EA000250B1 - Flameless combustor - Google Patents

Abstract

1. A flameless combustor for combustion of a fuel and oxidant mixture, the combustor comprising: a combustion chamber (14) in communication with an inlet and with a combustion product outlet (10); and a catalyst surface (20) within the combustion chamber (14) characterized in that the combustor further comprises a mixed fuel and oxidant supply (22) in communication with the inlet; and that the catalyst surface (20) is effective to cause oxidization of an amount of fuel wherein the oxidization of the amount of fuel does not result in a temperature above an uncatalyzed autoignition temperature of the fuel and oxidant mixture. 2. The combustor of Claim 1 wherein the catalyst surface (20) comprises a component selected from the group consisting of noble metals, semi-precious metals, transition metal oxides and mixtures thereof. 3. The combustor of Claim 1 wherein the catalyst surface (20) comprises palladium. 4. The combustor of Claim 1 wherein the catalyst surface (20) comprises platinum. 5. The combustor of Claim 1 further comprising a preheat section (22) wherein in the preheat section (22) heat can be exchanged between the fuel and oxidant mixture and the combustion products. 6. The combustor of any preceding Claim wherein the combustor is designed for heating a subterranean formation by combustion of a fuel and oxidant mixture; the combustion chamber (14) is defined by at least one combustion tubular (4, 10) which is located in a wellbore within the formation to be heated; and the combustor comprises a combustion gas outlet (10) within the wellbore for allowing combustion products to flow to the surface. 7. The combustor of Claim 6 wherein the catalyst surface area (20) is distributed within the combustion chamber (14) to result in an essentially constant temperature within the combustion chamber (14). 8. The combustor of Claim 6 wherein the combustion chamber (14) is defined by one or more tubular pipes (4, 10) placed within the wellbore. 9. The combustor of Claim 6 wherein the combustion gas outlet is an annular space (22) surrounding the combustion tubular (4). 10. The combustor of Claim 6 wherein the combustion gas outlet is a tubular (10) within the combustion chamber (14). 11. The combustor of Claim 6 wherein the combustion chamber (14) comprises an annular volume between a tubular (10) and a casing (4). 12. The combustor of Claim 11 wherein the tubular (10) is a conduit for return of combustion products to a wellhead. 13. The combustor of Claim 6 wherein the tubular (10) is a conduit containing another portion of the combustion chamber (14). 14. The combustor of any preceding Claim wherein the catalyst surface (20) is provided by a catalyst coating which covers at least part of the inner and/or outer surface of a tubular (10) within the combustion chamber (14). 15. The combustor of any preceding Claim wherein the inlet is located at one end of the combustion chamber (14) and the outlet is located at the other end of the combustion chamber. 16. A method of heating a subterranean formation by flameless combustion, the method comprising: installing a combustion tubular (10) which defines a downhole combustion chamber (14) in a wellbore (3) within the formation (1) to be heated and inducing fuel and oxidant to flow along a catalyst surface (20) within the combustion chamber (14); characterized in that the method further comprises feeding a fuel and oxidant mixture to the chamber (14) via an inlet; wherein the catalyst surface (20) is effective to cause oxidization of an amount of fuel at such a rate that the average temperature in the combustion chamber (14) remains below the uncatalyzed autoignition temperature of the fuel and oxidant mixture; and allowing combustion products to flow to the surface via a combustion product outlet conduit (10) within the wellbore (3). 17. The method of Claim 16 wherein the combustion chamber (14) is defined by a lower portion of a well casing (4) and a plug (23) near the bottom of the well casing (4) and the catalyst surface (20) is provided by a catalyst coating on the inner and/or outer surface of a tubular (10) which is co-axially suspended within the well casing (4) such that an axial spacing is maintained between a lower end of the suspended tubular (10) and the plug (23). 18. The method of Claim 17 wherein the suspended tubular (10) is used as a mixed fuel and air inlet conduit and the annular space (22) between the tubular (10) and the well casing (4) is used as a combustion product outlet conduit or vice versa. 19. The method of Claim 16, 17 or 18 wherein the method is used for heating a subterranean oil shale formation (1) of low permeability.

