KR19990076855A - Salt-Free Combustor - Google Patents

Abstract

A flameless combustor eliminates the flamme as a radiant heat source, which results in a more even temperature distribution throughout the length of the burner. Flameless combustion is accomplished by preheating the fuel and the combustion air to a temperature above the autoignition temperature of the mixture. The present invention lowers the autoignition temperature by placing a catalytic surface within the desired combustion chamber. Temperatures are maintained above the catalyzed autoignition temperature but less than the noncatalyzed autoignition temperatures for noncatalyzed reaction. Thus, the amount and location of reaction can be controlled by varying the amount and distribution of catalyst within the burner. Removing heat from the combustion chamber in amounts that correspond to the oxidation of fuel within different segments of the combustion chamber can result in low temperatures and relatively even distribution of heat from the burner.

Description

Salt-Free Combustor

The present invention relates to a combustion apparatus and method.

U.S. Patent Nos. 4,640,352 and 4,886,118 show conductive heating of low permeability underground formations containing oil to recover oil. Low permeability formations include diatomaceous earth, geological coal, tar sands, and shale containing. Low permeability formations are not suitable for improved oil recovery methods such as steam, carbon dioxide, or fire flooding. Flooding material tends to penetrate formations that are preferentially low permeable through the cracks. In contrast, conductive heating does not need to transport the fluid to the formation. Thus, the oil in the formation is not bypassed as in the flooding process. When the temperature of the formation is increased by conduction heating, the vertical temperature gradient tends to be relatively uniform because the formation usually has a relatively uniform thermal conductivity and specific heat. The transport of hydrocarbons during the thermal conduction process is due to the pressure drive, evaporation, and thermal expansion of the oil and water present in the absorption holes of the resulting rock. Hydrocarbons travel through small stresses created by thermal stress and by the expansion and evaporation of oil and water.

U. S. Patent No. 5,255, 742 discloses a salt free combustor useful for heating underground formations utilizing preheated fuel gas and / or combustion air mixed with combustion air to increase the fuel gas slightly enough without flame. The generation of NO _x is almost eliminated, and the cost of the heater can be sufficiently reduced by using the material as a cheap material. Preheating the fuel gas according to the method described in the prior art literature may result in the formation of coke if no CO ₂ , H ₂ , or steam is added to the fuel gas. It is also a time consuming method to start a known heater since it must work at a temperature above the noncatalytic autoignition temperature of the fuel gas mixture.

Catalytic combustors are also known. For example, US Pat. No. 3,928,961 discloses a catalytically supported thermal combustion apparatus in which the production of NO _x is removed by combustion above the autoignition temperature of the fuel but substantially below the temperature that produces oxides of nitrogen.

Metal surfaces coated with oxidation catalysts are disclosed, for example, in US Pat. Nos. 5,355,668 and 4,065,917. The patent proposes a catalyst coated surface on the components of a gas turbine engine. U.S. Patent No. 4,065,917 proposes the use of a catalyst coated surface to start a turbine and suggests a mass transfer control restriction phase of a start-up operation.

It is therefore an object of the present invention to provide a combustion method and apparatus which is salt free and prevents the formation of coke without the need for additives in the fuel gas stream. In another aspect of the present invention, there is provided a combustion method and apparatus that minimizes the production of NO _x . It is also an object of the present invention to provide a combustion distribution determined by the distribution of catalyst surfaces in a flameless combustion chamber and a combustion chamber in which fuel and oxidant can be initially mixed.

This and other objects are achieved by a flameless combustor for the combustion of fuel and oxidant compositions comprising:

Combustion chamber connected to the inlet and the combustion product outlet;

Supply of mixed fuel and oxidant connected to the inlet; And

In the combustion chamber the catalyst surface causes the oxidation of a certain amount of fuel and the oxidation of the amount of fuel does not exceed a temperature beyond the uncatalyzed autoignition temperature of the fuel and oxidant mixture.

The saltless combustor of the present invention minimizes the production of nitrogen oxides because the temperature due to adiabatic combustion of the fuel-oxidant mixture is avoided. No other measurement is therefore necessary to remove or prevent nitrogen oxides. The relatively large area and even heat distribution over a long distance are possible, and the reason why a relatively cheap material can be used for the combustor of the present invention is because of the low combustion temperature.

