FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. Title of the Invention
METHOD FOR OPERATING A CATALYTIC EVAPORATOR, AND USES OF THE METHOD
2. Applicant(s)
Name Nationality Address
FRAUNHOFER-GESELLSCHAFT
ZUR FÖRDERUNG DER
ANGEWANDTEN FORSCHUNG E.V.
German Hansastraße 27c 80686 München,
Germany
3. Preamble to the description
The following specification particularly describes the invention and the manner in which it is to be performed
2
The invention relates to a method for operating a catalytic evaporator
and uses of the method.
It is known to use catalytic evaporators to adjust the fuel properties of an
internal combustion engine. WO 2007/042246 A2 describes a method for
evaporating and reforming liquid fuels, in which in a first reaction chamber
the fuel is evaporated and strongly sub-stoichiometrically oxidized with the
supply of air by means of a first catalyst and in a second reaction
chamber the evaporated fuel is mixed with supplied air and then
reformed, the ratio of the air volume supplied in the first reaction chamber
to the air volume supplied in the second reaction chamber being set
between 30:70 and 70:30.
DE 10 2010 012 945 B4 discloses a method for evaporating liquid fuels
and/or combustibles, in which a liquid fuel and/or combustible is applied
to an absorbent material and an oxygen-containing gas mixture or
oxygen is introduced by air supply, the oxygen/fuel ratio being substoichiometric.
A device can be used for carrying out this method,
comprising a) a central, axially and radially air-permeable air supply, b) a
catalyst system which is arranged concentrically around the air supply
over at least part of the length thereof, c) a buffer zone arranged
concentrically around the catalyst system and d) an absorbent material
for fuel distribution that is arranged concentrically around the buffer zone,
wherein at least one gas-tight sealing element is fitted between the
components a) to d).
DE 10 2015 120 106 A1 discloses a method for adjusting the ignition
property of a fuel that uses a unit which has at least one distribution zone,
at least one oxidation zone and at least one conversion zone. In this
method, fuel is distributed in the distribution zone which has a distribution
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structure, at least part of the fuel is oxidized with at least one oxidant on at
least one catalyst on a catalyst support in the oxidation zone, and at least
part of the distributed fuel and/or of another supplied fuel is thermally
and/or catalytically converted in the conversion zone. The method is
characterized in that the ignition property of the fuel is adjusted by the
molar ratio of oxygen contained in the oxidant to the oxygen required for
the complete oxidation of the available fuel and/or the pressure in the
unit and/or the residence time and/or the temperature.
In general, a catalytic evaporator known per se can be used, for
example, as a preliminary process for homogeneously mixing fuel and
oxidant, e.g. air. At the same time, the fuel properties can be changed in
such a way that nitrogen oxides (NOx) and soot emissions are reduced
within the engine. The reaction products of reforming reactions (hydrogen
(H2) and carbon monoxide (CO)) are particularly effective for shifting the
fuel properties. The light-off temperatures of the components, hydrogen
and carbon monoxide, on the diesel oxidation catalyst are much lower
than those of diesel, so that when an engine is cold started, the exhaust
system reaches the operating temperature more quickly.
In addition, the evaporator can also be used for simultaneously heating
the exhaust gas after-treatment system.
A change in the fuel properties due to the catalytic evaporation method
can be achieved by increasing the operating pressure and increasing the
air ratio. The increase in the operating pressure is limited by the
supercharging of the internal combustion engine. The increase in the air
ratio leads to an increased temperature at the catalyst and therefore
cannot be increased arbitrarily.
4
Proceeding from the prior art, the object of the invention is thus to provide
a method of operating catalytic evaporators, which does not have the
disadvantages known from the prior art, in particular with which the fuel
properties can be shifted in a favorable manner with respect to the
properties of the original fuel.
According to the invention, this object is achieved by a method for
operating a catalytic evaporator according to claim 1 and the uses of the
method according to claims 10 to 13. Advantageous further
developments of the invention can be found in the subclaims.
According to the invention, a method for operating a catalytic
evaporator is proposed, 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/or
(b) the oxidant is supplied as a pulsating addition.