Description

This invention relates to a device of a flameless combustion chamber and method of its ignition.

In US patent No. 4,640,352 and 4,886,118 described conduction heating of low-permeability underground formations containing oil to extract oil from them. Low permeability formations include diatomites, lipids, coal tar sands and bituminous shale. Ways to increase oil recovery, such as steam irrigation, carbon dioxide or fire, are unattractive to low permeability formations. Irrigating materials tend to penetrate formations that have low permeability, preferably through fractures. Injected materials bypass most of the formation hydrocarbons. In contrast to these methods, conduction heating does not require the transfer of fluid into the formation. Therefore, oil inside the formation is not bypassed, as in the irrigation process. When the formation temperature increases by conduction heating, the vertical temperature profiles tend to be relatively uniform, since the formations usually have relatively equal thermal conductivity and specific heat capacity. Transportation of hydrocarbons in a thermoconduction process is carried out through pressure, evaporation and thermal expansion of oil and water trapped in the pores of the formation rock. Hydrocarbons move through small cracks formed by the expansion and evaporation of oil and water.

U.S. Patent No. 5,255,742 describes a flameless combustion chamber for heating subterranean formations using heated gaseous fuel and / or combustion air in which gaseous fuel is connected to combustion air, with gaseous fuel being supplied in increments that are small enough to eliminate the appearance of flame . The creation of NO is almost impossible, and the cost of heaters can be significantly reduced due to the use of less expensive materials of construction. Heating the gaseous fuel in accordance with the method described in this known source can lead to the formation of coke, if CO ₂ , H ₂ or steam is not added to the gaseous fuel. In addition, the launch of a known heater is a rather long process, since the heater must operate at temperatures above the temperature of the non-catalyzed autoignition of the gaseous fuel mixture.

Catalytic combustion chambers are also known. For example, US Pat. No. 3,928,961 describes a device for the catalytic combustion of fuel in which the formation of NO _x is caused by burning at temperatures above the auto-ignition temperatures of the fuel, but below temperatures leading to a significant formation of nitrogen oxides.

In US patent No. 5,355,668 and 4,065,917 described metal surface coated with an oxidation catalyst. These patents suggest catalytic surfaces on gas turbine engine parts. In the aforementioned U.S. Patent No. 4,065,917, it is proposed to use surfaces with a catalytic coating to run the turbine, and also suggests controlling the limited mass transfer phase in the startup operation.

Flameless combustion chamber and method of its ignition in accordance with the restrictive part of the independent claims of formula 1 and 16 of the present invention are known from US patent No. 3,817,332. In the known method, the fuel and the oxidizer are fed into the combustion chamber by means of separate supply pipelines, which in itself is expensive, but it is necessary to exclude the premature combustion of the fuel in the supply pipe.

Therefore, the objective of the present invention is to develop a flameless combustion chamber, in which the fuel and oxidizer can be connected initially, and the distributed combustion is determined by the distribution of catalytic surfaces inside the combustion chamber.

The present invention is also a method and device for flameless combustion, which do not require additives to the flow of gaseous fuel to prevent the formation of coke. The task of another aspect of the present invention is to develop a method and device for burning with minimal production of NO _x .

These and other tasks are carried out by means of a flameless combustion chamber for burning a mixture of fuel and oxidizer, containing:

axial combustion chamber communicating with the inlet device at one end and with the output for the combustion products at the other end;

a source of mixed fuel and oxidizer that communicates with the intake device;

catalytic surface located inside the axial combustion chamber, while the catalytic surface is designed to cause the oxidation of a certain amount of fuel, and the oxidation of this amount of fuel does not lead to a temperature above the temperature of non-catalyzed ignition of the mixture of fuel and oxidizer.

