U.S. patent application number 10/433792 was filed with the patent office on 2004-03-11 for catalytic combustion device with liquid fuel vaporisation on hot walls.
Invention is credited to Le Coz, Jean-Francois, Lebas, Etienne, Martin, Gerard, Niass, Tidjani.
Application Number | 20040048211 10/433792 |
Document ID | / |
Family ID | 8857509 |
Filed Date | 2004-03-11 |
United States Patent
Application |
20040048211 |
Kind Code |
A1 |
Martin, Gerard ; et
al. |
March 11, 2004 |
Catalytic combustion device with liquid fuel vaporisation on hot
walls
Abstract
The present invention relates to a catalytic combustion device
comprising a main combustion zone (20, 200) including at least one
catalytic section (5, 103) and at least one air/fuel mixing zone
(11, 117), said mixing zone comprising at least one pressurized air
inlet (1, 101) and injection means (12, 105) for injecting a liquid
fuel. According to the invention, injection means (12, 105) project
the liquid fuel onto a hot wall (13, 15, 107) of said device so as
to allow vaporization of said fuel on contact with this wall.
Inventors: |
Martin, Gerard; (Saint Genis
Laval, FR) ; Niass, Tidjani; (Lyon, FR) ; Le
Coz, Jean-Francois; (Nanterre, FR) ; Lebas,
Etienne; (Seyssuel, FR) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-9889
US
|
Family ID: |
8857509 |
Appl. No.: |
10/433792 |
Filed: |
June 6, 2003 |
PCT Filed: |
December 5, 2001 |
PCT NO: |
PCT/FR01/03850 |
Current U.S.
Class: |
431/7 ; 431/170;
431/243 |
Current CPC
Class: |
F23C 13/00 20130101;
F23R 3/30 20130101; F23D 9/00 20130101; F23R 3/40 20130101 |
Class at
Publication: |
431/007 ;
431/170; 431/243 |
International
Class: |
F23D 003/40; F23D
021/00; F23D 011/44 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 11, 2000 |
FR |
00/16107 |
Claims
1) A catalytic combustion device comprising a main combustion zone
(20, 200) including at least one catalytic section (5, 103), at
least one air/fuel mixing zone (11, 117), said mixing zone
comprising at least one pressurized air inlet (1, 101), and liquid
fuel injection means (12, 105), characterised in that injection
means (12, 105) project the liquid fuel onto a wall heated by the
combustion of the air/fuel mixture main combustion zone (13, 15,
107) so as to allow vaporization of said fuel on contact with said
wall.
2) A device as claimed in claim 1, characterised in that the fuel
is projected substantially perpendicular to hot wall (13, 15,
107).
3) A device as claimed in claim 1 or 2, characterised in that said
hot wall (15) consists at least partly of at least one of the walls
of main combustion zone (20).
4) A device as claimed in claim 1 or 2, further comprising a
combustion initiation zone (4, 102), characterised in that said hot
wall (13) consists at least partly of at least one of the walls of
combustion initiation zone (4).
5) A device as claimed in any one of claims 1 or 2, wherein at
least one postcombustion zone (14, 108) is arranged downstream from
main combustion zone (20, 200), characterised in that hot wall (15,
107) consists at least partly of at least one of the walls of said
postcombustion zone.
6) A device as claimed in any one of the previous claims,
characterised in that the means allowing injection of the liquid
fuel are injectors (12, 105) providing primary spraying such that
the size of the droplets coming from said injectors (12, 105)
ranges between 5 and 60 .mu.m, preferably between 10 and 40
.mu.m
7) A device as claimed in any one of the previous claims,
characterised in that hot wall (13, 15, 107) of the zone opposite
said injection means has a substantially plane shape.
8) A device as claimed in any one of claims 1 to 6, characterised
in that hot wall (13, 15, 107) of the zone opposite the injectors
has a concave curved shape.
9) A device as claimed in any one of the previous claims,
characterised in that the temperature of said hot wall (13, 15,
107) of said device is substantially equal to or higher than the
maximum boiling temperature of the liquid fuel on said wall.
10) A device as claimed in any one of the previous claims,
characterised in that wall (107) receiving the impact of the fuel
jets is equipped with means allowing to increase the heat transfer
from the hot zone to the spraying zone.
11) A device as claimed in any one of the previous claims,
characterised in that wall (107) is covered at least partly with an
insulating material, except for a zone (120) receiving the impact
of the fuel jets.
