EP2027061A1

EP2027061A1 - Method for regenerating a reformer

Info

Publication number: EP2027061A1
Application number: EP06742411A
Authority: EP
Inventors: Stefan Käding; Stefan Kah; Andreas Lindermeir; Marco Mühlner
Original assignee: Enerday GmbH
Current assignee: Enerday GmbH
Priority date: 2006-06-12
Filing date: 2006-06-12
Publication date: 2009-02-25
Also published as: AU2006344607A1; CN101479187A; CA2653415A1; BRPI0621741A2; JP2009539749A; US20100112392A1; DE112006003993A5; WO2007143960A1; EA200870481A1

Abstract

The invention relates to a method for regenerating a reformer to which, in continuous reformer operation, a mixture of fuel (12, 14) and oxidant (16, 18, 20) is fed, with an average air ratio ?1, wherein the air ratio is changed for the purpose of regeneration of the reformer. According to the invention, it is provided that the regeneration takes place in a phase where the reformer is switched off, and that the reformer is operated over several consecutive time intervals, with an increased air ratio ?2>?1 compared to the reformer operation. According to the invention, it can also be provided that the regeneration takes place in a start phase of the reformer, and that the reformer is continuously operated with an increased air ratio ?2>?1 compared to the reformer operation, until a critical temperature threshold has been reached. The invention also relates to a system with a reformer and a control for carrying out a method according to the invention.

Description

Process for regenerating a reformer

The invention relates to a method for regenerating a reformer, the continuous reformer operation, a mixture of fuel and oxidant is supplied with an average air ratio λi, wherein for the purpose of regeneration of the reformer, the air ratio is changed.

The invention further relates to a system with a reformer and a controller.

Generic methods have numerous fields of application. In particular, they serve to supply a hydrogen-rich gas mixture to a fuel cell, from which then on the basis of electrochemical processes electrical

Energy can be generated. Such fuel cells are used, for example, in the automotive sector as additional energy sources, so-called APUs ("auxiliary power unit").

The reforming process for converting fuel and oxidant to reformate can be done according to different principles. For example, catalytic reforming is known in which part of the fuel is oxidized in an exothermic reaction. A disadvantage of this catalytic reforming is the high heat generation, the system components, in particular the catalyst can irreversibly damage. Another possibility for generating a reformate from hydrocarbons is the "steam reforming". In this case, hydrocarbons are converted by means of water vapor in an endothermic reaction to hydrogen.

A combination of these two principles, that is, the reforming based on an exothermic reaction and the generation of hydrogen by an endothermic reaction in which the energy for steam reforming is derived from the combustion of the hydrocarbons, is referred to as autothermal reforming. However, there are the additional disadvantages that a supply of water must be provided. High temperature gradients between the oxidation zone and the reforming zone pose further problems in the temperature regime of the entire system.

In general, the reaction in which air and fuel are converted into a hydrogen-rich gas mixture in a reformer can be formulated as follows:

C _n H ₁ m ₁₁ + - ₂ O ₂ 2 → - ₂ H ₂ 2 + nCO

However, by imperfect reaction of hydrocarbons in this endothermic reaction, by-products such as residual hydrocarbons or soot may form, other than as described in the equation. These then at least partly settle on the reformer. This results in deactivation of the catalyst in the reformer, which can go so far that the catalyst is almost completely mixed with carbon black. The pressure loss occurring in the reformer thereby increases. The reformer becomes useless, or it must be regenerated.

According to the prior art, such regeneration is carried out in particular by the burning off of the soot deposited in the reformer. In this case, high temperatures can arise, which lead to a permanent, that is in particular irreversible damage to the catalyst or the carrier material. In addition, large temperature gradients at the start of soot burn-up make it difficult to control the reformer. Since oxygen can occur at the outlet of the reformer in the event of excess oxygen during the combustion process, it is not possible to use a reformer to be regenerated in this way in an SO fuel cell system.

DE 101 52 083 A1 describes a reformer to which fuel, steam and oxygen are supplied. As a solution for avoiding overheating, it is proposed in DE 101 52 083 A1 to carry out the regeneration in a pulsed manner by increasing the air ratio of the supplied mixture for limited time intervals. An influence on the reforming operation is inevitable, so that, for example, the fuel cell system removable e- lectric power is reduced.

The invention has for its object to enable the regeneration of a reformer while avoiding influencing the reforming operation.

This object is achieved with the features of the independent claims. Advantageous embodiments of the invention are indicated in the dependent claims.