Acceptable catalytic materials include noble metals, semi-noble metals, and transition metal oxides. In general, known oxidation catalysts are useful in the present invention. Mixtures of such metals or metal oxides may also be useful.

Salt-free combustors of the present invention are particularly useful as heat injectors for heating underground formations for the recovery of hydrocarbons. The catalyst surface also improves the operability and start-up operation of the heat injector. The present invention eliminates the need to move fuel and oxidant in separate conduits in the combustion zone within the heat injector. The result is very cost savings.

According to the invention there is also provided a method of heating underground formations by means of a salt free combustor. The method according to the invention comprises:

Installing a combustion tube defined as a downhole combustion chamber in a wellbore in the formation to be heated;

Supplying fuel and oxidant through the inlet to the room;

Introducing a fuel and oxidant mixture to flow along the surface of the catalyst in the combustion chamber, which causes oxidation of the desired amount of fuel at a rate such that the average temperature in the combustion chamber is below the uncatalyzed autoignition temperature of the fuel and oxidant mixture. ; And

The combustion product flows to the surface via the combustion product outlet conduit in the well bore.

Preferably the combustion chamber is defined as a plug near the bottom and bottom of the well casing and the catalyst surface is provided by catalyst coating on the inner and / or outer surface of the tube coaxially suspended in the well casing so that the axial space is suspended. Keep between the lower end of the tube and plug.

Also preferably a suspension tube may be used as the mixed fuel and air inlet conduit and an annular space between the suspension tube and the well casing or vice versa as the combustion product outlet conduit.

These and other features, objects and advantages of the combustor and method according to the invention will become apparent from the accompanying drawings:

1 shows a combustor according to the invention; And

2 is a plot of methane consumption versus temperature in a test apparatus illustrating the present invention.

Generally, unsalted combustion exceeds the spontaneous ignition temperature of the fuel gas mixture when the two streams are mixed at the temperature of the mixture of air and fuel gas, but as a result the combustion air is sufficiently below the temperature at which the mixing is limited by the mixing rate during oxidation. And by preheating the fuel gas. Without the catalyst surface, preheating the stream from about 815 ° C. to about 1260 ° C. and then mixing of fuel gas into the combustion air, which increases relatively small, will occur in the salt free combustor.

Since an effective catalyst surface is present, the temperature during the oxidation reaction occurring in the zones affected by the catalyst surface is very low. This lowered temperature is referred to below as the catalyzed spontaneous firing temperature. In the tube flow, the fluid in the boundary layer in contact with the catalyst surface will oxidize almost quantitatively, but if the bulk temperature remains below the uncatalyzed autoignition temperature of the mixture, the outside of the boundary layer will hardly oxidize. Thus, in the temperature range between the catalyzed autoignition temperature and the uncatalyzed autoignition temperature, the reaction is limited mass transfer at a relatively temperature independent rate. This is proposed in literature such as US Pat. No. 4,065,917. The mass transfer with limited reaction mechanism is utilized in the present invention to control the distribution of heat generation in the combustion chamber of the salt free combustor. Balancing heat generation and heat removal, the average stream temperature of the mixed oxidant, fuel and combustion products is between the catalyzed autoignition temperature and the uncatalyzed autoignition temperature.

The heater of the present invention can be adjusted by variations such as fuel-oxidant ratio, fuel-oxidant flow rate. Depending on the particular application, heat addition can be performed to adjust.

The main feature of the salt-free combustor of the present invention is to remove heat along the axis of the combustion chamber to keep the temperature well below the adiabatic combustion temperature. This virtually eliminates the production of NO _x s and also greatly reduces the need for metallurgy due to the relatively inexpensive combustor.

