KR100261783B1 - Multistage process for combustion fuel mixtures - Google Patents

Abstract

This invention is a combustion process having a series of stages in which a fuel/oxygen-gas-containing mixture (16, 18) is combusted stepwise using a series of specific catalysts and catalytic structures (figure 2) and, optionally, a final homogeneous combustion zone to produce a combusted gas at a selected temperature preferably between 1050 DEG and 1700 DEG C. Depending upon the pressure of operation, there may be two or three discrete catalytic stages (stages 1, 2 and 3). The choice of catalysts and the use of specific structures, including those employing integral heat exchange (44) results in a catalyst and its support which are stable due to their comparatively low temperature, do not deteriorate, and yet the product combustion gas is at a temperature suitable for use in a gas turbine, furnace, boiler, or the like, but has low NOx content. Neither fuel nor air is added to the combustion process except in the initial stage.

Description

Multistage process for fuel mixture combustion

Graph showing the relationship between homogeneous combustion temperature and palladium temperature of the first or pressure.

Close-up partial cross-sectional view of the walls of catalyst structures having catalysts 2a and b or only one side thereof.

3a, b, c degrees, 4a, b degrees, 5 degrees, 6a and b or all show variations of the integral heat exchange catalyst structure that can be used in the catalytic step of the present invention process.

Schematic diagram of the three stage catalytic test reactor used in the seventh or example.

8 and 9 or graph showing various operating temperatures as a function of preheating temperature.

A graph showing various operating temperatures during the tenth or long term steady state test.

A graph showing various operating temperatures during the eleventh or typical start-up procedure.

The present application discloses U.S. Application Nos. 07 / 617,976 to Tsurumi, Ezawa, and Dalla Betta, entitled “Combustible Mixture Combustion Process” (PA-0041); US application 617,977 to Dalabeta, Tsurumi, Ezawa, entitled "Multistage Process for Combustion of Fuel Mixes" (PA-0004); US Application No. 617,980 to Dalabeta, Tsurumi, Ezawa, entitled "Multistage Process for Combustion of Fuel Mixes Using Oxide Catalysts at High Temperature Stages" (PA-0038); Part of a continuation of U.S. Application No. 618,301 to Dalabeta, Ezawa, Tsurumi, Schlatter, and Nicholas, entitled “Two Stage Process for Combustion of Fuel Mixes” (PA-0030) The whole is integrated.

[Field of Invention]

The present invention employs a series of stages in which a fuel / oxygen-gas-containing mixture is burned in stages using a series of specific catalysts and catalyst structures, and optionally, combustion gases at a predetermined temperature of preferably 1050 ° C to 1700 ° C. A combustion process with a final uniform combustion zone for generating. Depending on the operating pressure, there are two or three distinct catalyst stages. By using specific structures, including those that select catalysts well and utilize integral heat exchange, catalysts and supports are obtained that are stable and do not degrade due to relatively low temperatures, and the resulting combustion gases are produced by gas turbines, It is at a temperature suitable for use in furnaces, boilers, etc., and its NOx content is low.

Except at the initial stage, fuel and air are not added to the combustion process.

[Background of invention]

With the advent of modern pollution control laws in the United States and around the world, important new methods of minimizing pollutants are being studied.

Firewood, coal, oil, natural gas, or any other fuel, seems to cause most of the pollution problems that exist today. Several types of contaminants, such as SO ₂ due to the presence of impurities in the fuel source, can be removed by removing the contaminants by subjecting the fuel to an impurity removal treatment or by treating the resulting exhaust gas.

Contaminants such as carbon monoxide resulting from incomplete combustion can be removed by post-combustion oxidation or by improving the combustion process. Another important pollutant, NOx (equilibrium mixture of most NO and trace amounts of NO ₂ ), can be treated by adjusting the combustion process to minimize the generation of foreign matter or by removing it later.

Nox is difficult to remove once produced because it is relatively stable and present at a low concentration in most exhaust gases. One breakup method used in automobiles is the use of carbon monoxide chemically to reduce NOx to nitrogen and at the same time to oxidize carbon monoxide to carbon dioxide.

But the need to react the two pollutants also leads to the conclusion that the first combustion reaction was inefficient.

Sulfur impurity can be removed from the fuel, and unlike such sulfur pollutants, it should be noted that removing nitrogen from the air supplied to the combustion process is clearly an impractical solution. Unlike in the case of carbon monoxide, improving combustion reactions will raise the level of NOx produced due to the high temperatures employed at that time.

However, the challenge of reducing combustion NOx continues, and several other methods have been proposed. However, the chosen method should not be in sharp conflict with the goal of generating combustion gases, ie its calorific value, recovered in a turbine, boiler or furnace.

Many recognize that the effective way to suppress NOx production is to limit the local and global temperatures to some temperature below 1800 ° C in the combustion zone. See, for example, column 1 of US Pat. No. 4,731,989 to Furya et al., Lines 52-59 and second column of US Pat. No. 4,088,135 to Hindin et al.

There are a number of temperature control methods, such as diluting with excess air, controlling combustion using one or several catalysts, or multistage combustion using various dilute or concentrated fuel mixtures. Combinations of these methods are also known.

One widely attempted approach is to use multistage catalyst combustion.

Most of these processes utilize multi-section catalysts with metal oxides or ceramic catalyst carriers. Typical of such disclosures are as follows.

It is clearly known to use such ceramic or metal oxide supports. The formed structure does not readily melt or oxidize unlike metal supports. Carefully designed ceramic supports for use in specific temperature ranges work well in that temperature range. Many such materials, however, may undergo phase changes or react with other components of the catalyst system at temperatures above 1100 ° C., for example, the gamma alumina phase turns into alpha alumina in the temperature range.

On top of that, such ceramic substrates are olefin brittle, ruptured and damaged by vibration, mechanical shock or thermal shock. Thermal shock is a special problem for catalytic combustion products used in gas turbines. At start-up and shutdown, large temperature gradients can occur in the catalyst, resulting in high mechanical stresses, resulting in rupture and fracture.

A typical effort to improve the high temperature stability of metal oxide or ceramic catalyst supports is the inclusion of alkaline earth metals or lanthanides or additional metals in the support, sometimes in parallel with other physical processing steps.

