WO2004054681A1

WO2004054681A1 - Evaporator

Info

Publication number: WO2004054681A1
Application number: PCT/EP2003/051037
Authority: WO
Inventors: Ludovicus Leonardus Gerardus Jacobs; Michiel Johannes Franciscus Maria Verhaak; Hendrik Martinus Wentinck
Original assignee: Hydrogensource Llc
Priority date: 2002-12-17
Filing date: 2003-12-17
Publication date: 2004-07-01
Also published as: AU2003299245A1

Abstract

The invention relates to an evaporator for the evaporation of water in a hot gas stream, comprising an inlet end, an outlet end, gas flow paths (3) extending from the inlet end to the outlet end and a hightemperature resistant water absorbing material (2) that at least partly defines the gas flow paths (3), wherein the water absorbing material (2) has a water absorbing capacity of at least 0.20 g per cubic centimetre. The invention further relates to a process for the evaporation of water using such evaporator, a fuel processor comprising such an evaporator, a process for the production of hydrogen using such a fuel processor and a fuel cell system comprising such a fuel processor and a fuel cell.

Description

EVAPORATOR

The present invention relates to an evaporator for the evaporation of water in a hot gas stream, a process for the evaporation of water using such evaporator, a fuel processor comprising such an evaporator, a process for the production of hydrogen using such a fuel processor and a fuel cell system comprising such a fuel processor and a fuel cell.

In a fuel processor, a hydrocarbonaceous fuel is converted in a hydrogen-rich gas stream that can be used in a fuel cell for the generation of electricity. Typically in a fuel processor, the hydrocarbonaceous fuel is first converted into a hot gas mixture comprising carbon monoxide and hydrogen in a partial oxidation or autothermal reforming zone. The thus-obtained hot gas mixture typically has a temperature in the range of from 600 to 1100°C and is subsequently reacted with steam at a water-gas shift conversion catalyst at a temperature in the range of 200 to 450 °C. This means that the hot gas mixture has to be cooled and water has to be evaporated between the partial oxidation/autothermal reforming zone and the water-gas shift conversion zone. It is advantageous to use the intrinsic heat of the hot gas mixture for the evaporation of water.

If water is added to a hot gas stream as very small droplets or a mist, then complete evaporation of the water will be easily achieved, even in hot gas streams having a relatively low linear velocity. Creation of very small droplets or a mist can for example be achieved by using a nozzle that supplies the water to the hot gas stream at a pressure that is typically at least 5 bar higher than the gas stream pressure, more usually at least 10 bar higher than the gas stream pressure. Disadvantages of the use of such nozzles is that high pressure is needed and that they have a limited turn-down ratio, typically about 3. Water supply means that add the water at a lower pressure difference, e.g. a pressure difference of less than 3 bar, are very suitable for a process wherein a large turn-down ratio of the gas throughput is required at a low water inlet pressure. Low pressure water supply means, however, typically supply water as relatively large droplets, typically larger than 1 mm. Complete evaporation of the water is therefore difficult to achieve, especially in a low turbulence gas stream.

It is known to further increase liquid-gas interactions by means of a static mixer. An example of a static mixer used for that purpose is a structure of superimposed individual corrugated metal sheets having an open cross-flow structure pattern. These structures are commercialised by Sulzer Chemtech as KATAPAK-M®. Such a structure and its use as static mixer is for example disclosed in Chem. Eng. Sci. 54 (1999) 1375-1381. Insertion of such a static mixer just downstream of water supply means that supplies water in relatively large droplets, still requires a relatively large length-to- diameter ratio of the static mixer to result in complete evaporation of the water.

In WO 01/79112 a fuel processor operating at a low gas flux and a low pressure is described that comprises an evaporator wherein hot effluent of a catalytic partial oxidation zone is used for the evaporation of water. The evaporator is in the form of a double-walled receptacle defining a water reservoir between its two walls into which a water supply conduit debouches. The water reservoir has an annular outlet for vapour at its upper end. The heat required for evaporation of the water is provided by heat exchange with hot effluent from a catalytic partial oxidation reaction zone.

The evaporator described in WO 01/79112 has a specific shape and its use is limited to a specific fuel processor design.