The flameless combustion chamber of the present invention results in minimal formation of nitrogen oxides, since temperatures, which should result from the adiabatic combustion of the fuel-oxidant mixture, are excluded. Other measures to prevent the formation of nitrogen oxides are therefore not required. It is possible to provide a relatively uniform distribution of heat over a large area and large lengths, and due to lower combustion temperatures, relatively inexpensive structural materials can be used for the combustion chamber of the present invention.

Suitable catalytic materials are noble metals, semi-precious metals and oxides of transition metals. Typically, the present invention uses known oxidation catalysts. Mixtures of such metals or oxides of these metals can also be used.

The flameless combustion chamber of the present invention is particularly useful as a heat injector for heating subterranean formations to extract hydrocarbons. The ability to work (operability) and the startup operation of such heat injectors can also be improved by means of catalytic surfaces. The present invention eliminates the need to transport fuels and oxidizers in separate pipelines to the combustion zone in such thermal injectors. This leads to significant cost savings.

According to the invention, a method is also provided for heating a subterranean formation by means of flameless combustion. The method according to the invention includes the following operations:

establish a cylinder (pipe) for combustion, limiting the downward combustion chamber, in the well, drilled in the formation to be heated;

fuel and oxidant are supplied to the chamber through the inlet;

force the mixture of fuel and oxidizer to flow along the catalytic surface inside the combustion chamber, while the catalytic surface can cause effective oxidation of the fuel at a rate at which the average temperature in the combustion chamber remains below the temperature of the non-catalytic self-ignition of the mixture of fuel and oxidizer; and allow the products of combustion to flow to the surface through the channel for the release of products of combustion inside the well.

Preferably, the combustion chamber is bounded by the lower part of the well casing and the stopper near the bottom of the well casing, and the catalytic surface is formed by applying a catalytic coating on the inner and / or outer surface of the cylinder (pipe) coaxially suspended inside the well casing with the formation of an axial gap between the lower end of the suspended cylinder and stopper.

It is also preferred when a suspended cylinder is used as an inlet for mixed fuel and air and an annular gap between the suspended cylinder and the well casing is used as an outlet for combustion products, or vice versa.

These and other features, objectives and advantages of the combustion chamber and the method of the present invention become apparent from the attached drawings, where FIG. 1 depicts a combustion chamber in accordance with the present invention; FIG. 2 is a plot of methane consumption versus temperature in a test device, clearly showing the present invention.

Usually flameless combustion is carried out by heating the combustion air and gaseous fuel, so that when two streams join, the temperature of the mixture exceeds the self-ignition temperature of the mixture, but to a temperature lower than the temperature that should lead to oxidation when mixed, limited only mixing speed. In the absence of a catalytic surface, heating the streams to a temperature in the range from about 815 ° C to about 1260 ° C, followed by interfering the gaseous fuel into the combustion air with relatively small increments will lead to flameless combustion.

With an effective catalytic surface, the temperature at which oxidation reactions occur in the zone affected by the catalytic surface is significantly reduced. Such a reduced temperature is referred to hereinafter as the catalyzed self-ignition temperature. In a turbulent flow, the fluid in the boundary layer in contact with the catalytic surface will oxidize almost quantitatively, but if the bulk temperatures remain below the non-catalyzed auto-ignition temperatures of the mixture, there is almost no oxidation outside the boundary layer. Consequently, the reactions in the temperature range between the catalyzed self-ignition temperature and the non-catalyzed autoignition temperature are reactions with limited mass transfer at a rate that is relatively independent of temperature. This is stated in US Pat. No. 4,065,917. This mechanism of reaction with limited mass transfer is used in the present invention to control the distribution of heat generation inside the combustion chamber in a flameless combustion chamber (in a flameless heater). Heat generation and heat extraction can be balanced so that the average temperature of the mixed oxidant, fuel and combustion products remains between the temperature of the non-catalyzed autoignition.

The heater of the present invention can be controlled by variables such as the ratio of fuel-oxidizer, fuel consumption-oxidizer. Thermal load can be adjusted for each specific application.