However, ceramics are also fragile materials, even though they contain materials that improve such high temperature stabilization. Japanese Patent Laid-Open No. 60-053724 teaches the use of a cylindrical ceramic catalyst having a hole in a cylindrical wall to more uniformly distribute fuel gas and temperature in the cylindrical catalysts so that cracking does not occur.

High temperatures (above 1100 ° C.) are also detrimental to the catalyst layer, resulting in the formation of low or inert materials by reduction of surface area, evaporation of the metal catalyst, and reaction of the catalyst component with the ceramic catalyst component.

Among the many catalysts introduced in the combustion literature, platinum group metals such as platinum, palladium, ruthenium, iridium and rhodium can be found, sometimes alone, sometimes in mixtures with other elements of the platinum group and sometimes with non-platinum group promoters or promoters. do.

Other combustion catalysts include metal oxides, in particular Group VIII and Group I metal oxides. For example, in Kaili et al., “Complete Oxidation of Methane on Perovskite Oxides” (Cataly-sis Letters 1 (1988) 299-306, JG Baltzer AG Scientific Publishing Co.,), _The use of perovskite oxide catalysts suitable for methanation represented by ₃ , in particular the oxide represented by La _1-x ME _x MnO ₃ (Me denotes Ca, Sr or Ba), is described.

Similarly, many articles by a group of researchers at Kyushu University in Japan describe combustion catalysts based on BaO · 6Al ₂ O ₃ : 1. Preparation of "large surface area BaO.6Al ₂ O ₃ . And characterization "Machida et al., Bull. Chem. Soc. Jpn., 61, 3659-3665 (1988), 2. "Hot Catalytic Combustion on Cationic-Substituted Barium Nitrate," Machida et al., Chemistry Letters, 767-770, 1987, 3. "BaO.6Al ₂ Electron Microscopic Analysis of O ₃ Formation ”Machida et al., J. Am. Ceram. Coc., 71 (12) 1142-47 (1988), 4. "The Effect of Additives on the Surface Area of Oxide Supports for Catalytic Combustion", J. Cat. 103-385-393 (1987), 5. “Surface Area and Catalytic Activity of Mn-Substituted Hexaaluminates Containing Multiple Cationic Components” Chem. Lett., 1461-1464, 1988.

Similarly, U.S. Patent No. 4,788,174 to Arai proposes a heat resistant catalyst suitable for catalytic combustion, which has the formula A _1-x C _x B _x Al _12-y O _19-a . Wherein A is at least one element selected from Ca, Ba and Sr; C is K and / or Rb; B is at least one element selected from Mn, Co, Fe, Ni, Cu and Cr; Z is one value ranging from 0 to about 0.4; x is a value ranging from 0.1 to 4 and y is a value ranging from about x to 2x; a is a value determined by the valence X, Y, Z and the values of x, y, z of each element A, C, B, and is represented by a = 1.5 {Xz (XY) + xZ-3y}.

In addition to the rigorous catalytic combustion process step, some processes employ a non-final step, which uniformly oxidizes all residual combustibles before recovering heat from the gas.

Most of the three stage catalytic combustion systems described above also have a post combustion stage.

For example, a series of Japanese patents (62-080419, 62-080420, 63-080847, 63-080848 and 63-080549), filed by Nippon Catalytic Chemical Company ("NSK"), have three stages of catalytic combustion and subsequent secondary combustion. Initiating the step. As mentioned above, the catalysts used in these processes differ in size from the catalysts used in the present invention. On top of that, these published patents suggest that when the post-burning step is used, only the gas temperature "750 ° C to 1100 ° C" obtained is reached.

In contrast, it can be seen that the process of the present invention achieves much higher adiabatic combustion temperatures when using the post-catalytic post-catalytic combustion stage.

Other combustion catalysts / post-catalyst post-combustion processes are also known. European patent application 0,198,948 (also assigned to NSK) shows a post-combustion stage following a two or three stage catalytic process. The on-combustion gas reaches on or 1300 ° C. and the outlet temperature from the catalyst (approximately total gas phase temperature) is described as 900 ° C.

However, the catalyst structures disclosed in the NSK publication cannot be protected from the adverse effects of combustion occurring in the catalyst zone and so the support deteriorates.

Furuya et al. (US Pat. No. 4,731,989) disclose a one-stage catalyst for subsequent injection of fuel and subsequent catalytic post-combustion.

In this case, by supplying a low fuel / air ratio mixture to the catalyst, it is limited to catalyst substrate temperature or 900 ° C or 1000 ° C. In order to obtain the higher gas temperatures required for certain processes such as gas turbines, additional fuel is injected after the catalyst and the fuel is allowed to burn uniformly in the postcatalyst zone. This process is complex and requires the installation of additional fuel injection devices in the hot gas stream leaving the catalyst. The inventive device described in this invention does not require fuel injection after the catalyst so that all fuel is applied at the catalyst inlet.

An important aspect of the practice of the present invention is the use of an integral heat exchange structure—preferably metal and at least in the late catalyst stage or stages of combustion. Generally, the basic idea is to place the catalyst layer on one wall facing the catalyst free side of the catalyst structure. Both sides are in contact with the flowing fuel-gas mixture. On one side heat is generated and on the other side the heat of reaction is transferred to the flowing gas.

Structures having integral heat exchange characteristics are shown in Japanese Patent Laid-Open Nos. 59-136,140 and 61-259,013. Similarly, US Pat. No. 4,870,824 to Young et al. Shows a one-stage catalytic combustion device using a monolithic catalyst in which the catalyst is disposed on a particular passage wall. In addition to many other differences, this structure is described as being used freely, not immediately in combination with other catalyst steps. On top of that, the stepwise use of structures with different catalytic metals is not disclosed in these publications.

In any of the processes shown in the discussion above, the catalyst support is metallic, and the catalyst support can be specifically modified to take advantage of the feature advantages of the catalysts, selectively applying integral heat exchange to control the catalyst substrate temperature, and especially low NOx generation. And combination catalyst systems that can achieve high gas temperatures while maintaining low catalyst (and support) temperatures.

[Summary of invention]

The present invention is a combustion process in which fuel is ebmixed at a specific fuel / air ratio to produce a combustible mixture having a desired adiabatic combustion temperature. The combustible mixture is then reacted in a series of catalytic structures and optionally in a homogeneous combustion zone. Combustion has a stage where the catalyst and total gas temperature are adjusted to relatively low values by the choice and structure of the catalyst.