There is a need in the art for a compact evaporator that can achieve complete evaporation of water, also if it is added at a low pressure difference and/or to a low turbulence hot gas stream. It has now been found this can be achieved by an evaporator that contains gas flow paths at least partly lined with water absorbing material.

Accordingly, the present invention relates to an evaporator for the evaporation of water in a hot gas stream, comprising an inlet end, an outlet end, gas flow paths extending from the inlet end to the outlet end and a high-temperature resistant water absorbing material that at least partly defines the gas flow paths, wherein the water absorbing material has a water absorbing capacity of at least 0.20 g per cubic centimetre.

The evaporator according to the invention contains gas flow paths similar to that in a static mixer which are at least partly lined with a water absorbing material in order to create a water hold-up. Thus, the residence time of the water is increased compared to an evaporator with gas flow paths that are not lined with water absorbing material.

The evaporator according to the invention may comprise more than one elements placed in series, each element comprising an inlet end, an outlet end, gas flow paths and a water absorbing material as herein above defined. For compactness reasons, it is preferred that the different elements are stacked on each other without a gap between them.

The evaporator may comprise one or more elements composed of an alternating stack of corrugated metal sheets and sheets of the water absorbing material. The corrugated metal sheets are stacked in the same way as in cross-flow structures, i.e. such that the flow channels formed by the "wave loops" of adjacent sheets enclose an angle in the range of 0 to 90° with respect to each other, preferably in the range of 40 to 90°. With respect to the longitudinal axis of the reactor wherein the evaporator is placed, the flow channels extend at an angle between 0 and 90°, preferably between 20 and 50°.

It is preferred that the evaporator comprises more than one of such cross-flow structure elements in series, wherein adjacent elements are rotated along their longitudinal axis with respect to each other in order to increase the radial dispersion of the gas/water mixture. Preferably, the angle of rotation is about 90°.

Alternatively, the evaporator may comprise one or more elements composed of a wound corrugated metal sheet and water absorbing sheet.

The evaporator may also be composed of the water absorbing material, such that the water absorbing material completely defines the gas flow paths. An example of such an evaporator is a honeycomb structure of a porous ceramic material, wherein the parallel gas flow paths are defined by the porous ceramic material which serves as the water absorbing material.

The evaporator according to the present invention may further comprise a static mixer element without water absorbing material, preferably downstream of the water absorbing material containing element (s).

Preferably, the evaporator has a length-to-diameter ratio of at most 2.0, more preferably in the range of from 0.5 to 1.5. Reference herein to diameter is to the equivalent diameter in case of an evaporator that does not have a round circular cross-section.

In order to be able to use the evaporator in a low gas velocity system wherein the pressure drop over the evaporator should be minimised, the total cross-sectional area of the gas flow paths is, at any point along the length of the evaporator, preferably at least 50% of the cross-sectional area of the evaporator, more preferably at least 70%. Reference herein to the total cross- sectional area of the gas flow paths is to the open cross-sectional area, i.e. the cross-sectional area not occupied by the metal sheets and the water absorbing material.

The average cross-sectional diameter of the gas flow paths is preferably at least 1 mm, more preferably in the range of from 2 to 6 mm. Reference herein to cross- sectional diameter is to the equivalent diameter of a flow path.

In order to create sufficient water hold-up in the evaporator according to the invention, the water absorbing capacity of the water absorbing material is at least 0.20 g water per cubic centimetre water absorbing material. Preferably, the water absorbing material has a water absorbing capacity of at least 0.30 g per cubic centimetre, more preferably at least 0.50 g per cubic centimetre. A suitable method for determining the water absorbing capacity or water holding capacity is according to ASTM D4250. Reference herein to the volume of the water absorbing material is to the volume of the water adsorbing material conditioned according to ASTM D685.

Preferably, the volume of the water absorbing material is in the range of from 10 to 50 % of the total volume of the evaporator, preferably of from 15 to 30 %.

In order to facilitate evaporation of the water absorbed, it is preferred that the water absorbing material is in such a form that it has a high surface area. Therefore, the water absorbing material is preferably in the form of one or more sheets. Sheets of fibrous materials, such as sheets of non-woven material or woven sheets are particularly suitable.