According to a first aspect of the invention, the invention is based on the method according to the invention in that the regeneration is carried out in a shutdown phase of the reformer by operating the reformer during several successive time intervals with an air ratio λ ₂ > λi which is increased compared to the reformer operation. In normal reformer operation, fuel and air are continuously fed to the reformer. Temperatures in the range above and above 650 ^° C. prevail. The reformer operates in thermal equilibrium, so that no increase in temperature is to be expected in steady-state operation. However, the described deposits in the catalyst gradually lead to a deactivation. Particularly in the case of mobile applications, for example in passenger cars or commercial vehicles, a fuel cell system and thus also the reformer are switched off regularly, at least during a longer standstill of the vehicle. Since no electrical energy is to be generated during the switch-off phase and an influence on the reformer operation with respect to energy generation is therefore irrelevant, the switch-off phase can be used advantageously for regeneration. It should be noted, however, that even during the shutdown phase with long-term increase in the air ratio, be it by reducing the amount of fuel supplied, by increasing the amount of air supplied or by both, excessive heating is expected, resulting in destruction of the catalyst or of the complete reformer. This is related to the fact that the Rußabbrandreaktion C + O ₂ -> CO ₂

exothermic. Likewise, after complete burning off of the catalyst, an oxygen discharge occurs at the end of the reformer, which would result in the destruction of the anode of an SO fuel cell. According to the method of the invention, it is now proposed that the fuel supply be reduced in a pulsed manner during the switch-off phase, wherein the individual pulses last only over a short period of time. Oxygen or air is brought to the soot deposit, so that the oxidation process can begin. Consequently, the temperature in the catalyst also increases. However, before the temperature is so high that the reformer can be damaged, the fuel supply is increased again. Thus, at the end of a time interval with a reduced feed rate, a part of the reformer is regenerated, that is, substantially soot-free or deposit-free. After reducing the air ratio of the reformer cools back to normal temperatures. This procedure may result in partial regeneration of the reformer or may be repeated until the complete reformer is regenerated. The regeneration takes place zone by zone. By pulsed reduction of the fuel can be ensured that no oxygen reaches the fuel cell anode, which can be problematic at fuel cell temperatures above 500 ⁰ C, since the anode material can be oxidized in the presence of oxygen from Ni to NiO, thereby destroying the anode material and the electrochemical reaction on the anode is inhibited.

The invention is advantageously developed in that the feed rate of the fuel during at least one of the successive time intervals is zero. wearing. Due to the complete shutdown of the fuel supply during the successive time intervals, an efficient burning of the deposits can take place. Not complete shutdown of the fuel supply leads to an increased water production in the reformer. This water is able to remove the soot and other deposits from the reformer according to the equation

C + H ₂ O → CO + H ₂

to remove.

It may also be useful to measure the oxygen content of the substances exiting the reformer, and that when a threshold is exceeded by the oxygen content, the reformer goes into continuous operation. The oxygen content at the outlet of the reformer thus serves as an indicator for the complete regeneration of the reformer. By proving the oxygen content, it can furthermore be ensured that no excessive amounts of oxygen strike the anode of an SO fuel cell.

In this context, it is useful that the oxygen content is measured by a lambda probe.

It can also be provided that the oxygen content is measured by a fuel cell. If you want to save the installation of a lambda probe, the electrical output values of the fuel cell can be used directly to detect an increase in the oxygen content. Other measurement methods for determining the lambda value can also be used, for example infrared or CO measurements. The method according to the invention is particularly useful in the context that, in a reformer with two fuel feeds, one of the fuel feeds operates during regeneration at a feed rate substantially equal to the feed rate in continuous operation. In a reformer with two fuel feeds, one thus has a greater possibility of variation with regard to a change in the fuel feed rate. This concerns in particular the possibility of a partially unchanged operation of the reformer, while in other areas of the reformer by functional changes a regeneration takes place, if this is desired during the reformer operation, ie outside the shutdown phase.

The process according to the invention is usefully developed in this connection by the reformer having an oxidation zone and a reforming zone that heat can be supplied to the reforming zone, that the oxidation zone is supplied with a mixture of fuel and oxidant using a first fuel feed, which after at least Partial oxidation of the fuel is at least partially fed to the reforming zone, that the reforming zone additionally fuel is fed using a second fuel supply and that the second fuel supply operates during the successive time intervals with a reduced feed rate. The additionally supplied fuel thus forms, together with the exhaust gas from the oxidation zone, the starting gas mixture for the reforming process. By mixing the fuel with the exhaust gas, a small λ value is provided (for example, λ = 0.4) and can be supplied with heat an endothermic reforming reaction take place. With regard to a regeneration during the reformer operation, ie outside the shutdown phase, it should be noted that the operation in the oxidation zone of the reformer can continue unchanged, while only the second fuel supply is switched off or reduced.