The Applicant has found that as the operating pressure rises, the palladium catalyst turns on or rises to "self-limit" and the fuel mixture turns on or falls to perform homogeneous combustion. Above about 10 atmospheres, for the most practical fuel / air ratio, the self-regulating temperature of the palladium catalyst and homogeneous combustion initial temperature or the same or "hot end" combustion catalyst stage can be sufficiently compatible to eliminate. have.

The process produces exhaust gases with very low NOx concentrations only at temperatures suitable for use in gas turbines, boilers or furnaces.

[Description of the Invention]

The present invention is a combustion process in which fuel is premixed at a specific fuel / air ratio to produce a combustible mixture having a desired adiabatic combustion temperature. The combustible mixture is then reacted in at least two separate catalyst structures and optionally in a homogeneous combustion zone. Combustion is staged such that the catalyst and total gas temperature are adjusted to relatively low values through the selection and configuration of the catalyst. As the operating pressure increases, the palladium catalyst turns on or rises to "self-control" and the fuel mixture turns on or falls to perform homogeneous combustion. The (up to carbon monoxide levels of less than about 10ppm) 1 is also described above, the partial pressure of O ₂ is increased (also increasing with an increase in growth or O ₂ concentration of chongap), the theoretical pressure needed to complete homogeneous combustion shown in the The palladium catalyst is lowered to the level at which combustion will commence. These two lines meet between 4 and 5 atm. When the air is compressed to a level above about 4 to 5 atmospheres, the homogeneous combustion reaction burns out completely in about 11 microseconds. Above 4 to 5 atmospheres, for the most practical fuel-to-air ratio, the area of the palladium control temperature and the homogeneous combustion temperature are equal or sufficiently compatible so that a three-stage “hot end” combustion catalyst can be removed if desired.

The process produces exhaust gases with very low NOx concentrations only at temperatures suitable for use in gas turbines, boilers and furnaces.

This process can be used in a wide range of process conditions using a variety of fuels.

As fuel sources for the process, gaseous hydrocarbons such as methane, ethane and propane are generally preferred, but most of the fuels that can be evaporated at the process temperatures discussed below are suitable. For example, the fuel may be liquid or gas at room temperature and pressure. Examples include but are not limited to the above mentioned low molecular weight hydrocarbons such as butane, pentane, hexane, heptane, octane, gasoline, and aromatic hydrocarbons such as benzene, toluene, ethylbenzene and xylene; naphtha; Diesel fuel, kerosene; Jet fuel; Other intermediate distillates; High specific gravity distillate fuel (preferably hydrogenated to remove nitrogen and sulfur compounds); Oxygen-containing fuels such as alcohol such as methanol, ethanol, isopropanol and butanol; Ethers such as diethyl ether, ethylphenyl ether, MTBE and the like. Low-BUT gases such as city gas or syngas may also be used as fuel.

The fuel is generally mixed in the fuel air in an amount that produces a mixture having a theoretical adiabatic combustion temperature higher than the catalyst or gas phase temperature actually occurring in the catalyst used in the process of the present invention. Adiabatic combustion temperature or 900 degrees C or more is preferable, and 1000 degrees C or more is the most preferable. Non-gaseous fuels must be evaporated before they contact the original catalytic zone. Combustion air may be pressurized to atmospheric pressure or lower (-0.25 pneumatic) or compressed to 35 pneumatic or higher. Steady gas turbines (those that can ultimately use the gas produced by this process) are often operated at instrument pressure in the range of 8 to 35 air pressures. As a result, this method can be operated from -0.25 air pressure to 35 air pressure, preferably 0 air pressure to 17 air pressure.

[1st catalyst zone]

The fuel / air mixture supplied to the first catalyst zone must be mixed well and heated to a temperature high enough to initiate the reaction in the first zone catalyst; At least about 325 ° C. is generally suitable for methane fuel in an exemplary palladium catalyst. This preheating can be achieved by partial combustion, heat exchange or compression using a pilot burner.

The first zone in the process contains a catalytic amount of palladium on an integral catalyst support that provides low resistance to gas flow. The support is preferably metallic. Palladium is very active at below 325 ° C against methanation and can ignite fuel at low temperatures. In some cases, it has also been observed that after the palladium initiates the combustion reaction, the catalyst rapidly raises the temperature from 750 ° C. to 800 ° C. at 1 air pressure or to about 940 ° C. at 10 total air pressures. These are the temperatures of each transition point in the thermogravimetric analysis (TGA) of the palladium / palladium oxide reactions shown below at or below the various pressures mentioned. In that respect, depending on the pressure, the catalytic reaction is substantially slowed down and the catalyst temperature or 750 ° C to 800 ° C or 940 ° C is decreased. This phenomenon is observed even when the fuel / air ratio can raise the theoretical adiabatic combustion temperature above 900 ° C or as high as 1700 ° C.

One reason for this temperature control phenomenon is the conversion of palladium oxide to palladium metal at the TGA transition point discussed above. At temperatures below 750 ° C. in one atmosphere of air, palladium is present primarily as palladium oxide. Palladium oxide appears to be an active catalyst for the oxidation of fuels. Above 750 ° C., palladium oxide is converted to palladium metal according to the following equilibrium.

Palladium metals appear to be substantially less active against hydrocarbon combustion, with a slight decrease in catalytic activity at temperatures above 750 ° C to 800 ° C. This transition self-controls the reaction; The combustion process rapidly raises the catalyst temperature to 750 ° C. to 800 ° C. at which self control of the temperature begins. It will rise as the O ₂ partial pressure increases, depending on this control temperature or the O ₂ pressure.

But a little attention is needed. Even high activity of palladium or low activity of palladium metal above 750 ° C. may be sufficient to raise the catalyst temperature above 800 ° C. to reach the adiabatic combustion temperature of the fuel / air mixture as mentioned above. ) "Can lead to combustion; It may lead to temperatures above 1100 ° C. or severe damage to the catalyst. The Applicant has discovered that runaway combustion can be controlled by controlling the supply of fuel and / or oxidant to the catalyst by adding a diffusion barrier over the catalyst bed. This diffusion layer broadens the operating range of the first stage catalyst to higher preheat temperatures, lower linear gas velocities, higher fuel / air ratio ranges and higher outlet gas temperatures. We also found that the control of the concentration of palladium metal on the substrate prevents "runaway", but there is a loss of relatively short catalyst life.