12) Application of the device as claimed in any one of the previous
claims to gas turbines provided with a heat recuperator.
13) Application of the device as claimed in any one of claims 1 to
11 to combustion chambers of annular geometry.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a catalytic combustion
device with vaporization of liquid fuel on a hot wall, thus
allowing to optimize the preparation of the air/fuel mixture in a
combustion zone.
[0002] Conventional combustion, carried out in the presence of a
flame and commonly used in combustion methods, is a process that is
difficult to control.
[0003] It occurs in a well-determined air/fuel concentration range
and leads, besides the formation of carbon dioxide and water, to
the production of pollutants such as carbon monoxide and nitrogen
oxides.
[0004] Because of the increasingly severe environmental regulations
relative to the pollutants emitted by combustion processes
(nitrogen oxides, unburnt fuels, carbon monoxide), it has become
necessary to find new technologies allowing such emissions to be
greatly decreased.
BACKGROUND OF THE INVENTION
[0005] Several conventional solutions are known to the man skilled
in the art:
[0006] Selective catalytic reduction of nitrogen oxides by ammonia
allows to reduce the NO.sub.x concentrations in fumes to about 10
ppm. This solution however requires a particular reactor downstream
from the combustion chamber, storage and use of ammonia, and the
installation and running costs of such a solution are high.
[0007] Injection of water or steam, which lowers the temperature
reached by the combustion gas, thus significantly reducing the
NO.sub.x contents to about 50 ppm. The cost of such a device is
low, but the running costs are high because of the intensive
purification of the water prior to injection and of the
overconsumption of fuel due to an energy efficiency decrease.
Furthermore, although water injection is sufficient to meet the
current standards, it will not meet the future NO.sub.x
standards.
[0008] Lean-burn combustion. As it is the case with the present
invention, this technology is based on the lowering of the
combustion temperatures. It allows the NO.sub.x concentrations to
be lowered down to about 20 ppm, but this decrease often occurs to
the detriment of the carbon monoxide and unburnt fuel emissions,
which are then increased.
[0009] Catalytic combustion is an attractive solution for meeting
the increasingly severe standards relative to pollution. In fact,
the catalytic combustion chamber advantageously replaces
conventional burners because it allows better control of the total
oxidation of the fuel in a very wide range of the air/fuel ratio
values, thus allowing to work under optimum conditions which
greatly reduce nitrogen oxides, unburnt fuel and carbon monoxide
emissions. It is well-known that the main characteristic of this
particular type of combustion is to provide complete oxidation of
the fuels at a relatively low temperature (below 1000.degree. C.)
in relation to a conventional combustion.
[0010] It may also be mentioned that catalytic combustion allows a
great variety of compounds to be burnt. The applications of
catalytic combustion are thus multiple: radiant panels and tubes,
catalytic stoves, gas turbines, cogeneration, burners for boilers,
catalytic sleeves for tubular reaction systems, hot gas production
in the field of direct contact heating and catalytic plate
reactors, etc. The possible fields of application of catalytic
combustion are described in the literature, for example in:
<<Catalytic Combustion: Current Status and Implications for
Energy Efficiency in the Process Industries, Heat Recovery System
& CHP, 13, No.5, pp. 383-390, 1993 >>.
[0011] Combustion catalysts are generally prepared from a
monolithic ceramic or metallic substrate on which a thin support
layer consisting of one or more heat-resisting oxides, whose
surface and porosity are greater than that of the monolithic
substrate, is deposited. The active phase comprising most often
essentially metals of the platinum group is dispersed on this
support layer.
[0012] Concerning the catalytic combustion processes in the field
of energy production and cogeneration, the commonest reactor
configuration is a reactor comprising several catalytic zones: the
inlet catalyst(s) being more specifically dedicated to the
initiation of the combustion reaction, the others being used to
stabilize the combustion reaction at high temperature; the number
of catalytic stages (or zones) is adjusted according to the
conditions imposed by the application considered. It is also
possible to replace the first catalytic reaction initiation zone by
a pilot burner allowing the reaction to be initiated.
[0013] In the conventional version of the catalytic combustion
chamber, i.e. with a mixing zone followed by the catalytic section,
preparation of the air/fuel mixture is one of the most critical
points.
[0014] Mixing has to be carried out as fast as possible and as
homogeneously as possible in order to limit self-ignition
risks.