It is particularly useful that heat can be supplied to the reforming zone from the exothermic oxidation in the oxidation zone. The heat energy generated in the oxidation zone is thus converted in the context of the reforming reaction, so that the net heat production of the overall process does not lead to problems in the temperature budget of the reformer.

Usefully, it is provided that the reforming zone has an oxidant feed, via which additionally oxidizing agent can be fed. In this way, another parameter for influencing the reforming is available, so that it can be optimized.

The invention is developed in a particularly useful way in that the additional fuel can be fed to an injection and mixture-forming zone and that the additional fuel can flow from the injection and mixture-forming zone into the reforming zone. This injection and mixture-forming zone is thus upstream in the flow direction of the reforming zone, so that the reforming zone is provided with a well-mixed starting gas for the reforming reaction.

In this context, it is particularly useful that the additional fuel is at least partly due to the thermal energy of the gas mixture emerging from the oxidation zone. - S -

is evaporated by evaporation. Thus, the heat of reaction from the oxidation can also be used advantageously for the evaporation process of the fuel.

Furthermore, it may be useful for the gas mixture produced in the oxidation zone to be fed to the reforming zone, bypassing the injection and mixture-forming zone. As a result, a further possibility for influencing the reforming process is available so that a further improvement of the reformate leaving the reformer can be achieved with regard to its application.

It can be provided that the regeneration takes place during each shutdown phase of the reformer. Thus, an optimally prepared system is available for the next reformer startup.

According to a second aspect, the invention is based on the method according to the invention in that the regeneration takes place in a starting phase of the reformer in that the reformer with an air ratio λ ₂ > λ _! as long as it is operated continuously until a critical temperature threshold is reached. During the starting phase, especially at the beginning of the starting phase, the temperatures occurring in the reformer are not critical. It is therefore not necessary to choose a pulsed reformer operation for the purpose of regeneration. Rather, regeneration of the reformer can be carried out continuously via the increased air ratio.

In particular, it is useful that the reformer is operated in the starting phase with an air ratio λ≥l. The Re- shaper therefore ultimately works like a burner, with air ratios of λ> 1 being uncritical at comparatively low temperatures of a downstream fuel cell system.

For example, it can be provided that the critical temperature threshold is defined by the fact that the reformer or components of the reformer have temperatures between 450 and 650 ° C.

It is likewise conceivable that the critical temperature threshold is defined by the fact that a fuel cell stack or components of the fuel cell stack downstream of the reformer have temperatures between 450 and 550 ^° C. If you end the regeneration during the start-up phase, for example, at a temperature of the fuel cell stack of 500 ⁰ C, it is avoided that in a further increase in temperature in the fuel cell stack of entering the fuel cell stack excess oxygen leads to damage to the anode side.

The invention is developed in a particularly advantageous manner by virtue of the fact that regeneration following the starting phase of the reformer takes place in that the reformer is operated for several successive time intervals with an increased air ratio compared to the reformer operation. Pulsed operation is useful after the startup phase to avoid overheating.

Usefully, it is provided that the regeneration takes place during each start-up phase of the reformer. Since the operation of the reformer in the manner of a burner can serve both the preheating of the system and the regeneration, can at every system start the advantageous regeneration are performed.

The invention further relates to a system with a reformer and a controller which enables a regeneration of the reformer, wherein the controller is suitable for controlling a method according to the invention.

The invention will now be described by way of example with reference to the accompanying drawings with reference to preferred embodiments.

Showing:

FIG. 1 shows a flow chart for explaining a method according to the invention;

FIG. 2 is a flowchart for explaining a regeneration during the reforming operation; and

Figure 3 is a schematic representation of a reformer according to the invention.