The self-control phenomenon keeps the temperature of the catalyst substrate substantially below the adiabatic combustion temperature. This prevents or substantially reduces the performance degradation of the catalyst due to high temperature operation.

Palladium metal is added in an amount sufficient to provide significant activity. The specific amount added depends on a number of requirements, such as economics, activity, lifespan, and the presence of contaminants. The theoretical maximum is likely to be sufficient to coat the maximum amount of support without causing excessive growth of microcrystals and subsequent loss of activity. This is clearly a competitive factor; It requires the highest active or higher surface coverage of the catalyst but can promote growth between higher coatings or adjacent microcrystals. In addition, the form of the catalyst support should be considered. If the support is used in a high space velocity environment, the catalyst loading will have to be high to sustain sufficient conversion even with a short residence time. The economic aspect is its universal purpose to use a minimum amount of catalyst to accomplish the desired task. As a result, the presence of contaminants in the fuel requires the use of higher load catalysts to counteract the degradation of the catalyst by deactivation.

The palladium metal content of this catalyst composite is generally very small, such as from 0.1% to about 25% by weight, preferably from 0.01% to about 20% by weight. The catalyst may optionally be contained up to the equivalent of one or more catalyst adducts selected from the low metals of Group IB or Group VIII. Preferred adduct catalysts are um, gold, ruthenium, rhodium, platinum, iridium, or osmium. More preferably silver and platinum. Palladium and certain adducts may be incorporated into the support in a variety of ways using palladium complexes, compounds or dispersions of metals. The compound or complex may be dissolved in water or hydrocarbons. They may precipitate out of solution. The liquid carrier should generally only be removed from the catalyst carrier by evaporation or decomposition while leaving palladium in dispersed form on the support. Examples of palladium complexes and compounds suitable for catalyst production for use in the present invention include palladium chloride, palladium diamine dinitrite, palladium tetraamine chloride, palladium 2-ethylhexanoic acid, sodium palladium chloride and other palladium salts or complexes and the like. Preferred supports for this catalyst zone contain metals. Although other support materials such as ceramics and various inorganic oxides are typically used as supports such as silica, alumina, silica-alumina, titanium oxide, zirconium oxide. And may be used with or without additives such as barium, cerium, lanthanum, or chromium added for stability. Corrugated sheet with longitudinal channels or passageways passing through at minimum pressure drop and fast space velocity (also interspersed with flat separator sheets), cylindrical (or a small amount of straw) or other atomic array hexagonal, spiral roll Metal supports in the form are preferred for this embodiment. These may be malleable and more easily attach and back to the surrounding structure, providing low flow resistance to thin films that can be easily manufactured on ceramic supports. Another practical advantage believed to be in metal supports is their ability to withstand thermal shock. This thermal shock occurs during turbine operation when the turbine is in operation and when it is stopped, in particular when the turbine is in a hurry stop. In this case, the turbine is suddenly started or the fuel supply is stopped because the material drop on the turbine (eg generator set) has been removed. The fuel is immediately stopped by the turbine to prevent overspeed. The method of the present application falls quickly from the on or combustion temperature of the combustion chamber to the temperature of the compressed air. This drop may drop 1000 degrees Celsius or more within 1 second. In this case, the catalyst is precipitated or otherwise placed in the walls in the channels or passages of the metal support at the specified amounts above. The catalyst may be introduced to the support in various formats.

The support may be completely covered, the downstream portion of the support may be covered, or one side of the support wall may be covered, resulting in an integral heat exchange relationship as discussed in connection with later steps below. Due to the demand for high total activity at low temperatures, the preferred form is a complete covering. However, each other may be used specially under special circumstances. Various forms of support material are satisfactory in this embodiment: any hot metal alloy consisting of aluminum, aluminum containing or aluminum treated steel, and a nickel alloy with a particular stainless steel or catalyst layer attached to the metal surface. Preferred materials are aluminum containing steels, which are those disclosed in US Pat. No. 4,414,023 to Aggen et al, US Pat. No. 4,331,631 to Chapman et al and 3,969,082 to Keynes et al. The same aluminum containing steel is the preferred material. Kawasaki Steel Company (River Lite 20-5 SR), Vereinigte Deutchse Metallwerke AG (AlumchromIRE) and Allegheny Ludlum Steel Like others sold by Steel (Alfa-IV), these steels contain enough molten aluminum so that when oxidized, aluminum forms alumina whiskers or crystals on the surface of the steel to further the washcoat. A rough and chemically active surface was provided for better tack. Washcoats may also be carried out using methods described in the art, for example gamma-alumina sol or sol of mixed oxides containing aluminum, Implementation of additives such as silicon, titanium, zirconium, and barium, cerium, lanthanum, chromium or various other compositions.For better adhesion of the washcoat, the first layer is Chapman. It may also be carried out containing a hydrous oxide, such as a dilute suspension of pseudo-boehmite alumina, described in US Pat. No. 4,729,782 to Chapman et al. However, preferably the first surface is coated with a zirconia suspension. And then calcined until drying and forming a high surface tacky oxide layer on the metal surface Washcoats may be applied in the form of coating on the surface, for example in disperse, direct coating, and washcoat materials. The aluminum structure may also be suitable for use in the present invention, and may be essentially treated or coated in the same way, as the aluminum alloy is somewhat softer and may be used to fabricate the shell of the method. As a result of deformation or melting at temperatures As a result, they are less desirable as supports. And if the washcoat and palladium are applied and calcined as a metal support, then one or more coatings of low or non-catalyst oxides are applied as diffusion barriers as described above. Prevents "runaway" temperature. This wall layer may be alumina, silica, zirconium titanium oxide or a variety of other oxides having low catalytic activity during combustion of fuels or mixed oxides or oxides and additives similar to those described for washcoat layers. Alumina is the least preferred of the materials mentioned. The wall layer will be substantially thicker than the washcoat at one percent of the thickness of the washcoat layer, but more preferably from 10 percent to 100 percent of the thickness of the washcoat layer. The preferred thickness will depend on the operating condition of the catalyst in fuel form, gas flow rate, preheat temperature and catalytic activity of the washcoat layer. It has also been found that the application of only diffusion wall coatings, for example up to 30 percent to 70 percent of the length of the catalyst structure, can provide sufficient protection against the catalyst under certain conditions. In washcoats, the wall layer or layers may be carried out using the application technique used to apply the paint. The catalyst structure can be sized and shaped to have a mean linear velocity through the channel within the catalyst structure of greater than about 0.2 n / sec and less than about 40 m / sec throughout the first catalyst zone structure. This lower limit is greater than the flame surface velocity for methane and the upper limit is the actual flame surface velocity for forms of the support that are readily commercially available. These average rates may be somewhat different for other fuels than methane. The first catalyst zone was made at a temperature of about 800 ° C. or less, preferably in the range of 450 ° C. to 700 ° C., more preferably 500 ° C. to 650 ° C., from the zone.