[0015] There are also cases where the temperature of the air at the
compressor outlet is too low to allow fast vaporization of the
fuel.
[0016] In order to obtain vaporization of a liquid fuel, one of the
easiest procedures consists in projecting the fuel at high velocity
onto a surface, preferably a plane surface, and perpendicular
thereto. Such injection modes are for example used for catalytic
cracking, but the grain sizes obtained remain rather coarse
(average diameter of the droplets of the order of several hundred
microns).
[0017] The work carried out by the applicant has shown that it is
possible to substantially improve the homogeneity of the air/fuel
mixture and therefore to optimize control of the catalytic
oxidation of the fuels, and to limit the discharge of pollutant
gases by improving the vaporization of the liquid fuel so as to
obtain finer droplets.
SUMMARY OF THE INVENTION
[0018] More precisely, the invention relates to a catalytic
combustion device comprising a main combustion zone including at
least one catalytic stage, at least one air/fuel mixing zone, said
mixing zone comprising at least one pressurized air inlet, and
injection means for injecting a liquid fuel, characterised in that
the injection means project the liquid fuel onto a wall heated by
the combustion of the air/fuel mixture in the main combustion zone,
so as to allow vaporization of said fuel on contact with this
wall.
[0019] The invention allows to substantially reduce the diameter of
the liquid droplets by sending a primary liquid jet onto a surface
whose temperature is higher than the maximum boiling temperature of
said fuel under the pressure conditions of the combustion zone.
[0020] This primary liquid jet can be advantageously sprayed by any
injector or spraying system known to the man skilled in the
art.
[0021] Injectors allowing primary spraying of the fuel with liquid
droplets whose average diameter ranges between 5 and 60 .mu.m
(10.sup.-6 metre), preferably between 10 and 40 .mu.m, are
generally used.
[0022] It has been found by the applicant that the surface
temperature of the wall encountered by the primary jet is
advantageously substantially equal to or greater, at the pressure
considered, than a first temperature T.sub.N of the wall
corresponding to a maximum boiling temperature of the liquid.
[0023] At this temperature T.sub.N, the intense thermal exchanges
between the wall and the fuel lead to an intense spraying of the
liquid fuel (also referred to as Nukiyama temperature). A
substantially equal temperature is understood to be a temperature
greater or less than said temperature by 100.degree. C., preferably
greater or less than said temperature by 50.degree. C., and most
preferably greater or less than said temperature by 20.degree.
C.
[0024] It has also been found by the applicant that it is possible,
according to another embodiment of the invention, to advantageously
obtain a great fragmentation of the liquid droplets from the
primary jet by applying a temperature substantially ranging between
said Nukiyama temperature and a temperature T.sub.L in the
neighbourhood of which and beyond which the thermal transfers are
reduced by the presence of a vapour film between the droplet and
the wall (referred to as Leidenfrost temperature).
[0025] It is also possible, without departing from the scope of the
invention, to apply a temperature greater than said Leidenfrost
temperature, above which the evaporation time of the liquid
droplets decreases as a result of the increase, with the wall, of
the heat transfers by conduction, convection and radiation.
[0026] Control of the wall temperature will thus condition the size
of the droplets and can be obtained by means of any technique known
to the man skilled in the art.
[0027] Such an injection strategy has many advantages during
preparation of the air/fuel mixture for catalytic combustion:
[0028] In relation to a conventional configuration of the catalytic
combustion device with premixer and catalytic section, a layout
with such an injection mode allows to obtain faster vaporization of
the liquid fuel, in particular those with rather high final
vaporization temperatures. This is the case with certain gas oils
for example. Under such conditions, premixing of the air with the
fuel can be obtained more rapidly.
[0029] The arrangement which is the object of the present invention
can also contribute to cooling the walls of the combustion or
postcombustion zones, or of the zone carrying the hot gases to the
expander.
[0030] In cases where the temperature of the air at the compressor
outlet feeding the catalytic combustion-device is insufficient to
obtain complete vaporization of the fuel, the proposed solution
allows to overcome this problem thanks to the heat transfer between
the combustion or postcombustion zone and the fuel injection
zone.
[0031] It allows to envisage a significant reduction in the total
volume of the combustion zone since the zone normally reserved for
vaporization of the fuel and premixing disappears.