Preferably, the amount of water absorbing material and the form of the water absorbing material is such that the free surface area of the water absorbing material is at least 100 m^ per mø of evaporator volume, more preferably the free surface area is in the range of from 200 to 500 m^ per m^ of evaporator volume. Reference herein to free surface area is to the available surface area, i.e. to surface area that is in open communication with a gas flow path. Thus, if both sides of the water absorbing sheet are in open communication with a gas flow path, then the surface area of both sides has to be taken into accoun .

Suitable high temperature resistant water absorbing materials are resistant to temperatures up to 1000 °C, preferable up to 1200 °C, more preferably up to 1400 °C. Examples of suitable high-temperature resistant water absorbing materials are ceramic materials, such as refractory oxides or quartz, or metals such as Fe, Cr and Al containing alloys. The invention further relates to a process for the evaporation of water, wherein a stream of hot gas and water are supplied to the inlet end of the evaporator as hereinbefore defined and a cooled steam-containing gas stream is exiting the outlet end of the evaporator.

Water is preferably added to the hot gas stream at a low pressure, more preferably at a pressure that is at most 3 bar higher than the operating pressure at the inlet end of the evaporator. A quench tube, i.e. a tube with holes from which water is dripping, can be suitably used to add water to the hot gas stream at such low pressure. The shape of the tube and the number of holes is preferably such that the water is evenly distributed over the cross-sectional area of the inlet end of the evaporator. In order to prevent coalescence of water drops from adjacent holes, the holes may be provided with vertical thread-like structures.

The evaporator according to the invention is particularly suitable for a process wherein the a linear velocity of the hot gas stream is low, typically below 15 m/s. Reference herein to the linear gas velocity is to the linear gas velocity at operating conditions.

The evaporator according to the invention is particularly suitable to be incorporated in a fuel processor. A fuel processor typically comprises in series a catalytic zone for the partial oxidation or autothermal reforming of the hydrocarbonaceous feed, a high temperature water-gas shift conversion zone (HTS) , a low temperature water-gas shift conversion zone (LTS) , and a zone for the catalytic selective oxidation of the remaining carbon monoxide. A fuel processor may contain a single water-gas shift conversion zone and the selective oxidation zone may be omitted. In a fuel processor, the evaporator is preferably placed between the catalytic zone for partial oxidation or autothermal reforming and the water-gas shift conversion zone. Under normal operation of such a fuel processor, hot effluent of the partial oxidation/autothermal reforming zone, typically having a temperature in the range of from 600 to 1100 °C is cooled to a temperature in the range of from 200 to 450 °C. Thus, the stream of hot gas preferably has a temperature in the range of from 600 to 1100 °C, more preferably of from 700 to 900 °C and the cooled steam-containing gas stream has preferably a temperature in the range of from 200 to 450 °C, more preferably of from 250 to 400 °C. In order to achieve this temperature reduction, the weight ratio of hot gas stream to water is preferably in the range of from 2.0 to 5.0, more preferably of from 3.0 to 4.5.

Alternatively, the evaporator according to the invention may be placed between the HTS and LTS or between the LTS and selective oxidation zone. It will be appreciated that the temperature of the hot gas stream will then be lower and that the weight ratio of hot gas stream to water will then be higher.

Accordingly, the invention further relates to a fuel processor comprising a first catalytic reaction zone for the partial oxidation or the autothermal reforming of a hydrocarbonaceous fuel, an evaporator as hereinbefore defined and a second catalytic reaction zone for water- gas shift conversion.

In a still further aspect, the invention relates to a process for the production of hydrogen from a hydrocarbonaceous fuel using the fuel processor according to the invention, wherein: a) the hydrocarbonaceous fuel is converted into a hot gas mixture comprising hydrogen and carbon monoxide by reacting it with an oxygen-containing gas in the first catalytic reaction zone; b) water is added to the hot gas mixture downstream of the first catalytic reaction zone and upstream of the evaporator; c) water is evaporated and the hot gas mixture cooled in the evaporator resulting in a steam-comprising gas mixture; and d) the steam-comprising gas mixture is converted into a gas mixture comprising carbon dioxide and hydrogen in the second reaction zone.

In a final aspect, the invention relates to a fuel cell system comprising the fuel processor according to the invention and a fuel cell.

