Method for operating a catalytic evaporator and use of such method

Abstract

A method for operating a catalytic vaporizer (1) is described, which involves feeding a fuel and an oxidant to the catalytic vaporizer, the method differing by the fact that (a) the feeding of the fuel is performed as a pulsed feed, and / or (b) the feeding of the oxidant is performed as a pulsed feed.

Description

Technical Field

[0001] The present invention relates to a method for operating a catalytic evaporator and the use of such method.

Background Art

[0002] It is known to use a catalytic evaporator to adjust the fuel characteristics of an internal combustion engine. WO2007 / 042246A2 describes a method for evaporating and reforming a liquid fuel, in which method, in a first reaction chamber, the fuel is evaporated and strongly oxidized quasi-stoichiometrically with the supply of air using a first catalyst, and in a second reaction chamber, the evaporated fuel is reformed by being mixed with the supplied air, and the ratio of the amount of air supplied in the first reaction chamber to the amount of air supplied in the second reaction chamber is set between 30:70 and 70:30.

[0003] DE102010012945B4 discloses a method for evaporating a liquid fuel and / or a combustible material, in which method, the liquid fuel and / or the combustible material is applied to an absorbent material, an oxygen-containing gas mixture or oxygen is introduced by an air supply, and the oxygen / fuel ratio is quasi-stoichiometric. To carry out this method, an apparatus is used which comprises a) an axially and radially air-permeable air supply part in the center, b) a catalyst system arranged concentrically around the air supply part over at least a part of the length of the air supply part, c) a buffer zone arranged concentrically around the catalyst system, and d) an absorbent material for fuel distribution arranged concentrically around the buffer zone, and at least one airtight sealing element is fitted between components a) to d).

[0004] DE102015120106A1 discloses a method for adjusting the ignition characteristics of a fuel using a unit having at least one distribution zone, at least one oxidation zone, and at least one conversion zone. In this method, the fuel is distributed in the distribution zone having a distribution structure, at least a part of the fuel is oxidized in the oxidation zone with at least one oxidant by at least one catalyst on a catalyst support, and at least a part of the distributed fuel and / or another supplied fuel is converted by heat and / or a catalyst in the conversion zone. The method is such that the ignition characteristics of the fuel are adjusted by the molar ratio of oxygen contained in the oxidant to the oxygen required for complete oxidation of the available fuel, and / or the pressure in the unit, and / or the residence time, and / or the temperature.

[0005] Generally, a catalyst evaporator known per se can be used as a pretreatment for uniformly mixing a fuel and an oxidant such as air, for example. At the same time, the fuel characteristics can be changed so that nitrogen oxides (NO X ) and soot emissions are reduced in the engine. The reaction products of the reforming reaction (hydrogen (H2) and carbon monoxide (CO)) are particularly effective in changing the fuel characteristics. The light-off temperatures of components such as hydrogen and carbon monoxide in a diesel oxidation catalyst are much lower than the light-off temperature of diesel, so when the engine is started at a low temperature, the exhaust system reaches the operating temperature more quickly.

[0006] Also, the evaporator can be used to simultaneously heat an exhaust gas aftertreatment system.

[0007] The change in fuel characteristics by the catalyst evaporation method can be achieved by increasing the operating pressure and increasing the air ratio. The increase in operating pressure is limited by supercharging the internal combustion engine. The increase in the air ratio results in an increase in the temperature in the catalyst, so it cannot be increased arbitrarily.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0009] Therefore, advancing from the prior art, the object of the present invention is to provide a method for operating a catalytic evaporator that does not have the drawbacks known from the prior art, and in particular, the fuel characteristics can be changed in a favorable manner with respect to the characteristics of the original fuel.

Means for Solving the Problems

[0010] According to the present invention, this object is achieved by a method for operating a catalytic evaporator according to claim 1 and the use of the method according to claims 10 to 13. Further advantageous developments of the present invention can be found in the dependent claims.

[0011] According to the present invention, there is provided a method for operating a catalytic evaporator, comprising the step of supplying fuel and an oxidant to the catalytic evaporator (1), (a) the fuel is supplied as a pulsed addition, and / or, (b) the oxidant is supplied as a pulsed addition, a method is proposed.

