula 4 comes to lie such that the amount of CO is very low, respectively in the gas stream path between the CPO catalyst 11 and a nearest HT shift 16.1 located downstream of the CPO catalyst and between the mutual HT shifts (16.1-16.2; 16.2-16.3) heat exchangers are included, which exchange heat between, on the one hand, the mixture supplied to the CPO catalyst 11 and, on the other hand, the mixture which flows through the series connected HT shifts downstream of the CPO catalyst. In this example the heat exchangers comprise a tubular inner wall 18, which encloses a space 20 in which the HT shifts are included. Each HT shift 16.1-16.3 is provided with two opposite sides which form respectively their inlet 22 and an outlet 24 of the HT shift. The HT shifts are arranged with respect to each other in a direction 26 coinciding with the normal of the above sides of the inlet and outlet 22, 24. An outlet 24 of a first HT shift 16.1 is located opposite an inlet 22 of a second HT shift 16.2. It further holds that the second HT shift 16.2 is included in a box-shaped chamber 28 having a bottom 30 and upright side walls 32. The bottom 30 is included between the inlet 22 of the second HT shift 16.2 and the outlet 24 of the first HT shift 16.1. The result is that the gas stream path from the first HT shift 16.1 to the second HT shift 16.2 extends respectively along an outer side of the bottom 30 of the box-shaped chamber 28, between the heat exchanger, i.e. the tubular inner wall 18 and an outer side of the upright side wall 32 of the box-shaped chamber 28, between the HT shift 16.2 and an inner side of the upright side wall 30 of the box-shaped chamber 28, to a space 34 located between the inner side of the bottom 30 of the box-shaped chamber 28 and the side of the second HT shift 16.2 which comprises the inlet 22. The first HT shift 16.1 and the third HT shift 16.3 are also provided with a box-shaped chamber 28. The gas stream path from the CPO catalyst to the inlet of the first HT shift 16.1 and the gas stream path from the outlet of the second HT shift 16.2 to the inlet of the third HT shift 16.3 is therefore quite analogous as discussed^" in relation to the gas stream path from the outlet of the first HT shift 16.1 to the inlet of the second HT shift 16.2. In this example each HT shift is of tubular design with two opposite open ends 22, 24, which form respectively the inlet and the outlet of the relevant HT shift. Axial axes of the HT shifts (arrow 26 in the drawing) coincide at least substantially with an axial axis of the tubular inner wall 18 of the above heat exchanger. The relevant heat exchanger is further provided with a tubular insulating outer wall 36 which encloses the tubular inner wall 28 completely but with an interspace.

The operation of the apparatus described thus far is as follows. The mixture 8 flowing into the vessel 2 will have a temperature of about

70 to 80°. The mixture 8 is passed via a space located between the inner wall 18 of the heat exchanger and the outer wall 36 of the heat exchanger to the CPO catalyst. Fig. 2 shows the temperature curve of the mixture flowing through respectively the CPO catalyst and HT shifts 16.1, 16.2 and 16.3. Plotted on the horizontal axis is the curve of the gas stream path 2 through the CPO catalyst and the HT shifts. Before the mixture flows into the CPO catalyst, the mixture will have a temperature of about 350-500°C (Fig. 2: 400°C).In the CPO catalyst the reactions of formula 1, 2, 3 and 4 occur. See curve A of Fig. 2. The mixture leaving the CPO catalyst will then have a temperature of about 685°C. Subsequently, the mixture flows from the CPO catalyst along the inner side of the inner wall 18 of the heat exchanger and has the result that it heats the mixture flowing on the outer side of the inner wall 18 from the vessel. The mixture flowing from the CPO catalyst to the inlet of the first HT shift 16.1 will correspondingly be cooled to, for instance, 575°C (see curve B). At the inlet of the first HT shift the mixture will therefore have a temperature which is lower than the temperature of the mixture at the outlet of the CPO catalyst. When the mixture flows through the first HT shift, the temperature thereof will increase, as indicated by curve C in Fig. 2. The temperature rises again to, for instance, 580°C. In the path from the HT shift 16.1 to th-e HT shift 16.2 the mixture will flow along the heat exchanger and cool again to, for instance, 450°C (curve D). If the fuel processor was provided with only one HT shift having the common length of 16.1, 16.2 and 16.3, the temperature of the mixture in the HT shift would rise further, as indicated by the dotted line in Fig. 2. At the end of the path of the HT shifts indicated in Fig. 2 by point Pi, this would mean that the amount of CO in the mixture was, for instance, even much more than 3%. In the processor according to the invention, however, a plurality of HT shifts are used, in which, for instance, the mixture leaving the first HT shift 16.1 is cooled by flowing along the inner side of the tubular inner wall 18 of the heat exchanger, which has the result that the mixture supplied to the inlet 22 of the second HT shift 16.2 has a lowered temperature of, for instance, 450° C. When the mixture then flows through the second HT shift, the temperature of the mixture will slowly rise again, as indicated by the curve 16.2 in Fig. 3. Quite analogously, the mixture leaving the second HT shift 16.2 will be cooled again by flowing along the inner wall 18 of the heat exchanger, which has the result that the mixture supplied to the third HT shift 16.3 has a temperature of, for instance, 370°C. The mixture leaving the third HT shift 16.3 has a lower temperature (for instance 355°C), as indicated in Fig. 2 by the point P₂). The result is that in respect of the mixture leaving the third HT shift 16.3 the reaction equilibrium of the reaction of formula 4 has shifted such that the amount of CO is much less than would have been the case m the point Pi of Fig. 2.