The evaporator, the process and the fuel processor according to the invention will now be further illustrated by means of schematic Figures 1 to 3.

Figure 1 shows a top view of part of an evaporator composed of an alternating stack of corrugated metal and water absorbing sheets.

Figure 2 shows a top view of part of an evaporator composed of a wound corrugated metal and water absorbing sheet.

Figure 3 shows a fuel processor comprising the evaporator according to the invention between the catalytic partial oxidation reaction zone and the HTS reaction zone.

In Figure 1 is shown part of an evaporator or evaporator element that is composed of corrugated metal sheets 1 and sheets 2 of water absorbing material. Sheets 1 and sheets 2 are alternating each other, thus forming gas flow paths 3 that are partly defined by the water absorbing sheets 2.

In Figure 2 is shown a top view of part of an evaporator that is composed of a sheet 1 of corrugated metal and a sheet 2 of water absorbing material which are wound around each other. Gas flow paths 3 are partly defined by the water absorbing sheets 2.

In Figure 3 is shown a fuel processor 4 comprising in series a reaction zone 5 for the catalytic partial oxidation (CPO) of a hydrocarbonaceous fuel, an evaporator 6, a high temperature water gas shift (HTS) reaction zone 7, a low temperature water gas shift (LTS) reaction zone 8, and a zone 9 for the selective oxidation of the remaining carbon monoxide. Hydrocarbonaceous fuel and air are fed to CPO reaction zone 5 via lines 10 and 11, respectively. The effluent of the CPO reaction zone 5 is led via line 12 to evaporator 6. Water is added to the effluent in line 12, just upstream of evaporator 6, via water supply line 13. A mixture of cooled effluent and steam is leaving evaporator 6 and led to HTS reaction zone 7 via line 14. HTS effluent is led via line 15 to LTS reaction zone 8 and LTS effluent is led via line 16 to selective oxidation zone 9. Air is added to zone 9 via air supply line 17. A hydrogen-rich gas stream is leaving fuel processor 4 via line 18 and may be fed to a fuel cell (not shown) .

The invention will be further illustrated by means of the following non-limiting examples. EXAMPLES

EXAMPLE 1 (comparative) Evaporator

An evaporator was constructed composed of three cylindrical cross-flow structure elements in series, stacked on each other. Each element had a length of 70 mm and a diameter of 220 mm. Adjacent elements were rotated 90° along their longitudinal axis with respect to one another. Each element was composed of a stack of corrugated Fecralloy® sheets having a corrugation depth of 4 mm, wherein the wave loops of adjacent sheets enclose an angle of 90° with respect to each other. Evaporation process

The above-described evaporator was placed in a fuel processor as shown in Figure 3, between the CPO reaction zone and the HTS reaction zone. A flow of 119 kg/h of CPO effluent having a temperature of 800 °C and comprising 26 vol% H2, 45 vol% N2, 14 vol% CO and 5 vol% CO2 was supplied to the evaporator. Water was added to the hot gas stream by means of a oval drip tube having 60 holes in such amount that the gas-to-water weight ratio was 3.3.

The temperature of the evaporator effluent was determined at different locations across the cross- sectional area of the evaporator outlet. The temperature of the evaporator effluent appeared to drop locally to temperatures below 100°C at certain moments in time. This shows that the water added to the CPO effluent was not completely evaporated. Temperature deviations over the cross-sectional area of the effluent outlet were in the range of from 90-190 °C, and raised to above 350 °C during the periods of incomplete evaporation. EXAMPLE 2 (invention)

Evaporator

An evaporator was constructed composed of three cylindrical elements in series, stacked on each other. Adjacent elements were rotated 90° along their longitudinal axis with respect to one another. Each element had a length of 70 mm and a diameter of 220 mm. The first and the second element were each composed of alternating sheets of quartz paper and corrugated Fecralloy®, wherein the wave loops of adjacent metal sheets enclosed an angle of 90° with respect to each other.

The corrugated metal sheets had a depth of corrugation of 4 mm. The quartz paper had a water absorbing capacity of approximately 1 g/cτr . The third and most downstream element was a static mixer element, composed of an alternating stack of the same corrugated metal sheets as used in the first two elements, but without the quartz paper sheets.