[0012] In step (a), a corresponding supply of the oxidant is brought about, and in step (b), the corresponding supply of the fuel may be continuous, specifically, these additions are not designed as pulsed additions.

[0013] Therefore, in the method according to the present invention, either or both of the fuel and the oxidant are added together in the form of pulses which are limited portions in time. The pulses can represent a continuous series of regular repetitions of the same kind of addition. As used herein, pulse addition differs from continuous addition in that pulse addition includes an interruption time without addition. The pulses for fuel addition and / or the pulses for oxidant addition can be of equal length or of different lengths.

[0014] In some embodiments, the pulsed addition (a) of fuel adds a first amount of fuel during a first period and / or a second amount of fuel during a second period and / or does not add fuel during a third period.

[0015] In some embodiments, the addition is (i) adding a first amount of fuel during a first period, not adding fuel during a third period, and having no requirement for the second period, or (ii) adding a first amount of fuel during a first period, adding a second amount of fuel during a second period, and not adding fuel during a third period, or (iii) adding a first amount of fuel during a first period, adding a second amount of fuel during a second period, and having no requirement for the third period and can be carried out by.

[0016] The terms "first", "second", and "third" are not meant to imply an order of addition but are used only to distinguish the additions. The terms "first amount" and "second amount" imply that these amounts are different from each other.

[0017] In some embodiments, with respect to the fuel supply, the above-mentioned first period can be from about 10 ms to about 10 s, the above-mentioned second period can be from about 10 ms to about 10 s, and the above-mentioned third period can be from about 10 ms to about 10 s. In other embodiments of the present invention, the first and / or second and / or third periods can be selected from between about 1 second and about 5 seconds.

[0018] The pulse can be adjusted according to the respective specific requirements regarding the operation of the catalytic evaporator, using parameters such as, for example, the amount of fuel in the pulse, and / or the duration of the pulse, and / or the time between two pulses (corresponding to the frequency of the pulses per unit time). A person skilled in the art can determine by simple experiments how to adjust the fuel addition pulses to obtain specific requirements and optimal results regarding the operation of the evaporator.

[0019] Surprisingly, it has been found that by adding fuel to the catalytic evaporator in pulses, the air ratio can be increased without exceeding the maximum temperature of the catalyst. In this way, the pulsed addition of fuel helps to change the fuel properties compared to the originally used fuel. In particular, the pulsed addition of fuel changes the fuel properties in such a way that the proportion of hydrogen and / or carbon monoxide is considerably increased. At the same time, the pulsed operation mode enables a faster switching from maximum output to minimum output.

[0020] The catalytic evaporator that can be used in the method according to the invention can provide a homogeneous mixing of fuel and an oxidizing agent such as, for example, air as a pretreatment. The catalytic evaporator can be used in a manner known per se for heating during exhaust gas aftertreatment so as to be used in the method according to the invention. In the method according to the invention, the fuel properties can be changed in such a way that nitrogen oxides (NO X ) and soot emissions are reduced in the engine. According to the invention, a particularly favorable and effective change in the fuel properties towards an increase in the amount of the reaction products (hydrogen (H2) and carbon monoxide (CO)) of the reforming reaction is achieved. Furthermore, in the method according to the invention, the evaporator can also be advantageously used for the simultaneous heating of the exhaust gas aftertreatment system. Moreover, in the method according to the invention, the light-off temperature of components such as hydrogen and carbon monoxide in the diesel oxidation catalyst is much lower than the light-off temperature of the diesel, so that when the engine is started cold, the exhaust system reaches the operating temperature more quickly.

[0021] The method according to the present invention has considerable cost and output advantages for a gas burner that burns fuel oil, and for a self-igniting internal combustion engine or a diesel engine, both inside the engine and in the exhaust gas aftertreatment system. Further, the method according to the present invention has considerable cost and output advantages when used inside an internal combustion engine with spark ignition.

[0022] As described above, the fuel is added in the form of pulsed addition. When operating a prior art catalytic evaporator, both the fuel and the oxidant are continuously added in predetermined amounts, that is, the amounts of the oxidant and fuel added remain constant over time. In the method according to the present invention, it has proven particularly advantageous that a preset amount of fuel is added over a specific period of time, and that a period during which no fuel is added, that is, a period during which the fuel addition is set to a "zero" value, follows. The amount of fuel added is in the range of the amount of fuel added to a catalytic evaporator previously used in the prior art and known from the prior art.