FIG. 1 shows a flow chart for explaining a method according to the invention. After the start of the reformer in step SO1, the reformer is operated with an air ratio λ≥l. This corresponds to a burner operation. The burner operation is used for regeneration, in particular carbon, carbon compounds, sulfur and sulfur compounds are removed from the reformer. Regeneration also affects other organic and inorganic compounds that are deposited in the reformer. In step S03 it is checked whether a temperature T is already an N critical value T _{κ has} exceeded. This critical value can be determined by the reformer himself, for example, the temperature upper limit permissible for the catalyst in the reforming zone, or else determined by the fuel cell stack downstream of the reformer. The latter should not be exposed to oxygen, especially at temperatures above 500 ^° C., so that a strong superstoichiometric oxygen introduction into the reformer above such a critical temperature should be avoided. If the critical temperature has not yet been reached, the reformer will continue to operate as a burner. However, if the critical temperature is exceeded, the reformer enters the normal reforming operation in step S04. If appropriate, pulsed operation, which is described in connection with FIG. 3, can take place for further regeneration. If the fuel cell system is switched off in step S05, the associated shutdown phase of the reformer can be used for further pulsed-mode regeneration according to step S06. Subsequently, the operation of the reformer is ended (step S07).

FIG. 2 shows a flowchart for explaining a regeneration during the reforming operation. After starting the regeneration of the reformer in step SO1, the fuel supply is turned off in step S02. Subsequently, in step S03, a temperature in the reformer is detected. In step S04, it is determined whether this detected temperature is greater than a predetermined threshold T _S χ. If this is not the case, the temperature in the reformer is again detected in step S03 when the fuel supply is switched off. If it is determined in step S04 that the temperature exceeds the threshold value T _s i, is in Step S05, the fuel supply is turned on again. Subsequently, the temperature in the reformer is detected again in step S06. In step S07, it is determined whether this detected temperature is smaller than a predetermined threshold T ₃₂ . If this is not the case, the temperature in the reformer is detected again in step S06; the fuel supply remains switched on. If it is determined in step S07 that the temperature is lower than the threshold temperature Ts _2r , the fuel supply is turned off again according to step S02, so that the next time interval to the reformer generation begins.

In parallel to the temperature monitoring, there is a monitoring for oxygen breakdown in the reformer according to step S08. This is to determine the end of the regeneration. Thus, if an oxygen breakthrough takes place, if the fuel supply is switched off, the fuel supply is turned on in accordance with step S09. Subsequently, the regeneration ends according to step S10.

FIG. 3 shows a schematic representation of a reformer according to the invention. The invention is not bound to the specific design of the reformer shown here. Rather, the regeneration according to the invention can take place in different types of reformers, as long as it is possible to reduce or interrupt the supply of fuel in the short term. The reformer 10 shown here, which is based on the principle of partial oxidation, preferably without supplying water vapor, fuel 12 and oxidizing agent 16 can be fed via respective feeders. As a fuel 12, for example diesel comes into question, the oxidizing agent 16 is usually air. The immediate at the beginning Combustion resulting heat of reaction can be partially removed in an optionally provided cooling zone 36. The mixture then continues into the oxidation zone 24, which may be realized as a pipe located within the reforming zone 26. In alternative embodiments, the oxidation zone is realized by a plurality of tubes or by a special tube guide within the reforming zone 26. In the oxidation zone, conversion of fuel and oxidant takes place in an exothermic reaction with λ »1. The resulting gas mixture 32 then enters an injection and mixture forming zone 30 in which it is mixed with injected fuel 14. The thermal energy of the gas mixture 32 can support the evaporation of the fuel 14. In addition, provision can be made for oxidizing agent to be fed into the injection and mixture-forming zone 30. The mixture thus formed then passes into the reforming zone 26, where it is reacted in an endothermic reaction with, for example, λ << 0.4. The heat 28 required for the endothermic reaction is removed from the oxidation zone 24. In order to optimize the reforming process, oxidizing agent 18 can additionally be fed into the reforming zone 26. Furthermore, it is possible to supply part of the gas mixture 34 generated in the oxidation zone 24 directly to the reforming zone 26, bypassing the injection and mixture-forming zone 30. The reformate 22 then flows out of the reforming zone 26 and is available for other applications.

Associated with the reformer is a controller 38 which can control, among other things, both the primary 12 and secondary fuel feeds 14. In order to regenerate the reforming zone 26 in the exemplary embodiment illustrated in FIG. 3, it may be sufficient to pulse-turn off the fuel feed 14 while the fuel feed 12 is operated at the same rate in order to maintain the oxidation in the reformer. The catalyst provided in the reforming zone 26 is then burned with combustion exhaust gases containing oxygen.

The features of the invention disclosed in the foregoing description, in the drawings and in the claims may be essential to the realization of the invention both individually and in any combination.