[0032] In general, the hot wall on which the fuel is sprayed is the
wall of the combustion or postcombustion zone or of the zone
carrying the hot gases resulting from the combustion or the wall of
the starting equipment which can be, for example, a flame
combustion chamber, an electric heater or any other device known to
the man skilled in the art.
[0033] According to an embodiment of the invention, the means
intended for injection of the liquid fuel are injectors allowing
primary spraying, whose orientation and characteristics are
calculated so as to obtain the most homogeneous possible
distribution of the fuel in the combustion air, and the size of the
droplets sent by said injector ranges between 5 and 60 .mu.m,
preferably between 10 and 40 .mu.m, and most preferably between 20
and 30 .mu.m.
[0034] Advantageously, the hot wall of the zone opposite said
injection means has a substantially plane shape.
[0035] It is also possible, without departing from the scope of the
invention, that the hot wall of the zone opposite the injectors has
a curved shape, concave for example.
[0036] It is advantageous that the zone receiving the impact of the
fuel jets is equipped with devices allowing to increase the heat
transfer from the hot zone to the spraying zone.
[0037] The device according to the present invention finds
applications for example in gas turbines equipped with a heat
recuperator or in combustion chambers having an annular
geometry.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] Other features and advantages of the present invention will
be clear from reading the description hereafter, given by way of
non limitative example, of two different embodiments of the device
according to the invention, with reference to the accompanying
figures wherein:
[0039] FIG. 1 shows an example of an embodiment where the fuel is
injected onto a hot wall of a combustion initiating device
consisting of a pilot burner, and
[0040] FIG. 2 shows another example of an embodiment where the fuel
is injected onto a hot wall of a postcombustion zone.
DETAILED DESCRIPTION
[0041] The combustion device diagrammatically shown in FIG. 1
comprises an inlet 1 for pressurized air coming from a compressor
(not shown in the figure). This air circulates in a peripheral
annular space 2 prior to reaching a distribution box 3 where it is
separated into a stream intended for a combustion initiation
device, here a pilot burner 4, and a stream sent to a catalytic
section 5.
[0042] A device, not shown in the figure, can be provided in the
vicinity of this distribution box 3 in order to separate the air in
an optimum way whatever the running conditions of the machine.
[0043] The pilot burner shown in FIG. 1 is a conventional flame
burner. It comprises a central fuel delivery line 6, an air box 7,
means 8 such as blades, for example, for adjusting the velocity and
the rotation of the combustion air before it enters combustion zone
9 of the pilot burner, an outlet zone 10 for the fumes produced by
the pilot burner, said outlet running right through catalytic
section 5.
[0044] This pilot burner can also be an equipment known to the man
skilled in the art and reputed to discharge low nitrogen oxides
amounts, such as for example systems in which the combustion air is
brought into rotation in blades, with injection of the fuel inside
the blades, or part thereof, or in the immediate vicinity of these
blades.
[0045] Main combustion zone 20 comprises an air/fuel mixing zone 11
arranged downstream from distribution box 3, liquid fuel mechanical
spray injectors 12 equally distributed for example on the periphery
of mixing zone 11 and of catalytic section 5.
[0046] Injectors 12 produce a liquid fuel jet sent onto hot wall 13
of pilot burner 4 and they allow primary spraying of this fuel with
liquid droplets whose average diameter ranges between 5 and 60
.mu.m (10.sup.-6 metre), preferably between 10 and 40 .mu.m.
[0047] This jet is preferably substantially perpendicular to the
hot wall. Substantially perpendicular means that the angle between
the surface of the hot wall in relation to the axis of the jet more
preferably ranges between 80.degree. and 100.degree..
[0048] Of course, this angle can range between 40.degree. and
140.degree., preferably between 60.degree. and 120.degree..
[0049] Wall 13 is heated by the combustion of the air/fuel mixture
in section 5 and by contact with the hot wall, the liquid fuel is
vaporized while dividing into very fine droplets which are some
microns in average diameter (10.sup.-6 m) and carried along by the
combustion air. The number of injectors, their orientation in
relation to the hot surface and the characteristics of the
injectors are calculated by the man skilled in the art so as to
obtain the most homogeneous possible distribution of the fuel in
the gaseous stream, once the fine droplets sprayed. The gaseous
air/fuel mixture flows then into catalytic section 5 which often
consists of one or more monoliths arranged in parallel or in
series, in order to limit pressure drops. When the combustion of
the air/fuel mixture is not complete in the catalytic section, it
continues in zone 14, referred to as postcombustion zone, provided
therefore.