[0023] In alternative (b) of the method according to the present invention, a first amount of oxidant can be added during the pulsed addition of the oxidant during the first period, and / or a second amount of oxidant can be added during the second period, and the oxidant does not have to be added during the third period.

[0024] In some embodiments, the addition is (i) in a manner where a first amount of oxidant is added during the first period, no oxidant is added during the third period, and there are no requirements for the second period, or (ii) in a manner where a first amount of oxidant is added during the first period, a second amount of oxidant is added during the second period, and no oxidant is added during the third period, or (iii) in a manner where a first amount of oxidant is added during the first period, a second amount of oxidant is added during the second period, and there are no requirements for the third period can be carried out.

[0025] The terms "first", "second", and "third" are used only to distinguish the additions and do not imply the order of addition. In this specification, the terms "first amount" and "second amount" imply that these amounts are different from each other.

[0026] In some embodiments, the above-mentioned first period can be from about 10 ms to about 10 s in alternative (b) considering the addition of the oxidant, the above-mentioned second period can be from about 10 ms to about 10 s, and a further period can be from about 10 ms to about 10 s. In other embodiments, the above-mentioned first period can be from about 1 s to about 5 s in alternative (b) considering the addition of the oxidant, the above-mentioned second period can be from about 1 s to about 5 s, and a further period can be from about 1 s to about 5 s.

[0027] The same advantages can be achieved with a pulsed addition of the oxidant as described above in connection with the pulsed addition of the fuel, and thus the above description in this regard is fully incorporated by reference.

[0028] Catalytic evaporators known per se from the prior art can be used in the method according to the invention. A person skilled in the art also knows how a catalytic evaporator can be operated in principle.

[0029] A particularly preferred catalytic evaporator, to which full reference is made with regard to the design details and the mode of operation, is described in DE102015120106A1. An apparatus for setting the ignition characteristics of at least one fuel is · at least one fuel inlet and at least one oxidant inlet, and · at least one distribution zone for distributing the fuel with at least one distribution structure for the fuel, · at least one oxidation zone for the oxidation of at least a part of the fuel, accommodating at least one catalyst support with at least one catalyst, · at least one conversion zone for the thermal conversion of at least a part of the catalyst and / or the fuel, · at least one outlet for the fuel having modified ignition characteristics and comprises The oxidizing agent inlet, the catalyst support, and the distribution zone are arranged and designed in such a way that heat generated in the oxidation zone can be transferred to a gas or gas mixture flowing into the distribution zone and / or the conversion zone.

[0030] In some embodiments, the catalytic evaporator used in the method according to the invention may have a catalyst, for example, which can be applied to a support. The support with the catalyst can be introduced into the reaction vessel in such a way that an intermediate space is formed between the inner surface of the reaction vessel and the surface of the catalyst.

[0031] The operating mode of the catalytic evaporator described above is described below by way of example. The formation of a good mixture of reactants is preferred for the stable and efficient operation of many chemical processes. Specifically, in an oxidation process such as combustion, for example, homogeneous mixing reduces emissions and prevents soot formation. For this purpose, liquid fuel can be converted into the gas phase. The advantages of mixing have been demonstrated for various uses (burners, particulate filters, reformers). The connection to an engine is particularly important. The aim is to adapt the evaporator for use inside an engine and to demonstrate a reduction in nitrogen oxides and soot emissions on an engine test stand.

[0032] When operating the catalytic evaporator, for example, liquid fuel is added inside the wall of the reactor of the catalytic evaporator, while air is added on the catalyst side. A small portion of the fuel oxidizes on the catalyst, and the heat generated is used to completely evaporate the fuel. The heat is mainly transferred by thermal radiation from the hot catalyst surface to the surface of the fuel film. The wall of the reactor into which the fuel is fed is always cooler than the fuel itself. Therefore, no deposits or adherents are formed.

[0033] Fuel is a chemical substance whose stored energy can be converted into energy usable by combustion. This example is fuel that is converted into motive power in an internal combustion engine. In some embodiments, the fuel can be selected from gasoline, diesel, bio-oil, pyrolysis oil, biodiesel, heavy oil, alcohol, Fischer-Tropsch fuel, dimethyl ether, diethyl ether, oxymethylene ether, ester, aldehyde, aromatic compound, amine, carboxylic acid, alkane, natural gas, camping gas, LPG, flare gas, landfill gas, biogas, and mixtures of at least two of these fuels. Specifically, liquid fuels can be used in the method according to the present invention. With these fuels, the aforementioned advantages are achieved in a particularly preferred manner.