The processor, however, further comprises measures, to be discussed below m more detail, for further shifting the reaction equilibrium, such that even less CO is contained in the mixture. To this end, the fuel processor is further provided with an LT shift 38 located downstream of the HT shifts

16 1-16 3 Furthermore, the fuel processor is provided with an inlet 40 for, in use, adding water to the mixture supplied to the LT shift for cooling the mixture. The mixture leaving the HT shift 16.3 has, for instance, a temperature of 355°C. By supplying water vapor to the mixture via the inlet 40, this will be cooled. The following favorable shifting of the thermodynamic equilibrium position occurs:

CO + H₂O → CO₂ + H₂ (6)

The processor may further be provided with means for adding the water via the inlet 40 in the form of steam. These means may, for instance, consist of a steam generator 42 comprising an electric heating unit, a hydrogen burner, or a natural gas burner and a heat exchanger. It is also possible that the inlet 40 comprises atomizing means for adding the water in atomized condition. The water in atomized condition may then have a temperature corresponding to room temperature. It is not necessary to heat water to steam. Instead thereof, the water may be supplied to the mixture after atomization without heating, i.e. without supplying extra energy, for cooling the mixture. Thus cooling the mixture to, for instance, 180°C is indicated in Fig. 2 by curve E. The cooled mixture is thus supplied to the LT shift 38. The LT shift comprises a known per se catalyst material. In this example the LT shift comprises a tubular (heat) insulating outer wall 44, and a tubular inner wall 36 which, in this example, coincides with the tubular (heat) insulating outer wall of the heat exchanger. The tubular outer wall and the tubular inner wall of the LT shift are arranged concentrically with respect to each other, the mixture, in use, flowing through the space formed between the tubular inner wall 36 and the tubular outer wall 44. Located outside the outer wall 44 is cooling water 45 having a temperature of, for instance, 20-100°C. By heating up this cooling water will be partially converted into steam 47 which is supplied via a line 49 to the mixture 8 flowing through the outlet 9. In LT shifts, too, the reaction equilibrium of formula 6 will be shifted such that the amount of carbon monoxide further decreases. Because the temperature of the mixture flowing through the LT shift has meanwhile strongly decreased, it has been ensured that the LT shift has a larger volume than the HT shifts. This means that the residence time of the mixture in the LT shift increases. The residence time is so long that the relatively slow reaction of Fig. 3 nevertheless has the result that the amount of carbon monoxide further decreases. The temperature rise of the mixture along the gas stream path flowing through the LT shift is indicated in Fig. 2 by curve F. When the mixture leaves the LT shift, the amount of CO will, for instance, be smaller than 1000 ppm.

In Fig. 1 the point at which the mixture flows into the LT shift is indicated by P₂, and the point at which the mixture leaves the LT shift is indicated by P₃. The processor further comprises a known per se PrOx 46 located in the gas stream path downstream of the LT shift, as well as an inlet 48 for adding oxygen to the mixture which has left the LT shift and flows to the PrOx.