In step (a), the corresponding supply of the oxidant can be effected and,
in step (b), the corresponding supply of the fuel can be continuous, in
particular if these additions are not designed as pulsating additions.
In the method according to the invention, therefore, either the fuel or the
oxidant or both together are added in the form of pulses, with pulses
being portions limited in time. They can represent a sequence of regularly
recurring additions of the same kind. The pulsating addition is here
different from a continuous addition in that the pulsating addition contains
addition-free pause times. The pulses for fuel additions and/or the pulses
for the oxidant additions can be of equal or different length.
In some embodiments, the pulsating addition of fuel (a) allows a first
amount of fuel to be added during a first time period and/or a second
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amount of fuel to be added during a second time period and/or no fuel
to be added during a third time period.
In some embodiments the additions can be made by
(i) adding the first amount of fuel during the first time period and no fuel
during the third time period, there being no requirement for a second time
period; or
(ii) adding the first amount of fuel during the first time period, adding the
second amount of fuel during the second time period and adding no fuel
during the third period
or
(iii) adding the first amount of fuel during the first time period and the
second amount of fuel during the second time period, there being no
requirement for a third period.
The designations "first", "second" and "third" do not indicate the order of
the additions, but are only used to distinguish the additions. The terms "first
amount" and "second amount" indicate that these amounts are different
from one another.
In some embodiments, with regard to the fuel supply, the above first time
period can be from about 10 ms to about 10 s; the above second time
period can be from about 10 ms to about 10 s, and the third time period
can be from about 10 ms to about 10 s. In other embodiments of the
invention, the first and/or the second and/or the third time period can be
selected between about 1 second and about 5 seconds.
The pulses can be adjusted according to the respective concrete
requirements for the operation of the catalytic evaporator, for example by
means of the following parameters: the amount of fuel in the pulse and/or
the duration of the pulse and/or the time between two pulses
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(corresponds to the frequency of the pulses per time). A person skilled in
the art can determine by simple experiments how to adjust the pulses of
the fuel addition in order to obtain the specific requirements and the
optimum results for the operation of the evaporator.
Surprisingly, it was 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 pulse addition of the fuel
helps to shift the fuel properties compared to the originally used fuel.
Above all, the pulsating addition of the fuel shifts the fuel properties in such
a way that the proportion of hydrogen and/or carbon monoxide is
significantly increased. At the same time, the pulse mode of operation
allows faster switching from maximum to minimum output.
The catalytic evaporator, which can be used in the method according to
the invention, can provide a homogeneous mixing of fuel and oxidant, for
example air, as a preliminary process. A catalytic evaporator, as it can be
used in the method according to the invention, can be used in a manner
known per se for heating during the exhaust gas after-treatment. With the
method according to the invention, the fuel properties can be changed
in such a way that nitrogen oxides (NOx) and soot emissions are reduced
within the engine. According to the invention, a particularly favorable and
effective shift of the fuel properties towards an increase in the amount of
reaction products of reforming reactions (hydrogen (H2) and carbon
monoxide (CO)) is achieved. Furthermore, in the method according to the
invention, the evaporator can also be used advantageously for the
simultaneous heating of the exhaust gas after-treatment system.
Furthermore, in the method according to the invention, the light-off
temperatures of the components, hydrogen and carbon monoxide, on
the diesel oxidation catalyst are considerably lower than those of diesel,
7
so that when an engine is cold started, the exhaust gas system reaches
operating temperature more quickly.
The method according to the invention has significant cost and power
advantages for gas burners that burn fuel oil and for self-ignition internal
combustion engines or diesel engines, both inside the engine and in
exhaust gas after-treatment systems. In addition, the method according to
the invention has significant cost and power advantages when used
inside the engine in the case of internal combustion engines with spark
ignition.
As described above, the fuel is added in the form of a pulsating addition.
When operating a catalytic evaporator according to the prior art, both
the fuel and the oxidant are added continuously in predetermined
amounts, i.e. the amount of oxidant and fuel added remains constant
over time. In the method according to the invention, it has proved to be
particularly advantageous that a preset amount of fuel is added over a
certain time, followed by a time period in which no fuel is added, i.e. a
time period in which the fuel addition is set to the value "zero". The amount
of fuel to be added is in the range of the amounts of fuel previously used
in the prior art and added to catalytic evaporators known from the prior
art.