[Second catalyst zone]

In the process, the second zone burns the gas partially in the first zone and produces even more limited combustion until it occurs in the presence of a catalyst structure with heat exchange capability. The catalyst may comprise a material selected from the precious metals of Mendeleeb Groups IB, VI, and VIII. If the pressure of the process is greater than about 4 atmospheres, the catalyst preferably contains palladium. At some pressures, the catalyst contains Group VIII precious metals such as platinum or palladium. If the catalyst contains palladium, it optionally contains the equivalent of one or more catalyst adducts selected from precious metals of Group IB or Group VIII. Preferred adduct catalysts are silver, gold, ruthenium, rhodium, platinum, iridium or osmium. Most preferred are silver and platinum.

This zone can be operated adiabatic with the heat generated from the partial combustion of the fuel resulting in an increase in gas temperature. No air or fuel was added between the first and second catalyst zones. The catalyst structure in this zone is preferably similar to that used in the first catalyst zone, except that the catalyst is carried out on at least part of only one side of the surface that forms the walls of the monolithic catalyst support structure. A portion cut out of a second A or high surface area metal oxide washcoat 10 is shown. The active metal catalyst 12 is applied to one side of the metal substrate 14. In this structure, the heat of reaction generated in the catalyst is easily conducted through the contact surface between the washcoat layer 10 and the gas stream 16 in FIG. 2B. Thanks to the relatively high thermal activity of the washcoat 10 and the metal 14, heat is equally reacted to the gas stream 16 and the gas stream 18 conducting and flowing equally along the passages A and B. This is distributed. This integral heat exchange structure will have a substrate or wall temperature given by equation (1).

The rise in wall temperature will be about half of the difference between the inlet temperature and theoretically the adiabatic combustion temperature. A sheet of metal coated on one side with a catalyst and coated on the other side with a non-catalyst may form a corrugated sheet 20 as shown in FIGS. 3A to 3C until a long ring opening channel structure is formed which causes low resistance to gas flow. ) Or a flat sheet 22 may be formed to form a plated or layered structure. The corrugated metal strip 30 coated on one side of the catalyst 32 may be combined with the separator strip 34 which is not coated with catalyst until the structure shown in FIG. 4A is formed. Alternatively, corrugated strips 36 and flat strips 38 coated on one side of the catalyst prior to assembly of the catalyst structure may be combined as shown in FIG. 4B. The structure forms channels with catalyst walls (40 in FIG. 4A and 42 in FIG. 4B) and channels with noncatalytic walls (44 in FIG. 4A and 46 in FIG. 4B). Catalyst structures arranged in such a way as to have a catalyst channel and a separate non-catalyst channel (limited integral heat exchange structure "L-IHE") have been described in the same pending application (agent litigation table PA-0097). This structure has a similar possibility of controlling the catalyst substrate temperature and the outlet gas temperature. The corrugated sheet 42 and the flat sheet 44 coated with one side of the catalyst may be arranged according to FIG. 5 in which the catalyst surface of each sheet is represented by a different channel so that all channels of the catalyst of the walls thereof are coated. In part and all the walls were coated with catalyst on one side and noncatalyst on the opposite side. The FIG. 5 structure will act differently from FIGS. 4A and 4B. The wall of FIG. 5 structure forms an integral heat exchange. However, since all channels contain a catalyst, there is a possibility that all the fuel is burned by the catalyst. When combustion takes place on the catalyst surface, the temperature of the catalyst and support will rise and heat will conduct on the catalyst and non-catalyst surfaces so that the gas stream will dissipate. This will help to limit the temperature of the catalyst substrate and will help to limit the palladium temperature to maintain the wall temperature at 750 ° C. to 800 ° C. at 1 air pressure or about 930 ° C. at 10 air pressures. A constant outlet gas temperature of 750 ° C. to 800 ° C. will be obtained for any fuel / air ratio with an adiabatic combustion temperature of at least about 800 ° C. at 1 pneumatic pressure or at least about 930 ° C. at 10 pneumatic pressures for sufficiently long catalyst or low gas velocities.

The structures shown in FIGS. 4A and 4B have the same gas flow through each of the catalytic and non-catalyst channels. With this structure, the maximum gas temperature rise will be produced by 50% combustion of the inlet fuel.

The structure shown in FIGS. 4A and 4B can be modified to control the fraction of fuel and oxygen reacted by changing the fraction of fuel and oxygen mixture flowing through the catalyst and non-catalyst channels. 6A or the corrugated flakes represent a structure having a structure in which the narrow 50 and light 52 corrugations alternate. The corrugated flakes are coated on one side to form the large catalyst channel 54 and the non-catalyst channel 56. In this structure approximately 80% of the gas stream will flow through the catalyst channel and 20% will flow through the non-catalyst channel. If the maximum outlet gas temperature or gas goes to the adiabatic combustion temperature, it will be about 80% of the expected temperature rise. Conversely, covering only the other side of the flakes (Fig. 6B) results in a structure having a maximum outlet gas temperature increase of 20% of the rise in thermal combustion temperature and only 20% of the gas flow through the catalyst channel 58. Appropriate designs of corrugation and size can achieve any conversion level of 5% to 95%, including integral heat exchange. It can calculate by the maximum outlet gas temperature or following formula (2);

To illustrate the process of this integrated heat exchange zone, it is assumed that gas 4 through the catalytic channel or gas stream partially from the first catalyst zone flows into structure 4a, which is 50% of the total flow.