Referring to FIG. 1, a combustor is shown in a heat injector well capable of carrying out the invention. The formation 1 to be heated is under the cladding 2. The well bore 3 extends through the shell coal to a position near the bottom of the formation, preferably to be heated. Vertical wells appear, but wellbore can be slanted or horizontal. Horizontal heat injector wells may be provided horizontally to the debris formation to recover hydrocarbons by the equilibrium dry method. Shallow oil formations are examples of formations when horizontal heaters are useful. Horizontal heaters can also be used effectively when the thin layer is heated to limit heat loss to the coal and base rock. In the embodiment shown in FIG. 1, the wellbore can be cast with a casing 4 and the bottom of the wellbore can be joined with cement 7 having characteristics suitable for maintaining high temperature and transferring heat. Cement 8, which is a good thermal insulator, is preferred for the top of the well bore to prevent heat loss from the system. The combustion mixture conduit 10 extends from the wellhead (if squeezed) to the bottom of the well bore.

Hot cement suitable for joining casings and conduits in the hot portion of the wellbore is useful. Examples are disclosed in US Pat. Nos. 3,507,332 and 3,180,748. Alumina content of greater than about 50% by weight of cement slurry solids substrates is preferred.

In the shallow formation, it is advantageous to use a hammer-drill heater directly in the formation. When hammer-drilling the heater directly into the formation, the joining of the heater in the formation is not necessary, but the top of the heater can be joined to prevent fluid loss on the surface.

The diameter selection of the casing 4 in the embodiment of FIG. 1 selects between the cost of the casing and the speed of heat that can be transferred to the formation. Due to the need for metallurgy, the casing is generally the most expensive component of the injection well. The heat that can be transferred to the formation increases greatly as the casing diameter increases. Casings with an inner diameter of about 10 to about 20 cm can typically transfer heat from the wellbore with an optimal choice between initial cost and capacity.

The cement plug 23 is at the bottom of the casing and the cement plug is sent down the casing during the joining operation to bring cement out of the bottom of the casing.

The catalyst surface 20 is provided in the combustion chamber 14 which provides a limited zone where the oxidation reaction temperature is low. As a coating covering at least a portion of the inner and / or outer surface of the lower part of the conduit 10, a distribution of the catalyst surface 20 is provided for dissipating heat into the combustion chamber. The catalyst surface is measured to achieve an almost even temperature that is distributed along the casing. A nearly even temperature profile in the casing results in more uniform heat distribution in the formation to be heated. The heat is distributed almost uniformly in the formation to utilize the heat more efficiently in the conduction heating hydrocarbon recovery method. In addition, the more uniform the temperature profile, the lower the maximum temperature for the same heat dissipation. Since the material of the burner and well system components defines the maximum temperature, an even temperature profile will increase the possible heat dissipation for the same material of the composition.

As the combustion product rises in the wellbore over the formation to be heated, heat is lowered below the flow conduit and the rising combustion product to exchange between the combustion air and the fuel gas. The heat exchange enables not only energy conservation but also the desired salt free combustor of the present invention. Preheat fuel gas and combustion air as the mixture of two streams, at temperatures above the catalyzed autoignition temperature of the mixture at the final mixing point, but below the uncatalyzed autoignition temperature, sufficiently migrates under each flow conduit. . Combustion is carried out on the catalyst surface and in the flameless combustor in the boundary layer in proximity to the effective catalyst surface, thus avoiding flame as a radiant heat source. Thus, heat is transferred from the well bore to essentially constant temperature.

In the operation of the combustor of the invention it is important to remove heat from the combustion chamber along the length of the combustor. In the application of the present invention to a wellbore heat injector, heat is transferred to the formation around the wellbore. The heaters of the present invention can also be used for other applications, such as for steam generators and chemical industry process heaters and reactors.

Fuel gas and combustion air are delivered to the bottom of the wellbore through a supply of mixed fuel and oxidant, represented as an annular volume surrounding the conduit. The mixed fuel and air react in a wellbore volume adjacent to the catalyst surface forming the combustion product. Combustion product rises above the well bore and exits the outlet (when squeezed) at the wellhead through the combustion product conduit 10. From the outlet, the combustion products can exit the atmosphere through the exhaust stack (if not in sight). Alternatively, the combustion gases are treated and removed, even though there is no nitrogen oxide and therefore need not be removed. Additional energy recovery from the combustion products by expansion turbines or heat exchangers is also preferred.