[0034] In some embodiments, the oxidant can include oxygen, or specifically a medium containing oxygen such as air or exhaust gas with residual oxygen. Thus, the aforementioned advantages are achieved in a particularly preferred manner.

[0035] Advantageously, as already explained above, the fuel properties are changed in a preferred manner. Therefore, the method according to the present invention is optimally adapted to change the fuel properties in such a way that emissions are reduced. Furthermore, the method according to the present invention can be used for an evaporator, specifically in a diesel engine of a passenger car, to lower the light-off temperature in an exhaust gas aftertreatment system of an internal combustion engine. Additionally, the method according to the invention is suitable for generating a reducing agent for a storage catalyst. This can be done according to U.S. Patent No. 7,386,977 (B2). In this patent publication, CO and H2 are generated from methane for regeneration. In the present invention, CO and H2 can be generated from diesel in a manner similar to that of U.S. Patent No. 7,386,977 (B2).

[0036] The present invention will be described in more detail below with reference to the drawings without limiting the overall concept of the present invention.

Brief Description of the Drawings

[0037]

Figure 1

Figure 2

Figure 3a

Figure 3b

Figure 3c

Figure 3d

Figure 3e

Figure 4a

Figure 4b

Figure 4c

Figure 4d

Figure 5a

Figure 5b

Figure 5c

Figure 5d

DETAILED DESCRIPTION OF THE INVENTION

[0038] Figure 1 shows a catalytic evaporator 1 that can be used in the method according to the present invention. The catalytic evaporator has a catalyst 2, and the catalyst 2 is applied to a metal mesh 3. The catalyst 2 and the metal mesh 3 can be made of materials known from the prior art. The metal mesh 3 with the catalyst 2 can be present in a reaction vessel 4. For clarity, Figure 1 shows the catalyst 2 with the metal mesh 3 withdrawn from the reaction vessel 4. When the metal mesh 3 with the catalyst 2 is inserted into the reaction vessel, an intermediate space is formed between the inner surface 5 of the reaction vessel 4 and the surface of the catalyst 2 on the metal mesh 3.

[0039] Figure 2 schematically shows the mode of operation of the catalytic evaporator shown in Figure 1. The formation of a good mixture of reactants is favorable for the stable and efficient operation of many chemical processes. Specifically, in oxidation processes such as combustion, for example, homogeneous mixing reduces emissions and prevents soot formation. During the operation of the catalytic evaporator, the liquid fuel is converted into the gas phase. The advantages of mixing have been proven for various applications (burners, particulate filters, reformers). The connection to the engine is particularly important. The evaporator can be adapted for use in an internal combustion engine, and the reduction of nitrogen oxides and soot emissions has been demonstrated on an engine test stand.

[0040] The liquid fuel is added to the inner surface of the reaction vessel 4, while air is added to the catalyst side. A small portion of the fuel is oxidized in the catalyst 2, and the heat generated in this process is used to completely evaporate the fuel. The heat is mainly transferred by thermal radiation from the hot surface of the catalyst 2 to the surface of the fuel film. Here, the wall of the reaction vessel 4 to which the fuel is applied can be at a lower temperature than the fuel itself. Therefore, no deposits or adherents are formed.

[0041] Figures 3a and 3b show the curves of the amount of added oxidant (here, air) and the amount of fuel. In the normal (i.e., continuous) operating mode shown in Figure 3a, the oxidant and fuel are continuously added in constant amounts over the operating period. In contrast (see Figure 3b), the addition of fuel is carried out as pulsed addition in the method according to the present invention. On the other hand, the addition of the oxidant is not carried out as pulsed addition and is carried out in the form of continuous addition as known from the prior art. In the case of pulsed addition of fuel, a period with fuel supply (e.g., 16.9 g / min in the example) is followed by a period without fuel supply (0 g / min). In the example of Figure 3b, the periods with and without fuel supply are each set to 3 seconds.