Approximately half of the gas stream will flow through the channel with catalyst wall 42 and through the channel with non-catalyst wall 46. Fuel combustion will occur at the catalyst surface and heat will dissipate into the gas flowing in the catalyst and non-catalyst channels. If the gas in zone (1) or 500 ° C and the fuel / air ratio corresponds to the theoretical adiabatic combustion temperature of 1300 ° C, combustion of the fuel in the catalyst channel will raise the temperature of all flowing gas. Heat is dissipated to the gas flowing in the catalyst and non-catalyst channels.

The calculated L-IHE wall temperature or as follows:

The calculated maximum gas temperature or is as follows:

However, at one air pressure, palladium will limit the wall temperature to 750 ° C. to 800 ° C. and will be the maximum outlet gas on or about <800 ° C. As can be seen in this case, palladium control controls the maximum outlet gas temperature and limits the wall temperature.

At 10 pneumatics the situation is different. Palladium controlled temperature or about 930 ° C. The wall will be limited to 900 ° C. by the L-IHE structure. In this case the L-IHE structure limits the wall and gas temperature.

The catalyst structure in this zone must have the same approximate catalyst loading on that surface with the catalyst as the first zone structure. It should be sized to maintain the prow at the same average linear velocity as the first zone and if a third catalyst step is desired the total outlet temperature is only in the range of 800 ° C., preferably 600 ° C. to 800 ° C. and most preferably It must be sized to reach between 700 ° C and 800 ° C. The catalyst may comprise a non-catalyst diffusion barrier layer as described for the first catalyst zone.

If a process using only two separate catalyst structures as a design is desired, the second catalyst zone should be designed such that the total temperature of the gases leaving the zone is above its spontaneous ignition temperature (if a homogeneous combustion zone is desired).

It is maintained at an adjustment temperature controlled by the support and catalyst temperatures or the relative size of the catalyst and non-catalyst channels, the inlet temperature, the theoretical adiabatic combustion temperature, and the second zone length. Same as the gas flux of the second catalyst zone or of the first zone.

[3rd catalyst zone]

In use, the third zone of the process receives the partially combusted gas from the second zone, has an integral heat exchange force and is preferably in the presence of a catalyst structure comprising as a metal-oxygen catalyst material or comprising platinum as catalyst material. More controlled combustion occurs. The metal-oxygen material preferably comprises at least one metal selected from those found in Mendelev Group (VIII) and Group (I). These materials are preferred because of their reaction stability at higher temperatures. Other combustion catalysts such as palladium, rhodium, osmium, iridium and the like may be used instead of or in combination with platinum. This zone may be essentially adiabatic in the process and further raises the gas temperature to a temperature at which homogeneous combustion may occur by catalytic combustion of at least a portion of the fuel or may be used in gas or direct furnaces or turbines.

The catalyst structure in this zone may be the same as used in the second zone. As indicated above, the catalyst used in this zone preferably comprises a metal-oxygen catalyst or platinum. Suitable metal-oxygen catalysts include the Mendelev group (V) (particularly Nb or V), group (VI) (particularly Cr), group (VIII transition) (particularly Fe, Co, Ni), and primary lanthanides (particularly Ce, Pr, Nd, Sa, Tb, La) metal oxides or mixed oxides. Additionally, the catalytic material may be selected from perovskite-type materials in the form of ABO ₃ , where A is a group (IIA) or (IA) metal (Ca, Ba, Sr, Mg, Be, K, Rb, Na, or Cs), and B is selected from group (VIII) transition metals, group (VIB), or group (IB) (especially Fe, Co, Ni, Mn, Cr, Cu).

Applicant has not yet found the importance of how these materials are prepared. As suggested in the literature, it is suitable to saturate the support with the desired metal or salt or complex solution of metals and carry out the calcination step.

These materials are typically active as combustion catalysts at temperatures of just above 650 ° C. but show considerable stability in that range. These materials do not exhibit the same temperature limiting behavior as palladium; The catalyst substrate may be raised to a temperature higher than 800 ° C. without prior measures.

When the L-IHE catalyst structure of FIG. 6 has 50% of the gas flow through the catalyst channel 3 and 50% of that through the non-catalyst channel 4 and the combustion is completed in the catalyst channel, the outlet gas of the third zone The temperature will be the average of the adiabatic combustion temperature and the inlet temperature as described above. Wall temperature and gas temperature or will be limited to equations (1) and (2) given above. Incomplete reactions in the catalyst channel will result in lower outlet gas temperatures.

If exhaust gas from zone 2 is at or above 800 ° C and the fuel / air mixture has a theoretical adiabatic combustion temperature of 1300 ° C and 50% of the gas mixture is completely burned in the catalyst channel, Will be at or 1050 ° C. (ie an average of 800 ° C. and 1300 ° C.). This will cause flue gas temperatures or rapid homogeneous combustion.

The structure of the third zone can take many forms and can at least partially burn the fuel entering the third zone by applying the catalyst in various ways. As an example, using the structures described above for FIGS. 6A and 6B will convert 80% or 20% of the gas mixture entering the third zone, respectively. It can be adjusted by the outlet gas temperature from the third zone or by the catalyst support design.

Therefore, as a design, Zone 3 shall be designed such that the total temperature of the gases discharged from Zone 3 is above its spontaneous ignition temperature (if Zone 4 homogeneous combustion zones are desired). It is maintained at an adjustment temperature controlled by the support and catalyst temperatures or the relative size of the catalyst and non-catalyst channels, the inlet temperature, the theoretical adiabatic combustion temperature, and the length of the third zone. It is obviously higher because of the flux or higher temperature of the gas in the third catalyst zone but in the same range as in the first and second zones.

Homogeneous combustion zone

The gases emitted from the previous combustion zone may be in suitable conditions for subsequent use if the temperature is correct; The gas is essentially free of NOx and is maintained at a temperature at which the catalyst and catalyst support allow for its long term stability. However, higher temperatures are required for multiple use. Many gas turbines have been designed, for example, for inlet temperatures of about 1260 ° C. As a result, the homogeneous combustion zone may be a suitable additive.

Homogeneous combustion zones need not be large. The gas residence time in the zone is essentially no more than about 11 or 12 milliseconds to achieve complete combustion (ie carbon monoxide <10 ppm) and to achieve adiabatic combustion temperatures. The following table is a function of the fuel- (methane) / air ratio, temperature and pressure of the total gas exiting the third catalyst zone, to achieve almost complete combustion as well as to achieve various adiabatic combustion temperatures (function of fuel / air ratio). The calculated residence time is shown. These reaction times were calculated using the homogeneous combustion model described by kee et al. And the kinetic rate constants (Sandia Natlonal Laboratory Report No. SAND 80-8003).