In the PrOx the following reactions occur:

H₂ + 2CO + O₂ → 2CO₂ + H₂ (7)

The amount of CO will therefore further decrease in the PrOx. In the PrOx the temperature rises from about 100 to 110°C, as shown in Fig. 2 by the curve H. Subsequently, the mixture leaves the PrOx via the line 50. In the line 50 the final product of the fuel processor therefore flows, which final product consists of a gas stream comprising hydrogen, nitrogen carbon dioxide, and water vapor.

Starting from the CPO catalyst, a substantially declining temperature gradient will be present in the radial direction R from the inside to the outside, as shown in Fig. 3.

The apparatus may further be provided with a fuel cell to which the hydrogen can be supplied via the line 50. In the fuel cell 52 the hydrogen is burned to generate electric energy and/or heat. It is likewise possible that a part of the hydrogen in line 50 is supplied via line 50' to the apparatus 42 when this^" is designed as a hydrogen burner for obtaining steam supplied to the inlet 40. It is also possible to supply electric energy E from the fuel cell 52 to the means 42 when these comprise an electric heating unit for generating steam. It is further possible that the electric heating elements 10 for heating the water 6 of the vessel 2 is fed by electric energy from the fuel cell 52. Of course, the electric heating elements 10 may also be replaced by a hydrogen burner 10 for heating the water 6, which hydrogen burner 10 is fed with a part of the hydrogen flowing through the line 50. This is likewise diagrammatically shown in Fig. 1. The product may further be provided with a heat exchanger 54 for exchanging heat between the mixture that has flown through the PrOx 46 and the water 6 contained in the vessel, so that the temperature of the mixture falls.

When the fuel processor is provided with the fuel cell 52, it is further possible that the heated water formed in the fuel cell 52 when burning hydrogen is supplied to the inlet 40 in the form of steam. In that case the fuel cell 52 also forms part of the means for forming steam.

As shown in Fig. 4, the apparatus may further be provided with a heat exchanger 53 included between the LTS and the PrOx in the gas stream path, with an inlet 53A for water of, for instance, 20-70°C, and an outlet 53B for water of, for instance, 100°C. The mixture then cools in the heat exchanger, for instance, from 200°C to 110°C. (See curve G of Fig. 2.) The outlet 53B may, for instance, communicate with the inlet 40. The heat exchanger 53 may then replace the steam generator 42. In the PrOx 46 the temperature of the mixture rises, as shown in curve H of Fig. 2. Downstream of the PrOx 46 the temperature then falls as a result of the water layer 51, as shown in curve I of

Figs. 5A and 5B show an apparatus for generating from a first and second gas stream at least a third and fourth gas stream, which third gas stream comprises a mixture of the first and second gas stream. More in particular, the apparatus is provided with a chamber 60 which encloses a space 62 in which a ventilator 64 is included. The chamber is provided with first and second inflow opening 66, 68, for supplying, in use, the first and second gas stream to respectively the first and second inflow opening 66, 68. The first and second gas stream are sucked in by the ventilator. The chamber further comprises first and second outflow opening 70, 72, the first and second gas stream, in use, being sucked in by the ventilator and being supplied to a first and second outflow opening separated from each other in the chamber.

The first outflow opening discharges into a first outlet 76 having a relatively large cross-section. The second outflow opening 72 discharges via a bifurcation into the first outlet 76 and the second outlet 78 having a relatively small cross-section when compared to the cross-section of the first outlet 76. This has the result that the flow resistance of the first outlet 76 is lower than the flow resistance of the second outlet 78. Furthermore, in the first and/or second outlet a controllable valve 79 is included to adjust the ratio of the amount of gas originating from the first and second gas stream in the third gas stream flowing from the first outlet 76. From the second outlet 78 flows the fourth gas stream which comprises a part of the second gas stream.

The third gas stream in the outlet 76 therefore comprises a combination of the first gas stream and the second gas stream which are supplied to respectively the first and second inflow opening 66, 68. The fourth gas stream of the outlet 78 only comprises a part of the second gas stream which is supplied to the second inflow opening 68. This is caused by the above difference in flow resistances. When the rotational speed of the ventilator 64 is varied, the size of the third and fourth gas stream will correspondingly vary, the ratio between the size of the fourth gas stream and the third gas stream remaining constant.