An important feature of the flameless chamber of the present invention is that heat is taken along the axis of the combustion chamber so that the temperature is maintained which is significantly lower than the adiabatic burning temperature. This almost eliminates the formation of NO _X oxides and also significantly reduces metallurgical requirements, which ensures the relative cheapness of the combustion chamber.

FIG. 1 shows a combustion chamber located inside a heat-injection well and designed to implement the present invention. The formation 1 to be heated is below the overburden 2. Well 3 passes the overburden down to a position, preferably near the bottom of the formation to be heated. A vertical well is shown, but the well may be inclined or horizontal. Horizontal injection wells can be drilled in formations that crack horizontally to extract hydrocarbons through a process of parallel drifts. Examples of formations in which horizontal heaters may be useful are shallow formations of bituminous shale. Horizontal heaters can also be effectively used in cases where thin layers are to be heated to limit heat losses in the overburden and bedrock. In the embodiment depicted in FIG. 1, the well is hardened with the housing 4. The lower part of the well may be cemented with cement 7 having characteristics suitable for withstanding elevated temperatures and heat transfer. To prevent heat losses from the system for the upper part of the well, cement 8, which is a good heat insulator, is preferred. The pipeline for the burned mixture 10 passes from the wellhead (not shown) to the bottom of the well.

High-temperature cements suitable for cementing the casing and pipelines inside the high-temperature sections of the well are widely known. Examples of such cements are described in US Pat. Nos. 3,507,322 and 3,180,748. An alumina content of greater than about 50% by weight by weight of solid particles in cement slurries is preferred.

In shallow formations, it may be useful to drive the heater with a borer directly into the formation. In the event that a heater is hammered directly into the formation with a borer, cementing the heater in the formation may be unnecessary, but the top of the heater may be cemented to prevent fluid loss to the surface.

The choice of the diameter of the casing 4 in the embodiment of FIG. 1 is an alternative between the high cost of housing and the rate at which heat can be transferred to the formation. Due to the metallurgical requirements, the housing is usually the most expensive component of the injection well. The amount of heat that can be transferred to the formation increases significantly with increasing diameter of the casing. The optimal choice between the initial cost and the ability to transfer heat from the well is usually a case with an inner diameter of from about 10 to about 20 cm.

A cement plug 23 is located at the bottom of the casing, while the cement plug is pressed down to the bottom of the casing during cementing of the casing to displace the cement from the bottom of the casing.

For the formation inside the combustion chamber 14 limited yuny. in which the oxidation reaction temperature is reduced, catalytic surfaces 20 are provided in the combustion chamber 14. The distribution of these catalytic surfaces 20 in the form of coatings that cover at least part of the inner and / or outer surface of the lower part of the pipeline 10 ensures the distribution of heat generation inside the combustion chamber . The catalytic surfaces are sized to achieve close to uniform temperature distribution along the length of the casing. A close to uniform temperature profile inside the casing results in a close to uniform distribution of heat within the formation to be heated. Close to uniform distribution of heat within the formation leads to more efficient use of heat in the process of extracting hydrocarbons by conductive heating. A more uniform temperature profile also results in lower maximum temperatures at the same heat generation. Since the choice of structural materials for the combustion chamber and the well system dictates maximum temperatures, uniform temperature profiles will increase the heat generation possible for the same construction materials.

When the combustion products rise in the well above the heated formation, there is a heat exchange between the combustion air and the gaseous fuel that descends in the respective flow channels and the rising combustion products. This heat exchange not only converts energy, but provides the necessary flameless combustion of the present invention. The gaseous fuel and combustion air when they are moved down in the respective channels are heated sufficiently so that the temperature of the mixture of the two streams at the time of final mixing is higher than the temperature of the catalyzed self-ignition of the mixture, but lower than the temperature of non-catalyzed self-ignition of the mixture. Combustion on the catalytic surface and flameless combustion inside the boundary layers adjacent to the effective catalytic surfaces, leads to the elimination of the flame as a source of heat radiation. Therefore, heat is transferred from the well essentially evenly.