LIST OF REFERENCE NUMBERS

12 fuel

14 fuel 16 oxidizer

18 oxidizing agents

20 oxidizing agents

22 Reformat

24 oxidation zone 26 reforming zone

28 heat

30 injection and mixture formation zone

34 gas mixture

36 cooling zone 38 control

Claims

A process for regenerating a reformer to which a mixture of fuel (12, 14) and oxidizer (16, 18, 20) having an average air ratio λi is fed in continuous reformer operation, the air ratio being changed for the purpose of regenerating the reformer, characterized in that the regeneration in a shutdown phase of the reformer takes place in that the reformer is operated during several successive time intervals with an over the reformer operation increased air ratio λ ₂ > λi.

2. The method according to claim 1, characterized in that the feed rate of the fuel (12, 14) during at least one of the successive time intervals is zero.

3. The method according to claim 1 or 2, characterized

that the oxygen content of the substances emerging from the reformer is measured, and

that when a threshold value is exceeded by the oxygen content of the reformer goes into continuous operation.

4. The method according to any one of the preceding claims, characterized in that the oxygen content is measured by a lambda probe.

5. The method according to any one of the preceding claims, characterized in that the oxygen content is measured by a fuel cell.

6. The method according to any one of the preceding claims, characterized in that in a reformer with two fuel feeds one of the fuel feeds during regeneration operates at a feed rate which substantially corresponds to the feed rate in continuous operation.

7. The method according to claim 6, characterized

in that the reformer has an oxidation zone (24) and a reforming zone (26),

that heat (28) can be supplied to the reforming zone (26),

in that the oxidation zone (24) is supplied with a mixture of fuel (12) and oxidizing agent (16, 18, 20) using a first fuel feed which, after at least partial oxidation of the fuel (12), can be fed at least partially to the reforming zone (26) is

in that the reforming zone (26) can additionally be supplied with fuel (14) using a second fuel feed, and the second fuel feed operates at reduced feed rate during the successive time intervals.

8. The method according to claim 7, characterized in that the reforming zone (26) heat (28) from the exothermic oxidation in the oxidation zone (24) can be fed.

9. The method according to claim 7 or 8, characterized marked, that the reforming zone (26) has an oxidant supply, via the additional oxidizing agent (16, 18, 20) can be fed.

10. The method according to any one of claims 7 to 9, characterized

that the additional fuel (14) of an injection and mixture-forming zone (30) can be supplied and

- That the additional fuel (14) from the injection and mixture forming zone (30) in the reforming zone (26) can flow.

11. The method according to any one of claims 7 to 10, characterized in that the additional fuel (14) by the thermal energy of the out of the oxidation zone (24) emerging gas mixture (34) is at least partially evaporated.

12. The method according to claim 10 or 11, characterized in that in the oxidation zone (24) generated gas mixture (34) partially bypassing the injection and Mixture forming zone (30) of the reforming zone (26) can be fed.

13. The method according to any one of the preceding claims, character- ized in that the regeneration during each

Shutdown phase of the reformer takes place.

14. A method for regenerating a reformer to which a mixture of fuel (12, 14) and oxidizing agent (16, 18, 20) with an average air ratio λi is supplied in continuous reformer operation, the air ratio being changed for the purpose of regenerating the reformer, in particular according to one of the preceding claims, characterized in that the regeneration takes place in a starting phase of the reformer characterized in that the reformer is continuously operated with a relation to the reformer operation increased air ratio λ ₂ > λi until a critical temperature threshold is reached.

15. The method according to claim 14, characterized in that the reformer is operated in the starting phase with an air ratio λ≥l.

16. The method according to claim 14 or 15, characterized in that the critical temperature threshold, is defined by the fact that the reformer or components of the reformer have temperatures between 450 and 650 ° C.

17. The method according to claim 14 to 16, characterized in that the critical temperature threshold, is defined in that a reformer downstream fuel cell stack or components of the fuel Substance cell stack temperatures between 450 and 550 ⁰ C have.

18. The method according to claim 14 or 17, characterized in that a regeneration following the starting phase of the reformer takes place in that the reformer is operated during several successive time intervals with respect to the reformer operation increased air ratio.

19. The method according to any one of the preceding claims, characterized in that the regeneration takes place during each starting phase of the reformer.

A system comprising a reformer and a controller (38) enabling regeneration of the reformer, the controller (38) being adapted to control a method according to any one of the preceding claims.