In alternative (b) of the method according to the invention, a first amount
of the oxidant can be added during the pulsating addition of the oxidant
during a first time period and/or a second amount of the oxidant during a
second time period and no oxidant during a third time period.
In some embodiments, the additions can be made in such a way that
8
(i) the first amount of oxidant is added during the first time period and no
oxidant is added during the third time period, there being no requirement
for a second 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 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, there
being no requirement for a third time period.
The designations "first", "second" and "third" do not indicate the order of
the additions, but are only used to distinguish the additions. The terms "first
amount" and "second amount" here indicate that these amounts are
different from one another.
In some embodiments, the above first time period can be from about 10
ms to about 10 s in alternative (b) concerning the addition of oxidant; the
above second time period can be from about 10 ms to about 10 s and
the further time period can be from about 10 ms to about 10 s. In other
embodiments, the above first time period can be from about 1 s to about
5 s in alternative (b) concerning the addition of oxidant; the above
second time period can be from about 1 s to about 5 s and the further
time period can be from about 1 s to about 5 s.
The same advantages can be achieved with the pulsating addition of the
oxidant as described above in connection with the pulsating addition of
the fuel, so that reference is made in full to the above explanations in this
respect.
9
Catalytic evaporators as 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 they can be operated in principle.
A particularly favorable catalytic evaporator is described in DE 10 2015
120 106 A1, to which reference is made in full in terms of the design details
and operating mode. The device for setting the ignition property of at
least one fuel contains
• at least one fuel inlet and at least one oxidant inlet,
• 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 at least partial oxidation of the
fuel, containing at least one catalyst support with at least one
catalyst,
• at least one conversion zone for the at least partial catalytic and/or
thermal conversion of the fuel, and
• at least one outlet for fuel with modified ignition property,
wherein the oxidant 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 conversion zone.
In some embodiments, the catalytic evaporator used in the method
according to the invention can have a catalyst, which can be applied,
for example, to a support. The support with the catalyst can be
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introduced into a reaction vessel in such a way that an intermediate
space is formed between the inner surface of the reaction vessel and the
catalyst surface.
The mode of operation of the above described catalytic evaporator is
described below by way of example. A good mixture formation of the
reactants is favorable for the stable and efficient operation of many
chemical processes. In particular in oxidation processes, for example
combustion, homogeneous mixing reduces emissions and prevents the
formation of soot. For this purpose, the liquid fuel can be converted into
the gas phase. The mixing advantages have been proven for various uses
(burner, particle filter, reformer). The linkage with an engine is particularly
significant. The aim is to adapt the evaporator to the use inside the engine
and to verify the reduction of nitrogen oxide and soot emissions on an
engine test stand.
When operating a catalytic evaporator, for example, the liquid fuel can
be added to the inside of the reactor wall of a 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 predominantly transferred by heat radiation from the hot
catalyst surface to the surface of the fuel film. The reactor wall onto which
the fuel is fed is always colder than the fuel itself. Therefore, no deposits or
incrustations are formed.
A fuel is a chemical substance the stored energy of which can be
converted into usable energy by combustion. An example of this is fuels
that are converted into motive force in internal combustion engines. In
some embodiments, the fuel can be selected from gasoline, diesel, biooils,
pyrolysis oils, biodiesel, heavy fuel oil, alcohols, Fischer-Tropsch fuels,
dimethyl ether, diethyl ether, oxymethylene ether, esters, aldehydes,
11
aromatic compounds, amines, carboxylic acids, alkanes, natural gas,
camping gas, LPG, flare gases, landfill gases, biogases and mixtures of at
least two of these fuels. In particular, liquid fuels can be used in the
method according to the invention. With these fuels the above described
advantages are achieved in a particularly favorable way.
In some embodiments, the oxidant can contain oxygen or media that
contain oxygen, in particular air or exhaust gases with residual oxygen.
Thus, the above described advantages are achieved in a particularly
favorable way.
