Method for operating a catalytic evaporator and uses of the method

Abstract

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

Claims

1. A method for operating a catalytic evaporator (1) comprising the step of: supplying fuel and an oxidant to the catalytic evaporator (1), wherein (a) the fuel is supplied as a pulsating addition and, (b) the oxidant is supplied as a pulsating addition including a first amount of the oxidant added during a first time period or a second amount of the oxidant added during a second time period or no oxidant added during a third time period.

2. The method of claim 1, wherein in the pulsating addition of the fuel a first amount of the fuel is added during a first time period or a second amount of the fuel is added during a second time period or no fuel is added during a third time period.

3. The method of claim 2, wherein (i) the first amount of fuel is added during the first time period and no fuel is added during the third time period, or (ii) the first amount of fuel is added during the first time period, the second amount of fuel is added during the second time period and no fuel is added during the third time period, or (iii) the first amount of fuel is added during the first time period and the second amount of fuel is added during the second time period.

4. The method of claim 2, wherein the first time period is 10 ms to 10 s or the second time period is 10 ms to 10 s or the third time period is 10 ms to 10 s.

5. The method of claim 1, wherein (i) the first amount of oxidant is added during the first time period and no oxidant is added during the third time period, or (ii) the first amount of oxidant is added during the first time period, the second amount of oxidant is added during the second time period and no oxidant is added during the third time period, or (iii) the first amount of oxidant is added during the first time period and the second amount of oxidant is added during the second time period.

6. The method of claim 1, wherein the first time period is 10 ms to 10 s or the second time period is 10 ms to 10 s or the third time period is 10 ms to 10 s.

7. The method of claim 1, wherein the fuel is selected from gasoline, diesel, bio-oils, pyrolysis oils, biodiesel, heavy fuel oil, alcohols, Fischer-Tropsch fuels, dimethyl ether, diethyl ethers oxymethylene ether, esters, aldehydes, aromatic compounds, amines, carboxylic acids, alkanes, natural gas, camping gas, LPG, flare gases, landfill gases, bio-gases and mixtures of at least two of these fuels.

8. The method of claim 1, wherein the oxidant contains oxygen or oxygen-containing media, in particular air or exhaust gases with residual oxygen.

9. The method of claim 1, wherein said method shifts properties of said fuel in such a way that emissions are reduced within the engine.

10. The method of claim 1, wherein said method reduces the light-off temperature in exhaust gas after-treatment systems of internal combustion engines.

11. The method of claim 1, wherein said method generates a reducing agent for storage catalysts.

12. The method of claim 1, wherein the first time period is 1 s to 5 s or the second time period is 1 s to 5 s or the third time period is 1 s to 5 s.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in more detail below by means of drawings without limitation of the general concept of the invention, wherein

(2) FIG. 1 shows a view of a catalytic evaporator which can be used as an example.

(3) FIG. 2 shows the principle of a mode of action of the catalytic evaporator of FIG. 1.

(4) FIGS. 3a to 3e show a comparison of the continuous mode of action and various pulsating modes of operation of a catalytic evaporator according to the invention, in which the fuel is added in a pulsating manner.

(5) FIGS. 4a to 4d show various pulsating additions of oxidant.

(6) FIGS. 5a-d show the fuel compositions as obtained according to the operating modes in FIGS. 3a and 3b.

(7) FIG. 1 shows a catalytic evaporator 1 as it can be used in the method according to the invention. The catalytic evaporator has a catalyst 2, which is applied to a metal mesh 3. Catalyst 2 and 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 the sake of clarity, FIG. 1 shows the catalyst 2 with the metal mesh 3 pulled out of reaction vessel 4. If the catalyst 2 with the metal mesh 3 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.

(8) FIG. 2 shows schematically the mode of action of the catalytic evaporator illustrated in FIG. 1. A good mixture formation of the reactant is favorable for the stable and efficient operation of many chemical processes. In particular in oxidation processes, e.g. combustion, homogeneous mixing reduces emissions and prevents the soot formation. During the operation of the catalytic evaporator, liquid fuels are converted into the gas phase. The mixing advantages have been proven for various applications (burner, particle filter, reformer). The linkage with an engine is particularly significant. The evaporator can be adapted to the internal engine use and the reduction of nitrogen oxide and soot emissions was proven on an engine test stand.

(9) The liquid fuel is added to the inner surface of the reactor vessel 4, while air is added on the catalyst side. A small portion of the fuel oxidizes on the catalyst 2 and the heat generated in this process is used to completely evaporate the fuel. The heat is transferred mainly by heat radiation from the hot surface of the catalyst 2 to the surface of the fuel film. The wall of the reactor vessel 4, onto which the fuel is applied, can here be colder than the fuel itself. Thus, no deposits or incrustations are formed.

(10) FIGS. 3a and 3b show the curves of the amounts of oxidant added (here: air) and the amounts of fuel. In the normal (i.e. continuous) mode of operation shown in FIG. 3a, the oxidant and the fuel are added continuously in constant amounts over the operating period. In contrast thereto (cf. FIG. 3b), the addition of the fuel is carried out as a pulsating addition in the method according to the invention. The addition of the oxidant, on the other hand, is not carried out as a pulsating addition, but rather as known from the prior art in the form of a continuous addition. In the case of the pulsating addition of the fuel, time periods with an addition of fuel (in the example 16.9 g/min) are followed by time periods without fuel supply (0 g/min). In the example on which FIG. 3b is based, the time periods with and without fuel supply are set to 3 seconds each.

(11) FIGS. 3c to 3e show further embodiments of the pulsating addition of fuel. In FIG. 3b, a first amount of fuel is added in a first time period, immediately followed by a second time period in which a smaller second amount of fuel is added. This is followed by another time period in which no fuel is introduced into the catalytic evaporator.

(12) FIG. 3d shows the pulsating additions of two different amounts of fuel and a time period of no fuel addition, as shown in FIG. 3c, with a time period of no fuel addition between each fuel addition.

(13) FIG. 3e shows the pulsating addition of two different amounts of fuel, with no time period without fuel being added.

(14) FIGS. 4a to 4d show the corresponding pulsating additions of oxidant with continuous addition of fuel, which additions correspond to FIGS. 3b to 3e, so that full reference is made to the above explanations which also apply to FIGS. 4a to 4d with regard to the result.

(15) FIGS. 5a to 5d compare the changes in the fuel composition during normal operation (FIGS. 5a and 5b) shown in FIG. 3a and the pulsating operation (FIGS. 5c and 5d) according to the invention, which is shown in figure 3b. Since the fuel is not continuously supplied in the method according to the invention, an air ratio higher than 0.2 can be run without overheating the catalyst. These high air ratios markedly increase the proportion of carbon monoxide (CO) and hydrogen (H.sub.2). It was thus possible to increase the CO proportion by a factor of three and the H.sub.2 proportion even by a factor of nine. Adapting the operating mode of a catalytic evaporator allows it to be used in dynamic applications, for example in a car engine.

(16) Of course, the invention is not limited to the embodiments illustrated in the drawings. Therefore, the above description should not be regarded as restrictive but as explanatory. The following claims are to be understood in such a way that a stated feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. If the description or the claims define “first” and “second” features, this designation is used to distinguish between two similar features without determining a ranking order.