OXYCOMBUSTION CHAMBER
The present invention relates to a combustion chamber comprising an enclosure (1) having at least one fuel injection means (2), at least one oxidizer injection means (3) and at least one combustion fumes withdrawal means (5), wherein enclosure (1) has the shape of a bent closed tube of any section, and the fuel (2) and oxidizer (3) injection means are arranged on enclosure (1) so as to be offset by an angle θ formed by each of the oxidizer and fuel injection positions with respect to centre (C) of the enclosure, ranging between 10° and 90°, and wherein the oxidizer injection means is a means of injecting an oxidant that is a gas with an oxygen concentration above 90%.
The present invention relates to the sphere of oxycombustion and more particularly to a combustion device whose geometry allows natural fumes recirculation and is suited to the constraints linked with the oxycombustion of a liquid or gaseous feed.
The current economic activity and the increasing energy requirements generate, through the use of fossil fuels, increasing emissions of CO2, a greenhouse gas, to the atmosphere. These CO2 emissions are suspected of being the source of the climate change observed, and notably of global warming.
A solution for reducing these emissions consists in capturing and sequestering the CO2 emitted. However, the associated additional costs in terms of investment and the penalties on the overall efficiency of the equipments are for the time being prohibitive. To date, no economically satisfactory solution is available. Research is currently being done in order to improve existing technologies, notably capture technologies.
Currently, the main CO2 capture technologies studied are:
post-combustion capture, i.e. direct capture of the CO2 present in air combustion fumes. This capture requires adding a dedicated CO2 separation unit,
precombustion capture, i.e. prior CO2 capture on the feed after a first stage of conversion to synthesis gas. This conversion generates a H2-rich gas that, once freed of its carbon-containing compounds, releases no CO2 during combustion,
oxycombustion capture: oxygen is substituted for air in the combustion stages. Fumes with a high CO2 content are thus present at the combustion equipment outlet and they can then be directly sequestered without requiring treatment in a CO2 separation unit. On the other hand, a dedicated oxygen production unit is required.
The present invention is concerned by the latter oxycombustion technique. In fact, this technique affords many advantages:
decreased amount of nitrogen oxide (NOx) formed (in the case of pure O2, and in the absence of nitrogen compounds in the feed),
decreased amount of fumes generated under iso-power conditions,
decreased amount of thermal losses (corresponding to the “useless” heating of the nitrogen through the combustion cycle),
the concentration of the possible pollutants such as nitrogen oxide and sulfur oxide (NOx and SOx) being higher, separation is easier,
most components are condensable by compression and the condensation heat can be advantageously used in the overall process scheme.
There still are many problems to be solved for oxycombustion. In fact, combustion in oxygen (O2) causes markedly higher flame temperatures that can locally reach 2500° C. Generally, under O2, a temperature increase ranging between 30% and 45% of the temperature obtained in air (in ° C.) in an adiabatic configuration is observed with commonly used fuels. This constraint therefore requires specific technologies since such temperatures are not “manageable” in compact chambers with usual designs, whatever the alloys and refractories used.
One of the privileged solutions for reducing these hot spots consists in conducting an advanced burnt gas recirculation so as to dilute and to homogenize the temperature profile around its mean value. This dilution by inert gases and this swirling (the person skilled in the art speaks of entrainment ratio for quantifying the swirling intensity) thus avoid the formation of hot spots responsible for local damage to the walls and/or internals of combustion chambers. The recirculation needs are essentially required for reasons related to NOx formation and thermal efficiency. It can be noted that the recirculation needs are less constraining for combustion in air than for oxycombustion.
On top of being able to act upon the homogeneity of the combustion and of the temperatures, it is necessary to act upon the mean temperature by cooling the chamber so as to be in a temperature range allowing for example to minimize the formation of pollutants while providing good combustion of the feed.
Some patents provide devices attempting to solve these problems posed by oxycombustion.
BACKGROUND OF THE INVENTIONPatent application US-2005/0,239,005 can notably be mentioned. This patent describes a specific burner that highlights the use of recirculation. It is a low NOx burner that can be used in a usual combustion chamber such as atmospheric ovens with a wide space between the burners and the internals (tubes, walls, etc.). This device thus requires specific burners. The fuel and the oxidizer are injected in parallel, which disturbs recirculation and does not allow to provide a combustion distributed over the entire volume of the chamber.