Pre-heating the fuel gas to conduct salt-free combustion without catalyst results in very high carbon unless the carbon former inhibitor is included in the fuel gas stream. Thus, it is not necessary to provide the carbon former inhibitor by operating the heater at a temperature below the carbon formation temperature. This is another important advantage of the present invention as the size of the conduit required increases as the volume of gas passed through the heater by the carbon inhibitor increases.

Cold start of the well heater of the present invention utilizes combustion as flame. Initial ignition can be achieved by injecting a pyrophoric material, an electrolyzer, a spark igniter, a temporarily low igniter into a wellbore, an electric heater. The burner is preferably brought to a temperature rapidly maintaining flameless combustion to minimize the time that flames are present in the wellbore. The rate of heating the burner is typically limited by the thermal gradient that the burner can withstand.

The combustion mixture conduit is used as heater resistance to raise the combustor to operating temperature. To use the conduit as heater resistance, electrical lead 15 is connected to other connectors in the combustion mixture conduit 10 near the wellhead under the clamp 16 or electrically insulated connectors to supply electrical energy. An electrical ground can be installed near the bottom of the borehole with one or more electrically conductive central concentrators 17 around the combustion mixture conduit 10. The medium pressure concentrator on the combustion mixture conduit above the electrical ground medium pressure concentrator is an electrically insulated central concentrator. Preferably at a temperature above the catalyzed autoignition temperature but below the uncatalyzed autoignition temperature, sufficient heat is applied to the location of the initial catalyst surface to result in the combustion mixture.

Varying the thickness of the combustion mixture conduit results in heat dissipation in a preselected section of the length of the fuel conduit. For example, in well heat injector applications, electrical heat is preferably applied to the bottom of the well bore to ignite the mixed gas stream with the highest concentration of fuel and burn the fuel before the exhaust gas flows back through the well bore. The thin section 21 provides a hot surface for initiation of the combustor in the combustion mixture conduit.

The oxidation reaction temperature of the fuel gas-oxidation mixture is lowered by providing a precious metal surface or other effective catalyst surface. The catalyst surface is preferably provided on the inside, outside or both inside and outside surfaces of the combustion product conduit 10. Alternatively, the surface, or a tube or other precious metal comprising the surface, may be placed separately in the combustor. Other surface coated precious metals may be provided, for example, outside the combustion product annulus of the flue gas conduit. The additional catalyst surface allows for complete combustion in the well bore when heat is desired to be generated.

The initiation of the saltless combustor of the present invention can be enhanced by supplying supplemental oxidants during the initiation phase or by the use of fuels with low autoignition temperatures such as hydrogen. Preferably the supplemental oxidant comprises supplemental oxygen and nitrogen oxides. Hydrogen may be provided along the natural gas stream and may be provided as a removal gas in which carbon monoxide and carbon dioxide are present.

The initiation of the oxidant and / or fuel is preferably heated only to a temperature sufficient for the combustor to operate as methane (natural gas) as fuel and as air as oxidant (eg, the combustor catalyzed spontaneous combustion of methane in air). Heated to a temperature above the temperature).

US Pat. No. 5,255,742 discloses generating heat for the start of a salt free combustor using an electrical resistive nichrome heater. The electric heater can be used in practice of the present invention.

Precious metals, such as palladium or platinum, transition metals, semi-precious metals, base metals or transition metals, may preferably be coated by coating on the surface in the combustion chamber to improve oxidation of the fuel at low temperatures. The metal is then oxidized as needed to provide a catalytically effective surface. The catalyst surface was found to be very effective at promoting oxidation of methane in air at temperatures as low as 260 ° C. The reaction occurs rapidly on the catalyst surface and near the boundary layer. The advantage of having a large catalyst surface in the combustion chamber is that it can greatly increase the temperature range in a salt free combustor that can be operated.