When operating the combustion chamber of the present invention, it is important that heat is removed from the combustion chamber along its length. In the case of applying the present invention to a heat injection well, heat is transferred to the formation around the well. The heater of the present invention can also be used in other applications, such as, for example, to generate steam and as process heaters in the chemical industry and reactors.

The gaseous fuel and combustion air are transported to the bottom of the well through the feed channel for the mixed fuel and oxidant (22), shown as an annular volume surrounding the flue gas channel. Mixed fuel and air react within the volume of the well adjacent to the catalytic surfaces to form combustion products. The combustion products are transferred to the wellhead through the pipeline for the combustion products 10 and out through the exhaust gas duct (not shown) at the wellhead. From the flue gas duct, combustion products can be released into the atmosphere through an exhaust pipe (not shown). Alternatively, the flue gases can be treated to remove pollutants, although nitrogen oxides should not be present and, therefore, there is no need to remove them. It may also be desirable to take additional heat energy from the combustion products through a turboexpander or heat exchanger.

Heating a gaseous fuel to ensure flameless combustion in the absence of a catalyst should lead to significant carbon formation if no decarburizing inhibitor is introduced into the gaseous fuel stream. The need to introduce such a decarburizing inhibitor, therefore, is eliminated due to the operation of the heater at a temperature below the carbon formation temperature. This is another significant advantage of the present invention, since the decarburizing inhibitor increases the volume of gases passing through the heater and, therefore, increases the required dimensions of the channels.

Cold starting the well heater of the present invention can use flame combustion. Initial ignition can be accomplished by injecting a pyrophoric material, an electric igniter, a spark igniter, temporarily lowering the igniter or a resistive electric heater into the well. The combustion chamber, preferably, is quickly brought to a temperature at which flameless combustion is maintained in order to minimize the period of time during which a flame exists inside the well. The heating rate of the combustion chamber is usually limited by thermal gradients permissible for the combustion chamber.

The channel for the combustible mixture can be used as a resistive heater to bring the combustion chamber to operating temperature. In order to use this channel as a resistive heater, an electrical supply wire 15 can be connected to the pipeline 10 for the combustible mixture by means of a clamp 16 or other connecting means near the well below the electrically insulating connection to supply electrical energy. Near the bottom of the well, electrical grounding may be provided with one or more centralizers 17 around conduit 10 for the mixture being burned. The centralizers on the pipeline for the burned mixture above electrically grounded centralizers are electrically insulated. In order for the combustible mixture to be located at the location of the initial catalytic surface, it has a temperature above the temperature of the catalyzed self-ignition, but below the temperature of the non-catalyzed self-ignition, preferably sufficient heat is supplied.

The thickness of the pipeline for the mixture to be burned may vary so that heat is released on a preselected segment along the length of the fuel line. For example, when used as a heat-injection chamber, it may be desirable to heat the lowermost part of the well by means of electricity to ensure ignition of the mixed gas stream at the highest concentration of fuel and to burn the fuel before the flue gases pass up the well. Thin section 21, shown in the pipeline for the combustible mixture, is designed to provide a surface with elevated temperature to start the combustion chamber.

The oxidation temperature of the gaseous fuel / oxidizer mixture is reduced by placing a surface of a noble metal or other effective catalytic surface. The catalytic surface, preferably, is placed either on one of the two surfaces, internal or external, or on the internal and external surfaces of the pipeline 10 for combustion products. Alternatively, the surface or cylinder, or other surface containing noble metal, may be separately placed inside the combustion chamber. In addition, noble metal coated surfaces can also be placed, for example, in an annular channel for combustion products outside the combustion gas pipeline. These additional catalytic surfaces can ensure complete combustion inside the well, in which heat is desired.