Patent application WO-2004/065,848 relates to a device based on an oval geometry which, although it favours loop recirculation of the fumes so as to dilute the reactants, does not provide very good combustion homogenization. Exchange is achieved with tubes running through the chamber, which may disturb recirculation.
U.S. Pat. No. 7,318,317 describes a turbine burner allowing loop recirculation of combustion gases in order to homogenize the combustion. In this device, the gases circulate only in a loop, which does not allow homogeneous recirculation.
The object of the present invention thus is to overcome one or more of the drawbacks of the prior art by providing a specific and original layout allowing to get round the constraints specific to oxycombustion. The combustion chamber thus has a geometry allowing natural recirculation of the fumes, suited to the constraints of oxycombustion. Furthermore, injection is carried out at various points so as to provide recirculation and dilution of the reactants, which allows to obtain a combustion distributed over the entire volume of the chamber without using dedicated burners.
SUMMARY OF THE INVENTIONThe present invention therefore provides a combustion chamber comprising an enclosure having at least one fuel injection means, at least one oxidizer injection means and at least one combustion fumes withdrawal means, wherein the enclosure has the shape of a bent closed tube of any section, and the fuel and oxidizer injection means are arranged on the enclosure so as to be offset by an angle θ formed by each of the oxidizer and fuel injection positions with respect to the centre of the enclosure, ranging between 10° and 90°, and wherein the oxidizer injection means is a means of injecting an oxidant that is a gas with an oxygen concentration above 90%.
According to an embodiment of the invention, the enclosure has the shape of a tube bent in a closed circle.
In another embodiment of the invention, the enclosure has the shape of a tube bent in an oval.
According to an embodiment of the invention, the section of the tube is circular, oval or polygonal.
In an embodiment of the invention, the section of the tube is triangular.
In the combustion chamber according to the invention, the withdrawal means is arranged within the circle formed by the enclosure so as to achieve low-angle withdrawal.
According to an embodiment of the invention, the fuel injection means consist of at least one injection pipe arranged in the radial plane of the enclosure on the outside thereof.
In an embodiment of the invention, the fuel injection pipe forms an angle of inclination α formed by the longitudinal axis of the pipe and the line passing through the fuel injection point and tangential to the trajectory of the gas circulation after the injection point, said angle α ranging between 5° and 80°.
According to an embodiment of the invention, the fuel injection means consist of at least two low-angle pipes arranged in opposition on the enclosure, a first pipe allowing injection at the top of the enclosure and a second pipe allowing injection at the bottom of the enclosure.
In an embodiment of the invention, the fuel injection pipes form an angle of inclination α′ defined with respect to the longitudinal axis of the pipe and the radial plane of the enclosure, ranging between 5° and 80°.
According to an embodiment of the invention, the oxidizer injection means consist of at least one injection pipe arranged in the radial plane of the enclosure on the outside thereof.
In an embodiment of the invention, the oxidizer injection pipe forms an angle of inclination β formed by the longitudinal axis of the pipe and the line passing through the fuel injection point and tangential to the trajectory of the gas circulation after the injection point, said angle β ranging between 5° and 80°.
According to an embodiment of the invention, the oxidizer injection means consist of at least two low-angle pipes arranged in opposition on the enclosure, a first pipe allowing injection at the top of the enclosure and a second pipe allowing injection at the bottom of the enclosure.
In an embodiment of the invention, the oxidizer injection pipes form an angle of inclination β′ defined with respect to the longitudinal axis of the pipe and the radial plane of the enclosure, ranging between 5° and 80°.
In the combustion chamber according to the invention, the withdrawal means forms an angle γ defined with respect to the longitudinal axis of the withdrawal means and the radius of the circle formed by the enclosure, and oriented in the direction of circulation of the fumes.
According to an embodiment of the invention, angle γ ranges between 20° and 85°.
According to an embodiment of the invention, the tube has a section whose size ranges between 100 mm and 2000 mm.
Other features and advantages of the invention will be clear from reading the description hereafter, with reference to the accompanying figures given by way of example, wherein:
As illustrated in
The enclosure can also be defined as a hollow volume generated by the displacement of any generating surface in the direction of a closed curve representing the locus of its barycenters.
Dimension d of the section of the tube (diameter or side for example) forming the enclosure ranges between 100 mm and 2000 mm.