The thermal reactor was used to evaluate the temperature at which the oxidation reaction occurred with various mixtures of fuel, oxidant and catalyst surface. The reactor was a 2.54 cm stainless steel pipe wrapped in an electrical resistance heating coil and covered with insulators. A temperature control thermometer was placed under the insulator adjacent to the outer surface of the pipe. Thermometers were also installed inside the pipe at the inlet, middle and outlet. The catalytic activity was tested by hanging a piece of precious metal or stainless steel with a precious metal coating on a pipe. Air preheated to a temperature below the target temperature for this test was injected into the electrically heated test compartment of the pipe. The power in the electric resistance heater was varied until the desired temperature was obtained in the test compartment to achieve a steady state measured by a thermometer protruding inside the pipe. The fuel was then injected through a mixed T tube into a stream of preheated air and flowed into an electrically heated test compartment. Four platinum ribbons 1/8 inch wide and about 16 inches long, coated on both sides with platinum or platinum, or stainless steel pieces 3/8 inch wide and about 1/16 inch thick and about 16 inches long The catalytic activity is tested. When the test compartment contained a catalyst coated piece or ribbon of precious metal and was at or above the catalyzed autoignition temperature, the addition of fuel caused a temperature increase at the internal intermediate and external thermometers. The temperature was not observed below the catalyzed autoignition temperature. When no catalyst coated piece or precious metal ribbon was present, the test compartment had to be heated to the autoignition temperature of the fuel before an increase in temperature was observed. The measured non-catalyzed and catalyzed autoignition temperatures are summarized in Table 1 together with the measured non-catalyzed or catalyzed autoignition temperatures referred to as the measured autoignition temperatures.

fuel Measured autoignition temperature ℃ Air flow rate CC / min Fuel concentration% in air volume% Volume in air% ACCEL% catalyst Natural gas 788 380 10.5 Natural gas 732 380 2.6 N ₂ O / 21 Natural gas 677 380 2.6 O _2/40 Dimethyl Ethet 510 380 2.6 Dimethyl ether 316 380 2.6 N ₂ O / 21 H ₂ 659 380 13 H ₂ 49 380 13 Pt 66.6% H ₂ 33.3% CO 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 380CC / min 100% N ₂ O Pt methane 310 380 13 - Pd H ₂ 149 380 13 - Pd 66.6% H ₂ 33.3% CO 154 380 13 - Pd

From the table it was found that adding N ₂ O to the fuel stream greatly reduced the measured autoignition temperature of the mixture. In addition, including hydrogen as fuel and the presence of the catalyst surface reduces the dynamic autoignition temperature.

Test the results of a 2.54 cm reactor in a distributed combustor application using a 3.048 m length test combustor. A 2.54 cm outer diameter fuel gas line is installed in a 5.08 cm inner combustion line. Fuel injection lines are installed to allow fuel to flow from the conduit to the fuel injection port located near the inlet end of the combustion line. Place the 5.08 cm internal combustion line in the insulated pipe and the thermometer along the fuel supply line. Use two different combustion lines. One combustion line is made from the "HAYNES 120" alloy piece. An electric brush plated on one side with palladium with an average thickness of 0.000254 cm is applied. The pieces are then brake formed, swedge and welded to a length of 3.048 m with a palladium coating on the inner surface. Another combustion line is a standard 7.62 cm pipe of the "HAYNES 120" alloy. A "MAXON" brush is used to feed the combustion gas to the 3.048 m long combustion pipe, varying the amount of air and / or other additives and mixing with the discharge from the "MAXON" burner in the mixing section between the burner and the combustion line. Combustion Lines In order to maintain a uniform temperature, three electric heaters, each with its own regulator, are placed along the outside and the length of the combustion line.

A series of tests are made with a heater with a palladium coated combustion line and a heater with a non-palladium coated combustion line. Fuel gas is injected through the fuel gas inlet when measured at about 0.635 m ³ / hour, a temperature of 15.5 ° C. and at atmospheric pressure, and at a rate of about 374 m ³ / hour of air containing burner air and secondary air do. Abundant fuel gas is supplied to the burner to provide the target temperature at the inlet of the fuel line. The percentage of combusted injected methane is shown as a function of the combustion line inlet temperature in FIG. 2 for the catalyzed arrangement (line A) and the uncatalyzed arrangement (line B). It can be seen from FIG. 2 that the lowest temperature of the instrument that can be operated is about 260 ° C. and oxidizes 55% of methane with a palladium coated combustion line. The minimum temperature of operation may be below 260 ° C, but the device is not useful at the lowest temperature. When using a combustion line without palladium coating, some oxidation of methane occurs at about 704 ° C., and oxidation of methane occurs rapidly at a temperature of about 816 ° C. At temperatures above 871 ° C., the presence of a palladium surface is not affected since the oxidation of methane occurs rapidly and completely with or without a palladium surface.