The start-up of the flameless combustion chamber of the present invention can be further improved by supplying auxiliary oxidants during the start-up phase or by using fuel having a lower autoignition temperature, such as hydrogen. Preferred auxiliary oxidizing agents include auxiliary oxygen and nitrous oxide. Hydrogen may be supplied along with a stream of natural gas or may be supplied as a carrier gas with the presence of carbon monoxide and carbon dioxide.

Start-up oxidizers and / fuel are preferably used only as long as the combustion chamber is heated to a temperature sufficient to allow working with methane (natural gas) as fuel and air as an oxidizer (i.e. the combustion chamber is heated to higher temperature catalyzed self-ignition of methane in the air).

In US patent No. 5,255,742 described the use of nichrome resistive heater to generate heat in the process of starting a flameless combustion chamber. This electric heater can be used in the implementation of the present invention.

To enhance the oxidation of the fuel at lower temperatures, electroplating, preferably by electrodeposition, of noble metals, such as palladium or platinum, semi-noble metals, non-precious metals or transition metals, may be applied to the surface inside the combustion chamber. If necessary, the metal can then be oxidized to obtain a catalytically active surface. It has been established that such catalytic surfaces are extremely effective for promoting methane oxidation in air at a temperature of about 260 ° C. This reaction quickly takes place on the catalytic surface and in the adjacent boundary layer. The advantage of having a significant catalytic surface inside the combustion chamber is that the temperature range within which the combustion chamber can operate can be significantly extended.

Examples

A thermal reactor was used to determine the temperatures at which oxidation reactions may occur for various combinations of fuels, oxidizers, and catalytic surfaces. The reactor had the appearance of a stainless steel pipe with a diameter of 2.54 cm, covered by an electric heating coil and covered with electrical insulation. To ensure that the temperature can be controlled, thermocouples adjacent to the outer surface of the pipe were placed under insulation. In addition, thermocouples were also placed inside the pipe, namely at the inlet, in the middle and at the outlet. To determine the catalytic activity inside the pipe, experienced tapes of noble metals or strips of stainless steel with a coating of noble metals were suspended. The pipe section heated by means of electricity was injected with air heated to a temperature slightly below the required test temperature. The power supplied to the resistive electric heater was changed until the required temperature of the test section was reached and the steady state was achieved inside the pipe. Then, the fuel was injected into the stream of preheated air through the mixing tee and allowed the stream to flow into the heated section of pipe. To determine the catalytic activity inside the pipe, four eighth of an inch wide (about 0.32 cm) and about sixteen inches long (40 cm) or stainless steel strips of three eighths of an inch (0.95 cm) thickness of about one sixteenth inch (0.16 cm) and a length of about sixteen inches (40 cm) coated with palladium or platinum on one or both sides. When the temperature of the test section containing catalytic coated strips or noble metal tapes was equal to or higher than the catalyzed autoignition temperature, the addition of fuel caused a temperature increase in the middle and at the pipe outlet, as shown by the corresponding thermocouples. Below the catalytic auto-ignition temperature, no such temperature increase was observed. In the absence of catalytic coated strips or noble metal tapes, the test section was heated to the autoignition temperature before a temperature increase was observed. The measured temperatures of the catalyzed self-ignition and non-catalyzed self-ignition are summarized in the table, while

Table

Fuel Measuring temp. self-ignition, ° C Air flow, cm ³ / min Close fuel in air, vol.% Permissible% of air, vol.% Catalyst Natural gas 788 380 10.5 Natural gas 732 380 2.6 N ₂ O / 21 Natural gas 677 380 2.6 O2 / 40 Dimethyl ether 510 380 2.6 Dimethyl ether 316 380 2.6 N ₂ O / 21 H ₂ 659 380 13 H2 49 380 13 Pt 66.6% H ₂ 33.3% with 676 380 13 66.6% H ₂ 33.3% co 213 380 13 Pt 66.6% H ₂ 33.3% co 211 380 13 N ₂ O / 44.7 Pt 66, 6% H ₂ 33.3% co 149 0 13 380 cm ³ / min 100% N ₂ O Pt Methane 310 380 13 - Pd H2 149 380 13 - Pd 66.6% H ₂ 33.3% co 154 380 13 - Pd

From the table it can be seen that the addition of N ₂ O to the fuel flow greatly reduces the measured auto-ignition temperature of the mixtures. In addition, the introduction of hydrogen as a fuel and the presence of a catalytic surface also greatly reduces the dynamic auto-ignition temperature.