In this example it holds that the chamber compπses a cylindrical outer wall which encloses a cylindrical space. The ventilator 64 is designed as a wheel, of which an axis of rotation 74 coincides with the axial axis of the chamber. Near its circumferential edge 73 the wheel is provided on both sides 75A, 75B.wιth blades 77. The first gas stream extends to a first side 75A of the wheel, and the second gas stream extends to a second side 75B of the wheel. In the axial direction of the chamber the first and second inflow opening 66, 68 are provided in the cylindrical outer wall in a staggered position. The first inflow opening and the first outflow opening are arranged at least substantially in a similar plane which is directed perpendicularly to the axial axis of the chamber It also holds that the second inflow opening and the second outflow opening are arranged at least substantially m a similar plane which is directed perpendicularly to the axial axis 74 of the chamber.

In particular it holds that the first outlet 76 of the apparatus of Figs 5A and 5B is connected with the inlet 4 of the vessel 2 of Fig. 1. The second outlet 78 can be connected with the inlet 48 as shown in Fig. 1 In that case the apparatus of Figs. 5A and 5B is further provided with a known per se gas block 82 having an air inlet 84 and a gas inlet 86 for supplying a mixture of CH₄ and air via a line 87 to the inflow opening 66. Furthermore, via an air inlet 88 air is supplied to the second inflow opening 68 By means of the valve 79 a desired ratio between the amount of air and CH₄ supplied to the inlet 4 can be adjusted Furthermore, by varying the rotational speed of the ventilator 64, the mixture supplied to the inlet 4 and the air supplied to the inlet 48 can be equally varied and modulated By varying the rotational speed, a constant energy flow can thus be regulated m the processor In other words, in use, to equally modulate the third and fourth gas stream, these are the gas streams which are supplied to respectively the inlet 4 and the inlet 48, the rotational speed of the ventilator is modulated

It further holds that the chamber is provided with two opposite side walls which are directed perpendicularly to the axial axis of the chamber, the first side wall 90A comprising a first circular groove 92A extending around the axial axis, in which the first inflow and outflow opening are provided, and the second side wall 90B comprising a second circular groove 92B extending around the axial axis, in which the second inflow and outflow opening are provided, The blades 77 of the wheel extend respectively along the first and second groove.

The invention is in no way limited to the above-described embodiments. The vessel 6, as shown in Fig. 1, may, for instance, be replaced by an apparatus as shown in Fig. 6. The inlet 4 and the outlet 9 shown herein correspond with the inlet 4 and the outlet 9 of Fig. 1. The alternative apparatus is provided with a vessel 6', in which a layer 96 of a material in the form of, for instance, balls, salzur etc. is provided. The inlet 4 discharges below the layer 96. The outlet 9 is located above the layer 96. Also located above the layer 96 is a spray nozzle 98, via which water is deposited by means of a pump 100 from a vessel 102 onto the upper side of the layer 96. This water flows through the layer in the material 96 to the bottom 104 of the vessel 6'. In a position located right above the bottom 104 the vessel 6' is in fluid communication with the vessel 102 by means of a line 108. The vessel 102 is further provided with means for heating the water located in the vessel. These means may consist of electric heating means, a burner, water originating from the above-mentioned fuel cell and/or originating from one of the heat exchangers mentioned before. By means of the pump 100 the water is pumped round from the bottom 104 via the line 108 to the vessel 102 and from the vessel 102 to the spray nozzle 98, after which the water flows via the inert material 96 to the bottom 104. The gaseous hydrocarbon, in this example CH₄ and oxygen, is again supplied to the inlet 4. This gas flows via the inert material 96 to the outlet 9. When the gas flows through the inert material 96, it will flow along the above water and thus be saturated with water vapor. In this example the temperature of the water that can be supplied via the spray nozzle 98 to the inert material 96 is of variable design and can be, for instance, about 70°C. Depending on the temperature of the water supplied to the spray nozzle, the mixture is more or less saturated with water vapor. The water temperature is therefore a variable, by means of which the amount of water vapor in the mixture 8 can be regulated. Furthermore, other variants of the lo