Advantageously, as already explained above, the fuel properties are
shifted in a favorable way. Therefore, the method according to the
invention is best suited to shift the fuel properties in such a way that
emissions are reduced. Furthermore, the method according to the
invention can be used for evaporators to reduce the light-off temperature
in exhaust gas after-treatment systems of internal combustion engines, in
particular in diesel engines of passenger cars. Moreover, the method
according to the invention is suitable for generating a reducing agent for
storage catalysts. This can be done in accordance with US 7,386,977 B2. In
this patent publication CO and H2 are generated from methane for
regeneration. With the present invention, CO and H2 can be generated
from diesel in a manner analogous to US 7,386,977 B2.
The invention will be explained in more detail below by means of drawings
without limitation of the general concept of the invention, wherein
Figure 1 shows a view of a catalytic evaporator which can be used as an
example.
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Figure 2 shows the principle of a mode of action of the catalytic
evaporator of figure 1.
Figures 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.
Figures 4a to 4d show various pulsating additions of oxidant.
Figures 5a-d show the fuel compositions as obtained according to the
operating modes in figures 3a and 3b.
Figure 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,
figure 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.
Figure 2 shows schematically the mode of action of the catalytic
evaporator illustrated in figure 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
13
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.
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.
Figures 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 figure 3a, the oxidant and the fuel are added
continuously in constant amounts over the operating period. In contrast
thereto (cf. figure 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 figure 3b is based,
the time periods with and without fuel supply are set to 3 seconds each.
Figures 3c to 3e show further embodiments of the pulsating addition of
fuel. In figure 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.
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Figure 3d shows the pulsating additions of two different amounts of fuel
and a time period of no fuel addition, as shown in figure 3c, with a time
period of no fuel addition between each fuel addition.
Figure 3e shows the pulsating addition of two different amounts of fuel,
with no time period without fuel being added.
Figures 4a to 4d show the corresponding pulsating additions of oxidant
with continuous addition of fuel, which additions correspond to figures 3b
to 3e, so that full reference is made to the above explanations which also
apply to figures 4a to 4d with regard to the result.
Figures 5a to 5d compare the changes in the fuel composition during
normal operation (Figures 5a and 5b) shown in figure 3a and the pulsating
operation (figures 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 (H2). It was thus
possible to increase the CO proportion by a factor of three and the H2
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.
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
15
designation is used to distinguish between two similar features without
determining a ranking order.
16
WE CLAIM:
1. Method for operating a catalytic evaporator (1) comprising the step
of:
supplying fuel and an oxidant to the catalytic evaporator (1),
characterized in that
(a) the fuel is supplied as a pulsating addition and/or
(b) the oxidant is supplied as a pulsating addition.
2. Method according to claim 1, characterized in that in the pulsating
addition of the fuel (a) a first amount of the fuel is added during a
first time period and/or a second amount of the fuel is added during
a second time period and/or no fuel is added during a third time
period.
3. Method according to claim 2, characterized in that
(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. Method according to claim 2 or 3, characterized in that the first time
period is 10 ms to 10 s or in that the second time period is 10 ms to 10
s or in that the third time period is 10 ms to 10 s.
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5. Method according to any of claims 1 to 4, characterized in that in
the pulsating addition of the oxidant (b) a first amount of the
oxidant is added during a first time period and/or a second amount
of the oxidant is added during a second time period and/or no
oxidant is added during a third time period.
6. Method according to claim 5, characterized in that
(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.
7. Method according to claim 5 or 6, characterized in that the first time
period is 10 ms to 10 s and/or in that the second time period is 10 ms
to 10 s and/or in that the further time period is 10 ms to 10 s or in that
the first time period is 1 s to 5 s and/or in that the second time period
is 1 s to 5 s and/or in that the further time period is 1 s to 5 s.
8. Method according to any of the preceding claims, characterized in
that 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.
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9. Method according to any of the preceding claims, characterized in
that the oxidant contains oxygen or oxygen-containing media, in
particular air or exhaust gases with residual oxygen.
10. Use of the method according to any of claims 1 to 9 in order to shift
the fuel properties in such a way that emissions are reduced within
the engine.
11. Use of the method according to any of claims 1 to 9 in order to
reduce the light-off temperature in exhaust gas after-treatment
systems of internal combustion engines.
12. Use of the method according to any of claims 1 to 9 for generating
a reducing agent for storage catalysts.