To test the results of testing the reactor with a diameter of 2.54 cm, an experimental combustion chamber with a length of 3,048 m was used as a dispersed combustion chamber. A pipe for supplying gaseous fuel with an outer diameter of 2.54 cm was placed inside the furnace tube with an inner diameter of 5.08 cm. fuel injection provided a channel for supplying fuel to the fuel injection hole located near the inlet end of the combustion tube. A furnace pipe with an inner diameter of 5.08 cm was placed inside an insulated pipe, while thermocouples were placed along the length of the fuel supply pipe. Used two flue pipes. One furnace tube was made of HAYNES 120 alloy. Electroplated coating of palladium to an average thickness of 0.00-0254 cm was applied to one side of the strip. Then the strip was shaped, wedged and welded to a 3.048 m long pipe with a palladium coating on the inner surface . The second flue pipe was a standard pipe with a diameter of 7.62 cm of HAYNES 120 alloy. To supply combustible gases to the flue pipe, the long-term temperature of catalyzed or non-catalyzed self-ignition is indicated in it as the measured auto-ignition temperature.

A MAXON burner was used at 3.048 m, and various amounts of air and / or other additives were mixed with the exhaust gases from the MAXON burner in the mixing compartment between the burner and the combustion tube. To maintain the same temperature inside the furnace tube, along the length of the furnace tube, three electric heaters were placed, each of which had its own regulator.

A series of tests was carried out, one of which was carried out with a palladium-coated furnace tube, and the other with a palladium-free furnace tube. The gaseous fuel was injected through the injection hole of the gaseous fuel at a speed of about 0.635 m ³ / h, measured at a temperature of 15.5 ° C and atmospheric pressure; moreover, the air was injected at a flow rate measured under the same conditions of about 374 m ³ / h, while the air included the air for the burner and auxiliary air. To achieve the desired temperature at the inlet of the combustion tube, a sufficient amount of gaseous fuel was supplied to the burner. The percentage of injected and burnt methane as a function of the inlet temperature of the furnace tube is shown in FIG. 2 as line A for the catalyzed configuration and as line B for the non-catalyzed configuration. From figure 2 it can be seen that the lowest temperature at which the combustion chamber can work is a temperature of about 260 ° C, while 55% of methane was oxidized by means of a palladium-coated pipe. The lowest operating temperature may be slightly lower than 260 ° C, but the existing equipment cannot operate at a lower temperature. When using a furnace pipe without a palladium coating, some methane oxidation occurred at a temperature of about 704 ° C, while the rapid oxidation of methane occurred at temperatures of about 816 ° C. At temperatures of 871 ° C and above, the presence of a palladium surface is ineffective, because methane is rapidly and completely oxidized, both with and without a palladium surface.

Independence of methane oxidation on temperature at temperatures below 704 ° C can confirm that methane inside the boundary layer near the surface of the palladium surface oxidizes rapidly and that methane transfer to this boundary layer, rather than dynamics, determines the degree to which methane is oxidized. At temperatures around 704 ° C and higher, thermal oxidation becomes prevalent, and the temperature dependence is due to this thermal oxidation.