The walls of the combustion chamber are made of a specific alloy such as Haynes 230©, Kanthal APM©, MA956© or HR120©, or any other material of the same type. Externally, these walls can be coated with materials allowing the reactor to be cooled from the outside. The outlet temperature of the chamber is thus adjusted and the walls are protected from the hot spots generated in the chamber. In cases where the chamber is not cooled by means of a dedicated device, an inner refractorization of the chamber can also be considered. The materials used for refractorization are, for example, ceramics or refractory cements, or any other material of the same type.
The combustion chamber comprises fuel injection means (2) and oxidizer injection means.
When the fuel is liquid, the fuel injection means is a nozzle, and this nozzle is advantageously provided with an internal ensuring mixing of the fuel with a spraying fluid.
When the fuel is a gas, such as natural gas for example, the injection nozzle is a high-velocity nozzle allowing to reach rates preferably above 100 m/s, for example a commercial injection nozzle of RegeMAT© type used by WS.
The present invention is of course not limited to these two types of fuel and it also encompasses the use of solid fuels. In this case, the injection nozzle can consist of a discharge valve wherein said fuel is carried by a fluid such as vapour for example.
The combustion chamber comprises oxidizer injection means (3), said oxidizer being, within the scope of the invention, either a gas with a very high oxygen concentration, usually above 90%, or pure oxygen.
These oxidizer injection means can be an injection nozzle, preferably tubular and made of a refractory material.
Oxidizer injection can be assisted by any means, such as recycled fumes, which affords the advantage of accelerating the oxidizer injection rate while limiting the concentration heterogeneities due to the injection of oxygen.
It is also possible to assist the injection of oxidizer by steam, which allows to reduce the formation of solid unburnt materials such as soot for example.
Typically, the oxidizer is injected with a high impulse, which allows a fast fume circulation to be maintained.
In any case, the injection means are understood to be pipes, i.e. tubes of circular, oval or polygonal shape in the rest of the description.
One of the features of the device according to the invention is that injection and withdrawal are carried out so as to limit the appearance of hot spots. The fuel and the oxidizer are therefore injected separately (thus without premixing) onto the outside axis of the enclosure and the angle of incidence of the pipes allowing injection is optimized so as to avoid any hot gas impact against the walls.
Positioning the injection means also requires considering the pipe location constraints.
For injection of the fuel according to a first variant illustrated in
However, constructing a combustion chamber according to the invention requires welding several elements and, in some cases, it is therefore not possible for injections to be provided exactly on the outside. According to a second variant of the invention, the injection means thus consist of a system of pairs of low-angle pipes (2′, 2″) in opposition with respect to radial plane (P), as illustrated in
These angles α and α′ are constrained by the construction limits and by spray angle (8). Angle α corresponds to the inclination required to compensate for the entrainment and keep a centered injection in the enclosure, it ranges between 5° and 80°, preferably between 15° and 50°. Angle α′ ranges between 5° and 80°.
The nozzles having a very low flexibility on the flow rates and air starting requiring a wide injection amplitude, at least one injection point is specified, but it is possible to claim several ones in series. The number of pipes used is thus adjusted so as to gain in flexibility on the flow rates without drastically modifying the flow rates per nozzle. The number of pipes ranges between 1 and 15, preferably between 2 and 10. Besides, this device improves the fuel distribution, which allows to improve the combustion quality and to avoid formation of hot spots.
For the injection of oxidizer and notably oxygen (or air for starting), pipe (3) used is arranged on the outside of the circle formed by enclosure (1), i.e. in the radial plane of the enclosure and inclined along an angle β to ensure a circulation after mixing that is in line with the enclosure. This angle characterizes the inclination of the pipe and it is defined as the angle formed by longitudinal axis (30) of the pipe and line (31) passing through the injection point and tangential to median circular axis (A) of gas circulation trajectory (4) after the injection point. It ranges between 5° and 80°, preferably between 15° and 45°. In case of setting problems, in the same way as for fuel injection, it is possible to use an injection with 2 pipes arranged in opposition. These pipes are arranged so as to allow injection at the top and at the bottom of the enclosure. In this case, the pipes form each an angle β′ (not shown) defined with respect to the longitudinal axis of the pipe and the radial plane of enclosure (1). This angle has to be minimal to maximize the induced entrainment, it ranges between 5° and 80°.