fuel processor of Fig. 1 are conceivable. Thus, for instance, it is possible to use more than three HT shifts. Also, at the inlets and outlets of the HT shifts other temperatures than those mentioned in the above examples may be used. Steam generated by means of the fuel processor 52 may, for instance, be supplied via a line 106 to the inlet 40. Also, electric energy generated by means of the fuel processor 52 can be supplied via the lines 108 and/or 110 to the steam generator 42 and/or the heating element 10. For the CPO catalyst, HT shift, PrOx, and LT shift all known catalysts may be used. The apparatus 6 may be replaced by any known per se system for introducing water vapor. The fuel processor according to the invention is preeminently suitable for use in microthermal power units in the domestic environment. This imposes special conditions. The processor must be transportable as a whole, from the factory to the user location, and may not contain fire or explosion dangerous materials during transport. After placement at the user location the thermal power plant, and therefore also the processor, must be able to be operational within about one hour. In the case of maintenance or failures when air enters the processor, no explosion or fire dangerous situations may arise. Besides, the processor must be designed so as to be as compact as possible.

The above conditions impose stringent requirements on the catalysts in the processor. The catalysts may not be pyrophoric, that is to say when air enters, no such temperature rise may occur, as a result of oxidation of the catalyst, that the catalyst or the possible combustible content of the processor catches fire. Also, the catalysts must have such a chemical composition that activation, if required, can take place within ca. 1 hour and can take place with process gas.

The catalytic activity must be so high that at a high space throughput speed (Nm³ process gas/m³ catalyst/hour), and therefore with small amounts of catalyst, a nearly complete conversion of, successively, methane and carbon monoxide is reached. The CPO and PrOx catalysts may, for instance, consist of noble metals, on a carrier material applied as coating onto a ceramic monolith. These types of catalysts are described in the open literature. Suitable active metal is, inter alia, platinum. The above catalysts nearly completely convert methane or carbon monoxide at throughput speeds up to at least 20,000 Nm³/m³/h.

The shift catalysts are characterized by a low volume, rapid activation in product gas and a non-pyrophoric character.

HTS catalysts that mav be used, for instance

1. Catalysts on the basis of platinum.

Platinum applied onto a γ-Al2θ₃ carrier. Pt content on the basis of the platinum plus carrier weight: 0.1-20 wt.%, preferably 1-10 wt.%. Other metals, such as Ru and Rh, are also useful (Ru as shift and methanization catalyst is described in the open literature).

Alternative carriers are, inter alia, silica-alumina, zirconia. The supported catalyst is applied onto a ceramic monolith by means of coating. Load of the coating: 50-400 g per liter of monolith, preferably 50-300 g/1. The channel density of the monolith: 30-1200 cpsi (= cells per inch²), preferably 100-800 cpsi, most preferably 100-600 cpsi.

Platinum has no activation time and is not pyrophoric. The CO shift activity is high, i.e. little catalyst material is required. It is a disadvantage that Pt converts a part of the CO in the process gas with H2 to CH₄ (loss of efficiency, power reduction of the fuel cell). The degree of methanization is a matter of the kinetics of the methanization with respect to that of the CO shift. χΛ.ccording as the temperature increases, the methanization relatively increases with respect to the CO shift. The problem may, for instance, be solved by using 2 instead of 3 HTS monoliths. The monolith directly behind the CPO catalyst has the highest temperature and produces the largest amount. This is replaced by a dummy monolith (= uncoated monolith) or disappears completely from the processor (compact design). The remaining monoliths are located in the cooler zone of the heat exchanger/shift structure Thus the temperatures are kept below 450°C, preferably below 400°C. At the reduced temperatures Pt monoliths are, in spite of the shorter residence time of the gas, still sufficiently active for the desired CO conversion (50-60%). Example in the table

Summarizing the advantages of platinum (rapid startup, no activation procedure, non-pyrophoπc, safe, high activity) can therefore be utilized without unacceptable losses of efficiency