Obviously, in the process used to maintain the gas turbine (e.g. total catalyst zone gas discharge temperature = 900 ° C, F / A ratio = 0.043, pressure = 10 atm air pressure), to achieve adiabatic combustion temperature and complete combustion The residence time is less than 5 milliseconds.

This will result in an overall combustion gas of less than 40 m / sec or a homogeneous combustion zone of less than 0.2 m in length (as discussed above with respect to the catalyst stage). In summary, the process uses a number of carefully crafted catalyst structures and catalytic methods to produce working gases that are substantially free of NOx and at temperatures comparable to conventional combustion processes. However, the catalyst and its support are not exposed to high temperatures that may damage such catalyst and support or shorten their useful life.

Example 1

This example shows an assembly of a three stage catalyst system.

[Stage 1]

The first step was prepared as follows: A 3% palladium / ZrO ₂ sol was prepared. A sample of 145 g of ZrO ₂ powder having a surface area of 45 m ₂ / mg was impregnated with 45 ml of a palladium solution prepared by dissolving Pd (HN ₃ ) ₂ (NO ₂ ) ₂ in HNO ₃ containing 0.83 g palladium / ml. This solid was dried and calcined in air at 500 ° C. and placed in a ball mill lined with a polymer containing 230 ml H ₂ O, 2.0 ml concentrated HNO ₃ and a cylindrical zirconia medium. The mixture was milled for 8 hours.

To 50 cc of this sol (containing about 35% by weight of solids), 36 ml of a palladium solution was added. The pH was adjusted to about 9 and 1.0 ml of hydrazine was added. Stir at room temperature to reduce palladium. Final palladium concentration or 20% by weight palladium / ZrO ₂ .

Cordierite monolithic ceramic honeycomb structures with 100 square cells per square inch were immersed in palladium / ZrO ₂ sol and excess sol was blown from the channel. The monolith was dried and calcined at 850 ° C. This monolith contained 6.1% ZrO ₂ and 1.5% palladium. This monolith was again immersed in the same palladium / ZrO ₂ sol to a depth of only 10 mm, then removed, taken out, dried and calcined. The final catalyst had 25% ZrO ₂ and 6.2% palladium at the 10.0 mm inlet.

[Step 2]

A second stage catalyst was prepared as follows.

ZrO ₂ colloidal sol was prepared. About 66 g of zirconium isopropoxide was hydrolyzed with 75 cc water and then mixed with 100 g of ZrO ₂ powder having a surface area of 100 m 2 / gm and 56 ml of additional water. This slurry was ball milled in a ball mill aligned with the polymer for 8 hours using a ZrO ₂ cylindrical medium. To this colloidal sol was added water and diluted to a concentration of 15% by weight ZrO ₂ .

The Fe / Cr / Al alloy foil was corrugated in a herringbone pattern and then oxidized at 900 ° C. in air to form alumina whiskers on the foil surface. ZrO ₂ sol was sprayed onto the corrugated foil. The coated foil was dried and calcined at 850 ° C. The final foil contained ₁₂ mg of ZrO ₂ per cm 2 of foil surface. Palladium 2-ethylhexanoic acid was dissolved in toluene at a concentration of 0.1 g palladium / ml. This solution was sprayed only onto the metal foil coated with ZrO ₂ and the foil was dried and calcined at 850 ° C. in air. The final foil contained about 0.5 mg palladium per cm 2 of foil surface.

The corrugated foil was formed to have a longitudinal channel extending in the axial direction of the structure, containing about 150 cells per square inch, with a length of 2 inches in diameter and 2 inches in length to prevent the corrugated foil from interlocking. The foil had a palladium / ZrO ₂ catalyst on only one surface and each channel consisted of a catalyst coating surface and a non-catalyst surface as shown in Figure 3A.

[Step 3]

A third stage catalyst was prepared as follows.

Alumina sol was prepared. About 125 g of gamma alumina having a surface area of 180 m 2 / g, 21 ml of concentrated nitric acid, and 165 ml of water were placed in a 1/2 gallon ball mill with a cylindrical alumina grinding medium and milled for 24 hours. This sol was diluted to 20% solids concentration.

The Fe / Cr / Al alloy foil was corrugated to form uniform straight channels in the foil strip. When rolled together with a flat foil strip, the helical structure formed a honeycomb structure with straight channels. The corrugated strip was first sprayed with a 5% clavable boehmite sol followed by the alumina sol prepared previously. Flat metal foil strips were sprayed in a similar manner. Only one side of each foil was coated in this way. The foil was then dried and calcined at 1100 ° C. Pt (NH ₃ ) 2 (NO ₂ ) ₂ was dissolved in nitric acid to give a solution of 0.13 g platinum / ml. This solution was sprayed onto the coated foil and the foil was treated with gas H ₂ S, dried and calcined at 1100 ° C. The "thickness" of the alumina coating on the metal foil was about 4 mg per cm 2 of flat foil surface. Platinum loading was about 20% of alumina.

[3 stage catalyst system]

The three catalysts described above were arranged inside the ceramic cylinder as shown in FIG. The thermocouple was placed at the marked position of this system. The thermocouple located in the catalyst section was sealed in the channel with ceramic cement to measure the temperature of the catalyst substrate. Gas thermocouples were suspended in the gas stream. The insulated catalyst section of FIG. 7 was installed in a reactor with a gas flow path of 50 mm in diameter. 150 SLPM of air was passed through an electric heater, a static gas mixer, and then through a catalyst system. 67 SLPM of natural gas was added above the static mixer. The air temperature was gradually raised by increasing the power to the electric heater. At 368 ° C. the off-gas temperature from steps 1, 2 and 3 or as shown in FIG. 8 began to rise. Above the preheating temperature of 380 ° C., the gas temperature of step 1 was constant or about 530 ° C., the gas discharge step 2 was about 780 ° C. and the gas discharge step 3 was about 1020 ° C. Homogeneous combustion occurred after the catalyst provided a gas temperature of about 1250 ° C. and was close to the adiabatic combustion temperature of the ion or this fuel / air ratio. Substrate temperature for step 3 or shown in FIG. As mentioned above, the stage 1 catalyst was extinguished at low temperature and self-controlled at substrate temperature or about 750 ° C. This catalyst cell density and gas flow rate resulted in an intermediate gas temperature of 540 ° C. Step 2 likewise self controlled the substrate temperature to 780 ° C and the gas temperature to 750 ° C. Step 3 limited the wall temperature to 1100 ° C.