Angle θ formed by each fuel and oxidizer injection position with the centre of the enclosure, i.e. the angle formed by lines (22, 32) passing through the fuel and oxidizer injection points and centre (C) of the enclosure, must range between 10° and 150°, preferably between 15° and 90°.
In a preferred embodiment of the invention, the richness defined as the quotient of the ratio of the flow rates of fuel/oxidizer in operation and of the fuel/oxidizer ratio under stoichiometric conditions ranges between 0.5 and 3.
The combustion chamber also comprises a means (5) for withdrawing the combustion fumes. This withdrawal means is arranged in a place where it does not disturb the recirculated gas circulation (4). Withdrawal means (5) thus is arranged inside the circle formed by enclosure (1) so as to achieve low-angle withdrawal. Longitudinal axis (51) of the withdrawal pipe therefore forms an angle γ with radius (r) of the circle formed at the outlet point of the withdrawal means. This withdrawal pipe is directed in the direction of circulation of the fumes and angle γ advantageously ranges between 20° and 85°. The withdrawal trajectory thus runs on from fumes circulation (4). The withdrawal pipe has a diameter S ranging between 10 mm and 250 mm.
During operation of the combustion chamber, a large flow of hot combustion fumes circulates and recirculates permanently in the loop of the toroid. In this case, one speaks of internal recycle in contrast with the external recycle techniques (that may also be considered for oxycombustion). This large flow of fumes is sustained by means of high injection rates in the chamber. Consequently, as they enter the chamber, the oxidizer and fuel jets undergo a strong swirl and a high dilution by the fumes. Swirling provides contacting of the reactants under conditions as diluted and as homogeneous as possible, as well as spreading of the reaction zone over the entire chamber. These fumes are sufficiently hot to cause auto-ignition of the reactants.
The fuel is first injected and swirled within the hot fumes. These fumes contain a small proportion of residual oxygen. The route of the mixture, from the fuel injection point to the oxidizer (air or O2) injection, therefore allows the gas to mix, to dilute and to partly react.
The oxidizer is then injected with a high impulse. This impulse allows to sustain fast circulation of the fumes and additional swirling. Combustion continues throughout the travel through the loop.
Part of these fumes is extracted in a zone where the fumes flow is not disturbed.
The temperature and the composition of the fumes are substantially homogeneous in the entire enclosure. This temperature ranges, under nominal operating conditions, between 600° C. and 2000° C., preferably between 800° C. and 1500° C., so as to limit NOx formation linked with possible parasitic air inflows or with the nitrogen of the oxidizer.
The high air/O2 injection rate ranging between 20 m/s and 500 m/s, preferably between 100 m/s and 250 m/s, sustains a high entrainment of the gases present in the combustion chamber. This high recirculation favours swirling and dilution of the species present so as to achieve a combustion as homogeneously distributed as possible in the volume of the chamber.
The consequences of this operation type are as follows:
combustion takes place in two stages
strong swirling is obtained at the injection points
the high circulation rate of the hot fumes spreads the combustion over the entire volume of the toroid and sustains the combustion.
A device that prevents formation of hot spots and provides a volume combustion over the entire combustion chamber is thus achieved.
Furthermore, the combustion being distributed over the entire enclosure and not concentrated in form of a flame at the level of the injection points, the temperature never exceeds 2000° C. and the hot spots are located at the centre of the toroid. The combined effects of wall cooling from the outside, of the absence of direct hot gas impacts and of the combustion homogeneity allow to obtain wall temperatures below 1000° C.
This layout (enclosure geometry, separate injections, central withdrawal) favours recirculation of the combustion fumes and homogeneous combustion over the entire chamber volume.
The imagined concept is besides particularly suited and interesting for low powers. In fact, in this power range, the geometry of the chamber according to the invention allows to ensure good recirculation over a small volume, whereas the use of pure oxygen causes, on usual geometries with low powers, an entrainment that is generally too low. This gas recirculation is attributable to the centrifugal force that minimizes the ratio of the outlet gas flow rate to the recirculated gas flow rate.
Besides, preheating due to the recirculation of the hot fumes allows to widen the operating flexibility and to cover, for example, a wide richness range.
Furthermore, with small geometries, the high surface area-to-volume ratio facilitates the possible cooling of the chamber and therefore the combustion quality control via control of the mean temperature of the chamber.