[0042] Figures 3c to 3e show further embodiments of pulsed addition of fuel. In Figure 3b, a first amount of fuel is added in a first period, and is immediately followed by a second period in which a smaller second amount of fuel is added. This is followed by another period in which no fuel is introduced into the catalytic evaporator.

[0043] Figure 3d shows the pulsed addition of two different amounts of fuel and the periods without fuel addition as shown in Figure 3c, with the periods without fuel addition being between each fuel addition.

[0044] Figure 3e shows the pulsed addition of two different amounts of fuel without periods without fuel addition.

[0045] Figures 4a to 4d show the corresponding pulsed addition of the oxidant with continuous addition of fuel, and their additions correspond to Figures 3b to 3e, so the above explanations are fully incorporated by reference, and those explanations also apply to Figures 4a to 4d with respect to the results.

[0046] Figures 5a to 5d compare the fuel composition during the normal operation shown in Figure 3a (Figures 5a and 5b) with the change in fuel composition during the pulse operation according to the present invention shown in Figure 3b (Figures 5c and 5d). Since the fuel is not continuously supplied in the method according to the present invention, air ratios greater than 0.2 can be operated without overheating the catalyst. These large air ratios significantly increase the proportions of carbon monoxide (CO) and hydrogen (H2). Therefore, it was possible to increase the proportion of CO by three times and further increase the proportion of H2 by nine times. Adapting the operating mode of the catalytic evaporator allows the catalytic evaporator to be used in dynamic applications, for example, in a vehicle engine.

[0047] Naturally, the present invention is not limited to the embodiments shown in the drawings. Therefore, the foregoing description should not be construed as limiting, but rather as illustrative. The following claims are to be understood in a manner such that the recited features are present in at least one embodiment of the invention. This does not exclude the presence of additional features. When the description or claim defines "first" and "second" features, this terminology is used to distinguish between two similar features without determining an order of ranking.

Explanation of Reference Numerals

[0048] 1 Catalytic evaporator 2 Catalyst 3 Metal mesh 4 Reaction vessel 5 Inner surface

Claims

1. A method for operating a catalytic evaporator (1) to reduce the light-off temperature in an exhaust gas aftertreatment system of an internal combustion engine, comprising: supplying fuel and an oxidant to the catalytic evaporator (1), wherein (a) the fuel is supplied as pulsed addition, and (b) the oxidant is supplied as pulsed addition, the fuel is a liquid fuel, a part of the liquid fuel is oxidized in a catalyst in the catalytic evaporator, and the generated heat is used to completely evaporate the liquid fuel, in the pulsed addition (a) of the fuel, a first amount of the fuel is added during a first period, a second amount of the fuel is added during a second period, and no fuel is added during a third period, the first period is from 10 ms to 10 s, the second period is from 10 ms to 10 s, and the third period is from 10 ms to 10 s.

2. In the pulsed addition (b) of the oxidant, a first amount of the oxidant is added during a first period, and / or a second amount of the oxidant is added during a second period, and / or no oxidant is added during a third period, characterized in that the method according to claim 1.

3. (i) the first amount of the oxidant is added during the first period and no oxidant is added during the third period, or (ii) the first amount of the oxidant is added during the first period, the second amount of the oxidant is added during the second period, and no oxidant is added during the third period, or (iii) the first amount of the oxidant is added during the first period and the second amount of the oxidant is added during the second period characterized in that the method according to claim 2.

4. In the pulsed addition (b) of the oxidant, the first period is from 10 ms to 10 s, and / or the second period is from 10 ms to 10 s, and / or the third period is from 10 ms to 10 s, or the first period is from 1 s to 5 s, and / or the second period is from 1 s to 5 s, and / or the third period is from 1 s to 5 s, characterized in that the method according to claim 2 or 3.

5. The method according to any one of claims 1 to 4, characterized in that the fuel is selected from gasoline, diesel, bio-oil, pyrolysis oil, biodiesel, heavy oil, alcohol, Fischer-Tropsch fuel, dimethyl ether, diethyl ether, oxymethylene ether, ester, aldehyde, aromatic compound, amine, carboxylic acid, alkane, natural gas, camping gas, LPG, flare gas, landfill gas, biogas, and a mixture of at least two of these fuels.

6. The method according to any one of claims 1 to 5, characterized in that the oxidizing agent contains oxygen or an oxygen-containing medium.

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