The resulting evaporator contained 2 m^ of free quartz paper surface and the total volume of quartz paper was 0.5 L. Evaporation process

The above-described evaporator was placed in a fuel processor as described in Example 1 and an evaporation process as described in Example 1 was carried out.

The temperature of the evaporator effluent was determined at different locations across the cross- sectional area of the evaporator outlet. Temperature variation as a function of runtime and temperature deviations over the cross-sectional area of the evaporator outlet appeared to be very small. The local effluent temperature was in the range of from 340 to 380 °C over the whole runtime. Thus, the water added was completely evaporated. Temperature deviations over the cross-sectional area of the effluent outlet were at most 40 °C.

Claims

C L I M S

1. Evaporator for the evaporation of water^' in a hot gas stream, comprising an inlet end, an outlet end, gas flow paths extending from the inlet end to the outlet end and a high-temperature resistant water absorbing material that at least partly defines the gas flow paths, wherein the water absorbing material has a water absorbing capacity of at least 0.20 g per cubic centimetre.

2. Evaporator according to claim 1, wherein the gas flow paths are at least partly formed by corrugated metal sheets.

3. Evaporator according to claim 2, comprising one or more elements composed of an alternating stack of corrugated metal sheets and sheets of the water absorbing material .

4. Evaporator according to any one of the preceding claims, wherein the water absorbing material is in the form of one or more sheets, preferably sheets of fibrous material .

5. Evaporator according to claim 1 comprising at least one honeycomb of porous ceramic material, wherein the porous ceramic material is the water absorbing material and the gas flow paths are defined by the porous ceramic material.

6. Evaporator according to any one of the preceding claims, having a length-to-diameter ratio of at most 2, preferably in the range of from 0.5 to 1.5.

7. Evaporator according to any one of the preceding claims, wherein the total cross-sectional area of the gas flow paths is at least 50% of the cross-sectional area of the evaporator, preferably at least 70%.

8. Evaporator according to any one of the preceding claims, wherein the water absorbing material has a water absorbing capacity of at least 0.30 g per cubic centimetre, preferably at least 0.50 g per cubic centimetre.

9. Evaporator according to any one of the preceding claims, wherein the volume of the water absorbing material is in the range of from 10 to 50 % of the total volume of the evaporator, preferably of from 15 to 30 %.

10. Evaporator according to any one of the preceding claims, wherein the free surface area of the water absorbing material is at least 100 m.2 per ιt.3 of evaporator volume, preferably in the range of from 200 to

500 mø per m^ of evaporator.

11. A process for the evaporation of water wherein a stream of hot gas and water are supplied to the inlet end of the evaporator according to any one of the preceding claims and a cooled steam-containing gas stream is exiting the outlet end of the evaporator.

12. A process according to claim 11, wherein the water is added to the stream of hot gas by means of a quench ring.

13. A process according to claim 11 or 12, wherein the stream of hot gas has a temperature in the range of from 600 to 1100 °C, preferably of from 700 to 900 °C and the cooled steam-containing gas stream has a temperature in the range of from 200 to 450 °C, preferably of from 250 to 400 °C.

14. A process according to any one of claims 11 to 13, wherein the weight ratio of hot gas stream to water is in the range of from 2.0 to 5.0, preferably of from 3.0 to 4.5.

15. Fuel processor comprising in series a first catalytic reaction zone for the partial oxidation or the autothermal reforming of a hydrocarbonaceous fuel, an evaporator according to any one of claims 1 to 10, and a second catalytic reaction zone for water-gas shift conversion.

16. A process for the production of hydrogen from a hydrocarbonaceous fuel using the fuel processor according to claim 15, wherein: a) the hydrocarbonaceous fuel is converted into a hot gas mixture comprising hydrogen and carbon monoxide by reacting it with an oxygen-containing gas in the first catalytic reaction zone; b) water is added to the hot gas mixture downstream of the first catalytic reaction zone and upstream of the evaporator; c) water is evaporated and the hot gas mixture cooled in the evaporator resulting in a steam-comprising gas mixture; and d) the steam-comprising gas mixture is converted into a gas mixture comprising carbon dioxide and hydrogen in the second reaction zone.

17. A fuel cell system comprising the fuel processor according to claim 16 and a fuel cell.