2 HTS catalysts on the basis of Fe2θ /Cr₂O₃

For this purpose, for instance, standard commercial Fe₂θ3/Cr2θ3 high temperature shift catalysts may be used The typical composition is 57-59 wt % Fe, on metal basis, 5-7 wt % Cr, on metal basis, and ca 1 wt % Cu, on metal basis, as promoter The catalysts are coated onto ceramic monoliths by known techniques The load and monolith characteristics are the same as for the Pt monoliths The activation of the monoliths occurs in process gas and is completed within 1 hour. During activation Fe2θ3 is reduced to Fe₃O₄. Fe₃O is slightly pyrophoric. Upon contact with air the catalyst in pellet form can develop such heat that fire dangerous situations arise. By applying the catalyst onto a monolith, a thin layer of catalyst in open channel structure is obtained. Excess Fβ3θ₄, as in the nucleus of pellets, which nevertheless, through diffusion inhibition, is not catalytically active, is no longer contained in the monolith and can give no heat problems during oxidation in the air. Through the open structure of the monolith, oxidation heat is rapidly discharged. The result is that upon exposure of a reduced monolith to the air the gas temperature in the channels rises by 35% only. Monoliths on the basis of Fe/Cr are less active than those on the basis of Pt. Three monoliths and maximum temperatures of 550 to 600°C are required for a sufficient conversion. This is no problem, because Fe/Cr catalysts have no methanization activity at all. In other words, with Fe/Cr the loss of efficiency is 0%.

The standard commercial LTS catalyst is CuO with ZnO (coprecipitation). This is, for instance, contained in the processor as a packed bed of catalyst pellets with a total volume of no less than 20 liters.

The active form in the shift is Cu metal. CuO can be very easily activated in process gas through reduction. However, the heat development is then such that upon a first startup the catalyst could become too hot and sinter.

In the first place, efforts may be directed to reducing, the amount of copper. This will give less dangerous heat development upon reduction and oxidation. However, this should not affect the activity, that is to say the CO conversion per unit of volume of catalyst.

Less copper while retaining activity is possible through finely divided application of the metal onto a carrier, such as alumina or silica. Typical loads are 5-30 wt.% Cu, preferably 10-20 wt.%. The copper is applied by methods known in the technique, such as impregnation of a Cu precursor, drying and calcining.

It is a disadvantage that CuO that is finely divided and sintering- resistant when located on a carrier, contrary to bulk CuO, is hard to reduce/activate at process temperatures of ca. 200°C. This can, for instance, be solved by addition of 0.1 to 1 wt.% of a metal, for instance Pt, which absorbs H₂ in the process gas and converts it into hydrogen atoms very active for reduction, which reduce CuO at lowered temperatures. The amount of platinum and the process temperature are such that no losses of efficiency through methanization occur.

An additional increase in the activity per unit of volume of catalyst is reached by increasing the steam/carbon ratio in the catalyst particles with respect to those in the process gas. This is possible by addition of water- absorbing materials. Suitable are zeolites (molecular sieves) such as A4, A5, 13X, which can take up ca. 10 wt.% H2O at the process temperature of 200°C.

Different forms are conceivable.

- Mixing of a milled commercial CuO/ZnO catalyst, or rather a Pt promoted Cu catalyst on carrier, with milled zeolite, which mixture is pressed or extruded to particles of the desired size. The catalyst/zeolite weight ratio may vary from 10:1 to 1:10, preferably 1:1 to 1:10.

- Applying Cu onto the zeolite itself. This is possible by (incipient wetness) impregnation of pre-formed zeolite particles, such as pellets or extrusions with a Cu precursor, for instance Cu citrate, drying, calcining, then impregnating with the reduction promoter, for instance Pt nitrate, drying and calcining.

- The above forms coated on a monolith.

The pyrophoric character of the zeolite systems is strongly reduced, because upon contact with the air the oxidation heat provides evaporation of the water in the zeolite. Per liter of zeolite, 50 to 100 liters can thus be released, which displaces-the air and prevents the temperatures in the catalyst bed from getting out of hand, which leads to catalyst deactivation and fire dangerous situations. When coated on a monolith, the locally strong heat development is further inhibited by the rapid heat discharge from the monolith.

Summarizing:

1. Less heat problems through less Cu in the reactor.

2. Less Cu feasible through increase in the activity via increase of Cu dispersion and addition of water-absorbing materials (higher steam/carbon ratio).

3. Increasing reducibility of highly disperse supported Cu in process gas through addition of reduction promoters (Pt).

4. Suppressing pyrophoric character by "extinguishing" with steam from the water-absorbing material. If required, coating on monolith. Such variants are each deemed to fall within the scope of the invention.