The temperature independence of oxidized methane below 704 ° C. has been demonstrated to indicate the extent to which methane is rapidly oxidized in the boundary layer at the surface of the palladium surface, and that the methane is oxidized by the movement of methane in the boundary layer, not kinetics. There is a tendency. At temperatures above about 704 ° C., thermal oxidation prevails and is temperature dependent due to the thermal oxidation.

Claims (19)

Combustion chamber connected to the inlet and the combustion product outlet; Mixed fuel and oxidant feeds connected to the inlet; And The catalyst surface results in the oxidation of a predetermined amount of fuel and the oxidation of the predetermined amount of fuel does not exceed a temperature above the uncatalyzed autoignition temperature of the fuel and oxidant mixture. The flameless combustor of claim 1, wherein the catalyst surface comprises a component selected from the group consisting of noble metals, semi-noble metals, transition metal oxides and mixtures thereof. The flameless combustor of claim 1, wherein the catalyst surface comprises palladium. The flameless combustor of claim 1, wherein the catalyst surface comprises platinum. The flameless combustor of claim 1, further comprising a preheating compartment in which heat is exchanged between the fuel and oxidant mixture and the combustion product in the preheating compartment. 6. The combustor of claim 1, wherein the combustor is designed to heat underground formations by combusting a fuel and oxidant mixture, wherein the combustion chamber is defined by one or more combustion tubes located in wellbore in the formations to be heated. 7. Salt-free combustor made with. 7. The flameless combustor of claim 6, wherein the catalyst surface area is distributed in the combustion chamber such that the temperature in the combustion chamber is essentially constant. The flameless combustor of claim 6, wherein the combustion chamber is defined by one or more tubular pipes located within the well bore. 7. The flameless combustor of claim 6, further comprising a combustion gas outlet that is an annular space surrounding the combustion tube. The flameless combustor according to claim 6, further comprising a combustion gas outlet that is a pipe in the combustion chamber. 7. The flameless combustor of claim 6, wherein the combustion chamber comprises an annular volume between the tube and the casing. 12. The flameless combustor of claim 11, wherein the tube is a conduit for returning combustion products to the wellhead. 7. The flameless combustor of claim 6, wherein the tube is a conduit comprising another portion of the combustion chamber. The flameless combustor according to any one of the preceding claims, wherein the catalyst surface is provided by a catalyst coating covering at least one portion of the inner and / or outer surface of the tube in the combustion chamber. The flameless combustor according to claim 1, wherein the inlet is at one end of the combustion chamber and the outlet is at the other end of the combustion chamber. Installing a combustion tube defined as a downhole combustion chamber in a well bore inside the formation to be heated; Supply fuel and oxidant to the chamber via an inlet; Introducing a fuel and oxidant mixture to flow along the catalyst surface in the combustion chamber, where the catalyst surface causes oxidation of the amount of fuel at a rate such that the combustion chamber is maintained below the uncatalyzed autoignition temperature of the fuel and oxidant mixture; Flowing the combustion product to the surface via the combustion product outlet conduit in the well bore. 17. The combustion chamber of claim 16, wherein the combustion chamber is defined as the well casing and the bottom of the plug near the bottom of the well casing and the catalyst surface is provided by a catalyst coating on the inner and / or outer surface of the suspension tube coaxially suspended in the well casing. A combustor characterized in that an axial space is maintained between the suspension tube and the lower end of the plug. 18. The method of claim 17, wherein the suspension tube is used as the mixed fuel and air inlet conduit and the annular space between the tube and the well casing is used as the reverse combustion product outlet conduit. 19. The method of any of claims 16-18, wherein the method is used to heat a low permeability underground oil shale formation.