[0050] Wall 15 which is in contact with postcombustion zone 14 or
with catalytic section 5 is also heated by the combustion of the
air/fuel mixture in catalytic section 5, and it is possible to
arrange injectors 12 opposite this wall.
[0051] According to a variant, in order to optimize spraying of the
droplets, wall 13 of pilot burner 4 opposite the injectors can have
a substantially plane shape, or even curved or concave so that all
of the liquid fuel droplets sent by the injector impact as
perpendicular as possible the hot surface where they are intended
to fragment and disintegrate.
[0052] Without departing from the scope of the invention, it is of
course possible to use any known device allowing such an effect to
be obtained, such as for example the presence of inserts of
substantially plane or convex curved shape.
[0053] FIG. 2 is another possible illustration of the
invention.
[0054] It also comprises an inlet 101 for pressurized air coming
from the compressor (not shown in the figure), a combustion
initiation device 102 (or pilot burner) and main combustion zone
200 with its catalytic section 103 proper.
[0055] The combustion air circulates in a substantially annular
peripheral space 104. The fuel is introduced by means of injectors
105 fastened to and substantially equally distributed on outer wall
106 of annular space 104. These injectors can be mechanical
(without spraying assistance) or air-blast injectors (with the
assistance of a spraying fluid) or any other equivalent device. The
jets produced by these injectors are sent onto hot wall 107 which
separates annular space 104 from zone 108, which can be a
postcombustion zone or simply a connection zone between catalytic
section 103 and the expander (not shown in the figure) and, on
contact with this hot wall, the liquid fuel is sprayed as very fine
droplets.
[0056] As described above, injectors 105 produce a fuel jet with a
primary spray containing liquid droplets whose average diameter
ranges between 5 and 60 .mu.m (10.sup.-6 metre), preferably between
10 and 40 .mu.m.
[0057] Advantageously, certain parts of wall 107 can be covered
with insulating materials in order to prevent hot spots which can
lead to an early ignition of the air/fuel mixture.
[0058] Conversely, zone 120 of wall 107, which receives the impact
of the jets, can be equipped with devices such as blades in order
to increase the heat transfer from hot zone 108 to spraying zone
104.
[0059] As in the previous case, the number of injectors, their
orientation in relation to the hot wall and their characteristics
are calculated by the man skilled in the art so as to obtain the
most homogeneous possible distribution of the fuel once the
droplets sprayed.
[0060] Annular zone 104 is ended by a distributor 109 which
distributes the air/fuel mixture among pilot burner 102 and main
catalytic section 103. This distribution can for example be
obtained by means of a mobile shutter 110 which alternately moves
in front of inlet 111 of catalytic section 103 or in front of inlet
112 of pilot burner 102, according to the running conditions of the
machine.
[0061] The pilot burner can be a device such as shown in FIG. 1. It
can also be a system as shown in FIG. 2, i.e. consisting of an
initiating catalytic section 121, fed by a circuit 113 arranged
after distributor 109. This catalytic section can be a metal
monolith preheated by Joule effect, by means of an electric power
supply consisting of any electricity source 114, of two metallic
connectors 115 arranged at each end of the monolith and of an
electric link 116 connecting said connectors 115 to electricity
source 114.
[0062] Main catalytic section 103 comprises a distribution box 117
for the air/fuel mixture, and this box can be equipped for example
with a perforated plate 118 intended to provide homogeneous feeding
of all the constituent channels of the monolith.
[0063] This plate 118 can also be a monolith of very limited
thickness, intended to stop any flame in case of unwanted
self-ignition of the air/fuel mixture, in space 119 between said
plate 118 and main catalytic section 103. The latter can consist of
one or more monoliths arranged in series or in parallel.
[0064] As in the previous case, a free space 108 can be provided
downstream from catalytic section 103, before the expander (not
shown), which is intended to complete the combustion of the
air/fuel mixture if it has not completely burned in the catalytic
section.
[0065] Catalytic sections 102 and 103 can use catalysts of
different nature. The catalyst of pilot burner 102 can for example
have a high precious metal content, precious metals being known for
their efficiency for catalytic combustion, and combustion can thus
start from 200.degree. C. or 250.degree. C.
[0066] The invention can also be applied to gas turbine
configurations with a heat recuperator or to combustion chambers
having an annular geometry.
* * * * *