Claims

1. A fuel processor for producing a gas stream which comprises hydrogen through catalytic combustion of a mixture which comprises at least one gaseous hydrocarbon compound, water vapor and oxygen, the fuel processor comprising a gas stream path along which the mixture is passed and a CPO catalyst included in the gas stream path, to which the mixture is supplied for the catalytic combustion, characterized in that in the gas stream path downstream of the CPO catalyst a plurality of series connected HT shifts are included through which, in use, the mixture leaving the CPO catalyst respectively flows.

2. A fuel processor according to claim 1, characterized in that in the gas stream path respectively between the CPO catalyst and the nearest HT shift located downstream of the CPO catalyst and between the HT shifts heat exchangers are included which exchange heat between, on the one hand, the mixture supplied to the CPO catalyst and, on the other hand, the mixture flowing through the series connected HT shifts downstream of the CPO catalyst.

3. A fuel processor according to claim 2, characterized in that each HT shift is provided with two opposite sides which form respectively an inlet and an outlet of the HT shift, the HT shifts being arranged with respect to each other in a direction coinciding with the normal of the above sides of the HT shifts, an outlet of a first HT shift being located opposite an inlet of a second HT shift and the second HT shift being included in a box-shaped chamber having a bottom and upright side walls, the bottom being located between the inlet of the second HT shift and the outlet of the first HT shift, and the gas stream path from the first HT shift to the second HT shift extending respectively along an outer side of the bottom of the box-shaped chamber, between the heat exchanger and an outer side of the upright side wall of the box-shaped chamber, between the second HT shift and an inner side of the ---0

upright side wall of the box-shaped chamber to a space located between the inner side of the bottom of the box-shaped chamber and the side of the second HT shift which comprises the inlet.

4. A fuel processor according to claim 3, characterized in that each HT shift is included in a box-shaped chamber.

5. A fuel processor according to claim 4, characterized in that the heat exchangers comprise a tubular inner wall, which encloses a space in which the HT shifts with the box-shaped chambers are included.

6. A fuel processor according to claim 5, characterized in that each HT shift is of tubular design with two opposite open ends which form respectively the inlet and the outlet of the HT shift, axial axes of the HT shifts coinciding at least substantially with an axial axis of the tubular inner wall of the heat exchanger.

7. A fuel processor according to claim 6, characterized in that the heat exchanger is further provided with a tubular insulating outer wall.

8. A fuel processor according to any one of the preceding claims, characterized in that, furthermore, an LT shift located downstream of the HT shifts is included in the gas stream path, the fuel processor further being provided with an inlet for, in use, adding water to the mixture supplied to the LT shift for cooling the mixture.

9. A fuel processor according to claim 8, characterized in that the processor is further provided with means for adding the water via the inlet in the form of steam.

10. A fuel processor according to claim 9, characterized in that the means comprise an electric heating unit or a hydrogen burner, a natural gas burner or a heat exchanger.

11. A fuel processor according to claim 8, characterized in that the inlet comprises atomizing means for adding the water in atomized condition.

12. A fuel processor according to any one of claims 8-11, characterized in that the LT shift comprises a tubular insulating outer wall and a tubular insulating inner wall which are arranged concentrically with respect to each other, the mixture, in use, flowing through the space formed between the tubular insulating inner wall and the tubular insulating outer wall, and the HT shifts and the CPO catalyst being included in a space enclosed by the tubular inner wall.

13. A fuel processor according to claims 7 and 12, characterized in that the tubular insulating outer wall of the heat exchanger coincides with the tubular insulating inner wall of the LT shift.

14. A fuel processor according to any one of the preceding claims 8-13, characterized in that the processor is further provided with a PrOx located in the gas stream path downstream of the LT shift as well as an inlet for adding oxygen to the mixture that has left the LT shift and flows to the PrOx.

15. A fuel processor according to claim 14, characterized in that in the gas stream path between the LT shifts and the PrOx a heat exchanger is included to further cool the mixture.

16. A fuel processor according to any one of the preceding claims, characterized in that the processor is further provided with a vessel which is filled with water and/or through which water flows, to which vessel, furthermore, the gaseous hydrocarbon compound and oxygen are supplied to be passed through and/or along the water to generate the above mixture supplied to the CPO catalyst, and means for regulating the temperature of the water to adjust the concentration of the water vapor in the mixture supplied to the CPO catalyst.