Claims (19)

CLAIM 1. Flameless combustion chamber for burning a mixture of fuel and oxidant containing the combustion chamber (14), communicating with the inlet device and output for combustion products (10); and a catalytic surface (20) inside the combustion chamber, characterized in that it further comprises a source of mixed fuel and oxidant (22) communicating with the inlet device; and the catalytic surface (20) is intended to cause oxidation of that amount of fuel that does not lead to a temperature above the temperature of the non-catalyzed self-ignition of the mixture of fuel and oxidizer. 2. Flameless combustion chamber at π. 1, characterized in that the catalytic surface (20) contains a component selected from the group including noble metals, semi-precious metals, oxides of transition metals, and mixtures thereof. 3. Flameless combustion chamber at π. 1, characterized in that the catalytic surface contains palladium. 4. Flameless combustion chamber at π. 1, characterized in that the catalytic surface contains platinum. 5. Flameless combustion chamber at π. 1, characterized in that it further comprises a heating section (22), in which heat exchange can occur between the mixture of fuel and oxidant and the combustion products. 6. Flameless combustion chamber according to any one of the preceding paragraphs, characterized in that it is intended for heating the underground formation by burning a mixture of fuel and oxidant, while the combustion chamber (14) is limited to at least one combustion tube (4, 10), located in the well inside the formation to be heated; and the combustion chamber contains output (10) for the combustion products located inside the well to allow the combustion products to flow to the surface. 7. Flameless combustion chamber according to claim 6, characterized in that the catalytic surface area (20) is dispersed within the combustion chamber (14) to achieve a substantially constant temperature inside the combustion chamber (14). 8. Flameless combustion chamber according to claim 6, characterized in that the combustion chamber (14) is limited to one or more pipes (4, 10) located inside the well. 9. Flameless combustion chamber according to claim 6, characterized in that the outlet for the combustion products is an annular space (22) surrounding the combustion tube (4). 10. Flameless combustion chamber according to claim 6, characterized in that the outlet for the products of combustion is a pipe (10) located inside the combustion chamber (14). 11. Flameless combustion chamber according to claim 6, characterized in that the combustion chamber (14) is an annular volume between the pipe (10) and the casing (4). 12. Flameless combustion chamber according to and. 11, characterized in that the pipe (10) is a channel for the return of combustion products to the wellhead. 13. Flameless combustion chamber according to and. 10, characterized in that the pipe (10) is a channel that includes another part of the combustion chamber (14). 14. Flameless combustion chamber according to any one of the preceding paragraphs, characterized in that the catalytic surface (20) is made in the form of a coating on at least part of the inner and / or outer surface of the pipe (10) inside the combustion chamber (14). 15. Flameless combustion chamber according to any one of the preceding paragraphs, characterized in that the inlet device is located at one end of the combustion chamber (14) and the outlet is located at the other end of the combustion chamber. 16. A method of warming up a subterranean formation by means of flameless combustion, including the installation of a flue pipe (10) limiting the downward combustion chamber (14) in the well (3) inside the formation (1) to be heated, and ensuring the forced flow of fuel and oxidizer along the catalytic surface ( 20) inside the combustion chamber (14), characterized in that they carry out an additional supply of the mixture of fuel and oxide 15 into the chamber (14) through the inlet device; in which the catalytic surface (20) is designed to cause the effective oxidation of a certain amount of fuel at a rate at which the average temperature in the combustion chamber (14) remains below the temperature of the non-catalyzed self-ignition of the mixture of fuel and oxidant; and provide a flow of combustion products to the surface through the outlet channel (10) inside the well (3). 17. The method according to p. 16, characterized in that use the combustion chamber (14), which is limited to the lower part of the casing of the well (4) and stopper (23) near the bottom of the casing of the well (4), and the catalytic surface (20) is made in the form a catalytic coating on the inner and / or outer surface of the pipe (10) suspended coaxially inside the well casing (4) with the formation of an axial gap between the lower end of the suspended pipe (10) and the stopper (23). 18. The method according to p. 17, characterized in that the suspended pipe (10) is used as the inlet channel for the mixed fuel and air and the annular gap (22) between the pipe (10) and the well casing (4) is used as the exhaust channel for combustion products, or vice versa. 19. A method according to any one of claims 16, 17 or 18, characterized in that formations of bituminous shale (1) with low permeability are used as a formation for heating.