Limiting the substrate temperature to 750 ° C. to 780 ° C. in steps 1 and 2 provided excellent long term catalyst stability. This stability was demonstrated for 100 hours as shown in FIG. The catalyst system was re-ignited by maintaining the inlet air temperature at 400 ° C. and increasing the methane flow rate to increase the fuel / air ratio.

This initiation process is shown in FIG. Step 1 achieved an exhaust gas temperature of 540 ° C. at fuel / air = .033 and maintained this temperature at fuel / air ratios up to .045. Complete homogeneous combustion in the post-catalytic zone was achieved at a fuel / air ratio of .045.

The invention is illustrated by direct explanation and examples. The embodiments are by way of example only and are not intended to limit the invention as claimed later in any way.

Those skilled in the art will also recognize equivalent methods for carrying out the invention described in these claims. Such equivalents are considered to be within the scope of the claimed invention.

Claims (24)

A combustion process of a combustible mixture, comprising: (a) contacting a combustible mixture composed of an oxygen-containing gas and a fuel that needs to reach a desired temperature during combustion, with a catalyst structure consisting of two or more catalytic stages, wherein palladium is It exists as the only catalytic material, which is located in the catalyst structure such that a portion of the combustible mixture does not come into contact with the catalyst, so that only a portion of the fuel burns in the catalyst structure and the temperature of the partially burned combustible mixture outside the catalyst structure And (b) burning the residual fuel remaining in the combustible mixture outside the catalyst structure to raise the temperature to the desired temperature. The combustion process of claim 1, wherein the catalyst structure is divided into three stages, and the second stage catalyst contains palladium. The method according to claim 2, wherein the combustible mixture released in the first step is on or 500 ° C. to 650 ° C., and the second step is released to 750 ° C. to 800 ° C., and the third step is released to 850 ° C. to 1050 ° C. Combustion process of the combustible mixture, characterized in that. 2. The process of claim 1 wherein the desired temperature after combustion is 1050 ° C to 1700 ° C. The catalyst structure of claim 1, wherein the catalyst structure is positioned so that a portion of the combustible mixture does not come into contact with the catalyst, and comprises a catalyst support having a plurality of longitudinal passages for the passage of the combustible mixture. Combustion process of a combustible mixture, characterized in that the catalytic material is located only in part. 6. The process of claim 5 wherein the catalyst support is a corrugated metal structure. The combustion process of claim 1, wherein the catalyst structure in which the catalyst material is positioned so that a portion of the combustible mixture does not come into contact with the catalyst is composed of a catalyst support having a catalyst having a diffusion wall therein. . 3. The process of claim 2, wherein the third stage catalyst contains platinum. The method according to claim 8, wherein the combustible mixture released in the first step is on or 500 ° C. to 650 ° C., and the second step is released from 750 ° C. to 800 ° C., and the third step is released from 850 ° C. to 1050 ° C. Combustion process of the combustible mixture, characterized in that. The process of claim 1 wherein the catalyst structure is divided into three stages and the third stage catalyst is comprised of palladium, rhodium, osmium, iridium or platinum. 3. The process of claim 2, wherein the total temperature of the gas leaving the second stage is between 750 ° C and 950 ° C. 2. The process of claim 1, wherein the oxygen-containing gas is air and is compressed to at least 4 atmospheres (gauge). The combustion process of claim 1, wherein the first stage catalyst consists of palladium on a metal support. 15. The process of claim 13, wherein the first stage catalyst consisting of palladium on a metal support further comprises a wall layer covering at least a portion of the palladium. 15. The process of claim 14 wherein the wall layer is comprised of zirconia. 9. The method of claim 8, further comprising combusting the remaining non-combustion fuel in a third step to generate a gas having a temperature that is higher than the temperature of the gas leaving the second step and less than about 1700 ° C. Combustion process of combustible mixtures. 3. The second stage catalyst of claim 2, wherein the catalyst surface of each sheet is in contact with another channel, a portion of the walls of all channels are coated with a catalyst, one side of all walls is coated with a catalyst and the opposite surface is a noncatalyst. By arranging the support structure of corrugated or flat sheet coated on one side with a catalyst so as to be a surface, the temperature of the catalyst and the support rises when combustion occurs on the catalyst surface, and heat is transferred into the gas flow on both sides of the catalyst and non-catalyst surface. Combustion process of the combustible mixture, characterized in that the dissipation. The combustion process of claim 8, wherein the first and / or second stage catalyst further comprises one or more Group IB metals or Group VIII metals. 3. The process of claim 2, wherein the second stage catalyst structure is a limited integral heat exchange structure. 20. The process of claim 19, wherein the temperature of the gas leaving the second stage is 750 deg. C-800 deg. The process of claim 8, wherein the third stage catalyst comprises Mendelev Group V (particularly Nb), Group VI (particularly Cr), Group VIII transition elements (particularly Fe, Co or Ni) and the first lanthanide series (particularly Ce, Pr, Nd, Sa, Tb or La) metal oxides or mixed oxides or perovskite-like materials in the form of ABO ₃ (A is a Group IIA or Group IA metal (Ca, Ba, Sr, Mg, Be, K, Rb, Na) Or Cs), and B is one or more metal-oxygen catalysts selected from group VIII transition elements, group VIB, or group IB (in particular, selected from Fe, Co, Ni, Mn, Cr or Cu). Combustion process of combustible mixtures, characterized in that the substance. The combustion process of a combustible mixture according to claim 1, wherein the oxygen-containing gas is air and is compressed to an air pressure of 0-35 atm (gauge). 10. The process of claim 8 wherein the first and / or third stage catalyst is on a support having an integral heat exchange surface. 3. The method of claim 2, further comprising the step of burning the remaining non-combustion fuel in a fourth step to generate a gas having a temperature higher than the temperature of the gas leaving the third step and less than about 1700 ° C. Combustion process of combustible mixtures.