17. A fuel processor according to claim 14 and 16, characterized in that the processor is further provided with a heat exchanger for exchanging heat between the mixture which has flown through the PrOx and the water contained in the vessel so that the temperature of the mixture forming the gas stream comprising hydrogen falls.

18 A fuel processor according to any one of the preceding claims, characterized in that the processor is further provided with a fuel cell for generating electric energy from the hydrogen formed.

19 A fuel processor according to claim 9 or 11 and according to claim 18, characterized in that the above means for forming steam or atomized water comprise the fuel cell.

20 A fuel processor for producing hydrogen through catalytic combustion of a mixture which comprises at least one gaseous hydrocarbon compound, water vapor and oxygen, provided with a CPO catalyst to which the mixture is supplied for the catalytic combustion, characterized in that the processor is further provided with a vessel which is filled with water, to which vessel, furthermore, the gaseous hydrocarbon compound and oxygen are supplied to be passed through and/or along the water to generate the above mixture, and means for regulating the temperature of the water to adjust the concentration of the water vapor m the mixture.

21 An apparatus for generating from a first and second gas stream a third and fourth gas stream, the third gas stream comprising a mixture of the first and second gas stream, provided with a chamber enclosing a space in which a ventilator is included, the chamber being provided with a first and second inflow opening for, in use, supplying the first and second gas stream to respectively the first and second inflow opening and a first and second outflow opening, the first and second gas stream, in use, being sucked in by the ventilator and being supplied, separated from each other in the chamber, to respectively a first and second outflow opening, the first outflow opening discharging mto a first outlet, and the second outflow opening discharging mto the first outlet and a second outlet via a bifurcation, a controllable valve being included in the first and/or second outlet to adjust the ratio of the amount of gas originating from the first and second gas stream in the third gas stream from the first outlet, the fourth gas stream comprising a part of the second gas stream flowing through the second outlet

22. An apparatus according to claim 21, characterized in that the chamber comprises a cylindrical outer wall which encloses a cylindrical space, the ventilator being designed as a wheel, of which an axis of rotation coincides with an axial axis of the chamber, the wheel on both sides being provided near its circumferential edge with blades, and the first gas stream extending on a first side of the wheel where the blades are, the second gas stream extending on a second side of the wheel where the blades are located.

23. An apparatus according to claim 22, characterized in that the first and second inflow opening are provided in the cylindrical outer wall of the chamber in axial direction of the chamber in a staggered position, the first inflow opening and the first outflow opening being arranged at least substantially in a similar plane directed perpendicularly to the axial axis of the chamber, and the second inflow opening and the second outflow opening being arranged at least substantially in a similar plane directed perpendicularly to the axial axis of the chamber.

24. An apparatus according to claim 23, characterized in that the chamber is provided with two opposite side walls directed perpendicularly to the axial axis of the chamber, the first side wall comprising a first circular groove extending around the axial axis, in which the first inflow and outflow opening is included, and the second side wall comprising a second circular groove extending around the axial axis, in which the second inflow and outflow opening is included, and the blades of the wheel extending respectively along the first and second groove.

25. A fuel processor according to any one of the preceding claims 14 or 17, characterized in that the processor is further provided with an apparatus according to claim 22, 23 or 24, the first gas stream consisting of a mixture of air and a gaseous hydrocarbon compound and the second gas stream consisting of air, the third gas consisting of a mixture of the first and second gas stream and the fourth gas stream consisting of a fraction of the second gas stream, the third gas stream being supplied to the gas stream path and the fourth gas stream being added to the mixture supplied to the PrOx.

26. A fuel processor according to claim 25, characterized in that, in use, to equally modulate the third and fourth gas stream the rotational speed of the ventilator is modulated.

27. A fuel processor according to any one of claims 1-20 or 25, 26, characterized in that the processor is further provided with an absorber through which the gaseous hydrocarbon compound is supplied to clean the gaseous hydrocarbon compound, the absorber comprising, for instance, activated carbon.

28. A fuel processor according to any one of claims 16 or 17, characterized in that the processor is provided with an ionization vessel for cleaning the water used to obtain the mixture.