The possibility of lowering the temperature of the hearth down to relatively low temperatures (unlike air combustion chambers) without stopping the combustion allows to jointly consider, with suitable richnesses, other applications such as partial oxidation, production of hydrogen or of oxygen compounds such as methanol.
It must be clear to the person skilled in the art that the present invention should not be limited to the details given above and that it allows embodiments in many other specific forms without departing from the field of application of the invention. The present embodiments should therefore be considered by way of illustration and they can be modified without however departing from the scope defined by the accompanying claims.
Claims
1) A combustion chamber comprising an enclosure having at least one fuel injection means, at least one oxidizer injection means and at least one combustion fumes withdrawal means, wherein the enclosure has the shape of a bent closed tube of any section, and the fuel and oxidizer injection means are arranged on the enclosure so as to be offset by an angle θ formed by each of the oxidizer and fuel injection positions with respect to centre of the enclosure, ranging between 10° and 90°, and wherein the oxidizer injection means is a means of injecting an oxidant that is a gas with an oxygen concentration above 90%.
2) A combustion chamber as claimed in claim 1, wherein the enclosure has the shape of a tube bent in a closed circle.
3) A combustion chamber as claimed in claim 1, wherein the enclosure has the shape of a tube bent in an oval.
4) A combustion chamber as claimed in claim 1, wherein the section of the tube is circular, oval or polygonal.
5) A combustion chamber as claimed in claim 1, wherein the section of the tube is triangular.
6) A combustion chamber as claimed in claim 1, wherein the withdrawal means is arranged within the circle formed by the enclosure so as to achieve low-angle withdrawal.
7) A combustion chamber as claimed in claim 1, wherein the fuel injection means comprises at least one injection pipe arranged in the radial plane of the enclosure on the outside thereof.
8) A combustion chamber as claimed in claim 7, wherein the fuel injection pipe forms an angle of inclination α formed by a longitudinal axis of the pipe and line passing through the fuel injection point and tangential to median circular axis of gas circulation trajectory after the injection point, said angle α ranging between 5° and 80°.
9) A combustion chamber as claimed in claim 1, wherein the fuel injection means comprises at least two low-angle pipes arranged in opposition on the enclosure, a first pipe allowing injection at the top of the enclosure and a second pipe allowing injection at the bottom of the enclosure.
10) A combustion chamber as claimed in claim 9, wherein the fuel injection pipes form an angle of inclination α′ defined with respect to a longitudinal axis of the pipe and the radial plane of the enclosure, ranging between 5° and 80°.
11) A combustion chamber as claimed in claim 1, wherein the oxidizer injection means comprises at least one injection pipe arranged in the radial plane of the enclosure on the outside thereof.
12) A combustion chamber as claimed in claim 11, wherein the oxidizer injection pipe forms an angle of inclination β formed by a longitudinal axis of the pipe and line passing through the fuel injection point and tangential to median circular axis of gas circulation trajectory after the injection point, said angle β ranging between 5° and 80°.
13) A combustion chamber as claimed in claim 1, wherein the oxidizer injection means comprises at least two low-angle pipes arranged in opposition on the enclosure, a first pipe allowing injection at the top of the enclosure and a second pipe allowing injection at the bottom of the enclosure.
14) A combustion chamber as claimed in claim 13, wherein the oxidizer injection pipes form an angle of inclination β′ defined with respect to the longitudinal axis of the pipe and the radial plane of enclosure, ranging between 5° and 80°.
15) A combustion chamber as claimed in claim 1, wherein the withdrawal means forms an angle γ defined with respect to the longitudinal axis of the withdrawal means and radius of the circle formed by the enclosure, and oriented in the direction of circulation of the fumes.
16) A combustion chamber as claimed in claim 15, wherein angle γ ranges between 20° and 85°.
17) A combustion chamber as claimed in claim 1, wherein the tube has a section whose size ranges between 100 mm and 2000 mm.
Type: Application
Filed: Jul 16, 2009
Publication Date: Aug 4, 2011
Inventors: Jérôme Colin (Versailles), Ali Hoteit (Lyon), Willi Nastoll (Lyon), André Nicolle (Nanterre)
Application Number: 13/058,676
International Classification: F23C 3/00 (20060101); F23C 9/08 (20060101); F23L 7/00 (20060101); F23L 1/00 (20060101);
